Evaluation of bubble content in aqueous alumina slurries

Entrapped air bubble is one of the main defects in slurry processing of ceramics. For preventing bubble occurrence or removing them efficiently, an improved knowledge of bubble behaviors in slurries is indispensable. In this paper, effects of particle characteristics, solid loading and dispersant concentration on bubble content in aqueous alumina slurries were studied experimentally. The results showed that the characteristics of initial powders, i.e. particle size distribution and shape, significantly affected the bubble content in slurries. The bubble contents were drastically enhanced by smaller and irregular particles with a higher specific surface area. Moreover, the bubble contents were also greatly increased with increasing solid loadings, and this influence was more pronounced for the particles with a higher specific surface area. No noticeable change in bubble content was resulted from varying the dispersant concentration. A new parameter, solid surface area per unit volume of slurry has been introduced to interpret these effects of powders. It is found that the bubble content shows a parabolic increase as a function of the parameter.