Materials

23 pages, 3710 KiB

Open AccessArticle

Investigation and Optimization of Process Parameters on Growth Rate in Al₂O₃ Atomic Layer Deposition (ALD) Using Statistical Approach

by Dongqing Pan and Yu Lei

Materials 2025, 18(9), 1918; https://doi.org/10.3390/ma18091918 - 23 Apr 2025

Abstract

The improvement in ALD growth rate has always been challenging due to its slow atomic-scale depositions. Although Al₂O₃ ALD is one of the most widely used ALD processes, the effects of its process parameters on growth rate have not been [...] Read more.

The improvement in ALD growth rate has always been challenging due to its slow atomic-scale depositions. Although Al₂O₃ ALD is one of the most widely used ALD processes, the effects of its process parameters on growth rate have not been systematically analyzed using statistical approaches. These statistical methods offer better efficiency and effectiveness compared to traditional techniques for studying complex processes like ALD. This paper presents a systematic investigation and optimization of four process parameters on growth rate of Al₂O₃ ALD thin films using a full factorial design of experiments (DOE) approach. Statistical analysis revealed that deposition temperature is the only statistically significant factor in Al₂O₃ ALD process, while argon gas flow rate, pulsing time and purging time are tested nonsignificant. Significant interactions were found between deposition temperature and purging time, and between pulsing time and purging time, with all other interactions being nonsignificant. Optimal process settings for higher deposition rate were identified: the temperature and gas flow rate are set at lower levels, while pulsing time and purging time are set at higher levels. Full article

(This article belongs to the Special Issue Materials Innovation Through Atomic Layer Deposition: Process Optimization, Material Properties, and Applications)

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15 pages, 5445 KiB

Open AccessArticle

Effect of Nb/C Ratio on Microstructure and Mechanical Properties of B50A789G Precipitation Hardening Stainless Steel

by Shuai Liu, Jiqing Zhao, Ruishan Xin, Yudong He, Gang Yang and Bin Yang

Materials 2025, 18(9), 1917; https://doi.org/10.3390/ma18091917 - 23 Apr 2025

Abstract

In this study, the microstructural evolution and mechanical properties of B50A789G steels with different Nb/C ratios (7, 9, 11, and 13) after tempering at 495 °C were investigated through mechanical property testing, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope [...] Read more.

In this study, the microstructural evolution and mechanical properties of B50A789G steels with different Nb/C ratios (7, 9, 11, and 13) after tempering at 495 °C were investigated through mechanical property testing, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The role of Nb in B50A789G steel was also explored. The results indicate that, at the same tempering time, the strength and hardness of the steel increase with increasing the Nb/C ratio. The maximum tensile strength exceeded 1240 MPa when the Nb/C ratio reached 13. With prolonged tempering time, the tensile strength of steels with low Nb/C ratios (7 and 9) gradually decreases, whereas steels with high Nb/C ratios (11 and 13) exhibit a decline in tensile strength only after 6 h of tempering. In contrast, the impact toughness shows an opposite trend to the strength. As the Nb/C ratio increases, both coarse primary NbC and nanoscale NbC precipitates in the steel gradually increase. The primary roles of Nb in B50A789G steel are grain refinement strengthening and precipitation strengthening. For steels with Nb/C ≤ 11, the improvement in strength is attributed to the combined effects of grain refinement strengthening and precipitation strengthening provided by Nb. However, for steels with Nb/C > 11, the increase in strength is primarily driven by the precipitation-strengthening effect of the nanoscale NbC phase. Full article

(This article belongs to the Section Metals and Alloys)

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16 pages, 1047 KiB

Open AccessArticle

Kinetic Study and Simulation of Titanium Carbide-Supported, Platinum-Doped Tetrahedral Amorphous Carbon Electrodes for Hydrogen Evolution Reaction

by Harunal Rejan Ramji, Nicolas Glandut, Jean-Christophe Orlianges, Joseph Absi and Soh Fong Lim

Materials 2025, 18(9), 1916; https://doi.org/10.3390/ma18091916 - 23 Apr 2025

Abstract

This paper presents the kinetic study of titanium carbide (TiC)-supported, platinum-doped tetrahedral amorphous carbon (taC:Pt) referred to as TiC-taC, for the hydrogen evolution reaction (HER). This study employs the Volmer–Heyrovsky–Tafel (VHT) mechanism. A theoretical approach was utilized to investigate the kinetic properties of [...] Read more.

This paper presents the kinetic study of titanium carbide (TiC)-supported, platinum-doped tetrahedral amorphous carbon (taC:Pt) referred to as TiC-taC, for the hydrogen evolution reaction (HER). This study employs the Volmer–Heyrovsky–Tafel (VHT) mechanism. A theoretical approach was utilized to investigate the kinetic properties of these materials for an HER in 0.5 M H₂SO₄. TiC-taC exhibited Volmer-dominated reactions with a Tafel slope of 40 mV/dec and the overpotential at 10 mA/cm² was 185 mV. In contrast, isolated TiC and taC:Pt recorded significantly higher Tafel slopes with 60–110 mV/dec and overpotentials of 871 mV and 1009 mV, respectively. The developed model was tested in one dimension (1D) for individual TiC and taC:Pt. The simulated kinetics parameters were determined for both TiC and taC:Pt, revealing that TiC follows the VHT steps, while taC:Pt follows the VH steps. The simulation results show excellent coherence with the experimental results. Further simulation of the hybrid TiC-taC electrocatalyst was conducted considering surface diffusion and edge effects in two (2D) and three dimensions (3D). To the best of our knowledge, this FEM simulation approach is the first to be reported due to the unique geometry of the TiC-taC catalyst enabling the assumption of surface diffusion and edge effect. The introduction of edge effects on the taC:Pt side of the TiC support significantly enhanced the current output, aligning closely with experimental results. The edge exhibited distinct kinetic properties compared to both TiC and taC:Pt. The kinetic parameters determined from the simulation demonstrated strong agreement with experimental findings. Adding the edge effects was essential to explaining the higher current output from the TiC-taC electrode. It exhibited unique kinetic properties not observed in either TiC or taC:Pt alone, acting as a pump where it absorbs c_Hs from neighbouring sites due to surface diffusivity and releases H2 via the Heyrovsky reaction. While surface diffusion had a lesser effect, the simulation indicated its positive influence on the HER. Full article

(This article belongs to the Special Issue Laser, Plasma, and Radiation Processing of Advanced Functional Materials for Magnetic, Electrotechnical and Electrochemical Applications)

12 pages, 2547 KiB

Open AccessArticle

Optical and Dielectric Properties of BaF₂:(Er,Yb) Co-Doped Crystal

by Marius Stef, Carla Schornig and Gabriel Buse

Materials 2025, 18(9), 1915; https://doi.org/10.3390/ma18091915 - 23 Apr 2025

Abstract

A BaF₂ single crystal co-doped with Er³⁺ and Yb³⁺ was grown by the vertical Bridgman technique and investigated for its optical and dielectric properties. Judd–Ofelt analysis yielded intensity parameters Ω₂ = 0.59, Ω₄ = 0.38, and [...] Read more.

