Ultra fine particle/powder (UFP) of metal is generated by hydrogen reduction of MCl
2 (M=Ni, Co, Fe) vapor. The effect of reaction temperature, hydrogen flow rate, residence time and total flow rate are discussed and it is concluded that the partial pressure of MCl
2 (g), P
MCl2, has the greatest influence on the average particle size. Smaller P
MCl2 gives smaller median diameter.
The particle size distributions are almost log-normal and their geometric standard deviations distribute between 1.36 and 1.60 independently on the median diameters.
A simple model without any adjustable parameters is proposed based on the following assumputions;
1. the reaction is instantaneous irreversible one and the initial reaction product is metal atom or cluster (called monomer),
2. because of very high supersaturation, monomers can start coagulation/coalescence among themselves.
The numerical computation was done and compared with the experimental result. It is concluded though this model is very simple it explains the experiments facts fairly well.
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