A Kinetics of Hydrogen Reduction of Nickel Oxide at Moderate Temperature

Nano-metallic nickel powders are highly-valued materials applied in energy, electronic devices and aerospace, which is known to be produced by the gaseous phase reduction method of NiCl₂. In the case of a gaseous reduction method, size control is difficult due to the agglomeration of nickel powders. Therefore, a method of producing highly-valued nickel nano-powders from Ni(OH)₂ has been proposed. Considering the reduction behavior of bulk nickel oxide has been reported to follow the topo-chemical model. However, reduction behavior of nano-particle is expected to be unknown state. It is necessary to clarify the mechanism of nickel oxide nano-particle reduction. Therefore, in this study, the temperature dependence and particle size dependence on the reduction behavior of from micro scale to nano scale particle was confirmed through TGA experiment. Also, the reduction mechanism of nickel oxide powder was also investigated based on kinetic considerations using the grain topo-chemical model. It was confirmed that the reduction reaction of nickel oxide powder undergoes through the 2nd Avrami model and reduction rate can be expressed by function of temperature and particle size of the powder. Due to the part of the diffusion, the particle size of the powder also affects the rate constant of the reduction reaction.g _(x)= k·f (d)·t.