Journals > > Topics > RESEARCH PAPER
RESEARCH PAPER|202 Article(s)
Yang LIU, Youjun LU, Yanrui LI, Liqun LIN, Zhenxia YUAN, and Zhenkun HUANG
In this study, the synthesis is feasibility and formulation design of HfN composite lanthanum silicate ceramics were explored. The feasibility of HfN synthesis by ternary reaction of HfO2-Si3N4-La2O3 system was verified by experiments, and the relationship between reaction pathway of HfO2-Si3N4 binary system and Hf-Si-La-O-N was studied. Considering that the lanthanum silicate salt in the reaction of HfO2-SiO2-La2O3 ternary system was contained in the Si3N4-SiO2-La2O3 system, lanthanum silicate was extended to the HfO2-Si3N4-La2O3-SiO2-HfN (Hf-Si-La-O-N) system, which clarified the coexistence of HfN and the lanthanum salt phases in the system. Experimental phase diagrams of HfO2-SiO2-La2O3 ternary system and Hf-Si-La-O-N system at 1500 ℃ were proposed. The results show that intermediate product Hf7O8N4 formed in the synthesis of HfN at high temperature in HfO2-Si3N4 binary system. Introduction of La2O3 promoted the system to generate HfN which was beneficial to reduce the burning loss rate of ceramics. There existed HfN and La4.67Si3O13, La5Si3NO12, LaSiNO2, La4Si2N2O7, La2Hf2O7 five lanthanum salt phases in the Hf-Si-La-O-N system. In this study, the synthesis is feasibility and formulation design of HfN composite lanthanum silicate ceramics were explored. The feasibility of HfN synthesis by ternary reaction of HfO2-Si3N4-La2O3 system was verified by experiments, and the relationship between reaction pathway of HfO2-Si3N4 binary system and Hf-Si-La-O-N was studied. Considering that the lanthanum silicate salt in the reaction of HfO2-SiO2-La2O3 ternary system was contained in the Si3N4-SiO2-La2O3 system, lanthanum silicate was extended to the HfO2-Si3N4-La2O3-SiO2-HfN (Hf-Si-La-O-N) system, which clarified the coexistence of HfN and the lanthanum salt phases in the system. Experimental phase diagrams of HfO2-SiO2-La2O3 ternary system and Hf-Si-La-O-N system at 1500 ℃ were proposed. The results show that intermediate product Hf7O8N4 formed in the synthesis of HfN at high temperature in HfO2-Si3N4 binary system. Introduction of La2O3 promoted the system to generate HfN which was beneficial to reduce the burning loss rate of ceramics. There existed HfN and La4.67Si3O13, La5Si3NO12, LaSiNO2, La4Si2N2O7, La2Hf2O7 five lanthanum salt phases in the Hf-Si-La-O-N system.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 443 (2021)
Li ZHANG, Xianfeng YANG, Xiewen XU, Jinyu GUO, Zhe ZHOU, Peng LIU, and Zhipeng XIE
Dense and porous zirconia ceramics were 3D printed with granular feedstock and screw extrusion mechanism on the basis of the traditional fused deposition method. The printability of granular feedstock, microstructure of the body and mechanical properties of ceramic materials were studied. The unsupported structure with maximum inclination 165° and span 5.5 mm were obtained. Effects of the two filling modes of printing on the flexural strength and Weibull modulus of the dense zirconia ceramics were compared. The results showed that the “single line+rectangle” filling mode was more conducive to achieve higher density and better mechanical properties than the traditional single line filling mode. Materials with bending strength of 637.8 MPa and Weibull modulus of 9.1 were obtained. The compressive behavior of porous zirconia ceramics prepared with different porosities were studied, showing an exponential law between compressive strength and porosity. There was only elasticity stage on the stress-strain curve for the samples with high porosity, while collapse stage may appear for the samples with low porosity. There was no collapse stage for both samples. Dense and porous zirconia ceramics were 3D printed with granular feedstock and screw extrusion mechanism on the basis of the traditional fused deposition method. The printability of granular feedstock, microstructure of the body and mechanical properties of ceramic materials were studied. The unsupported structure with maximum inclination 165° and span 5.5 mm were obtained. Effects of the two filling modes of printing on the flexural strength and Weibull modulus of the dense zirconia ceramics were compared. The results showed that the “single line+rectangle” filling mode was more conducive to achieve higher density and better mechanical properties than the traditional single line filling mode. Materials with bending strength of 637.8 MPa and Weibull modulus of 9.1 were obtained. The compressive behavior of porous zirconia ceramics prepared with different porosities were studied, showing an exponential law between compressive strength and porosity. There was only elasticity stage on the stress-strain curve for the samples with high porosity, while collapse stage may appear for the samples with low porosity. There was no collapse stage for both samples.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 436 (2021)
