Mechanism of the combined coating-mechanofusion processing of powders

The mechanism of coating of a coarse granular material by a fine cohesive powder in a rocking-type mixer, presented in a previous publication, is here extended to the case of mixers with higher mechanical energy input, such as high-speed-stirred mixer and high-shear mill. The influence of fines concentration, agitation speed and mixing time on some physical properties of the mixture is discussed, and photographic material showing the particles' surface modification with time is supplied. The rate and degree of dispersion of fines onto the coarser particles' surface and, therefore, the homogeneity of the mixture, depend on the type and strength of the forces imparted to the powder and, consequently, on the type of mixer used. The flowability and packing characteristics of the mixture are controlled by two factors: the surface texture of the non-coated portion of the coarse particles and the amount and degree of dispersion of the coating agent over the bulk material. Mixing for a short period of time in the high-shear mill results in a surface fusion of the particles and penetration of the fines into the body of the larger particles.