A BaF₂ single crystal co-doped with Er³⁺ and Yb³⁺ was grown by the vertical Bridgman technique and investigated for its optical and dielectric properties. Judd–Ofelt analysis yielded intensity parameters Ω₂ = 0.59, Ω₄ = 0.38, and Ω₆ = 0.27 (×10⁻²⁰ cm²), with a quality factor χ = 1.41, indicating strong radiative transitions. Under UV and near-UV excitation, emissions at 321, 405, 518, and 536 nm were observed, with radiative lifetimes ranging from 1.1 to 3.4 ms. A single dielectric relaxation process was identified, with activation energy of 0.58 eV and associated with trigonal NNN dipoles. The NNN dipole concentration was estimated at ~2.5 × 10¹⁸ cm⁻³. These results support the suitability of Er³⁺,Yb³⁺ co-doped BaF₂ crystals for luminescent and dielectric applications in advanced photonic materials. Full article

(This article belongs to the Section Optical and Photonic Materials)

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27 pages, 8140 KiB

Open AccessArticle

Bio-Based Poly(3-hydroxybutyrate) and Polyurethane Blends: Preparation, Properties Evaluation and Structure Analysis

by Beata Krzykowska, Anna Fajdek-Bieda, Aneta Jakubus, Joanna Kostrzewa, Anita Białkowska, Maciej Kisiel, Štěpánka Dvořáčková, Wiesław Frącz and Iwona Zarzyka

Materials 2025, 18(9), 1914; https://doi.org/10.3390/ma18091914 - 23 Apr 2025

Abstract

The present work deals with polymer blends produced from poly(3-hydroxybutyrate), P3HB and polyurethane. Linear polyurethane (PU) was here synthesized by reacting polypropylene glycol with 4,4′-diphenylmethane diisocyanate, and was used in amounts of 5, 10 and 15 wt. %. The polymers were melt-mixed using [...] Read more.

The present work deals with polymer blends produced from poly(3-hydroxybutyrate), P3HB and polyurethane. Linear polyurethane (PU) was here synthesized by reacting polypropylene glycol with 4,4′-diphenylmethane diisocyanate, and was used in amounts of 5, 10 and 15 wt. %. The polymers were melt-mixed using a twin-screw extruder after prior premixing. The obtained blends were tested by differential scanning calorimetry analysis (DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Their thermal and mechanical properties, including impact resistance, hardness, tensile and flexural properties, were also determined, and the surface topography and roughness were analyzed. FTIR analysis of the prepared blends confirmed the interactions of PU with the P3HB matrix via hydrogen bonding. Analysis of the surface topography of the samples showed that the higher the PU content, the greater the regularity and homogeneity of the surface structure. The roughness of the P3HB blend containing 5 w. % PU was the greatest. SEM images of the fracture surfaces of the blend samples explain the mechanism of the improvement of their mechanical properties. The obtained polymer blends were characterized by significantly lower hardness, and better impact strength and relative elongation at break compared to native P3HB. The DSC results confirm a decrease in the glass transition, melting and crystallization temperatures with increasing amounts of PU in the blends. The lower melting temperature and the higher degradation temperature of the resulted blends than native P3HB make the processing conditions easier, and prevent the degradation of the material. The best mechanical and thermal properties were shown by blends containing 10 wt. % of PU. Full article

(This article belongs to the Special Issue Progressive Technologies and Materials in Mechanical and Materials Engineering)

17 pages, 4371 KiB

Open AccessArticle

A Convolution-Based Coding Metasurface for Wide-Angle Beam Steering for Enhanced 5G Wireless Communications

by Jing Wang, Yan Chen, Benxian Wang, Xin Liu, Junfei Gao, Qi Xue and Xiaojun Huang

Materials 2025, 18(9), 1913; https://doi.org/10.3390/ma18091913 - 23 Apr 2025

Abstract

With the rapid development of 5G communication technology, there is an increasing demand for high-performance antennas and beam control technologies, making the development of novel metamaterial structures capable of precise electromagnetic wave manipulation a current research hotspot. This paper presents a coding metasurface [...] Read more.

With the rapid development of 5G communication technology, there is an increasing demand for high-performance antennas and beam control technologies, making the development of novel metamaterial structures capable of precise electromagnetic wave manipulation a current research hotspot. This paper presents a coding metasurface specifically designed for 5G communication applications, operating at a frequency of 3.5 GHz. The design employs a unique annular metasurface unit structure capable of achieving both single-beam and dual-beam functionalities. Through convolution operations, precise control over the reflection angle is achieved, with an adjustable range from 51.5° to 17.5° and a resolution of 10°. This design overcomes the inherent limitations of traditional gradient coding methods, providing a comprehensive framework for wide-angle reflection control in metasurface design. The research results demonstrate that the coding metasurface can effectively control the reflection direction of electromagnetic waves at 3.5 GHz, exhibiting dual-polarization modulation capabilities and maintaining stable performance under oblique incidence conditions within 20°. Experimental validation confirms the beam control functionality of the design in real-world environments, highlighting its potential to enhance signal reception sensitivity and transmission efficiency in 5G wireless communications. This work opens new avenues for research in reconfigurable and intelligent metasurfaces, with potential applications extending beyond 5G to future 6G networks and Internet of Things (IoT) systems. Full article

16 pages, 10275 KiB

Open AccessArticle

Structure Formation and Properties of Activated Supersulfate Cement

by Leonid Dvorkin, Vadim Zhitkovsky, Izabela Hager, Tomasz Tracz and Tomasz Zdeb

Materials 2025, 18(9), 1912; https://doi.org/10.3390/ma18091912 - 23 Apr 2025

Abstract

The article investigates the characteristics of the phase composition and structure of supersulfated cement (SSC) during hardening using X-ray, electron microscopy, and ultrasonic analysis methods. The influence of different types of activators, hardening accelerators, and superplasticizers on the type and morphology of the [...] Read more.

