Zircon （mesh size ≤ 44μm ） and carbon black （mesh size ≤30μm ） were used as the starting materials, weighed with re（zircon） ： re（carbon black） of 100 ： 20 and mixed fully. The specimens with the diameter...Zircon （mesh size ≤ 44μm ） and carbon black （mesh size ≤30μm ） were used as the starting materials, weighed with re（zircon） ： re（carbon black） of 100 ： 20 and mixed fully. The specimens with the diameter of 20ram and length of 5ram were prepared by pressing at 100 MPa, then dried at 120℃ for 12h, put into a furnace with 1. 5L ·min^-1 argon gas and fired at 1450℃, 1500℃, 1550℃, 1600℃ and 1650℃ for 4h, respectively. The chemical composition, phase composition and microstructure of the specimens were studied by chemical analysis, X-ray diffraction and scanning electronic microscope, and the carbothermal reduction reaction process was discussed by thermodynamic analysis. The results showed that the ZrO2-SiC composite could be synthesized by carbothermal reduction reaction using zircon and carbon black as the starting materials in argon atmosphere. The composite with different composition was obtained by controlling the firing temperature and partial pressure of CO gas. The proper temperature to synthesize ZrO2-SiC composite was 1600℃ in this experiment.展开更多
Ultrahigh-temperature ceramics were added to C/C composites to meet their application requirement in a high-temperature oxidizing environment. C/C-ZrB2-SiC composites were fabricated by high-solid-loading slurry impre...Ultrahigh-temperature ceramics were added to C/C composites to meet their application requirement in a high-temperature oxidizing environment. C/C-ZrB2-SiC composites were fabricated by high-solid-loading slurry impregnation with polymer infiltration and pyrolysis. The dispersion and rheological behavior of ZrB2 slurry and the microstructural, mechanical, and ablation properties of the C/C-ZrB2-SiC composites were investigated. Results indicated that a well-dispersed and low-viscosity ZrB2 slurry was obtained using 0.40 wt.% polyethyleneimine as a dispersant at pH 5. Ceramics were uniformly distributed in the short-cut fiber layer and needle-punched area. The flexural strength of the C/C-ZrB2-SiC composites was 309.30 MPa. The composites exhibited satisfactory ablation resistance under the oxyacetylene flame of 2500℃, and the mass and linear ablation rates were 0.40 mg/s and 0.91 μm/s, respectively. A continuous and compact Zr O2 layer, which could effectively reduce the diffusion rate of oxygen and protect the composites from being ablated, was formed.展开更多
The partially stabilized ZrO2 (PSZ) particles were introduced into TiB2 ceramics to improve its density and mechanical properties. The results show that the addition of PSZ is very effective not only in bettering the ...The partially stabilized ZrO2 (PSZ) particles were introduced into TiB2 ceramics to improve its density and mechanical properties. The results show that the addition of PSZ is very effective not only in bettering the sinterability but also in enhancing the flexural strength and fracture toughness of TiB2.展开更多
The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding witho...The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding without any amorphous glassy phase, such the SiO2 structure. Based on the fractography and the observation of crack propagation path from indentation, it is concluded that the toughening of such composite at room temperature can be attributed to the high interfacial binding energy, the refinement of the MoSi2 matrix and the deflection and bridging behavior in the crack propagation.展开更多
The utilization of metal oxide‐zeolite catalysts in the syngas‐to‐olefin reaction is a promising strategy for producing C_(2)–C_(4) olefins from non‐petroleum resources.However,the effect of the crystal phase of ...The utilization of metal oxide‐zeolite catalysts in the syngas‐to‐olefin reaction is a promising strategy for producing C_(2)–C_(4) olefins from non‐petroleum resources.However,the effect of the crystal phase of metal oxides on the catalytic activity of these oxides is still ambiguous.Herein,typical metal oxides(ZnO/ZrO_(2))with different crystal phases(monoclinic(m‐ZrO_(2))and tetragonal(t‐ZrO_(2)))were employed for syngas conversion.The(ZnO/m‐ZrO_(2)+SAPO‐34)composite catalyst exhibited 80.5%selectivity for C_(2)–C_(4) olefins at a CO conversion of 27.9%,where the results are superior to those(CO conversion of 16.4%and C_(2)–C_(4) olefin selectivity of 76.1%)obtained over(ZnO/t‐ZrO_(2)+SAPO‐34).The distinct differences are ascribed to the larger number of hydroxyl groups,Lewis acid sites,and oxygen defects in ZnO/m‐ZrO_(2) compared to ZnO/t‐ZrO_(2).These features result in the formation of more formate and methoxy intermediate species on the ZnO/m‐ZrO_(2) oxides during syngas conversion,followed by the formation of more light olefins over SAPO‐34.The present findings provide useful information for the design of highly efficient ZrO_(2)‐based catalysts for syngas conversion.展开更多
Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity ...Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity and cracks were not observed at weld interfaces of all the joints. Penetration of filler material in to voids and pores existing in the Cf-SiC composites was observed. Average shear strength of 25.7 MPa was achieved for joints of Cf-SiC composites. By incorporation of Cf-SiC(CVD) ground short fibre reinforcement the(ZrB_2-SiC-B_4C-YAG) composite was machinable with tungsten carbide tool. The joint and machined composites were resistance to oxidation and thermal shock when exposed to the oxy-propane flame at 2300℃ for 300s. The combination of(ZrB_2-SiC-B_4C-YAG) and Cf-SiC based composites can be used for making parts like thermal protection system or nozzles for high temperature applications.展开更多
Phase pure ZrB2-SiC composite powders were prepared after 1 450℃/3 h via carbothermal reduction route,by using ZrSiO4,B2O3 and carbon as the raw materials.The influences of firing temperature as well as the type and ...Phase pure ZrB2-SiC composite powders were prepared after 1 450℃/3 h via carbothermal reduction route,by using ZrSiO4,B2O3 and carbon as the raw materials.The influences of firing temperature as well as the type and amount of additive on the phase composition of final products were detailedly investigated.The results indicated that the onset formation temperature of ZrB2-SiC was reduced to 1 400℃by the present conditions,and oxide additive（including CoSO4·7H2O,Y2O3 and TiO2）was effective in enhancing the decomposition of raw ZrSiO4,therefore accelerating the synthesis of ZrB2-SiC.Moreover,microstructural observation showed that the as-prepared ZrB2 and SiC respectively had well-defined hexagonal columnar and fibrous morphology.Furthermore,the methodology of back-propagation artificial neural networks（BP-ANNs）was adopted to establish a model for predicting the reaction extent（e g,the content of ZrB2-SiC in final product）in terms of various processing conditions.The results predicted by the as-established BP-ANNs model matched well with that of testing experiment（with a mean square error in 10^（-3） degree）,verifying good effectiveness of the proposed strategy.展开更多
Effects of interlayer composition on bonding strength and interfacial microstructure of green joined CePO_4-ZrO_2 ceramics were studied. Green bodies of 25%CePO_4/ZrO_2 and ZrO_2 ceramics were joined by using interlay...Effects of interlayer composition on bonding strength and interfacial microstructure of green joined CePO_4-ZrO_2 ceramics were studied. Green bodies of 25%CePO_4/ZrO_2 and ZrO_2 ceramics were joined by using interlayer composed of CePO_4 and ZrO_2 at 1450 ℃ for 120 min without applied pressure.The effects of CePO_4/(CePO_4+ZrO_2) ratio on the bond strength of the joints were investigated. Under the experimental conditions, the grain size of the particles grown in the joint is smaller than those in joined ceramics. The microstructure of the joint is more homogeneous than that of the matrix and without obvious cracks, pores and other defects.展开更多
文摘Zircon （mesh size ≤ 44μm ） and carbon black （mesh size ≤30μm ） were used as the starting materials, weighed with re（zircon） ： re（carbon black） of 100 ： 20 and mixed fully. The specimens with the diameter of 20ram and length of 5ram were prepared by pressing at 100 MPa, then dried at 120℃ for 12h, put into a furnace with 1. 5L ·min^-1 argon gas and fired at 1450℃, 1500℃, 1550℃, 1600℃ and 1650℃ for 4h, respectively. The chemical composition, phase composition and microstructure of the specimens were studied by chemical analysis, X-ray diffraction and scanning electronic microscope, and the carbothermal reduction reaction process was discussed by thermodynamic analysis. The results showed that the ZrO2-SiC composite could be synthesized by carbothermal reduction reaction using zircon and carbon black as the starting materials in argon atmosphere. The composite with different composition was obtained by controlling the firing temperature and partial pressure of CO gas. The proper temperature to synthesize ZrO2-SiC composite was 1600℃ in this experiment.
基金Project(GFZX0101040101-2012C20X) supported by the National Basic Research Program of ChinaProject(2017JJ2320) supported by the Natural Science Foundation of Hunan Province,China
文摘Ultrahigh-temperature ceramics were added to C/C composites to meet their application requirement in a high-temperature oxidizing environment. C/C-ZrB2-SiC composites were fabricated by high-solid-loading slurry impregnation with polymer infiltration and pyrolysis. The dispersion and rheological behavior of ZrB2 slurry and the microstructural, mechanical, and ablation properties of the C/C-ZrB2-SiC composites were investigated. Results indicated that a well-dispersed and low-viscosity ZrB2 slurry was obtained using 0.40 wt.% polyethyleneimine as a dispersant at pH 5. Ceramics were uniformly distributed in the short-cut fiber layer and needle-punched area. The flexural strength of the C/C-ZrB2-SiC composites was 309.30 MPa. The composites exhibited satisfactory ablation resistance under the oxyacetylene flame of 2500℃, and the mass and linear ablation rates were 0.40 mg/s and 0.91 μm/s, respectively. A continuous and compact Zr O2 layer, which could effectively reduce the diffusion rate of oxygen and protect the composites from being ablated, was formed.
文摘The partially stabilized ZrO2 (PSZ) particles were introduced into TiB2 ceramics to improve its density and mechanical properties. The results show that the addition of PSZ is very effective not only in bettering the sinterability but also in enhancing the flexural strength and fracture toughness of TiB2.
