Hydrothermal reaction kinetics. The decomposition of nickel(II)hydroxide

The fractional extent of decomposition of ripened Ni(OH)2 into green NiO in alkaline hydrothermal conditions under nitrogen is given by the rate law 3√α = k(OH-)t where k 2.4 x 10-5 kg mol-1s-1 at 561 K and (OH-) represents concentration of OH-. The Arrhenius activation energy is 220 +- 25 kJ mol-1. The reaction is accelerated moderately by O2 (giving black NiOsub(1+x)) and strongly by added NiO. A reaction mechanism involving dissolution of Ni(OH)2 as Ni(OH)3- (aq) and rate-determining, surface-controlled reprecipitation of this as NiO is proposed. The results are of technological interest in connection with the corrosion of nickel alloy components such as heat exchangers in water cooled nuclear power plants