Thermal diffusion as a purification tool.

In the field of physical sciences and in chemical process technology, the purification of materials is very often most important. In many situations conventional processes such as distillation and crystallization are not applicable as in the case of closely boiling liquids, organic dyes, biologicals and colloids. I n such cases, the less conventional techniques assume a great importance. Of the many unusual techniques, thermal diffusion, which is based on the fact that application of a temperature gradient on a homogeneous solution establishes a concentration gradient, has been widely investigated both theoretically and experimentally. Because of its special application it continues to receive considerable attention from researchers as a tool of purification in spite of the fact that i t is a n expensive process. I n the present paper, i t is proposed to briefly discuss some aspects of thermal diffusion as a purification technique.