| The comprehensive utilization of resource has been a technically problem that needs to be solved for a long time. In the present work, a special technology was investigated to make a complete, waste and pollution free, and valuable utilization of the boron-rich slag. Ceramic composite matetial is one of the functional composites that was studied earlier, and possesses extensive potential application. The BN/Sialon multiphase ceramics which is prepared with pure nitride and oxide as raw materials is costly. Microwave sintering is the method of using microwave heating to sinter materials with advantages of high efficiency, high energy utilization, pollution-free, speeding up the rapid heating, lowering the sintering temperature and uniforming microstructure of the material etc. From the perspective of resource comprehensive utilization, using microwave and conventional sintering method and considering the principle of reducing the manufacturing cost of composite ceramics BN/α'-Sialon, the paper investigated the synthesis ofα'-Sialon-AlN-BN powder through the method of carbon thermal reduction-nitridation (CRN) with born-rich slag as principal raw materials, ascertained the suitable synthetic craft.Firstly, this paper described the features and applications of boron-rich slag, the present status, principle and progress of microwave sintering technology. The composition, structure, performance, sintering methods and industrial applications of Sialon ceramics were described in detail. It focused on the core part of sintering unit, that is, sintering resonator, the design of insulation and processing parameters.Secondly, phase-equilibrium in the Si-C-O-N, Al-C-O-N, B-C-O-N systems was analyzed, thermodynamic predomination region diagrams of different gas phase and gas phase versus temperature for the system were drawn. The effects of initial compostion, carbon content, synthetic temperature, holding time and N2 flow rate on the synthesis process of the a'-Sialon-AlN-BN powder were studied systematically, and the synthetic mechanism was discussed. The results show that with increase of the x value, the amount of a'-Sialon, BN and AlN, the solubility of Ca2+ and Mg2+, and the amount of elongateded a'-Sialon grains increase. The phase composition of end product is mostly the same in different carbon content, with the increase of carbon content, the content of a'-Sialon is increasing firstly and decreasing later while the content of BN keeps constant, and decomposition of a'-Sialon occurs with excessively high synthetic temperature and long holding time. The increase of N2 flow rate effects slightly on the phase composition of product, but it increases obviously mass loss rate of the samples. The involatilization of SiO, an intermediate product, results in a mass loss of the samples, which is enhanced with the increase of synthesis temperature, holding time.As a result, the optimum processing condition is:sintering at 1450℃for 6h with N2 flow rate 1000ml/min and a carbon content 1.2 times in 1.4 value of the stoichiometric one. Under the conditions, the phase composition of conduct isα'-Sialon,BN,AlN and a small number of SiC, the grain of a'-Sialon is prismatical while BN is flocculent. Compared with conventional technology, microwave sintering ofα'-Sialon-AlN-BN composite powder has a clear advantage of efficiency, time-saving and energy-saving. The sintering temperature is lower than the conventional above 50℃, the sintering holding time has a reduction of at least 2h compared with conventional process. It provides a highly efficient, energy saving, economic good method of the industrial production. |
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