The influence of Ti + TiC additive on thermal stability and decomposition kinetics of nanosized MgH₂ phase in Mg-based  mechanical alloys 

Abstract

Mechanical alloys Mg + 10 wt.% Ti and Mg + 5 wt.% Ti + 5 wt.% TiC (MАs) 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 МAs 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 = k₀ exp(–E_a/RT) (the Arrhenius equation). The tested materials showed high potential as hydrogen storage alloys, especially for stationary applications.