Dispersion and flocculation behavior of metal oxide powders in organic solvent

The relation between the flocculation and dispersion of metaloxide powders and the properties of solvents, such as dielectric constant and solubility parameter was investigated for TiO2, Al2O3 and Fe-2 O-3. The median diamete r of these metal oxides was measured in many organic solvents, from which t he effect of the solvents on the flocculation and dispersion of metal oxide powders was considered. The metal oxide powders of Al2O3, TiO2 and Fe2O3 tend to disperse in a solv ent of higher polarity, whereas they are apt to flocculate in a solvent of low dielectric constant, because the Hamaker constant between the particles becomes larger in such a solvent. There are, however, some solvents that d o not show these tendencies. It is possible to evaluate the flocculation an d dispersion of these metal oxide powders in many solvents by using Hansen' s three-dimensional solubility parameters (f(p), f(d) and f(h)). For each m etal oxide powder there exists a solvent producing optimal dispersion, and the optimal dispersion point of f(p), f(d) and f(h) is determined by the co mbination of metal oxide powder and the solvent.