Multi-point BET specific surface area how to choose points - Database & Sql Blog Articles

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Multi-point BET equation pressure point selection principle The pressure point measurement and calculation range (0.05-0.35) given on the instrument is only suitable for most mesoporous samples, not necessarily suitable for your sample.  See the BET result and judge the point. Whether the range and C constant are reasonable.


Do not use too low relative pressure point data:
Some data points approach the origin (0,0). These too low pressure points are not enough to form a monolayer, so they cannot be used to calculate the specific surface.

 Do not use too high relative pressure point data:


♦ Incorrect points lead to poor linear regression coefficients
 ♦C constant is negative (negative intercept is “disabled”)
 ♦ The upper limit of BET is easily calculated by the maximum value of single-point BET (see the figure below right)

 ♦ Not all samples can be calculated according to the right figure to find the maximum point  ♦ Some samples can not find the maximum value of BET, but increase with the pressure, which means
Wireless area in the range of P/P0<0.15 ♦ Say: BET is not applicable to this type of special sample



抛 Abandon the low-end non-equilibrium pressure (see Figure 1 on the right)
 Calculate no less than three points, preferably five points
总是 Always use data points that are equidistant or as equidistant as possible. Unless the statistical test confirms a significant deviation, do not discard the intermediate data points.  Confirm the behavior of the sample at higher pressures on BET:
 If the BET curve is up-regulated within the “normal” range, it indicates that the adsorption amount of the sample is higher than the BET theoretical value, and the data needs to be taken at a lower pressure (common to the microporous sample).
 If the BET curve is bent in the “normal” range (see Figure 2), it indicates that the adsorption amount of the sample is lower than the BET theoretical value, and the multilayer adsorption form is strengthened (in the 2-4 nm narrow mesopores due to capillary condensation) Exist
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2, MCM-48, and some MCM-41, stearic acid and stearate)