The article investigates the characteristics of the phase composition and structure of supersulfated cement (SSC) during hardening using X-ray, electron microscopy, and ultrasonic analysis methods. The influence of different types of activators, hardening accelerators, and superplasticizers on the type and morphology of the newly formed phases during SSC hardening was studied. The effect of a polycarboxylate-type superplasticizer and calcium chloride on the standard consistency and setting times of SSC was experimentally determined. It was established that the introduction of the superplasticizer reduces the standard consistency by 10–16%. Experimental data showed higher effectiveness of phosphogypsum as a sulfate activator compared to gypsum stone. The strength increase of SSC at 7 days reached up to 35%, and at 28 days, up to 15%. Based on the kinetics of ultrasonic wave propagation during SSC hardening, the main stages of structure formation and the influence of cement composition on these stages were determined. The experimental results demonstrate the effect of SSC composition on its standard consistency, setting time, and mechanical properties. The impact of the type of activator and admixtures on the change in SSC strength during storage was investigated. It was found that the addition of a polycarboxylate-type superplasticizer significantly reduces the strength loss of SSC during long-term storage. Using mathematical modeling, experimentally obtained statistical models of strength were developed, which allow for the quantitative evaluation of individual and combined effects, as well as the determination of optimal SSC compositions. Full article

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

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12 pages, 2913 KiB

Open AccessArticle

Structural and Magnetic Characterization of Mechanically Alloyed (Fe₂O₃)_1−x(Al₂O₃)_x Solid Solutions via Pulsed Neutron Powder Diffraction

by Dong Luo, Hayato Nakaishi, Takeshi Yabutsuka, Takashi Saito, Takashi Kamiyama, Masato Hagihala and Shigeomi Takai

Materials 2025, 18(9), 1911; https://doi.org/10.3390/ma18091911 - 23 Apr 2025

Abstract

Neutron powder diffraction experiments were carried out to characterize mechanochemically synthesized (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions with corundum-type structure, focusing on their lattice and magnetic structures with varying temperature and composition. The neutron diffraction [...] Read more.

Neutron powder diffraction experiments were carried out to characterize mechanochemically synthesized (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions with corundum-type structure, focusing on their lattice and magnetic structures with varying temperature and composition. The neutron diffraction experiments for (Fe₂O₃)_0.5(Al₂O₃)_0.5 in the temperature range between 4 K and 300 K reveal that no significant structural phase transition occurred. The behavior of temperature variation of lattice parameters is different from α-Fe₂O₃ and α-Al₂O₃ and reveals the thermal expansion coefficients of α_a = 5.76(2) × 10⁻⁶ K⁻¹ and α_c = 6.19(5) × 10⁻⁶ K⁻¹ between 200 K and 300 K. The room temperature neutron diffraction of (Fe₂O₃)_1−x(Al₂O₃)_x shows a linear decrease in lattice parameters with the aluminum substitution, following Vegard’s law, along with a decrease in the magnetic moment, indicating the dilution effect on spin interactions. With the increase in the aluminum substitution from x = 0 to 0.5, the deduced magnetic moment decreases from 2.224 μ_B to 0.862 μ_B. Full article

(This article belongs to the Section Materials Chemistry)

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20 pages, 4700 KiB

Open AccessArticle

The Effects of In Situ Growth of SiC Nanowires on the Electromagnetic Wave Absorption Properties of SiC Porous Ceramics

by Jingxiong Liu, Genlian Li, Tianmiao Zhao, Zhiqiang Gong, Feng Li, Wen Xie, Songze Zhao and Shaohua Jiang

Materials 2025, 18(9), 1910; https://doi.org/10.3390/ma18091910 - 23 Apr 2025

Abstract

In situ-grown SiC nanowires (SiCnws) on SiC porous material (SiCnws@SiC) were prepared using sol–gel and carbothermal reduction methods, which substantially improves the electromagnetic wave absorption property of composite material. The crystallinity and purity of SiCnws are the best when the sintering temperature is [...] Read more.

In situ-grown SiC nanowires (SiCnws) on SiC porous material (SiCnws@SiC) were prepared using sol–gel and carbothermal reduction methods, which substantially improves the electromagnetic wave absorption property of composite material. The crystallinity and purity of SiCnws are the best when the sintering temperature is 1600 °C. When the ratio of the carbon source (C) to the silicon source (Si) is 1:1, SiCnws@SiC composite exhibits excellent electromagnetic wave absorption performance, the minimum reflection loss is −56.95 dB at a thickness of 2.30 mm, and the effective absorption bandwidth covers 1.85 GHz. The optimal effective absorption bandwidth is 4.01 GHz when the thickness is 2.59 mm. The enhancement of the electromagnetic wave absorption performance of SiCnws is mainly attributed to the increase in the heterogeneous interface and multiple reflection and scattering caused by the network structure, increasing dielectric loss and conduction loss. In addition, defects could occur during the growth of SiCnws, which could become the center of dipole polarization and increase the polarization loss of composite materials. Therefore, in situ growth of SiCnws on SiC porous ceramics is a promising method to improve electromagnetic wave absorption. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

26 pages, 9546 KiB

Open AccessArticle

Mix Design of Pervious Concrete in Geotechnical Engineering Applications

by Maurizio Ziccarelli

Materials 2025, 18(9), 1909; https://doi.org/10.3390/ma18091909 - 23 Apr 2025

Abstract

This paper presents a comprehensive experimental study on the mix design and performance of permeable concrete for geotechnical applications, focusing on its hydraulic conductivity, durability, and filter properties. Characterized by high porosity and minimal or no fine aggregates, classical pervious concretes are effectively [...] Read more.

This paper presents a comprehensive experimental study on the mix design and performance of permeable concrete for geotechnical applications, focusing on its hydraulic conductivity, durability, and filter properties. Characterized by high porosity and minimal or no fine aggregates, classical pervious concretes are effectively utilized in various civil and environmental engineering applications, including drainage systems and erosion control. This research examines the influence of the particle size distribution of aggregates on the filter properties of permeable concrete for applications in geotechnical engineering (draining piles, deep trench drains, and draining backfill). It emphasizes the importance of resistance to clogging to maintain adequate residual hydraulic conductivity and to prevent the internal erosion of soils into which permeable concrete drains are installed. The experimental results indicate that including sand in the aggregates strongly enhances the filtering capacity of pervious concrete. These findings suggest that if the mix design of permeable concrete is developed considering the grain size distribution of the base soils, the concrete will meet long-term drainage requirements (sufficient residual hydraulic conductivity), exhibit good resistance to physical clogging, provide excellent protection for the base soils against internal erosion, and contribute to the overall stability of geotechnical systems. Full article

(This article belongs to the Special Issue Advanced Experimental Technology, Theory and Numerical Methods in Geomaterials and Concrete Materials)

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20 pages, 7246 KiB

Open AccessArticle

Coated Mg Alloy Implants: A Spontaneous Wettability Transition Process with Excellent Antibacterial and Osteogenic Functions

by Sijia Yan, Shu Cai, You Zuo, Hang Zhang, Ting Yang, Lei Ling, Huanlin Zhang, Jiaqi Lu and Baichuan He

Materials 2025, 18(9), 1908; https://doi.org/10.3390/ma18091908 - 23 Apr 2025

Abstract

AZ31B magnesium alloy (wt.%: Al 2.94; Zn 0.87; Mn 0.57; Si 0.0112; Fe 0.0027; Cu 0.0008; Ni 0.0005; Mg remaining) has appropriate mechanical properties, good biodegradability and biocompatibility and can be used as a good orthopedic implant material. AZ31B magnesium alloy with a [...] Read more.

