Materials

17 pages, 8119 KiB

Open AccessEditor’s ChoiceArticle

Unsupervised Deep Learning for Advanced Forming Limit Analysis in Sheet Metal: A Tensile Test-Based Approach

by Aleksandra Thamm, Florian Thamm, Annette Sawodny, Sally Zeitler, Marion Merklein and Andreas Maier

Materials 2023, 16(21), 7001; https://doi.org/10.3390/ma16217001 - 1 Nov 2023

Cited by 1 | Viewed by 1558

Abstract

An accurate description of the formability and failure behavior of sheet metal materials is essential for an optimal forming process design. In this respect, the forming limit curve (FLC) based on the Nakajima test, which is determined in accordance with DIN EN ISO [...] Read more.

An accurate description of the formability and failure behavior of sheet metal materials is essential for an optimal forming process design. In this respect, the forming limit curve (FLC) based on the Nakajima test, which is determined in accordance with DIN EN ISO 12004-2, is a wide-spread procedure for evaluating the formability of sheet metal materials. Thereby the FLC is affected by influences originating from intrinsic factors of the Nakajima test-setup, such as friction, which leads to deviations from the linear strain path, biaxial prestress and bending superposition. These disadvantages can be circumvented by an alternative test combination of uniaxial tensile test and hydraulic bulge test. In addition, the forming limit capacity of many lightweight materials is underestimated using the cross-section method according to DIN EN ISO 12004-2, due to the material-dependent occurrence of multiple strain maxima during forming or sudden cracking without prior necking. In this regard, machine learning approaches have a high potential for a more accurate determination of the forming limit curve due to the inclusion of other parameters influencing formability. This work presents a machine learning approach focused on uniaxial tensile tests to define the forming limit of lightweight materials and high-strength steels. The transferability of an existing weakly supervised convolutional neural network (CNN) approach was examined, originally designed for Nakajima tests, to uniaxial tensile tests. Additionally, a stereo camera-based method for this purpose was developed. In our evaluation, we train and test materials, including AA6016, DX54D, and DP800, through iterative data composition, using cross-validation. In the context of our stereo camera-based approach, strains for different materials and thicknesses were predicted. In this cases, our method successfully predicted the major strains with close agreement to ISO standards. For DX54D, with a thickness of 0.8 mm, the prediction was

0.659

(compared to ISO’s

0.664

). Similarly, for DX54D, 2.0 mm thickness, the predicted major strain was

0.780

(compared to ISO

0.705

), and for AA6016, at 1.0 mm thickness, a major strain of

0.314

(in line with ISO

0.309

) was estimated. However, for DP800 with a thickness of 1.0 mm, the prediction yielded a major strain of

0.478

(as compared to ISO

0.289

), indicating a divergence from the ISO standard in this particular case. These results in general, generated with the CNN stereo camera-based approach, underline the quantitative alignment of the approach with the cross-section method. Full article

(This article belongs to the Special Issue Forming Process and Mechanical Behavior Analysis of Light Metals and Alloys)

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14 pages, 3685 KiB

Open AccessEditor’s ChoiceArticle

Collagen-Coated Hyperelastic Bone Promotes Osteoblast Adhesion and Proliferation

by Andrei Gresita, Iman Raja, Eugen Petcu and Michael Hadjiargyrou

Materials 2023, 16(21), 6996; https://doi.org/10.3390/ma16216996 - 1 Nov 2023

Cited by 1 | Viewed by 1296

Abstract

Successfully reconstructing bone and restoring its dynamic function represents a significant challenge for medicine. Critical size defects (CSDs), resulting from trauma, tumor removal, or degenerative conditions, do not naturally heal and often require complex bone grafting. However, these grafts carry risks, such as [...] Read more.

Successfully reconstructing bone and restoring its dynamic function represents a significant challenge for medicine. Critical size defects (CSDs), resulting from trauma, tumor removal, or degenerative conditions, do not naturally heal and often require complex bone grafting. However, these grafts carry risks, such as tissue rejection, infections, and surgical site damage, necessitating the development of alternative treatments. Three-dimensional and four-dimensional printed synthetic biomaterials represent a viable alternative, as they carry low production costs and are highly reproducible. Hyperelastic bone (HB), a biocompatible synthetic polymer consisting of 90% hydroxyapatite and 10% poly(lactic-co-glycolic acid, PLGA), was examined for its potential to support cell adhesion, migration, and proliferation. Specifically, we seeded collagen-coated HB with MG-63 human osteosarcoma cells. Our analysis revealed robust cell adhesion and proliferation over 7 days in vitro, with cells forming uniform monolayers on the external surface of the scaffold. However, no cells were present on the core of the fibers. The cells expressed bone differentiation markers on days 3 and 5. By day 7, the scaffold began to degrade, developing microscopic fissures and fragmentation. In summary, collagen-coated HB scaffolds support cell adhesion and proliferation but exhibit reduced structural support after 7 days in culture. Nevertheless, the intricate 3D architecture holds promise for cellular migration, vascularization, and early osteogenesis. Full article

(This article belongs to the Special Issue Bio-Inspired and Biomimetic Materials for Healthcare: From Nature to Clinics)

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17 pages, 7395 KiB

Open AccessEditor’s ChoiceArticle

Influence of Surface Preparation on the Microstructure and Mechanical Properties of Cold-Sprayed Nickel Coatings on Al 7075 Alloy

by Wojciech Żórawski, Anna Góral, Medard Makrenek, Lidia Lityńska-Dobrzyńska and Paweł Czaja

Materials 2023, 16(21), 7002; https://doi.org/10.3390/ma16217002 - 1 Nov 2023

Viewed by 1055

Abstract

This work presents the effect of surface roughness (Al 7075) on the microstructure and mechanical properties of cold-sprayed nickel coatings. Coating analysis included substrate surfaces and coating geometry, microstructure characterization, microhardness, nanohardness, elastic modulus, and adhesion. The results show that the surface preparation [...] Read more.

This work presents the effect of surface roughness (Al 7075) on the microstructure and mechanical properties of cold-sprayed nickel coatings. Coating analysis included substrate surfaces and coating geometry, microstructure characterization, microhardness, nanohardness, elastic modulus, and adhesion. The results show that the surface preparation had a significant effect on coating adhesion and microstructure. The coating deposited at the highest gas temperature revealed a dense microstructure, showing very good adhesion of the impacting powder particles to the substrate and good bonding between deposited layers. The Ni grains with different shapes (elongated, equiaxed) and sizes of a few dozen to several hundred nanometres were present in the splats. An increase in temperature caused significant growth in coating thickness as a result of the powder grains’ higher velocity. Moreover, higher gas temperature resulted in the enhancement of micro- and nanohardness, elastic modulus, and adhesion. The adhesive bond strength of Ni coatings in the tested temperature ranges from 500 °C to 800 °C increased with the increase in the surface roughness of the substrate. For the Al 7075 coarse grit-blasted (CG) substrate with the highest roughness, the adhesion reached the highest value of 44.6 MPa when the working gas was at a temperature of 800 °C. There were no distinct dependencies of surface roughness and thickness on the mechanical properties of the cold-sprayed nickel coating. Full article

(This article belongs to the Special Issue Quality, Microstructure and Properties of Metal Alloys (Second Volume))

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13 pages, 4111 KiB

Open AccessEditor’s ChoiceArticle

Synergetic Effect and Phase Engineering by Formation of Ti₃C₂T_x Modified 2H/1T-MoSe₂ Composites for Enhanced HER

by Lei Xiao, Qichao Yang, Xiangyang Zhu, Yang Wei and Jing Wang

Materials 2023, 16(21), 6991; https://doi.org/10.3390/ma16216991 - 31 Oct 2023

Cited by 1 | Viewed by 1339

Abstract

The typical semi conductivity and few active sites of hydrogen evolution of 2H MoSe₂ severely restrict its electrocatalytic hydrogen evolution performance. At the same time, the 1T MoSe₂ has metal conductivity and plentiful hydrogen evolution sites, making it feasible to optimize [...] Read more.

The typical semi conductivity and few active sites of hydrogen evolution of 2H MoSe₂ severely restrict its electrocatalytic hydrogen evolution performance. At the same time, the 1T MoSe₂ has metal conductivity and plentiful hydrogen evolution sites, making it feasible to optimize the electrocatalytic hydrogen evolution behavior of MoSe₂ using phase engineering. In this study, we, through a simple one-step hydrothermal method, composed 1T/2H MoSe₂, and then used newly emerging transition metal carbides with several atomic-layer thicknesses Ti₃C₂T_x to improve the conductivity of a MoSe_2-based electrocatalyst. Finally, MoSe₂@Ti₃C₂T_x was successfully synthesized, according to the control of the additional amount of Ti₃C₂T_x, to form a proper MoSe₂/ Ti₃C₂T_x heterostructure with a better electrochemical HER performance. As obtained MoSe₂@4 mg-Ti₃C₂T_x achieved a low overpotential, a small Tafel slope and this work offers additional insight into broadened MoSe₂ and MXenes-based catalyst’s electrochemical application. Full article

(This article belongs to the Special Issue Electrochemical Material Science and Electrode Processes)

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11 pages, 4019 KiB

Open AccessEditor’s ChoiceArticle

Study on the Stability of Cu-Ni Cluster Components and the Effect of Strain on Its Structure

by Xiaochuan Zeng, Cuizhu He, Xuejun Li and Qiaodan Hu

Materials 2023, 16(21), 6952; https://doi.org/10.3390/ma16216952 - 30 Oct 2023

Viewed by 1033

Abstract

Solute clusters are one of the important mechanisms of irradiation embrittlement of ferritic steels. It is of great significance to study the stability of solute clusters in ferritic steels and their effects on the mechanical properties of the materials. Molecular dynamics was used [...] Read more.

Solute clusters are one of the important mechanisms of irradiation embrittlement of ferritic steels. It is of great significance to study the stability of solute clusters in ferritic steels and their effects on the mechanical properties of the materials. Molecular dynamics was used to study the binding energy, defect energy, and interaction energy of 2 nm-diameter Cu-Ni clusters in the ferritic lattice, which have six categories of Cu-Ni clusters, such as the pure Cu cluster, the core–shell structural cluster with one layer to four layers of Ni atoms and the pure Ni cluster. It was found that Cu-Ni clusters have lower energy advantages than pure Ni clusters. Through shear strain simulation of the three clusters, the structure of 2 nm diameter clusters does not undergo phase transformation. The number of slip systems and the length of dislocation lines in the cluster system are positively correlated with the magnitude of the critical stress of material plastic deformation. Full article

(This article belongs to the Special Issue Key Materials in Nuclear Reactors)

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13 pages, 4155 KiB

Open AccessEditor’s ChoiceArticle

Cyclic Voltammetry of C.I. Disperse Orange 62 in an Aqueous Electrolyte

by Thomas Bechtold, Noemí Aguiló-Aguayo and Tung Pham

Materials 2023, 16(21), 6901; https://doi.org/10.3390/ma16216901 - 27 Oct 2023

Viewed by 1089

Abstract

Disperse dyes are an important group of colorants for dyeing polyester fibers. Approximately 30.000 tons of disperse dyes are released into the waste water annually from spent dyebaths. Therefore, methods for decolorizing such dyes are of general interest. The reductive after-treatment of disperse [...] Read more.

