真空碳热还原过程中二氧化硅的挥发行为

摘要

为了解在真空碳热还原过程中SiO2的还原特性以及还原过程中的主要影响因素,对二氧化硅的还原过程进行热力学分析,得出化学反应自由能和临界温度.在系统压力为2～200 Pa条件下,以分析纯SiO2和Fe2O3为原料,采用XRD,S EM,EDS和化学成分分析等手段,研究Fe/Si摩尔比、配碳量、反应时间、还原剂粒度和升温速率对硅的挥发率和还原反应速率的影响.实验结果表明:在100 Pa条件下,SiO2的临界反应温度为1 330～1 427K.SiO2发生气化反应生成的SiO气体挥发至石墨冷凝系统歧化生成Si和SiO2,造成硅的损失,且有部分SiO气体和石墨反应生成SiC;增大Fe/Si摩尔比和配碳量以及减小还原剂粒度均降低了硅的挥发率,提高了SiO2还原反应速率;延长反应时间和提高升温速率增加了硅的挥发率.%In order to research the reduction characteristics of silica by carbothermic reduction in vacuum, the Gibbs free energy and critical temperature of the Si oxide deoxidized reaction by C were calculated and analyzed thermodynamically. The pure SiO2 powder was mixed to make pellets with Fe2O3 and coal powders, and the effects of Fe/Si molar ratio, carbon content, reaction time, reductant grain size and heating rate on the volatilization ratio and reaction rate of silica in carbothermic reduction were investigated by means of XRD, SEM, EDS and chemical composition analysis in vacuum (2-200 Pa). The results show that the critical temperature of SiO2 is 1 330-1 427 K when the system pressure is 100 Pa. After SiO2 converses to SiO, SiO disproportionats into Si and SiO2 in the graphite condensing system, and some of SiO with graphite transform into SiC. With the increase of Fe/Si molar ratio, carbon content and the decreases of reductant grain size, the volatilization ratio of silicon decreases, but the rale of reaction increases. With the rise of heating rate and reaction time, the volatilization ratio of silicon increases.