AZ31B magnesium alloy (wt.%: Al 2.94; Zn 0.87; Mn 0.57; Si 0.0112; Fe 0.0027; Cu 0.0008; Ni 0.0005; Mg remaining) has appropriate mechanical properties, good biodegradability and biocompatibility and can be used as a good orthopedic implant material. AZ31B magnesium alloy with a superhydrophobic surface exhibits excellent corrosion resistance and antibacterial adhesion performance, but superhydrophobic surfaces also hinder osteoblast adhesion and proliferation on the implants, resulting in unsatisfactory osteogenic properties. Therefore, it is necessary to achieve the wettability transition of the superhydrophobic surface at an early stage of implantation. In this work, superhydrophobic hydroxyapatite (HA)/calcium myristate (CaMS)/myristic acid (MA) composite coatings were prepared on AZ31B magnesium alloy using the hydrothermal and immersion methods. The composite coatings can spontaneously undergo the wettability transition from superhydrophobic to hydrophilic after complete exposure to simulated body fluid (SBF, a solution for modeling the composition and concentration of human plasma ions) for 9 h. The wettability transition mainly originated from the deposition and growth of the newly formed CaMS among the HA nanopillars during immersing, which deconstructed the micro-nano structure of the superhydrophobic coatings and directly exposed the HA to the water molecules, thereby significantly altering the wettability of the coatings. Benefiting from the superhydrophobic surface, the composite coating exhibited excellent antibacterial properties. After the wettability transition, the HA/CaMS/MA composite coating exhibited superior osteoblast adhesion performance. This work provides a strategy to enable a superhydrophobic coating to undergo spontaneous wettability transition in SBF, thereby endowing the coated magnesium alloy with a favorable osteogenic property. Full article

(This article belongs to the Section Biomaterials)

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31 pages, 11063 KiB

Open AccessArticle

The Role of Ceramics in the Configuration of a New Solar Thermal Collection System for Domestic Hot Water and Heating

by Jordi Roviras Miñana and Vicente Sarrablo Moreno

Materials 2025, 18(9), 1907; https://doi.org/10.3390/ma18091907 - 23 Apr 2025

Abstract

The work presented in this study aims to demonstrate the capacity of ceramic materials in the configuration of solar thermal collectors (CSTs) for the production of domestic hot water (DHW) and heating in buildings. Currently, the ceramic tile and panel manufacturing sector presents [...] Read more.

The work presented in this study aims to demonstrate the capacity of ceramic materials in the configuration of solar thermal collectors (CSTs) for the production of domestic hot water (DHW) and heating in buildings. Currently, the ceramic tile and panel manufacturing sector presents very advanced manufacturing systems at a technological level that allows the generation of pieces with high physical and mechanical performances. Especially, their high resistances to extreme temperatures and good thermal conductivities position these materials as great candidates in the field of CSTs. In addition, ceramic materials tend to be durable and corrosion resistant, which makes them a very reliable option in the long term. The results obtained in the test campaign and presented in the article confirm the capacity of ceramics to meet the basic requirements of a CST system for buildings in terms of absorption, energy performance, watertightness, and resistance to water pressure, among other aspects, and make it possible to advance new research to improve the behaviors, performances, and architectural integration of ceramic collectors. Full article

(This article belongs to the Special Issue Advance in Sustainable Construction Materials, Second Volume)

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22 pages, 30600 KiB

Open AccessArticle

In Situ Evaluation of Epoxy Self-Healing Coating by Encapsulated Linseed Oil in Poly(Urea–Formaldehyde–Melamine) Microcapsules

by Lucas Henrique de Oliveira Souza, Michele Fedel, Fernando Cotting and Wagner Reis da Costa Campos

Materials 2025, 18(9), 1906; https://doi.org/10.3390/ma18091906 - 23 Apr 2025

Abstract

The development of self-healing coatings represents a promising approach to enhance the durability of metal substrates exposed to corrosive environments, demanding thorough in situ investigations. In this study, poly(urea–formaldehyde–melamine) (PUF) microcapsules containing linseed oil (LO) were synthesized via in situ polymerization to act [...] Read more.

The development of self-healing coatings represents a promising approach to enhance the durability of metal substrates exposed to corrosive environments, demanding thorough in situ investigations. In this study, poly(urea–formaldehyde–melamine) (PUF) microcapsules containing linseed oil (LO) were synthesized via in situ polymerization to act as healing agents in protective coatings. The microcapsules were characterized using scanning electron microscopy (SEM), optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The capsules exhibited a regular spherical morphology with an average diameter of 96 µm and an LO encapsulation efficiency of 81 wt%. TGA confirmed their thermal stability up to 200 °C, while FTIR verified the successful encapsulation of LO. For performance evaluation, 10 wt% of the microcapsules was incorporated into an epoxy matrix and applied to carbon steel. Corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in 0.1 mol/L of NaCl solution over 500 h. The coating with microcapsules exhibited a |Z|_0.01 of 10⁶ Ω·cm², higher than the 10⁴ Ω·cm² observed for the coating without microcapsules, indicating improved barrier properties. Raman spectroscopy confirmed the auto-oxidation of LO at damaged areas, evidencing the self-healing mechanism. Although full barrier recovery was not achieved, the system effectively delayed corrosion progression. Full article

(This article belongs to the Special Issue Construction and Applications in Functional Polymers)

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18 pages, 4764 KiB

Open AccessArticle

Hemp Concrete with Mineral Additives as a Durable and Fire-Resistant Material in Green Construction

by Elżbieta Janowska-Renkas, Anna Król, Igor Klementowski and Michał Sokolski

Materials 2025, 18(9), 1905; https://doi.org/10.3390/ma18091905 - 23 Apr 2025

Abstract

In this work, to enhance the compressive strength and evaluate the fire resistance of hemp concrete, we incorporated mineral additives such as FBC fly ash and metakaolin. This paper investigates the thermal conductivity, compressive strength, flammability, and fire resistance of hempcrete and the [...] Read more.

In this work, to enhance the compressive strength and evaluate the fire resistance of hemp concrete, we incorporated mineral additives such as FBC fly ash and metakaolin. This paper investigates the thermal conductivity, compressive strength, flammability, and fire resistance of hempcrete and the influence of mineral additives in the form of fly ash from fluidized bed combustion (FBC) and metakaolin on these properties. A fly ash content of 20% by weight of the binder resulted in an increase of 26% in compressive strength and about 6% in thermal conductivity compared to hemp concrete without mineral additives. The use of metakaolin in the amount of 15% by weight of the binder resulted in a 21% increase in compressive strength values with an increase in the thermal conductivity coefficient of only 0.5%. Flammability tests by direct application of a gas torch flame to the specimen surface proved the lack of flammability and spontaneous fire extinguishing ability of hempcrete. In turn, fire resistance tests showed much higher resistance to high temperatures for hempcrete modified with metakaolin, where the recorded mass loss during a 15 min test at 500 °C was ca. 58% less than in hempcrete without mineral additives, and when FBC fly ash was used, the mass loss was ca. 37% less. The obtained results are satisfactory in terms of the physico-mechanical properties of hempcrete. They also enable the replacement of traditional construction materials with waste-derived materials from other sectors of the economy, which, in the long term, will contribute to the development of green construction and support the principles of the circular economy. Full article

(This article belongs to the Section Green Materials)

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14 pages, 4308 KiB

Open AccessArticle

Mechanical Stress-Induced Defects in Thick a-PbO Layers

by Janos Rado, Amy Stieh, Attila Csík, Sándor Kökényesi and Alla Reznik

Materials 2025, 18(9), 1904; https://doi.org/10.3390/ma18091904 - 23 Apr 2025

Abstract

Amorphous lead oxide (a-PbO) X-ray photoconductors show potential for applications in direct conversion medical imaging detectors within the diagnostic energy range. a-PbO enables large-area deposition at low temperatures and exhibits no signal lag. Low dark current can be maintained through specialized blocking layers, [...] Read more.

