Using the common static BET method (Nitrogen adsorption-desorption isotherms), the BET surface area of a mineral waste is measured as 1 m2/g. Can anyone help me to find a more precise method for measuring the low surface area of such material?
For measuring low surface areas accurately with BET you have to use krypton instead of nitrogen. Hope this helps.
thats right prof but if you dont have Krypton you can use Nitrogen but increase the amount of sample 1gm or 2 gm to decreas the error
check this paper:
http://www.sciencedirect.com/science/article/pii/S0167299107800085
To measured low surface area, the best is to use Krypton, but this is a very expensive gas and normally aren’t available in the laboratory. Another method is use Ar in liquid nitrogen. The idea is reduce the vapor pressure of the adsorbate to reduce the error in the measured free volume. The saturated pressure of N2 at 77 K is approximately 750 Torr (depend of the atmospheric pressure), for Kr is 2.3 Torr. Ar is approximately 200 Torr. Obviously the best is Kr, but in many laboratories is impossible have Kr. If you have many samples, very good, but for low quantities of samples is problematic.
Instead of the expensive Krypton you can use a simulation model which can calculate the surface area via the pore volume distribution. One of this is the CPSM. I'm available to simulate your nitrogen hysteresis loop using the CPSM code. Just sent me data.
1 m2.g-1 is usually still OK for N2 physisorption on commercial equipments. As suggested by Ahmed Helal, you simply need to increase the amount of sample in the cell. Ideally you should reach 5 m2 of sample surface in the cell. If the volume of the standard cell is not enough to accomodate your sample, you will need to buy a large volume cell
Inverse Gas Chromatography can be used for powders with low surface area (
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