The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance ...The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than 4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 MPa, but that of the samples without CaO is only 60 MPa. Fracture toughness is improved obviously by CaO doping, the samples doped with 2% CaO have the maximum fracture toughness of 2.12 MPa ·m1/2 , which is about two times of that of the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.展开更多
Zirconium carbide(ZrC)nanoparticles with an average size of 5.6 nm were synthesized through laser fragmentation(LF)from as-received 20-60 nm ZrC particles,and LF-ZrC nanoparticle dispersion-strengthened tungsten(LF-WZ...Zirconium carbide(ZrC)nanoparticles with an average size of 5.6 nm were synthesized through laser fragmentation(LF)from as-received 20-60 nm ZrC particles,and LF-ZrC nanoparticle dispersion-strengthened tungsten(LF-WZC)samples were fabricated by spark plasma sintering method.The average grain size of LF-WZC is 1.91μm and most ZrC particles in LF-WZC are smaller than 10 nm.LF-WZC exhibits finer grain size,higher yield strength and hardness but lower ductility as compared with W-ZrC samples using as-received ZrC(WZC).The results showed that finer ZrC nanoparticles dispersed in tungsten can enhance the strength by hindering the motion of dislocations,but they may also introduce stress concentra-tion and thus reduce the ductility.The thermal shock resistance of the WZC and LF-WZC samples was investigated using an electron beam device.The LF-WZC sample also exhibits a higher cracking threshold(0.33-0.44 GW·m^(−2))than WZC(0.22-0.33 GW·m^(−2))at room temperature.The enhanced thermal shock resistance of LF-WZC could be attributed to its high yield strength.展开更多
The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance(TSR) of ultra-high temperature ceramics(UHTCs) are studied by investigating the TS...The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance(TSR) of ultra-high temperature ceramics(UHTCs) are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.展开更多
Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the ...Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si_2 BC_3 N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength(532.1 MPa) and fracture toughness(6.66 MPa m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.The enhanced properties should be attributed to:(1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation;(2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the "pull out" of MWCNTs.展开更多
Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics d...Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics designed in this study are expected to be used as thermal storage materials in solar thermal power generation based on the high density and excellent thermal shock resistance.The influences of calcined bauxite addition and sintering temperature on the microstructures,phase compositions,and physical properties of the samples were investigated.Results demonstrated that the introduction of calcined bauxite containing two bonding phases greatly reduced the lowest sintering temperature to 1400℃.The SiC-mullite Al2O3 composite with 40 wt%calcined bauxite sintered at 1500℃exhibited optimum performance.The density and bending strength were 2.27 g·cm^-3 and 77.05 MPa.The bending strength increased by 24.58%and no cracks were observed after 30 thermal shock cycles,while general clay would reduce the thermal shock resistance of SiC.The SiC-mullite-Al2O3 composites with satisfied performance are expected to be used as thermal storage materials in solar thermal power generation systems.展开更多
In this paper,a high-yield Hf-modified SiHfBOC ceramic precursor was developed,and a high-pressure assisted impregnation pyrolysis method was proposed to achieve the preparation of 3D PyC–Cf/SiHfBOC composites.This h...In this paper,a high-yield Hf-modified SiHfBOC ceramic precursor was developed,and a high-pressure assisted impregnation pyrolysis method was proposed to achieve the preparation of 3D PyC–Cf/SiHfBOC composites.This high-pressure assisted impregnation method significantly improves impregnation filling effect of the precursor in and between fiber bundles compared to dozens of traditional impregnation cycles.After undergoing just 9 precursor infiltration pyrolysis(PIP)cycles,the composites achieved relative density of approximately 90%and density of 1.64 g/cm^(3).The critical temperature difference of the 3D PyC–Cf/SiHfBOC composites after the shock of room temperature(RT)–1000℃is