I'm working on surface area determination and also complete isotherm for gas adsorption on natural clay and modified clay. But the results ( the points ) did not complete and remained at the last adsorption point (0.995 P/Po) . can you give me an idea
Dear Christian Weinberger,
Thank you for the valuable answer and advice. Actually, I repeated the analysis twice, 1st time using about 0.12 g natural clay sample, the tolerance was (0) and equ. was (3) , the 2nd time, the sample weight was about 0.25 g of the sample with Tolerance (3) and equ. (3) . but both analysis did not come to end near P/P0 =1 .
Christian above gave you great advices. The key is to be careful near P/P0=1, because any small deviation and the gas will totally condense and fill your cell, it will so adsorb so much that the equipment will try to measure taking very long times.
Can you show your isotherm? Probably there is a very large uptake at your highest P/P0.
Dear Fernando Vallejos-Burgos
Thank you for the answer, I will try to show the isotherm as soon as possible.
I thought the care should be taken at the initial low pressures not near 1 , so I'm grateful for the advice, but how the care should be taken near P/Po =1 ?? I mean what to control ?? tolerance and equilibration ?? or other settings ??
First question is 'do you really need the value so near P/P0=1?' How about stopping at 0.97 or 0.98? Should be enough for most practical purposes.
Also check the shape of the isotherm: is there anything interesting there that you really need in your analysis?
Personally, I would just be practical and avoid getting too close...
Dear Fernando Vallejos-Burgos
I have attached the isotherm. Actually, maximum P/Po was 0.95, and as you see it stopped at 0.9
Dear Christian Weinberger
I don't use a filler rod for the analysis, I use 6 mm sample cell only.
The regulators of N2 and He gases were higher than recommended by Quantachrom (8-10 psi) , actually, both were more than 1.5 bar which means more than 20 psi .
I'm very grateful for your answers.
I have changed the gas regulators on both He and N2 gases with accurate regulators and adjusted the pressures between 5-8 psi ( as recommended by the instrument manual ) then I have repeated the analysis 2 more times, the analysis stops after 0.90 of P/Po , even 0.95 is not obtained.
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