Kinetics of property change associated with atmospheric humidity changes in alumina powder granules with PVA binder

A microcompression testing machine was used on single Al2O3 powder granules to study their stress–strain behavior as a function of relative humidity. The test granules were prepared by spray-drying slurries containing 3 mass% poly(vinyl alcohol) and Al2O3 powder. The stress–strain curves and granule strength were determined at regular time intervals, after step changes in atmospheric humidity. When stress was applied, deformation increased rapidly with the stress. This stress corresponded to the fracture strength of the granule. In a dry atmosphere, the granules deformed linearly with increasing stress, and a rapid change in strain was noted above a certain critical value of increased stress. In a wet atmosphere, the granules deformed continuously at lower stress. The mechanical properties of the granules changed rapidly with time when the atmospheric relative humidity was changed. Within 3 min of exposure to a new atmosphere, the mechanical properties of the granules reached equilibrium values. The change in properties with humidity was controlled by moisture diffusion in the granules and was reversible.