微波还原鲕状赤铁矿中铁晶粒的形核生长机理

采用Avrami-Erofeyev模型对微波还原鲕状赤铁矿含碳球团过程中铁晶粒的形核与生长动力学进行了研究，并采用XRD、SEM、EDX对还原样物相组成、铁晶粒形貌尺寸、元素组成分布等进行了测试分析。研究结果表明，在1 173~1 473 K下20 min时间内可获得金属化率77.6%~92.6%；微波还原鲕状赤铁矿球团过程中铁晶粒形核速率与铁晶粒生长速率与模型拟合度高，1 173~1 473 K下置信度R2范围分别为0.941 1~0.997 7与0.948 4~0.984 8。拟合得出了动力学参数，获得铁晶粒形核活化能为51.21 kJ/mol、生长活化能为18.05 kJ/mol，还原速率受形核速度控制。通过与常规加热对比发现，微波场中铁晶粒形核与生长速率更快。扫描电镜观察发现铁晶粒的生长形态部分为球形熔滴状、部分为蠕虫状链晶，视域内最大单个铁晶粒尺寸约为10 μm。 

Nucleation and Growth Mechanism of Iron Grains in Oolitic Hematite Reduced via Microwave Heating

The nucleation and growth kinetics of iron grains in oolitic hematite coke-bearing pellets reduced by microwave heating were studied by Avrami-Erofeyev model. The phase composition, morphology and grain size, element composition and distribution of reduced sample were analyzed by XRD, SEM and EDX techniques. The results showed that the metallization rate was 77.6~92.6% at 1 173~1 473 K in 20 minutes. The nucleation and growth rate of iron grains in oolitic hematite coke-bearing pellets reduced at 1 173~1 473 K were found well-fitting to the selected model with the corresponding R2 coefficient ranges of 0.9411~0.9977 and 0.9484~0.9848, respectively. The kinetic parameters were obtained by fitting. The nucleation activation energy and growth activation energy were given as 51.21 kJ/mol and 18.05 kJ/mol, which indicated that the reduction process was controlled by iron grain nucleation rate. Compared with the conventional heating conducted by previous researchers, it could be found that the nucleation and growth rate of iron grains was faster in microwave field. The analysis of SEM showed that the morphologies of iron grains were spherical and partly vermicular, and the maximum single iron grain size in the field of view was about 10 micrometers.