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12 pages, 2073 KiB

Open AccessArticle

Preparation and Properties of Lightweight Aggregates from Discarded Al₂O₃-ZrO₂-C Refractories

by Shuli Sun, Junfeng Qu, Mengyong Sun, Xinming Ren, Cheng Gong, Xin Mu, Wenyu Zan, Zhangyan Zhou, Chengji Deng and Beiyue Ma

Materials 2024, 17(16), 3968; https://doi.org/10.3390/ma17163968 - 9 Aug 2024

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Abstract

Refractory materials are an important pillar for the stable development of the high-temperature industry. A large amount of waste refractories needs to be further disposed of every year, so it is of great significance to carry out research on the recycling of used [...] Read more.

Refractory materials are an important pillar for the stable development of the high-temperature industry. A large amount of waste refractories needs to be further disposed of every year, so it is of great significance to carry out research on the recycling of used refractories. In this work, lightweight composite aggregate was prepared by using discarded Al₂O₃-ZrO₂-C refractories as the main raw material, and the performance of the prepared lightweight aggregate was improved by adjusting the calcination temperature and introducing light calcined magnesia additives. The results showed that the cold compressive strength and thermal shock resistance of the lightweight aggregates were significantly improved with increasing calcination temperature. Moreover, the introduction of light calcined magnesia can effectively improve the apparent porosity, cold compressive strength, and thermal shock resistance of the prepared lightweight aggregates at the calcination temperature of 1400 °C. Consequently, this work provides a useful reference for the resource utilization of used refractories, while the prepared lightweight aggregates are expected to be applied in the field of high-temperature insulation. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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11 pages, 3882 KiB

Open AccessArticle

Mullite-Fibers-Reinforced Bagasse Cellulose Aerogels with Excellent Mechanical, Flame Retardant, and Thermal Insulation Properties

by Shuang Wang, Miao Sun, Junyi Lv, Jianming Gu, Qing Xu, Yage Li, Xin Zhang, Hongjuan Duan and Shaoping Li

Materials 2024, 17(15), 3737; https://doi.org/10.3390/ma17153737 - 28 Jul 2024

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Abstract

Cellulose aerogels are considered as ideal thermal insulation materials owing to their excellent properties such as a low density, high porosity, and low thermal conductivity. However, they still suffer from poor mechanical properties and low flame retardancy. In this study, mullite-fibers-reinforced bagasse cellulose [...] Read more.

Cellulose aerogels are considered as ideal thermal insulation materials owing to their excellent properties such as a low density, high porosity, and low thermal conductivity. However, they still suffer from poor mechanical properties and low flame retardancy. In this study, mullite-fibers-reinforced bagasse cellulose (Mubce) aerogels are designed using bagasse cellulose as the raw material, mullite fibers as the reinforcing agent, glutaraldehyde as the cross-linking agent, and chitosan as the additive. The resulted Mubce aerogels exhibit a low density of 0.085 g/cm³, a high porosity of 93.2%, a low thermal conductivity of 0.0276 W/(m∙K), superior mechanical performances, and an enhanced flame retardancy. The present work offers a novel and straightforward strategy for creating high-performance aerogels, aiming to broaden the application of cellulose aerogels in thermal insulation. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
(a) SEM image of raw MF. (b) Schematic illustration of the fabrication process of Mubce aerogels. (c) SEM image of as-prepared Mubce-150 aerogels (MF are encapsulated within the BCE, as marked by the yellow arrow, while others are nestled between layers of BCE, as pointed out by the blue arrow). The optical image of (d) Mubce-150 aerogels with different shapes and (e) the photo of the aerogel standing on a petal. And (f) pore size distribution curve of Mubce aerogels obtained by mercury intrusion porosimetry. Full article ">Figure 2
(a) FTIR spectra of MF, BCE aerogels, and Mubce-150 aerogels; C 1s survey spectra of (b) BCE and (c) Mubce-150 aerogels. N 1s survey spectra of (d) BCE and (e) Mubce-150 aerogels; (f) XRD pattern of BCE and Mubce-150 aerogels; SEM images of (g) BCE aerogels, (h) Mubce-50 aerogels, (i) Mubce-100 aerogels, (j) Mubce-150 aerogels, and (k) Mubce-200 aerogels. And (l) schematic diagram of enhanced mechanical properties of BCE aerogels. Full article ">Figure 3
(a) Stress–strain curves of BCE and Mubce aerogels. (b) The corresponding compressive strength and density. (c) Photographs of Mubce-150 aerogel withstanding 1561 times its own weight. (d) Stress–strain curves of Mubce-150 aerogels at different compressive strains. Fatigue test of (e) Mubce-150 aerogels and (f) BCE aerogels under 40% compressive strain. Full article ">Figure 4
(a) Thermal conductivity of Mubce-150 aerogels at different temperatures. (b) Comparison of the volume density and thermal conductivity of Mubce aerogels with other reported aerogels [<a href="#B24-materials-17-03737" class="html-bibr">24</a>,<a href="#B31-materials-17-03737" class="html-bibr">31</a>,<a href="#B32-materials-17-03737" class="html-bibr">32</a>,<a href="#B33-materials-17-03737" class="html-bibr">33</a>,<a href="#B34-materials-17-03737" class="html-bibr">34</a>,<a href="#B35-materials-17-03737" class="html-bibr">35</a>]. (c) Temperature variation curve of the upper surface of the samples heated at 160 °C for 60 min and infrared images of the samples at different heating times on a heating stage. Optical photographs of (d) BCE and (e) Mubce-150 aerogels heated by butane torch flame (aerogel specimen sizes are 90 × 90 × 15 mm3). (f) Optical image of Mubce-150 aerogels under butane flame for 45s. SEM iages of Mubce-150 aerogels: (g) area far away from the butane torch flame, (h) carbonized region not directly in contact with the butane torch flame, and (i) ablation region in direct contact with the butane torch flame. And (j) Heat Release Rate (HRR), (k) Total Heat Release (THR), and (l) Mass Loss Rate (MLR) curves of BCE and Mubce-150 aerogels. Full article ">

