Crystals

22 pages, 8797 KiB

Open AccessArticle

Distortion and Residual Stress Reduction Using Asynchronous Heating Sources for Multi-Robot Coordinated Wire-Arc Directed Energy Deposition

by Yongzhe Li, Chenxiao Zhang, Caowei Huang, Xiaoyu Wang, Guangjun Zhang and Yijun Zhou

Crystals 2025, 15(2), 155; https://doi.org/10.3390/cryst15020155 - 2 Feb 2025

Abstract

Multi-robot coordinated wire-arc directed energy deposition (MRC-WA-DED) has proliferated in recent decades, employing asynchronous independent heating sources to deposit material simultaneously. Beyond enhancing efficiency, MRC-WA-DED introduces a synergic effect between the heating sources, resulting in a controllable thermal field on the deposit component. [...] Read more.

Multi-robot coordinated wire-arc directed energy deposition (MRC-WA-DED) has proliferated in recent decades, employing asynchronous independent heating sources to deposit material simultaneously. Beyond enhancing efficiency, MRC-WA-DED introduces a synergic effect between the heating sources, resulting in a controllable thermal field on the deposit component. This research aims to investigate if the synergic effect is beneficial for residual stress and distortion reduction and how it can be applied to enhance the quality of MRC-WA-DEDed parts. A finite element model was developed to compare the thermodynamic response of WA-DED when both coordinated heating sources (CHSs) and a single heating source (SHS) are applied. Simulation and deposition experiments were carried out to clarify the influence of different coordination strategies on the fabricated component’s thermal behavior, stress distribution, and distortion conditions. The results indicate that the synergic effect of CHSs leads to a smoother temperature gradient than that accomplished by a SHS, reducing the maximum distortion of a single layer by 49.1%. As validated by actual depositions, the residual stress, maximum distortion, and hardness of a ten-layer component were reduced by 6.5%, 11.2%, and 18.6%, respectively. Full article

(This article belongs to the Special Issue Advanced Welding and Additive Manufacturing)

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18 pages, 4654 KiB

Open AccessArticle

The Effect of Different Laser Powers on the Properties of Ni65A Cladding Reinforced by WC

by Mengqiong Huang, Jincheng Yu, Jinyi Wang, Guilin Xu and Xin Jin

Crystals 2025, 15(2), 154; https://doi.org/10.3390/cryst15020154 - 2 Feb 2025

Abstract

In this paper, the effects of different laser powers on the microstructure, microhardness, and wear resistance of Ni65A/WC composite coatings were investigated by using laser cladding technology. The morphology, phase structure, elemental distribution, wear behaviour, and property changes of the fused coatings were [...] Read more.

In this paper, the effects of different laser powers on the microstructure, microhardness, and wear resistance of Ni65A/WC composite coatings were investigated by using laser cladding technology. The morphology, phase structure, elemental distribution, wear behaviour, and property changes of the fused coatings were systematically characterised and analysed. The mechanism of power parameters on coating properties was summarised. The results show that different laser powers significantly affect the microstructure of the coating and the distribution of the enhanced phase WC. Under the 800 W power condition, the WC particles were not sufficiently dissolved and the organisation was not dense. The hardness and abrasion resistance were low. Under 1200 W power conditions, the enhanced phases were uniformly dispersed. The best microstructure densities and homogeneity were observed. The generated hard phase and matrix toughness achieved a good balance. The hardness of the coating reached 375 HV while also showing optimum wear resistance and stable friction behaviour. Under 1600 W power conditions, although the hard phase was completely dissolved and re-precipitated, some areas of tissue coarsening made the wear resistance slightly inferior to that at 1200 W. The 2000 W power condition resulted in a significant deterioration in the coating properties due to the increase in cracks and pores caused by the overheating of the melt pool. For this reason, 1200 W power conditions proved to be the ideal parameter range for optimising the microstructure and mechanical properties of Ni65A/WC composite coatings. The study in this paper can provide an important reference for the design of high-performance wear-resistant coatings. Full article

(This article belongs to the Special Issue Recent Trends in Laser Cladding and Surface Alloying)

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20 pages, 7604 KiB

Open AccessArticle

Copper-Substituted Calcium Orthophosphate (Ca_xCu_1-x)HPO₄.nH₂O for Humidity Detection

by Yurii Milovanov, Mehran Dadkhah, Ahmed Sabry Afify and Jean-Marc Tulliani

Crystals 2025, 15(2), 153; https://doi.org/10.3390/cryst15020153 - 1 Feb 2025

Abstract

Calcium orthophosphate material (Ca_1-xCu_x)HPO₄.nH₂O (0.4 ≤ x ≤ 1) with the gradual replacement of Ca²⁺ with Cu²⁺ ions were synthesized by a chemical precipitation technique. Samples were characterized by X-ray diffraction (XRD), scanning [...] Read more.