Meng GUO, Fengnian ZHANG, Yang MIAO, Yufeng LIU, Jun YU, and Feng GAO
High entropy La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 perovskite ceramics powder were prepared using coprecipitation method combined with calcination process, and synthesis temperature of the high entropy perovskite ceramics was significantly reduced. The phases and morphology of the ceramics powder were characterized by different methods. The results show that when the calcination temperature is 800 ℃, perovskite structure with a small amount of second phase was formed in the ceramics powder. When the calcination temperature is 1000 ℃, pure perovskite structure is formed in the La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 high entropy ceramics powder. Three electrode system was used to test the electrical properties of the working electrode made from the La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 high entropy ceramics powder, including cyclic voltammetry (CV) test and constant current charge-discharge (GCD) test. At the current density of 1 A/g, specific capacity of the working electrode reaches 154.8 F/g, while the current density increased to 10 A/g, the electrode material can still maintain 47%(73 F/g) of the initial specific capacity. All results indicate that high entropy La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 perovskite ceramics have good rate properties. High entropy La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 perovskite ceramics powder were prepared using coprecipitation method combined with calcination process, and synthesis temperature of the high entropy perovskite ceramics was significantly reduced. The phases and morphology of the ceramics powder were characterized by different methods. The results show that when the calcination temperature is 800 ℃, perovskite structure with a small amount of second phase was formed in the ceramics powder. When the calcination temperature is 1000 ℃, pure perovskite structure is formed in the La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 high entropy ceramics powder. Three electrode system was used to test the electrical properties of the working electrode made from the La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 high entropy ceramics powder, including cyclic voltammetry (CV) test and constant current charge-discharge (GCD) test. At the current density of 1 A/g, specific capacity of the working electrode reaches 154.8 F/g, while the current density increased to 10 A/g, the electrode material can still maintain 47%(73 F/g) of the initial specific capacity. All results indicate that high entropy La(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)O3 perovskite ceramics have good rate properties.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 431 (2021)
Yiliang WANG, Yunlong AI, Shuwei YANG, Bingliang LIANG, Zhenhuan ZHENG, Sheng OUYANG, Wen HE, Weihua CHEN, Changhong LIU, Jianjun ZHANG, and Zhiyong LIU
High-entropy oxides have attracted more and more attention due to their unique structures and potential applications. In this work, M3O4(M=FeCoCrMnMg) high entropy oxide powders were synthesized by a facile solid-state reaction method. The powders were characterized by different methods. Furthermore, M3O4/Ni foam (M3O4/NF) electrode was prepared by a coating method, followed by investigation of its supercapacitor performance. The results showed that, with the increase of calcining temperature, Fe2O3(H)/Co3O4(S)/Cr2O3(E) and Mn2O3(B) dissolved successively in the crystal lattice of spinel structure. After M3O4 powders being calcined at 900 ℃ for 2 h, single spinel structure (FCC, Fd-3m, a=0.8376 nm) was obtained with uniform distribution of Fe, Co, Cr, Mn, and Mg elements, the typical characteristic of high entropy oxide. In addition, the mass specific capacitance of M3O4/NF composite electrode is 193.7 F·g-1, with 1 mol/L KOH as electrolyte and 1 A·g-1 as current density, which indicated that the M3O4 high entropy oxide can be considered as a promising candidate for the electrode material in the field of supercapacitor applications. High-entropy oxides have attracted more and more attention due to their unique structures and potential applications. In this work, M3O4(M=FeCoCrMnMg) high entropy oxide powders were synthesized by a facile solid-state reaction method. The powders were characterized by different methods. Furthermore, M3O4/Ni foam (M3O4/NF) electrode was prepared by a coating method, followed by investigation of its supercapacitor performance. The results showed that, with the increase of calcining temperature, Fe2O3(H)/Co3O4(S)/Cr2O3(E) and Mn2O3(B) dissolved successively in the crystal lattice of spinel structure. After M3O4 powders being calcined at 900 ℃ for 2 h, single spinel structure (FCC, Fd-3m, a=0.8376 nm) was obtained with uniform distribution of Fe, Co, Cr, Mn, and Mg elements, the typical characteristic of high entropy oxide. In addition, the mass specific capacitance of M3O4/NF composite electrode is 193.7 F·g-1, with 1 mol/L KOH as electrolyte and 1 A·g-1 as current density, which indicated that the M3O4 high entropy oxide can be considered as a promising candidate for the electrode material in the field of supercapacitor applications.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 425 (2021)