as high as 650℃,which is twice that of traditional ceramic materials,showing good thermal shock resistance.Under the effect of Hf modification,a dense HfO_(2)–SiO_(2)oxide layer(thickness of 93μm)was formed in situ on the surface of the 3D PyC–Cf/SiHfBOC composites,effectively preventing further erosion of the composite matrix by high-temperature oxidation gas.Even in the ultra-high-temperature oxygen-containing environment at 1800℃,it still exhibits an excellent non-ablative result(with a linear ablation rate of 0.83×10^(−4)mm/s).This work not only enriches the basic research on lightweight ultra-high-temperature ceramic composites converted from Hf ceramic precursors,but also provides strong technical support for their applications in ultra-high-temperature non-ablative thermal protection materials for high-speed aircraft.展开更多
The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC conc...The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC concen-tration increased from 0 to 22.9vol.%,the tensile strength of pitch-based C/C(Carbon/Carbon) composites initially in-creased and then decreased,so was the tensile modulus.The coefficients of thermal expansion(CTE) were in the sequence of 10.2vol.%<0<22.9vol.%in Z direction.Under the same temperature conditions,PyC layer had a positive-going influence on the TC of the C/C composite,the composite with 22.9vol.%PyC concentrations possessed the highest TC value.The thermal shock resistance of the material with 10.2vol.%PyC concentrations showed the highest value.It is logical to conclude that by adding the a suitable PyC concentration into the carbon fabrics,thermo- mechanical properties,the major concerns for the safety design of load-bearing structural parts,can be tailored,which increase the reliability of pitch-based C/C composites as a structure unit.展开更多
To improve oxidation resistance of carbon/carbon (C/C) composites, a SiC/SiC-MoSi2-ZrB2 double-layer ceramic coating was prepared on C/C composites by two-step pack cementation. The phase compositions and microstruc...To improve oxidation resistance of carbon/carbon (C/C) composites, a SiC/SiC-MoSi2-ZrB2 double-layer ceramic coating was prepared on C/C composites by two-step pack cementation. The phase compositions and microstructures of as-prepared multilayer coating were characterized by X-ray diffraction and scanning electron microscopy. The oxidation resistance at 1773 K and the effect of thermal shock between 1773 K and room temperature on mechanical performance of coated specimens were investigated. The results show that the SiC/SiC-MoSi2-ZrB2 coating exhibits dense structure and is composed of SiC, Si, MoSi2 and ZrB2. It can protect C/C composites from oxidation at 1773 K for more than 510 h with weight loss of 0.5%. The excellent anti-oxidation performance of the coating is due to the formation of SiO2-ZrSiO4 complex glassy film. The coating can also endure the thermal shocks between 1773 K and room temperature for 20 times with residual flexural strength of 86.1%.展开更多
Conventional MgO-C bricks(graphite content>14 wt.%)produce a great deal of greenhouse gas emission,while low-carbon MgO-C bricks have serious thermal shock resistance during high-temperature service.To enhance the ...Conventional MgO-C bricks(graphite content>14 wt.%)produce a great deal of greenhouse gas emission,while low-carbon MgO-C bricks have serious thermal shock resistance during high-temperature service.To enhance the high-temperature mechanical property and thermal shock resistance of low-carbon MgO-C bricks,a novel route of introducing ZrSiO_(4) powder into low-carbon MgO-C bricks was reported in such refractories with 2 wt.% flaky graphite.The results indicate that the low-carbon MgO-C brick with 0.5 wt.%ZrSiO_(4) addition has the maximum hot modulus of rupture at 1400℃ and the corresponding specimen fired in the carbon embedded atmosphere has the maximum residual strength ratio(98.6%)after three thermal shock cycles.It is found that some needle-like AlON and plate-like Al_(2)O_(3)-ZrO_(2) composites were in situ formed in the matrices after the low-carbon MgO-C bricks were coked at 1400℃,which can enhance the high-temperature mechanical property and thermal shock resistance due to the effect of fiber toughening and particle toughening.Moreover,CO_(2) emission of the newly developed low-carbon MgO-C bricks is reduced by 58.3% per ton steel after using them as the working lining of a 90 t vacuum oxygen decarburization ladle.展开更多