10 pages, 4552 KiB

Open AccessArticle

Effects of Alumina Bubble Addition on the Properties of Corundum–Spinel Castables Containing Cr₂O₃

by Haonan Chen, Xingfu Shi, Jing Chen, Mengyang Sang, Haoxuan Ma, Xinhong Liu and Quanli Jia

Materials 2024, 17(13), 3139; https://doi.org/10.3390/ma17133139 - 27 Jun 2024

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Abstract

Purging plugs made of corundum–spinel castables containing Cr₂O₃ have been widely utilized in secondary refining process. However, their poor thermal shock resistance has greatly limited the improvement of their service life. Aiming to enhance their properties, we introduced alumina bubbles [...] Read more.

Purging plugs made of corundum–spinel castables containing Cr₂O₃ have been widely utilized in secondary refining process. However, their poor thermal shock resistance has greatly limited the improvement of their service life. Aiming to enhance their properties, we introduced alumina bubbles (ABs) to corundum–spinel castables, and the effects of the AB addition on the properties of the castables are studied in this manuscript. The results indicate that the apparent porosity, permanent linear change, cold strength, and hot strength all increased with an increasing AB amount. The thermal shock resistance of the samples with the AB addition was improved; the residual strength and residual strength ratio of the sample with 4 wt% ABs was the best. The effects of ABs on the tabular alumina aggregate distribution and relationship between the cold strength of the samples and the AB content was evaluated via the box dimension method. With the increments of AB content, the box dimension value of the tabular alumina within the samples significantly decreased, indicating that the tabular alumina aggregate distribution was related to the amount of ABs. In addition, the relationship between the box dimension and the strength was also established. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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(a,d) surficial morphology of ABs, (b,e) internal morphology of ABs, (c) XRD pattern of ABs, and (f) floating state of ABs in water. Full article ">Figure 2
Physical properties of the samples. (a) AP, (b) BD, (c) PLC, (d) CMOR, and (e) CCS. Full article ">Figure 3
(a) HMOR and (b) TSR of the samples with different amounts of ABs. Full article ">Figure 4
Digital photos of the cross-sections and binarized pictures of the samples: (a,b) AB0, (c,d) AB2, (e,f) AB4, and (g,h) AB6. (Here, yellow circles refer to ABs). Full article ">Figure 5
The equations of linear regression of the samples: (a)AB0, (b) AB2, (c) AB4, and (d) AB6. Full article ">Figure 6
Schematic diagram of the volume content of ABs in castables. Full article ">Figure 7
The fracture morphologies of AB2 fired at (a) 1100 °C, (b) 1400 °C, and (c) 1600 °C. Full article ">Figure 8
SEM photos and schematic diagrams of crack propagation in the samples: (a,b) AB0 and (c,d) AB4. Full article ">

