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14 pages, 6604 KiB

Open AccessArticle

(Ca₀.₂₅La₀.₅Dy₀.₂₅)CrO₃ Ceramic Fiber@Biomass-Derived Carbon Aerogel with Enhanced Solute Transport Channels for Highly Efficient Solar Interface Evaporation

by Wei Zhang, Liyan Xue, Jincheng Zhang, Meng Zhang, Kaixian Wang, Minzhong Huang, Fan Yang, Zhengming Jiang and Tongxiang Liang

Materials 2024, 17(10), 2205; https://doi.org/10.3390/ma17102205 - 8 May 2024

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Abstract

The use of solar interface evaporation for seawater desalination or sewage treatment is an environmentally friendly and sustainable approach; however, achieving efficient solar energy utilization and ensuring the long-term stability of the evaporation devices are two major challenges for practical application. To address [...] Read more.

The use of solar interface evaporation for seawater desalination or sewage treatment is an environmentally friendly and sustainable approach; however, achieving efficient solar energy utilization and ensuring the long-term stability of the evaporation devices are two major challenges for practical application. To address these issues, we developed a novel ceramic fiber@bioderived carbon composite aerogel with a continuous through-hole structure via electrospinning and freeze-casting methods. Specifically, an aerogel was prepared by incorporating perovskite oxide (Ca₀.₂₅La₀.₅Dy₀.₂₅)CrO₃ ceramic fibers (CCFs) and amylopectin-derived carbon (ADC). The CCFs exhibited remarkable photothermal conversion efficiencies, and the ADC served as a connecting agent and imparted hydrophilicity to the aerogel due to its abundant oxygen-containing functional groups. After optimizing the composition and microstructure, the (Ca₀.₂₅La₀.₅Dy₀.₂₅)CrO₃ ceramic fiber@biomass-derived carbon aerogel demonstrated remarkable properties, including efficient light absorption and rapid transport of water and solutes. Under 1 kW m⁻² light intensity irradiation, this novel material exhibited a high temperature (48.3 °C), high evaporation rate (1.68 kg m⁻² h⁻¹), and impressive solar vapor conversion efficiency (91.6%). Moreover, it exhibited long-term stability in water evaporation even with highly concentrated salt solutions (25 wt%). Therefore, the (Ca₀.₂₅La₀.₅Dy₀.₂₅)CrO₃ ceramic fiber@biomass-derived carbon aerogel holds great promise for various applications of solar interface evaporation. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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19 pages, 7040 KiB

Open AccessArticle

High-Entropy Diborides—Silicon Carbide Composites by Reactive and Non-Reactive Spark Plasma Sintering: A Comparative Study

by Ekaterina Pakhomova, Giacomo Cao, Roberto Orrù, Sebastiano Garroni, Paolo Ferro and Roberta Licheri

Materials 2024, 17(3), 718; https://doi.org/10.3390/ma17030718 - 2 Feb 2024

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Abstract

The reactive spark plasma sintering (R-SPS) method was compared in this work with the two-step SHS–SPS route, based on the combination of the self-propagating high-temperature synthesis (SHS) with the SPS process, for the fabrication of dense (Hf_0.2Mo_0.2Ti_0.2Ta [...] Read more.

The reactive spark plasma sintering (R-SPS) method was compared in this work with the two-step SHS–SPS route, based on the combination of the self-propagating high-temperature synthesis (SHS) with the SPS process, for the fabrication of dense (Hf_0.2Mo_0.2Ti_0.2Ta_0.2Nb_0.2)B₂–SiC and (Hf_0.2Mo_0.2Ti_0.2Ta_0.2Zr_0.2)B₂–SiC ceramics. A multiphase and inhomogeneous product, containing various borides, was obtained at 2000 °C/20 min by R-SPS from transition metals, B₄C, and Si. In contrast, if the same precursors were first reacted by SHS and then processed by SPS under the optimized condition of 1800 °C/20 min, the desired ceramics were successfully attained. The resulting sintered samples possessed relative densities above 97% and displayed uniform microstructures with residual oxide content <2.4 wt.%. The presence of SiC made the sintering temperature milder, i.e., 150 °C below that needed by the corresponding additive-free system. The fracture toughness was also markedly improved, particularly when considering the Nb-containing system processed at 1800 °C/20 min, whereas the fracture toughness progressively decreased (from 7.35 to 5.36 MPa m^1/2) as the SPS conditions became more severe. SiC addition was found to inhibit the volatilization of metal oxides like MoO₃ formed during oxidation experiments, thus avoiding mass loss in the ceramics. The benefits above also likely took advantage of the fact that the two composite constituents were synthesized in parallel, according to the SHS–SPS approach, rather than being produced separately and combined subsequently, so that strong interfaces between them were formed. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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13 pages, 10100 KiB

Open AccessArticle

Structure and Properties of High-Entropy Boride Ceramics Synthesized by Mechanical Alloying and Spark Plasma Sintering

by Nikolay Razumov, Tagir Makhmutov, Artem Kim and Anatoliy Popovich

Materials 2023, 16(20), 6744; https://doi.org/10.3390/ma16206744 - 18 Oct 2023

Cited by 1 | Viewed by 777

Abstract

This manuscript shows the study of the structure, mechanical, and chemical properties of high-entropy borides MeB₂ (Me = Ti, Ta, Nb, Hf, Zr). High-entropy borides were synthesized by mechanical alloying and spark plasma sintering. A chemically homogeneous powder with a low iron [...] Read more.