The in-situ synthesized mullite bonded SiC ceramics for solar thermal tower plant were prepared from Silicon carbide (SIC), manufactured aluminum hydroxide (Al(OH)3) and Suzhou kaolin via semi-dry pressing and p...The in-situ synthesized mullite bonded SiC ceramics for solar thermal tower plant were prepared from Silicon carbide (SIC), manufactured aluminum hydroxide (Al(OH)3) and Suzhou kaolin via semi-dry pressing and pressureless firing. The results indicate that sample B3 (designed mullite content 15 wt%) fired at 1 400 ℃ exhibited optimal performance with a bending strength of 97.41 MPa. Sample B3 can withstand 30-cycles thermal shock without cracking (wind cooling from 1 100 ℃ to room temperature), and the bending strength after thermal shock decreased by 17.92%. When the service temperature is 600℃, the thermal diffusivity, specific heat capacity, thermal conductivity and heat capacity are 6.48× 10-2 cm:.s-1, 0.69 kJ·kg-1. K-1, 9.62 W·m-1·K-1 and 977.76 kJ·kg-1, respectively. The XRD and SEM results show that SiC, mullite, or-quartz, and tridymite are connected closely, which gives the material a good bending strength. After 30-time thermal shock cycles, the structure of samples becomes loose. SiC grains are intersectingly arranged with rodshape mullite, exhibiting a favorable thermal shock resistance. The addition of Al(OH)3 and Suzhou kaolin can accelerate the synthesis of mullite, thus to reduce the firing temperature effectively. The volume effect of tfidymite is relatively small, improving the thermal shock resistance of materials. A higher designed muUite content yields a lower loss rate of bending strength. The mullite content should not be more than 15 wt% or else the bending strength would be diminished.展开更多
基金Project(2005CB623703) supported by the National Basic Research Program of China
文摘The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than 4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 MPa, but that of the samples without CaO is only 60 MPa. Fracture toughness is improved obviously by CaO doping, the samples doped with 2% CaO have the maximum fracture toughness of 2.12 MPa ·m1/2 , which is about two times of that of the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.
基金This work was financially supported by the National Key R&D Program of China(Grant Nos.2017YFE0302400,2017YFA0402800,and 2017YFE0300403)the National Natural Science Foundation of China(Grant Nos.51671184,11735015,51801203,and 11575231).
文摘Zirconium carbide(ZrC)nanoparticles with an average size of 5.6 nm were synthesized through laser fragmentation(LF)from as-received 20-60 nm ZrC particles,and LF-ZrC nanoparticle dispersion-strengthened tungsten(LF-WZC)samples were fabricated by spark plasma sintering method.The average grain size of LF-WZC is 1.91μm and most ZrC particles in LF-WZC are smaller than 10 nm.LF-WZC exhibits finer grain size,higher yield strength and hardness but lower ductility as compared with W-ZrC samples using as-received ZrC(WZC).The results showed that finer ZrC nanoparticles dispersed in tungsten can enhance the strength by hindering the motion of dislocations,but they may also introduce stress concentra-tion and thus reduce the ductility.The thermal shock resistance of the WZC and LF-WZC samples was investigated using an electron beam device.The LF-WZC sample also exhibits a higher cracking threshold(0.33-0.44 GW·m^(−2))than WZC(0.22-0.33 GW·m^(−2))at room temperature.The enhanced thermal shock resistance of LF-WZC could be attributed to its high yield strength.
基金Project supported by the National Natural Science Foundation of China(Nos.11472066 and11172336)the Chongqing Natural Science Foundation(No.cstc2013jcyj A50018)+1 种基金the Program for New Century Excellent Talents in University(No.ncet-13-0634)the Fundamental Research Funds for the Central Universities(Nos.CDJZR13240021 and CDJZR14328801)
文摘The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance(TSR) of ultra-high temperature ceramics(UHTCs) are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.
基金supported financially by National Natural Science Foundation of China (NSFC, Grant Nos. 51702065 and 51621091)China Postdoctoral Science Foundation (Grant No. 2018M631924)
文摘Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si_2 BC_3 N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength(532.1 MPa) and fracture toughness(6.66 MPa m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.The enhanced properties should be attributed to:(1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation;(2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the "pull out" of MWCNTs.