Disperse dyes are an important group of colorants for dyeing polyester fibers. Approximately 30.000 tons of disperse dyes are released into the waste water annually from spent dyebaths. Therefore, methods for decolorizing such dyes are of general interest. The reductive after-treatment of disperse dyes using reducing agents, such as Na₂S₂O₄, is a widely used process to improve rub fastness through dye reduction. Electrochemical dye reduction could be an alternative process for reductive dye treatment. In this work C.I. Disperse Orange 62 was used as a representative dye to study the direct cathodic reduction of a disperse dye with cyclic voltammetry. As anticipated for dispersed organic matter, relatively low current densities were observed, which strongly depend on the state of dispersion of the dye. The current density was increased by using dispersions prepared through dye precipitation from DMF solution and by the use of N-cetyl-N,N,N,-trimethyl-ammonium bromide as a cationic surfactant. The results demonstrate the successful cathodic reduction of a dispersed organic dye; however, the low solubility of the reaction products in the aqueous electrolyte hinders an efficient cathodic dye reduction. Full article

(This article belongs to the Special Issue Electrochemistry of Organic Compounds and Their Applications)

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22 pages, 4675 KiB

Open AccessEditor’s ChoiceArticle

Screening Ba_0.9A_0.1MnO₃ and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (A = Mg, Ca, Sr, Ce, La) Sol-Gel Synthesised Perovskites as GPF Catalysts

by Nawel Ghezali, Álvaro Díaz Verde and María José Illán Gómez

Materials 2023, 16(21), 6899; https://doi.org/10.3390/ma16216899 - 27 Oct 2023

Cited by 4 | Viewed by 1187

Abstract

Ba_0.9A_0.1MnO₃ (BM-A) and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A) (A = Mg, Ca, Sr, Ce, La) perovskite-type mixed oxides were synthesised, characterised, and used for soot oxidation in simulated Gasoline Direct Injection (GDI) [...] Read more.

Ba_0.9A_0.1MnO₃ (BM-A) and Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A) (A = Mg, Ca, Sr, Ce, La) perovskite-type mixed oxides were synthesised, characterised, and used for soot oxidation in simulated Gasoline Direct Injection (GDI) engine exhaust conditions. The samples have been obtained by the sol-gel method in an aqueous medium and deeply characterised. The characterization results indicate that the partial substitution of Ba by A metal in BaMnO₃ (BM) and BaMn_0.7Cu_0.3O₃ (BMC) perovskites: (i) favours the hexagonal structure of perovskite; (ii) improves the reducibility and the oxygen desorption during Temperature-Programmed Desorption (O₂-TPD) tests and, consequently, the oxygen mobility; (iii) mantains the amount of oxygen vacancies and of Mn(IV) and Mn(III) oxidation states, being Mn(IV) the main one; and (iv) for Ba_0.9A_0.1Mn_0.7Cu_0.3O₃ (BMC-A) series, copper is partially incorporated into the structure. The soot conversion data reveal that Ba_0.9La_0.1Mn_0.7Cu_0.3O₃ (BMC-La) is the most active catalyst in an inert (100% He) reaction atmosphere, as it presents the highest amount of copper on the surface, and that Ba_0.9Ce_0.1MnO₃ (BM-Ce) is the best one if a low amount of O₂ (1% O₂ in He) is present, as it combines the highest emission of oxygen with the good redox properties of Ce(IV)/Ce(III) and Mn(IV)/Mn(III) pairs. Full article

(This article belongs to the Special Issue Sol-Gel Technology Applied to Materials Science: Synthesis, Characterization and Applications)

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17 pages, 5028 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Bioactive Glass and Zinc Oxide Nanoparticles with Enamel Remineralization and Antimicrobial Capabilities

by Ryota Nagasaki, Keiji Nagano, Takashi Nezu and Masahiro Iijima

Materials 2023, 16(21), 6878; https://doi.org/10.3390/ma16216878 - 26 Oct 2023

Viewed by 1370

Abstract

Background: We investigated the effect of bioactive glass and zinc oxide nanoparticles on enamel remineralization, as well as their antimicrobial effect on cariogenic microbes. This is the first study that investigated the properties of bioactive glass and zinc oxide nanoparticles with mixed materials. [...] Read more.

Background: We investigated the effect of bioactive glass and zinc oxide nanoparticles on enamel remineralization, as well as their antimicrobial effect on cariogenic microbes. This is the first study that investigated the properties of bioactive glass and zinc oxide nanoparticles with mixed materials. Methods: Fluoride gel (F), bioactive glass microparticles (µB), bioactive glass nanoparticles (nB), zinc oxide nanoparticles (Z), and a mixed suspension of nB and Z (nBZ) were prepared and characterized by scanning and transmission electron microscopy, zeta potential measurement, X-ray diffraction, and acid buffering capacity testing. Further, we performed a remineralization cycle test of 28 days, and nanoindentation testing was carried out during the immersion period, and then the enamel surfaces were examined using scanning electron microscopy. Additionally, the antimicrobial effects of the sample suspensions were evaluated by measuring their minimum microbicidal concentrations against various cariogenic microbes. Results: Our results revealed that nB had a near-circular shape with an amorphous structure and a considerably large specific surface area due to nanoparticulation. Additionally, nB possessed a rapid acid buffering capacity that was comparable to that of μB. In the remineralization test, faster recovery of mechanical properties was observed on the enamel surface immersed in samples containing bioactive glass nanoparticles (nB and nBZ). After remineralization, demineralized enamel immersed in any of the samples showed a rough and porous surface structure covered with mineralized structures. Furthermore, nBZ exhibited a broad antimicrobial spectrum. Conclusions: These results demonstrated that bioactive glass and zinc oxide nanoparticles have superior demineralization-suppressing and remineralization-promoting effects. Full article

(This article belongs to the Special Issue The Search for Real Biologically Active Dental Materials of the Future)

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11 pages, 627 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Stress Concentration in Functionally Graded Plates with Linearly Increasing Young’s Modulus

by Hassan Mohamed Abdelalim Abdalla, Daniele Casagrande and Francesco De Bona

Materials 2023, 16(21), 6882; https://doi.org/10.3390/ma16216882 - 26 Oct 2023

Cited by 4 | Viewed by 1296

Abstract

In this article, the strain and stress analyses of functionally graded plates with circular holes that are subject to a uniaxial far-field traction load are analytically considered. The Young’s modulus is assumed to vary linearly along the radial direction around the hole. The [...] Read more.

In this article, the strain and stress analyses of functionally graded plates with circular holes that are subject to a uniaxial far-field traction load are analytically considered. The Young’s modulus is assumed to vary linearly along the radial direction around the hole. The adoption of such a type of inhomogeneity variation can be justified as follows. Firstly, and among all the possible variations of stiffness, the linear one is indeed the simplest inhomogeneity distribution. Surprisingly however, according to our knowledge extent, the associated elastic fields were not yet addressed in the literature. Secondly, a linearly varying stiffness could reasonably imply a remarkable advantage from a technological point of view. In fact, unlike nonlinearly varying stiffness plates, manufacturing routes are only required to handle constant variations throughout the radial domain. After recalling the basic equations for plane stress elasticity, the displacement, strain, and stress fields around the hole were numerically tackled and discussed for different stiffness ratios. A comparison was also carried out with other Young’s modulus distributions that have been commonly employed in the literature. Full article

(This article belongs to the Section Advanced Composites)

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14 pages, 3835 KiB

Open AccessEditor’s ChoiceArticle

Martensitic Phase-Transforming Metamaterial: Concept and Model

by Sosuke Kanegae, Masayuki Okugawa and Yuichiro Koizumi

Materials 2023, 16(21), 6854; https://doi.org/10.3390/ma16216854 - 25 Oct 2023

Viewed by 1231

Abstract

We successfully developed a mechanical metamaterial that displays martensitic transformation for the first time. This metamaterial has a bistable structure capable of transitioning between two stable configurations through shear deformation. The outer shape of the unit cell of this structure is a parallelogram, [...] Read more.

We successfully developed a mechanical metamaterial that displays martensitic transformation for the first time. This metamaterial has a bistable structure capable of transitioning between two stable configurations through shear deformation. The outer shape of the unit cell of this structure is a parallelogram, with its upper and lower sides forming the bases of two solid triangles. The vertices from these triangles within the parallelogram are linked by short beams, while the remaining vertices are linked by long beams. The elastic energy of the essential model of the metamaterial was formulated analytically. The energy barrier between these two stable configurations consists of the elastic strain energy due to the tensile deformation of the short beams, the compressive deformation of the long beams, and the bending deformation of the connecting hinges. One example of a novel metamaterial was additively manufactured via the materials extrusion (MEX) process of thermoplastic polyurethane. The metamaterial exhibited deformation behaviors characteristic of martensitic transformations. This mechanical metamaterial has the potential to obtain properties caused by martensitic transformation in actual materials, such as the shape memory effect and superelasticity. Full article

(This article belongs to the Special Issue Acoustic and Mechanical Metamaterials: Recent Advances)

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16 pages, 4388 KiB

Open AccessEditor’s ChoiceArticle

Durability Analysis of CFRP Adhesive Joints: A Study Based on Entropy Damage Modeling Using FEM

by Yutong Li, Huachao Deng, Maruri Takamura and Jun Koyanagi

Materials 2023, 16(20), 6821; https://doi.org/10.3390/ma16206821 - 23 Oct 2023

Cited by 2 | Viewed by 1292

Abstract

Experimental methodologies for fatigue lifetime prediction are time-intensive and susceptible to environmental variables. Although the cohesive zone model is popular for predicting adhesive fatigue lifetime, entropy-based methods have also displayed potential. This study aims to (1) provide an understanding of the durability characteristics [...] Read more.

Experimental methodologies for fatigue lifetime prediction are time-intensive and susceptible to environmental variables. Although the cohesive zone model is popular for predicting adhesive fatigue lifetime, entropy-based methods have also displayed potential. This study aims to (1) provide an understanding of the durability characteristics of carbon fiber-reinforced plastic (CFRP) adhesive joints by incorporating an entropy damage model within the context of the finite element method and (2) examine the effects of different adhesive layer thicknesses on single-lap shear models. As the thickness of the adhesive layer increases, damage variables initially increase and then decrease. These peak at 0.3 mm. This observation provides a crucial understanding of the stress behavior at the resin–CFRP interface and the fatigue mechanisms of the resin. Full article

(This article belongs to the Special Issue Advanced Composite Material Design and Manufacturing Technology for Aerospace Engineering (2nd Edition))

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30 pages, 5370 KiB

Open AccessEditor’s ChoiceArticle

A Method for Predicting the Creep Rupture Life of Small-Sample Materials Based on Parametric Models and Machine Learning Models

by Xu Zhang, Jianyao Yao, Yulin Wu, Xuyang Liu, Changyin Wang and Hao Liu

Materials 2023, 16(20), 6804; https://doi.org/10.3390/ma16206804 - 22 Oct 2023

Cited by 4 | Viewed by 1917

Abstract

In view of the differences in the applicability and prediction ability of different creep rupture life prediction models, we propose a creep rupture life prediction method in this paper. Various time–temperature parametric models, machine learning models, and a new method combining time–temperature parametric [...] Read more.

In view of the differences in the applicability and prediction ability of different creep rupture life prediction models, we propose a creep rupture life prediction method in this paper. Various time–temperature parametric models, machine learning models, and a new method combining time–temperature parametric models with machine learning models are used to predict the creep rupture life of a small-sample material. The prediction accuracy of each model is quantitatively compared using model evaluation indicators (RMSE, MAPE, R²), and the output values of the most accurate model are used as the output values of the prediction method. The prediction method not only improves the applicability and accuracy of creep rupture life predictions but also quantifies the influence of each input variable on creep rupture life through the machine learning model. A new method is proposed in order to effectively take advantage of both advanced machine learning models and classical time–temperature parametric models. Parametric equations of creep rupture life, stress, and temperature are obtained using different time–temperature parametric models; then, creep rupture life data, obtained via equations under other temperature and stress conditions, are used to expand the training set data of different machine learning models. By expanding the data of different intervals, the problem of the low accuracy of the machine learning model for the small-sample material is solved. Full article

(This article belongs to the Special Issue Analytical and Computational Methods in Material and Mechanical Engineering)

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13 pages, 11044 KiB

Open AccessEditor’s ChoiceArticle

Tellurium Corrosion of Type 304/304L Stainless Steel, Iron, Chromium, and Nickel in High-Temperature Liquid Sodium

by Yi Xie

Materials 2023, 16(20), 6798; https://doi.org/10.3390/ma16206798 - 21 Oct 2023

Cited by 3 | Viewed by 1145

Abstract

Investigating tellurium (Te) corrosion on structural materials is crucial for sodium-cooled fast reactors (SFRs) due to radionuclide presence and knowledge gaps. In this study, Type 304/304L stainless steel (SS304), chromium (Cr), iron (Fe), and nickel (Ni) samples were immersed in low-oxygen environments with [...] Read more.

