Papers by Author: Chong Hai Wang

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Authors: Chang Ling Zhou, Yan Yan Wang, Zhi Qiang Cheng, Chong Hai Wang, Jie Fan, Cheng Gong Sun, Bao Lin Feng
Abstract: ZrB2-SiC and ZrB2-SiC-C ultra-high temperature ceramics (UHTCs) were fabricated by pressureless sintering under an argon atmosphere. The mass and linear ablation rates were tested in an oxyacetylene flame with high velocity. The microstructure and phase transformation of the ZrB2-based UHTCs were characterized by scanning electron microscopy along with energy dispersive spectrometry. Results show that the UHTCs have excellent properties of ablation resistance at ultra-high temperature. The values of mass and linear ablation rates were lower in the ZrB2-SiC UHTCs than those measured for ZrB2-SiC-C. The effect of C addition on the ablation resistant was not obvious but it influenced the microstructure of the ZrB2-SiC UHTCs. And the ablation resistant mechanisms of ZrB2-based UHTCs were discussed according to microstructure analysis.
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Authors: Hong Sheng Wang, Ling Li, Chong Hai Wang, Yong Li, Qi Hong Wei
Abstract: In this study, 2.5 dimensional quartz fibers reinforced fused silica (2.5D SiO2f/SiO2) composites were prepared by in-situ solidification vacuum-assisted liquid-phase infiltration method using Si-sol and tetraethoxysilane. Composites’ tensile strength and compressive strength were tested by universal testing machine, and the microstructures of the specimen were observed by scanning electron microscopy (FEI Sirion 200). The ultimate sintering temperature was chosen by the differential thermal analysis of tetraethoxysilane gel and the effect of sintering temperature on the composites’ tensile strength. Densification behavior, mechanical properties and microstructures of the composites were investigated. The results show that tetraethoxysilane infiltration process is an efficient route for the preparation of SiO2f/SiO2 composites, after two cycles when the weight was no longer increased using Si-Sol infiltration, the density of SiO2f/SiO2 composites increases from 1.63 to 1.74g/cm3, while the tensile strength and compressive strength, respectively, increase from 31.2 to 52.7MPa and 59.0 to 129.7 MPa. And the interface de-bonding and distinct fibers pull-out of the fracture faces show that it is non-brittle fracture. The enhanced mechanism of tetraethoxysilane infiltration was also analyzed in this paper.
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Authors: Qi Hong Wei, Chong Hai Wang, Zhi Qiang Cheng, Ling Li, Hong Sheng Wang, Zhong Hua Wei, Fang Gao
Abstract: In this paper, XRD was engaged in studying phase transformation of quartz fibers, SEM was engaged in studying the surface micromorphology of quartz fibers heat treated at different temperatures, and the tensile strength was measured by a single fiber strength electronics instrument. The results indicate that surface infiltration agent have been iliminated after heat treatment at 500°C, and the tensile strength decreaced significantly. The higher the temperature was, the more the tensile strength decreaced. There were no significant phase transformation and no crystallization heat treatmented at 500~800°C. But there were some round and strip bulges, and scap defects on the surface. With temperature increasing,some scab defects and bulges began to flake off, and some new rifts and cracks were formed. This was one of the important factors that decreaced tensile strength markedly.
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Authors: Yong Li, Qi Hong Wei, Ling Li, Chong Hai Wang, Xiao Li Zhang, Fang Gao
Abstract: In this paper, negative thermal expansion coefficient eucryptite powders were prepared by sol-gel method using silica-sol as starting material. The raw blocks were obtained by dry pressing process after the powder was synthesized, and then the raw blocks were heat-treated at 600º, 1150º, 1280º, 1380º, 1420º and 1450°C, respectively. Variations of density, porosity and thermal expansion coefficient at different heat treatment temperatures were investigated. Phase transformation and fracture surface morphology of eucryptite heat-treated at different temperatures, respectively, were observed by XRD and SEM. The results indicate that, with the increasing heat- treatment temperature, the grain size and the bending strength increased, porosity decreased, thermal expansion coefficient decreased continuously. Negative thermal expansion coefficient of -5.3162×10-6~-7.4413×10-6 (0~800°C) was obtained. But when the heat-treatment temperature was more than 1420°C, porosity began to increase, bending strength began to decrease, which were the symbols of over-burning, while the main crystal phase didn’t change.
