日本金属学会誌

J. Japan Inst. Metals, Vol. 57, No. 1 (1993),
pp. 54-62

Evaporation Rate of Molten Al in Inert Gas Flows and Characteristics of Condensed Particles

Seiji Yokoyama, Sadao Kokubo, Katsuyoshi Saito, Koin Ito and Masahiro Kawakami

Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi

Abstract:

As a fundamental study of gas evaporation method for preparation of ultra fine particles, molten aluminum was evaporated in a cold gas stream of Ar, He and an Ar+He gas mixture with the levitation melting method. Effects of temperature, gas flow rate and He molar fraction, xHe, in Ar+He mixed gas on the evaporation rate (Production rate of condensed particle) and the particle diameter distribution were investigated. The experimental results were discussed analyzing the temperature distribution around the levitated specimen and using the homogeneous nucleation theory. In this experiment, the aluminum vapor condensed in the boundary layer of diffusion. The evaporation rate and particle diameter were affected by the condensing conditions.
The results obtained were summarized as follows:

(1) Evaporation rate

Evaporation rate increased with increasing temperature and gas flow rate. The evaporation rate in He was larger than that in Ar. The evaporation rate in the Ar+He gas mixture increased slightly with increasing xHe. The rate observed in He was similar to the theoretical one, while the evaporation rate observed in Ar was 0.56 times as small as the theoretical one.

(2) Condensed particle

Both the mean particle diameter and the variance of particle diameter distribution were increased with increasing temperature and with decreasing gas flow rate. They obtained in Ar were larger than in He. They were unaffected by xHe. The mean diameter was estimable from the collision number of nuclei and the distance for particle growth after nucleation. The variance was also estimable from the growth distance.


(Received June 29, 1992)

Keywords:

aluminum, evaporation rate, condensed particle, nucleation, particle diameter distribution, mean particle diameter, variance


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