自蔓延还原合成BN反应机理

结合差热分析 ,通过研究B2 O3 和Al在不同温度下的反应以及在不同氮气压力中的自蔓延实验 ,探讨了B2 O3 Al N2 体系自蔓延还原合成BN的反应机理。结果表明 :铝热还原B2 O3 的反应是一个分步过程 ,低于 82 0℃时 ,B2 O3 与Al缓慢反应生成Al4 B2 O9;高于 82 0℃时 ,B2 O3 与Al剧烈反应生成Al4 B2 O9;高于 10 5 0℃时 ,Al与在低温生成的Al4 B2 O9反应生成Al18B4 O3 3 ;在更高的温度下 ,Al18B4 O3 3 继续被Al还原成B。还原反应生成的B多为无定形态 ,还原出的B在高压氮气中被氮化成BN。生成的BN中 ,部分为六方BN ,另一部分为未知晶体结构的BN ,其形态近似立方体。

Behavior of titanium dioxide in alumina carbothermic reduction-chlorination process in vacuum

Behaviors of TiO2 in the alumina carbothermic reduction and chlorination process in vacuum at different temperatures were investigated experimentally by means of XRD,SEM and EDS.In the preparation of materials,the molar ratio of Al2O3 to C was 1：4,and 10% TiO2 and excess AlCl3 were added.The results show that TiC is produced by C and TiO2 after TiO2 transforms from anatase into rutile gradually.In the temperature range of 1 763？1 783 K,the compounds of Ti and Al are not found in slags and condensate.The purity of aluminum reaches 98.35%,and TiO2 does not participate in alumina carbothermic reduction process and chlorination process in vacuum.

Carbothermic reduction of alumina with carbon in vacuum

Carbothermic reduction alumina in vacuum was conducted, and the products were analysed by means of XRD and gas chromatography. Thermodynamic analysis shows that in vacuum the initial carbothermic reduction reaction temperature reduces compared with that under normal pressure, and the preferential order of products is Al404C, Al4C3, Al2OC, Al20 and A1. Experiment results show that the carbothermic reduction products of alumina are A1404C and A14C3, and neither A12OC, Al20 or Al was found. During the carbothermic reduction process, the reaction rate of Al203 and carbon decreases gradually with increasing time. Meanwhile, lower system pressure or higher temperature is beneficial to the carbothermic reduction of alumina process. A1404C is firstly formed in the carbothermic reaction, and then A14C3 is formed in lower system pressure or at higher temperature.