Amorphous lead oxide (a-PbO) X-ray photoconductors show potential for applications in direct conversion medical imaging detectors within the diagnostic energy range. a-PbO enables large-area deposition at low temperatures and exhibits no signal lag. Low dark current can be maintained through specialized blocking layers, similar to those used in multilayer amorphous selenium (a-Se) structures in commercial detectors. However, the current state of a-PbO technology faces challenges in thick layer deposition, leading to crystalline inclusions and cracks. Our proposed stress-induced crystallization model reveals that intrinsic stress in a-PbO layers amplifies with thickness, leading to crystallographic defects. These defects, which are associated with the stable phase of β-PbO, contribute to increased dark current and initiate layer cracking. We calculate the thermal expansion coefficient of a-PbO, indicating a thermomechanical mismatch between the photoconductor and the substrate as the primary source of stress. Furthermore, we demonstrate that layer deposition parameters significantly impact heat accumulation within the growing layer, thereby facilitating temperature-induced crystallization. Our study suggests that relieving stress in grown a-PbO layers by eliminating thermal expansion coefficient mismatches between different layers in a-PbO blocking structures, coupled with optimizing deposition parameters to prevent heat accumulation during layer growth, may inhibit or even prevent stress-induced crystallization and the emergence of structural defects in thick a-PbO layers. Full article

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13 pages, 5578 KiB

Open AccessArticle

Investigation of the Etching Resistance of Yttrium Oxyfluoride Coating Deposited via Atmospheric Plasma Spraying Against Cl₂/O₂ Plasma

by Zaifeng Tang, Yukun Lv, Kaiqu Ang, Bing Wang, Xiaojun Jiang, Yuwei Wang, Jin Xu, Hua Meng, Hongli Chen, Ying Shi and Linjun Wang

Materials 2025, 18(9), 1903; https://doi.org/10.3390/ma18091903 - 23 Apr 2025

Abstract

Chlorine-based plasma is widely used in key etching applications. However, while etching the wafer materials, chlorine plasma can cause damage to the internal components of the etching chamber, which adversely affects the equipment’s lifespan. As a result, selecting appropriate coating materials for the [...] Read more.

Chlorine-based plasma is widely used in key etching applications. However, while etching the wafer materials, chlorine plasma can cause damage to the internal components of the etching chamber, which adversely affects the equipment’s lifespan. As a result, selecting appropriate coating materials for the chamber’s internal components is essential for mitigating corrosion. The etch resistance of these coatings directly impacts not only the quality of wafer production but also the operational safety and maintenance cycle of the etching equipment. In this study, three yttrium oxyfluoride coatings with different oxygen contents (3%, 6%, and 9%) were prepared using atmospheric plasma spraying technology. The etch resistance of these YOF coatings, as well as yttrium oxide coating, was systematically investigated under a Cl₂/O₂ plasma environment. Transmission electron microscopy analysis revealed that at the initial stage, Cl⁻ formed a protective layer on the surface of the YOF coatings, effectively slowing down further etching by Cl⁻. Among the samples, the YOF 6% coating exhibited the best etching resistance, which is primarily attributed to its higher capacity for Cl⁻ adsorption. Overall, YOF coatings demonstrated excellent resistance in chlorine-based plasma environments, with YOF 6% in particular showing great potential as an ideal protective material for etching chamber components. Full article

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14 pages, 2616 KiB

Open AccessArticle

The Impact of Three-Dimensional Printer Technology on the Accuracy of Dental Implant Models

by Alexander Strunz, Lara Berger, Anna Seidel, Johannes Ries, Werner Adler, Manfred Wichmann and Ragai Edward Matta

Materials 2025, 18(9), 1902; https://doi.org/10.3390/ma18091902 - 23 Apr 2025

Abstract

This study examines the impact of different 3D printing technologies on the accuracy of implant positions in printed dental models, a crucial factor in implant-supported prosthetics. A standardized titanium model with three bone-level implants was scanned using an industrial scanner to create a [...] Read more.

This study examines the impact of different 3D printing technologies on the accuracy of implant positions in printed dental models, a crucial factor in implant-supported prosthetics. A standardized titanium model with three bone-level implants was scanned using an industrial scanner to create a virtual reference model. Ten intraoral scans of the same model were performed, and the generated STL files were used to design physical models printed with three different 3D printers: two utilizing digital light processing (DLP) technology and one employing stereolithography (SLA) (n = 30). The printed models were then rescanned, and deviations from the reference STL file were analyzed. Results showed that the SLA printer exhibited the highest deviations (0.26 ± 0.17 mm), whereas the DLP printers demonstrated greater accuracy, with one DLP system (0.07 ± 0.02 mm) performing slightly better than the other (0.12 ± 0.13 mm). The SLA printer exhibited the most significant errors in the vestibulo-oral and occlusal-apical directions. The findings suggest that DLP printers offer superior precision for implant-supported restorations in digital workflows. Clinically, the choice of 3D printing technology significantly impacts model accuracy, emphasizing the importance of selecting the appropriate printer based on the required precision. Full article

(This article belongs to the Special Issue Advanced Dental Materials: From Design to Application, Second Volume)

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18 pages, 930 KiB

Open AccessArticle

Ion Release from Endodontic and Restorative Dental Materials: Effects of pH and Time

by Zbigniew Raszewski, Katarzyna Chojnacka, Małgorzata Ponto-Wolska and Marcin Mikulewicz

Materials 2025, 18(9), 1901; https://doi.org/10.3390/ma18091901 - 22 Apr 2025

Abstract

Background: Root canal sealers remain in long-term contact with dental tissues, raising concerns about their potential adverse effects. Methods: This study evaluates the physicochemical properties and ion-release profiles of three dental materials: zinc oxide/eugenol-based sealer, zinc phosphate cement (luting agent), and glass-ionomer cement [...] Read more.

