Self-propagating high temperature synthesis of BaFe12O19, Mg0.5Zn0.5Fe2O4 and Li0.5Fe2.5O4; time resolved X-ray diffraction studies (TRXRD)

Barium ferrite (BaFe12O19), lithium ferrite (Li0.5Fe2.5O4) and magnesium zi nc ferrite (Mg0.5Zn0.5Fe2O4) have been prepared by self propagating high te mperature synthesis (SHS) reactions from iron, iron(III) oxide and metal ox ides and peroxides. The driving force for the reactions is the oxidation of iron powder. Reactions were carried out under an oxygen flow and with the addition of sodium perchlorate as an internal oxidising agent. Reactions we re also carried out in the presence of an applied magnetic field of 1.1 T. Pre-organisation of the reactant mixture in an applied field led to increas es in synthesis wave velocity (from 2 to 5 mm s(-1)) and temperature. The r eactions were studied by time resolved X-ray powder diffraction on Station 16.4 of the CLRC Daresbury Laboratory. A white beam of X-rays was used in c ombination with three fixed energy sensitive detectors. Spectra were acquir ed with scan intervals of 100-250 ms and an effective 2 theta range of 10-6 0 degrees. Transformation of reactants to products occurred on the order of 200 ms in all of the systems studied with the exception of the applied fie ld barium ferrite synthesis where an intermediate of Fe3O4 was observed. La ttice expansion effects during SHS enabled the rates of cooling in the syst em to be investigated. All of the materials synthesised by SHS were examine d both before and after annealing by X-ray powder diffraction, energy dispe rsive X-ray analysis (EDXA), scanning electron microscopy (SEM), FTIR, Moss bauer spectroscopy and vibrating sample magnetometry.