Materials

12 pages, 3929 KiB

Open AccessArticle

Advantages of Porcine Xenograft over Autograft in Sinus Lift: A Randomised Clinical Trial

by Francisco Correia, Daniel Humberto Pozza, Sónia Gouveia, António Campos Felino and Ricardo Faria-Almeida

Materials 2021, 14(12), 3439; https://doi.org/10.3390/ma14123439 - 21 Jun 2021

Cited by 18 | Viewed by 3725

Abstract

This study aimed to compare the performance of intra-oral autologous bone grafts versus porcine xenografts in a two-step lateral window sinus lift. This split-mouth randomised controlled trial sequentially enrolled 12 patients with a 6-month follow-up. For each patient, a simultaneous randomised bilateral maxillary [...] Read more.

This study aimed to compare the performance of intra-oral autologous bone grafts versus porcine xenografts in a two-step lateral window sinus lift. This split-mouth randomised controlled trial sequentially enrolled 12 patients with a 6-month follow-up. For each patient, a simultaneous randomised bilateral maxillary sinus lift was performed and filled with autologous bone from the mandible (control) or a porcine xenograft (test). A bone biopsy sample was collected during the implant placement for histological and histomorphometric analysis. CT scans were performed at the beginning and at the end of the trial to assess radiological evolution. A comparison of initial and six-month CT scans indicated statistically significant increases in bone level for both materials (7.8 ± 2.4 mm for autologous and 8.7 ± 2.2 mm for xenograft, p < 0.05), and there were no significant differences between the performance of the two materials over time (p = 0.26). The histological analysis showed various stages of the remodelling process and no cells or other signs of inflammation or infection were visible in both groups. The porcine xenografts presented similar results for the studied variables when compared to autologous bone, being a reasonable alternative for a sinus lift. Full article

(This article belongs to the Special Issue Biomaterials Development and Evaluation for Dentistry)

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33 pages, 18667 KiB

Open AccessArticle

Rational Choice of Reinforcement of Reinforced Concrete Frame Corners Subjected to Opening Bending Moment

by Michał Szczecina and Andrzej Winnicki

Materials 2021, 14(12), 3438; https://doi.org/10.3390/ma14123438 - 21 Jun 2021

Cited by 5 | Viewed by 2877

Abstract

This paper discusses a choice of the most rational reinforcement details for frame corners subjected to opening bending moment. Frame corners formed from elements of both the same and different cross section heights are considered. The case of corners formed of elements of [...] Read more.

This paper discusses a choice of the most rational reinforcement details for frame corners subjected to opening bending moment. Frame corners formed from elements of both the same and different cross section heights are considered. The case of corners formed of elements of different cross section is not considered in Eurocode 2 and is very rarely described in handbooks. Several reinforcement details with both the same and different cross section heights are presented. The authors introduce a new reinforcement detail for the different cross section heights. The considered details are comprised of the primary reinforcement in the form of straight bars and loops and the additional reinforcement in the form of diagonal bars or stirrups or a combination of both diagonal stirrups and bars. Two methods of static analysis, strut-and-tie method (S&T) and finite element method (FEM), are used in the research. FEM calculations are performed with Abaqus software using the Concrete Damaged Plasticity model (CDP) for concrete and the classical metal plasticity model for reinforcing steel. The crucial CDP parameters, relaxation time and dilatation angle, were calibrated in numerical tests in Abaqus. The analysis of results from the S&T and FE methods allowed for the determination of the most rational reinforcement details. Full article

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16 pages, 5658 KiB

Open AccessArticle

Fast Solution Synthesis of NiO-Gd_0.1Ce_0.9O_1.95 Nanocomposite via Different Approach: Influence of Processing Parameters and Characterizations

by Jorge Durango-Petro, Christopher Salvo, Jonathan Usuba, Gonzalo Abarzua, Felipe Sanhueza and Ramalinga Viswanathan Mangalaraja

Materials 2021, 14(12), 3437; https://doi.org/10.3390/ma14123437 - 21 Jun 2021

Cited by 5 | Viewed by 2722

Abstract

The synthesis of the nickel oxide-gadolinium doped ceria (NiO-GDC with 65:35 wt. %) nanocomposite powders with a stoichiometry of Gd_0.1Ce_0.9O_1.95 was performed via fast solution combustion technique; using three different mixing methods: (i) CM (metal cations in an [...] Read more.

The synthesis of the nickel oxide-gadolinium doped ceria (NiO-GDC with 65:35 wt. %) nanocomposite powders with a stoichiometry of Gd_0.1Ce_0.9O_1.95 was performed via fast solution combustion technique; using three different mixing methods: (i) CM (metal cations in an aqueous solution), (ii) HM (hand mortar), and (iii) BM (ball milling). The nanocomposite powders were calcined at 700 °C for 2 h and characterized by Transmission Electron Microscopy (TEM), X-ray fluorescence (XRF), and X-ray Diffraction XRD. The TEM and XRD analyses evidenced the well-dispersed NiO and GDC crystallites with the absence of secondary phases, respectively. Later, the calcined powders (NiO-GDC nanocomposites) were compacted and sintered at 1500 °C for 2 h. The microhardness of the sintered nanocomposites varies in accordance with the synthesis approach: a higher microhardness of 6.04 GPa was obtained for nanocomposites synthesized through CM, while 5.94 and 5.41 GPa were obtained for ball-milling and hand-mortar approach, respectively. Furthermore, it was observed that regardless of the long time-consuming ball-milling process with respect to the hand mortar, there was no significant improvement in the electrical properties. Full article

(This article belongs to the Special Issue Novel Ceramic Materials for the Energy Transition)

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15 pages, 2665 KiB

Open AccessArticle

Selenite Substituted Calcium Phosphates: Preparation, Characterization, and Cytotoxic Activity

by Antonia Ressler, Maja Antunović, Matija Cvetnić, Marica Ivanković and Hrvoje Ivanković

Materials 2021, 14(12), 3436; https://doi.org/10.3390/ma14123436 - 21 Jun 2021

Cited by 13 | Viewed by 3006

Abstract

The aim of this study was to prepare a biomimetic selenium substituted calcium phosphate system for potential application in osteosarcoma therapy. Calcium phosphate (CaP) systems substituted with selenite ions were prepared by the wet precipitation method, using biogenic CaCO₃ (derived from cuttlefish [...] Read more.

