ASTM D4641-94(1999)e1 PDF

SCOPE 1.1 This practice covers the calculation of pore size distributions for catalysts and catalyst carriers from nitrogen desorption isotherms. The computational procedure is particularly useful for determining how the pore volume is distributed in catalyst samples containing pores whose sizes range from approximately 15 to 1000 Å (10 Å-1 nm) in radius. It should be used with caution when applied to isotherms for samples containing pores both within this size range and pores larger than 1000 Å in radius. In such instances the isotherms rise steeply near / Po = 1 and the total pore volume cannot be well defined. The calculations should be begun at a point on the isotherm near saturation preferably in a region near / Po = 0.99, establishing an upper limit on the pore size distribution range to be studied. Simplifications are necessary regarding pore shape. A cylindrical pore model is assumed, and the method treats the pores as non-intersecting, open-ended capillaries which are assumed to function independently of each other during the adsorption or desorption of nitrogen. Note 1-This practice is designed primarily for manual computation and a few simplifications have been made for this purpose. For computer computation the simplified expressions may be replaced by exact expressions. 1.2 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.