This manuscript shows the study of the structure, mechanical, and chemical properties of high-entropy borides MeB₂ (Me = Ti, Ta, Nb, Hf, Zr). High-entropy borides were synthesized by mechanical alloying and spark plasma sintering. A chemically homogeneous powder with a low iron content (0.12%) was obtained in a planetary mill by rotating the planetary disk/pots at 200–400 rpm and a processing time of 7.5 h. The structure, mechanical, and chemical properties of the resulting high-entropy borides have been studied. A single-phase hexagonal structure is formed during spark plasma sintering of mechanically alloyed powders at 2000 °C. The microhardness of the samples ranged from 1763 to 1959 HV. Gas-dynamic tests of the synthesized materials showed that an increase in the content of Zr and Hf in the composition increases the thermal-oxidative resistance of the material. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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12 pages, 1420 KiB

Open AccessArticle

X-ray Photoelectron Spectroscopy Analysis of Scandia-Ceria-Stabilized Zirconia Composites with Different Transport Properties

by Iraida N. Demchenko, Kostiantyn Nikiforow, Maryna Chernyshova, Yevgen Melikhov, Yevgen Syryanyy, Nadiia Korsunska, Larysa Khomenkova, Yehor Brodnikovskyi and Dmytro Brodnikovskyi

Materials 2023, 16(16), 5504; https://doi.org/10.3390/ma16165504 - 8 Aug 2023

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Abstract

This work aims to study a possible modification in the electronic structure of scandia-ceria-stabilized zirconia (10Sc1CeSZ) ceramics sintered at different temperatures. In addition to using X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy to investigate the structural and electrical properties, we [...] Read more.

This work aims to study a possible modification in the electronic structure of scandia-ceria-stabilized zirconia (10Sc1CeSZ) ceramics sintered at different temperatures. In addition to using X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy to investigate the structural and electrical properties, we employed X-ray photoelectron spectroscopy (XPS) to determine the chemical state information of the atoms involved, along with compositional analysis. As expected, a significant increase in grain ionic conductivity with the sintering temperature was present. This increase was accompanied by a decrease in the porosity of the samples, an increase in the grain size, and a transformation from the rhombohedral to the cubic phase. The phase transformation was detected not only using XRD, but also using XPS and, for this type of ceramic, XPS detected this transformation for the first time. In addition to the changes in the structural characteristics, the increase in the ionic conductivity was accompanied by a modification in the electronic structure of the ceramic surface. The XPS results showed that the surface of the ceramic sintered at the lower temperature of 1100 °C had a higher amount of Zr–OH bonds than the surface of the ceramic sintered at the higher temperature of 1400 °C. The existence of these Zr–OH bonds was confirmed using Fourier-transform infrared spectroscopy (FTIR). From this result, taken together with the difference between the oxygen/zirconium ratios in these ceramics, also identified using XPS, we conclude that there were fewer oxygen vacancies in the ceramic sintered at the lower temperature. It is argued that these two factors, together with the changes in the structural characteristics, have a direct influence on the conductive properties of the studied ceramics sintered at different temperatures. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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12 pages, 3273 KiB

Open AccessArticle

On the Effect of Standard Deviation of Cationic Radii on the Transition Temperature in Fluorite-Structured Entropy-Stabilized Oxides (F-ESO)

by Luca Spiridigliozzi, Mauro Bortolotti and Gianfranco Dell’Agli

Materials 2023, 16(6), 2219; https://doi.org/10.3390/ma16062219 - 10 Mar 2023

Cited by 5 | Viewed by 1010

Abstract

It is confirmed that Fluorite-structured Entropy-Stabilized Oxides (F-ESO) can be obtained with multicomponent (5) equimolar systems based on cerium, zirconium, and other rare earth elements, selected according to the predictor already proposed by the authors. Indeed, in the present study, three different samples [...] Read more.