Calcium orthophosphate material (Ca_1-xCu_x)HPO₄.nH₂O (0.4 ≤ x ≤ 1) with the gradual replacement of Ca²⁺ with Cu²⁺ ions were synthesized by a chemical precipitation technique. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Then, the prepared powders were deposited onto an alumina substrate with interdigitated Pt electrodes by the spin coating method and polyvinyl alcohol (PVA) as a binder. Successively, the sensors were investigated from 0% to 90% at room temperature under various conditions, including humidity, nitrogenous oxide, methane, carbon dioxide and ammonia. The results evidenced that at 90% RH, the sensitivity of sensors significantly increased with the increase in the Cu content. Moreover, the sensors exhibited good repeatability and, after 1 year of aging, the sensor response was equal to 34% that of the freshly prepared sensor. Finally, there was no interference in the presence of other gases (nitrogenous oxide 2.5 ppm, methane 10 ppm, carbon dioxide 500 ppm and ammonia 4 ppm). Full article

(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)

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15 pages, 3550 KiB

Open AccessArticle

Enhancing Perovskite Solar Cell Stability by TCO Layer Presence Beneath MACl-Doped Perovskites

by Minkyu Song, Jinyoung Kim and Gyu Min Kim

Crystals 2025, 15(2), 152; https://doi.org/10.3390/cryst15020152 - 1 Feb 2025

Abstract

Perovskite solar cells (PSCs) have emerged as a promising photovoltaic technology, yet their stability under environmental stressors remains a critical challenge. This study examines the substrate-dependent degradation mechanisms of perovskite films and evaluates the role of methylammonium chloride (MACl) incorporation. Devices fabricated on [...] Read more.

Perovskite solar cells (PSCs) have emerged as a promising photovoltaic technology, yet their stability under environmental stressors remains a critical challenge. This study examines the substrate-dependent degradation mechanisms of perovskite films and evaluates the role of methylammonium chloride (MACl) incorporation. Devices fabricated on ITO and glass substrates exhibited markedly different stability behaviors under high-humidity conditions. ITO substrates delayed the phase transition from the black α-phase to the yellow δ-phase due to stronger substrate–film interactions and reduced defect densities, while glass substrates facilitated rapid degradation through moisture infiltration and grain boundary instability. MACl incorporation enhanced the initial crystallinity and optoelectronic properties of the perovskite films, as evidenced by superior power conversion efficiency and photon absorption. However, residual MACl under humid conditions introduced structural instability, particularly on glass substrates. To address these challenges, a fully coated ITO structure, referred to as the Island Type design, was proposed. This structure eliminates exposed glass regions, leveraging the stabilizing properties of ITO to suppress moisture infiltration and prolong device durability. The findings provide a comprehensive understanding of the interplay between substrate properties and material composition in PSC stability and highlight the potential of structural optimizations to balance efficiency and durability for commercial applications. Full article

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14 pages, 3993 KiB

Open AccessArticle

Mineralogical Characteristics and Color Origin of Nephrite Containing Pink Minerals

by Ye Yuan, Youxuan Li and Miao Shi

Crystals 2025, 15(2), 151; https://doi.org/10.3390/cryst15020151 - 1 Feb 2025

Abstract

Recently, a variety of nephrite containing localized pink mineral aggregates has emerged on the market, which is sometimes referred to as “peach blossom jade” by some merchants. Currently, there is limited research on this type of nephrite containing pink minerals, and its detailed [...] Read more.

