The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite ...The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature展开更多
β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanica...β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanical properties of the materials was展开更多
In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oi...In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oil-paper insulation is set up. Complex permittivity of oil-paper insulation respectively composed by new or aged oil and insulation paper with different DP are tested, and complex permittivity of oil-paper insulation respectively composed by insulation respectively composed by new oil and insulation paper with different DP and low or high moisture content are tested. The test results are analyzed, and the analysis results show that the degree of polymerization of insulation paper has an influence on complex permittivity of oil-paper insulation though influencing the distribution of moisture and acids between oil and paper.展开更多
A_2B_2O_7 system compounds, which usually present three phase structures mainly based on the ionic radius ratios of r_A and r_B(r_A/r_B), have been studied for potential applications in many fields, such as thermal ba...A_2B_2O_7 system compounds, which usually present three phase structures mainly based on the ionic radius ratios of r_A and r_B(r_A/r_B), have been studied for potential applications in many fields, such as thermal barrier coatings, luminescence powders, fast-ion conductors, photocatalysts, and matrices for immobilization of highly active radionuclides. Since 2005, La_2Hf_2O_7 was fabricated into transparent ceramics and much more attentions were paid on A_2B_2O_7 transparent ceramics for new applications. In this review, the development of A_2B_2O_7 system transparent ceramics was described. The structure characteristics, powder synthesis method, and sintering techniques of the final A_2B_2O_7 transparent ceramics were summarized. After that, the mostly reported A_2Hf_2O_7, A_2Zr_2O_7, and A_2Ti_2O_7 system transparent ceramics were systematically introduced. The potential application fields and future development trends were also discussed, focusing on scintillators, optical elements, and other luminescent materials.展开更多
The nanoindentation loading curves measured on fused silica were analyzed based on the theoretical relationship derived by Malzbender et al.(J Mater Res 2000, 15: 1209–1212). It was found that the ratio of the applie...The nanoindentation loading curves measured on fused silica were analyzed based on the theoretical relationship derived by Malzbender et al.(J Mater Res 2000, 15: 1209–1212). It was found that the ratio of the applied load to the square of the displacement, P/(h+h_d)~2, does not keep constant during loading segment of the nanoindentation test. Considering the existence of the indentation size effect, an empirical method for the determination of the load-independent hardness by analyzing the nanoindentation loading curves was proposed.展开更多
The indentation hardness of a given material is usually load-dependent and such a phenomenon is generally referred to as the indentation size effect(ISE).The existence of ISE means that,if hardness is used as a materi...The indentation hardness of a given material is usually load-dependent and such a phenomenon is generally referred to as the indentation size effect(ISE).The existence of ISE means that,if hardness is used as a material selection criterion,it is clearly insufficient to quote a single hardness number.Several empirical or semi-empirical equations,including the Meyer’s law,the Hays-Kendall approach,the energy-balance approach,the proportional specimen resistance(PSR)model and the modified PSR model,etc.,have been proposed for the description of the variation of the indentation size with the applied test load and for determining the so-called load-independent hardness.This paper reviews these existing empirical equations,with a special emphasis on the analysis and the application of the modified PSR model.展开更多
High-temperature mechanical properties of medium-entropy carbide ceramics have attracted significant attention.Tailoring the microstructure is an effective way to improve these high-temperature mechanical properties,w...High-temperature mechanical properties of medium-entropy carbide ceramics have attracted significant attention.Tailoring the microstructure is an effective way to improve these high-temperature mechanical properties,which can be affected by the evolution of the enthalpy and entropy,as well as by lattice distortion and sluggish diffusion.In this study,the effects of equiatomic Zr/(Ti,Nb)substitution(Zr content of 10-40 at%)on the microstructure and high-temperature strength of(Ti,Zr,Nb)C medium-entropy ceramics were investigated.The grain size of the(Ti,Zr,Nb)C medium-entropy ceramics was refined from 9.4±3.7 to 1.1±0.4μm with an increase in the Zr content from 10.0 to 33.3 at%.A further increase in the Zr content to 40 at%resulted in a slight increase in the grain size.At 1900℃,the(Ti,Zr,Nb)C medium-entropy ceramics with the Zr contents of 33.3 and 40 at%exhibited ultra-high flexural strengths of 875±43 and 843±71 MPa,respectively,which were higher than those of the transition metal carbides previously reported under similar conditions.Furthermore,relatively smooth grain boundaries,which were detected at a test temperature of 1000℃,transformed into curved and serrated boundaries as the temperature increased to 1900℃,which may be considered the primary reason for the improved high-temperature flexural strength.The associated mechanism was analyzed and discussed in detail.展开更多
To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi_2O_3 reference electrode, focusing on its output accuracy. When...To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi_2O_3 reference electrode, focusing on its output accuracy. When the above sensor was tested in a flow of gas with known oxygen partial pressure, pO_2, a linear relationship between lgpO_2 and the electromotive force(EMF) was observed, and the correlation slope exhibited a positive deviation from Nernstian behavior. EMF measurements performed in molten NaCl–KCl indicated that the oxygen content of this salt mixture increased with increasing oxygen partial pressure in the covering gas, in agreement with Henry's law. Moreover, the EMF exhibited a linear decrease with increasing melt temperature of molten NaCl–KCl, in agreement with the theoretical model. Finally, a relationship between the structure of molten NaCl–KCl and its oxygen diffusion behavior was established. As a result, the developed sensor was demonstrated to be well suited for determining the oxygen content of molten salts.展开更多
文摘The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature
文摘β-sialon/nano-size SiC composite ceramic with DyAG(Dy3Al5O12) as grain boundary phase was fabricated through hot-pressing. The effect of nano-size SiC on densification, phase composition, microstructure and mechanical properties of the materials was
文摘In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oil-paper insulation is set up. Complex permittivity of oil-paper insulation respectively composed by new or aged oil and insulation paper with different DP are tested, and complex permittivity of oil-paper insulation respectively composed by insulation respectively composed by new oil and insulation paper with different DP and low or high moisture content are tested. The test results are analyzed, and the analysis results show that the degree of polymerization of insulation paper has an influence on complex permittivity of oil-paper insulation though influencing the distribution of moisture and acids between oil and paper.