基金the National Natural Science Foundation of China (No. 59895150-04-02).
文摘The in situ synthesized MoSi2-SiC composite is proved to be of higher fracture toughness than the monolithic MoSi2. The TEM and HREM study reveals that the interface between MoSi2/SiC is of direct atomic bonding without any amorphous glassy phase, such the SiO2 structure. Based on the fractography and the observation of crack propagation path from indentation, it is concluded that the toughening of such composite at room temperature can be attributed to the high interfacial binding energy, the refinement of the MoSi2 matrix and the deflection and bridging behavior in the crack propagation.
文摘The utilization of metal oxide‐zeolite catalysts in the syngas‐to‐olefin reaction is a promising strategy for producing C_(2)–C_(4) olefins from non‐petroleum resources.However,the effect of the crystal phase of metal oxides on the catalytic activity of these oxides is still ambiguous.Herein,typical metal oxides(ZnO/ZrO_(2))with different crystal phases(monoclinic(m‐ZrO_(2))and tetragonal(t‐ZrO_(2)))were employed for syngas conversion.The(ZnO/m‐ZrO_(2)+SAPO‐34)composite catalyst exhibited 80.5%selectivity for C_(2)–C_(4) olefins at a CO conversion of 27.9%,where the results are superior to those(CO conversion of 16.4%and C_(2)–C_(4) olefin selectivity of 76.1%)obtained over(ZnO/t‐ZrO_(2)+SAPO‐34).The distinct differences are ascribed to the larger number of hydroxyl groups,Lewis acid sites,and oxygen defects in ZnO/m‐ZrO_(2) compared to ZnO/t‐ZrO_(2).These features result in the formation of more formate and methoxy intermediate species on the ZnO/m‐ZrO_(2) oxides during syngas conversion,followed by the formation of more light olefins over SAPO‐34.The present findings provide useful information for the design of highly efficient ZrO_(2)‐based catalysts for syngas conversion.
基金financial support from the Defence Research and Development Organisation, Ministry of Defence, Govt. of India, New Delhi in order to carry out the present study under project DMR-295
文摘Filler materials of(ZrB_2-SiC-B_4C-YAG) composite were developed for gas tungsten arc welding(GTAW) of the ZrB_2-SiC and Cf-SiC based composites to themselves and to each other. Reaction with filler material,porosity and cracks were not observed at weld interfaces of all the joints. Penetration of filler material in to voids and pores existing in the Cf-SiC composites was observed. Average shear strength of 25.7 MPa was achieved for joints of Cf-SiC composites. By incorporation of Cf-SiC(CVD) ground short fibre reinforcement the(ZrB_2-SiC-B_4C-YAG) composite was machinable with tungsten carbide tool. The joint and machined composites were resistance to oxidation and thermal shock when exposed to the oxy-propane flame at 2300℃ for 300s. The combination of(ZrB_2-SiC-B_4C-YAG) and Cf-SiC based composites can be used for making parts like thermal protection system or nozzles for high temperature applications.
基金Funded by National Natural Science Foundation of China(Nos.51502212,51672194 and 51472184)Hubei Province Natural Science Foundation of China(No.2018CFB760)+1 种基金Program for Innovative Teams of Outstanding Young and Middle-aged Researchers in the Higher Education Institutions of Hubei Province(No.T201602)Key Program of Natural Science Foundation of Hubei Province(No.2017CFA004)
文摘Phase pure ZrB2-SiC composite powders were prepared after 1 450℃/3 h via carbothermal reduction route,by using ZrSiO4,B2O3 and carbon as the raw materials.The influences of firing temperature as well as the type and amount of additive on the phase composition of final products were detailedly investigated.The results indicated that the onset formation temperature of ZrB2-SiC was reduced to 1 400℃by the present conditions,and oxide additive（including CoSO4·7H2O,Y2O3 and TiO2）was effective in enhancing the decomposition of raw ZrSiO4,therefore accelerating the synthesis of ZrB2-SiC.Moreover,microstructural observation showed that the as-prepared ZrB2 and SiC respectively had well-defined hexagonal columnar and fibrous morphology.Furthermore,the methodology of back-propagation artificial neural networks（BP-ANNs）was adopted to establish a model for predicting the reaction extent（e g,the content of ZrB2-SiC in final product）in terms of various processing conditions.The results predicted by the as-established BP-ANNs model matched well with that of testing experiment（with a mean square error in 10^（-3） degree）,verifying good effectiveness of the proposed strategy.
文摘Effects of interlayer composition on bonding strength and interfacial microstructure of green joined CePO_4-ZrO_2 ceramics were studied. Green bodies of 25%CePO_4/ZrO_2 and ZrO_2 ceramics were joined by using interlayer composed of CePO_4 and ZrO_2 at 1450 ℃ for 120 min without applied pressure.The effects of CePO_4/(CePO_4+ZrO_2) ratio on the bond strength of the joints were investigated. Under the experimental conditions, the grain size of the particles grown in the joint is smaller than those in joined ceramics. The microstructure of the joint is more homogeneous than that of the matrix and without obvious cracks, pores and other defects.