The aim of this study was to prepare a biomimetic selenium substituted calcium phosphate system for potential application in osteosarcoma therapy. Calcium phosphate (CaP) systems substituted with selenite ions were prepared by the wet precipitation method, using biogenic CaCO₃ (derived from cuttlefish bone), CO(NH₂)₂-H₃PO₄, and Na₂SeO₃·5H₂O as reagents. Starting reaction mixtures were prepared based on the formula for selenite-substituted hydroxyapatite, Ca₁₀(PO₄)_6-x(SeO₃)_x(OH)₂, with Ca/(P + Se) molar ratio of 1.67 and Se/(P + Se) molar ratio of: 0, 0.01, 0.05, and 0.10, respectively. The prepared CaP powders were characterized by Fourier transform infrared spectrometry, elemental analysis, scanning electron microscopy, X-ray powder diffraction analysis and Rietveld refinement studies. Phase transformation and ion release were analyzed during 7 days of incubation in simulated body fluid at 37 °C. The metabolic activity of healthy and osteosarcoma cell lines was assessed by cell cytotoxicity and viability test. The as-prepared powders were composed of calcium-deficient carbonated hydroxyapatite (HAp), octacalcium phosphate (OCP), and amorphous calcium phosphate (ACP). Along with the selenite substitution, the presence of Sr²⁺, Na⁺, and Mg²⁺ was detected as a result of using cuttlefish bone as a precursor for Ca²⁺ ions. Inductively coupled plasma mass spectrometry analysis showed that the Se/(P + Se) molar ratios of selenite substituted powders are lower than the nominal ratios. Heat treated powders were composed of HAp, α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). Doping CaP structure with selenite ions improves the thermal stability of HAp. The powder with the Se/(P + Se) molar ratio of 0.007 showed selective toxicity to cancer cells. Full article

(This article belongs to the Special Issue Collection of Papers in Materials Science from Croatia)

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19 pages, 11735 KiB

Open AccessArticle

NBT-Pluronic F-127 Hydrogels Printed on Flat Textiles as UV Radiation Sensors

by Elżbieta Sąsiadek, Malwina Jaszczak, Joanna Skwarek and Marek Kozicki

Materials 2021, 14(12), 3435; https://doi.org/10.3390/ma14123435 - 21 Jun 2021

Cited by 11 | Viewed by 2482

Abstract

This work reports on the surface-modified woven fabrics for use as UV radiation sensors. The cotton and polyamide fabrics were printed with radiochromic hydrogels using a screen-printing method. The hydrogels used as a printing paste were composed of water, poly(ethylene oxide)-block-poly(propylene [...] Read more.

This work reports on the surface-modified woven fabrics for use as UV radiation sensors. The cotton and polyamide fabrics were printed with radiochromic hydrogels using a screen-printing method. The hydrogels used as a printing paste were composed of water, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) as a gel matrix and nitro blue tetrazolium chloride as a radiation-sensitive compound. The development of the hydrogels’ colour occurs after exposure to UV radiation and its intensity increases with increasing absorbed dose. The features of the NBT-Pluronic F-127 radiochromic hydrogels and the fabrics printed with the hydrogels were examined using UV-Vis and reflectance spectrophotometry as well as scanning electron microscopy (SEM). The effects of NBT concentration and UV radiation type (UVA, UVB, UVC) on dose responses of the hydrogels and printed fabrics were also examined. The results obtained reveal that the fabrics printed with NBT-Pluronic F-127 hydrogels can be potentially useful as UV radiation sensors. Full article

(This article belongs to the Section Smart Materials)

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18 pages, 11302 KiB

Open AccessArticle

Towards Enhancing the Potential of Injection Molding Tools through Optimized Close-Contour Cooling and Additive Manufacturing

by Sebastian Gries, Guillaume Meyer, Andreas Wonisch, Reinhard Jakobi and Christian Mittelstedt

Materials 2021, 14(12), 3434; https://doi.org/10.3390/ma14123434 - 21 Jun 2021

Cited by 6 | Viewed by 2867

Abstract

This work deals with the parametric optimization of the position and form of a conformal cooling used in the injection molding industry. Based on a literature survey, an optimization routine concerning the parameter optimization of cooling system designs was developed and implemented with [...] Read more.

This work deals with the parametric optimization of the position and form of a conformal cooling used in the injection molding industry. Based on a literature survey, an optimization routine concerning the parameter optimization of cooling system designs was developed and implemented with the help of the software package Moldflow. The main objective of the optimization is to reduce the cooling time; the second is to obtain an optimized homogeneous temperature distribution over the complete tool surface. To enable a comparison of the new close-contour solution with a classical manufacturing process, an optimized cooling system simulation, based on a conventional manufacturing solution, was established. It can be shown that the optimized close-contour cooling design offers significant advantages that cannot be exploited using classical manufacturing. Finally, the additive manufacturing of a prototype in the framework of powder bed fusion is documented as a proof of concept. Full article

(This article belongs to the Special Issue Polymers and Injection Molding Simulation)

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18 pages, 7150 KiB

Open AccessArticle

Effect of Co Substitution and Thermo-Magnetic Treatment on the Structure and Induced Magnetic Anisotropy of Fe_84.5_−xCo_xNb₅B_8.5P₂ Nanocrystalline Alloys

by Aleksandra Kolano-Burian, Przemyslaw Zackiewicz, Agnieszka Grabias, Anna Wojcik, Wojciech Maziarz, Maciej Szlezynger, Patryk Wlodarczyk, Maciej Kowalczyk and Lukasz Hawelek

Materials 2021, 14(12), 3433; https://doi.org/10.3390/ma14123433 - 21 Jun 2021

Cited by 7 | Viewed by 2548

Abstract

In the present work, we investigated in detail the thermal/crystallization behavior and magnetic properties of materials with Fe_84.5-xCo_xNb₅B_8.5P₂ (x = 0, 5, 10, 15 and 20 at.%) composition. The amorphous ribbons were manufactured on [...] Read more.

In the present work, we investigated in detail the thermal/crystallization behavior and magnetic properties of materials with Fe_84.5-xCo_xNb₅B_8.5P₂ (x = 0, 5, 10, 15 and 20 at.%) composition. The amorphous ribbons were manufactured on a semi-industrial scale by the melt-spinning technique. The subsequent nanocrystallization processes were carried out under different conditions (with/without magnetic field). The comprehensive studies have been carried out using differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, hysteresis loop analyses, vibrating sample magnetometry and Mössbauer spectroscopy. Moreover, the frequency (up to 300 kHz) dependence of power losses and permeability at a magnetic induction up to 0.9 T was investigated. On the basis of some of the results obtained, we calculated the values of the activation energies and the induced magnetic anisotropies. The X-ray diffraction results confirm the surface crystallization effect previously observed for phosphorous-containing alloys. The in situ microscopic observations of crystallization describe this process in detail in accordance with the calorimetry results. Furthermore, the effect of Co content on the phase composition and the influence of annealing in an external magnetic field on magnetic properties, including the orientation of the magnetic spins, have been studied using various magnetic techniques. Finally, nanocrystalline Fe_64.5Co₂₀Nb₅B_8.5P₂ cores were prepared after transverse thermo-magnetic heat treatment and installed in industrially available portable heating equipment. Full article

(This article belongs to the Special Issue Nanocomposite Magnetic Materials for Energy Conversion)

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13 pages, 3449 KiB

Open AccessArticle

Feasibility of Cobalt-Free Nanostructured WC Cutting Inserts for Machining of a TiC/Fe Composite

by Edwin Gevorkyan, Mirosław Rucki, Tadeusz Sałaciński, Zbigniew Siemiątkowski, Volodymyr Nerubatskyi, Wojciech Kucharczyk, Jarosław Chrzanowski, Yuriy Gutsalenko and Mirosław Nejman

Materials 2021, 14(12), 3432; https://doi.org/10.3390/ma14123432 - 21 Jun 2021

Cited by 23 | Viewed by 2446

Abstract

The paper presents results of investigations on the binderless nanostructured tungsten carbide (WC) cutting tools fabrication and performance. The scientific novelty includes the description of some regularities of the powder consolidation under electric current and the subsequent possibility to utilize them for practical [...] Read more.

