chapter  4
Pages 13

Powders are employed in many pharmaceutical processes. They are more difficult to handle and process than liquids and gases primarily because their flow properties are fundamentally different. Unlike fluids, a particulate mass will resist stresses less than a limiting value without continuous deformation, and many common powders will not flow because the stresses imposed, for example, by gravity are insufficiently high. Often additional processes that improve flow, such as granulation and fluidization, are adopted to facilitate powder transport and powder feeding.