Mossbauer spectroscopy study of the high energy ball milling (HEBM) synthesis kinetics of CoFe_2O_4 from Co(OH)_2 and α-Fe_2O_3

摘要

Room temperature mechanochemical synthesis of single phase nanosized particles of CoFe_2O_4 by HEBM of stoichiometric mixtures of Co(OH)_2 and α-Fe_2O_3 under wet acetone was achieved after 25 hours of continuous ball milling. The particle size and lattice constant were 98.13 nm, and 8.398 A after 10 hours, while 31.96 nm and 8.343 A after 25 hours. The coercivity (25 hours state) was 12.78 mT with saturation and remanent magnetizations of 27.52 Am~2/kg and 3.94 AmVkg respectively due to small amount of a magnetic phase. Mossbauer spectroscopy measurements showed very limited reaction in 5 hours, with the single phase forming directly to superparamagnetic particles. The quadrupole splitting of the doublets was in the range of 0.24-1.14 mm/s, with corresponding isomer shift range of 0.80 -0.67 mm/s. The DSC measurements of the single phase material showed that it was metastable with characteristic stages whose activation energies were determined by the modified Kissinger kinetic analyses to be in the range of 3.51 kJ/mol to 11.89 kJ/mol.