The thermal decomposition of almandine garnet from Zoltye Vody, Ukraine, ha
s been studied using Fe-57 Mossbauer spectroscopy. Room temperature Mossbau
er 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 (heatin
g 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 nanopar
ticles. gamma -Fe2O3 nanoparticles are transformed into epsilon -Fe2O3 and
consequently into alpha -Fe2O3 at higher temperatures. The mechanism and ki
netics of the individual structural transformations depend on experimental
conditions - mainly on the heating temperature and size of the particles.