Evaluation of gas switch effect on isothermal gas-solid reactions in a thermogravimetric analyzer

The effect of gas switching during isothermal gas-solid reactions were evaluated by taking CO2 gasification of graphite in a thermogravimetric analyzer as an example. The evolution behavior of the gases during gasification with or without the gas switch step were recorded and analyzed by an on-line mass spectrometer. The gasification curve from the procedure with gas switch step showed an obvious difference with that obtained from all CO2 atmosphere. For the procedure with gas switch step, the reaction indeed occurs in a mixture atmosphere of CO2 and the inert gas initially, which greatly restrict the gasification reaction and completely changes the reaction rate curve trends. Moreover, the effect of gas switching is in proportion to the gasification temperature. With the increase of the gasification temperature, the effect of gas switching becomes more significant. The activation energy calculated using the data from the gas switch method become lower for the gas diffusion effect. This research indicate that the previous study which does not consider the gas switch effect would contain some errors on the evaluation of the samples reactivity and kinetic parameters. Estimate the gas evolution behavior is needed before doing the isothermal gas-solid reaction experiments using the gas switch method.