Vacuum effect on the mechanism of composite particle formation in physical preparation

Abstract Using the apparatus which has been described in a previous paper (H. Kaga, Y. Taya, H. Katayama, Y. Hamaguchi and K. Mukaida, Powder Technol., 91 (1997) 147), two types of composite particles were prepared under various reduced pressures: alumina core particles coated by Cu guest particles which are much finer than the core particles, and Cu core particles coated by alumina guest particles which are much finer than the Cu core particles. From the experimental results for the alumina core–Cu guest composition, it was found that the oxygen content in the Cu layer varied with the difference of residual pressure. Fragments of alumina core particles due to frictional action during the physical treatment process were seen to disperse in the Cu surface layer. In the Cu core–alumina guest composition, micro-dimples on the surface of the Cu core particles were observed as the result of being depressed by hard alumina guest particles. Fine Cu particles were detected close to the surface of the alumina layer. For longer processing times, a grain boundary-like surface was observed in the Cu layer suggesting some sintering had been undergone during the process. Consequently, the temperature rise was estimated to be up to around 1000 K. Several gaseous substances were also found during the processing.