Investigating tellurium (Te) corrosion on structural materials is crucial for sodium-cooled fast reactors (SFRs) due to radionuclide presence and knowledge gaps. In this study, Type 304/304L stainless steel (SS304), chromium (Cr), iron (Fe), and nickel (Ni) samples were immersed in low-oxygen environments with Te in liquid sodium at 773 K for 30 days. At 10 ppm oxygen, SS304 showed multiple oxide layers, including a compact NaCrO₂ interlayer and porous Na-Fe-Ni-O outer layers. Tellurium penetrated through the porous layers but was hindered by the NaCrO₂ interlayer. At 0.01 ppm oxygen, Cr had no oxide layer, while Fe and Ni had unstable ones. Tellurium-induced pitting was deeper in Fe and Ni compared to Cr. Oxygen levels and Cr composition are critical factors affecting stable oxide compound layer formation and mitigating Te-induced pitting. Full article

(This article belongs to the Section Corrosion)

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16 pages, 7283 KiB

Open AccessEditor’s ChoiceArticle

Network Structure and Luminescent Properties of ZnO–B₂O₃–Bi₂O₃–WO₃:Eu³⁺ Glasses

by Aneliya Yordanova, Margarita Milanova, Reni Iordanova, Margit Fabian, Lyubomir Aleksandrov and Petia Petrova

Materials 2023, 16(20), 6779; https://doi.org/10.3390/ma16206779 - 20 Oct 2023

Cited by 2 | Viewed by 1399

Abstract

In this study, we investigated the influence of Bi₂O₃ and WO₃ on both structure and optical properties of 50ZnO:(49 − x)B₂O₃:1Bi₂O₃:xWO₃; x = 1, 5, 10 glasses doped with [...] Read more.

In this study, we investigated the influence of Bi₂O₃ and WO₃ on both structure and optical properties of 50ZnO:(49 − x)B₂O₃:1Bi₂O₃:xWO₃; x = 1, 5, 10 glasses doped with 0.5 mol% Eu₂O₃. IR spectroscopy revealed the presence of trigonal BØ₃ units connecting superstructural groups, [BØ₂O]⁻ metaborate groups, tetrahedral BØ₄⁻ units in superstructural groupings (Ø = bridging oxygen atom), borate triangles with nonbridging oxygen atoms, [WO₄]²⁻ tetrahedral, and octahedral WO₆ species. Neutron diffraction experimental data were simulated by reverse Monte Carlo modeling. The atomic distances and coordination numbers were established, confirming the short-range order found by IR spectra. The synthesized glasses were characterized by red emission at 612 nm. All findings suggest that Eu³⁺ doped zinc borate glasses containing both WO₃ and Bi₂O₃ have the potential to serve as a substitute for red phosphor with high color purity. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application)

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14 pages, 2178 KiB

Open AccessEditor’s ChoiceArticle

Dual-Emissive Monoruthenium Complexes of N(CH₃)-Bridged Ligand: Synthesis, Characterization, and Substituent Effect

by Si-Hai Wu, Zhe Zhang, Ren-Hui Zheng, Rong Yang, Lianhui Wang, Jiang-Yang Shao, Zhong-Liang Gong and Yu-Wu Zhong

Materials 2023, 16(20), 6792; https://doi.org/10.3390/ma16206792 - 20 Oct 2023

Cited by 1 | Viewed by 1118

Abstract

Three monoruthenium complexes 1(PF₆)₂–3(PF₆)₂ bearing an N(CH₃)-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)₂(L)](PF₆)₂, where L [...] Read more.

Three monoruthenium complexes 1(PF₆)₂–3(PF₆)₂ bearing an N(CH₃)-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)₂(L)](PF₆)₂, where L is a 2,5-di(N-methyl-N’-(pyrid-2-yl)amino)pyrazine (dapz) derivative with various substituents, and bpy is 2,2′-bipyridine. The photophysical and electrochemical properties of these compounds have been examined. The solid-state structure of complex 3(PF₆)₂ is studied by single-crystal X-ray analysis. These complexes show two well-separated emission bands centered at 451 and 646 nm (Δλ_max = 195 nm) for 1(PF₆)₂, 465 and 627 nm (Δλ_max = 162 nm) for 2(PF₆)₂, and 455 and 608 nm (Δλ_max = 153 nm) for 3(PF₆)₂ in dilute acetonitrile solution, respectively. The emission maxima of the higher-energy emission bands of these complexes are similar, while the lower-energy emission bands are dependent on the electronic nature of substituents. These complexes display two consecutive redox couples owing to the stepwise oxidation of the N(CH₃)-bridged ligand and ruthenium component. Moreover, these experimental observations are analyzed by computational investigation. Full article

(This article belongs to the Special Issue Advanced Materials for Luminescent Applications)

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24 pages, 8416 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Grain-Growth Mean-Field Models Regarding Predicted Grain Size Distributions

by Marion Roth, Baptiste Flipon, Nathalie Bozzolo and Marc Bernacki

Materials 2023, 16(20), 6761; https://doi.org/10.3390/ma16206761 - 19 Oct 2023

Cited by 2 | Viewed by 1082

Abstract

Mean-field models have the ability to predict the evolution of grain size distribution that occurs through thermomechanical solicitations. This article focuses on a comparison of mean-field models under grain-growth conditions. Different microstructure representations are considered and discussed, especially regarding the consideration of topology [...] Read more.

Mean-field models have the ability to predict the evolution of grain size distribution that occurs through thermomechanical solicitations. This article focuses on a comparison of mean-field models under grain-growth conditions. Different microstructure representations are considered and discussed, especially regarding the consideration of topology in the neighborhood construction. Experimental data obtained with a heat treatment campaign on 316L austenitic stainless steel are used for the identification of material parameters and as a reference for model comparisons. Mean-field models are also applied to both mono- and bimodal initial grain size distributions to investigate the potential benefits of introducing neighborhood topology in microstructure prediction models. This article demonstrates that improvements in the predictions can be obtained in monomodal cases for topological models. In the bimodal test, no comparison with experimental data was performed as no data were available. But relative comparisons between models indicated few differences in the predictions. Although of interest, the consideration of neighborhood topology in grain-growth mean-field models generally results in only small improvements compared to classical mean-field models, especially in terms of implementation complexity. Full article

(This article belongs to the Special Issue Modeling and Simulation of Solid State Phenomena in Metals and Alloys)

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14 pages, 10278 KiB

Open AccessEditor’s ChoiceArticle

The Characteristic of

{10 \bar{1} 2} < 10 \bar{1} \bar{1} >

Twin of Ti-10V-2Fe-3Al under Planar Wave Detonation

by Tong Wang, Ping Yang, Jin Zhang and Xin-Fu Gu

Materials 2023, 16(20), 6739; https://doi.org/10.3390/ma16206739 - 18 Oct 2023

Viewed by 1040

Abstract

The microstructure evolution of the twin of TB6 (Ti-10V-2Fe-3Al) under planar wave detonation was studied. The initial microstructure of the alloy consists of an α and β phase. It is found that twin deformation is operated in only the α phase due to [...] Read more.

The microstructure evolution of the twin of TB6 (Ti-10V-2Fe-3Al) under planar wave detonation was studied. The initial microstructure of the alloy consists of an α and β phase. It is found that twin deformation is operated in only the α phase due to the limited slip system in this phase. α grains are mainly rotated from

{10 \bar{1} 0}

to

{0002}

during the deformation due to the

{10 \bar{1} 2} < 10 \bar{1} \bar{1} >

twin. Twin variant selection is found in this study, and the orientation of all

{10 \bar{1} 2}

twins is oriented at

{0002}

in different α grains with different deformation degrees. The twin variant selection is well explained based on the strain relaxation along the loading axis and the Schmid factor for twinning shear. Full article

(This article belongs to the Special Issue Quality, Microstructure and Properties of Metal Alloys (Second Volume))

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13 pages, 6242 KiB

Open AccessEditor’s ChoiceArticle

Improved Energy Storage Density and Efficiency of Nd and Mn Co-Doped Ba_0.7Sr_0.3TiO₃ Ceramic Capacitors Via Defect Dipole Engineering

by Hyunsu Choi, Srinivas Pattipaka, Yong Hoon Son, Young Min Bae, Jung Hwan Park, Chang Kyu Jeong, Han Eol Lee, Sung-Dae Kim, Jungho Ryu and Geon-Tae Hwang

Materials 2023, 16(20), 6753; https://doi.org/10.3390/ma16206753 - 18 Oct 2023

Cited by 2 | Viewed by 1626

Abstract

In this paper, we investigate the structural, microstructural, dielectric, and energy storage properties of Nd and Mn co-doped Ba_0.7Sr_0.3TiO₃ [(Ba_0.7Sr_0.3)_1−xNd_xTi_1−yMn_yO₃ (BSNTM) ceramics ( [...] Read more.

In this paper, we investigate the structural, microstructural, dielectric, and energy storage properties of Nd and Mn co-doped Ba_0.7Sr_0.3TiO₃ [(Ba_0.7Sr_0.3)_1−xNd_xTi_1−yMn_yO₃ (BSNTM) ceramics (x = 0, 0.005, and y = 0, 0.0025, 0.005, and 0.01)] via a defect dipole engineering method. The complex defect dipoles

{(M n}_{T i}^{”} - V_{O}^{∙ ∙})^{∙}

and

{(M n}_{T i}^{”} - V_{O}^{∙ ∙})

between acceptor ions and oxygen vacancies capture electrons, enhancing the breakdown electric field and energy storage performances. XRD, Raman, spectroscopy, XPS, and microscopic investigations of BSNTM ceramics revealed the formation of a tetragonal phase, oxygen vacancies, and a reduction in grain size with Mn dopant. The BSNTM ceramics with x = 0.005 and y = 0 exhibit a relative dielectric constant of 2058 and a loss tangent of 0.026 at 1 kHz. These values gradually decreased to 1876 and 0.019 for x = 0.005 and y = 0.01 due to the Mn²⁺ ions at the Ti⁴⁺- site, which facilitates the formation of oxygen vacancies, and prevents a decrease in Ti⁴⁺. In addition, the defect dipoles act as a driving force for depolarization to tailor the domain formation energy and domain wall energy, which provides a high difference between the maximum polarization of P_max and remnant polarization of P_r (ΔP = 10.39 µC/cm²). Moreover, the complex defect dipoles with optimum oxygen vacancies in BSNTM ceramics can provide not only a high ΔP but also reduce grain size, which together improve the breakdown strength from 60.4 to 110.6 kV/cm, giving rise to a high energy storage density of 0.41 J/cm³ and high efficiency of 84.6% for x = 0.005 and y = 0.01. These findings demonstrate that defect dipole engineering is an effective method to enhance the energy storage performance of dielectrics for capacitor applications. Full article

(This article belongs to the Special Issue Ferromagnetic and Ferroelectric Materials: Synthesis, Applications, and Techniques)

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14 pages, 2510 KiB

Open AccessEditor’s ChoiceArticle

Machine Learning Prediction of the Redox Activity of Quinones

by Ilia Kichev, Lyuben Borislavov, Alia Tadjer and Radostina Stoyanova

Materials 2023, 16(20), 6687; https://doi.org/10.3390/ma16206687 - 14 Oct 2023

Cited by 1 | Viewed by 1358

Abstract

The redox properties of quinones underlie their unique characteristics as organic battery components that outperform the conventional inorganic ones. Furthermore, these redox properties could be precisely tuned by using different substituent groups. Machine learning and statistics, on the other hand, have proven to [...] Read more.

