Adhesion Force Arising from Solid Salt Bridge Formed after Drying of Liquid Bridge

Abstract

Water bridges formed among particles in industrial processes often contain soluble impurities such as salts. When such bridges are exposed to dry air, water in the bridges will vaporize and the salts crystalizes to form solid bridges.
Solid bridges between two glass spheres were formed from NaCl, KCl, KNO₃ and Na₂SO₄ solution by controlling humidity, and their tensile strength was measured. It was found from these experiments that 1) the adhesion force of a solid salt bridge which was uniformly formed in the gap between two spheres was one to two orders of magnitude larger than that of a water bridge without crystallization; 2) the average adhesion force of solid bridges was proportional to the 1/2 power of the product of salt volume and particle radius; and 3) the adhesion force of bridges of NaCl and KCl was influenced by the surrounding humidity, which was below their deliquescent points, because they adsorbed water until complete recrystallization took place.