Iron exchange processes between mullite and coexisting silicate melts at high temperatures

Abstract

The iron distributions between mullites and coexisting silicate glasses were investigated in sinter-mullite and fused-mullite samples between 1670 and 1350 °C with electron microprobe analysis. A reciprocal dependence exists between iron incorporation into mullite and the annealing temperature, though the amount of iron incorporation is also correlated with the bulk iron content of the samples. Increasing Fe2O3 entry into mullite causes equimolar but reciprocal decrease of AI2O3, while SiO2 values slightly increase or remain constant. With respect to the iron distributions two temperature regions can be distinguished: Firstly, a temperature field extending between about 1670 and 1450 °C with small standard deviations of the iron oxide contents of mullite and of the coexisting glass phase. This indicates equilibria of iron distributions in mullite, and between mullite and the coexisting silicate glass. Secondly, a temperature field extending below about 1500 °C with widespread iron oxide composition ranges in mullite and between mullite and the coexisting glass phase. This indicates non-equilibria of iron distributions in mullite, and between mullite and the coexisting silicate glass.