Thermal Decomposition of Tin(II) Oxyhydroxide and Subsequent Oxidation in Air: Kinetic Deconvolution of Overlapping Heterogeneous Processes

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The reaction pathway and mechanistic features of the synthesis of SnO2 via the oxidative decomposition of tin(II) oxyhydroxide in air were investigated using thermoanalytical techniques and morphological observations. Furthermore, the detailed kinetics of each component process were analyzed by applying an empirical kinetic deconvolution method. The thermal behavior of tin(II) oxyhydroxide in air is characterized by two overall processes: (1) the mass-change process, which involves thermal decomposition (mass loss) and in situ oxidation (mass gain), followed by (2) crystal growth of the product SnO2. The mass-change process comprises largely overlapping consecutive processes such as primary endothermic thermal decomposition and subsequent exothermic oxidation. It was deduced from the kinetic results that the overall mass-change process is regulated by the overlapping structures of the surface product layers of the primary and subsequent reactions and the counter diffusion of the H2O generated in the primary reaction and the reactant O2 required for the subsequent reaction in the outer layer. The crystal growth of the as-produced SnO2 occurs via two concurrent kinetic processes that result in the development of a two-dimensional stacking structure. These kinetic features are the key to controlling the overall reaction process and the morphology of the SnO2 product.