The paper presents results of investigations on the binderless nanostructured tungsten carbide (WC) cutting tools fabrication and performance. The scientific novelty includes the description of some regularities of the powder consolidation under electric current and the subsequent possibility to utilize them for practical use in the fabrication of cutting tools. The sintering process of WC nanopowder was performed with the electroconsolidation method, which is a modification of spark plasma sintering (SPS). Its advantages include low temperatures and short sintering time which allows retaining nanosize grains of ca. 70 nm, close to the original particle size of the starting powder. In respect to the application of the cutting tools, pure WC nanostructure resulted in a smaller cutting edge radius providing a higher quality of TiC/Fe machined surface. In the range of cutting speeds, v_c = 15–40 m/min the durability of the inserts was 75% of that achieved by cubic boron nitride ones, and more than two times better than that of WC-Co cutting tools. In additional tests of machining 13CrMo4 material at an elevated cutting speed of v_c = 100 m/min, binderless nWC inserts worked almost three times longer than WC-Co composites. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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13 pages, 3151 KiB

Open AccessArticle

A Study on Heat Storage and Dissipation Efficiency at Permeable Road Pavements

by Ching-Che Yang, Jun-Han Siao, Wen-Cheng Yeh and Yu-Min Wang

Materials 2021, 14(12), 3431; https://doi.org/10.3390/ma14123431 - 21 Jun 2021

Cited by 13 | Viewed by 2459

Abstract

The main contributing factor of the urban heat island (UHI) effect is caused by daytime heating. Traditional pavements in cities aggravate the UHI effect due to their heat storage and volumetric heat capacity. In order to alleviate UHI, this study aims to understand [...] Read more.

The main contributing factor of the urban heat island (UHI) effect is caused by daytime heating. Traditional pavements in cities aggravate the UHI effect due to their heat storage and volumetric heat capacity. In order to alleviate UHI, this study aims to understand the heating and dissipating process of different types of permeable road pavements. The Ke Da Road in Pingtung County of Taiwan has a permeable pavement materials experiment zone with two different section configurations which were named as section I and section II for semi-permeable pavement and fully permeable pavement, respectively. The temperature sensors were installed during construction at the depths of the surface course (0 cm and 5 cm), base course (30 cm and 55 cm) and subgrade (70 cm) to monitor the temperature variations in the permeable road pavements. Hourly temperature and weather station data in January and June 2017 were collected for analysis. Based on these collected data, heat storage and dissipation efficiencies with respect to depth have been modelled by using multi regression for the two studied pavement types. It is found that the fully permeable pavement has higher heat storage and heat dissipation efficiencies than semi-permeable pavement in winter and summer monitoring period. By observing the regressed model, it is found that the slope of the model lines are almost flat after the depth of 30 cm. Thus, from the view point of UHI, one can conclude that the reasonable design depth of permeable road pavement could be 30 cm. Full article

(This article belongs to the Special Issue Temperature Reduction Technologies Meet Asphalt Pavement: Green and Sustainability)

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13 pages, 5082 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Modern 11%Cr Heat-Resistant Steel Weld Joints

by Grzegorz Golański, Jacek Słania, Marek Sroka, Paweł Wieczorek, Michał Urzynicok and Ryszard Krawczyk

Materials 2021, 14(12), 3430; https://doi.org/10.3390/ma14123430 - 21 Jun 2021

Cited by 3 | Viewed by 2185

Abstract

In addition to good high-temperature creep resistance and adequate heat resistance, steels for the power industry must have, among other things, good weldability. Weldability of such steels is one of the criteria determining whether or not the material is suitable for applications in [...] Read more.

In addition to good high-temperature creep resistance and adequate heat resistance, steels for the power industry must have, among other things, good weldability. Weldability of such steels is one of the criteria determining whether or not the material is suitable for applications in the power industry. Therefore, when materials such as martensitic steel Thor 115 (T115) are introduced into the modern power industry, the quality and properties of welded joints must be assessed. The paper presents the results of metallographic and mechanical investigations of T115 martensitic steel welded joints. The analysis was carried out on joints welded with two filler metals: WCrMo91 (No. 1) and EPRI P87 (No. 2). The scope of the investigations included: microstructural investigations carried out using optical, scanning and transmission electron microscopy and mechanical testing, i.e., Vickers microhardness and hardness measurement, static tensile test and impact test. The macro- and microstructural investigations revealed correct structure of the weld, without welding imperfections. The microstructural investigations of joint No. 1 revealed a typical structure of this type of joint, i.e., the martensitic structure with numerous precipitates, while in joint No. 2, the so-called Nernst’s layers and δ-ferrite patches were observed in the weld fusion zone as well as the heat affected zone (HAZ). The mechanical properties of the test joints met the requirements for the base material. A slight influence of the δ-ferrite patch on the strength properties of joint No. 2 was observed, and its negative effect on the impact energy of HAZ was visible. Full article

(This article belongs to the Special Issue Electron Microscopy for Understanding of the Relationship between the Structure, the Properties and the Functions of Metals, Semiconductors, Ceramics, Carbon Materials, Composites and Coatings)

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17 pages, 30863 KiB

Open AccessArticle

On Coolant Flow Rate-Cutting Speed Trade-Off for Sustainability in Cryogenic Milling of Ti–6Al–4V

by Asif Iqbal, Guolong Zhao, Hazwani Suhaimi, Malik Muhammad Nauman, Ning He, Juliana Zaini and Wei Zhao

Materials 2021, 14(12), 3429; https://doi.org/10.3390/ma14123429 - 21 Jun 2021

Cited by 6 | Viewed by 2285

Abstract

Application of cryogenic fluids for efficient heat dissipation is gradually becoming part and parcel of titanium machining. Not much research is done to establish the minimum quantity of a cryogenic fluid required to sustain a machining process with respect to a given material [...] Read more.

