Abstract
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\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$${\\text{g}}_{{({\\text{x}})}} = {\\text{k}} \\cdot {\\text{f}}({\\text{d}}) \\cdot {\\text{t}}$$\\end{document}
Highlights
Nickel powder is mainly used for nickel–cadmium batteries, nickel hydrogen batteries, and multi-layer ceramic capacitors [1, 2]
Drop tube furnace is used to reduce nickel oxide to be reduced by hydrogen gas
This study aims at the kinetic analysis of the reduction reaction period and to investigate the influence of temperature and particle size during the reduction period
Summary
Nickel powder is mainly used for nickel–cadmium batteries, nickel hydrogen batteries, and multi-layer ceramic capacitors [1, 2]. Conventional process for making nickel powder can be represented by hydrothermal process and chemical deposition process. Hydrothermal process has uneven growth of particles and chemical vapor deposition has the agglomeration problem, which causes production decreases. A novel flash ironmaking process developed at the University of Utah [3–8], expected to solve these problems. Drop tube furnace is used to reduce nickel oxide to be reduced by hydrogen gas. In the case of drop tube furnace, reduction time limited as traveling time. Reduction mechanism should be analyzed, and can be predicted
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