基金financial supports from the National Key R&D Program of China (No.2017YFB0310500)the National Natural Science Foundation of China (No.51602326)
文摘A_2B_2O_7 system compounds, which usually present three phase structures mainly based on the ionic radius ratios of r_A and r_B(r_A/r_B), have been studied for potential applications in many fields, such as thermal barrier coatings, luminescence powders, fast-ion conductors, photocatalysts, and matrices for immobilization of highly active radionuclides. Since 2005, La_2Hf_2O_7 was fabricated into transparent ceramics and much more attentions were paid on A_2B_2O_7 transparent ceramics for new applications. In this review, the development of A_2B_2O_7 system transparent ceramics was described. The structure characteristics, powder synthesis method, and sintering techniques of the final A_2B_2O_7 transparent ceramics were summarized. After that, the mostly reported A_2Hf_2O_7, A_2Zr_2O_7, and A_2Ti_2O_7 system transparent ceramics were systematically introduced. The potential application fields and future development trends were also discussed, focusing on scintillators, optical elements, and other luminescent materials.
文摘The nanoindentation loading curves measured on fused silica were analyzed based on the theoretical relationship derived by Malzbender et al.(J Mater Res 2000, 15: 1209–1212). It was found that the ratio of the applied load to the square of the displacement, P/(h+h_d)~2, does not keep constant during loading segment of the nanoindentation test. Considering the existence of the indentation size effect, an empirical method for the determination of the load-independent hardness by analyzing the nanoindentation loading curves was proposed.
文摘The indentation hardness of a given material is usually load-dependent and such a phenomenon is generally referred to as the indentation size effect(ISE).The existence of ISE means that,if hardness is used as a material selection criterion,it is clearly insufficient to quote a single hardness number.Several empirical or semi-empirical equations,including the Meyer’s law,the Hays-Kendall approach,the energy-balance approach,the proportional specimen resistance(PSR)model and the modified PSR model,etc.,have been proposed for the description of the variation of the indentation size with the applied test load and for determining the so-called load-independent hardness.This paper reviews these existing empirical equations,with a special emphasis on the analysis and the application of the modified PSR model.
基金Financial supports from the National Natural Science Foundation of China(Nos.52172076,52032001,11575275,and 52102081)the State Key Laboratory of High Performance Ceramics and Superfine Microstructure are greatly appreciated.
文摘High-temperature mechanical properties of medium-entropy carbide ceramics have attracted significant attention.Tailoring the microstructure is an effective way to improve these high-temperature mechanical properties,which can be affected by the evolution of the enthalpy and entropy,as well as by lattice distortion and sluggish diffusion.In this study,the effects of equiatomic Zr/(Ti,Nb)substitution(Zr content of 10-40 at%)on the microstructure and high-temperature strength of(Ti,Zr,Nb)C medium-entropy ceramics were investigated.The grain size of the(Ti,Zr,Nb)C medium-entropy ceramics was refined from 9.4±3.7 to 1.1±0.4μm with an increase in the Zr content from 10.0 to 33.3 at%.A further increase in the Zr content to 40 at%resulted in a slight increase in the grain size.At 1900℃,the(Ti,Zr,Nb)C medium-entropy ceramics with the Zr contents of 33.3 and 40 at%exhibited ultra-high flexural strengths of 875±43 and 843±71 MPa,respectively,which were higher than those of the transition metal carbides previously reported under similar conditions.Furthermore,relatively smooth grain boundaries,which were detected at a test temperature of 1000℃,transformed into curved and serrated boundaries as the temperature increased to 1900℃,which may be considered the primary reason for the improved high-temperature flexural strength.The associated mechanism was analyzed and discussed in detail.
基金the Shanghai Institute of Ceramics and Chinese Academy of Sciences for support
文摘To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi_2O_3 reference electrode, focusing on its output accuracy. When the above sensor was tested in a flow of gas with known oxygen partial pressure, pO_2, a linear relationship between lgpO_2 and the electromotive force(EMF) was observed, and the correlation slope exhibited a positive deviation from Nernstian behavior. EMF measurements performed in molten NaCl–KCl indicated that the oxygen content of this salt mixture increased with increasing oxygen partial pressure in the covering gas, in agreement with Henry's law. Moreover, the EMF exhibited a linear decrease with increasing melt temperature of molten NaCl–KCl, in agreement with the theoretical model. Finally, a relationship between the structure of molten NaCl–KCl and its oxygen diffusion behavior was established. As a result, the developed sensor was demonstrated to be well suited for determining the oxygen content of molten salts.