The redox properties of quinones underlie their unique characteristics as organic battery components that outperform the conventional inorganic ones. Furthermore, these redox properties could be precisely tuned by using different substituent groups. Machine learning and statistics, on the other hand, have proven to be very powerful approaches for the efficient in silico design of novel materials. Herein, we demonstrated the machine learning approach for the prediction of the redox activity of quinones that potentially can serve as organic battery components. For the needs of the present study, a database of small quinone-derived molecules was created. A large number of quantum chemical and chemometric descriptors were generated for each molecule and, subsequently, different statistical approaches were applied to select the descriptors that most prominently characterized the relationship between the structure and the redox potential. Various machine learning methods for the screening of prospective organic battery electrode materials were deployed to select the most trustworthy strategy for the machine learning-aided design of organic redox materials. It was found that Ridge regression models perform better than Regression decision trees and Decision tree-based ensemble algorithms. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application)

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12 pages, 9218 KiB

Open AccessEditor’s ChoiceArticle

Characterization of the Metal Fused Filament Fabrication Process for Manufacturing of Pure Copper Inductors

by Philipp Schüßler, Jonas Franke, Steffen Czink, Steffen Antusch, Daniel Mayer, Stephan Laube, Thomas Hanemann, Volker Schulze and Stefan Dietrich

Materials 2023, 16(20), 6678; https://doi.org/10.3390/ma16206678 - 13 Oct 2023

Cited by 6 | Viewed by 1551

Abstract

This work presents a comprehensive investigation into the optimization of critical process parameters associated with metal fused filament fabrication (Metal-FFF) for the production of copper-based components. The study focused on three different commercial and one self-manufactured filament, each with unique chemical compositions. These [...] Read more.

This work presents a comprehensive investigation into the optimization of critical process parameters associated with metal fused filament fabrication (Metal-FFF) for the production of copper-based components. The study focused on three different commercial and one self-manufactured filament, each with unique chemical compositions. These filaments were systematically optimized and the density was characterized for all processing steps, as well as the electrical conductivity on the specimen scale. Remarkably, two of the studied filaments exhibited exceptional properties after sintering with forming gas (up to 94% density and

55.75

M

S

/

m

electrical conductivity), approaching the properties measured for established manufacturing methods like metal injection molding. Finally, the research was extended to component-scale applications, demonstrating the successful fabrication of inductors with integrated cooling channels. These components exhibited water tightness and were used in induction hardening experiments, validating the practical utility of the optimized Metal-FFF process. In summary, the results show great promise in advancing the utilization of Metal-FFF in industrial contexts, particularly in the production of high-performance copper components. Full article

(This article belongs to the Section Metals and Alloys)

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12 pages, 2179 KiB

Open AccessEditor’s ChoiceArticle

Anisotropic Properties of Epitaxial Ferroelectric Lead-Free 0.5[Ba(Ti_0.8Zr_0.2)O₃]-0.5(Ba_0.7Ca_0.3)TiO₃ Films

by Nicholas Cucciniello, Alessandro R. Mazza, Pinku Roy, Sundar Kunwar, Di Zhang, Henry Y. Feng, Katrina Arsky, Aiping Chen and Quanxi Jia

Materials 2023, 16(20), 6671; https://doi.org/10.3390/ma16206671 - 13 Oct 2023

Cited by 2 | Viewed by 1429

Abstract

As the energy demand is expected to double over the next 30 years, there has been a major initiative towards advancing the technology of both energy harvesting and storage for renewable energy. In this work, we explore a subset class of dielectrics for [...] Read more.

As the energy demand is expected to double over the next 30 years, there has been a major initiative towards advancing the technology of both energy harvesting and storage for renewable energy. In this work, we explore a subset class of dielectrics for energy storage since ferroelectrics offer a unique combination of characteristics needed for energy storage devices. We investigate ferroelectric lead-free 0.5[Ba(Ti_0.8Zr_0.2)O₃]-0.5(Ba_0.7Ca_0.3)TiO₃ epitaxial thin films with different crystallographic orientations grown by pulsed laser deposition. We focus our attention on the influence of the crystallographic orientation on the microstructure, ferroelectric, and dielectric properties. Our results indicate an enhancement of the polarization and strong anisotropy in the dielectric response for the (001)-oriented film. The enhanced ferroelectric, energy storage, and dielectric properties of the (001)-oriented film is explained by the coexistence of orthorhombic-tetragonal phase, where the disordered local structure is in its free energy minimum. Full article

(This article belongs to the Special Issue Ferromagnetic and Ferroelectric Materials: Synthesis, Applications, and Techniques)

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10 pages, 2782 KiB

Open AccessEditor’s ChoiceCommunication

Cubic Nonlinearity of Graphene-Oxide Monolayer

by Tikaram Neupane, Uma Poudyal, Bagher Tabibi, Wan-Joong Kim and Felix Jaetae Seo

Materials 2023, 16(20), 6664; https://doi.org/10.3390/ma16206664 - 12 Oct 2023

Cited by 2 | Viewed by 964

Abstract

The cubic nonlinearity of a graphene-oxide monolayer was characterized through open and closed z−scan experiments, using a nano-second laser operating at a 10 Hz repetition rate and featuring a Gaussian spatial beam profile. The open z−scan revealed a reverse saturable absorption, indicating a [...] Read more.

The cubic nonlinearity of a graphene-oxide monolayer was characterized through open and closed z−scan experiments, using a nano-second laser operating at a 10 Hz repetition rate and featuring a Gaussian spatial beam profile. The open z−scan revealed a reverse saturable absorption, indicating a positive nonlinear absorption coefficient, while the closed z−scan displayed valley-peak traces, indicative of positive nonlinear refraction. This observation suggests that, under the given excitation wavelength, a two-photon or two-step excitation process occurs due to the increased absorption in both the lower visible and upper UV wavelength regions. This finding implies that graphene oxide exhibits a higher excited-state absorption cross-section compared to its ground state. The resulting nonlinear absorption and nonlinear refraction coefficients were estimated to be approximately ~2.62 × 10⁻⁸ m/W and 3.9 × 10⁻¹⁵ m²/W, respectively. Additionally, this study sheds light on the interplay between nonlinear absorption and nonlinear refraction traces, providing valuable insights into the material’s optical properties. Full article

(This article belongs to the Special Issue Advanced Graphene and Graphene Oxide Materials)

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15 pages, 10779 KiB

Open AccessEditor’s ChoiceArticle

Phosphorus-Doped Hollow Tubular g-C₃N₄ for Enhanced Photocatalytic CO₂ Reduction

by Manying Sun, Chuanwei Zhu, Su Wei, Liuyun Chen, Hongbing Ji, Tongming Su and Zuzeng Qin

Materials 2023, 16(20), 6665; https://doi.org/10.3390/ma16206665 - 12 Oct 2023

Cited by 5 | Viewed by 1574

Abstract

Photocatalytic CO₂ reduction is a tactic for solving the environmental pollution caused by greenhouse gases. Herein, NH₄H₂PO₄ was added as a phosphorus source in the process of the hydrothermal treatment of melamine for the first time, and [...] Read more.

Photocatalytic CO₂ reduction is a tactic for solving the environmental pollution caused by greenhouse gases. Herein, NH₄H₂PO₄ was added as a phosphorus source in the process of the hydrothermal treatment of melamine for the first time, and phosphorus-doped hollow tubular g-C₃N₄ (x-P-HCN) was fabricated and used for photocatalytic CO₂ reduction. Here, 1.0-P-HCN exhibited the largest CO production rate of 9.00 μmol·g⁻¹·h⁻¹, which was 10.22 times higher than that of bulk g-C₃N₄. After doping with phosphorus, the light absorption range, the CO₂ adsorption capacity, and the specific surface area of the 1.0-P-HCN sample were greatly improved. In addition, the separation of photogenerated electron–hole pairs was enhanced. Furthermore, the phosphorus-doped g-C₃N₄ effectively activated the CO₂ adsorbed on the surface of phosphorus-doped g-C₃N₄ photocatalysts, which greatly enhanced the CO production rate of photocatalytic CO₂ reduction over that of g-C₃N₄. Full article

(This article belongs to the Special Issue Advanced Photocatalytic Materials for Environmental and Energy Applications)

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14 pages, 27546 KiB

Open AccessEditor’s ChoiceArticle

Ce/Mn/Cr: (Re,Y)₃Al₅O₁₂ Phosphor Ceramics (Re = Gd, Tb and Lu) for White LED Lighting with Significant Spectral Redshift and Improved Color-Rendering Index

by Yukun Li, Svenja Hanson, Cheng Heng Pang, Peng Lyu and Jun Jiang

Materials 2023, 16(20), 6667; https://doi.org/10.3390/ma16206667 - 12 Oct 2023

Cited by 1 | Viewed by 1326

Abstract

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y_0.997−xRe_xCe_0.003)₃(Al_0.9748 Mn²⁺_0.024Cr³⁺_0.0012)₅O₁₂(Re_x = 0, Gd_0.333 [...] Read more.

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y_0.997−xRe_xCe_0.003)₃(Al_0.9748 Mn²⁺_0.024Cr³⁺_0.0012)₅O₁₂(Re_x = 0, Gd_0.333, Gd_0.666, Gd_0.997, Tb_0.333, Tb_0.666, Tb_0.997 and Lu_0.997 were prepared by solid-state reaction and vacuum sintering, and exhibited potential for high-quality, solid-state lighting. Doping with Cr³⁺ and Mn²⁺ effectively enhanced the red component of Ce³⁺ spectra through the intense energy transfer from Ce³⁺ ions to Mn²⁺/Cr³⁺ ions. The crystal field splitting of [GdO₈] and [TbO₈] was more extensive than that of [YO₈], causing a massive redshift in the Ce³⁺ emission peaks from 542 to 561 and 595 nm, while [LuO₈] had an opposite effect and caused a blueshift with a peak position at 512 nm. White LED devices incorporating Ce/Mn/Cr: (Gd_0.333Y_0.664)₃Al₅O₁₂ phosphor ceramic exhibited a high CRI of 83.97, highlighting the potential for enhancing the red-light component of white LED lighting. Full article

(This article belongs to the Special Issue Study on Rare Earth Doped Luminescent Materials and Transparent Ceramics)

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16 pages, 3821 KiB

Open AccessEditor’s ChoiceArticle

Mg, Zn Substituted Calcium Phosphates—Thermodynamic Modeling, Biomimetic Synthesis in the Presence of Low-Weight Amino Acids and High Temperature Properties

by Diana Rabadjieva, Rumiana Gergulova, Kostadinka Sezanova, Daniela Kovacheva and Rositsa Titorenkova

Materials 2023, 16(20), 6638; https://doi.org/10.3390/ma16206638 - 11 Oct 2023

Cited by 2 | Viewed by 1354

Abstract

The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs’ enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg [...] Read more.

The preparation of specially doped calcium phosphates (CaPs) is receiving a great deal of attention from researchers due to CaPs’ enhanced capabilities for application in medicine. Complexation and precipitation in a complicated electrolyte system including simulated body fluids that are enriched with Mg²⁺ and Zn²⁺ ions and modified with glycine, alanine and valine were first evaluated using a thermodynamic equilibrium model. The influence of the type and concentration of amino acid on the incorporation degree of Mg and Zn into the solid phases was predicted. Experimental studies, designed on the basis of thermodynamic calculations, confirmed the predictions. Amorphous calcium phosphates double-doped with Mg and Zn were biomimetically precipitated and transformed into Mg, Zn-β—tricalcium phosphates (TCP) upon calcination. The Rietveld refinement confirmed that Mg²⁺ and Zn²⁺ substituted Ca²⁺ only at the octahedral sites of β-TCP, and in some cases, fully displacing the Ca²⁺ from them. The resulting Mg, Zn-β–TCP can serve as a reservoir for Mg and Zn ions when included in the formulation of a biomaterial for bone remodeling. The research conducted reveals the effect of combining mathematical models with experimental studies to pre-evaluate the influence of various additives in the design of materials with predetermined properties. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application)

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18 pages, 4700 KiB

Open AccessEditor’s ChoiceArticle

Ultra-High-Temperature Ceramic-Doped Inorganic Polymers for Thermo-Structural Fiber-Reinforced Composites

by Valentina Medri, Annalisa Natali Murri, Elettra Papa, Claudio Mingazzini, Matteo Scafè and Elena Landi

Materials 2023, 16(20), 6649; https://doi.org/10.3390/ma16206649 - 11 Oct 2023

Viewed by 1813

Abstract

New inorganic nanostructured matrices for fiber-reinforced composites with enhanced high-temperature stability were developed from alkali aluminosilicate polymers doped with different ultra-high-temperature ceramic (UHTC) particles. The alkali aluminosilicate matrices were synthesized at room temperature with a high SiO₂:Al₂O₃ ratio [...] Read more.