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Authors: Ting Yan Tian, Chang Ling Zhou, Feng Sun, Zhi Qiang Cheng, Chong Hai Wang, Yu Jun Zhang
Abstract: An oxidation kinetics model of hot-pressed ZrB2-SiC composites was established and then proved by experiments. The relationship between oxidation rate and temperature was attained by reaction activation energy and frequency factor at the different oxidation stages. Results showed that the relations between the oxidation gain of unit area and the oxidation time are linear, conic and parabolic, respectively, during the stage of the oxidation prophase, midterm and anaphase.
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Authors: Fang Gao, Chong Hai Wang, Ling Li, Da Qian Chen, Ping Zhai, Qi Hong Wei, Hong Sheng Wang
Abstract: It is an effective way to decrease dielectric constant of microwave transparent materials by improving porosity rate. Network -Si3N4 porous transparent materials were prepared by gas pressure sintering (GPS) with Y2O3 additions. Porosity rate of silicon nitride using pore former with different content starch, polytetrafluoroethylene (PTEE) powder respectively and their compounded component were discussed in this paper. It is concluded that porosity rate can be improved by all the three, starch is most favorable to improve porosity but great volume rebound after cold iso-static pressing were happened and easily lead to crack of green body. Method of pore-making by step on principle of pore formers discharging in different temperature range used to get high strength and porosity green body. Series of porous silicon nitride microwave transparent materials were prepared with porosity rate from 48% to 67%, bending strength from 162MPa to 59MPa and dielectric constant from 3.41 to 2.37.
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Authors: Fang Gao, Jian Liu, Chong Hai Wang
Abstract: Porous silicon nitride with pore forming agent of starch were prepared by cold isostatic pressing, forming problem of complex shapes were solved by methods of carbonization of starch and decreasing forming pressure. Products of porous silicon nitride had the performance parameter with density 1.5g/cm3, porosity over 55%, bending strength over 100 MPa.
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Authors: Jie Fan, Chang Ling Zhou, Chong Hai Wang, Yan Yan Wang, Rui Xiang Liu
Abstract: With the background of thermal protection applications of anti-oxidation carbon fiber reinforced composites, carbon fiber reinforced ultra-high temperatureceramics with homogeneous disperse complex matrix of C-ZrB2-SiC (C/C-ZrB2-SiC) was prepared. Carbon fiber performs were deposited with pyrolytic carbon by chemical vapor infiltration method. Subsequently, the composite precursors were prepared by completely mutually dissolving of ZrB2 polymeric precursor and polycarbosilane dimethylbenzene solution. Then the nano-dispersed ZrB2-SiC composite ceramic was introduced into the C/C preforms by polymer impregnant and pyrolysis process. The C/C-ZrB2-SiC composite shows excellent ablation behavior with the ablating rate of 8*10-4mm/s. The microstructural and compositional characterizations of the C/C-ZrB2-SiC composites indicates that ZrB2 nanoparticle is distributed homogeneously in the continuous SiC phase, which is beneficial to enhance ultra-high temperature ablation resistance of the composites.
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Authors: Cheng Gong Sun, Jin Ye Niu, Chong Hai Wang, Chang Ling Zhou, Bao Lin Feng, Jie Fan, Yan Yan Wang, Jian Shan Hao
Abstract: With AlN, Al2O3 and Al powders as starting materials, ALON powders were prepared by high temperature solid state reaction at 1650°C, 1750°C and 1850°C respectively. Nitrogen gas at 1atm was selected as reaction atmosphere. X-ray diffraction analysis and scanning electron microscope analysis were carried out for the as-prepared ALON powders. In this paper, single-component γ-ALON porous materials were obtained at temperatures below 1800 degree with void ratio more than 75%, which is prone to be grinded to powders less than 1μm and applicable for the preparation of transparent ceramics. Aluminum oxynitride spinel γ-ALON transparent ceramics were successfully obtained with the as-prepared ALON powders. The volume density of the transparent ceramics was 3.67g/cm2, which is 99.3 percent of the theoretical density of γ-ALON materials. The bending strength of the transparent ceramics was 296MPa and the transmittance was about 75% in the wavelength range of 1.2 to 5.3μm.
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Authors: Wei Ru Zhang, Chong Hai Wang, Ling Li, Jian Liu, Wen Chen
Abstract: The Si-B-O-N microwave-transparent materials were prepared by gas pressure sintering (GPS).The effect of BN and nano-SiO2 contents on the mechanical and dielectric properties of the composites was studied. The microstructural characteristic and reinforced mechanism of the composites were also investigated. The results showed that a series of Si-B-O-N wave-transparent materials could be obtained by controlling the contents of raw materials and technological parameter. The bending strength of composites is from 74.7MPa to 174.83MPa, the dielectric constant is from 3.5 to 4.2 and the tangent of loss angle is from 0.5×10-3 to 4.5×10-3.
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