Application of cryogenic fluids for efficient heat dissipation is gradually becoming part and parcel of titanium machining. Not much research is done to establish the minimum quantity of a cryogenic fluid required to sustain a machining process with respect to a given material removal rate. This article presents an experimental investigation for quantifying the sustainability of milling a commonly used titanium alloy (Ti–6Al–4V) by varying mass flow rates of two kinds of cryogenic coolants at various levels of cutting speed. The three cooling options tested are dry (no coolant), evaporative cryogenic coolant (liquid nitrogen), and throttle cryogenic coolant (compressed carbon dioxide gas). The milling sustainability is quantified in terms of the following metrics: tool damage, fluid cost, specific cutting energy, work surface roughness, and productivity. Dry milling carried out the at the highest level of cutting speed yielded the worst results regarding tool damage and surface roughness. Likewise, the evaporative coolant applied with the highest flow rate and at the lowest cutting speed was the worst performer with respect to energy consumption. From a holistic perspective, the throttle cryogenic coolant applied at the highest levels of mass flow rate and cutting speed stood out to be the most sustainable option. Full article

(This article belongs to the Special Issue Additive and Subtractive Manufacturing of Advanced Materials: Applications, Future Trends and Perspectives of Industry 4.0)

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11 pages, 2337 KiB

Open AccessArticle

Assessing the Interfacial Dynamic Modulus of Biological Composites

by Yaniv Shelef, Avihai Yosef Uzan, Ofer Braunshtein and Benny Bar-On

Materials 2021, 14(12), 3428; https://doi.org/10.3390/ma14123428 - 21 Jun 2021

Cited by 5 | Viewed by 2206

Abstract

Biological composites (biocomposites) possess ultra-thin, irregular-shaped, energy dissipating interfacial regions that grant them crucial mechanical capabilities. Identifying the dynamic (viscoelastic) modulus of these interfacial regions is considered to be the key toward understanding the underlying structure–function relationships in various load-bearing biological materials including [...] Read more.

Biological composites (biocomposites) possess ultra-thin, irregular-shaped, energy dissipating interfacial regions that grant them crucial mechanical capabilities. Identifying the dynamic (viscoelastic) modulus of these interfacial regions is considered to be the key toward understanding the underlying structure–function relationships in various load-bearing biological materials including mollusk shells, arthropod cuticles, and plant parts. However, due to the submicron dimensions and the confined locations of these interfacial regions within the biocomposite, assessing their mechanical characteristics directly with experiments is nearly impossible. Here, we employ composite-mechanics modeling, analytical formulations, and numerical simulations to establish a theoretical framework that links the interfacial dynamic modulus of a biocomposite to the extrinsic characteristics of a larger-scale biocomposite segment. Accordingly, we introduce a methodology that enables back-calculating (via simple linear scaling) of the interfacial dynamic modulus of biocomposites from their far-field dynamic mechanical analysis. We demonstrate its usage on zigzag-shaped interfaces that are abundant in biocomposites. Our theoretical framework and methodological approach are applicable to the vast range of biocomposites in natural materials; its essence can be directly employed or generally adapted into analogous composite systems, such as architected nanocomposites, biomedical composites, and bioinspired materials. Full article

(This article belongs to the Section Biomaterials)

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13 pages, 1380 KiB

Open AccessArticle

Photobiomodulation with Red and Near-Infrared Light Improves Viability and Modulates Expression of Mesenchymal and Apoptotic-Related Markers in Human Gingival Fibroblasts

by Ievgeniia Kocherova, Artur Bryja, Katarzyna Błochowiak, Mariusz Kaczmarek, Katarzyna Stefańska, Jacek Matys, Kinga Grzech-Leśniak, Marzena Dominiak, Paul Mozdziak, Bartosz Kempisty and Marta Dyszkiewicz-Konwińska

Materials 2021, 14(12), 3427; https://doi.org/10.3390/ma14123427 - 21 Jun 2021

Cited by 17 | Viewed by 3483

Abstract

Photobiomodulation (PBM), also called low-level laser treatment (LLLT), has been considered a promising tool in periodontal treatment due to its anti-inflammatory and wound healing properties. However, photobiomodulation’s effectiveness depends on a combination of parameters, such as energy density, the duration and frequency of [...] Read more.

Photobiomodulation (PBM), also called low-level laser treatment (LLLT), has been considered a promising tool in periodontal treatment due to its anti-inflammatory and wound healing properties. However, photobiomodulation’s effectiveness depends on a combination of parameters, such as energy density, the duration and frequency of the irradiation sessions, and wavelength, which has been shown to play a key role in laser-tissue interaction. The objective of the study was to compare the in vitro effects of two different wavelengths—635 nm and 808 nm—on the human primary gingival fibroblasts in terms of viability, oxidative stress, inflammation markers, and specific gene expression during the four treatment sessions at power and energy density widely used in dental practice (100 mW, 4 J/cm²). PBM with both 635 and 808 nm at 4 J/cm² increased the cell number, modulated extracellular oxidative stress and inflammation markers and decreased the susceptibility of human primary gingival fibroblasts to apoptosis through the downregulation of apoptotic-related genes (P53, CASP9, BAX). Moreover, modulation of mesenchymal markers expression (CD90, CD105) can reflect the possible changes in the differentiation status of irradiated fibroblasts. The most pronounced results were observed following the third irradiation session. They should be considered for the possible optimization of existing low-level laser irradiation protocols used in periodontal therapies. Full article

(This article belongs to the Special Issue Laser Processing of Biocompatible Materials: From Fundamentals to Applications)

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10 pages, 4578 KiB

Open AccessArticle

Influence of Welding Speeds on the Morphology, Mechanical Properties, and Microstructure of 2205 DSS Welded Joint by K-TIG Welding

by Shuwan Cui, Shuwen Pang, Dangqing Pang and Zhiqing Zhang

Materials 2021, 14(12), 3426; https://doi.org/10.3390/ma14123426 - 21 Jun 2021

Cited by 17 | Viewed by 2678

Abstract

In this paper, 8.0 mm thickness 2205 duplex stainless steel (DSS) workpieces were welded with a keyhole tungsten inert gas (K-TIG) welding system under different welding speeds. After welding, the morphologies of the welds under different welding speed conditions were compared and analyzed. [...] Read more.

In this paper, 8.0 mm thickness 2205 duplex stainless steel (DSS) workpieces were welded with a keyhole tungsten inert gas (K-TIG) welding system under different welding speeds. After welding, the morphologies of the welds under different welding speed conditions were compared and analyzed. The microstructure, two-phase ratio of austenite/ferrite, and grain boundary characteristics of the welded joints were studied, and the microhardness and tensile properties of the welded joints were tested. The results show that the welding speed has a significant effect on the weld morphology, the two-phase ratio, grain boundary misorientation angle (GBMA), and mechanical properties of the welded joint. When the welding speed increased from 280 mm/min to 340 mm/min, the austenite content and the two-phase ratio in the weld metal zone (WMZ) decreased. However, the ferrite content in the WMZ increased. The proportion of the Σ3 coincident site lattice grain boundary (CSLGB) decreased as the welding speed increased, which has no significant effect on the tensile strength of welded joints. The microhardness of the WMZ and the tensile strength of the welded joint gradually increased when the welding speed was 280–340 mm/min. The 2205 DSS K-TIG welded joints have good plasticity. Full article

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10 pages, 36578 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Composite Mechanism of Nano-Fe₂O₃/Asphalt Based on Molecular Simulation and Experiments

by Yuhao He, Qing Zeng, Yaru Liu, Peng Liu, Yuqin Zeng, Zhenghong Xu and Qicheng Liu

Materials 2021, 14(12), 3425; https://doi.org/10.3390/ma14123425 - 21 Jun 2021

Viewed by 2177

Abstract

Asphalt, as an indispensable binder in road paving, plays an important role in transportation development. However, the mechanism of action between the modifier and asphalt cannot be fully explained by the existing test methods. This paper combines molecular simulations with experiments to provide [...] Read more.

