Effect of Ambient Atmosphere and the Rate of Heating on the Behavior of Thermal Decomposition Titanium Hydride (TiH2) Powder

Understanding the thermal decomposition mechanism of titanium hydride, especially determining of the best conditions of the primary heat-treatment of this material, would be an important step on the process of production of Al foams. In this research, the STA diagram of titanium hydride powder with the heating rate of 10ºC/min in the presence of Argon gas with %99.99 purity and, also, STA diagrams of this powder with the heating rates 5, 10, 20, 25, 30ºC/min at air were determined. In addition, the DSC diagram with the heating rate of 10ºC/min at 500ºC was studied and determined. Results showed that titanium hydride powder (TiH1.924) decomposes in two stages TiH1.924→δ-TiHX→α-Ti, at 534ºC and 624ºC, respectively. The thermal decomposition mechanism of TiH2 complexes, in conventional atmosphere, is quite complex and different in comparison with the similar condition in the Argon gas. In the presence of air, hydrogen comes out from titanium hydride during eight stages. In the DTG diagram a minimum was noticed, at the temperature of 835ºC, which can be the sign of reducing of the rate of oxidation and weight gaining of the powder. The thermal decomposition mechanism of TiH2 powder seems to be under control of both internal diffusion (diffusion of hydrogen and oxygen atoms within the layers of α solid solution, titanium oxide and titanium hydride) and the chemical reaction (titanium oxidation). The temperature of hydrogen excretion from TiH2, in the presence of air, increased relative to its excretion, in the presence of the argon gas at the first stage from 534ºC to 550ºC and at the second stage from 642ºC to 660ºC. Based on the results of this work it seems that the most appropriate temperature, for the primary heat treatment of TiH2 powder, is between 300-500ºC