Titanium Absorption, The Hydrogen Isotope Effect Studies

Isotope effects of titanium-hydrogen system in thermodynamics and kinetics were studied. There is few report on thermodynamic and kinetic characteristics of titanium tritide reaction up to now. Isotope effects of hydrogen for absorption protium-deuterium mixture in titanium were firstly studied.The p-c-T curves of absorbing protium, deuterium and tritium in titanium were measured using method of step equilibrium on an experimental apparatus of metal hydride. The three sets of p-c-T curves for protium, deuterium and tritium have the same trend, they have one plateau at temperature below 300℃ and two plateau at temperature above 300℃. The thermodynamic parameters of the different phases were determined according to the Van't Hoff equation. It is observed that there are obvious thermodynamic isotope effects when absorbing protium, deuterium and tritium in titanium. The equilibrium pressure increase in the sequence H, D, T at the same temperature and the same atomic ratio but the enthalpy changes and the entropy changes take the order of T, D and H from small to large. The lagging effect was not observed in reversible process of titanium absorbing and desorbing hydrogen on our experimental condition.The pressure changes during the absorption of protium, deuterium and tritium in titanium were investigated at 550~750℃ by using the method of reaction rate analysis in a constant volume system and then the rate constants of absorbing protium, deuterium and tritium in titanium are calculated. The results show that the rate constants increase with raising temperature. The activation energy value of absorbing protium, deuterium and tritium in titanium obtained by this analysis are (55.6±2.4)kJ/mol, (110.2±3.0)kJ/mol and (155.7 ±3.2)kJ/mol respectively. The activation energy is the highest for tritium and the lowest for protium. This means that there are remarkable kinetic isotope effects during absorbing protium, deuterium and tritium in titanium and tritiation of titanium is the most difficult process.The pressure changes during the desorption of TiH_x, TiD_x , TiT_x were investigated at 350~550℃ by using the method of reaction rate analysis in a constant volume system. The results show that the rate constants of the desorption increase with raising temperature. The activation energy of desorption for TiH_x, TiD_x , TiT_x are (27.1 ±0.4)kJ/mol, (42.3 ± 1.9)kJ/mol and (62.1 ±1.6) kJ/mol respectively. The desorption activation energy of titanium tritide is higher than that for titanium deuteride and titanium protide. There are remarkabledesorbing kinetics isotope effects and it can also prove that titanium tritide is more stable than titanium deuterium and titanium deuterium is more stable than titanium protide .To meet the need of the research on isotope effects of mixed hydrogen isotope gas, we set up an analysis method of mixed hydrogen isotope composition through introducing the single atom ionization quotient and compression ratio correction factor of molecular pump on MAT253 spectrometer. We used this method to determine six samples of different concentration and found that this method was effective for H2-D2 mixed gas and its relative standard deviation is below 0.3%.The characteristic of absorbing H2-D2 mixture were researched under the same experimental condition and the separation factors of hydrogen isotopes were measured. It was found that there is a linear relation between the separation factor's logarithm and absolute temperature's reciprocal as In a =-0.13 + 107/T. The separation factors of titanium absorbing different composition's mixed gas in 200 °C are measured and found that composition of mixed gas has not an effect on the separation factor in the same temperature. It was found that when titanium absorbs H2-D2 mixture there is an obvious isotope effect and the separation factors are independent of H/D ratio in the mixture when titanium absorbing H2-D2 mixture.