Modeling of Temperature Fields and Gas-Dynamic Flows in the Zone of Placement of Lithium Ceramics Samples During Tga Studies

Abstract

Modeling of thermogravimetric experiments is an essential tool for understanding the physical and chemical processes that occur during research. This approach helps improve data quality and gain a better understanding of what is going on during thermogravimetric analysis.This paper describes the procedure for modeling a TGA experiment on a Mettler Toledo TGA/DSC 3+ gravimeter, which, together with a mass spectrometer, a humidity generator, and an analytical balance, is part of the TiGRа analytical complex (NNC RK, Kurchatov, Kazakhstan). A description is given of the problem of modeling heat transfer processes in a gravimeter, the process of mass transfer of the reaction gas and reaction products in the gravimeter chamber, as well as the processes of chemical interaction of lithium ceramics with the reaction gas during TGA experiments. Helium with an admixture of oxygen and water vapor was considered as the purge gas.Calculations carried out using the developed model show that at a purge gas supply rate of 100 ml/s, the temperature gradient across the samples will be 2–2.5 ℃, and the gas velocity in the pebble bed will not exceed 0.5 mm/s. It has been established that the concentrations of CO2 carried away by the helium flow above the backfill and in the exit zone (in the sampling zone of the mass analyzer) at different temperatures can differ up to 22 times. Thus, using the developed model, it is possible to calculate the concentrations of CO2, CO, and H2 at any point of the thermogravimeter furnace directly above the test sample, inside and/or outside the pebble bed, in the area of the reaction mixture inlet and in the sampling area of the mass analyzer, etc. Also, if necessary, it is possible to determine the coefficients for recalculating concentrations in different sections of the pebble bed relative to the measured value. Using this model, it is possible to determine the parameters of chemical reactions – the initial concentration of carbon in the pebble bed, the activation energy of the reactions, and the concentration of O2 and H2O impurities in the purge helium, achieving the coincidence of the calculated and recorded curves using a mass analyzer. The developed model has a practical potential for further expansion of its analytical capabilities by refining the list of chemical reactions.