The glass-ceramics were prepared with the spodumene mineral as the main raw material,and the effects of ZrO_(2)replacing TiO_(2)on the samples were systematically investigated.The results show that the substitution of...The glass-ceramics were prepared with the spodumene mineral as the main raw material,and the effects of ZrO_(2)replacing TiO_(2)on the samples were systematically investigated.The results show that the substitution of ZrO_(2)for TiO_(2)is not conductive to precipitate𝛽β-quartz solid solution phase,but can improve the transparency and flexural strength of glass-ceramics.And the glass-ceramic with the highest visible light transmittance(87%)and flexural strength(231.80 MPa)exhibits an ultra-low thermal expansion of-0.028×10^(-7)K^(-1)in the region of 30-700℃.展开更多
(ZrMg)xY2-2xMo3O12(x=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,and 1)ceramics have been synthesized to obtain less hygroscopicity and negative thermal expansion.With increasing the substitution of(ZrMg)^6+(ion radius 7....(ZrMg)xY2-2xMo3O12(x=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,and 1)ceramics have been synthesized to obtain less hygroscopicity and negative thermal expansion.With increasing the substitution of(ZrMg)^6+(ion radius 7.2×10^-11 m)for Y3+(ion radius 9×10^-11 m),the crystal water are reduced obviously.The linear thermal expansion coefficient is improved with increasing the content of(ZrMg)^6+.The material shows near zero thermal expansion(-0.12×10^-6 K^-1,430-870 K)with x=0.7.Meanwhile,ZrMgMo3O12 shows low non-hygroscopicity and negative thermal expansion,but low softening temperature.After substituting amount of Y^3+for(ZrMg)^6+in ZrMgMo3O12(x=0.8),the softening temperature increases remarkably(750 K to 830 K)and it presents near zero thermal expansion.展开更多
Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after ther...Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after thermolysis specimens were heat treated at a temperature of 1400℃ for 10 h in nitrogen atmosphere. The thermal expansion coefficient of VT50-derived amorphous Si-C-N ceramic increases from 1.98×10-6/K at 400℃ to 3.09×10-6/K at 1000℃, of NCP200-derived amorphous Si-C-N ceramic increases from 2.35×10-6/K at 400℃ to 3.45×10-6/K at 1000℃, and of T2-l-derived amorphous Si-B-C-N ceramic increases from 2.08×10-6/K at 400℃ to 3.18×10-6/K at 1000℃. No glass transition for these amorphous ceramic materials was detected, indicating that as-thermolyzed precursor-derived Si-(B-)C-N ceramic materials are amorphous solids, but not glasses.展开更多
Firstly,the relation between the coefficient of thermal expansion(CTE)and the volume fraction of TiO_(2) was investigated, and also the influence of relative density of ceramic on the CTE was studied.The results show ...Firstly,the relation between the coefficient of thermal expansion(CTE)and the volume fraction of TiO_(2) was investigated, and also the influence of relative density of ceramic on the CTE was studied.The results show that the volume fraction of TiO_(2) and the relative density both make influence on the CTE of ZrO_(2)-TiO_(2) ceramic.According to the results,the ZrO_(2)-TiO_(2)(volume fraction of TiO_(2) is 27%)ceramic die with the similar CTE(8.92×10^(-6) ℃^(-1))to Ti6Al4V was fabricated.Secondly,to evaluate the dimensional accuracy of the workpiece superplastically formed,the Ti6Al4V impression experiment was performed.The result shows that the dimensional inaccuracy of workpiece is 0.003.Thirdly,in order to evaluate the practicability,the experiment of superplastic forming Ti6Al4V using ZrO_(2)-TiO_(2) cylinder ceramic die was carried out.The Ti6Al4V cylinder shows good shape retention and surface quality,and high dimensional accuracy.The ceramic dies seem to be adequate for superplastic forming the high accuracy Ti6Al4V, and the trials have confirmed the potential of the ZrO_(2)-TiO_(2) ceramic die.展开更多
With Al2O3, Dy2O3, and SiO2 as starting materials, the basic glass of Al2O3-Dy2O3-SiO2 system was prepared by conventional melting technology, and their thermal expansion coefficients （TECs） at different anneal time...With Al2O3, Dy2O3, and SiO2 as starting materials, the basic glass of Al2O3-Dy2O3-SiO2 system was prepared by conventional melting technology, and their thermal expansion coefficients （TECs） at different anneal time were investigated. TECs of the basic glass, which were heat-treated under different temperature, were also investigated. The result showed that TECs of the basic glass gradually approached a fixed value as the anneal time was extended, which suggested that most of the inner stress had been eliminated. After heat treatment, the contents of Dy2O3, Dy2Si2O7, and a new crystal increased up to 1200 ℃ and decreased below 1250 ℃, which was consistent with the TEC change of crystallized samples. This suggests that the crystal has a direct effect on TECs of the crystallized samples.展开更多
Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3...Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3, and SiO2 were studied respectively. Experimental results showed that Dy2O3 and Al2O3 had a positive effect on the coefficient of thermal expansion of glass, whereas, SiO2 had a negative effect. The coefficient of thermal expansion of glass showed an apparent linear relation to the contents of these three raw materials, from which an estimation model was built, to calculate the coefficient of thermal expansion of sealing glass. Relative errors of the calculating results to testing results were no more than 2%, which suggested that the estimation model was reasonable. This study provides a good theory reference for the practical utilizing of this sealing material, through which a proper glass composition for good sealing could be easily found.展开更多
High-entropy(HE)ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding.Among oth...High-entropy(HE)ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding.Among others,HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures.Herein,we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions,with four to seven transition metals,with the intent of understanding the thermal lattice expansion following different composition or synthesis process.As a result,we were able to control the average thermal expansion(TE)from 1.3×10^(−6)to 6.9×10^(−6)K^(−1)depending on the combination of metals,with a variation of in-plane to out-of-plane TE ratio ranging from 1.5 to 2.8.展开更多
A preferable honeycomb ceramics of Al2TiO5-TiO2-SiO2 doped by CeO2 and Er2O3 with high performance was prepared by means of extrusion molding and the effects of CeO2 and Er2O3 on the mechanical strength, thermal stabi...A preferable honeycomb ceramics of Al2TiO5-TiO2-SiO2 doped by CeO2 and Er2O3 with high performance was prepared by means of extrusion molding and the effects of CeO2 and Er2O3 on the mechanical strength, thermal stability, and sintering temperature of ATS ceramics were mainly investigated. The experimental results and the microscopic analysis by scanning electron microscope, X-ray powder diffxaction, and TG-DSC showed that adding CeO2 and Er2O3 into ATS could prohibit the growth of their crystal grains and make their size uniform, which finally decrease its sintering temperature, and also enhance its mechanical performance as well as thermal stability. After the reforming, ATS doped by 0.5% CeO2 ＋0.5% Er2O3 was sintered at 1250 ℃, its bending strength reached to 177A MPa and thermal expansion coefficient was 3.8 ~ 10^-6/℃ at 25 - 1000℃, which provided a promising basis of making monolithic honeycomb catalyst of deNOx.展开更多
The cordierite ceramic with a high strength and a low thermal expansion coefficient was prepared by using mixtures of Ce4 +-modified cordierite amorphous powder and oxide powders of MgO, Al2O3 and SiO2 as starting mat...The cordierite ceramic with a high strength and a low thermal expansion coefficient was prepared by using mixtures of Ce4 +-modified cordierite amorphous powder and oxide powders of MgO, Al2O3 and SiO2 as starting materials. The transformation procedure of the powders was analyzed by XRD method and the surface morphology of ceramics was examined by SEM method. The flexural strength was measured in a mechanical property testing machine using the Three-Point-Bending sample. Experimental results show that the ceramic added with 10%(mass fraction) of Ce4+-modified amorphous powder is composed ofα-cordierite and small amount of CeO2 particles, and has a porosity of 15% (volume fraction) and a flexural strength of 32.6 MPa when sintered at 1350℃for 3 h. It is suggested that this low-cost process is suitable for preparing the components such as supports of vehicle exhaust converters and diesel particulate trappers.展开更多
Effects of doping CeO2 and Er2O3 on the mechanical strength, thermal expansion coefficient, sintering temperature of TiO2-SiO2 ceramics were investigated. The experimental results and the microscopic analysis of SEM, ...Effects of doping CeO2 and Er2O3 on the mechanical strength, thermal expansion coefficient, sintering temperature of TiO2-SiO2 ceramics were investigated. The experimental results and the microscopic analysis of SEM, XRD, TG-DSC, FT-IR and TEM show that adding CeO2 and Er2O3 into TiO2-SiO2 ceramics can prohibit the growth of its crystal grains, make their size uniform and form them into a dense structure, which finally enhance its mechanical behaviors, and the lower thermal expansion coefficient that leads to an excellent property of thermal shock resistance. After the reforming TiO2-SiO2 ceramics doped by CeO2 was sintered at 1380℃, the bending strength reached to 83 MPa, and the thermal expansion coefficient was 9.8×10-6/℃within the temperature range of 25 ~ 800℃, which provides a promising basis of making equipped honeycomb catalyst of deNOx.展开更多
