ABSTRACT
This chapter discusses the correlation between particle size and the physical behavior of a powder, with particular emphasis on pharmaceutical processes. The processing of most pharmaceutical products that incorporate powders will have a step that involves vibration. Vertically vibrated powders have provoked significant interest among physicists. Vibration-in particular, sonic vibration-historically has been used in industrial powder processing. Size segregation can also occur for nonvibratory powder transfer. In chute flow, fingers of powder appear across the advancing powder front due to the size segregation mechanism. In general, particle size descriptors relevant to powder-handling processes are the geometric diameter and volume diameter. Both of these diameters determine the interparticulate forces and contact areas between powder particles. Powders have been dispersed as aerosols for delivery to the lungs or airways since the invention of the modern dry powder inhaler in the 1960s. The efficiency of dispersion must also be considered in the design and formulation of dry powder aerosols.
