The Experts below are selected from a list of 4623 Experts worldwide ranked by ideXlab platform
Yanchun Zhou - One of the best experts on this subject based on the ideXlab platform.
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low thermal conductivity and high porosity zrc and hfc ceramics prepared by in situ reduction reaction Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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high porosity and low thermal conductivity high entropy zr0 2hf0 2ti0 2nb0 2ta0 2 c
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Jie Zhang, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2 Ta0.2)C was prepared by a simple method combing in-situ reaction and Partial Sintering. Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C possesses homogeneous microstructure with grain size in the range of 100–500 nm and pore size in the range of 0.2–1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m−1 K−1, low thermal diffusivity of 0.74 mm2·s−1 and good high temperature stability. The combination of these properties renders porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.
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Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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High strength and high porosity YB2C2 ceramics prepared by a new high temperature reaction/ Partial Sintering process
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultrahigh temperature ceramics (UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/Partial Sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during Sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa. The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
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preparation of porous yb4 ceramics using a combination of in situ borothermal reaction and high temperature Partial Sintering
Journal of The European Ceramic Society, 2015Co-Authors: Qiangqiang Guo, Huimin Xiang, Xin Sun, Xiaohui Wang, Yanchun ZhouAbstract:Abstract A novel method for preparing high porosity and high strength porous YB 4 ceramics was developed combining the in-situ borothermal reaction synthesis and high temperature Partial Sintering. Since pores could be produced by gasses such as B 2 O 3 and CO generated in the reaction between Y 2 O 3 and B 4 C, high porosity porous YB 4 ceramics were obtained after synthesis at 1650 °C and Sintering at 1780 °C for 2 h in vacuum, respectively. Using this new and simple method, porous YB 4 with controllable porosities of 60–70% and compressive strengths of 7.4–19.9 MPa were obtained depending on the green density. The phase composition, porosity, pore size distribution and compressive behavior of the porous YB 4 ceramics were systematically investigated. The effects of vacuum on synthesis of YB 4 and pore forming mechanism were also discussed in detail.
Heng Chen - One of the best experts on this subject based on the ideXlab platform.
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low thermal conductivity and high porosity zrc and hfc ceramics prepared by in situ reduction reaction Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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high porosity and low thermal conductivity high entropy zr0 2hf0 2ti0 2nb0 2ta0 2 c
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Jie Zhang, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2 Ta0.2)C was prepared by a simple method combing in-situ reaction and Partial Sintering. Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C possesses homogeneous microstructure with grain size in the range of 100–500 nm and pore size in the range of 0.2–1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m−1 K−1, low thermal diffusivity of 0.74 mm2·s−1 and good high temperature stability. The combination of these properties renders porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.
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High strength and high porosity YB2C2 ceramics prepared by a new high temperature reaction/ Partial Sintering process
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultrahigh temperature ceramics (UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/Partial Sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during Sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa. The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
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Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
Huimin Xiang - One of the best experts on this subject based on the ideXlab platform.
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low thermal conductivity and high porosity zrc and hfc ceramics prepared by in situ reduction reaction Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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high porosity and low thermal conductivity high entropy zr0 2hf0 2ti0 2nb0 2ta0 2 c
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Jie Zhang, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are promising for ultrahigh-temperature thermal insulation applications. However, the main limitations for their applications are the high thermal conductivity and densification of porous structure at high temperatures. In order to overcome these obstacles, herein, porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2 Ta0.2)C was prepared by a simple method combing in-situ reaction and Partial Sintering. Porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C possesses homogeneous microstructure with grain size in the range of 100–500 nm and pore size in the range of 0.2–1 μm, which exhibits high porosity of 80.99%, high compressive strength of 3.45 MPa, low room temperature thermal conductivity of 0.39 W·m−1 K−1, low thermal diffusivity of 0.74 mm2·s−1 and good high temperature stability. The combination of these properties renders porous high entropy (Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)C promising as light-weight ultrahigh temperature thermal insulation materials.
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Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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High strength and high porosity YB2C2 ceramics prepared by a new high temperature reaction/ Partial Sintering process
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultrahigh temperature ceramics (UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/Partial Sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during Sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa. The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
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preparation of porous yb4 ceramics using a combination of in situ borothermal reaction and high temperature Partial Sintering
Journal of The European Ceramic Society, 2015Co-Authors: Qiangqiang Guo, Huimin Xiang, Xin Sun, Xiaohui Wang, Yanchun ZhouAbstract:Abstract A novel method for preparing high porosity and high strength porous YB 4 ceramics was developed combining the in-situ borothermal reaction synthesis and high temperature Partial Sintering. Since pores could be produced by gasses such as B 2 O 3 and CO generated in the reaction between Y 2 O 3 and B 4 C, high porosity porous YB 4 ceramics were obtained after synthesis at 1650 °C and Sintering at 1780 °C for 2 h in vacuum, respectively. Using this new and simple method, porous YB 4 with controllable porosities of 60–70% and compressive strengths of 7.4–19.9 MPa were obtained depending on the green density. The phase composition, porosity, pore size distribution and compressive behavior of the porous YB 4 ceramics were systematically investigated. The effects of vacuum on synthesis of YB 4 and pore forming mechanism were also discussed in detail.
Fu-zhi Dai - One of the best experts on this subject based on the ideXlab platform.
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low thermal conductivity and high porosity zrc and hfc ceramics prepared by in situ reduction reaction Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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High strength and high porosity YB2C2 ceramics prepared by a new high temperature reaction/ Partial Sintering process
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultrahigh temperature ceramics (UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/Partial Sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during Sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa. The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
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Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
Jiachen Liu - One of the best experts on this subject based on the ideXlab platform.
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low thermal conductivity and high porosity zrc and hfc ceramics prepared by in situ reduction reaction Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.
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High strength and high porosity YB2C2 ceramics prepared by a new high temperature reaction/ Partial Sintering process
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultrahigh temperature ceramics (UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/Partial Sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during Sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa. The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
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Low thermal conductivity and high porosity ZrC and HfC ceramics prepared by in-situ reduction reaction/Partial Sintering method for ultrahigh temperature applications
Journal of Materials Science & Technology, 2019Co-Authors: Heng Chen, Huimin Xiang, Fu-zhi Dai, Jiachen Liu, Yanchun ZhouAbstract:Abstract Porous ultra-high temperature ceramics (UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and Partial Sintering has been developed for preparing porous ZrC and HfC with low conductivity. In this process, porous ZrC and HfC are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The as-prepared porous ZrC and HfC exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m−1 K−1, and compressive strength of 8.28 and 5.51 MPa, respectively. These features render porous ZrC and HfC promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous NbC, TaC as well as TiC have been prepared by this method.