Abstract
We have investigated the relationship between environmental conditions and changes on the crystal surface of sodium chloride using an electron probe surface roughness analyzer. The following results were obtained.
1) The surface-roughness of crystal increased in proportion to the increase in temperature and relative humidity. Relative humidity was more effective than temperature.
2) The relative humidity under which the crystal surface-roughness begins to change (Ψt) depended upon temperature, and it decreased in proportion to the increase in temperature.
3) When relative humidity was oscillated at constant temperature, the oscillations did not effect a change in the crystal surface-roughness.
4) When relative humidity was Ψt or below, the adsorbed water on the crystal surface and the molecular water in the air did not change the crystal surface-roughness. When relative humidity was over Ψt, they changed the crystal surface-roughness. These phenomena that changed the crystal surface-roughness we called active water and active humidity.
5) We have made a model elucidating the relationship between the interaction of water and sodium chloride and the caking of high purity salt using active water and active humidity.
6) The caking strength of high-purity salt showed a positive correlation to the accumulated active humidity.
