Reactions and Morphologies of Mg and Mg/Teflon/Viton Particles during Oxidation

A thorough investigation on the reactions and morphologies of Mg particles and Mg/Teflon/Viton (MTV) during oxidation were conducted via thermal gravity-differential scanning calorimetry (TG-DSC) and scanning electronic microscopy. The results showed that the oxidation of Mg is fast. It merely changed the metallic luster of Mg before 550 degrees C, and only a few particles changed to a white irregular shape at 600 degrees C. However, all of the Mg particles oxidized to porous irregular shaped MgO at 650 degrees C. Herein, the oxidation of Mg particles ended by its melting point, and the whole process is a solid-gas-phase reaction. On the other hand, when MTV reacted in air, the reaction could be divided into two stages: the fluorination of Mg and the oxidation of the exceeded Mg. In the first stage, a dense MgF2 shell was formed by the solid-solid fluorination. The dense MgF2 shell could impede the oxidation of Mg. As a result, the oxidation of Mg began after its melting. Furthermore, liquid Mg could vaporize at higher temperature, which could burst out from the MgF2 shell and react with oxygen. The MgF2 shell exhibited a dense feature, not only protecting the Mg particles from the heterogeneous oxidation at lower temperature, but also facilitates the homogeneous oxidation at higher temperature.