Papers by Author: Hai Long Wang

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Authors: Ming Liang Li, Hai Long Wang, Rui Zhang, Jing Li, Jun Hao Li
Abstract: SiC powders with nickel powders and sintering aids were prepared by pressureless sintering at 1500oC under a N2 atmosphere. XRD, TEM, SEM techniques were used to characterize the phases and microstructure of the specimens. The thermoelectric properties of SiC matrix composites were investigated by measuring the Seebeck coefficient and the electrical conductivity. The main phase of all samples was -SiC, the Ni2Si can be observed with adding nickel powders. The largest electric conductivity was close to 3.5 m-1-1 at about 973K. The highest Seeback coefficient was up to 1800 V/K at 1073K. The transition from n-type to p-type was occurred.
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Authors: Bing Bing Fan, Hai Long Wang, Li Guan, De Liang Chen, Rui Zhang
Abstract: Using the density functional theory method, we have characterized the geometrical structures and adsorption energy of water clusters adsorption on graphite surface. When one water molecule inter- acts with graphite surface, one of the H-O bonds formed hydrogen-bond with carbon atom in graphite sheet; in the two water molecules structure, the linear dimmer nearly parallel to the graphite surface, and also formed the hydrogen-bond; when the number of water molecules increased to six, all the H-O bond that point to the graphite surface has formed Hydrogen-bond with it. The binding energy of the water clusters with a graphite surface depends only on the number of water molecules that form hydrogen bond.
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Authors: Hai Long Wang, Shi Xun Zhang, De Liang Chen, Qian Fei Han, Hong Xia Lu, Hong Liang Xu, Chang An Wang, Rui Zhang
Abstract: ZrB2 powder has been prepared through carbothermal reduction boronization of zirconia/boron carbide/carbon mixtures heating assisted by microwave. The powder characteristics were investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen absorption (BET model) and scanning electron microscope (SEM). The experiments indicated that excessive B4C is necessary and the carbothermic reaction reacts severely at a higher temperature and complete at 1600oC. The crystallite size has ranged from 50-100 nm, according to the calculated surface area. Highest purity of ZrB2 powder, which was synthesized at 1600oC, is 99.67 wt%. The surface area of ZrB2 powder synthesis at 1600oC is 18.33 m2/g. Vibration of temperature should affect the purity of ZrB2, as the sub reaction acted.
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Authors: Hong Liang Xu, De Liang Chen, Hai Long Wang, Hong Xia Lu, Rui Zhang, Shao Kang Guan, Qin Fu Liu
Abstract: Coal gangue was used as the main material to fabricate floor tiles in this paper. The mixture of coal gangue, quartz, feldspar and bentonite, with the weight percentage of 55, 20, 20 and 5, was wetly milled, dried, and then pressed into green compacts. The obtained compacts were sintered at 1180-1240 oC and the floor tiles were obtained. The obtained tiles were characterized by XRD, SEM, linear shrinkage, water absorption, bulk density and flexural strength. The results indicate that the tiles were composed of glassy phases, quartz and mullite phases. The phase composition, microstructure, physico-mechanical properties of the samples change with the sintering temperature. The tile sintered at 1220 oC achieves the linear shrinkage, water absorption and bulk density values of 6.18%, 0.16%, 2.45 g/cm3, respectively. Its flexural strength reaches the maximum of 92.0 MPa.
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Authors: Yao Ma, Jian Li, Hai Long Wang, Rui Zhang
Abstract: Polycrystalline cubic boron nitride (PcBN) composites were sintered by high pressure and high temperature sintering (HPHT) at 1450 °C for 3 min under a pressure of 5.0 GPa. Aluminium,boron carbide and carbon in the starting mixture reacts with cubic boron nitride (cBN) to form Al3BC3 and AlN bonding among cBN grains during sintering. X-ray diffraction (XRD) and Scanning electron microscope (SEM) were used to analyze phases and micro-structure of the sintered samples. The dense structure of super hard cBN grains bonded together with Al3BC3 and AlN offers superior hardness and high strength. The Vickers hardness of PcBN composites was 45±5 GPa, and the strength of PcBN composites was 345±15 MPa.