New inorganic nanostructured matrices for fiber-reinforced composites with enhanced high-temperature stability were developed from alkali aluminosilicate polymers doped with different ultra-high-temperature ceramic (UHTC) particles. The alkali aluminosilicate matrices were synthesized at room temperature with a high SiO₂:Al₂O₃ ratio and then further functionalized by doping with 4–5 wt % of micrometric SiC, ZrB₂, ZrC, and HfC powders and finally thermally stabilized as glass–ceramics at 750 °C. The different UHTC-doped matrices were characterized according to their dimensional and microstructural changes after thermal cycling in air flux at 1000 °C. The first results showed that carbide-based UHTC powders improved the thermal stability of the matrices, preventing the excessive swelling of the material and the formation of detrimental voids that might result in the lack of adhesion with reinforcing fibers. Contrarily, the addition of ZrB₂ resulted in an excessive matrix swelling at high temperature, thus proving no efficacy compared to the undoped matrix. Impregnation tests carried out on C-fiber fabrics showed good processability, adhesion to the fibers, and fracture pull-out, especially for carbide-based matrices. Full article

(This article belongs to the Special Issue Advances in Functional Ceramic Materials: Fabrication, Properties, and High-Temperature Applications)

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17 pages, 2966 KiB

Open AccessEditor’s ChoiceReview

Molecular Design Concept for Enhancement Charge Carrier Mobility in OFETs: A Review

by Yang Zhou, Keke Zhang, Zhaoyang Chen and Haichang Zhang

Materials 2023, 16(20), 6645; https://doi.org/10.3390/ma16206645 - 11 Oct 2023

Cited by 6 | Viewed by 1842

Abstract

In the last two decades, organic field-effect transistors (OFETs) have garnered increasing attention from the scientific and industrial communities. The performance of OFETs can be evaluated based on three factors: the charge transport mobility (μ), threshold voltage (V_th), and current on/off [...] Read more.

In the last two decades, organic field-effect transistors (OFETs) have garnered increasing attention from the scientific and industrial communities. The performance of OFETs can be evaluated based on three factors: the charge transport mobility (μ), threshold voltage (V_th), and current on/off ratio (I_on/off). To enhance μ, numerous studies have concentrated on optimizing charge transport within the semiconductor layer. These efforts include: (i) extending π-conjugation, enhancing molecular planarity, and optimizing donor–acceptor structures to improve charge transport within individual molecules; and (ii) promoting strong aggregation, achieving well-ordered structures, and reducing molecular distances to enhance charge transport between molecules. In order to obtain a high charge transport mobility, the charge injection from the electrodes into the semiconductor layer is also important. Since a suitable frontier molecular orbitals’ level could align with the work function of the electrodes, in turn forming an Ohmic contact at the interface. OFETs are classified into p-type (hole transport), n-type (electron transport), and ambipolar-type (both hole and electron transport) based on their charge transport characteristics. As of now, the majority of reported conjugated materials are of the p-type semiconductor category, with research on n-type or ambipolar conjugated materials lagging significantly behind. This review introduces the molecular design concept for enhancing charge carrier mobility, addressing both within the semiconductor layer and charge injection aspects. Additionally, the process of designing or converting the semiconductor type is summarized. Lastly, this review discusses potential trends in evolution and challenges and provides an outlook; the ultimate objective is to outline a theoretical framework for designing high-performance organic semiconductors that can advance the development of OFET applications. Full article

(This article belongs to the Special Issue New Advances in π-Conjugated Materials)

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16 pages, 3618 KiB

Open AccessEditor’s ChoiceArticle

3D Composite U(VI) Adsorbents Based on Alginate Hydrogels and Oxidized Biochar Obtained from Luffa cylindrica

by Andreas Ayiotis, Efthalia Georgiou, Panagiotis S. Ioannou, Ioannis Pashalidis and Theodora Krasia-Christoforou

Materials 2023, 16(19), 6577; https://doi.org/10.3390/ma16196577 - 6 Oct 2023

Viewed by 1167

Abstract

3D naturally derived composites consisting of calcium alginate hydrogels (CA) and oxidized biochar obtained from Luffa cylindrica (ox-LC) were synthesized and further evaluated as adsorbents for the removal of U(VI) from aqueous media. Batch-type experiments were conducted to investigate the effect of various [...] Read more.

3D naturally derived composites consisting of calcium alginate hydrogels (CA) and oxidized biochar obtained from Luffa cylindrica (ox-LC) were synthesized and further evaluated as adsorbents for the removal of U(VI) from aqueous media. Batch-type experiments were conducted to investigate the effect of various physicochemical parameters on the adsorption performance of materials. The maximum adsorption capacity (q_max) was 1.7 mol kg⁻¹ (404.6 mg·g⁻¹) at pH 3.0 for the CA/ox-LC with a 10% wt. ox-LC content. FTIR spectroscopy indicated the formation of inner-sphere complexes between U(VI) and the surface-active moieties existing on both CA and ox-LC, while thermodynamic data revealed that the adsorption process was endothermic and entropy-driven. The experimental data obtained from the adsorption experiments were well-fitted by the Langmuir and Freundlich models. Overall, the produced composites exhibited enhanced adsorption efficiency against U(VI), demonstrating their potential use as effective adsorbents for the recovery of uranium ions from industrial effluents and seawater. Full article

(This article belongs to the Special Issue Bioresources as Precursor for Novel Nanostructured Materials towards Environmental Remediation (Volume II))

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16 pages, 6647 KiB

Open AccessEditor’s ChoiceArticle

Carbon-Based Composites with Mixed Phosphate-Pyrophosphates with Improved Electrochemical Performance at Elevated Temperature

by Sonya Harizanova, Trajche Tushev, Violeta Koleva and Radostina Stoyanova

Materials 2023, 16(19), 6546; https://doi.org/10.3390/ma16196546 - 4 Oct 2023

Cited by 2 | Viewed by 3404

Abstract

Sodium iron phosphate-pyrophosphate, Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a [...] Read more.

Sodium iron phosphate-pyrophosphate, Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) emerges as an excellent cathode material for sodium-ion batteries. Because of lower electronic conductivity, its electrochemical performance depends drastically on the synthesis method. Herein, we provide a simple and unified method for synthesis of composites between NFPP and reduced graphene oxide (rGO) and standard carbon black, designed as electrode materials for both sodium- and lithium-ion batteries. The carbon additives affect only the morphology and textural properties of the composites. The performance of composites in sodium and lithium cells is evaluated at elevated temperatures. It is found that NFPP/rGO outperforms NFPP/C in both Na and Li storage due to its hybrid mechanism of energy storage. In sodium half-cells, NFPP/rGO delivers a reversible capacity of 95 mAh/g at 20 °C and 115 mAh/g at 40 °C with a cycling stability of 95% and 88% at a rate of C/2. In lithium half-cells, the capacity reaches a value of 120 mAh/g at 20 and 40 °C, but the cycling stability becomes worse, especially at 40 °C. The electrochemical performance is discussed on the basis of ex situ XRD and microscopic studies. The good Na storage performance of NFPP/rGO at an elevated temperature represents a first step towards its commercialization. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application)

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25 pages, 14309 KiB

Open AccessEditor’s ChoiceArticle

Fe₃O₄ Magnetic Nanoparticles Obtained by the Novel Aerosol-Based Technique for Theranostic Applications

by Piotr Pawlik, Barbara Błasiak, Marcin Pruba, Arkadiusz Miaskowski, Oskar Moraczyński, Justyna Miszczyk, Boguslaw Tomanek and Joanna Depciuch

Materials 2023, 16(19), 6483; https://doi.org/10.3390/ma16196483 - 29 Sep 2023

Cited by 1 | Viewed by 1785

Abstract

This work is aimed at presenting a novel aerosol-based technique for the synthesis of magnetite nanoparticles (Fe

_{3}

O

_{4}

NPs) and to assess the potential medical application of their dispersions after being coated with TEA-oleate. Refinement of the processing conditions led to [...] Read more.

This work is aimed at presenting a novel aerosol-based technique for the synthesis of magnetite nanoparticles (Fe

_{3}

O

_{4}

NPs) and to assess the potential medical application of their dispersions after being coated with TEA-oleate. Refinement of the processing conditions led to the formation of monodispersed NPs with average sizes of ∼5–6 nm and narrow size distribution (FWHM of ∼3 nm). The NPs were coated with Triethanolammonium oleate (TEA-oleate) to stabilize them in water dispersion. This allowed obtaining the dispersion, which does not sediment for months, although TEM and DLS studies have shown the formation of small agglomerates of NPs. The different behaviors of cancer and normal cell lines in contact with NPs indicated the diverse mechanisms of their interactions with Fe

_{3}

O

_{4}

NPs. Furthermore, the studies allowed assessment of the prospective theranostic application of magnetite NPs obtained using the aerosol-based technique, particularly magnetic hyperthermia and magnetic resonance imaging (MRI). Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Biological, Medical and Environmental Applications (Volume II)—the 15th Anniversary of Materials)

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15 pages, 1571 KiB

Open AccessEditor’s ChoiceReview

Brief Narrative Review on Commercial Dental Sealants—Comparison with Respect to Their Composition and Potential Modifications

by Aleksandra Piszko, Paweł J. Piszko, Adam Lubojański, Wojciech Grzebieluch, Maria Szymonowicz and Maciej Dobrzyński

Materials 2023, 16(19), 6453; https://doi.org/10.3390/ma16196453 - 28 Sep 2023

Cited by 3 | Viewed by 2052

Abstract

The scope of this paper is to compare different dental sealants and flow materials indicated for sealing pits and fissures considering their chemical formula. The narrative review aims to address the following questions: What is the essence of different dental sealants’ activity, how [...] Read more.

The scope of this paper is to compare different dental sealants and flow materials indicated for sealing pits and fissures considering their chemical formula. The narrative review aims to address the following questions: What is the essence of different dental sealants’ activity, how does their chemical formula affect their mechanisms of caries prevention, and what makes a dental sealant efficient mean of caries prevention? Another vital issue is whether the sealants that contain fluoride, or any other additions, have potentially increased antimicrobial properties. An electronic search of the PubMed, Cochrane, Web of Science, and Scopus databases was performed. The following keywords were used: (dental sealants) AND (chemical composition). Additionally, information about composition and indications for clinical use provided by manufacturers were utilized. All of the considered materials are indicated for use both in permanent and primary dentition for sealing fissures, pits, and foramina caeca. The selection of suitable material should be made individually and adjusted to conditions of the sealing procedure and patient’s needs. Cariostatic mechanisms increasing sealants’ effectiveness such as fluoride release are desired in modern dentistry appreciating preventive approach. The review aims are to find crucial elements of sealants’ composition which affect their cariostatic mechanisms. Full article

(This article belongs to the Special Issue Elements Content and Release from Tissues and Biomaterials In Vivo and In Vitro)

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41 pages, 12583 KiB

Open AccessEditor’s ChoiceReview

Enhancing Fatigue Life and Strength of Adhesively Bonded Composite Joints: A Comprehensive Review

by Hossein Malekinejad, Ricardo J. C. Carbas, Alireza Akhavan-Safar, Eduardo A. S. Marques, Fernando Castro Sousa and Lucas F. M. da Silva

Materials 2023, 16(19), 6468; https://doi.org/10.3390/ma16196468 - 28 Sep 2023

Cited by 16 | Viewed by 4907

Abstract

Adhesive bonding is widely seen as the most optimal method for joining composite materials, bringing significant benefits over mechanical joining, such as lower weight and reduced stress concentrations. Adhesively bonded composite joints find extensive applications where cyclic fatigue loading takes place, but this [...] Read more.