Jianjun ZENG, Kuibao ZHANG, Daimeng CHEN, Haiyan GUO, Ting DENG, and Kui LIU
High-entropy ceramic is a hot topic in the recent study of ceramic materials. High-entropy ceramics with excellent properties is the development trend of ceramic materials. In this research, high-entropy transparent ceramic was synthesized by combustion method combined with vacuum sintering. The result indicates that the mean grain size of high-entropy (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7 powder is about 8 nm. And the high-entropy powder is disordered deficient fluorite structure. The final transparent ceramics sintered in vacuum furnace at different temperatures exhibit ordered pyrochlore structure. Sintering temperature has little effect on the transmittance of ceramics. And the in-line transmittance of as-prepared transparent ceramic can reach 74% at 1730 nm. There are many absorption peaks in the transmittance spectrum. With the increase of sintering temperature, the body density and grain size of ceramics increase, but the HV hardnesses decrease. High-entropy ceramic is a hot topic in the recent study of ceramic materials. High-entropy ceramics with excellent properties is the development trend of ceramic materials. In this research, high-entropy transparent ceramic was synthesized by combustion method combined with vacuum sintering. The result indicates that the mean grain size of high-entropy (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7 powder is about 8 nm. And the high-entropy powder is disordered deficient fluorite structure. The final transparent ceramics sintered in vacuum furnace at different temperatures exhibit ordered pyrochlore structure. Sintering temperature has little effect on the transmittance of ceramics. And the in-line transmittance of as-prepared transparent ceramic can reach 74% at 1730 nm. There are many absorption peaks in the transmittance spectrum. With the increase of sintering temperature, the body density and grain size of ceramics increase, but the HV hardnesses decrease.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 418 (2021)
Jiatong ZHU, Zhihao LOU, Ping ZHANG, Jia ZHAO, Xuanyu MENG, Jie XU, and Feng GAO
Single-phase solid solution monoclinic structure high-entropy tantalates (Nd1/6Sm1/6Eu1/6Gd1/6Dy1/6Ho1/6) TaO4(6RETaO4), (Nd1/5Sm1/5Eu1/5Gd1/5Dy1/5)TaO4(5RETaO4), (Nd1/4Sm1/4Eu1/4Gd1/4)TaO4(4RETaO4) were prepared by solid state method. STEM-EDS result shows the rare earth elements are uniformly distributed without segregation. The ferroelastic domain observed through SEM derived from the second ferroelastic phase transition. The thermal expansion experiment suggests the good thermal stability below 1200 ℃, where the thermal expansion coefficient of 6RETaO4 reaches 9.25×10-6K-1 at 1200 ℃. Due to the increase of phonon scattering derived from high-entropy effect, RETaO4 ceramics exhibit lower intrinsic thermal conductivity (2.98-1.23 W·m-1·K-1, 100-1000 ℃) and enhanced mechanical properties (6RETaO4, (9.97±2.2) GPa), which indicates that it is a potential material for thermal barrier coatings. Single-phase solid solution monoclinic structure high-entropy tantalates (Nd1/6Sm1/6Eu1/6Gd1/6Dy1/6Ho1/6) TaO4(6RETaO4), (Nd1/5Sm1/5Eu1/5Gd1/5Dy1/5)TaO4(5RETaO4), (Nd1/4Sm1/4Eu1/4Gd1/4)TaO4(4RETaO4) were prepared by solid state method. STEM-EDS result shows the rare earth elements are uniformly distributed without segregation. The ferroelastic domain observed through SEM derived from the second ferroelastic phase transition. The thermal expansion experiment suggests the good thermal stability below 1200 ℃, where the thermal expansion coefficient of 6RETaO4 reaches 9.25×10-6K-1 at 1200 ℃. Due to the increase of phonon scattering derived from high-entropy effect, RETaO4 ceramics exhibit lower intrinsic thermal conductivity (2.98-1.23 W·m-1·K-1, 100-1000 ℃) and enhanced mechanical properties (6RETaO4, (9.97±2.2) GPa), which indicates that it is a potential material for thermal barrier coatings.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 411 (2021)
Weiwei SANG, Hongsong ZHANG, Huahui CHEN, Bin WEN, and Xinchun LI
