 The fitted Avrami exponents vary within the range n=0.5-1.1, close to the values reported by Huang et. al for the hydrolysis of MgH2 in 0.5-4.5 wt.% aqueous solutions of NH4Cl. According to ref. , the values of n close to 0.5 correspond to diffusion as the rate-limiting step while the higher values of n testify about possible contribution of the nucleation and growth mechanism.