For some materials, its surface area is one of its important physical properties, and directly affects its performance during use, such as: catalyst materials, battery materials, pharmaceutical raw materials and so on. However, the surface structure of the material is extremely complicated, so we need to determine the surface of the material by certain methods. Common methods for measuring surface area include: gas adsorption,
X
Suspected of small angle diffraction method, direct measurement method, etc. Different methods use different methods, and the general method is gas adsorption.
Researchers have conducted many theoretical studies on the possibility of gas adsorption for measuring surface area, among which
Brunauer
,
Emmett
with
Teller
The proposed model and calculation formula are the most famous, called
BET
law. Currently
BET
The method is the standard method for workers to measure the surface area of ​​solids and is the most common method.
BET
The method calculates the surface area per unit mass of the material, also known as the specific surface area, in units
m 2 /g
.
It is well known that the gas adsorption method tests the gas adsorption amount of a material under a plurality of different relative pressures under isothermal conditions, and after such a point is connected, an isothermal adsorption-desorption curve is formed. Specific surface area is measured on an isothermal adsorption curve
3-5
a point, use
BET
The equation is calculated and calculated. So the question is, what kind of point calculation is used to calculate the specific surface area is meaningful?
According to theory and long-term practice, currently prescribed
BET
The selection range is
P/P 0 : 0.05-0.3
. But for different samples, this interval will also need to be changed. Especially microporous materials. In general, microporous materials are used in calculations.
BET
The point will be relatively small relative pressure, the common is in relative pressure
10-3
Within the interval, even smaller. No matter which interval the selection point is, be sure to ensure
C
The value is positive and the correlation coefficient is
0.999
the above. As long as these two points are guaranteed, the obtained specific surface area value is meaningful.
Well, the problem is coming again. Within the above range, we are guaranteeing
C
Positive value and correlation coefficient at
0.999
Above, there may be different specific surface values, which one is right? The answer is, as long as the above two conditions are guaranteed,
BET
The value is a valid value. If you want to compare with other data, try to ensure that the points are consistent.
These years
BET
Are you right?
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