Determination of optimum operating conditions based on energy requirements for particle coating in a dry process

This paper describes the method for determining the optimum operating conditions of equipment on dry coating processes based on the energy requirement for immobilizing the fine materials on the surface of coarser particles. In the model system consisting of the spherical copper particles (host particles) and the submicron-sized fine alumina particles (guest particles), the guests are immobilized by embedding onto the surface of the host with a high-speed elliptical-rotor-type powder mixer (HEM) to which Zirconia beads are added. The embedding process is approximated by the intruding process of the diamond indenter at the measurement of Vickers hardness of copper plate, and the energy required for embedding is estimated. We have found that both the allowable deformation of copper particles in a single compression by the rotor and the depth of embedding of alumina particles are important parameters in the determination of operating conditions (the rotor speed and the operation time). When the allowable deformation is set to be approximately 0.5% (corresponding to the strain in the intermediate region between the elastic and plastic ones of copper particle), the shape and size distribution of copper particles can be maintained throughout the coating process. Furthermore, the surface condition of coated particles can be controlled quantitatively by the depth of embedding.