Background: Root canal sealers remain in long-term contact with dental tissues, raising concerns about their potential adverse effects. Methods: This study evaluates the physicochemical properties and ion-release profiles of three dental materials: zinc oxide/eugenol-based sealer, zinc phosphate cement (luting agent), and glass-ionomer cement (restorative material) under acidic (pH 4) and neutral (pH 7) conditions over 24 h and 30 days to determine their behavior and bioactivity in vitro. The materials were evaluated for their setting time, consistency, film thickness, solubility, and ion release using atomic emission spectrometry. The influence of pH and exposure time on ion release was analyzed using multiple regression analysis. Results: All tested materials met the ISO standards for their respective categories. The zinc oxide/eugenol and zinc phosphate cements released increased levels of zinc in acidic environments (pH 4), suggesting potential antimicrobial properties. The glass-ionomer cement exhibited higher silicon and strontium release under a neutral pH (pH 7), indicating potential remineralization effects. Silver from the zinc oxide/eugenol material was below the detection limit of the applied method, suggesting minimal ion release under the tested conditions. Maximum zinc release from root canal sealer occurred after 30 days at pH 4 (1.39 ± 0.26 mg), while the highest silicon release from glass-ionomer cement was observed at pH 7 after 30 days (1.03 ± 0.21 mg). Conclusions: Zinc oxide/eugenol materials exhibited increased zinc release under acidic conditions. In contrast, the restorative and luting materials demonstrated distinct ion-release patterns, aligning with their respective intended applications rather than endodontic purposes. Full article

(This article belongs to the Special Issue Bioactive Materials for Additive Manufacturing)

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25 pages, 2002 KiB

Open AccessArticle

Study on FEM Simulation Algorithm of Local Warm Forming of Advanced High-Strength Steel

by Tao Wang, Di Li, Xiao-Kun Wang, Hong-Pai Zhu, Jun-Jie Liu, Ning Jiang, Xiao-Zhi Feng and Shao-Xun Liu

Materials 2025, 18(9), 1900; https://doi.org/10.3390/ma18091900 - 22 Apr 2025

Abstract

Advanced high-strength steels (AHSSs) are prone to process defects such as fracture and springback during forming operations. Local warm forming technology represents an innovative forming process that applies targeted heating to specific stamping features of high-strength steel blanks. This study focuses on dual-phase [...] Read more.

Advanced high-strength steels (AHSSs) are prone to process defects such as fracture and springback during forming operations. Local warm forming technology represents an innovative forming process that applies targeted heating to specific stamping features of high-strength steel blanks. This study focuses on dual-phase steel DP780 as the research material, obtaining mechanical property parameters at various temperatures through uniaxial tensile tests. Based on investigations into temperature-dependent constitutive models and heat-transfer analysis methods, Abaqus VUMAT and UMAT subroutines were developed using Fortran language to establish a local warm forming simulation algorithm that incorporates predictions of fracture failure and springback. A U-shaped component was designed for local warm forming bend-stretch tests, with experimental data compared against results from the developed algorithm. This validation confirmed the algorithm’s capability to accurately predict local warm forming behaviors of U-shaped components. Leveraging the validated algorithm, sensitivity analyses were conducted to examine the influence of local warm forming process parameters on springback, with the response surface methodology employed to quantitatively assess the effects of heating temperature and localized heating zones on springback characteristics. Full article

21 pages, 8847 KiB

Open AccessArticle

The Importance of Laser Beam Power on the Microstructure and Wear Behavior of Al-WC Composite Layers Produced by Laser Surface Alloying

by Natalia Makuch and Piotr Dziarski

Materials 2025, 18(9), 1899; https://doi.org/10.3390/ma18091899 - 22 Apr 2025

Abstract

Laser alloying was used to form metal matrix composite layers strengthened by WC particles. The process parameters were selected in such a way that there was no complete melting of the WC particles. Four different laser beam powers (from 0.65 kW to 1.3 [...] Read more.

Laser alloying was used to form metal matrix composite layers strengthened by WC particles. The process parameters were selected in such a way that there was no complete melting of the WC particles. Four different laser beam powers (from 0.65 kW to 1.3 kW) were used, generating different temperature distributions during processing. The temperature across the laser track axis was determined according to the mathematical model proposed by Ashby and Esterling. All layers produced contained unmelted WC particles in an aluminum-based matrix. The depth of the WC-Al composite layers strongly depended on the applied laser beam power. The lowest thickness of 198 ± 36 µm was measured for the layer produced at a laser beam power of 0.65 kW. A twofold increase in power P was the reason for obtaining a thickness th_AZ = 387 ± 21 µm. The power of the laser beam also affected the percentage of the substrate material (7075 alloy) in the molten pool during the laser processing. As a result, the highest amount of substrate material was obtained for the WC-Al composite layer produced using the highest laser beam power P = 1.3 kW. Simultaneously, this layer was characterized by the lowest percentage of tungsten carbide particles in this layer. The temperature profile along the axis of the laser track and also the maximum temperature reached confirmed the difference in the bonding between the reinforcing WC particles and the metal matrix. For P = 0.65 kW, too low a temperature was reached for the tungsten carbide particles to overmelt, resulting in poor bonding to the metallic matrix in the layer. Moreover, the layer showed serious defects such as discontinuity, porosity, and cracks. As a result, the WC-Al composite layer produced at the lowest laser beam power was characterized by a wear resistance lower (I_mw = 6.094 mg/cm²/h) than the 7075 alloy without surface layer (I_mw = 5.288 mg/cm²). The highest wear resistance was characteristic of the 7075 alloy laser alloyed with a laser beam power equal to 1.17 kW (I_mw = 2.475 mg/cm²/h). This layer showed satisfactory quality and adhesion to the substrate material. Full article

(This article belongs to the Special Issue Advanced High-Performance Metal Matrix Composites (MMCs))

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14 pages, 6755 KiB

Open AccessArticle

Study on the Influence of Nickel Plating on the Structure and Properties of Aluminum/Steel Bimetallic Bonding

by Yufei Zhang, Guowei Zhang, Mingjie Wang and Hong Xu

Materials 2025, 18(9), 1898; https://doi.org/10.3390/ma18091898 - 22 Apr 2025

Abstract

Aluminum/steel bimetal combines the advantages of aluminum alloy and steel, greatly leveraging the value of various industrial fields, especially in improving engine performance and fuel economy. However, it is very difficult to prepare products with good interface bonding strength. The fundamental issue stems [...] Read more.

