Comparison between BET and HJr methods

Livingstone [88,89] and Emmett [90] have found that in the linear BET region, O.OS x 0.35, a linear HJr plot is only obtained for 50 c 250. For c = 2, 5 and 10 and x 0.4 there is no linear relationship, while for 1(X) the range of mutual validity of the two equations is limited to the region 0.01 0.13. Smith and Bell [91] extended this enquiry to the n-layer BET equation. 

Both the BET and the HJr methods are open to criticism in that they involve the arbitrary selection of constants (k and o) which undoubtedly depend on the nature of the solid surface. 

However, the adsorption of nitrogen at -195 C on the majority of solids is characterized by c values in the range 50-240, so that the surface areas obtained by the two equations are in agreement. 

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