Developing novel ceramic materials with excellent thermophysical properties is one of the hotspots in the field of thermal barrier coatings. The (Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7 high-entropy ceramic was fabricated via high-temperature solid-state reaction. The crystal structure, microstructure, phase stability and thermophysical properties were investigated. Results indicate that (Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7 high-entropy ceramic has single defective fluorite structure, its elements are homogenously distributed, its grain size ranges from 0.2 to 3 μm. After high-temperature thermal cycling, the sample still remains single fluorite structure, showing excelleent phase stability at high temperature. Thermal conductivity lies in the range of 0.72-0.74 W/(m·K), lower than that of 7YSZ. Thermal expansion coefficient at 1200 ℃ is 5.6×10-6 K-1, lower than requirement of thermal barrier coatings (TBCs) for surface ceramic layer. However, its thermal expansion coefficient is close to that of the silicon-based ceramics substrate of environmental barrier coatings (EBCs) ((3.4-5.5)×10-6 K-1). Developing novel ceramic materials with excellent thermophysical properties is one of the hotspots in the field of thermal barrier coatings. The (Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7 high-entropy ceramic was fabricated via high-temperature solid-state reaction. The crystal structure, microstructure, phase stability and thermophysical properties were investigated. Results indicate that (Sm0.2Gd0.2Dy0.2Y0.2Yb0.2)3TaO7 high-entropy ceramic has single defective fluorite structure, its elements are homogenously distributed, its grain size ranges from 0.2 to 3 μm. After high-temperature thermal cycling, the sample still remains single fluorite structure, showing excelleent phase stability at high temperature. Thermal conductivity lies in the range of 0.72-0.74 W/(m·K), lower than that of 7YSZ. Thermal expansion coefficient at 1200 ℃ is 5.6×10-6 K-1, lower than requirement of thermal barrier coatings (TBCs) for surface ceramic layer. However, its thermal expansion coefficient is close to that of the silicon-based ceramics substrate of environmental barrier coatings (EBCs) ((3.4-5.5)×10-6 K-1).
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 405 (2021)
Jianfeng CAI, Hongxiang WANG, Guoqiang LIU, and Jun JIANG
With the fascinating properties observed in high entropy alloys, the idea of high entropy design has been applied to many material fields. Thermoelectric materials have some particular requirements for high entropy structure according to their transport characteristics. Here, we revealed that the high entropy structure for thermoelectrics required less lattice distortion, and the doping sites should have less influence on the Fermi surface. In the designed compound of Cu0.8Ag0.2Zn0.1Ga0.4Ge0.1In0.4Te2, the room-temperature thermal conductivity is reduced by 80% as compared to the matrix, and the maximum ZT is enhanced to 1.02. In SnTe, the solid solution of AgSbSe2 reduces the room-temperature thermal conductivity by 80%, reaching 1.3 W·m-1·K-1. This study shows that the high entropy structure following the proposed designing rules could be an important strategy for thermoelectrics. With the fascinating properties observed in high entropy alloys, the idea of high entropy design has been applied to many material fields. Thermoelectric materials have some particular requirements for high entropy structure according to their transport characteristics. Here, we revealed that the high entropy structure for thermoelectrics required less lattice distortion, and the doping sites should have less influence on the Fermi surface. In the designed compound of Cu0.8Ag0.2Zn0.1Ga0.4Ge0.1In0.4Te2, the room-temperature thermal conductivity is reduced by 80% as compared to the matrix, and the maximum ZT is enhanced to 1.02. In SnTe, the solid solution of AgSbSe2 reduces the room-temperature thermal conductivity by 80%, reaching 1.3 W·m-1·K-1. This study shows that the high entropy structure following the proposed designing rules could be an important strategy for thermoelectrics.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 399 (2021)
Yanan SUN, Li YE, Wenying ZHAO, Fenghua CHEN, Wenfeng QIU, Weijian HAN, Wei LIU, and Tong ZHAO
High entropy carbide ceramics have been proposed in recent years for their promising properties as high hardness, high modulus and low thermal conductivity. Liquid polymer precursor method, of which multiple elements distribute homogeneously during the pyrolysis process, is considered to be favorable in fabricating high entropy ceramics. However, few reports have studied the synthesis of liquid precursor. In this work, liquid polymer precursor of (Ti, Zr, Hf, Ta)C were synthesized by co-hydrolysis and polycondensation of equiatomic metal containing monomers, and adding allyl-functional novolac resin (AN) as carbon source. The obtained polymer precursors of high entropy carbide ceramics (PHECs) were soluble in propyl alcohol and stable for months. The corresponding high entropy carbide ceramic nano powders were obtained by pyrolyzing PHEC at 1800 ℃ for 2 h in vacuum. The precursors and ceramic powders were characterized by different methods. Results reveal that the