| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1998: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1997: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
The formation of metal clusters by a supersonic expansion of vapor has been investigated both experimentally and theoretically. In the experiment, metal (silver or zinc) was vaporized in a crucible, and the vapor effused into a high vacuum through a nozzle (typically 2mm in diameter). In order to detect the cluster formation in the supersaturated vapor caused by the adiabatic expansion, a retarding field method was used. It was found that the cluster could be destroyed by the ionization and electrical acceleration. Three kinds of nozzles were tested, namely, a cylindrical nozzle, and wide and narrow divergent nozzles, and it was found that the wide divergent nozzle is most effective for the production of clusters. Further, the effect of temperature difference between nozzle and crucible was investigated. It was found that the cluster formation was most pronounced when the nozzle temperature is about 100 K lower than that of crucible, which indicates that the heat transfer from the nozzle wall to the vapor flow affects the cluster formation. In addition to the experiments, a molecular dynamic simulation was performed to investigate the properties of cluster in a supersaturated vapor, and the reduction of surface tension coefficient with the decrease of cluster size was revealed. By considering the surface tension reduction in the estimation of nucleation rate, the cluster formation was analyzed based on the temperature and pressure field obtained by a numerical simulation of the nozzle flow. The surface tension reduction drastically increases the nucleation rate, however, the predicted cluster size was too large. Therefore, the heat generation due to the latent heat of condensation and heat transfer between cluster and vapor were taken into account in the analysis. The calculated result well explains experimental results for the low melting point metal, Zn.
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