Adhesive bonding is widely seen as the most optimal method for joining composite materials, bringing significant benefits over mechanical joining, such as lower weight and reduced stress concentrations. Adhesively bonded composite joints find extensive applications where cyclic fatigue loading takes place, but this might ultimately lead to crack damage and safety issues. Consequently, it has become essential to study how these structures behave under fatigue loads and identify the remaining gaps in knowledge to give insights into new possibilities. The fatigue life of adhesively bonded composite joints is influenced by various parameters, including joint configuration and material properties of adherends and adhesive. Numerous studies with varying outcomes have been documented in the literature. However, due to the multitude of influential factors, deriving conclusive insights from these studies for practical design purposes has proven to be challenging. Hence, this review aims to address this challenge by discussing different methods to enhance the fatigue performance of adhesively bonded composite joints. Additionally, it provides a comprehensive overview of the existing literature on adhesively bonded composite joints under cyclic fatigue loading, focusing on three main aspects: Adherends modification, adhesive modification, and joint configurations. Since the effect of modifying the adhesive, adherends, and joint configurations on fatigue performance has not been comprehensively studied in the literature, this review aims to fill this gap by compiling and comparing the relevant experimental data. Furthermore, this review discusses the challenges and limitations associated with the methods that can be used to monitor the initiation and propagation of fatigue cracks. Full article

(This article belongs to the Special Issue Advances in Service Life Evaluation of Metallic and Composite Materials)

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15 pages, 6282 KiB

Open AccessEditor’s ChoiceArticle

Hot-Cracking Mechanism of Laser Welding of Aluminum Alloy 6061 in Lap Joint Configuration

by Km Rakhi, Seunggu Kang and Joonghan Shin

Materials 2023, 16(19), 6426; https://doi.org/10.3390/ma16196426 - 27 Sep 2023

Cited by 3 | Viewed by 2374

Abstract

Laser welding, known for its distinctive advantages, has become significantly valuable in the automotive industry. However, in this context, the frequent occurrence of hot cracking necessitates further investigation into this phenomenon. This research aims to understand the hot-cracking mechanism in aluminum alloy (AA) [...] Read more.

Laser welding, known for its distinctive advantages, has become significantly valuable in the automotive industry. However, in this context, the frequent occurrence of hot cracking necessitates further investigation into this phenomenon. This research aims to understand the hot-cracking mechanism in aluminum alloy (AA) 6061, welded using a laser beam in a lap joint setup. We used an array of material characterization methods to study the effects of processing parameters on the cracking susceptibility and to elucidate the hot-cracking mechanism. A laser power of 2000 W generated large hot cracks crossing the whole weld zone for all welding speed conditions. Our findings suggest that using a heat input of 30 J/mm significantly mitigates the likelihood of hot cracking. Furthermore, we observed that the concentrations of the alloying elements in the cracked region markedly surpassed the tolerable limits of some elements (silicon: 2.3 times, chromium: 8.1 times, and iron: 2.7 times, on average) in AA6061. The hot-cracking mechanism shows that the crack initiates from the weld root at the interface between the two welded plates and then extends along the columnar dendrite growth direction. Once the crack reaches the central region of the fusion zone, it veers upward, following the cooling direction in this area. Our comprehensive investigation indicates that the onset and propagation of hot cracks are influenced by a combination of factors, such as stress, strain, and the concentration of alloying elements within the intergranular region. Full article

(This article belongs to the Special Issue Welding and Joining Processes of Metallic Materials)

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14 pages, 1477 KiB

Open AccessEditor’s ChoiceArticle

Pt-Coated Ni Layer Supported on Ni Foam for Enhanced Electro-Oxidation of Formic Acid

by Antanas Nacys, Dijana Simkunaitė, Aldona Balciunaite, Ausrine Zabielaite, Daina Upskuviene, Ramunas Levinas, Vitalija Jasulaitiene, Vitalij Kovalevskij, Birute Simkunaite-Stanyniene, Loreta Tamasauskaite-Tamasiunaite and Eugenijus Norkus

Materials 2023, 16(19), 6427; https://doi.org/10.3390/ma16196427 - 27 Sep 2023

Cited by 1 | Viewed by 1286

Abstract

A Pt-coated Ni layer supported on a Ni foam catalyst (denoted PtNi/Ni_foam) was investigated for the electro-oxidation of the formic acid (FAO) in acidic media. The prepared PtNi/Ni_foam catalyst was studied as a function of the formic acid (FA) concentration [...] Read more.

A Pt-coated Ni layer supported on a Ni foam catalyst (denoted PtNi/Ni_foam) was investigated for the electro-oxidation of the formic acid (FAO) in acidic media. The prepared PtNi/Ni_foam catalyst was studied as a function of the formic acid (FA) concentration at bare Pt and PtNi/Ni_foam catalysts. The catalytic activity of the PtNi/Ni_foam catalysts, studied on the basis of the ratio of the direct and indirect current peaks (j^d)/(j^nd) for the FAO reaction, showed values approximately 10 times higher compared to those on bare Pt, particularly at low FA concentrations, reflecting the superiority of the former catalysts for the electro-oxidation of FA to CO₂. Ni foams provide a large surface area for the FAO, while synergistic effects between Pt nanoparticles and Ni-oxy species layer on Ni foams contribute significantly to the enhanced electro-oxidation of FA via the direct pathway, making it almost equal to the indirect pathway, particularly at low FA concentrations. Full article

(This article belongs to the Section Catalytic Materials)

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16 pages, 3283 KiB

Open AccessEditor’s ChoiceArticle

Effect of B₂O₃ on the Structure, Properties and Antibacterial Abilities of Sol-Gel-Derived TiO₂/TeO₂/B₂O₃ Powders

by Albena Bachvarova-Nedelcheva, Reni Iordanova, Angelina Stoyanova, Nelly Georgieva, Veronica Nemska and Tsvetelina Foteva

Materials 2023, 16(19), 6400; https://doi.org/10.3390/ma16196400 - 25 Sep 2023

Viewed by 1273

Abstract

This paper studies the influence of B₂O₃ on the structure, properties and antibacterial abilities of sol-gel-derived TiO₂/TeO₂/B₂O₃ powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in [...] Read more.

This paper studies the influence of B₂O₃ on the structure, properties and antibacterial abilities of sol-gel-derived TiO₂/TeO₂/B₂O₃ powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in the degree of decomposition of Ti butoxide in the presence of H₃BO₃ and H₆TeO₆ acids. The phase transformations of the obtained gels in the temperature range of 200–700 °C were investigated by XRD. Composite materials containing an amorphous phase and different crystalline phases (metallic Te, α-TeO₂, anatase, rutile and TiTe₃O₈) were prepared. Heating at 400 °C indicated a crystalline-to-amorphous-phase ratio of approximately 3:1. The scanning electron microscopy (SEM) analysis showed the preparation of plate-like TiO₂ nanoparticles. The IR results showed that the short-range order of the amorphous phases that are part of the composite materials consists of TiO₆, BO₃, BO₄ and TeO₄ structural units. Free B₂O₃ was not detected in the investigated compositions which could be related to the better connectivity between the building units as compared to binary TiO₂/B₂O₃ compositions. The UV-Vis spectra of the investigated gels exhibited a red shift of the cut-off due to the presence of boron and tellurium units. The binary sample achieved the maximum photodegradation efficiency (94%) toward Malachite green dye under UV irradiation, whereas the ternary sample photoactivity was very low. The compositions exhibited promising antibacterial activity against E. coli NBIMCC K12 407. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application)

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11 pages, 3088 KiB

Open AccessEditor’s ChoiceArticle

Tailoring of the Structural, Optical, and Electrical Characteristics of Sol-Gel-Derived Magnesium-Zinc-Oxide Wide-Bandgap Semiconductor Thin Films via Gallium Doping

by Chien-Yie Tsay, Shih-Ting Chen and Hsuan-Meng Tsai

Materials 2023, 16(19), 6389; https://doi.org/10.3390/ma16196389 - 25 Sep 2023

Cited by 3 | Viewed by 1242

Abstract

The Ga-doped Mg_0.2Zn_0.8O (GMZO) transparent semiconductor thin films were prepared using the sol-gel and spin-coating deposition technique. Changes in the microstructural features, optical parameters, and electrical characteristics of sol-gel-synthesized Mg_0.2Zn_0.8O (MZO) thin films affected by [...] Read more.

The Ga-doped Mg_0.2Zn_0.8O (GMZO) transparent semiconductor thin films were prepared using the sol-gel and spin-coating deposition technique. Changes in the microstructural features, optical parameters, and electrical characteristics of sol-gel-synthesized Mg_0.2Zn_0.8O (MZO) thin films affected by the amount of Ga dopants (0–5 at%) were studied. The results of grazing incidence X-ray diffraction (GIXRD) examination showed that all as-prepared MZO-based thin films had a wurtzite-type structure and hexagonal phase, and the incorporation of Ga ions into the MZO nanocrystals refined the microstructure and reduced the average crystallite size and flatness of surface roughness. Each glass/oxide thin film sample exhibited a higher average transmittance than 91.5% and a lower average reflectance than 9.1% in the visible range spectrum. Experimental results revealed that the optical bandgap energy of the GMZO thin films was slightly higher than that of the MZO thin film; the Urbach energy became wider with increasing Ga doping level. It was found that the 2 at% and 3 at% Ga-doped MZO thin films had better electrical properties than the undoped and 5 at% Ga-doped MZO thin films. Full article

(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))

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10 pages, 4177 KiB

Open AccessEditor’s ChoiceArticle

Understanding the Effect of Electron Beam Melting Scanning Strategies on the Aluminum Content and Materials State of Single Ti-6Al-4V Feedstock

by Katie O’Donnell, Maria J. Quintana and Peter C. Collins

Materials 2023, 16(19), 6366; https://doi.org/10.3390/ma16196366 - 23 Sep 2023

Viewed by 1363

Abstract

Research on the additive manufacturing of metals often neglects any characterization of the composition of final parts, erroneously assuming a compositional homogeneity that matches the feedstock material. Here, the composition of electron-beam-melted Ti-6Al-4V produced through three distinct scanning strategies (linear raster and two [...] Read more.

Research on the additive manufacturing of metals often neglects any characterization of the composition of final parts, erroneously assuming a compositional homogeneity that matches the feedstock material. Here, the composition of electron-beam-melted Ti-6Al-4V produced through three distinct scanning strategies (linear raster and two point melting strategies, random fill and Dehoff fill) is characterized both locally and globally through energy-dispersive spectroscopy and quantitative chemical analysis. As a result of the different scanning strategies used, differing levels of preferential vaporization occur across the various parts, leading to distinct final compositions, with extremes of ~5.8 wt.% Al and ~4.8 wt.% Al. In addition, energy-dispersive spectroscopy composition maps reveal specific features in both the XY and XZ planes (with Z being the build direction) as a result of local inhomogeneous preferential vaporization. The subsequent change in composition significantly modifies the materials’ state of parts, wherein parts and local regions with higher aluminum contents lead to higher hardness levels (with a ~50 HV difference) and elastic property values and vice versa. While varying scan strategies and scan parameters are known to modify the microstructure and properties of a part, the effect on composition cannot, and should not, be neglected. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing and Welding Technologies of Metals: Alloys, Simulation and Monitoring)

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22 pages, 13530 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Various Intrinsic Defect Criteria to Plot Kitagawa–Takahashi Diagrams in Additively Manufactured AlSi10Mg

by Mohammed Intishar Nur, Meetkumar Soni, Mustafa Awd and Frank Walther

Materials 2023, 16(18), 6334; https://doi.org/10.3390/ma16186334 - 21 Sep 2023

Cited by 1 | Viewed by 1570

Abstract

Selective laser melting is a form of additive manufacturing in which a high-power density laser is used to melt and fuse metallic powders to form the final specimen. By performing fatigue and tensile tests under various loading conditions, the study sought to establish [...] Read more.