Aluminum/steel bimetal combines the advantages of aluminum alloy and steel, greatly leveraging the value of various industrial fields, especially in improving engine performance and fuel economy. However, it is very difficult to prepare products with good interface bonding strength. The fundamental issue stems from the presence of an excessively thick interface layer and brittle intermetallic compounds. Therefore, this study employed a 50 μm-thick Ni interlayer to control the interface layer thickness, thereby enhancing the Al/steel interfacial bonding strength. A systematic investigation was conducted on the effects of hot dip duration on the interfacial microstructure and mechanical properties of Al/steel bimetal. The influence of hot dip duration on the microstructure and mechanical properties of aluminum/steel bimetal interface was systematically studied. The results show that the 50 μm Ni intermediate layer was used to effectively control the transition layer thickness and improve the interfacial bonding strength of aluminum steel. The thickness of the interface layer gradually increases with the increase in the hot-immersion time. The thickness of the interface layer composed of the two phases of τ₁-Al₂Fe₃Si₃ and FeAl₃ on the steel side increases first and then decreases, while the interface layer composed of the two phases of τ₅-Al₈Fe₂Si and Fe₂Al₅ on the aluminum side decreases first and then increases. When the hot dip time is 240 s, the shear strength of Al/steel bimetal with 50 μm Ni interlayer showed 75% enhancement compared to Ni-free counterparts. Full article

(This article belongs to the Section Metals and Alloys)

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20 pages, 12981 KiB

Open AccessArticle

Utilizing 3D Printing and Distributed Optic Fiber to Achieve Temperature-Sensitive Concrete

by Qiuju Zhang, Yujia Li, Yuefan Huang, Yangbo Li, Yahui Yang and Yutao Hu

Materials 2025, 18(9), 1897; https://doi.org/10.3390/ma18091897 - 22 Apr 2025

Abstract

The distribution of temperature-induced cracks in mass concrete structures is extensive and random, making it difficult for existing detection methods to accurately identify the specific location and initiation time of cracking. Therefore, there is an urgent need for an intelligent, precise, and efficient [...] Read more.

The distribution of temperature-induced cracks in mass concrete structures is extensive and random, making it difficult for existing detection methods to accurately identify the specific location and initiation time of cracking. Therefore, there is an urgent need for an intelligent, precise, and efficient monitoring approach capable of acquiring real-time information on the evolution of the internal temperature field in concrete structures during their early-age curing process. A novel temperature-sensitive concrete system was developed by synchronously integrating distributed optical fibers with three-dimensional printed concrete (3DPC) to enable both temperature monitoring and signal transmission. To validate the effectiveness of the proposed method, experimental testing and numerical simulations were conducted on cubic 3D-printed fiber-reinforced concrete to analyze the temporal evolution of their internal temperature fields. The results show that, during the system calibration process, the temperature measured by the distributed temperature sensing (DTS) system was highly consistent with the environmental temperature curve, with fluctuations controlled within ±1 °C. In addition, the numerical simulation results closely aligned with the experimental data, with discrepancies maintained within 5%, demonstrating the feasibility of utilizing 3D printing technology to impart temperature sensitivity to concrete materials. This integrated approach offers a promising pathway for advancing smart concrete technology, providing an effective solution for accurate sensing and control of internal temperatures in concrete structures. It holds substantial potential for practical applications in civil engineering projects. Full article

(This article belongs to the Special Issue Sustainable Cementitious Materials for Civil and Transportation Engineering—2nd Edition)

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12 pages, 7173 KiB

Open AccessArticle

Sb³⁺-Doped Rb₂HfCl₆ Perovskites as High-Performance Thermally Stable Single-Component Phosphors for White Light-Emitting Diodes

by Yanbiao Li and Yuefeng Gao

Materials 2025, 18(9), 1896; https://doi.org/10.3390/ma18091896 - 22 Apr 2025

Abstract

Stable and efficient inorganic lead-free double perovskites are crucial for high-reliability optoelectronic devices. However, dual-doped perovskite phosphors often suffer from poor color stability due to differences in thermal activation energies and electron–phonon interactions between the doped ions. To address this, single-doped Sb³⁺ [...] Read more.

Stable and efficient inorganic lead-free double perovskites are crucial for high-reliability optoelectronic devices. However, dual-doped perovskite phosphors often suffer from poor color stability due to differences in thermal activation energies and electron–phonon interactions between the doped ions. To address this, single-doped Sb³⁺-incorporated Rb₂HfCl₆ perovskite crystals were synthesized via a co-precipitation method. Under UV excitation, Rb₂HfCl₆:Sb exhibits broad dual emission bands, attributed to singlet and triplet self-trapped exciton radiative transitions induced by Jahn–Teller distortion in [SbCl₆]³⁻ octahedra. This dual emission endows the material with high sensitivity to excitation wavelengths, enabling tunable luminescence from cyan to orange-red across 400–800 nm. Utilizing this dual emission, a white LED was fabricated, showcasing a high color rendering index and excellent long-term stability. Remarkably, the material exhibits breakthrough thermal stability, maintaining more than 90% of its emission intensity at 100 °C, while also exhibiting remarkable resistance to humidity and oxygen exposure. Compared to co-doped phosphors, Rb₂HfCl₆:Sb offers advantages such as environmental friendliness, simple fabrication, and stable performance, making it an ideal candidate for WLEDs. This study demonstrates notable progress in developing thermally stable and reliable optoelectronic devices. Full article

(This article belongs to the Section Energy Materials)

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23 pages, 6254 KiB

Open AccessArticle

Influence of Deposition Temperature on Microstructure and Properties of Tantalum Oxide Sputtered Coatings

by Maria P. Nikolova and Iliyan Tzvetkov

Materials 2025, 18(9), 1895; https://doi.org/10.3390/ma18091895 - 22 Apr 2025

Abstract

To increase the wear and corrosion resistance of (α + β) titanium-aluminium-vanadium (Ti6Al4V) alloy, ceramic tantalum oxide coatings were deposited by direct current (DC) magnetron sputtering at three different substrate temperatures—400, 450, and 500 °C. The crystallographic structure, surface morphology, chemical compositions, film [...] Read more.

To increase the wear and corrosion resistance of (α + β) titanium-aluminium-vanadium (Ti6Al4V) alloy, ceramic tantalum oxide coatings were deposited by direct current (DC) magnetron sputtering at three different substrate temperatures—400, 450, and 500 °C. The crystallographic structure, surface morphology, chemical compositions, film adhesion, and hardness of the coatings were described using XRD, SEM, EDS, scratch tests, and microhardness measurements. The samples’ ability to withstand corrosion was assessed using electrochemical studies. Results revealed that thin films have an amorphous or crystalline structure dependent on temperature. The film’s thicknesses varied between 560 and 600 nm. With the increase in deposition temperature, the hardness of the film rose. All oxide coatings were tightly adherent to the titanium alloy substrate, and critical force increased from about 8.6 up to 20 N when the temperature rose from 400 to 500 °C. During the polarisation investigations, after 1 h of immersion, a drop in current density (j_corr) verified an improvement in the corrosion resistance of the amorphous and well-crystalline coatings. A two-layer model of the surface film accurately describes the coated systems’ electrochemical behaviour. However, according to the EIS analysis, the well-crystalline film deteriorates greatly, whereas the amorphous film prevents penetration during the 7-day immersion test in SBF. The wettability tests demonstrated the hydrophilic nature of the coatings, and after seven days, the mineralisation of calcium phosphate proves the coatings become bioactive in simulated bodily fluid (SBF). Thus, we produced films of tantalum oxide, which, with the proper deposition parameters, may prove to be appropriate surfaces for titanium-based implant bio-applications. Full article

(This article belongs to the Special Issue Surface Engineering & Coating Technologies for Corrosion and Tribocorrosion Resistance—3rd Edition)

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17 pages, 9317 KiB

Open AccessArticle

Finite Element Simulation and Optimization of Process Parameters for Titanium Chip Crusher

by Jianghua Huang, Zeling Zhao, Xiaomin Huang, Tao Liu and Hongchao Ji

Materials 2025, 18(9), 1894; https://doi.org/10.3390/ma18091894 - 22 Apr 2025

Abstract

Titanium alloy has been widely used in aerospace, military, and national defense, and other high-tech fields due to its advantages of light weight, high specific strength, excellent corrosion resistance, excellent heat resistance, and good low-temperature performance. In the turning of titanium alloys, a [...] Read more.