Recently, a variety of nephrite containing localized pink mineral aggregates has emerged on the market, which is sometimes referred to as “peach blossom jade” by some merchants. Currently, there is limited research on this type of nephrite containing pink minerals, and its detailed mineral composition characteristics and coloration mechanisms remain unclear. In this study, four samples of nephrite containing pink minerals were systematically investigated using conventional gemological tests, as well as modern analytical techniques such as X-ray powder diffraction (XRD), infrared spectroscopy (IR), laser Raman spectroscopy, ultraviolet–visible (UV-Vis) absorption spectroscopy, electron probe microanalysis (EPMA), and X-ray fluorescence spectroscopy (XRF). These techniques were employed to elucidate the mineral composition, chemical composition, spectroscopic features, and coloration origins of the samples. The results indicate that the primary mineral constituent of the samples is tremolite, with accessory minerals including zoisite, muscovite, orthoclase, andesine, diopside, and prehnite. The major chemical components of the samples are SiO₂, CaO, and MgO, along with minor amounts of Al₂O₃, K₂O, and FeO_T. The overall green hue of the samples is positively correlated with Fe content. The pink mineral present in the samples is predominantly Mn-bearing zoisite, and the pink coloration of zoisite is primarily attributed to the energy level transitions of Mn²⁺ at approximately 540 nm and 440 nm. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

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13 pages, 2934 KiB

Open AccessArticle

Nonlinear Optical Bistability in a Bragg Reflector Multilayered Structure with MoS₂

by Songqing Tang, Xilei Dong, Leyong Jiang, Haishao Chen, Zhuoya Sun, Fuping Zhang, Yangbin Zhu and Yunyang Ye

Crystals 2025, 15(2), 150; https://doi.org/10.3390/cryst15020150 - 31 Jan 2025

Abstract

The special band structure of bilayer MoS₂ makes it show strong nonlinear optical characteristics in the visible band, which provides a new way to develop visible nonlinear devices. In this paper, we present a theoretical analysis of the optical bistability (OB) in [...] Read more.

The special band structure of bilayer MoS₂ makes it show strong nonlinear optical characteristics in the visible band, which provides a new way to develop visible nonlinear devices. In this paper, we present a theoretical analysis of the optical bistability (OB) in a silver–Bragg reflector structure by embedding bilayer MoS₂ at the visible band. The nonlinear OB phenomenon is achieved due to the nonlinear conductivity of the bilayer MoS₂ and the excitation of the optical Tamm state at the interface between the silver and the Bragg reflector. It is found that the hysteresis behavior and the threshold width of the OB can be effectively tuned by varying the incident light wavelength. In addition, the optical bistable behavior of the structure can be adjusted by varying the position of the MoS₂ inset in the defect layer, the incident angle, and the structural parameters of the spacer layer. We believe the above results can provide a new paradigm for the construction of controllable bistable devices. Full article

(This article belongs to the Special Issue Advances of Nonlinear Optical Materials)

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20 pages, 11058 KiB

Open AccessArticle

Additive Manufacturing of High-Performance Ti-Mo Alloys Used on a Puncture Needle: The Role of Linear Energy Density in Microstructure Evolution and Mechanical Properties

by Xuesong Dai, Yue Sun and Jitai Han

Crystals 2025, 15(2), 149; https://doi.org/10.3390/cryst15020149 - 31 Jan 2025

Abstract

This study involved the preparation of dense Ti-10wt.%Mo alloys using selective laser melting (SLM) with a powder combination of pure titanium (Ti) and pure molybdenum (Mo). Integrating temperature stress numerical simulations and actual data elucidates the correlation between linear laser energy density and [...] Read more.

This study involved the preparation of dense Ti-10wt.%Mo alloys using selective laser melting (SLM) with a powder combination of pure titanium (Ti) and pure molybdenum (Mo). Integrating temperature stress numerical simulations and actual data elucidates the correlation between linear laser energy density and residual stress. The impact of linear energy density on the surface roughness, densification behavior, microstructural development, and mechanical properties of SLM-processed Ti-10Mo components was also examined. As linear energy density diminished from 0.125 J/mm to 0.233 J/mm, surface roughness reduced from 18.2 μm to 4.4 μm, while relative compactness increased from 94.9% to 99.8%, respectively. It is necessary to reduce the friction between the puncture needle or implant needle and human tissue, enhancing comfort and precision. The microstructural investigation revealed that SLM-processed Ti-10Mo alloys consist of a phase combination of hexagonal tight-packed (hcp) α-Ti and body-centered cubic (bcc) β-Ti, with heterogeneous conchoidal microstructures found in the samples. Furthermore, as the laser energy input increased, Mo powder particles were mostly fully melted, leading to a significant rise in the microhardness value. The as-built Ti-10Mo alloys exhibited a high ultimate tensile strength of 860 MPa and an elongation of 32.9% at a linear laser energy density of 0.15 J/mm, with the fracture morphology indicating a mixed fracture mode mostly characterized by ductile fracture. This research can enhance the prospective bio-application of Ti-Mo alloys. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