Asphalt, as an indispensable binder in road paving, plays an important role in transportation development. However, the mechanism of action between the modifier and asphalt cannot be fully explained by the existing test methods. This paper combines molecular simulations with experiments to provide a research and analysis tool to evaluate the “structure−performance” relationship of asphalt. From the trend of experimental results, the optimal content of Nano-Fe₂O₃ is 1% to 3%. The AFM micrograph of the asphalt material shows that at 3%, the Nano-Fe₂O₃ can be effectively dispersed in the asphalt and the unique “ bee structures “ of the asphalt can be adsorbed around the modifier. Molecular dynamics studies and results show that when Nano-Fe₂O₃ are incorporated into the asphalt and have a strong adsorption force on the colloidal structure of asphalt, the “ bee structures “ can be adsorbed around the Nano-Fe₂O₃. In the range of 208–543 K, the sol-gel structure of asphalt in the Nano-Fe₂O₃/asphalt composite system is gradually disrupted. Full article

(This article belongs to the Section Construction and Building Materials)

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12 pages, 2488 KiB

Open AccessArticle

Capture of Fullerenes in Cages and Rings by Forming Metal-π Bond Arene Interactions

by Citlalli Rios, Bertha Molina and Roberto Salcedo

Materials 2021, 14(12), 3424; https://doi.org/10.3390/ma14123424 - 21 Jun 2021

Cited by 1 | Viewed by 1956

Abstract

Nowadays, the task of the selectively capture of fullerene molecules from soot is the subject of several studies. The low solubility of fullerenes represents a drawback when the goal is to purify them and to carry out chemical procedures where they participate. There [...] Read more.

Nowadays, the task of the selectively capture of fullerene molecules from soot is the subject of several studies. The low solubility of fullerenes represents a drawback when the goal is to purify them and to carry out chemical procedures where they participate. There are different molecules that can act as a kind of cocoon, giving shelter to the fullerene cages in such a way that they can be included in a solution or can be extracted from a mix. In this work, a theoretical study of some known and new proposed organic molecules of this kind is presented. In all cases, the interaction occurs with the help of a metallic atom or ion which plays the role of a bridge, providing a place for a metallocene like interaction to occur. The thermodynamic arguments favoring the formation of this adduct species are addressed as well as the nature of the bond by means QTAIM parameters and frontier molecular orbitals analysis. Full article

(This article belongs to the Special Issue Theoretical Chemistry of Fullerenes and Related Materials)

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17 pages, 1586 KiB

Open AccessArticle

Concrete Modular Pavement Structures with Optimized Thickness Based on Characteristics of High Performance Concrete Mixtures with Fibers and Silica Fume

by Audrius Vaitkus, Judita Gražulytė, Ovidijus Šernas, Martynas Karbočius and Rafal Mickevič

Materials 2021, 14(12), 3423; https://doi.org/10.3390/ma14123423 - 21 Jun 2021

Cited by 4 | Viewed by 2617

Abstract

Usually, C30/37 strength class concrete is used to construct concrete pavements on a rigid, semi-rigid or flexible base. Concrete with such a strength delivers essential design characteristics: flexural strength and tensile splitting strength are between 4.5–5.4 MPa and 2.8–3.7 MPa, respectively. Design characteristics [...] Read more.

Usually, C30/37 strength class concrete is used to construct concrete pavements on a rigid, semi-rigid or flexible base. Concrete with such a strength delivers essential design characteristics: flexural strength and tensile splitting strength are between 4.5–5.4 MPa and 2.8–3.7 MPa, respectively. Design characteristics can be significantly increased by densifying the concrete mixture, i.e., adding silica fume, steel or polypropylene macro fibers. As high-performance concrete characteristics are 20–60% higher than those for standard concrete (C30/37), new possibilities to reduce the thickness of concrete pavement slabs appear. The theoretical analysis of concrete pavement structures with high-performance concrete mixtures (C40/50, C45/55 and C50/60) showed that slab thickness could be reduced by 6–39% compared to a standard concrete pavement structure depending on the concrete properties and design method. From all those pavement structures, three concrete mixtures were determined as the most rational ones in terms of PCP thickness reduction and total pavement cost: (i) with 49.5 kg/m³ of steel fibers and 25.2 kg/m³ of silica fume; (ii) with 10.0 kg/m³ of polypropylene fibers (type A); (iii) with 49.5 kg/m³ of steel fibers. Full article

(This article belongs to the Special Issue Study on Advanced Cement-Based Materials and Their Applications)

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20 pages, 23764 KiB

Open AccessReview

A Review on Cement Asphalt Emulsion Mortar Composites, Structural Development, and Performance

by Hussaini Abdullahi Umar, Xiaohui Zeng, Xuli Lan, Huasheng Zhu, Yirui Li, Hong Zhao and Haichuan Liu

Materials 2021, 14(12), 3422; https://doi.org/10.3390/ma14123422 - 21 Jun 2021

Cited by 12 | Viewed by 3559

Abstract

The use of cement emulsified asphalt mortar (CA mortar) in the track structure of high-speed speed railways has been gaining considerations by many researchers due to its coupled merits of the strength of cement as well as the flexibility of asphalt material. The [...] Read more.

