Abstract
The angles of repose of spherical glass powder and α-alumina were measured in various aqueous solutions in order to examine the effect of interparticle force on the angle of repose. NaCl, Na-pirophosphate, Na-polyphosphate and Na-polyacrylate were used for this purpose. The angles of repose were very small within a certain range of concentration of dispersing agents, for example, 10-4∼10-3mol/L of Na-pirophosphate. The measurements of apparent particle size and sedimentation volume confirmed that the powder particles were dispersed in these solutions. In the solution of NaCl, the angle of repose increased slightly with increase of concentration. Abnormally high values were obtained with Na-polyacrylate.
In the state of dispersion, for example, in 10-3mol/L Na-pirophosphate, the angle of repose decreased with the decrease of particle size and seemed to be constant in the range smaller than a certain particle size, increasing with the decrease of particle size in the solution of flocculating agent. In these two states, however, the angles of repose became nearly similar as the particle size increased.
According to the Verwey-Overbeek theory, the interparticle potentials were obtained by the measurements of ζ-potential. From these results it was explained that the angles of repose were very small and almost constant in the range where the repulsive force were larger than the weight of a particle and that they took another constant value where the weight of a particle were larger than the attractive force.
