The crystallisation kinetics of iron rich glass in different atmospheres

The crystallisation kinetics of powder and bulk iron-rich glass, based on zinc hydrometallurgy hazardous waste, were investigated in air and nitrogen atmospheres. The activation energy of crystal growth, EC, and the Avrami parameter, n, were estimated by means of differential thermal analysis. The kind and amount of crystal phases, formed during the thermal treatment and their relative ratio were evaluated by X-ray diffraction analysis. The kinetics results sustain that the pyroxene phase grows on a fixed number of magnetite nuclei. The activation energy of crystal growth on the surface and in the bulk are similar in air and nitrogen atmospheres. When the powder glass sample is heat-treated in air, surface oxidation of Fe2+ into Fe3+ inhibits crystallisation resulting in the decrease of the percentage of crystal phase and the change of the Avrami parameter value.