基金Funded by the National Key Research and Development Program of Science and Technology of China(No.2018YFB1501002).
文摘Mullite and corundum co-bonded SiC-based composite ceramics(SiC-mullite-Al2O3)were prepared by using SiC,calcined bauxite and kaolin via pressureless carbon-buried sintering.The low-cost SiC-based composite ceramics designed in this study are expected to be used as thermal storage materials in solar thermal power generation based on the high density and excellent thermal shock resistance.The influences of calcined bauxite addition and sintering temperature on the microstructures,phase compositions,and physical properties of the samples were investigated.Results demonstrated that the introduction of calcined bauxite containing two bonding phases greatly reduced the lowest sintering temperature to 1400℃.The SiC-mullite Al2O3 composite with 40 wt%calcined bauxite sintered at 1500℃exhibited optimum performance.The density and bending strength were 2.27 g·cm^-3 and 77.05 MPa.The bending strength increased by 24.58%and no cracks were observed after 30 thermal shock cycles,while general clay would reduce the thermal shock resistance of SiC.The SiC-mullite-Al2O3 composites with satisfied performance are expected to be used as thermal storage materials in solar thermal power generation systems.
基金the National Natural Science Foundation of China(No.52032003)National Natural Science Foundation of China(Nos.51972082,52102093,and 52172041)+1 种基金Postdoctoral Research Foundation of China(No.2021M690817)the Science Foundation of National Key Laboratoryof Science and Technology on Advanced Composites in Special Environments.
文摘In this paper,a high-yield Hf-modified SiHfBOC ceramic precursor was developed,and a high-pressure assisted impregnation pyrolysis method was proposed to achieve the preparation of 3D PyC–Cf/SiHfBOC composites.This high-pressure assisted impregnation method significantly improves impregnation filling effect of the precursor in and between fiber bundles compared to dozens of traditional impregnation cycles.After undergoing just 9 precursor infiltration pyrolysis(PIP)cycles,the composites achieved relative density of approximately 90%and density of 1.64 g/cm^(3).The critical temperature difference of the 3D PyC–Cf/SiHfBOC composites after the shock of room temperature(RT)–1000℃is as high as 650℃,which is twice that of traditional ceramic materials,showing good thermal shock resistance.Under the effect of Hf modification,a dense HfO_(2)–SiO_(2)oxide layer(thickness of 93μm)was formed in situ on the surface of the 3D PyC–Cf/SiHfBOC composites,effectively preventing further erosion of the composite matrix by high-temperature oxidation gas.Even in the ultra-high-temperature oxygen-containing environment at 1800℃,it still exhibits an excellent non-ablative result(with a linear ablation rate of 0.83×10^(−4)mm/s).This work not only enriches the basic research on lightweight ultra-high-temperature ceramic composites converted from Hf ceramic precursors,but also provides strong technical support for their applications in ultra-high-temperature non-ablative thermal protection materials for high-speed aircraft.
文摘The effect of pyrocarbon(PyC) concentration on the thermal physical and mechanical properties of quasi 3dimensional carbon fiber fabrics reinforced pitch-based carbon matrix composites was investigated.As the PyC concen-tration increased from 0 to 22.9vol.%,the tensile strength of pitch-based C/C(Carbon/Carbon) composites initially in-creased and then decreased,so was the tensile modulus.The coefficients of thermal expansion(CTE) were in the sequence of 10.2vol.%<0<22.9vol.%in Z direction.Under the same temperature conditions,PyC layer had a positive-going influence on the TC of the C/C composite,the composite with 22.9vol.%PyC concentrations possessed the highest TC value.The thermal shock resistance of the material with 10.2vol.%PyC concentrations showed the highest value.It is logical to conclude that by adding the a suitable PyC concentration into the carbon fabrics,thermo- mechanical properties,the major concerns for the safety design of load-bearing structural parts,can be tailored,which increase the reliability of pitch-based C/C composites as a structure unit.