14 pages, 6961 KiB

Open AccessArticle

Oxide Scale Microstructure and Scale Growth Kinetics of the Hot-Pressed SiBCN-Ti Ceramics Oxidized at 1500 °C

by Hao Peng, Haobo Jiang, Daxin Li, Zhihua Yang, Wenjiu Duan, Dechang Jia and Yu Zhou

Materials 2024, 17(13), 3118; https://doi.org/10.3390/ma17133118 - 25 Jun 2024

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Abstract

In this study, the SiBCN-Ti series ceramics with different Ti contents were fabricated, and the oxidation resistance and microstructural evolution of the ceramics at 1500 °C for different times were explored. The results show that with the increase in oxidation time, pores and [...] Read more.

In this study, the SiBCN-Ti series ceramics with different Ti contents were fabricated, and the oxidation resistance and microstructural evolution of the ceramics at 1500 °C for different times were explored. The results show that with the increase in oxidation time, pores and bubbles are gradually formed in the oxide layer. When the oxidation time is less than or more than 4 h, the Ti(C, N) in the ceramics will maintain its initial structure or mostly transform to TiN. The introduction of Ti content can promote the formation of rutile silicate glass, thus healing the cracks and improving the oxidation resistance of the ceramics effectively. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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9 pages, 2626 KiB

Open AccessArticle

Preparation and Electromagnetic Wave Absorption Properties of N-Doped SiC Nanowires

by Ranran Shi, Zheng Liu, Wenxiu Liu and Jianlei Kuang

Materials 2023, 16(17), 5765; https://doi.org/10.3390/ma16175765 - 23 Aug 2023

Cited by 3 | Viewed by 980

Abstract

Enhancing the conductivity loss of SiC nanowires through doping is beneficial for improving their electromagnetic wave absorption performance. In this work, N-doped SiC nanowires were synthesized using three different methods. The results indicate that a large amount of Si₂ON will be [...] Read more.

Enhancing the conductivity loss of SiC nanowires through doping is beneficial for improving their electromagnetic wave absorption performance. In this work, N-doped SiC nanowires were synthesized using three different methods. The results indicate that a large amount of Si₂ON will be generated during the microwave synthesis of SiC nanowires in a nitrogen atmosphere. In addition, the secondary heat-treatment of the as-synthesized SiC nanowires under nitrogen atmosphere will significantly reduce their stacking fault density. When ammonium chloride is introduced as a doped nitrogen source in the reaction raw material, the N-doped SiC nanowires with high-density stacking faults can be synthesized by microwave heating. Therefore, the polarization loss induced by faults and the conductivity loss caused by doping will synergistically enhance the dielectric and EMW absorption properties of SiC nanowires in the range of 2–18 GHz. When the filling ratio of N-doped SiC nanowires is 20 wt.%, the composite shows a minimum reflection loss of –22.2 [email protected] GHz, and an effective absorption (RL ≤ –10 dB) bandwidth of 4.24 GHz at the absorber layer thickness of 2.2 mm. Further, the N-doped SiC nanowires also exhibit enhanced high-temperature EMW absorption properties with increasing temperature. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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14 pages, 3533 KiB

Open AccessArticle

Synthesis and Structural and Strength Properties of xLi₂ZrO₃-(1-x)MgO Ceramics—Materials for Blankets

by Dmitriy I. Shlimas, Daryn B. Borgekov, Artem L. Kozlovskiy and Maxim V. Zdorovets

Materials 2023, 16(14), 5176; https://doi.org/10.3390/ma16145176 - 23 Jul 2023

Cited by 1 | Viewed by 760

Abstract

The article considers the effect of doping with magnesium oxide (MgO) on changes in the properties of lithium-containing ceramics based on lithium metazirconate (Li₂ZrO₃). There is interest in this type of ceramics on account of their prospects for application [...] Read more.

