Thermal decomposition of almandine garnet: Mossbauer study

The thermal decomposition of almandine garnet from Zoltye Vody, Ukraine, has been studied using Fe-57 Mossbauer spectroscopy. Room temperature Mossbauer spectrum of the initial powdered sample is characterised by one doublet corresponding to Fe2+ in dodecahedral position 24c. In the room temperature spectra of all heated almandine samples, a doublet corresponding to gamma -Fe2O3 nanoparticles appeared. Depending on experimental conditions (heating temperature and time), the additional spectral lines of alpha -Fe2O3 and epsilon -Fe2O3 were observed in Mossbauer spectra. It is obvious that the thermal transformation of almandine garnet in air is related to the primary formation of gamma -Fe2O3 superparamagnetic nanoparticles. gamma -Fe2O3 nanoparticles are transformed into epsilon -Fe2O3 and consequently into alpha -Fe2O3 at higher temperatures. The mechanism and kinetics of the individual structural transformations depend on experimental conditions - mainly on the heating temperature and size of the particles.