Micropore testing technology

Generally, the pores on the surface of the micro-nano powder are divided into three categories according to their size. Large pores with a pore diameter greater than 50 nm are mesopores or mesopores with pore diameters between 2 and 50 nm. In theory, the pore size distribution measured by nitrogen adsorption method is only suitable for mesopores. With the continuous advancement of technology, the range of pores measured by the nitrogen adsorption method can be expanded to the range of 0.35 ~ 500nm. The largest pores need to be measured by the mercury intrusion method. 0.35nm has reached the limit of micropores, and it is meaningless to be small. The technique of measuring micropores is very complicated, because micropore filling can occur only when the relative pressure of nitrogen is very low (<0.01). The pore size of 0.5 ~ 1nm can only be generated when the nitrogen partial pressure is less than 0.00001, dynamic The method is powerless. The static volume method requires a nitrogen pressure of less than 1Pa. In order to measure finer pores, a molecular pump is often used. It is also advantageous to use argon as the adsorbate. The pressure of micropore filling is higher than that of nitrogen. The feasible method is to use CO2 as the adsorbate for adsorption at room temperature, and the vacuum of the molecular turbopump stage is not needed. Changing the adsorbate involves many other problems and is generally not used. There are many methods for micropore analysis, including DR method, t-graph method, αs-graph method, HK, SF method, NLDFT method, etc., among which the t-graph method is relatively practical. In the t-graph method, the adsorption amount V is defined as a function of the adsorption statistical layer thickness t. The key is to select an appropriate t curve. From the Vt diagram, the specific surface area, micropore diameter, and micropore volume can be easily obtained. There are many applications in the analysis of microporous materials such as activated carbon, and the effect is very good.