20 pages, 16771 KiB

Open AccessArticle

A Comparison of the Hot Deformation Behavior and Constitutive Model of the GH4079 Alloy

by Weifeng Ying, Jia Hou, Shengnan Jiang and Jianan Wang

Crystals 2025, 15(2), 148; https://doi.org/10.3390/cryst15020148 - 31 Jan 2025

Abstract

In this paper, GH4079 alloy was thermally compressed under processing conditions of 1025 °C–1200 °C and 0.001 s⁻¹–1 s⁻¹. This article established the strain compensation Arrhenius constitutive equation, the improved Johnson–Cook constitutive equation, and the strain compensation Arrhenius constitutive [...] Read more.

In this paper, GH4079 alloy was thermally compressed under processing conditions of 1025 °C–1200 °C and 0.001 s⁻¹–1 s⁻¹. This article established the strain compensation Arrhenius constitutive equation, the improved Johnson–Cook constitutive equation, and the strain compensation Arrhenius constitutive model based on phase transition temperature segmentation and calculated the correlation coefficient (R) and local relative error (AARE) to verify the accuracy of the model, respectively. Finally, a certain microstructural analysis was combined. It can be concluded that the rheological stress of alloy GH4079 gradually decreases with the increase in temperature and strain rate. The AARE values of these three models are 21.09%, 20.47%, and 10.62%, respectively. The strain compensation Arrhenius model based on phase transition temperature segments can better describe the thermal deformation behavior of GH4079. By integrating this model, appropriate processing conditions can be selected to regulate the microstructural organization and achieve optimization during the practical application of the alloy. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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6 pages, 170 KiB

Open AccessEditorial

Crystallization of High-Performance Metallic Materials

by Wangzhong Mu and Chao Chen

Crystals 2025, 15(2), 147; https://doi.org/10.3390/cryst15020147 - 30 Jan 2025

Abstract

Crystallization includes liquid/solid and solid/solid phase transitions, important processes for improving engineering material performance, which have attracted significant attention in the community. The current Special Issue (SI) entitled ‘Crystallization of High-Performance Metallic Materials’ has collected twelve research papers focusing on different [...] Read more.

Crystallization includes liquid/solid and solid/solid phase transitions, important processes for improving engineering material performance, which have attracted significant attention in the community. The current Special Issue (SI) entitled ‘Crystallization of High-Performance Metallic Materials’ has collected twelve research papers focusing on different aspects of the crystallization of metallic materials, e.g., the solidification of steel, fatigue and fracture behaviors of magnesium composites, nucleation of intermetallic compounds in aluminum alloys, microstructure evolution in nickel-based super-alloys, etc. The summary of crystallization behaviors at different temperature ranges in different metallic materials contributes to the state of the art of engineering material development. Full article

(This article belongs to the Special Issue Crystallization of High Performance Metallic Materials)

28 pages, 10098 KiB

Open AccessReview

A Short Review of Advancements in Additive Manufacturing of Cemented Carbides

by Zhe Zhao, Xiaonan Ni, Zijian Hu, Wenxin Yang, Xin Deng, Shanghua Wu, Yanhui Li, Guanglin Nie, Haidong Wu, Jinyang Liu and Yong Huang

Crystals 2025, 15(2), 146; https://doi.org/10.3390/cryst15020146 - 30 Jan 2025

Abstract

Cemented carbides, renowned for their exceptional strength, hardness, elastic modulus, wear resistance, corrosion resistance, low coefficient of thermal expansion, and chemical stability, have long been indispensable tooling materials in metal cutting, oil drilling, and engineering excavation. The advent of additive manufacturing (AM), commonly [...] Read more.

