Caking Phenomenon in Sodium Chloride Powder under High-Humidity Environments

Abstract

Sodium chloride powder is known to undergo caking in high-humidity environments, but its mechanism and conditions have yet to be clarified. In this study, we examined the effects of the moisture absorption rate of sodium chloride under plural high-humidity environment on the caking phenomena. Thus, we prepared several experimental equations for calculating moisture flow in sodium chloride powder. Caking was found to occur with estimated sodium chloride moisture absorption rates up to approximately 0.8 mg·h⁻¹, and the caking strength increased gradually with a duration of moisture absorption by sodium chloride. In addition, the measurement results for the amount of moisture in the powder were very close to the results calculated using the experimental equations. When the sodium chloride moisture absorption rate was low, the amount of moisture in the powder took a long time to reach a steady state. We thought that this result is natural because the speed of moisture flow due to diffusion in sodium chloride powder was very low under these conditions.