PHYSICOCHEMICAL INVESTIGATION OF THE DECOMPOSITION PRODUCTS OF AMMONIUM METAL CARBOXYLATES - AMMONIUM FERRIC OXALATE HYDRATE

Thermogravimetry and differential thermal analysis show that ammonium ferric oxalate trihydrate decomposes completely at 275 degrees C givin g Fe2O3. The decomposition takes place via seven weight loss processes ; five endothermic peaks maximize at 90, 125, 190, 220 and 235 degrees C, and two exotherms at 245 and 260 degrees C. Product analysis by me ans of IR spectroscopy and X-ray diffractometry indicate the formation of (NH4)(3)Fe(C2O4)(3) at 125 degrees C and H3Fe(C2O4)(3) at 235 degr ees C. The latter decomposes immediately to Fe-2(CO3)(3) to give Fe2O3 at 260 degrees C. The formed Fe2O3 undergoes a phase transformation t hrough an exothermic effect at 275 degrees C, giving rise to a maghemi te structure (gamma-Fe2O3). Surface area measurements and scanning ele ctron microscopy show that Fe2O3 is the final product at 300 degrees C . This has a surface area of 114 m(2) g(-1) and gives a crystalline po rous material.