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Design, Processing and Properties of High Entropy Ceramics

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced and Functional Ceramics and Glasses".

Deadline for manuscript submissions: 10 June 2024 | Viewed by 5724

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Dr. Giuseppe Viola

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School of Engineering and Materials Science, Queen Mary University of London, London, UK
Interests: ferroelectric ceramics; bismuth titanate; ceramics; ferroelectric materials; magnetic properties; dielectrics
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Dear Colleagues,

The present Special Issue aims to collect insightful papers on the latest development of high entropy ceramics, which are attracting increasing research interests within the materials science community, for a broad range of applications. High entropy materials have been conceived about twenty years ago when a novel approach based on the combination of multiple elements in the equimolar ratio was proposed to design new metallic alloys. High entropy alloys have shown outstanding mechanical properties, and excellent high temperature and chemical stability. Subsequently, the concept of high entropy design has been successfully applied to ceramics, and a considerable amount of high entropy oxides, nitrides and carbides have been developed, with better properties compared to their traditional counterparts. Nowadays, the field of high entropy ceramics is continuously expanding because of the vast amount of elemental combinations that can be realized to obtain new materials with outstanding properties. High entropy ceramics offer significant advantages for various application sectors, including aerospace, energy conversion and storage, catalysis, tribology, and corrosion engineering, among others.

This Special Issue will be focused on all aspects of high entropy ceramics, including the rational design criteria, fabrication methods, properties, and applications. Original contributions in the form of short communications, full-length articles, and reviews to share and disseminate the latest studies on all types of high entropy ceramics are specifically suitable for this compilation.

Dr. Giuseppe Viola
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

high entropy ceramics
compositional design criteria
synthesis
fabrication methods
structure and microstructure
properties

Published Papers (5 papers)

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Research

11 pages, 55460 KiB

Open AccessArticle

Preparation of a (Ca,Sr,Ba)ZrO₃ Crucible by Slip Casting for the Vacuum Induction Melting of NiTi Alloy

by Shijia Ding, Mingliang Li, Hailong Wang, Jinpeng Zhu, Gang Shao, Hongliang Xu, Hongxia Lu and Rui Zhang

Materials 2024, 17(8), 1924; https://doi.org/10.3390/ma17081924 - 22 Apr 2024

Viewed by 310

Abstract

Vacuum induction melting is a more energy-efficient process for the preparation of a titanium alloy with good homogeneity and low cost. But the crucial problem for this technology is in developing a crucible refractory with high stability. In the present work, a novel (Ca,Sr,Ba)ZrO₃ crucible was prepared by slip casting and its performance in melting NiTi alloy was studied. The results showed that a single solid solution was formed with a homogeneous distribution of metal elements after sintering at 1500 °C. It was found that the total content of oxygen and nitrogen remaining in the TiNi alloy after melting in the (Ca,Sr,Ba)ZrO₃ crucible was 0.0173 wt.%, which fulfills the ASTM standard on biomedical TiNi alloys. The good resistance of the (Ca,Sr,Ba)ZrO₃ crucible to molten NiTi has a relationship with the sluggish diffusion effect of high-entropy ceramics. This study provides insights into the process of designing highly suitable crucible material for melting a NiTi alloy. Full article

(This article belongs to the Special Issue Design, Processing and Properties of High Entropy Ceramics)

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15 pages, 11880 KiB

Open AccessArticle

Medium- and High-Entropy Rare Earth Hexaborides with Enhanced Solar Energy Absorption and Infrared Emissivity

by Hongye Wang, Yanyu Pan, Jincheng Zhang, Kaixian Wang, Liyan Xue, Minzhong Huang, Yazhu Li, Fan Yang and Heng Chen

Materials 2024, 17(8), 1789; https://doi.org/10.3390/ma17081789 - 12 Apr 2024

Viewed by 325

Abstract

The development of a new generation of solid particle solar receivers (SPSRs) with high solar absorptivity (0.28–2.5 μm) and high infrared emissivity (1–22 μm) is crucial and has attracted much attention for the attainment of the goals of “peak carbon” and “carbon neutrality”. To achieve the modulation of infrared emission and solar absorptivity, two types of medium- and high-entropy rare-earth hexaboride (ME/HEREB₆) ceramics, (La_0.25Sm_0.25Ce_0.25Eu_0.25)B₆ (MEREB₆) and (La_0.2Sm_0.2Ce_0.2Eu_0.2Ba_0.2)B₆ (HEREB₆), with severe lattice distortions were synthesized using a high-temperature solid-phase method. Compared to single-phase lanthanum hexaboride (LaB₆), HEREB₆ ceramics show an increase in solar absorptivity from 54.06% to 87.75% in the range of 0.28–2.5 μm and an increase in infrared emissivity from 76.19% to 89.96% in the 1–22 μm wavelength range. On the one hand, decreasing the free electron concentration and the plasma frequency reduces the reflection and ultimately increases the solar absorptivity. On the other hand, the lattice distortion induces changes in the B–B bond length, leading to significant changes in the Raman scattering spectrum, which affects the damping constant and ultimately increases the infrared emissivity. In conclusion, the multicomponent design can effectively improve the solar energy absorption and heat transfer capacity of ME/HEREB₆, thus providing a new avenue for the development of solid particles. Full article

(This article belongs to the Special Issue Design, Processing and Properties of High Entropy Ceramics)

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11 pages, 3606 KiB

Open AccessArticle

High Entropy Borides Synthesized by the Thermal Reduction of Metal Oxides in a Microwave Plasma

by Bria Storr, Carolina Amezaga, Luke Moore, Seth Iwan, Yogesh K. Vohra, Cheng-Chien Chen and Shane A. Catledge