Selective laser melting is a form of additive manufacturing in which a high-power density laser is used to melt and fuse metallic powders to form the final specimen. By performing fatigue and tensile tests under various loading conditions, the study sought to establish the impact of internal defects on the specimens’ fatigue life. Scanning electron microscopy and finite element simulation were conducted to determine the defect characteristics and the stress intensity factor of the specimens. Four different methods were used to determine the intrinsic defect length of the specimen, using data such as grain size, yield strength, and hardness value, among others. Kitagawa–Takahashi and El-Haddad diagrams were developed using the results. A correction factor hypothesis was established based on the deviation of measured data. Using Paris law, fatigue life was determined and compared to the experimental results later. The study aims to select one or more approaches that resemble experimental values and comprehend how internal defects and loading situations affect fatigue life. This study’s findings shed light on how internal defects affect the fatigue life of selective laser-melted AlSi10Mg specimens and can aid in improving the fatigue life prediction method of additively manufactured components, provided an appropriate intrinsic crack criterion is selected. Full article

(This article belongs to the Special Issue Advances in Modeling Fatigue Damage and Fracture of Engineering Materials)

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13 pages, 6112 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Al and Ti Additions on Solid Solution Strengthening and Precipitation Hardening in CoNiFe Medium-Entropy Alloys

by Piotr Bała, Kamil Górecki, Rafał Dziurka and Tomasz Kozieł

Materials 2023, 16(18), 6297; https://doi.org/10.3390/ma16186297 - 20 Sep 2023

Cited by 4 | Viewed by 1594

Abstract

The effect of Al and Ti additions on the microstructure and properties of CoNiFe alloys was studied in this paper. The investigations were conducted on four specially designed and produced arc furnace alloys (from 3 to 5 components, with medium to high entropy). [...] Read more.

The effect of Al and Ti additions on the microstructure and properties of CoNiFe alloys was studied in this paper. The investigations were conducted on four specially designed and produced arc furnace alloys (from 3 to 5 components, with medium to high entropy). Samples in various states were analyzed, i.e., as-cast, after homogenization, after solution heat treatment, and after solution heat treatment and aging. The obtained samples were characterized by: SEM observations, EDS, XRD, TEM analyses, and finally, hardness measurements. The solid solution strengthening coming from the addition of 5 at. pct. Al was negligible, while the effect from the 5 at. pct. of Ti addition was significant. The precipitation hardening effect related to the presence of the (CoNi)₃Ti phase caused by the Ti addition is comparable with the total effect of the Al and Ti addition, which caused the precipitation of (NiCo)₃AlTi. Full article

(This article belongs to the Special Issue Mechanical Performance and Microstructural Characterization of Light Alloys)

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19 pages, 16020 KiB

Open AccessEditor’s ChoiceArticle

Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel

by Xiaogang Li, Junfeng Nie, Xin Wang, Kejian Li and Haiquan Zhang

Materials 2023, 16(18), 6294; https://doi.org/10.3390/ma16186294 - 20 Sep 2023

Cited by 2 | Viewed by 1228

Abstract

The formation and evolution of microstructures at the Ni/Fe interface in dissimilar metal weld (DMW) between ferritic steel and austenitic stainless steel were investigated. Layered martensitic structures were noted at the nickel-based weld metal/12Cr2MoWVTiB steel interface after welding and post-weld heat treatment (PWHT). [...] Read more.

The formation and evolution of microstructures at the Ni/Fe interface in dissimilar metal weld (DMW) between ferritic steel and austenitic stainless steel were investigated. Layered martensitic structures were noted at the nickel-based weld metal/12Cr2MoWVTiB steel interface after welding and post-weld heat treatment (PWHT). The formation of the interfacial martensite layer during welding was clarified and its evolution during PWHT was discussed by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), focused ion beam (FIB), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), transmission kikuchi diffraction (TKD), phase diagrams, and theoretical analysis. In as-welded DMW, the Ni/Fe interface structures consisted of the BCC quenched martensite layer and the FCC partially mixed zone (PMZ), which was the result of inhomogeneous solid phase transformation due to the chemical composition gradient. During the PWHT process, the BCC interfacial microstructure further evolved to a double-layered structure of tempered martensite and quenched martensite newly formed by local re-austenitization and austenite–martensite transformation. These types of martensitic structures induced inhomogeneous hardness distribution near the Ni/Fe interface, aggravating the mismatch of interfacial mechanical properties, which was a potential factor contributing to the degradation and failure of DMW. Full article

(This article belongs to the Special Issue Physical Metallurgy of Metals and Alloys II)

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13 pages, 7400 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamic and Microstructural Analysis of Lead-Free Machining Aluminium Alloys with Indium and Bismuth Additions

by Simon Rečnik, Maja Vončina, Aleš Nagode and Jožef Medved

Materials 2023, 16(18), 6241; https://doi.org/10.3390/ma16186241 - 16 Sep 2023

Cited by 2 | Viewed by 1273

Abstract

The present study comprises an investigation involving thermodynamic analysis, microstructural characterisation, and a comparative examination of the solidification sequence in two different aluminium alloys: EN AW 6026 and EN AW 1370. These alloys were modified through the addition of pure indium and a [...] Read more.

The present study comprises an investigation involving thermodynamic analysis, microstructural characterisation, and a comparative examination of the solidification sequence in two different aluminium alloys: EN AW 6026 and EN AW 1370. These alloys were modified through the addition of pure indium and a master alloy consisting of indium and bismuth. The aim of this experiment was to evaluate the potential suitability of indium, either alone or in combination with bismuth, as a substitute for toxic lead in free-machining aluminium alloys. Thermodynamic analysis was carried out using Thermo-Calc TCAL-6 software, supplemented by differential scanning calorimetry (DSC) experiments. The microstructure of these modified alloys was characterised using SEM–EDS analysis. The results provide valuable insights into the formation of different phases and eutectics within the alloys studied. The results represent an important contribution to the development of innovative, lead-free aluminium alloys suitable for machining processes, especially for use in automatic CNC cutting machines. One of the most important findings of this research is the promising suitability of indium as a viable alternative to lead. This potential stems from indium’s ability to avoid interactions with other alloying elements and its tendency to solidify as homogeneously distributed particles with a low melting point. In contrast, the addition of bismuth does not improve the machinability of magnesium-containing aluminium alloys. This is primarily due to their interaction, which leads to the formation of the Mg₃Bi₂ phase, which solidifies as a eutectic with a high melting point. Consequently, the presence of bismuth appears to have a detrimental effect on the machining properties of the alloy when magnesium is present in the composition. Full article

(This article belongs to the Special Issue Advanced Light Metal and Alloys: Preparation, Characterization, and Applications)

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15 pages, 6250 KiB

Open AccessEditor’s ChoiceArticle

From Transparent to Opaque: A Route towards Multifunctional Parts Injected with a Single Material

by Luís D. Pedroso, António J. Pontes, António Alves, Fernando M. Duarte and Olga S. Carneiro

Materials 2023, 16(18), 6219; https://doi.org/10.3390/ma16186219 - 15 Sep 2023

Cited by 1 | Viewed by 1229

Abstract

The technological, social and economic development observed in recent decades brought an exponential increase in consumption and inherent new challenges. Recycling is one of the best solutions to minimize the environmental impact of raw materials. However, multi-material components are difficult or even impossible [...] Read more.

The technological, social and economic development observed in recent decades brought an exponential increase in consumption and inherent new challenges. Recycling is one of the best solutions to minimize the environmental impact of raw materials. However, multi-material components are difficult or even impossible to recycle. The present work focuses on the reduction in the number of different materials used in multifunctional components. In particular, it intends to assess the potential of injecting molding grades of polypropylene (PP) to produce parts with transparency (haze) gradients. Firstly, several polypropylene grades of different types were identified and injected under various thermal processing conditions, i.e., injection temperature and mold temperature, in order to vary the cooling rate, influencing the growth rate of the spherulites and eventually the presence/absence of α and β crystalline zones. The injected parts’ optical properties were then characterized, and the most promising PP grades were identified and selected for subsequent work, namely grade DR 7037.01, showing the widest range of haze (from 29.2 to 68.7%). and PP070G2M, presenting the highest haze value (75.3%). Finally, in an attempt to understand the origin of the haze variations observed, the parts injected with the selected PP grades were further characterized through differential scanning calorimetry (DSC) and polarized light microscopy. It was concluded that the main factor causing the observed haze difference was, apart from the size of the spherulites, the presence of internal layers with different birefringence and, therefore, different refractive indices. Full article

(This article belongs to the Special Issue Advances in Thermal and Mechanical Properties of Polymeric Materials)

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13 pages, 3774 KiB

Open AccessEditor’s ChoiceArticle

Double-Forming Mechanism of TaO_x-Based Resistive Memory Device and Its Synaptic Applications

by Dongyeol Ju, Sunghun Kim, Subaek Lee and Sungjun Kim

Materials 2023, 16(18), 6184; https://doi.org/10.3390/ma16186184 - 13 Sep 2023

Viewed by 1141

Abstract

The bipolar resistive switching properties of Pt/TaO_x/InO_x/ITO-resistive random-access memory devices under DC and pulse measurement conditions are explored in this work. Transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the structure and chemical compositions of the [...] Read more.

The bipolar resistive switching properties of Pt/TaO_x/InO_x/ITO-resistive random-access memory devices under DC and pulse measurement conditions are explored in this work. Transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the structure and chemical compositions of the devices. A unique two-step forming process referred to as the double-forming phenomenon and self-compliance characteristics are demonstrated under a DC sweep. A model based on oxygen vacancy migration is proposed to explain its conduction mechanism. Varying reset voltages and compliance currents were applied to evaluate multilevel cell characteristics. Furthermore, pulses were applied to the devices to demonstrate the neuromorphic system’s application via testing potentiation, depression, spike-timing-dependent plasticity, and spike-rate-dependent plasticity. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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16 pages, 5555 KiB

Open AccessEditor’s ChoiceArticle

Automated Fiber Placement Path Planning and Analysis of Pressure Vessels

by Bo Wang, Lihua Wen, Jinyou Xiao, Shiyu Wang, Ping Ren, Liqiang Wang, Lei Zu and Xiao Hou

Materials 2023, 16(18), 6187; https://doi.org/10.3390/ma16186187 - 13 Sep 2023

Cited by 1 | Viewed by 1999

Abstract

The automated fiber placement (AFP) process faces a crucial challenge: the emergence of out-of-plane buckling in thermoplastic prepreg tows during steering, significantly impeding the quality of composite layup. In response, this study introduces a novel approach: the development of equations for wrinkle-free fiber [...] Read more.

The automated fiber placement (AFP) process faces a crucial challenge: the emergence of out-of-plane buckling in thermoplastic prepreg tows during steering, significantly impeding the quality of composite layup. In response, this study introduces a novel approach: the development of equations for wrinkle-free fiber placement within composite pressure vessels. The investigation encompasses a detailed analysis of prepreg trajectories in relation to shell geometry, accompanied by an in-depth understanding of the underlying causes of wrinkling on dome surfaces. Moreover, a comprehensive model for shell coverage, grounded in placement parameters, is meticulously established. To validate the approach, a simulation tool is devised to calculate press roller motions, ensuring the uniform fiber dispersion on the mandrel and achieving flawless coverage of the shell without wrinkles. This innovative strategy not only optimizes the AFP process for composite layup but also remarkably enhances the overall quality of composite shells. As such, this research carries significant implications for the advancement of composite manufacturing techniques and the concurrent improvement in material performance. Full article

(This article belongs to the Special Issue Advanced Manufacturing Technologies of Thermoplastic Composites)

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17 pages, 7526 KiB

Open AccessEditor’s ChoiceArticle

Long-Term Oxidation Susceptibility in Ambient Air of the Semiconductor Kesterite Cu₂ZnSnS₄ Nanopowders Made by Mechanochemical Synthesis Method

by Katarzyna Lejda, Magdalena Ziąbka, Zbigniew Olejniczak and Jerzy Franciszek Janik

Materials 2023, 16(18), 6160; https://doi.org/10.3390/ma16186160 - 11 Sep 2023

Cited by 1 | Viewed by 1160

Abstract

The often overlooked and annoying aspects of the propensity of no-oxygen semiconductor kesterite, Cu₂ZnSnS₄, to oxidation during manipulation and storage in ambient air prompted the study on the prolonged exposure of kesterite nanopowders to air. Three precursor systems were [...] Read more.