The use of cement emulsified asphalt mortar (CA mortar) in the track structure of high-speed speed railways has been gaining considerations by many researchers due to its coupled merits of the strength of cement as well as the flexibility of asphalt material. The asphalt to cement ratio (A/C) and the compatibility among constituent materials are crucial to the properties of CA mortar. To improve the performance properties and application of CA mortar, it is imperative to have a broad understanding of the composition mechanisms and compatibility between constituent materials. This paper summarizes interesting research outcomes related to the composition and properties of CA mortar. The consumption of water by cement promotes the breakdown of emulsified asphalt, likewise, the adsorption of asphalt droplets on the surface of cement grains retards the hydration process of cement. An appropriate A/C is required for the cement hydration rate to match the speed of demulsification of asphalt emulsion. Depending on the type and properties for which the CA mortar is designed to possess, the A/C ranges from 0.2 to 0.6 for type 1 (CAM I), and 0.6 to 1.2 for type 2 (CAM II). This paper also discusses measures taken to improve performance properties, compatibility, the interaction between constituent materials of CA mortar, and the use of additives as a partial replacement of cement in CA mortar production. The current review also suggests areas of interest for future research studies. This paper is useful to those who aim to understand or study the composition mechanisms and performance properties of CA mortar. Full article

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16 pages, 5759 KiB

Open AccessArticle

Negative Poisson’s Ratio-Spacer Design and Its Thermo-Mechanical Coupling Analysis Considering Specific Force Output

by Qianqian Yuan, Yongsheng Zhu, Ke Yan, Yiqing Cai and Jun Hong

Materials 2021, 14(12), 3421; https://doi.org/10.3390/ma14123421 - 21 Jun 2021

Viewed by 2371

Abstract

Aiming at the problems of a complex structure or poor controllability of the existing bearing preload control devices, a method of self-regulation via a negative Poisson’s ratio (NPR) spacer is proposed. Firstly, the principle of preload automatic adjustment at the bearing operation was [...] Read more.

Aiming at the problems of a complex structure or poor controllability of the existing bearing preload control devices, a method of self-regulation via a negative Poisson’s ratio (NPR) spacer is proposed. Firstly, the principle of preload automatic adjustment at the bearing operation was introduced and the NPRs with three types of cell structures were analyzed. Furthermore, a thermo-mechanical coupling analysis model of the NPR spacer was established and the deformation and force output characteristics of the NPR spacer were studied and experimentally verified. It is found that the concave hexagonal cell structure has the optimal deformation characteristics for bearing preload adjustment. When the temperature is considered, the absolute value of Poisson’s ratio of the NPR spacer decreases as the speed increases and the elongation of the NPR spacer and the output forces are much larger than those without temperature consideration. With the increase in temperature or rotating speed, the axial elongation and output forces of the NPR spacer increases while the effect of temperature is relatively larger. Full article

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10 pages, 1538 KiB

Open AccessArticle

Research into the Strength of an Open Wagon with Double Sidewalls Filled with Aluminium Foam

by Oleksij Fomin, Mykola Gorbunov, Juraj Gerlici, Glib Vatulia, Alyona Lovska and Kateryna Kravchenko

Materials 2021, 14(12), 3420; https://doi.org/10.3390/ma14123420 - 20 Jun 2021

Cited by 34 | Viewed by 2588

Abstract

The research is concerned with the use of double walls filled with aluminium foam for an open wagon in order to decrease the dynamic stresses during the operational modes. The research presents the strength calculation for the bearing structure of an open wagon [...] Read more.

The research is concerned with the use of double walls filled with aluminium foam for an open wagon in order to decrease the dynamic stresses during the operational modes. The research presents the strength calculation for the bearing structure of an open wagon with consideration of the engineering solutions proposed. It was found that the maximum equivalent stresses appeared in the bottom section of the centre sill behind the back support; they amounted to about 315 MPa and did not exceed the allowable values. The maximum displacements were detected in the middle section of the centre sill and amounted to 9.6 mm. The maximum deformations were 1.17 × 10⁻². The research also presents the strength calculation for a weld joint in the maximum loaded zones of the bearing structure of an open wagon and gives the results of a modal analysis of the bearing structure of the improved open wagon. It was found that the critical oscillation frequencies did not exceed the allowable values. The results of the research may be useful for those who are concerned about designing innovative rolling stock units and improving the operational efficiency of railway transport. Full article

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16 pages, 5055 KiB

Open AccessArticle

Surface Properties and Morphology of Boron Carbide Nanopowders Obtained by Lyophilization of Saccharide Precursors

by Dawid Kozień, Piotr Jeleń, Joanna Stępień, Zbigniew Olejniczak, Maciej Sitarz and Zbigniew Pędzich

Materials 2021, 14(12), 3419; https://doi.org/10.3390/ma14123419 - 20 Jun 2021

Cited by 5 | Viewed by 2213

Abstract

The powders of boron carbide are usually synthesized by the carbothermal reduction of boron oxide. As an alternative to high-temperature reactions, the development of the carbothermal reduction of organic precursors to produce B₄C is receiving considerable interest. The aim of this [...] Read more.

The powders of boron carbide are usually synthesized by the carbothermal reduction of boron oxide. As an alternative to high-temperature reactions, the development of the carbothermal reduction of organic precursors to produce B₄C is receiving considerable interest. The aim of this work was to compare two methods of preparing different saccharide precursors mixed with boric acid with a molar ratio of boron to carbon of 1:9 for the synthesis of B₄C. In the first method, aqueous solutions of saccharides and boric acid were dried overnight at 90 °C and pyrolyzed at 850 °C for 1 h under argon flow. In the second method, aqueous solutions of different saccharides and boric acid were freeze-dried and prepared in the same way as in the first method. Precursors from both methods were heat-treated at temperatures of 1300 to 1700 °C. The amount of boron carbide in the powders depends on the saccharides, the temperature of synthesis, and the method of precursor preparation. Full article

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8 pages, 1207 KiB

Open AccessArticle

Behavior of Ternary Mixtures of Hydrogen Bond Acceptors and Donors in Terms of Band Gap Energies

by Alberto Mannu, Francesca Cardano, Salvatore Baldino and Andrea Fin

Materials 2021, 14(12), 3418; https://doi.org/10.3390/ma14123418 - 20 Jun 2021

Cited by 2 | Viewed by 2450

Abstract

Three ternary mixtures composed by choline chloride (ChCl), ethylene glycol (EG), and a second hydrogen bond donor (HBD) as ethanol (A), 2-propanol (B), and glycerol (C) were studied in terms of composition related to the band gap energy (BGE). A Design of Experiments [...] Read more.

Three ternary mixtures composed by choline chloride (ChCl), ethylene glycol (EG), and a second hydrogen bond donor (HBD) as ethanol (A), 2-propanol (B), and glycerol (C) were studied in terms of composition related to the band gap energy (BGE). A Design of Experiments (DoE) approach, and in particular a Simple Lattice three-components design, was employed for determining the variation of the BGE upon the composition of each system. UV-VIS analysis and subsequent Tauc plot methodology provided the data requested from the DoE, and multivariate statistical analysis revealed a drop of the BGE in correspondence to specific binary compositions for systems A and B. In particular, a BGE of 3.85 eV was registered for the mixtures ChCl/EtOH (1:1) and ChCl/2-propanol (1:1), which represents one of the lowest values ever observed for these systems. Full article

(This article belongs to the Special Issue Advances and Applications in Deep Eutectic Solvents Technology)

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18 pages, 8924 KiB

Open AccessArticle

Effect of Fe and Cr on the Macro/Micro Tribological Behaviours of Copper-Based Composites

by Zhongyi Zhang, Haibin Zhou, Pingping Yao, Kunyang Fan, Yongqiang Liu, Lin Zhao, Yelong Xiao, Taimin Gong and Minwen Deng

Materials 2021, 14(12), 3417; https://doi.org/10.3390/ma14123417 - 20 Jun 2021

Cited by 7 | Viewed by 2091

Abstract

Fe and Cr are regarded as two of the most important friction components in Cu-based composites (Cu–BCs). In this study, the microstructural detection and micro- and macro-tribology evaluation of Cu–BCs containing Fe and Cr were performed. The results indicated that both Fe and [...] Read more.

