Physico-Geometrical Mechanism and Overall Kinetics of Thermally Induced Oxidative Decomposition of Tin(II) Oxalate in Air: Formation Process of Microstructural Tin(IV) Oxide

Abstract

This study focuses on the physico-geometrical mechanism and the overall kinetics of the microstructural tin(IV) oxide formation process by the thermally induced oxidative decomposition of tin(II) oxalate in flowing air. Two tin(II) oxalate samples with different morphologies were subjected to a kinetic study involving thermogravimetrical and morphological observations. The reactions exhibited different behaviors at different steps (multistep behaviors); therefore, the overall reactions were resolved into each reaction step using kinetic analyses based on the cumulative kinetic equation. Oxidative decomposition is characterized by a phase boundary controlled reaction initiated by the surface reaction. The formation of the surface product layer at an early stage of the reaction inhibits diffusion of the product and reactant gases. Gaseous diffusion channels are produced via reformulation of the surface product layer by the reaction itself, and the residual reaction advances in the manner of autocatalytic reaction. The kinetic behavior is regulated by the self-generated reaction conditions under specific, transiently formed structural characteristics of the reacting particles, which vary depending on the applied reaction conditions. Therefore, the process control of the oxidative decomposition is an important factor for controlling the microstructure and physicochemical properties of the resulting tin(IV) oxide.