It is confirmed that Fluorite-structured Entropy-Stabilized Oxides (F-ESO) can be obtained with multicomponent (5) equimolar systems based on cerium, zirconium, and other rare earth elements, selected according to the predictor already proposed by the authors. Indeed, in the present study, three different samples owning a standard deviation (SD in the following) of their cationic radii greater than the threshold value (i.e., SD > 0.095 with cationic radii measured in Å) needed to ensure the formation of the single-phase fluorite structure, were prepared via co-precipitation method. After a calcination step at 1500 °C for 1 h, the entropy-driven transition from multiple phases to single-phase fluorite-like structure has been actually confirmed. Thus, with the aim of defining the temperature at which such entropy-driven transition occurred, and identifying possible relation between such temperature and the actual value of SD, the phase evolution of all the prepared samples as a function of temperature (ranging from 800 °C to 1300 °C) was analyzed by in situ High Temperature X-ray Diffraction. An apparent inverse correlation between the standard deviation and the entropy-driven transition temperature has been identified, i.e., the higher the former, the lower the latter. These results, based on the conducted basic structural analysis, provide further support to the SD-based empirical predictor developed by the authors, suggesting that high values of SD could bring additional contribution to the overall entropy of the system, other than the configurational one. Thus, this SD-driven entropy contribution directly increases with the increasing of the standard deviation of the cationic radii of a given F-ESO. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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14 pages, 2657 KiB

Open AccessArticle

Analysis of the Electroconsolidation Process of Fine-Dispersed Structures Out of Hot Pressed Al₂O₃–WC Nanopowders

by Edwin Gevorkyan, Mirosław Rucki, Zbigniew Krzysiak, Volodymyr Chishkala, Wojciech Zurowski, Wojciech Kucharczyk, Voskan Barsamyan, Volodymyr Nerubatskyi, Tomasz Mazur, Dmitrij Morozow, Zbigniew Siemiątkowski and Jacek Caban

Materials 2021, 14(21), 6503; https://doi.org/10.3390/ma14216503 - 29 Oct 2021

Cited by 23 | Viewed by 1443

Abstract

Fabrication of alumina–tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after [...] Read more.

Fabrication of alumina–tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after a temperature of 1000 °C was reached. Due to the varying dominance of different physical processes affecting the grains, appropriate heating rates and pressure at different stages ensured that a structure with submicron grains was obtained. With directly applied alternating current, it was found that the proportion Al₂O₃ (50 wt.%)–WC provided the highest fracture toughness, and a sintering temperature above 1600 °C was found to be disadvantageous. High heating rates and a short sintering time enabled the process to be completed in 12 min, saving energy and time. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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9 pages, 2241 KiB

Open AccessArticle

Effect of Processing Conditions on the Flash Onset Temperature in Hydroxyapatite

by Changhun Hwang and Jondo Yun

Materials 2021, 14(18), 5229; https://doi.org/10.3390/ma14185229 - 11 Sep 2021

Cited by 3 | Viewed by 1318

Abstract

When heat and electric field are applied to the sample, sintering takes place within a short time of a few seconds by the flash phenomenon that occurs. In what condition flash does occur is a main issue for the flash sintering technique. In [...] Read more.

When heat and electric field are applied to the sample, sintering takes place within a short time of a few seconds by the flash phenomenon that occurs. In what condition flash does occur is a main issue for the flash sintering technique. In this study, the effect of processing conditions such as sintering atmosphere, sample size, density and grain size on the flash onset of hydroxyapatite was investigated. In a vacuum atmosphere, a flash occurred at a lower temperature by 50–100 °C than in air. The smaller the thickness of the sample, the higher the flash onset temperature due to the larger specific surface area. Flash was also observed in samples which were presintered, having a density of 86–100% and a grain size of 0.2–0.9 μm. When the density and grain size of the sample were higher and larger, the flash onset temperature was higher. It was because the diffusion and conduction path through the grain boundary and the inner surface of the pores with high defect concentration are blocked with an increase of density or grain size. When an electric field was applied during flash sintering, a color change of the sample was observed and the reason was discussed. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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9 pages, 2222 KiB

Open AccessArticle

Spark Plasma Sintering of LiFePO₄: AC Field Suppressing Lithium Migration

by Nan Luo, Yong Lin, Jian Guo, Emanuele Quattrocchi, Huaijiu Deng, Jian Dong, Francesco Ciucci, Filippo Boi, Chunfeng Hu and Salvatore Grasso

Materials 2021, 14(11), 2826; https://doi.org/10.3390/ma14112826 - 25 May 2021

Cited by 8 | Viewed by 2708

Abstract

Our work proposes a comparison between Spark Plasma Sintering of LiFePO₄ carried out using an Alternating Current (AC) and Direct Current (DC). It quantifies the Li-ion migration using DC, and it validates such hypothesis using impedance spectroscopy, X-ray photoelectron spectroscopy and inductively [...] Read more.

Our work proposes a comparison between Spark Plasma Sintering of LiFePO₄ carried out using an Alternating Current (AC) and Direct Current (DC). It quantifies the Li-ion migration using DC, and it validates such hypothesis using impedance spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy. The use of an AC field seems effective to inhibit undesired Li-ion migration and achieve high ionic conductivity as high as 4.5 × 10⁻³ S/cm, which exceeds by one order of magnitude samples processed under a DC field. These results anticipate the possibility of fabricating a high-performance all-solid-state Li-ion battery by preventing undesired Li loss during SPS processing. Full article

(This article belongs to the Special Issue High-Entropy Ceramics: Synthesis and Applications)

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