The BJH provides false results you must the 

DFT method it is included in the software of the Autosorb

equipment produced by Quantachromr

Dear Christoffer,

This is a very interesting question and I've also been wondering about it. The manual of my MM instrument just says 'Good for statistical thickness curves', and the MicroActive manual also doesn't explain it. I also searched for papers using the terms 'Faas' and 'BJH' etc, but couldn't find anything. I hope somebody can explain it to us.

The answer above, by Rolando, is quite simplistic. The BJH model has its limitations and those have been extensively documented in literature, but DFT models applied on adsorbent-adsorptive systems for which they weren't developed will generally provide 'falser' results than BJH. DFT is great if there is a model for the system you're studying, but statements like the one above that DFT makes BJH obsolete are at this time only valid for a limited number of materials with 'simple' and uniform pore geometries and homogeneous surface chemistries. The models and theories are definitely improving fast, but for unordered, heterogeneous systems there will probably never be a DFT model that is better than BJH, simply because there is not enough information in a single isotherm for complexer models to yield unique solutions.

(though I sincerely hope somebody proves me wrong because I could make good use of better models)

regards,

Pieter

Hi,

I am asking myself the same question. I found the following on the internet:

"The Faas method was delveloped by George Steven Faass in 1981 in order to create a more accurate distribution. The Faas method includes a correction that adjusts the change in multilayer thickness during intervals in which no cores are emptied"

Source: https://notebook.community/RJC0514/micromeritics/documentation/BJH

thanks Victor,

that brings us a step closer. Faass seems to be spelled with double s, that might be one of the reasons I couldn't find much...

Using your information I found this dissertation: http://hdl.handle.net/1853/32965

but access is restricted unfortunately...

regards,

Pieter

I have confirmed in the Micromeritics that it's a spelling mistake in the references.

the proper reference for this correction should be as follows:

"CORRELATION OF GAS ADSORPTION, MERCURY INTRUSION, AND ELECTRON MICROSCOPY PORE PROPERTY DATA FOR POROUS GLASSES"

A Thesis Presented to The Faculty of the Division of Graduate Studies By George Steven Faass - Georgia Institute of Technology

June 1981

But I also didn't manage to read the document.

Hi,

Another clue for solving this question was provided by a friend who used to work for Micromeritics:

"The Faas correction employs the concept of thickness of an adsorbed layer in a circular pore versus the simple application of thickness on a flat surface.

This usage is fundamentally correct for cylindrical pores.

Old MIC software used the Faas correction by default in applications such as the TriStar 3000. Additional corrections for BJH were added in the mid 2000s and at that time we gave the user a choice for the application of these corrections.

Broekoff de Boer uses a correction in the thickness function – the thickness on a curved surface is greater than the thickness on a flat surface. This was demonstrated by Derjaguin – the FAAS correction is a modification for BJH to do the same."

Both equations – by Harkins-Jura (1944) and by Halsey (1948) – Faass (1981, usually referred as Halsey Faas correction) describe the statistical thickness, only in different way – according to H-J, t2=13.99/[(034-log(p/p0)], while H-F gives formula t3=3.54[5/log(p/p0)].

Thanks V. Tsitsishvili ,

That would be consistent with was said above, if the Faass correction corrects for surface curvature, then the thickness should be going to infinity as p/p° approaches 1, which your H-F equation does and H-J does not.

But I think there is a minus missing in your H-F equation: log(p/p°) is always negative, so t would also be negative?