Though the hydrolysis of MgH2 starts immediately when in contact with water, it is quickly interrupted because of the formation of a passive magnesium hydroxide layer, which prevents further diffusion of water molecules to the surface of MgH2 particles. As a result, the hydrolysis Reaction 2 is quickly stagnated and stops when the H2 yield achieves 10-20% of the theoretical one. Various methods were suggested to improve the process performance, for example, ball milling , ultra-sonification , alloying of the pristine magnesium with other elements , use of alcoholysis instead of hydrolysis .