基金supported by the National Natural Science Foundation of China(Nos.50902111 and 51272213)NPU Foundation for Fundamental Researchthe Research Fund of the State Key Laboratory of Solidification Processing(NWPU),China(No.73-QP-2010)
文摘To improve oxidation resistance of carbon/carbon (C/C) composites, a SiC/SiC-MoSi2-ZrB2 double-layer ceramic coating was prepared on C/C composites by two-step pack cementation. The phase compositions and microstructures of as-prepared multilayer coating were characterized by X-ray diffraction and scanning electron microscopy. The oxidation resistance at 1773 K and the effect of thermal shock between 1773 K and room temperature on mechanical performance of coated specimens were investigated. The results show that the SiC/SiC-MoSi2-ZrB2 coating exhibits dense structure and is composed of SiC, Si, MoSi2 and ZrB2. It can protect C/C composites from oxidation at 1773 K for more than 510 h with weight loss of 0.5%. The excellent anti-oxidation performance of the coating is due to the formation of SiO2-ZrSiO4 complex glassy film. The coating can also endure the thermal shocks between 1773 K and room temperature for 20 times with residual flexural strength of 86.1%.
基金Enterprise Research and Development Project of Beijing Lirr High-Temperature Materials Co.,Ltd.(2020-02)Key Scientific Research Project for Universities and Colleges in Henan Province(19A430028)+1 种基金the Excellent Youth Research Project of Anhui Province(2022AH030135)the PhD Research Funding of Suzhou University(2021BSK041).
文摘Conventional MgO-C bricks(graphite content>14 wt.%)produce a great deal of greenhouse gas emission,while low-carbon MgO-C bricks have serious thermal shock resistance during high-temperature service.To enhance the high-temperature mechanical property and thermal shock resistance of low-carbon MgO-C bricks,a novel route of introducing ZrSiO_(4) powder into low-carbon MgO-C bricks was reported in such refractories with 2 wt.% flaky graphite.The results indicate that the low-carbon MgO-C brick with 0.5 wt.%ZrSiO_(4) addition has the maximum hot modulus of rupture at 1400℃ and the corresponding specimen fired in the carbon embedded atmosphere has the maximum residual strength ratio(98.6%)after three thermal shock cycles.It is found that some needle-like AlON and plate-like Al_(2)O_(3)-ZrO_(2) composites were in situ formed in the matrices after the low-carbon MgO-C bricks were coked at 1400℃,which can enhance the high-temperature mechanical property and thermal shock resistance due to the effect of fiber toughening and particle toughening.Moreover,CO_(2) emission of the newly developed low-carbon MgO-C bricks is reduced by 58.3% per ton steel after using them as the working lining of a 90 t vacuum oxygen decarburization ladle.
基金Funded by the National Basic Research Program(973 Program)(No.2010CB227105)
文摘The in-situ synthesized mullite bonded SiC ceramics for solar thermal tower plant were prepared from Silicon carbide (SIC), manufactured aluminum hydroxide (Al(OH)3) and Suzhou kaolin via semi-dry pressing and pressureless firing. The results indicate that sample B3 (designed mullite content 15 wt%) fired at 1 400 ℃ exhibited optimal performance with a bending strength of 97.41 MPa. Sample B3 can withstand 30-cycles thermal shock without cracking (wind cooling from 1 100 ℃ to room temperature), and the bending strength after thermal shock decreased by 17.92%. When the service temperature is 600℃, the thermal diffusivity, specific heat capacity, thermal conductivity and heat capacity are 6.48× 10-2 cm:.s-1, 0.69 kJ·kg-1. K-1, 9.62 W·m-1·K-1 and 977.76 kJ·kg-1, respectively. The XRD and SEM results show that SiC, mullite, or-quartz, and tridymite are connected closely, which gives the material a good bending strength. After 30-time thermal shock cycles, the structure of samples becomes loose. SiC grains are intersectingly arranged with rodshape mullite, exhibiting a favorable thermal shock resistance. The addition of Al(OH)3 and Suzhou kaolin can accelerate the synthesis of mullite, thus to reduce the firing temperature effectively. The volume effect of tfidymite is relatively small, improving the thermal shock resistance of materials. A higher designed muUite content yields a lower loss rate of bending strength. The mullite content should not be more than 15 wt% or else the bending strength would be diminished.