Abstract
Ball-milling of thirty-two kinds of powders were investigated. Equation (1) was applied for rate of increase of surface area. dS/dt=k1 exp (-k2S)(1) Parameter k1, was proportional to 1/Mohrs' es hardness and tended to be small for the samples with high melting point. Rarameter k2 was small for the sample with high melting point and little solubility in water.
Critical particle size, Dc2, was found at which maximum porosity in loosest packing was obtained not only for crushed samples but for samples of equal particle size. For particles below Dc2, gravitational force of a particle may be negligibly small compared with cohesive force between particles. Dmin was proportional to Dc2. Parameter k1 tended to decrease and k2 to increase with increase of ρ·Dmin. Rate of increase of surface area by ball-milling is considered to depend on coherency of powder particles expressed as a function of surface energy, melting point, solubility in water, true density and so on.
