Influence of heat treatment on phase transformation of clay–iron oxide composite

Magnetic clay composite prepared by the method of precipitation of iron oxide onto the clay surface was subjected to a heat treatment. The presence of iron oxide phase in composite before the heating was determined by the Mössbauer spectroscopy method as γ-Fe2O3. Structural changes of maghemite in clay composite after heating at selected temperatures in N2 and Ar/H2 atmosphere were studied using Mössbauer spectroscopy, X-ray diffraction, TG/DSC and SEM methods. It was shown the full transformation of γ-Fe2O3 to α-Fe2O3 in the inert atmosphere at temperature 650 °C and only a partial transformation to Fe3O4 in the reductive atmosphere at 300 °C.

► Magnetic clay composite was prepared and subjected to a heat treatment. ► The clay/maghemite composite was heated in two atmospheres under two temperatures. ► Phase transformation was reliably studied by XRD method and Mössbauer spectroscopy.