ABSTRACT
Size reduction of a massive solid phase in a gaseous environment can be achieved by two different means: applying stress at two particle surfaces simultaneously and applying stress at a single particle surface. Dispersion of a powder into a liquid requires deflocculation. This may present a problem when there is no stabilizing effect such as surface charges or polymers effecting steric stabilization. Shear effects a duplicate effect on dispersions: it may disrupt aggregates, and it may bring particles together inducing coagulation. Thus, the final particle size reached is the outcome of two counteracting processes. Low local polymer concentrations are likely to occur when the polymer is added to an already existing dispersion, shortly after addition of the polymer, even when the overall concentration of the polymer is high enough to lead to a stable dispersion. Treatment of a coagulated dispersion by ultrasonics may result in pronounced deaggregation. Ultrasonics have been found not only to disperse aggregates but to enhance reaggregation.
