Effect of iron on mechanical activation and structural evolution of hematite-graphite mixture

In this study the effect of iron on mechanical activation (MA) and structural evolution of hematite (H) and graphite (G) mixture has been investigated. Different amounts of iron powder (0-10 wt%) were added to H-G mixture (with C/O = 1). Then the H-G-iron mixtures were mechanically treated by a planetary ball mill for different time periods (0-10 h). X-ray diffraction (XRD) results demonstrated that a fraction of H particles reduces to magnetite (M) and G peaks completely disappear due to mechanical milling. In addition, H crystallite size and structural microstrain were obtained performing different procedures based on integral breadth analysis of obtained XRD patterns. The obtained results showed that H crystallite size decreases tremendously and its structural microstrain increases as a result of increasing milling time and iron intensifies these changes. Moreover, the concept of ɛ/d was proposed as the MA parameter. The variations in H amorphization degree and dislocation density were also investigated, showing the major impact of both milling time and iron content. Furthermore, scanning electron microscopy (SEM) studies were carried out in order to investigate the induced changes in the structure due to milling and also to study the effect of iron on structural evolution and its mechanism. SEM observations revealed that mechanical milling produces a compacted composite structure of particles. Additionally, MA in the presence of iron increases the stored energy in powder mixture. So, iron not only intensifies the induced changes in the structure but also accelerates the MA process.