Cemented carbides, renowned for their exceptional strength, hardness, elastic modulus, wear resistance, corrosion resistance, low coefficient of thermal expansion, and chemical stability, have long been indispensable tooling materials in metal cutting, oil drilling, and engineering excavation. The advent of additive manufacturing (AM), commonly known as “3D printing”, has sparked considerable interest in the processing of cemented carbides. Among the various AM techniques, Selective Laser Melting (SLM), Selective Laser Sintering (SLS), Selective Electron Beam Melting (SEBM), and Binder Jetting Additive Manufacturing (BJAM) have garnered frequent attention. Despite the great application potential of AM, no single AM technique has been universally adopted for the large-scale production of cemented carbides yet. The SLM and SEBM processes confront substantial challenges, such as a non-uniform sintering temperature field, which often result in uneven sintering and frequent post-solidification cracking. SLS notably struggles with achieving a high relative density of carbides. While BJAM yields WC-Co samples with a lower incidence of cracking, it is not without flaws, including abnormal WC grain growth, coarse WC clustering, Co-rich pool formation, and porosity. Three-dimensional gel-printing, though possessing certain advantages from its sintering performance, falls short in dimensional and geometric precision control, as well as fabrication efficiency. Cemented carbides produced via AM processes have yet to match the quality of their traditionally prepared counterparts. To date, the specific densification and microstructure evolution mechanisms during the AM process, and their interrelationship with the feedstock carbide material design, printing/sintering process, and resulting mechanical behavior, have not been thoroughly investigated. This gap in our knowledge impedes the rapid advancement of AM for carbide processing. This article offers a succinct overview of additive manufacturing of cemented carbides, complemented by an analysis of the current research landscape. It highlights the benefits and inherent challenges of these techniques, aiming to provide clarity on the present state of the AM processing of cemented carbides and to offer insights into potential future research directions and technological advancements. Full article

(This article belongs to the Special Issue High-Performance Metallic Materials)

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12 pages, 4780 KiB

Open AccessArticle

Mathematical Modeling to Predict the Formation of Micrometer-Scale Crystals Using Reverse Anti-Solvent Crystallization

by Jianhua Wang, Fawei Wang, Xu Wen, Yankang Zhang, Jiapeng Wang and Yucun Liu

Crystals 2025, 15(2), 145; https://doi.org/10.3390/cryst15020145 - 29 Jan 2025

Abstract

The reverse addition process in anti-solvent crystallization is safer and more efficient than sieving when dealing with energetic compounds. A new mathematical model has been developed to understand the crystal size mechanism during the reverse addition of solvent in a binary system. This [...] Read more.

The reverse addition process in anti-solvent crystallization is safer and more efficient than sieving when dealing with energetic compounds. A new mathematical model has been developed to understand the crystal size mechanism during the reverse addition of solvent in a binary system. This model incorporates droplet dynamics, distribution moments, and mass balance constraints. It can be used to predict the appropriate crystal size for designing explosive recipes with a desired particle size distribution to maximize energy output. The model was validated by conducting reverse-addition crystallization of sodium chloride in a deionized water/ethanol binary system at temperatures ranging from 10 to 50 degrees Celsius. The predicted results closely matched the experimental findings, which were confirmed using a Laser Particle Size Analyzer and Electron Microscope Scanning. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Third Edition)

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18 pages, 8358 KiB

Open AccessArticle

Corrosion Behavior and Mechanism of High-Aluminum Inconel 625 in Chlorinated Salts

by Ying Wei, Junjia Cao, Yuehong Zheng, Haicun Yu, Penghui Yang and Peiqing La

Crystals 2025, 15(2), 144; https://doi.org/10.3390/cryst15020144 - 29 Jan 2025

Abstract

Concentrated solar power plant (CSP) technology holds significant application value in the renewable energy sector for converting solar radiation into thermal and electrical energy. As a heat storage medium for next-generation solar thermal power stations, chloride salts exhibit strong corrosive effects on structural [...] Read more.

