The mechanism of liquid bridge formation between two identical spherical particles was theoretically and experimentally analyzed, taking the effect of liquid impurity into account. A modified Kelvin equation, in which the decrease in vapor pressure caused by soluble impurities (salts) contained in the liquid was taken into account, was applied to evaluate the formation and profiles of liquid bridges. It was found that a liquid bridge containing soluble salts could be more easily formed than one formed by pure water, and that the profiles were expressed as functions of the surrounding humidity and solute concentration. In the experiment, bridges formed by Na2SO4, CaCl2 and NaCl solution between two convex glass lenses which were left in a thermohygrostat were observed by a steromicroscope. The effects of humidity and solute concentration on liquid bridge formation could be well explained by the theoretical analysis. It is pointed out that soluble impurities contained in usual wet-powder processing operation have a significant effect on bridge formation between particles after they are dried out.
