Characterization of Micro-Structural Changes of Mechanically-Activated Ilmenite

Structural changes of mechanically-activated ilmenite during milling by a planetary mill are monitored and determined as a function of the milling time. The maximum specific BET surface area of 10.76 m2/g is obtained after 150 min of milling. The results obtained indicate that agglomeration of the particles occurs after 45 min of milling. The maximum X-ray amorphization degree of ca. 95% has been calculated after 150 min of milling. Estimation of the stored energy reveals that the X-ray amorphization degree has a dominant contribution to the excess enthalpy of the activated materials. The surface-weighted crystallite size in the ground ilmenite reaches 4.45 nm, which corresponds to the volume-weighted crystallite size of 8 nm and 11.18 nm obtained by the Williamson-Hall and Rietveld methods, respectively. After 150 min of mechanical activation, the root mean square strain, , increases to 0.78%, which corresponds to the strains of 1.43% and 1.04% obtained from the Williamson-Hall and Rietveld methods, respectively. Reduction in the crystallite size leads to the contraction of the ilmenite unit cell after 150 min. The reaction rate constant of the ilmenite dissolution increases by over 58 times after 150 min of milling. Activation energy of the dissolution reaction decreases from 57.45 kJ/mol to 41.09 kJ/mol after 150 min of milling.