1990 Volume 27 Issue 6 Pages 399-403
The specific surface area of a powder determined by air-permeability method is generally calculated by the Kozeny-Carman equation. The equation is, however, not rigorous for fine powders because of the influence of the molecular flow of gas through the bed. Modified equations, typically Carman's equation, were proposed nearly 40 years ago. The latter always gives a larger value than the former. The difference between them is not negligible even for 10-micron meter powders, and it increases rapidly with the fineness of the powder. Since the effect of molecular flow modification is nonlinear, the calculated surface area by the Kozeny-Carman equation seems to be a very misleading measure even if it is used simply as a relative value for monitoring. A specific surface area of powder determined by the air-permeability method should almost always be calculated by the Carman's equation and not by the Kozeny-Carman equation.
