Home – Home – Jornals – Chemistry for Sustainable Development 2018 number 5

Processes of thermal decomposition of iron (III) oxalate placed into pores of structured mesoporous silica (SBA-15) were investigated. Synchronous thermal analysis of samples was carried out in inert (argon) and oxidizing (a mixture of argon and 20 % oxygen) media. The composition of gas thermolysis products was detected mass spectrometrically. The initial salt and solid-phase products of its decomposition were characterised by X-ray phase analysis and Mössbauer spectroscopy. It is well known that the process of thermolysis of iron (III) oxalate under inert atmosphere conditions proceeds in two stages: intermediate decomposition to anhydrous iron (II) oxalate and then the final one to Fe₃O₄ and α-Fe at 150–180 and 310–400 °C, respectively. Oxidative thermolysis occurs in a single step. In other words, iron (III) oxide is formed from the initial salt that is later crystallised into hematite phase. However, this step is complex. Instantaneous oxidation of anhydrous iron (II) oxalate formed as an intermediate explains high exothermicity of the process. It was found that the temperature of the initial decomposition step was reduced from 150 to 80 °C for a precursor placed into SBA-15 silica matrix pores in both oxidative and inert media. Herewith, the finishing temperature of the step for oxidative thermolysis is increased almost by 100 °C. Gas evolution spikes and extremes in the calorimetric curve of the second step of decomposition in argon are reduced by 30–40 °C. An increase in the reactivity of fine particles and the amorphous state of iron (III) oxalate explained a reduction in gas evolution peaks. In order to describe the behaviour of the precursor, upon oxidative thermolysis likely reactions determining the process were suggested.