Fe and Cr are regarded as two of the most important friction components in Cu-based composites (Cu–BCs). In this study, the microstructural detection and micro- and macro-tribology evaluation of Cu–BCs containing Fe and Cr were performed. The results indicated that both Fe and Cr formed diffusion interfaces with the copper matrix. Because of the generation of a defect interface layer, the Cr/Cu interface exhibited a low bonding strength. Owing to the excellent binding interface between Fe and Cu, the high coefficient of friction (COF) of Fe, and the formation of a mechanical mixing layer promoted by Fe, the Cu–BCs containing Fe presented better friction performance under all braking energy per unit area (BEPUA) values. The main wear mechanism of Cu–BCs containing Fe and Cr changed from abrasion to delamination with an increase in BEPUA, and the delamination of Cu–BCs containing Fe was induced by breaks in the mechanical mixed layer (MML). Full article

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16 pages, 10036 KiB

Open AccessArticle

Corrosion Fatigue Damages of Rebars under Loading in Time

by Yaroslav Blikharskyy, Jacek Selejdak and Nadiia Kopiika

Materials 2021, 14(12), 3416; https://doi.org/10.3390/ma14123416 - 20 Jun 2021

Cited by 29 | Viewed by 2769

Abstract

Nowadays, a relatively small number of studies concern the study of corrosion processes in reinforced concrete structures under load. Additionally, rather little research has been carried out concerning changes in the stress–strain state parameters of structures under the simultaneous action of aggressive environment [...] Read more.

Nowadays, a relatively small number of studies concern the study of corrosion processes in reinforced concrete structures under load. Additionally, rather little research has been carried out concerning changes in the stress–strain state parameters of structures under the simultaneous action of aggressive environment and load. This issue requires additional experimental and theoretical investigation. Determination of mechanical properties, fatigue characteristics and susceptibility to corrosion cracking was performed on samples of reinforcing St3GPF steel. The chemical composition of steel was determined by structural analysis. The spectral method for the determination of alloying elements and impurities in steels is based on the excitation of iron atoms and admixtures by electric discharge, decomposition of radiation into a spectrum, followed by its registration on photoplate with the use of electrograph. Experimental tests of samples in an aggressive environment under the action of statically applied tensile force showed that corrosion damage has little effect on the strength characteristics. At the same time, the decrease in area reduction and the decrease in strain were recorded. Additionally, the action of cyclic loads in an aggressive environment leads to a significant reduction in the fatigue limit to values from 20 to 24% of the yield strength of the original samples, which is 2–3 times lower than the fatigue limit of undamaged samples. Full article

(This article belongs to the Special Issue Manufacturing and Fatigue Properties of Materials)

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19 pages, 8772 KiB

Open AccessArticle

Experimental Investigation of the Performance of a Hybrid Self-Healing System in Porous Asphalt under Fatigue Loadings

by Shi Xu, Xueyan Liu, Amir Tabaković and Erik Schlangen

Materials 2021, 14(12), 3415; https://doi.org/10.3390/ma14123415 - 20 Jun 2021

Cited by 21 | Viewed by 2490

Abstract

Self-healing asphalt, which is designed to achieve autonomic damage repair in asphalt pavement, offers a great life-extension prospect and therefore not only reduces pavement maintenance costs but also saves energy and reduces CO₂ emissions. The combined asphalt self-healing system, incorporating both encapsulated [...] Read more.

Self-healing asphalt, which is designed to achieve autonomic damage repair in asphalt pavement, offers a great life-extension prospect and therefore not only reduces pavement maintenance costs but also saves energy and reduces CO₂ emissions. The combined asphalt self-healing system, incorporating both encapsulated rejuvenator and induction heating, can heal cracks with melted binder and aged binder rejuvenation, and the synergistic effect of the two technologies shows significant advantages in healing efficiency over the single self-healing method. This study explores the fatigue life extension prospect of the combined healing system in porous asphalt. To this aim, porous asphalt (PA) test specimens with various healing systems were prepared, including: (i) the capsule healing system, (ii) the induction healing system, (iii) the combined healing system and (iv) a reference system (without extrinsic healing). The fatigue properties of the PA samples were characterized by an indirect tensile fatigue test and a four-point bending fatigue test. Additionally, a 24-h rest period was designed to activate the built-in self-healing system(s) in the PA. Finally, a damaging and healing programme was employed to evaluate the fatigue damage healing efficiency of these systems. The results indicate that all these self-healing systems can extend the fatigue life of porous asphalt, while in the combined healing system, the gradual healing effect of the released rejuvenator from the capsules may contribute to a better induction healing effect in the damaging and healing cycles. Full article

(This article belongs to the Special Issue Experimental Testing and Constitutive Modelling of Pavement Materials)

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16 pages, 4864 KiB

Open AccessArticle

The Influence of Titanium Dioxide on Silicate-Based Glasses: An Evaluation of the Mechanical and Radiation Shielding Properties

by Badriah Albarzan, Mohamed Y. Hanfi, Aljawhara H. Almuqrin, M. I. Sayyed, Haneen M. Alsafi and K. A. Mahmoud

Materials 2021, 14(12), 3414; https://doi.org/10.3390/ma14123414 - 20 Jun 2021

Cited by 26 | Viewed by 2734

Abstract

The mechanical and radiation shielding features were reported for a quaternary Na₂O-CaO-SiO₂-TiO₂ glass system used in radiation protection. The fundamentals of the Makishima–Mazinize model were applied to evaluate the elastic moduli of the glass samples. The elastic moduli, [...] Read more.

The mechanical and radiation shielding features were reported for a quaternary Na₂O-CaO-SiO₂-TiO₂ glass system used in radiation protection. The fundamentals of the Makishima–Mazinize model were applied to evaluate the elastic moduli of the glass samples. The elastic moduli, dissociation energy, and packing density increased as TiO₂ increased. The glasses’ dissociation energy increased from 62.82 to 65.33 kJ/cm³, while the packing factor slightly increased between 12.97 and 13.00 as the TiO₂ content increased. The MCNP-5 code was used to evaluate the gamma-ray shielding properties. The best linear attenuation coefficient was achieved for glass samples with a TiO₂ content of 9 mol%: the coefficient decreased from 5.20 to 0.14 cm⁻¹ as the photon energy increased from 0.015 to 15 MeV. Full article

(This article belongs to the Special Issue Radiation Shielding Materials)

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17 pages, 6212 KiB

Open AccessArticle

The Combined Use of Gentamicin and Silver Nitrate in Bone Cement for a Synergistic and Extended Antibiotic Action against Gram-Positive and Gram-Negative Bacteria

by John Jackson, Joey Lo, Eric Hsu, Helen M. Burt, Ali Shademani and Dirk Lange

Materials 2021, 14(12), 3413; https://doi.org/10.3390/ma14123413 - 20 Jun 2021

Cited by 14 | Viewed by 2716

Abstract

Using bone cement as a carrier, gentamicin was for years the default drug to locally treat orthopedic infections but has lost favor due to increasing bacterial resistance to this drug. The objective of this study was to investigate the effect of combining gentamicin [...] Read more.