The often overlooked and annoying aspects of the propensity of no-oxygen semiconductor kesterite, Cu₂ZnSnS₄, to oxidation during manipulation and storage in ambient air prompted the study on the prolonged exposure of kesterite nanopowders to air. Three precursor systems were used to make a large pool of the cubic and tetragonal polytypes of kesterite via a convenient mechanochemical synthesis route. The systems included the starting mixtures of (i) constituent elements (2Cu + Zn + Sn + 4S), (ii) selected metal sulfides and sulfur (Cu₂S + ZnS + SnS + S), and (iii) in situ made copper alloys (from the high-energy ball milling of the metals 2Cu + Zn + Sn) and sulfur. All raw products were shown to be cubic kesterite nanopowders with defunct semiconductor properties. These nanopowders were converted to the tetragonal kesterite semiconductor by annealing at 500 °C under argon. All materials were exposed to the ambient air for 1, 3, and 6 months and were suitably analyzed after each of the stages. The characterization methods included powder XRD, FT-IR/UV-Vis/Raman/NMR spectroscopies, SEM, the determination of BET/BJH specific surface area and helium density (d_He), and direct oxygen and hydrogen-content analyses. The results confirmed the progressive, relatively fast, and pronounced oxidation of all kesterite nanopowders towards, mainly, hydrated copper(II) and zinc(II) sulfates, and tin(IV) oxide. The time-related oxidation changes were reflected in the lowering of the energy band gap E_g of the remaining tetragonal kesterite component. Full article

(This article belongs to the Special Issue Advanced Nanostructured Materials for Solar Energy Conversion)

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29 pages, 9500 KiB

Open AccessEditor’s ChoiceReview

Zirconium Carbide for Hypersonic Applications, Opportunities and Challenges

by Glenn R. Peterson, Ryan E. Carr and Ernesto E. Marinero

Materials 2023, 16(18), 6158; https://doi.org/10.3390/ma16186158 - 11 Sep 2023

Cited by 5 | Viewed by 2166

Abstract

At ultra-high temperatures, resilient, durable, stable material choices are limited. While Carbon/Carbon (C/C) composites (carbon fibers and carbon matrix phases) are currently the materials of choice, zirconium carbide (ZrC) provides an option in hypersonic environments and specifically in wing leading edge (WLE) applications. [...] Read more.

At ultra-high temperatures, resilient, durable, stable material choices are limited. While Carbon/Carbon (C/C) composites (carbon fibers and carbon matrix phases) are currently the materials of choice, zirconium carbide (ZrC) provides an option in hypersonic environments and specifically in wing leading edge (WLE) applications. ZrC also offers an ultra-high melting point (3825 K), robust mechanical properties, better thermal conductivity, and potentially better chemical stability and oxidation resistance than C/C composites. In this review, we discuss the mechanisms behind ZrC mechanical, thermal, and chemical properties and evaluate: (a) mechanical properties: flexure strength, fracture toughness, and elastic modulus; (b) thermal properties: coefficient of thermal expansion (CTE), thermal conductivity, and melting temperature; (c) chemical properties: thermodynamic stability and reaction kinetics of oxidation. For WLE applications, ZrC physical properties require further improvements. We note that materials or processing solutions to increase its relative density through sintering aids can have deleterious effects on oxidation resistance. Therefore, improvements of key ZrC properties for WLE applications must not compromise other functional properties. We suggest that C/C-ZrC composites offer an engineering solution to reduce density (weight) for aerospace applications, improve fracture toughness and the mechanical response, while addressing chemical stability and stoichiometric concerns. Recommendations for future work are also given. Full article

(This article belongs to the Special Issue Advances in Functional Ceramic Materials: Fabrication, Properties, and High-Temperature Applications)

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22 pages, 17872 KiB

Open AccessEditor’s ChoiceArticle

Computational Exploration of Phenolic Compounds in Corrosion Inhibition: A Case Study of Hydroxytyrosol and Tyrosol

by Hassane Lgaz and Han-seung Lee

Materials 2023, 16(18), 6159; https://doi.org/10.3390/ma16186159 - 11 Sep 2023

Cited by 7 | Viewed by 1571

Abstract

The corrosion of materials remains a critical challenge with significant economic and infrastructural impacts. A comprehensive understanding of adsorption characteristics of phytochemicals can facilitate the effective design of high-performing environmentally friendly inhibitors. This study conducted a computational exploration of hydroxytyrosol (HTR) and tyrosol [...] Read more.

The corrosion of materials remains a critical challenge with significant economic and infrastructural impacts. A comprehensive understanding of adsorption characteristics of phytochemicals can facilitate the effective design of high-performing environmentally friendly inhibitors. This study conducted a computational exploration of hydroxytyrosol (HTR) and tyrosol (TRS) (potent phenolic compounds found in olive leaf extracts), focusing on their adsorption and reactivity on iron surfaces. Utilizing self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations, molecular dynamics (MD) simulations, and quantum chemical calculations (QCCs), we investigated the molecules’ structural and electronic attributes and interactions with iron surfaces. The SCC-DFTB results highlighted that HTR and TRS coordinated with iron atoms when adsorbed individually, but only HTR maintained bonding when adsorbed alongside TRS. At their individual adsorption, HTR and TRS had interaction energies of −1.874 and −1.598 eV, which became more negative when put together (−1.976 eV). The MD simulations revealed parallel adsorption under aqueous and vacuum conditions, with HTR demonstrating higher adsorption energy. The analysis of quantum chemical parameters, including global and local reactivity descriptors, offered crucial insights into molecular reactivity, stability, and interaction-prone atomic sites. QCCs revealed that the fraction of transferred electron ∆N aligned with SCC-DFTB results, while other parameters of purely isolated molecules failed to predict the same. These findings pave the way for potential advancements in anticorrosion strategies leveraging phenolic compounds. Full article

(This article belongs to the Special Issue Advances in the Corrosion and Protection of Metals (Second Volume))

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22 pages, 17392 KiB

Open AccessEditor’s ChoiceArticle

Characterization and Design of Three-Phase Particulate Composites: Microstructure-Free Finite Element Modeling vs. Analytical Micromechanics Models

by Sebak Oli and Yunhua Luo

Materials 2023, 16(18), 6147; https://doi.org/10.3390/ma16186147 - 10 Sep 2023

Viewed by 1162

Abstract

Three-phase particulate composites offer greater design flexibility in the selection of phase materials and have more design variables than their two-phase counterparts, thus providing larger space for tailoring effective properties to meet intricate engineering requirements. Predicting effective elastic properties is essential for composite [...] Read more.

Three-phase particulate composites offer greater design flexibility in the selection of phase materials and have more design variables than their two-phase counterparts, thus providing larger space for tailoring effective properties to meet intricate engineering requirements. Predicting effective elastic properties is essential for composite design. However, experimental methods are both expensive and time intensive, whereas the scope of analytical micromechanics models is limited by their inherent assumptions. The newly developed microstructure-free finite element modeling (MF-FEM) approach has been demonstrated to be accurate and reliable for two-phase particulate composites. In this study, we investigate whether the MF-FEM approach can be applied to three-phase particulate composites and, if applicable, under which conditions. The study commences with a convergence analysis to establish the threshold ratio between the element size and the RVE (representative volume element) dimension. We then validate the MF-FEM approach using experimental data on three-phase composites from the existing literature. Subsequently, the MF-FEM method serves as a benchmark to assess the accuracy of both traditional and novel analytical micromechanics models, in predicting the effective elasticity of two distinct types of three-phase particulate composites, characterized by their small and large phase contrasts, respectively. We found that the threshold element-to-RVE ratio (1/150) for three-phase composites is considerably smaller than the ratio (1/50) for two-phase composites. The validation underscores that MF-FEM predictions align closely with experimental data. The analytical micromechanics models demonstrate varying degrees of accuracy depending on the phase volume fractions and the contrast in phase properties. The study indicates that the analytical micromechanics models may not be dependable for predicting effective properties of three-phase particulate composites, particularly those with a large contrast in phase properties. Even though more time-intensive, the MF-FEM proves to be a more reliable approach than the analytical models. Full article

(This article belongs to the Special Issue Finite Element Modeling of Microstructures in Composite Materials)

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21 pages, 6351 KiB

Open AccessEditor’s ChoiceArticle

From Bioresources to Thermal Insulation Materials: Synthesis and Properties of Two-Component Open-Cell Spray Polyurethane Foams Based on Bio-Polyols from Used Cooking Oil

by Krzysztof Polaczek, Maria Kurańska, Elżbieta Malewska, Małgorzata Czerwicka-Pach and Aleksander Prociak

Materials 2023, 16(18), 6139; https://doi.org/10.3390/ma16186139 - 9 Sep 2023

Cited by 3 | Viewed by 1828

Abstract

Open-cell spray polyurethane foams are widely used as highly efficient thermal insulation materials with vapor permeability and soundproofing properties. Unfortunately, for the production of commercial foams, mainly non-renewable petrochemical raw materials are used. The aim of this study was to determine the possibility [...] Read more.

Open-cell spray polyurethane foams are widely used as highly efficient thermal insulation materials with vapor permeability and soundproofing properties. Unfortunately, for the production of commercial foams, mainly non-renewable petrochemical raw materials are used. The aim of this study was to determine the possibility of completely replacing petrochemical polyols (the main raw material used in the synthesis of polyurethanes, alongside isocyanates) with bio-polyols obtained from used cooking oils, classified as waste materials. The research consisted of three stages: the synthesis of bio-polyols, the development of polyurethane foam systems under laboratory conditions, and the testing of developed polyurethane spray systems under industrial conditions. The synthesis of the bio-polyols was carried out by using two different methods: a one-step transesterification process using triethanolamine and a two-step process of epoxidation and opening oxirane rings with diethylene glycol. The obtained bio-polyols were analyzed using gel chromatography and nuclear magnetic resonance spectroscopy. The developed polyurethane foam formulations included two types of fire retardants: halogenated tris(1-chloro-2-propyl) phosphate (TCPP) and halogen-free triethyl phosphate (TEP). In the formulations of polyurethane systems, reactive amine catalysts were employed, which become incorporated into the polymer matrix during foaming, significantly reducing their emission after application. The foams were manufactured on both a laboratory and industrial scale using high-pressure spray machines under conditions recommended by commercial system manufacturers: spray pressure 80–100 bar, component temperature 45–52 °C, and component volumetric ratio 1:1. The open-cell foams had apparent densities 14–21.5 kg/m³, thermal conductivity coefficients 35–38 mW/m∙K, closed-cell contents <5%, water vapor diffusion resistance factors (μ) <6, and limiting oxygen indexes 21.3–21.5%. The properties of the obtained foams were comparable to commercial materials. The developed polyurethane spray systems can be used as thermal insulation materials for insulating interior walls, attics, and ceilings. Full article

(This article belongs to the Special Issue Advances in Development and Characterization of Polyurethane Foams)

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15 pages, 6302 KiB

Open AccessEditor’s ChoiceArticle

Advanced Fabrication Method and Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics

by Qingqing Chen, Yuan Zhang, Liuxin Chao, Ningning Dong, Yu Zhou and Guobing Ying

Materials 2023, 16(18), 6130; https://doi.org/10.3390/ma16186130 - 8 Sep 2023

Cited by 2 | Viewed by 1547

Abstract

Silicon nitride ceramics are regarded as a promising material for high-temperature structural applications due to their remarkable characteristics, including high strength, hardness, thermal conductivity, low dielectric properties, and resistance to creep at elevated temperatures. However, their susceptibility to catastrophic fracture at high temperatures [...] Read more.

Silicon nitride ceramics are regarded as a promising material for high-temperature structural applications due to their remarkable characteristics, including high strength, hardness, thermal conductivity, low dielectric properties, and resistance to creep at elevated temperatures. However, their susceptibility to catastrophic fracture at high temperatures remains a concern. Herein, Si₃N₄/BN fibrous monolithic ceramics have been successfully prepared by employing wet-spinning and hot-pressing techniques. We delved into the design and optimization of the spinning slurry and examined how the Si₃N₄/BN fiber diameter affects the ceramics’ microstructure and mechanical properties. The spinning slurry exhibited exceptional stability and spinnability. Decreasing the fiber diameter contributed to material densification and improved mechanical properties. Notably, when the fiber diameter is 0.9 mm, the fabricated Si₃N₄/BN fibrous monolithic ceramics demonstrate a carbon content of 0.82%, a three-point bending strength of 357 ± 24 MPa, and a fracture toughness of 8.8 ± 0.36 MPa·m^1/2. This investigation offers valuable insights into producing high-performance Si₃N₄/BN composite ceramics utilizing hot-pressing technology. Full article

(This article belongs to the Special Issue Advanced Ceramics Composites and Its Applications)

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