Characterization of iron phosphate glasses prepared by microwave heating

Abstract

Phosphate glasses have been prepared by melting batch materials in electric furnaces, induction furnaces, and in microwave ovens. In the present work mixtures of (NH4)2HPO4 and Fe3O4 or Fe2O3 were exposed to microwave energy, heated to 1200°C, and cast to produce iron phosphate glasses. Glasses were also produced in electric furnaces for comparison. The material was analyzed by X-ray diffraction, Mössbauer spectroscopy, and differential thermal analysis. For magnetite-based glasses produced in an electric furnace, the Fe2+/(Fe2++Fe3+) ratio is compatible with the value in the batch material. The Fe2+/(Fe2++Fe3+) ratio is higher for glasses produced in a microwave oven. Glasses with nominal composition 55Fe3O4–45P2O5 (mol%) produced in an electric furnace present an arranged magnetic phase with hyperfine field that could be associated to hematite (estimated to be 21%). All the glasses submitted to heat treatments for crystallization present the following crystalline phases: FePO4, Fe3(PO4)2, Fe(PO3)3, Fe(PO3)2 and Fe7(PO4)6. The amount of these phases depends on the glass composition, and glass preparation procedure. Microwave heating allows to reach melting temperatures at high heating rates, making the procedure easy and economical, but care should be taken concerning the final Fe2+/(Fe2++Fe3+) ratio.