The article considers the effect of doping with magnesium oxide (MgO) on changes in the properties of lithium-containing ceramics based on lithium metazirconate (Li₂ZrO₃). There is interest in this type of ceramics on account of their prospects for application in tritium production in thermonuclear power engineering, as well as several other applications related to alternative energy sources. During the investigations undertaken, it was found that variation in the MgO dopant concentration above 0.10–0.15 mol resulted in the formation of impurity inclusions in the ceramic structure in the form of a MgLi₂ZrO₄ phase, the presence of which resulted in a rise in the density of the ceramics, along with elevation in resistance to external influences. Moreover, during experimental work on the study of the thermal stability of the ceramics to external influences, it was found that the formation of two-phase ceramics resulted in growth in the preservation of stable strength properties during high-temperature cyclic tests. The decrease in strength characteristics was observed to be less than 1%. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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12 pages, 4289 KiB

Open AccessArticle

Study of the Aid Effect of CuO-TiO₂-Nb₂O₅ on the Dielectric and Structural Properties of Alumina Ceramics

by Rafael I. Shakirzyanov, Natalia O. Volodina, Kayrat K. Kadyrzhanov, Artem L. Kozlovskiy, Dmitriy I. Shlimas, Gulzada A. Baimbetova, Daryn B. Borgekov and Maxim V. Zdorovets

Materials 2023, 16(14), 5018; https://doi.org/10.3390/ma16145018 - 15 Jul 2023

Cited by 2 | Viewed by 854

Abstract

The aim of this work is to study the structural, dielectric, and mechanical properties of aluminum oxide ceramics with the triple sintering additive 4CuO-TiO₂-2Nb₂O₅. With an increase in sintering temperature from 1050 to 1500 °C, the average [...] Read more.

The aim of this work is to study the structural, dielectric, and mechanical properties of aluminum oxide ceramics with the triple sintering additive 4CuO-TiO₂-2Nb₂O₅. With an increase in sintering temperature from 1050 to 1500 °C, the average grain size and the microhardness value at a load of 100 N (HV0.1) increased with increasing density. It has been shown that at a sintering temperature of 1300 °C, the addition of a 4CuO-TiO₂-2Nb₂O₅ additive increases the low-frequency permittivity (2–500 Hz) in alumina ceramic by more than an order of magnitude due to the presence of a quadruple perovskite phase. At the same time, the density of such ceramics reached 89% of the theoretical density of α-Al₂O₃, and the microhardness value HV0.1 was 1344. It was observed that the introduction of 5 wt.% 4CuO-TiO₂-2Nb₂O₅ in the raw mixture remarkably increases values of shrinkage and density of sintered ceramics. Overall, the results of this work confirmed that introducing the 4CuO-TiO₂-2Nb₂O₅ sintering additive in the standard solid-phase ceramics route can significantly reduce the processing temperature of alumina ceramics, even when micron-sized powders are used as a starting material. The obtained samples demonstrated the potential of α-Al₂O₃ with the triple additive in such applications as electronics, microwave technology, and nuclear power engineering. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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15 pages, 12203 KiB

Open AccessArticle

Effect of Zr₂Al₄C₅ Content on the Mechanical Properties and Oxidation Behavior of ZrB₂-SiC-Zr₂Al₄C₅ Ceramics

by Qilong Guo, Liang Hua, Hao Ying, Ronghao Liu, Mei Lin, Leilei Li and Jing Wang

Materials 2023, 16(12), 4495; https://doi.org/10.3390/ma16124495 - 20 Jun 2023

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Abstract

ZrB₂-SiC-Zr₂Al₄C₅ multi-phase ceramics with uniform structure and high density were successfully prepared through the introduction of in situ synthesized Zr₂Al₄C₅ into ZrB₂-SiC ceramic via SPS at 1800 °C. A [...] Read more.

ZrB₂-SiC-Zr₂Al₄C₅ multi-phase ceramics with uniform structure and high density were successfully prepared through the introduction of in situ synthesized Zr₂Al₄C₅ into ZrB₂-SiC ceramic via SPS at 1800 °C. A systematic analysis and discussion of the experimental results and proposed mechanisms were carried out to demonstrate the composition-dependent sintering properties, mechanical properties and oxidation behavior. The results showed that the in situ synthesized Zr₂Al₄C₅ could be evenly distributed in the ZrB₂-SiC ceramic matrix and inhibited the growth of ZrB₂ grains, which played a positive role in the sintering densification of the composite ceramics. With increasing Zr₂Al₄C₅ content, the Vickers hardness and Young’s modulus of composite ceramics gradually decreased. The fracture toughness showed a trend that first increased and then decreased, and was increased by about 30% compared with ZrB₂-SiC ceramics. The major phases resulting from the oxidation of samples were ZrO₂, ZrSiO₄, aluminosilicate and SiO₂ glass. With increasing Zr₂Al₄C₅ content, the oxidative weight showed a trend that first increased then decreased; the composite ceramic with 30 vol.% Zr₂Al₄C₅ showed the smallest oxidative weight gain. We believe that the presence of Zr₂Al₄C₅ results in the formation of Al₂O₃ during the oxidation process, subsequently resulting in a lowering of the viscosity of the glassy silica scale, which in turn intensifies the oxidation of the composite ceramics. This would also increase oxygen permeation through the scale, adversely affecting the oxidation resistance of the composites with high Zr₂Al₄C₅ content. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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11 pages, 7177 KiB

