Solved problem:

Nitrogen was employed to determine the surface area of 1.0 g sample of silica gel and results obtained shown in table below. The sample of silica gel was maintained at the normal boiling point of liquid nitrogen (77K). One molecule of nitrogen occupies 16.2  × 10^-20 m² area of plane surface. Calculate the specific surface area of silica gel by the BET method. The saturated vapor pressure p₀ of nitrogen at 77K  is 101.3 kPa.

Solution:

The BET equation in following form is used.

The   is plotted as function of  . The plot is shown in Fig 1

Table  1. Calculation for plot of BET equation

Fig. 3. Linear plot of BET equation

Intercept = 943.5 m^-3               ;           Slope = 137486 m^-3
Monolayer volume

Then surface area for 1 gm sample can be determined as :
 

As initially 1 gm sample was used, specific surface area of sample = 31.4 m²/g

 

Book reference

 

•  S. Lowell, Joan E. Shields, Martin A. Thomas ,Characterization Of Porous Solids And Powders: Surface Area, Pore Size And Density - Springer, 2006

•  J.J. Carberry , Chemical and catalytic reaction Engineering, Dover Publications, 2001

•  J. M. Thomas & W. J. Thomas, Principles and Practice of Heterogeneous Catalysi, VCH, 1997

•  Sam Zhang, Lin Li, Ashok Kumar, Materials Characterization Techniques, CRC Press, 2009

•  Y. Leng, Materials Characterization: Introduction to microscopic and spectroscopic methods, John Wiley & Sons, 2008