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Authors: Shi Xun Zhang, Jian Li, Yao Ma, Hai Long Wang, Rui Zhang
Abstract: SiC-Al3BC3-cBN composites with different contents of cBN were fabricated by high pressure and high temperature sintering (HPHT) at 1450 °C for 3 min under a pressure of 5.0 GPa using SiC, Al, B4C and C as additives. The effect of SiC content on the density and mechanical properties of SiC-Al3BC3-cBN composites was investigated. X-ray diffraction (XRD) and Scanning electron microscope (SEM) were used to analyze phases and micro-structure of the sintered samples. The hardness of SiC-Al3BC3-cBN composites decreased with the increasing of SiC content, However, the fracture strength of SiC-Al3BC3-cBN composites increased with the increasing of SiC content.
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Authors: Hai Long Wang, Chang An Wang, Rui Zhang, Xing Hu, Dai Ning Fang
Abstract: In this paper, ZrB2-based ceramics containing up to 15 vol% nano-SiC whiskers were prepared by hot pressing at 1950°C under 20MPa pressure in flow argon. SEM and XRD techniques were used to characterize the sintered compacts. A fine and homogeneous microstructure was observed. The relative density of ZrB2-based ceramic containing 10vol% SiC whiskers reached to 97.7%. The bending strength and fracture toughness of the composite were 550 MPa and 8.08 MPa·m1/2 respectively, while those of the monolithic ZrB2 ceramic (0 vol% SiC whiskers added) were 424 MPa and 4.52 MPa·m1/2 respectively. The grain size of the ZrB2-based ceramics was reduced greatly by the addition of nano-SiC whiskers during the sintering process.
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Authors: Li Na Wang, Bing Bing Fan, Rui Zhang, Hai Long Wang, De Liang Chen
Abstract: High-temperature anti-oxidation coating was prepared by a milling process, which mainly composed of flake graphite and hexagonal BN (hBN). The coating was brushed on the sliding plate surface and dried in air for 24 h, The surface of the sliding plate painted was smooth and without peeling, suggesting a strong bonding strength. The samples were heated at 1200 °C for 20 min to evaluate the mass-loss rate. The mass-loss rate of the slide gate painted is 3.7%, less than the un-painted 5.1%. XRD and SEM techniques were used to characterize the as-heated samples. The results showed that the surface of the slide plate painted was skin rolling. And the graphite reacted with oxygen at an elevated temperature to reduce oxygen concentration. In addition, hBN also reacted with oxygen to form B2O3, which also has an oxygen-resistant role in the sliding plates. These coatings exhibited unique oxidation-resistant properties, and the service life of the coated sliding plates was obviously improved.
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Authors: Chang An Wang, Hai Long Wang, Yong Huang, Dai Ning Fang
Abstract: ZrB2/SiC ceramic composites reinforced by nano-SiC whiskers and SiC particles have been prepared by hot-pressing at 1950°C for 1hr under 20 MPa pressure in flow argon atmosphere. Effects of SiC addition on microstructure, mechanical properties and thermal ablation/oxidation behavior of ZrB2/SiC composites were investigated. The results showed that the addition of SiC effectively improved the densification of ZrB2/SiC composites and almost full dense ZrB2/SiC composites were obtained when the amount of SiC increased up to 20 vol%. Flexural strength and fracture toughness of the ZrB2/SiC composites were also enhanced; the maximum strength and toughness reached 600 MPa and 8.81 MPa·m1/2 at SiC additions of 20 vol % and 30 vol%, respectively. The composites possessed good resistance to flame ablation and could keep the whole shape without distinct peeling or cracking after flame ablation by oxyacetylene flame for 3 mins. The more SiC added, the better resistance to flame ablation the composites displayed.
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Authors: Chang An Wang, Hai Long Wang, Lei Yu, Yong Huang
Abstract: Ultra-fine and high-pure zirconium diboride powders were prepared by carbothermal reduction boronization of zirconia/boron carbide/carbon mixtures. Fine-scale mixing of the reactants was achieved by solution-based processing in which zirconium oxychloride (ZrOCl2⋅8H2O) as the zirconia-bearing precursor was precipitated in the suspension of boron carbide (B4C) and carbon powders in water. The carbothermal reduction boronization reaction was substantially completed at relatively low temperatures (<1600°C) and the resulting products (ZrB2 powders) had small average grain sizes (1~2 μm) and high purity (>99.6 wt%). The experiments indicated that excessive B4C and C were necessary during the carbothermal reduction boronization because of volatilization of boron and carbon elements. The effects of temperature and holding time on the synthesis of ZrB2 powders were also discussed.
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