A Thermogravimetric Study on Oxidation Process of Porous Nickel in Molten Alkali Carbonates at 650 °C

Abstract

The oxidation process of porous nickel plaques in molten alkali carbonates with different'compositions at 923 K has been studied by using the thermogravimetric analysis under various gas compositions. It was shown that the oxidation process consists of two stages with different oxidation rates. The rate of the first oxidation stage is very close to the rate of gas phase oxidation, and that of the second oxidation stage, which appears immediately after the first oxidation stage, is constant to the final oxidation state of lithiated NiO, depending on O₂partial pressures and Li/K composition ratios. The second stage was attributed to the real process during the in situ oxidation of porous nickel impregnated with carbonate melts, and its rate was discussed in terms of the local cell oxidation of nickel by dissolved oxygen in the melt. It was concluded that the oxidation process is controlled by O₂- and CO₂ mixed diffusion through a thin melt film on nickel particles.