Titanium alloy has been widely used in aerospace, military, and national defense, and other high-tech fields due to its advantages of light weight, high specific strength, excellent corrosion resistance, excellent heat resistance, and good low-temperature performance. In the turning of titanium alloys, a significant quantity of continuous chips with poor breakability is generated. Recycling these titanium chips can effectively reduce raw material costs and minimize environmental impacts, as it decreases the dependency on primary titanium sources. The titanium chip crushing process is an indispensable part of the titanium chip recovery process, and the double-teeth roll crushing process is the most commonly used metal crushing process. Finite element simulation is an efficient, time-saving, and resource-saving method to optimize the titanium chip crushing process. In this paper, the stress change in the process of titanium chip crushing is analyzed by finite element simulation, and the influence of the number of cutter roller teeth and the speed of the cutter roller on the crushing effect of the titanium chip is analyzed. The optimal process parameters of the titanium chip crusher were obtained by response surface optimization, and the accuracy of the finite element simulation was verified by experiments, which provided a theoretical and practical basis for optimizing the titanium chip crushing process. Full article

(This article belongs to the Special Issue Alloy Strengthening Mechanisms, Microstructural Control, and Performance Optimization)

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25 pages, 10572 KiB

Open AccessArticle

Electrochemical Formation and Characterization of Functional Ag-Re Coatings

by Oksana Bersirova, Valeriy Kublanovsky, Svetlana Kochetova and Olena Bondar

Materials 2025, 18(9), 1893; https://doi.org/10.3390/ma18091893 - 22 Apr 2025

Abstract

Silver-white, matte, smooth, and durable deposits of silver-rhenium, with thicknesses ranging from 2.0 to 13.7 μm and containing 0.15 to 13.5 wt.% Re, were obtained with a current efficiency of 66–98% from a developed dicyanoargentate–perrhenate bath based on a borate–phosphate–carbonate silver-plating electrolyte. This [...] Read more.

Silver-white, matte, smooth, and durable deposits of silver-rhenium, with thicknesses ranging from 2.0 to 13.7 μm and containing 0.15 to 13.5 wt.% Re, were obtained with a current efficiency of 66–98% from a developed dicyanoargentate–perrhenate bath based on a borate–phosphate–carbonate silver-plating electrolyte. This study was focused on the influence of bath composition, the [Ag(I)]:[ReO₄⁻] ratio, surfactant additives, applied current density, temperature, and stirring, on the alloys’ composition, structure, morphology, microhardness, adhesion, and porosity. A voltammetric analysis was conducted, considering the influence of ethanolamines on electrode processes. In baths with triethanolamine (TEA), coatings similar to a silver matrix with rhenium doped in mass fractions are likely achievable. Monoethanolamine (MEA) is recommended due to its process-activating properties. All coatings were nanocrystalline (τ = 28.5–35 nm). For deposits containing less than 10 wt.% Re, characteristic silver XRD peaks were observed, while for other deposits, additional peaks attributed probably to Re(VII) and Re(VI) oxides. A linear relationship H_v − τ^−1/2, typical for Hall–Petch plots, was obtained, confirming that grain boundaries play a crucial role in mechanical properties of coatings. The conditions for stable electrochemical synthesis of promising functional Ag-Re coatings of predetermined composition (0.7–1.5 wt.% Re) were proposed for practical use in power electronics and energy sectors for manufacturing electrical contacts operating across a wide temperature range. This was realized by deposition from an Ag-rich bath in the area of mixed electrochemical kinetics, at potential values corresponding to the region of half the limiting current: j = 2.5–6 mA cm⁻², t = 19–33 °C. Full article

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

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18 pages, 4617 KiB

Open AccessArticle

Exploring the Mechanism of Microstructural Changes in Ultra-High-Performance Concrete Under Microwave Influence: Experiments and Molecular Dynamics Simulation

by Jingyuan Chen, Kunyang Yu, Shuangxin Li and Dengao Liu

Materials 2025, 18(9), 1892; https://doi.org/10.3390/ma18091892 - 22 Apr 2025

Abstract

To elucidate the mechanisms of microstructural changes in ultra-high-performance concrete (UHPC) under microwave exposure, this study characterizes the microstructure at multiple scales using a combination of microscopic experiments and molecular dynamics simulations. The hydration products, pore structure, morphology, and interface transition zone (ITZ) [...] Read more.

To elucidate the mechanisms of microstructural changes in ultra-high-performance concrete (UHPC) under microwave exposure, this study characterizes the microstructure at multiple scales using a combination of microscopic experiments and molecular dynamics simulations. The hydration products, pore structure, morphology, and interface transition zone (ITZ) of UHPC specimens were analyzed using mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Molecular dynamics simulations were employed to investigate the uniaxial tensile behavior, free volume, and radial distribution of calcium silicate hydrate (C-S-H) gel, the primary hydration product. The results indicate that microwave curing significantly reduces the pore volume of specimens, with a daily average reduction of 0.15% in the early stages. This accelerated reduction in porosity effectively diminishes the number of high-risk pores. The hydration products formed under microwave curing exhibit higher density and enhanced internal pore optimization. Simulation findings suggest that the non-thermal effects of microwaves play a more significant role in the structural evolution. The molecular orientation of C-S-H changes after oscillation, leading to more ordered molecular arrangements. Mechanical oscillation also expels free volume from the crystal cells, promoting a more compact overall structure and increasing the tensile strength by up to 1 GPa. Full article

(This article belongs to the Special Issue Advanced Cement-Based Composite Materials and Composite Intelligent Design)

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1 pages, 129 KiB

Open AccessCorrection

Correction: Firmino et al. High-Efficiency Adsorption Removal of Congo Red Dye from Water Using Magnetic NiFe₂O₄ Nanofibers: An Efficient Adsorbent. Materials 2025, 18, 754

by Hellen C. T. Firmino, Emanuel P. Nascimento, Keila C. Costa, Luis C. C. Arzuza, Rondinele N. Araujo, Bianca V. Sousa, Gelmires A. Neves, Marco A. Morales and Romualdo R. Menezes

Materials 2025, 18(9), 1891; https://doi.org/10.3390/ma18091891 - 22 Apr 2025

Abstract

Keila C [...] Full article

(This article belongs to the Special Issue Nanoarchitectonics in Materials Science, Second Edition)

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Materials, Volume 18, Issue 9 (May-1 2025) – 28 articles

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