Papers by Author: Jia Ping Wang

Abstract: Based on SiC aggregate, SiC powder and ultra-fine SiC powder as the main starting materials and B₄C as additive, the newly-developed self-bonded SiC material was pressed and fired at 2200°C for 10 hours in Ar environment in the high-temperature furnace. The phase composition and microstructure were investigated. In the paper, traditional self-bonded SiC material and Si3N4-bonded SiC material were taken for comparison with the newly-developed self-bonded SiC material in terms of strength, thermal conductivity, cryolite resistance, molten alkali resistance and oxidation resistance etc. The results show that the newly-developed self-bonded SiC material contains 98.42% α-SiC and presents obvious higher thermal conductivity than traditional self-bonded SiC material and much better cryolite resistance, molten alkali resistance and oxidation resistance than traditional self-bonded SiC and Si3N4-bonded SiC materials.

Abstract: α-Si₃N₄ possesses excellent sintering activity, which is used to prepare high performance Si₃N₄-based ceramics and composite refractory. Si₃N₄ powder is always synthesized by nitriding silicon in controlled-atmosphere furnace whose furnace volume is very small(effective volume: 1840×1420×1660mm), the extreme reaction heat is difficult to diffuse, which leads to high reaction temperature and conversion of α-Si₃N₄ to β-Si₃N₄, thus α-Si₃N₄ is difficult to be obtained in controlled-atmosphere furnace. While flame-isolation nitridation shuttle kiln has much larger furnace volume to conduct reaction heat (effective volume: 11500×4190×1684mm), so it owns homogeneous temperature field and stable low-temperature environment which benefits the preparation of α-Si₃N₄. Thermodynamic analysis of Si-N system is shown that Si₃N₄ can be formed by two formats: direct nitridation of Si(s) and indirect nitridation of SiO(g); to ensure completely nitridation, the particle size of silicon powder should be less than 88μm. With reclaimed powder from polysilicon cutting slurry as starting materials, both reactive α-Si₃N₄ and SiC mixed powder were successfully prepared in flame-isolation nitridation shuttle kiln. Because of the gas-gas reaction between SiO(g) and N₂(g), α-Si₃N₄ is fiber-like and in favor of processing high quality Si₃N₄-based materials.

Abstract: The reaction between Si₃N₄ and AlF₃ had been investigated in CO atmosphere at high temperature. Experimental results are shown that the reaction between Si₃N₄ and AlF₃ is accelerated with the rise of temperature. At the temperature of 950 (aluminum electrolytic operation temperature is 935±15), there is obvious reaction between Si₃N₄ and AlF₃; under this experiment condition, Si₃N₄ converted into Si₂N₂O partly, Si₂N₂O can also react with AlF₃. The reaction products of Si₃N₄ with AlF₃ are SiF₄ (g) and AlN, while the reaction products of Si₂N₂O with AlF₃ are SiF₄ (g) and Al₈O₃N₆. So, during the usage of Si₃N₄-bonded SiC sidewall brick in aluminum electrolysis cells, the content of Si₃N₄ in Si₃N₄-SiC block are reduced which can bring down the corrosion of aluminum electrolyte to the sidewall materials.

Abstract: Si-Si₃N₄-SiC composites was prepared by firing at 1450°C for 8hrs in air atmosphere with SiC, Si₃N₄, Si as principal raw materials. Si-Si₃N₄-SiC composites has good performance and its services life is 5~7 times than that of oxides sagger. This paper also studies the material attack mechanism and observes the microstructure of Si-Si₃N₄-SiC composites which has been used 15 cycles.

Abstract: Excellent Fe₃Si-Si₃N₄-SiC composites were successfully prepared with FeSi₇₅ and SiC as main starting materials by nitridation reaction(at 1300°C for 8Hrs). The effect of ferrosilicon alloy addition amount on material properties was studied; the ferrosilicon nitridation mechanism was analyzed through chemical thermodynamics; phase composition, microstructure, alkali resistance of products were also investigated. The results show that when ferrosilicon addition amount is 12wt%, the comprehensive property of Fe₃Si-Si₃N₄-SiC is the best. The nitridation products are fiber-like α-Si₃N₄ and rod-like β-Si₃N₄, which makes better mechanical behavior due to fiber reinforcement; a great deal of Fe₃Si intermetallic compounds uniformly distribute in matrix, which is one of the products of Fe-Si nitridation and as a plastic phase forming in grain boundary optimizes the performance of products. Chemical thermodynamic analysis shows that the fiber-like α-Si₃N₄ is formed by SiO(g) and N₂(g) reaction which also increases the rate of nitridation. Fe₃Si-Si₃N₄-SiC material has good performance. Now it has been successfully applied to one 2000M³ domestic steel plant, the blast furnace operation goes well.