X-ray diffraction studies on dry milled zinc ferrites

Unmilled and dry milled zinc ferrites were subjected to X-ray diffraction studies and the XRD patterns are shown in figure. XRD pattern indicates presence of small amount of a-Fe2O3 in all milled samples whose percentage is found to be increasing with milling time. In 10 hours milled sample ZnO phase is also detected suggesting decomposition of ZnFe2O4 to a-Fe2O3 and ZnO. The broad shape of the diffraction peaks replicates the formation of fine particle structure with small crystallite size distribution and existence of strong internal lattice strains which is introduced during high energy ball milling. Average size of the particle, which is calculated by Debye Scherer formula, were in the nanometer range and found to be decreasing with milling time. By 10 hours milling, size reduces to around 11nm while the initial coprecipitated sample was with a grain size of around 16nm. This decrease in particle size as the milling time increases is due to the fact that the kinetic energy generated by the series of collisions among balls is transferred to the zinc ferrite powder. The sudden decrease in grain size is not achieved in this case as in the case of particles prepared by the solid-state reaction method. The reason is that the coprecipitated zinc ferrite which is the starting material, itself is of nanometer sized before the start of milling. Also there are reports that within 24 minutes of milling, size reduction may attain its maximum. A great reduction in size with prolonged milling is not achievable due to the high local temperature and pressure generated during the combustion as a result of the high energy ball milling. Also the difficulty in maintaining the very high stress during milling slows down reduction of grain size.