Using bone cement as a carrier, gentamicin was for years the default drug to locally treat orthopedic infections but has lost favor due to increasing bacterial resistance to this drug. The objective of this study was to investigate the effect of combining gentamicin with silver nitrate in bone cement against S. aureus and P. aeruginosa. Antibacterial effects (CFU counts) of gentamicin and silver were initially studied followed by studies using subtherapeutic concentrations of each in combination. The release rates from cement were measured over 10 days and day 7 release samples were saved and analyzed for antibiotic activity. A strong synergistic effect of combining silver with gentamicin was found using both dissolved drugs and using day 7 bone cement release media for both Gram-positive and Gram-negative bacteria. The cement studies were extended to vancomycin and tobramycin, which are also used in bone cement, and similar synergistic effects were found for day 7 release media with P. aeruginosa but not S. aureus. These studies conclude that the combined use of low loadings of gentamicin and silver nitrate in bone cement may offer an economical and much improved synergistic method of providing anti-infective orthopedic treatments in the clinic. Full article

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20 pages, 309 KiB

Open AccessEditorial

Testing of Materials and Elements in Civil Engineering

by Krzysztof Schabowicz

Materials 2021, 14(12), 3412; https://doi.org/10.3390/ma14123412 - 20 Jun 2021

Cited by 14 | Viewed by 4803

Abstract

This issue is proposed and organized as a means to present recent developments in the field of testing of materials in civil engineering. For this reason, the articles highlighted in this issue should relate to different aspects of testing of different materials in [...] Read more.

This issue is proposed and organized as a means to present recent developments in the field of testing of materials in civil engineering. For this reason, the articles highlighted in this issue should relate to different aspects of testing of different materials in civil engineering, from building materials and elements to building structures. The current trend in the development of materials testing in civil engineering is mainly concerned with the detection of flaws and defects in elements and structures using destructive, semi-destructive, and nondestructive testing. The trend, as in medicine, is toward designing test equipment that allows one to obtain a picture of the inside of the tested element and materials. Very interesting results with significance for building practices of testing of materials and elements in civil engineering were obtained. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)

19 pages, 9059 KiB

Open AccessEditor’s ChoiceArticle

A Cellulose-Derived Nanofibrous MnO₂-TiO₂-Carbon Composite as Anodic Material for Lithium-Ion Batteries

by Shun Li, Ming Yang, Guijin He, Dongmei Qi and Jianguo Huang

Materials 2021, 14(12), 3411; https://doi.org/10.3390/ma14123411 - 20 Jun 2021

Cited by 3 | Viewed by 2483

Abstract

A bio-inspired nanofibrous MnO₂-TiO₂-carbon composite was prepared by utilizing natural cellulosic substances (e.g., ordinary quantitative ashless filter paper) as both the carbon source and structural matrix. Mesoporous MnO₂ nanosheets were densely immobilized on an ultrathin titania film precoated [...] Read more.

A bio-inspired nanofibrous MnO₂-TiO₂-carbon composite was prepared by utilizing natural cellulosic substances (e.g., ordinary quantitative ashless filter paper) as both the carbon source and structural matrix. Mesoporous MnO₂ nanosheets were densely immobilized on an ultrathin titania film precoated with cellulose-derived carbon nanofibers, which gave a hierarchical MnO₂-TiO₂-carbon nanoarchitecture and exhibited excellent electrochemical performances when used as an anodic material for lithium-ion batteries. The MnO₂-TiO₂-carbon composite with a MnO₂ content of 47.28 wt % exhibited a specific discharge capacity of 677 mAh g⁻¹ after 130 repeated charge/discharge cycles at a current rate of 100 mA g⁻¹. The contribution percentage of MnO₂ in the composite material is equivalent to 95.1% of the theoretical capacity of MnO₂ (1230 mAh g⁻¹). The ultrathin TiO₂ precoating layer with a thickness ca. 2 nm acts as a crucial interlayer that facilitates the growth of well-organized MnO₂ nanosheets onto the surface of the titania-carbon nanofibers. Due to the interweaved network structures of the carbon nanofibers and the increased content of the immobilized MnO₂, the exfoliation and aggregation, as well as the large volume change of the MnO₂ nanosheets, are significantly inhibited; thus, the MnO₂-TiO₂-carbon electrodes displayed outstanding cycling performance and a reversible rate capability during the Li⁺ insertion/extraction processes. Full article

(This article belongs to the Special Issue Feature Paper in Section Materials Chemistry)

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9 pages, 2232 KiB

Open AccessArticle

EPR Spectroscopy as a Tool to Characterize the Maturity Degree of Humic Acids

by Bozena Debska, Ewa Spychaj-Fabisiak, Wiesław Szulc, Renata Gaj and Magdalena Banach-Szott

Materials 2021, 14(12), 3410; https://doi.org/10.3390/ma14123410 - 20 Jun 2021

Cited by 9 | Viewed by 3679

Abstract

The major indicator of soil fertility and productivity are humic acids (HAs) arising from decomposition of organic matter. The structure and properties of HAs depend, among others climate factors, on soil and anthropogenic factors, i.e., methods of soil management. The purpose of the [...] Read more.

The major indicator of soil fertility and productivity are humic acids (HAs) arising from decomposition of organic matter. The structure and properties of HAs depend, among others climate factors, on soil and anthropogenic factors, i.e., methods of soil management. The purpose of the research undertaken in this paper is to study humic acids resulting from the decomposition of crop residues of wheat (Triticum aestivum L.) and plant material of thuja (Thuja plicata D.Don.ex. Lamb) using electron paramagnetic resonance (EPR) spectroscopy. In the present paper, we report EPR studies carried out on two types of HAs extracted from forest soil and incubated samples of plant material (mixture of wheat straw and roots), both without soil and mixed with soil. EPR signals obtained from these samples were subjected to numerical analysis, which showed that the EPR spectra of each sample could be deconvoluted into Lorentzian and Gaussian components. It can be shown that the origin of HAs has a significant impact on the parameters of their EPR spectra. The parameters of EPR spectra of humic acids depend strongly on their origin. The HA samples isolated from forest soils are characterized by higher spin concentration and lower peak-to-peak width of EPR spectra in comparison to those of HAs incubated from plant material. Full article

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Materials, Volume 14, Issue 12 (June-2 2021) – 299 articles

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