Gd2Zr207 has been considered as a promising thermal barrier coating candidate, but its toughness and thermal expansion coefficient （TEC） need to be improved. In this study, Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0, 0.1, 0.3, ...Gd2Zr207 has been considered as a promising thermal barrier coating candidate, but its toughness and thermal expansion coefficient （TEC） need to be improved. In this study, Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0, 0.1, 0.3, 0.5, 0.7） compounds were produced to improve the toughness and enlarge the TEC. Gd2Zr207 and Gd1.9Zr2.1O7.05 exhibited pyrochlore structure, while Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0.3, 0.5, 0.7） consisted of pyrochlore and t＇-ZrO2 phases. With increasing ZrO2 content, the pyrochlore in the compounds had decreased lattice parameter, and its ordering degree decreased when χ 〈 0.3, then it almost kept unchanged with higher ZrO2 content. Among the Gd2-xZr2 ＋xO7 ＋χ/2 ceramics investigated, the toughness of the compounds in- creased with increasing ZrO2 content, while Gd1.7Zr23O7.15 exhibited the largest TEC. The related mechanisms were discussed in detail.展开更多
Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxi...Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxidizing-free capacity[1–3].Nevertheless,grain growth,sintering and creep deformation at high operation temperatures are still serious problems for Al2O3f/Al2O3 ceramic matrix composites,which can lead to a reduction in the strength and damage tolerance[2].Moreover,Al2O3 can be corroded by the high temperature water vapor in combustion environments and yields volatile products,such as Al(OH)3[4].Consequently,environmental barrier coatings(EBCs)are necessary for Al2O3f/Al2O3 ceramic matrix composites,which can protect Al2O3f/Al2O3 CMC from high temperature and flowing combustion gas corrosion and thus increase the high temperature capability and the service life of components.展开更多
Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ce...Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics.Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance.However,the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application.Inspired by the high entropy effect,a novel rare earth monosilicate solid solution(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)was designed to improve the overall performance.The as-synthesized(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)shows very low thermal conductivity(1.07 W·m-1·K-1 at 600℃).Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties.The thermal expansion coefficient of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)can be decreased to(4.0–5.9)×10^(-6)K^(-1)due to severe lattice distortion and chemical bonding variation,which matches well with that of SiC((4.5–5.5)×10^(-6)K^(-1)).In addition,(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)presents good resistance to CMAS corrosion.The improved performance of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)highlights it as a promising environmental barrier coating candidate.展开更多
The thermal characteristic of cristobalite plays an important role in the application of casting industry. Because the phase transition of silica glass and cristobalite has low volume change, the block cristobalite ha...The thermal characteristic of cristobalite plays an important role in the application of casting industry. Because the phase transition of silica glass and cristobalite has low volume change, the block cristobalite had been manufactured by calcining fused silica ceramic, the XRD, SEM and thermal characteristics of the cristobalite had been tested. The result shows the formation of porous structure in the block cristobalite, and thermal expansion rate of the phase transition of β/αcristobalite reaches 1.5% at the temperature range of 250-290 ℃.展开更多
文摘The glass-ceramics were prepared with the spodumene mineral as the main raw material,and the effects of ZrO_(2)replacing TiO_(2)on the samples were systematically investigated.The results show that the substitution of ZrO_(2)for TiO_(2)is not conductive to precipitate𝛽β-quartz solid solution phase,but can improve the transparency and flexural strength of glass-ceramics.And the glass-ceramic with the highest visible light transmittance(87%)and flexural strength(231.80 MPa)exhibits an ultra-low thermal expansion of-0.028×10^(-7)K^(-1)in the region of 30-700℃.
