The Influence of Ti plus TiC Additive on Thermal Stability and Decomposition Kinetics of Nanosized MgH2 Phase in Mg-Based Mechanical Alloys

Mechanical alloys Mg + 10 wt.% Ti and Mg + 5 wt.% Ti + 5 wt.% TiC (MAs) were synthesized by reactive mechanical alloying (RMA). Thermal stability and hydrogen desorption kinetics of the nanosized MgH2 phase in the obtained MAs were examined by means of thermal desorption spectroscopy at a hydrogen pressure of 0.1 MPa. The stabilizing effect of Ti on the nanocrystalline structure and growth of the crystallites (grains) of the MgH2 phase during the cycling was also evaluated. It has been established that the complex doping by Ti and TiC leads to a significant improvement in the desorption of hydrogen in the nanosized MgH2 phase of MAs. The role of Ti and TiC as alloying elements in improving the hydrogen desorption kinetics of MAs was studied. The catalytic effect of adding 5 wt.% Ti + 5 wt.% TiC to magnesium in improving the kinetics of hydrogen desorption is significantly lower than the catalytic effect of adding 10 wt.% Ti. Due to such alloying, the decrease in the thermodynamic stability of MgH2 is not established. The average rate of the reaction does not depend on the hydrogen concentration and is equal to the rate constant k = = k(0) exp(-Ea/RT) (the Arrhenius equation). The tested materials showed high potential as hydrogen storage alloys, especially for stationary applications.