Study by Mössbauer spectroscopy of iron oxides in ceramic brick on the basis of inter-shale clay and brown coal tailings

Abstract

The distribution of iron ions during firing of ceramic bricks made of inter-shale clay and brown coal tailings was achieved by employing the M¨ossbauer effect without the use of traditional natural materials. It is revealed that in samples containing high amounts of iron oxide (8%) the strength and frost resistance is higher compared to the samples containing Fe2O3 is < 6%. Calculation of areas of doublets spectrum showed that ferrous compounds on the surface (under a predominantly oxidizing environment) of the studied samples are mostly represented by hematite, and in the center (recovery environment) — magnetite. Studies have shown that in the inner parts of the ceramic samples, the opposite processes occur — there is a tendency to decrease the content of hematite and increase in the amount of magnetite by reduction of iron oxides with oxides of carbon. The recovery of Fe2+ and the early formation of the liquid phase promotes the progress of the reaction of formation of mullite. Among these reactions is the formation of spinel (hercynite and mullite). Hematite and magnetite contribute to the emergence of solid solutions and the formation of molten phases in the early stages of firing, which initiates the formation of mullite. With the emergence of solid solutions by partial substitution: Fe3+, Al3+ mullite is formed with a different chemical composition, which contributes to strengthening the structure of the ceramic material. Refs 25. Figs 2. Tables 4.