Materials 2023, 16(12), 4475; https://doi.org/10.3390/ma16124475 - 20 Jun 2023

Viewed by 1403

Abstract

Metal oxide thermal reduction, enabled by microwave-induced plasma, was used to synthesize high entropy borides (HEBs). This approach capitalized on the ability of a microwave (MW) plasma source to efficiently transfer thermal energy to drive chemical reactions in an argon-rich plasma. A predominantly single-phase hexagonal AlB2-type structural characteristic of HEBs was obtained by boro/carbothermal reduction as well as by borothermal reduction. We compare the microstructural, mechanical, and oxidation resistance properties using the two different thermal reduction approaches (i.e., with and without carbon as a reducing agent). The plasma-annealed HEB (Hf_0.2, Zr_0.2, Ti_0.2, Ta_0.2, Mo_0.2)B₂ made via boro/carbothermal reduction resulted in a higher measured hardness (38 ± 4 GPa) compared to the same HEB made via borothermal reduction (28 ± 3 GPa). These hardness values were consistent with the theoretical value of ~33 GPa obtained by first-principles simulations using special quasi-random structures. Sample cross-sections were evaluated to examine the effects of the plasma on structural, compositional, and mechanical homogeneity throughout the HEB thickness. MW-plasma-produced HEBs synthesized with carbon exhibit a reduced porosity, higher density, and higher average hardness when compared to HEBs made without carbon. Full article

(This article belongs to the Special Issue Design, Processing and Properties of High Entropy Ceramics)

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14 pages, 5880 KiB

Open AccessArticle

Rare-Earth-Zirconate Porous High-Entropy Ceramics with Unique Pore Structures for Thermal Insulating Applications

by Hengchang Wang, Jie Xu, Jiatong Zhu, Xuanyu Meng, Lang Lin, Ping Zhang and Feng Gao

Materials 2023, 16(8), 3040; https://doi.org/10.3390/ma16083040 - 12 Apr 2023

Cited by 1 | Viewed by 1421

Abstract

Porous high-entropy ceramics are a new alternative material for thermal insulation. Their better stability and low thermal conductivity are due to lattice distortion and unique pore structures. In this work, rare-earth-zirconate ((La_0.25Eu_0.25Gd_0.25Yb_0.25)₂(Zr_0.75Ce_0.25)₂O₇) porous high-entropy ceramics were fabricated by a tert-butyl alcohol (TBA)-based gel-casting method. The regulation of pore structures was realized through changing different initial solid loadings. The XRD, HRTEM, and SAED results showed that the porous high-entropy ceramics had a single fluorite phase without impurity phases, exhibiting high porosity (67.1–81.5%), relatively high compressive strength (1.02–6.45 MPa) and low thermal conductivity (0.0642–0.1213 W/(m·K)) at room temperature. Porous high-entropy ceramics with 81.5% porosity demonstrated excellent thermal properties, showing a thermal conductivity of 0.0642 W/(m·K) at room temperature and 0.1467 W/(m·K) at 1200 °C. The unique pore structure with a micron size contributed to their excellent thermal insulating performance. The present work provides the prospect that rare-earth-zirconate porous high-entropy ceramics with tailored pore structures are expected to be thermal insulation materials. Full article

(This article belongs to the Special Issue Design, Processing and Properties of High Entropy Ceramics)

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8 pages, 2252 KiB

Open AccessArticle

Synthesis and Ultrahigh Pressure Compression of High-Entropy Boride (Hf_0.2Mo_0.2Nb_0.2Ta_0.2Zr_0.2)B₂ to 220 GPa

by Seth Iwan, Christopher Perreault and Yogesh K. Vohra

Materials 2023, 16(1), 158; https://doi.org/10.3390/ma16010158 - 24 Dec 2022

Viewed by 1313

Abstract

The high-entropy boride (Hf_0.2Mo_0.2Nb_0.2Ta_0.2Zr_0.2)B₂ material was synthesized under high-pressures and high-temperatures in a large-volume Paris-Edinburgh (PE) press from a ball-milled powder mix of HfO₂, MoO₃, Nb₂O_5, Ta₂O₅, ZrO₂, carbon black, and boron carbide. The transformation process was monitored in situ by energy-dispersive x-ray diffraction with conversion starting at 1100 °C and completed by 2000 °C with the formation of a single hexagonal AlB₂-type phase. The synthesized sample was recovered, powdered, and mixed with platinum pressure marker and studied under high pressure by angle-dispersive x-ray diffraction in a diamond anvil cell. The hexagonal AlB₂-type phase of (Hf_0.2Mo_0.2Nb_0.2Ta_0.2Zr_0.2)B₂ was found to be stable up to the highest pressure of 220 GPa reached in this study (volume compression V/V₀ = 0.70). The third order Birch-Murnaghan equation of state fit to the high-pressure data up to 220 GPa results in an ambient pressure unit cell volume

V_{0} = 28.16 \pm 0.04 Å^{3}, bulk modulus

K_{o}

= 407 ± 6 GPa, pressure derivative of bulk-modulus

K_{0}^{'}

= 2.73 ± 0.045 GPa. Our study indicates that this high-entropy boride (Hf_0.2Mo_0.2Nb_0.2Ta_0.2Zr_0.2)B₂ material is stable to ultrahigh pressures and temperatures and exhibit high bulk modulus similar to other incompressible transition metal borides like ReB₂ and Os₂B₃. Full article

(This article belongs to the Special Issue Design, Processing and Properties of High Entropy Ceramics)

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