基金Funded by National Natural Science Foundation of China(Nos.61704156,11847099 and 10974183).
文摘(ZrMg)xY2-2xMo3O12(x=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,and 1)ceramics have been synthesized to obtain less hygroscopicity and negative thermal expansion.With increasing the substitution of(ZrMg)^6+(ion radius 7.2×10^-11 m)for Y3+(ion radius 9×10^-11 m),the crystal water are reduced obviously.The linear thermal expansion coefficient is improved with increasing the content of(ZrMg)^6+.The material shows near zero thermal expansion(-0.12×10^-6 K^-1,430-870 K)with x=0.7.Meanwhile,ZrMgMo3O12 shows low non-hygroscopicity and negative thermal expansion,but low softening temperature.After substituting amount of Y^3+for(ZrMg)^6+in ZrMgMo3O12(x=0.8),the softening temperature increases remarkably(750 K to 830 K)and it presents near zero thermal expansion.
文摘Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after thermolysis specimens were heat treated at a temperature of 1400℃ for 10 h in nitrogen atmosphere. The thermal expansion coefficient of VT50-derived amorphous Si-C-N ceramic increases from 1.98×10-6/K at 400℃ to 3.09×10-6/K at 1000℃, of NCP200-derived amorphous Si-C-N ceramic increases from 2.35×10-6/K at 400℃ to 3.45×10-6/K at 1000℃, and of T2-l-derived amorphous Si-B-C-N ceramic increases from 2.08×10-6/K at 400℃ to 3.18×10-6/K at 1000℃. No glass transition for these amorphous ceramic materials was detected, indicating that as-thermolyzed precursor-derived Si-(B-)C-N ceramic materials are amorphous solids, but not glasses.
文摘Firstly,the relation between the coefficient of thermal expansion(CTE)and the volume fraction of TiO_(2) was investigated, and also the influence of relative density of ceramic on the CTE was studied.The results show that the volume fraction of TiO_(2) and the relative density both make influence on the CTE of ZrO_(2)-TiO_(2) ceramic.According to the results,the ZrO_(2)-TiO_(2)(volume fraction of TiO_(2) is 27%)ceramic die with the similar CTE(8.92×10^(-6) ℃^(-1))to Ti6Al4V was fabricated.Secondly,to evaluate the dimensional accuracy of the workpiece superplastically formed,the Ti6Al4V impression experiment was performed.The result shows that the dimensional inaccuracy of workpiece is 0.003.Thirdly,in order to evaluate the practicability,the experiment of superplastic forming Ti6Al4V using ZrO_(2)-TiO_(2) cylinder ceramic die was carried out.The Ti6Al4V cylinder shows good shape retention and surface quality,and high dimensional accuracy.The ceramic dies seem to be adequate for superplastic forming the high accuracy Ti6Al4V, and the trials have confirmed the potential of the ZrO_(2)-TiO_(2) ceramic die.
基金Project supported by the Ministry of Science and Technology of China (2006CB601104)
文摘With Al2O3, Dy2O3, and SiO2 as starting materials, the basic glass of Al2O3-Dy2O3-SiO2 system was prepared by conventional melting technology, and their thermal expansion coefficients （TECs） at different anneal time were investigated. TECs of the basic glass, which were heat-treated under different temperature, were also investigated. The result showed that TECs of the basic glass gradually approached a fixed value as the anneal time was extended, which suggested that most of the inner stress had been eliminated. After heat treatment, the contents of Dy2O3, Dy2Si2O7, and a new crystal increased up to 1200 ℃ and decreased below 1250 ℃, which was consistent with the TEC change of crystallized samples. This suggests that the crystal has a direct effect on TECs of the crystallized samples.