Open AccessArticle

Low-Temperature Fabrication of Plate-like α-Al₂O₃ with Less NH₄F Additive

by Haiyang Chen, Bin Li, Meng Liu, Xue Yang, Jie Liu, Tingwei Qin, Zejian Xue, Yun Xing and Junhong Chen

Materials 2023, 16(12), 4415; https://doi.org/10.3390/ma16124415 - 15 Jun 2023

Cited by 1 | Viewed by 1220

Abstract

Fluorinated compounds are effective mineralization agents for the fabrication of plate-like α-Al₂O₃. However, in the preparation of plate-like α-Al₂O₃, it is still an extremely challenging task to reduce the content of fluoride while ensuring a [...] Read more.

Fluorinated compounds are effective mineralization agents for the fabrication of plate-like α-Al₂O₃. However, in the preparation of plate-like α-Al₂O₃, it is still an extremely challenging task to reduce the content of fluoride while ensuring a low synthesis temperature. Herein, oxalic acid and NH₄F are proposed for the first time as additives in the preparation of plate-like α-Al₂O₃. The results showed that plate-like α-Al₂O₃ can be synthesized at a low temperature of 850 °C with the synergistic effect of oxalic acid and 1 wt.% NH₄F. Additionally, the synergistic effect of oxalic acid and NH₄F not only can reduce the conversion temperature of α-Al₂O₃ but also can change the phase transition sequence. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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FTIR spectra of: (a) the specimens A2–A5; (b) local amplification at 1200–400 cm−1. Full article ">Figure 2
SEM pictures of A2–A5: (a) A2; (b) A3; (c) A4; (d) A5. Full article ">Figure 3
XRD patterns of the alumina phases received from A2–A5 at different calcination temperatures: (a) A2; (b) A3; (c) A4; (d) A5. Full article ">Figure 4
XRD patterns of: (a) the transition Al2O3 as obtained from A5 at 800 °C for distinct times; (b) local amplification at 2θ = 30°–50°. Full article ">Figure 5
XPS spectrum of transition Al2O3 as-obtained from A5 at 500 °C (a); the overall XPS spectrum and the individual lines of: (b) O 1s; and (c) Al 2p (d) F 1s. Full article ">Figure 6
TG-DSC curves of: (a) Al(OH)3; (b) A1; (c) A5. Full article ">Figure 7
SEM images of α-Al2O3 obtained from A2–A5 at different temperatures: (a) A2-950; (b) A3-950; (c) A4-950; (d) A5-950; (e) A4-850; (f) A5-800. Full article ">

Review

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25 pages, 5472 KiB

Open AccessReview

Principles and Methods for Improving the Thermoelectric Performance of SiC: A Potential High-Temperature Thermoelectric Material

by Yun Xing, Bo Ren, Bin Li, Junhong Chen, Shu Yin, Huan Lin, Jie Liu and Haiyang Chen

Materials 2024, 17(15), 3636; https://doi.org/10.3390/ma17153636 - 23 Jul 2024

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Abstract

Thermoelectric materials that can convert thermal energy to electrical energy are stable and long-lasting and do not emit greenhouse gases; these properties render them useful in novel power generation devices that can conserve and utilize lost heat. SiC exhibits good mechanical properties, excellent [...] Read more.

Thermoelectric materials that can convert thermal energy to electrical energy are stable and long-lasting and do not emit greenhouse gases; these properties render them useful in novel power generation devices that can conserve and utilize lost heat. SiC exhibits good mechanical properties, excellent corrosion resistance, high-temperature stability, non-toxicity, and environmental friendliness. It can withstand elevated temperatures and thermal shock and is well suited for thermoelectric conversions in high-temperature and harsh environments, such as supersonic vehicles and rockets. This paper reviews the potential of SiC as a high-temperature thermoelectric and third-generation wide-bandgap semiconductor material. Recent research on SiC thermoelectric materials is reviewed, and the principles and methods for optimizing the thermoelectric properties of SiC are discussed. Thus, this paper may contribute to increasing the application potential of SiC for thermoelectric energy conversion at high temperatures. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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