Concentrated solar power plant (CSP) technology holds significant application value in the renewable energy sector for converting solar radiation into thermal and electrical energy. As a heat storage medium for next-generation solar thermal power stations, chloride salts exhibit strong corrosive effects on structural components. To enhance corrosion resistance of the heated body in molten salt environments, Inconel 625 is modified by incorporating aluminum, which facilitates the formation of a protective oxide film. In this study, High-Aluminum Inconel 625, after cold rolling and solution treatment, was immersed in a NaCl-KCl-MgCl₂ eutectic chloride melt at 650 °C for 200 h. Post-corrosion analysis revealed the formation of an alumina layer on the surface, effectively mitigating corrosion. Increased aluminum content resulted in thicker alumina layers and the formation of oxidation products, such as Cr₂O₃, Fe₂O₃, MoO₂, and MgCr₂O₄ spinel structures, significantly enhancing the alloy’s corrosion resistance. The Inconel 625 cold-rolled plate with 5.31 wt% Al exhibited the best corrosion resistance (3510 μm/year), making it a promising candidate for use in next-generation CSP heat storage and exchange components. Full article

(This article belongs to the Special Issue Recent Advances in Microstructure and Properties of Metals and Alloys)

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19 pages, 8427 KiB

Open AccessArticle

Spectroscopic Ellipsometry and Wave Optics: A Dual Approach to Characterizing TiN/AlN Composite Dielectrics

by Mohamed El Hachemi, Nikhar Khanna and Emanuele Barborini

Crystals 2025, 15(2), 143; https://doi.org/10.3390/cryst15020143 - 29 Jan 2025

Abstract

In this paper, we present a method for retrieving the optical properties of a nano-designed

TiN / AlN

composite dielectric, using spectroscopic ellipsometry for experimental measurements and wave optics simulations for numerical analysis. Composite cermets have gained attention for solar–thermal energy conversion, but [...] Read more.

In this paper, we present a method for retrieving the optical properties of a nano-designed

TiN / AlN

composite dielectric, using spectroscopic ellipsometry for experimental measurements and wave optics simulations for numerical analysis. Composite cermets have gained attention for solar–thermal energy conversion, but their fundamental optical properties are not well understood. While characterizing uniformly deposited layers is generally straightforward, the process becomes more complex for nanoparticulate composites. The refractive index is essential for investigating and tuning the optical characteristics of the composite. Our method employs COMSOL Multiphysics software, validated by experimental spectroscopic ellipsometry studies. The strong agreement between experimental and numerical results supports this approach as a rational way to design material models for optical property studies across a broad spectrum. Full article

(This article belongs to the Special Issue Design, Development and Processing of Aluminium Alloys and Their Composite Materials)

16 pages, 19149 KiB

Open AccessArticle

Research on the Microstructure and Properties of Arc-Sprayed Austenitic Stainless Steel and Nickel-Based Alloy Composite Coatings with Different Spraying Distances

by Jingang Yan, Zhenming Yang, Limin Zhang and Jianxin Wang

Crystals 2025, 15(2), 142; https://doi.org/10.3390/cryst15020142 - 28 Jan 2025

Abstract

1Cr18Ni9Ti and Monel composite metal coatings with five different spraying distances were prepared by arc spraying technology. The density, hardness, friction, and wear properties and acid corrosion rate of the coatings with different spraying distances were studied by X-ray diffraction, scanning electron microscopy, [...] Read more.

1Cr18Ni9Ti and Monel composite metal coatings with five different spraying distances were prepared by arc spraying technology. The density, hardness, friction, and wear properties and acid corrosion rate of the coatings with different spraying distances were studied by X-ray diffraction, scanning electron microscopy, Rockwell hardness test, and friction and wear test. Research shows that the spraying distance has a significant effect on the density, hardness, porosity, friction, and wear properties and corrosion rate of the coating. When the spraying distance is 250 mm, the coating has the maximum density and hardness, the minimum porosity and corrosion rate, and the minimum friction coefficient and wear volume. Cu3.8ni and cr0.19fe0.7ni0.11 compounds in the coating have significant effects on the friction, wear, and hardness of the coating. The results show that too-high or too-low spraying distance will lead to pores and large particle agglomeration in the coating, which will affect the surface physical properties of the coating. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

14 pages, 7978 KiB

Open AccessArticle

Upcycling Spent Selective-Catalytic-Reduction Catalyst to Produce Titanium Carbide Through Molten-Salt Electrolysis

by Weigang Cao, Qi Zhu, Long Zheng, Jiahao Jin, Xiangpeng Li and Yanan Xu

Crystals 2025, 15(2), 141; https://doi.org/10.3390/cryst15020141 - 28 Jan 2025

Abstract

The molten-salt electrolytic method was employed to recycle spent SCR catalyst to prepare TiC compound. A systematic investigation has been carried out through thermodynamic calculation and experimental analysis. The effects of graphite content, cell voltage, electrolyzing temperature, and electrolyzing time on electrolytic products [...] Read more.

