Dispersion forces and plastic deformation in tablet bond.

A model for tablet bond formation is developed. It assumes that attraction forces arise from dispersion forces between surfaces with spherical curvature. The radius of these surfaces depends on the amount of plastic deformation produced during compression. The radius of curvature is calculated by using Hertz's equation for elastic deformation, which is assumed to hold during decompression. The number of contact points per unit cross section is taken as a simple multiple of a number deduced from the particle size, the indentation hardness values, and the solid fraction. A similar approach is used to replace the area per contact point produced when under compression. The resulting equation is used to estimate the bonding index. Values corresponding to the lower range of experimentally determined bonding indices are obtained. Arguments are presented to suggest that large values of the bonding index (tensile strength/indentation hardness) probably result principally from plastic (including viscoelastic) deformation during decompression. Nondispersion forces may contribute but are not believed to be of sufficient magnitude to account for the total bond for materials that exhibit a large value of the bonding index.