The Research On The Preparation Regularities Of Ultra-fine Metal Powders Utilizing Inert Gas Evaporation And Condensation Technique At Reduced Pressures

Evaporation and condensation technique is an effective method for the preparation of ultra-fine metallic and alloy powders. A few developed countries abroad have successfully used it in commercial production at the present. However, there still exists a great distance between the developed countries and our country. In order to master this key technique, the aim of this thesis is focused on the preparation processing regularities of ultra-fine metallic powders utilizing inert gas evaporation and condensation technique at reduced pressures.In this paper a novel ultra-fine powder collector has been designed. Induction electric current was used to heat the metal for the preparation of ultra-fine powders. The rule of evaporation of molten metal and the effects of processing parameters on the evaporation rate of molten metal, the productivity, the morphology, the mean particle size and the particle size distribution of ultra-fine metallic powders are systematically investigated. The conclusions are as follows:(1) The evaporation rate of molten metal and the productivity of ultra-fine metallic powders can be remarkably increased by elevating evaporation temperature of molten metal, decreasing the pressure of inert gas, elevating the evaporation area of molten metal and the height of the molten metal surface in the crucible.(2)The mean particle size, the particle size distribution and the morphology of the as-prepared ultra-fine metallic powders are greatly affected by the evaporation temperature of molten metal and the pressure of inert gas, namely, the mean particle size will increase and the particle size distribution will become broader along with increasing evaporation temperature or gas pressure. Additionally, great differences exist in the morphology of ultra-fine metallic powders produced at different conditions . Small particle are generally in the spherical shape, while the bigger particles are triangle or polygon or other special crystal morphology. Therefore the morphology, the mean particle size and the particle size distribution of ultra-fine metallic powders can be controlled by adjusting the evaporation temperature of molten metal and the pressure of inert gas.(3) Under the experiment conditions, the crystal structure of the as-prepared ultra-fine metallic powders is almost the same as that of the bulk metal without obvious oxidation.