The molten-salt electrolytic method was employed to recycle spent SCR catalyst to prepare TiC compound. A systematic investigation has been carried out through thermodynamic calculation and experimental analysis. The effects of graphite content, cell voltage, electrolyzing temperature, and electrolyzing time on electrolytic products were explored. The results show that a suitable amount of graphite content, high cell voltage, and a high electrolyzing temperature are beneficial to promote the formation of TiC compounds. It has also been found that the electroreduction of spent SCR catalyst/graphite can completely transform it into TiC compound in a relatively short time. The final electrolytic product is confirmed to be a solid solution of (Ti, W, Si, V)C. Meanwhile, the electrolytic process and reaction mechanism were investigated through the analysis of intermediates and the thermodynamic calculation. The electrolytic product has a potential application as reinforcement in metal matrix, which is a high additional-value utilization for spent SCR catalysts. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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18 pages, 953 KiB

Open AccessArticle

Complexes of Cd(II) with Nicotinamide, Nitrate, and Oxalate as Mixed Ligands: Synthesis, Characterization, and Biological Activity

by Laurentiu Pricop, Ioana Cristina Marincas, Anamaria Hanganu, Mihaela Ganciarov, Augustin M. Mădălan and Maria Olimpia Miclăuș

Crystals 2025, 15(2), 140; https://doi.org/10.3390/cryst15020140 - 27 Jan 2025

Abstract

Three complexes of Cd(II), [Cd(NA)₂(NO₃)₂(H₂O)₂] (1), [Cd(NA)₂(NO₃)₂(H₂O)₂]·2NA (2), and [Cd(ox)(NA)(H₂O)]·H₂O (3) (NA = nicotinamide, ox = oxalate) were synthesized and characterized. Complexes (1) and (2) are mononuclear, while complex (3) is a bidimensional polymeric coordination compound, with oxalate anions bridging metal ions in [...] Read more.

Three complexes of Cd(II), [Cd(NA)₂(NO₃)₂(H₂O)₂] (1), [Cd(NA)₂(NO₃)₂(H₂O)₂]·2NA (2), and [Cd(ox)(NA)(H₂O)]·H₂O (3) (NA = nicotinamide, ox = oxalate) were synthesized and characterized. Complexes (1) and (2) are mononuclear, while complex (3) is a bidimensional polymeric coordination compound, with oxalate anions bridging metal ions in two different ways: µ₂ bis-bidentate chelating manner and µ₄ bis-bidentate bis-monodentate manner. The stereochemistry of Cd(II) in compounds (1) and (3) is a distorted pentagonal bipyramid, while in compound (2) it is a regular octahedron. Complexes (1) and (2) demonstrated significant activity against Enterococcus faecalis and Escherichia coli, showcasing their potential as effective antibacterial agents and inhibitors of microbial adhesion. The complexes were characterized by means of single-crystal X-ray diffraction, elemental analysis, FTIR (all complexes), ¹H NMR, ¹³C NMR, fluorescence spectroscopy, and antimicrobial activity (complexes (1) and (2)). Full article

(This article belongs to the Special Issue Structural Studies in Drug Discovery and Development: From the Lead to the Pharmaceutical Form, 2nd Edition)

53 pages, 13954 KiB

Open AccessReview

Progress in Icephobic Coatings for Wind Turbine Protection: Merging Chemical Innovation with Practical Implementation

by Ghazal Minoofar, Amirhossein Jalali Kandeloos, Mohammad Sadegh Koochaki and Gelareh Momen

Crystals 2025, 15(2), 139; https://doi.org/10.3390/cryst15020139 - 27 Jan 2025

Abstract

Ice accumulation on wind turbine blades poses a significant challenge to turbine performance and safety, and these issues have led to extensive research on developing effective anti-icing methods. Polymer-based icephobic coatings have emerged as promising solutions, given their passive nature and low energy [...] Read more.