基金Project supported by the Ministry of Science and Technology of China (2006CB601104)
文摘Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3, and SiO2 were studied respectively. Experimental results showed that Dy2O3 and Al2O3 had a positive effect on the coefficient of thermal expansion of glass, whereas, SiO2 had a negative effect. The coefficient of thermal expansion of glass showed an apparent linear relation to the contents of these three raw materials, from which an estimation model was built, to calculate the coefficient of thermal expansion of sealing glass. Relative errors of the calculating results to testing results were no more than 2%, which suggested that the estimation model was reasonable. This study provides a good theory reference for the practical utilizing of this sealing material, through which a proper glass composition for good sealing could be easily found.
基金financial support for the XRPD experiments (proposals nr. 20200101 and 20210215)supported by the U.S. National Science Foundation through Grant CMMI-1902069
文摘High-entropy(HE)ultra-high temperature ceramics have the chance to pave the way for future applications propelling technology advantages in the fields of energy conversion and extreme environmental shielding.Among others,HE diborides stand out owing to their intrinsic anisotropic layered structure and ability to withstand ultra-high temperatures.Herein,we employed in-situ high-resolution synchrotron diffraction over a plethora of multicomponent compositions,with four to seven transition metals,with the intent of understanding the thermal lattice expansion following different composition or synthesis process.As a result,we were able to control the average thermal expansion(TE)from 1.3×10^(−6)to 6.9×10^(−6)K^(−1)depending on the combination of metals,with a variation of in-plane to out-of-plane TE ratio ranging from 1.5 to 2.8.
基金Project supported by National High Technology Research and Development Program of China (863 Program,2006AA02Z211)Nation-al Natural Science Foundation of China (20376034)Natural Science Foundation of Jiangsu Province (BK2006181)
文摘A preferable honeycomb ceramics of Al2TiO5-TiO2-SiO2 doped by CeO2 and Er2O3 with high performance was prepared by means of extrusion molding and the effects of CeO2 and Er2O3 on the mechanical strength, thermal stability, and sintering temperature of ATS ceramics were mainly investigated. The experimental results and the microscopic analysis by scanning electron microscope, X-ray powder diffxaction, and TG-DSC showed that adding CeO2 and Er2O3 into ATS could prohibit the growth of their crystal grains and make their size uniform, which finally decrease its sintering temperature, and also enhance its mechanical performance as well as thermal stability. After the reforming, ATS doped by 0.5% CeO2 ＋0.5% Er2O3 was sintered at 1250 ℃, its bending strength reached to 177A MPa and thermal expansion coefficient was 3.8 ~ 10^-6/℃ at 25 - 1000℃, which provided a promising basis of making monolithic honeycomb catalyst of deNOx.
基金Project supported by New Century Excellent Talents in University (NCET), 2004
文摘The cordierite ceramic with a high strength and a low thermal expansion coefficient was prepared by using mixtures of Ce4 +-modified cordierite amorphous powder and oxide powders of MgO, Al2O3 and SiO2 as starting materials. The transformation procedure of the powders was analyzed by XRD method and the surface morphology of ceramics was examined by SEM method. The flexural strength was measured in a mechanical property testing machine using the Three-Point-Bending sample. Experimental results show that the ceramic added with 10%(mass fraction) of Ce4+-modified amorphous powder is composed ofα-cordierite and small amount of CeO2 particles, and has a porosity of 15% (volume fraction) and a flexural strength of 32.6 MPa when sintered at 1350℃for 3 h. It is suggested that this low-cost process is suitable for preparing the components such as supports of vehicle exhaust converters and diesel particulate trappers.
