I want to know the equation that I should use when I calculated the surface area using a plot like this one in the attachment. What are the parameters required for the calculation?
Dear all, the attached files give more details. My Regards
Please follow the link:
https://particle.dk/methods-analytical-laboratory/surface-area-bet-2/#:~:text=The%20specific%20surface%20determined%20by,method%20used%20complies%20with%20Ph.
Abdelkader BOUAZIZ Thank you very much. My question was focusing definitely on this point considering the calculation of monolayer capacity. It is different from the conventional one. It is usually calculated by 1/(slope + intercept). How it was calculated in this case? What is the meaning of E in this equation shown in the attachment?
Every thing is straight. Please see page 6 in the 2nd document. Good Luck
Hi;
Surface measurement according to Brunauer, Emmett and Teller is equivalent to determining the amount of gas required to form a monomolecular or "monolayer" layer of gas on the solid. Knowing the cross-section and number of gas molecules that make up the monolayer, the surface area of the solid can easily be calculated.
These authors assume that the condensation rate on the uncovered surface is equal to the evaporation rate of the molecules of the first layer and that all the layers, except the first one, immediately influenced by the surface, are equivalent to each other and have properties identical to those of the liquefied gas.
The mathematical formulation of these conditions leads, after development, to the equation B.E.T.:
(P/P0)/(V(1-P/P0)) = 1/(Vm C)+((C-1))/(Vm C) P/P0
where V is the total volume of gas adsorbed at the measured pressure P; Vm is the volume required to cover the surface of a monomolecular layer of gas; Po is the saturating pressure of the gas at the adsorption temperature and C is a constant. By taking the first member of this equation as the ordinate and P/Po as the abscissa, a straight line of slope (C - l)/(Vm C) is obtained, with the intercept at the origin being 1/Vm C. Vm can be calculated from these values. If Vm is known, the specific surface area A of the sample will be given by:
A = (Vm S0)/w
where w is the weight of the sample, Vm is defined above; So, the area covered by a monomolecular layer, is calculated from :
S0 = (N σ)/M
N is the Avogadro number, 𝞂 is the section of an adsorbed molecule and M is the molar volume. The exact value of the 𝞂 section of the nitrogen molecule is 16.2 Å2/molecule.
With my best regards
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