ABSTRACT
Spray drying (Fig. 21) is another technique widely used to produce spheroidal materials. It was previously described as an intermediate process step; here we consider it as a final operation. The process described in Chapter 9 produces spheres 1/16 in. or greater in size, whereas spray drying produces microspheres that are generally smaller than 60 mesh and are useful primarily in fluidized beds. This process also is more art than science, but one who has experience in spray drying can quite well predict from viscosities, solids contents, and film-forming characteristics whether the slurry will produce suitable microspheres and, if so, what the best operating temperature, gas velocity, spray head types, and rotation speed would be. In general, it can be said that gel-forming materials—materials that shrink and coalesce on drying or that are film-forming materials — ordinarily can be spray dried to form a satisfactory product.