Ice accumulation on wind turbine blades poses a significant challenge to turbine performance and safety, and these issues have led to extensive research on developing effective anti-icing methods. Polymer-based icephobic coatings have emerged as promising solutions, given their passive nature and low energy requirements. However, developing effective icephobic coatings is a complex task. In addition to anti-icing properties, factors such as mechanical strength, durability, and resistance to UV, weathering, and rain erosion must be carefully considered to ensure these coatings withstand the harsh conditions faced by wind turbines. The main challenge in coating engineering is mastering the chemistry behind these coatings, as it determines their performance. This review provides a comprehensive analysis of the suitability of current icephobic coatings for wind turbine applications, emphasizing their alignment with present industrial standards and the underlying coating chemistry. Unlike previous works, which primarily focus on the mechanical aspects of icephobicity, this review highlights the critical yet underexplored role of chemical composition and explores recent advancements in polymer-based icephobic coatings. Additionally, earlier studies largely neglect the specific standards required for industrial applications on wind turbines. By demonstrating that no existing coating fully meets all necessary criteria, this work underscores both the urgency of developing icephobic coatings with improved durability and the pressing need to establish robust, application-specific standards for wind turbines. The review also combines insights from cutting-edge research on icephobic coatings that are coupled with active de-icing methods, known as the hybrid approach. By organizing and summarizing these innovations, the review aims to accelerate the development of reliable and efficient wind energy systems to pave the way for a cleaner and more sustainable future. Full article

(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)

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28 pages, 13067 KiB

Open AccessReview

Tamm Plasmons: Properties, Applications, and Tuning with Help of Liquid Crystals

by Victor Yu. Reshetnyak, Igor P. Pinkevych, Michael E. McConney, Timothy J. Bunning and Dean R. Evans

Crystals 2025, 15(2), 138; https://doi.org/10.3390/cryst15020138 - 27 Jan 2025

Abstract

This article provides a brief overview of the research on localized optical states called Tamm plasmons (TPs) and their potential applications, which have been extensively studied in recent decades. These states arise under the influence of incident light at the interface between a [...] Read more.

This article provides a brief overview of the research on localized optical states called Tamm plasmons (TPs) and their potential applications, which have been extensively studied in recent decades. These states arise under the influence of incident light at the interface between a metal film and a medium with the properties of a Bragg mirror, or between two media with the properties of a Bragg mirror. The localization of the states in the interfacial region is a consequence of the negative dielectric constant of the metal and the presence of a photonic band gap of the Bragg reflector. Optically, TPs appear as resonant reflection dips or peaks in the transmission and absorption spectra in the region corresponding to the photonic band gap. The relative simplicity of creating a Tamm structure and the significant sensitivity of TPs to its parameters make them attractive for applications. The formation of broadband and tunable TP modes in hybrid structures containing, in particular, rugate filters and porous distributed Bragg reflectors are considered. Considerable attention is paid to TP designs that include liquid crystals, which allow for the remote tuning of the TP spectrum without the mechanical restructuring of the system. The application of TPs in sensors, thermal emitters, absorbers, laser generation, and the experimental capabilities of TP-liquid crystal devices are also discussed. Full article

(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)

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14 pages, 2436 KiB

Open AccessArticle

Dependence of GaN Exciton Energy on Temperature

by Xiancheng Liu, Peng Chen, Zili Xie, Xiangqian Xiu, Dunjun Chen, Hong Zhao, Yi Shi, Rong Zhang and Youdou Zheng

Crystals 2025, 15(2), 137; https://doi.org/10.3390/cryst15020137 - 26 Jan 2025

Abstract

In this paper, we investigate the relationship between GaN exciton energy and temperature by using high-quality, strain-free GaN epilayers. Traditional models, such as Varshni’s model and the Bose–Einstein model, are primarily based on empirical fitting and give little or no consideration to electron–phonon [...] Read more.

In this paper, we investigate the relationship between GaN exciton energy and temperature by using high-quality, strain-free GaN epilayers. Traditional models, such as Varshni’s model and the Bose–Einstein model, are primarily based on empirical fitting and give little or no consideration to electron–phonon interactions, which prevents them from accurately calculating GaN exciton energy over a wide temperature range. Considering the interaction of electrons and phonons, we use singular functions, linear functions and power functions to express the phonon density of GaN, and then 2BE, singular-linear, power-law-delta, and power-law-v models are proposed. All of them provide results that are more consistent with actual measurements compared to traditional models. Among them, the singular-linear model summarizes the contributions of acoustic and optical phonons. The error associated with the singular-linear model is smaller than that of the 1BE and Varshni models across nearly the entire temperature range. Therefore, the singular-linear model is a better choice. Full article

(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)

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