基金Project supported by the National Natural Science Foundation of China (20376034) Social Development Fund of Jiangsu Province (BS2005053)
文摘Effects of doping CeO2 and Er2O3 on the mechanical strength, thermal expansion coefficient, sintering temperature of TiO2-SiO2 ceramics were investigated. The experimental results and the microscopic analysis of SEM, XRD, TG-DSC, FT-IR and TEM show that adding CeO2 and Er2O3 into TiO2-SiO2 ceramics can prohibit the growth of its crystal grains, make their size uniform and form them into a dense structure, which finally enhance its mechanical behaviors, and the lower thermal expansion coefficient that leads to an excellent property of thermal shock resistance. After the reforming TiO2-SiO2 ceramics doped by CeO2 was sintered at 1380℃, the bending strength reached to 83 MPa, and the thermal expansion coefficient was 9.8×10-6/℃within the temperature range of 25 ~ 800℃, which provides a promising basis of making equipped honeycomb catalyst of deNOx.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.51501127 and 51375332)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20120032110031)
文摘Gd2Zr207 has been considered as a promising thermal barrier coating candidate, but its toughness and thermal expansion coefficient （TEC） need to be improved. In this study, Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0, 0.1, 0.3, 0.5, 0.7） compounds were produced to improve the toughness and enlarge the TEC. Gd2Zr207 and Gd1.9Zr2.1O7.05 exhibited pyrochlore structure, while Gd2-xZr2 ＋xO7 ＋χ/2 （χ = 0.3, 0.5, 0.7） consisted of pyrochlore and t＇-ZrO2 phases. With increasing ZrO2 content, the pyrochlore in the compounds had decreased lattice parameter, and its ordering degree decreased when χ 〈 0.3, then it almost kept unchanged with higher ZrO2 content. Among the Gd2-xZr2 ＋xO7 ＋χ/2 ceramics investigated, the toughness of the compounds in- creased with increasing ZrO2 content, while Gd1.7Zr23O7.15 exhibited the largest TEC. The related mechanisms were discussed in detail.
基金financial supported by the National Natural Science Foundation of China(Nos.51672064 and U1435206).
文摘Al2O3f/Al2O3 ceramic matrix composites(CMC)are promising candidate materials of blades and combustor liners of future gas turbines in light of their higher temperature capability,higher environmental stability and oxidizing-free capacity[1–3].Nevertheless,grain growth,sintering and creep deformation at high operation temperatures are still serious problems for Al2O3f/Al2O3 ceramic matrix composites,which can lead to a reduction in the strength and damage tolerance[2].Moreover,Al2O3 can be corroded by the high temperature water vapor in combustion environments and yields volatile products,such as Al(OH)3[4].Consequently,environmental barrier coatings(EBCs)are necessary for Al2O3f/Al2O3 ceramic matrix composites,which can protect Al2O3f/Al2O3 CMC from high temperature and flowing combustion gas corrosion and thus increase the high temperature capability and the service life of components.
基金This work was financially supported by Guangdong Basic and Applied Basic Research Foundation for Distinguished Young Scholars(Grant No.2021B1515020083)Guang Dong Basic and Applied Basic Research Foundation for Young Scholars(Grant No.21201910240002803)+1 种基金Shenzhen Science and Technology Program(Grant Nos.GXWD20201231165807008,20200831172254001)Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.2021qntd10).
文摘Low thermal conductivity,compatible thermal expansion coefficient,and good calcium–magnesium–aluminosilicate(CMAS)corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics.Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance.However,the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application.Inspired by the high entropy effect,a novel rare earth monosilicate solid solution(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)was designed to improve the overall performance.The as-synthesized(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)shows very low thermal conductivity(1.07 W·m-1·K-1 at 600℃).Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties.The thermal expansion coefficient of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)can be decreased to(4.0–5.9)×10^(-6)K^(-1)due to severe lattice distortion and chemical bonding variation,which matches well with that of SiC((4.5–5.5)×10^(-6)K^(-1)).In addition,(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)presents good resistance to CMAS corrosion.The improved performance of(Ho_(0.25)Lu_(0.25)Yb_(0.25)Eu_(0.25))_(2)SiO_(5)highlights it as a promising environmental barrier coating candidate.
基金Project supported by the State Key Program of National Natural Science of China(No. 41130746)
文摘The thermal characteristic of cristobalite plays an important role in the application of casting industry. Because the phase transition of silica glass and cristobalite has low volume change, the block cristobalite had been manufactured by calcining fused silica ceramic, the XRD, SEM and thermal characteristics of the cristobalite had been tested. The result shows the formation of porous structure in the block cristobalite, and thermal expansion rate of the phase transition of β/αcristobalite reaches 1.5% at the temperature range of 250-290 ℃.
