Thermal decomposition of ammonium ferrocyanide, (NH4)4[Fe(CN)6], was investigated by means of thermal analysis and 57Fe Mössbauer spectroscopy. Thermal analysis (TG and DSC) showed multistep decomposition mechanism with the total mass loss of 70% corresponding to complete transformation of the precursor to Fe2O3. Ammonium ferrocyanide was heated in a furnace starting from room temperature up to selected temperature in the range from 60 °C to 350 °C. After the heat treatment up to given temperature, the sample was characterized by room temperature Mössbauer spectroscopy. The decomposition mechanism is based on a sequential formation of (NH4)3[FeIII(CN)6], (NH4)3[FeII(CN)5], Fe4III[FeII(CN)6]3 (Prussian Blue), and finally Fe2O3. Mössbauer spectroscopy allowed to determine valence states of Fe atoms in the phases unambiguously. Thermal decomposition of ammonium ferrocyanide thus presents a simple method of synthesis of Prussian Blue nanoparticles as well as amorphous Fe2O3 nanoparticles. Amorphous Fe2O3 can be further crystallized to β-Fe2O3, γ-Fe2O3 and/or α-Fe2O3 polymorphs.

Topics
Polymorphism, Thermal analysis, Nanoparticle, Minerals, Transition metal oxides, Mossbauer spectroscopy
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