Formation and transformation kinetics of amorphous iron(III) oxide during the thermally induced transformation of ferrous oxalate dihydrate in air.

Focusing on the formation and transformation of amorphous Fe(2)O(3) in the course of the thermally induced transformations of ferrous oxalate dehydrate in air, the kinetics and physico-geometric mechanisms of the respective reaction steps were investigated systematically by means of thermoanalytical methods, complemented by other techniques. The final product of α-Fe(2)O(3) is produced by heating the sample to 700 K via intermediates of poorly crystalline anhydrous FeC(2)O(4) and amorphous Fe(2)O(3), where the external shape and size of the original sample particles are retained during the overall course of reactions. The initial parts of all the three distinguished reaction steps, that is, thermal dehydration of crystalline water, oxidative decomposition of anhydrous FeC(2)O(4) and crystallization of amorphous Fe(2)O(3), are controlled kinetically by the formation or reconstruction of the surface product layers. The surface product layers play important roles of regulating the physico-geometric kinetic behavior of the established parts of the reactions. The oxidative decomposition of intermediate anhydrous FeC(2)O(4), characterized as the formation process of amorphous Fe(2)O(3), arrests in the final stage of the reaction. The as-produced amorphous Fe(2)O(3), protected probably by the outer shell of the surface product layer and the residual anhydrous FeC(2)O(3), crystallizes to α-Fe(2)O(3) being induced by the surface crystallization. Aiming to contribute notably toward provision of the establishment of the novel fabrication routes of nanosized iron oxides by the controlled crystallization of amorphous Fe(2)O(3), the possible factors controlling and/or affecting the formation and transformation kinetics of amorphous Fe(2)O(3) were discussed.