Once the sample is cleaned, it is transferred to an external Dewar (or other
In a constant temperature bath), it is kept at a constant temperature. Then, make a small amount of gas
The adsorbate, the adsorbate, gradually enters the sample tube that is evacuated. Enter sample
The adsorbent molecules of the quality tube quickly reach the solid sample (ie, the adsorbent).
The surface of a hole. If the sample has both micropores and mesopores, then the adsorption
The isotherm should contain the following stages:?
1)
Micropore filling (relative pressure less than 0.01) at very low pressure:
The initial section of the isotherm containing the microporous sample showed a significant large and steep rise and then bent
Qucheng platform. The data of this curve can characterize the micropore volume and micropore
cloth. Because the pore size is close to the diameter of the gas molecule, choose the correct suction
The attached gas is very necessary. ?
2)
Single layer adsorption zone: as more and more gas molecules are introduced into the system
System, when the micropores are filled, the adsorbate molecules will form on the entire adsorbent surface.
A thin layer. The adsorption isotherm exhibits a knee-like curvature. ?
3)
Multi-layer adsorption zone: immediately after the adsorption curve enters the platform zone, indicating
Surface multi-layer adsorption occurs here.BET
Theory is exactly at this levelThe adsorption curve data of the segment calculates the specific surface area. ?
4)
Capillary condensation zone: when the relative pressure is greater than 0.4, continuously
Layer adsorption is accompanied by a capillary condensation process. Capillary condensation is in the pore
The process of converting the adsorbed gas into a liquid with an increase in the partial pressure ratio, describing this
The classical equation of Cheng is the Kelvin equation. This equation quantifies the equilibrium gas pressure
The ratio of the size of the capillary to which the gas can be condensed. Using Barrett,?
Joyner? and? Halenda? (BJH)?
Calculation methods such as law can be based on balanceThe gas pressure calculates the pore size to obtain a cumulative or differential pore size distribution map. ?
?
As the adsorption mass equilibrium pressure tends to be saturated, the pores of the adsorbent will be
The adsorbate is completely filled. If you know the density of the adsorbate, you can calculate
The volume occupied by it, and then the total hole of the sample can be calculated accordingly
volume. If we reverse the adsorption process at this time, from the system
By reducing the amount of gas, the desorption isotherm can be obtained. ?
? Because of the different mechanisms of adsorption and desorption, the adsorption and desorption isotherms are very
Less able to overlap. The hysteresis of the isotherm is related to the pore shape of the solid particles. ? 
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