This study focuses on the mechanism that governs the CO2-induced oxidation of Zn powder in a dropping state via a one-dimensional drop-tube furnace system. Parameters including temperature, CO2 concentration, residence time, and particle size were considered. Results showed that the oxidation of Zn powder with CO2 can be divided into three periods according to reaction temperature. Based on the oxidation of spherical Zn particles in the dropping state at a representative temperature for each period, the reaction mechanism was characterized by a shell–core model with three temperature regimes. Meanwhile, equations for the reaction rates were formulated using nonlinear regression analysis. This model is consistent with scanning electron microscopy and transmission electron microscopy results. In addition, the theory of anion coordination polyhedron growth units for crystals was applied to explain the nucleation, growth, and final morphology of ZnO crystals.

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