ceramic sample pyrolyzed at 800 ℃ are composed of t-ZrO2 and oxide solid solutions, and carbothermal reduction reaction began after pyrolyzed at 1000 ℃, with carbide solid solutions being generated. After being pyrolyzed at 1800 ℃, the samples convert to target high entropy carbide ceramics. As-obtained ceramics are characterized to be high purity with uniform distribution of nanosized particles (~100 nm). The synthesized precursor has high ceramic yield (28.6wt%), low viscosity (150 mPa·s), and good solubility in polar solvents. Therefore, the proposed liquid polymer precursor method is reliable in preparation of high entropy ceramic nano powders, ceramic fibers and ceramic matrix composites. High entropy carbide ceramics have been proposed in recent years for their promising properties as high hardness, high modulus and low thermal conductivity. Liquid polymer precursor method, of which multiple elements distribute homogeneously during the pyrolysis process, is considered to be favorable in fabricating high entropy ceramics. However, few reports have studied the synthesis of liquid precursor. In this work, liquid polymer precursor of (Ti, Zr, Hf, Ta)C were synthesized by co-hydrolysis and polycondensation of equiatomic metal containing monomers, and adding allyl-functional novolac resin (AN) as carbon source. The obtained polymer precursors of high entropy carbide ceramics (PHECs) were soluble in propyl alcohol and stable for months. The corresponding high entropy carbide ceramic nano powders were obtained by pyrolyzing PHEC at 1800 ℃ for 2 h in vacuum. The precursors and ceramic powders were characterized by different methods. Results reveal that the ceramic sample pyrolyzed at 800 ℃ are composed of t-ZrO2 and oxide solid solutions, and carbothermal reduction reaction began after pyrolyzed at 1000 ℃, with carbide solid solutions being generated. After being pyrolyzed at 1800 ℃, the samples convert to target high entropy carbide ceramics. As-obtained ceramics are characterized to be high purity with uniform distribution of nanosized particles (~100 nm). The synthesized precursor has high ceramic yield (28.6wt%), low viscosity (150 mPa·s), and good solubility in polar solvents. Therefore, the proposed liquid polymer precursor method is reliable in preparation of high entropy ceramic nano powders, ceramic fibers and ceramic matrix composites.
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 393 (2021)
Shasha LÜ, Yufei ZU, Guoqing CHEN, Bojun ZHAO, Xuesong FU, and Wenlong ZHOU
As promising high-temperature structural materials, refractory high-entropy alloys have widely applications due to their excellent mechanical properties, high-temperature stability and oxidation resistance. For further improving the mechanical properties, ceramic-reinforced refractory high-entropy alloy matrix composites were prepared by utilizing in-situ reaction sintering. The supersaturated body centered cubic (BCC) solid solution of Cr0.5MoNbWTi doped with nonmetallic elements of carbon, nitrogen and oxygen was prepared by mechanical alloying. During spark plasma sintering, (Nb,Ti)(N,C) and Ti2O3 ceramic reinforcements were formed by in-situ reaction between nonmetallic and metallic elements. The ceramic reinforcements were well dispersed in BCC matrix. The formation mechanism and the strengthening effects of the ceramic reinforcements were discussed in this paper. With the assistance of the fine-grained ceramic reinforcements, the composites exhibited ultra-high ambient-temperature strength (4033 MPa), ambient-temperature hardness (11.57 GPa), and superior high-temperature yield strength (572 MPa at 1400 ℃). As promising high-temperature structural materials, refractory high-entropy alloys have widely applications due to their excellent mechanical properties, high-temperature stability and oxidation resistance. For further improving the mechanical properties, ceramic-reinforced refractory high-entropy alloy matrix composites were prepared by utilizing in-situ reaction sintering. The supersaturated body centered cubic (BCC) solid solution of Cr0.5MoNbWTi doped with nonmetallic elements of carbon, nitrogen and oxygen was prepared by mechanical alloying. During spark plasma sintering, (Nb,Ti)(N,C) and Ti2O3 ceramic reinforcements were formed by in-situ reaction between nonmetallic and metallic elements. The ceramic reinforcements were well dispersed in BCC matrix. The formation mechanism and the strengthening effects of the ceramic reinforcements were discussed in this paper. With the assistance of the fine-grained ceramic reinforcements, the composites exhibited ultra-high ambient-temperature strength (4033 MPa), ambient-temperature hardness (11.57 GPa), and superior high-temperature yield strength (572 MPa at 1400 ℃).
Journal of Inorganic Materials
- Publication Date: Apr. 20, 2021
- Vol. 36, Issue 4, 386 (2021)
Topics
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20