Sample pretreatment conditions for specific surface and pore size testing

The properties of the solid surface are closely related to the pretreatment conditions of the sample. The pretreatment conditions must be carefully studied and controlled to prevent changes in the surface properties and internal structure of the solid during the pretreatment process. Therefore, it is required to understand the nature of the sample in advance. For microporous materials, even the helium can be adsorbed due to the large size of the micropores. The nitrogen used in the measurement of specific surface area can be strongly adsorbed on the acidic sites of complex oxides and hydroxides such as zeolite. For substances with a pore structure, the pretreatment temperature is too low to sufficiently remove the adsorbed water and other adsorbed molecules in the pores; if the temperature is too high, condensation and dehydration between hydroxyl groups are likely to occur, or pores and surface changes are caused by sintering. Therefore, it is necessary to select an appropriate temperature for pretreatment. It is best to use thermal analysis and other methods to grasp the desorption temperature of the adsorbate, the structural change temperature of the sample, the phase transition temperature, and the decomposition temperature in advance to determine the best pretreatment conditions.

Except for special cases such as quality management, the pretreatment conditions must be determined when measuring the amount of meteorological adsorption and liquid phase adsorption, so that the molecules originally adsorbed on the sample are completely removed, or a certain amount of adsorbate is adsorbed in advance.

In the pretreatment process, protective gas is often used. For samples that are prone to surface reactions such as redox and samples that require strict removal of the original adsorbed molecules (such as metal powder and activated carbon), high vacuum or high purity nitrogen, high purity helium and other inert gases are required for pretreatment. When the powder sample is evacuated too quickly, the powder contained in the powder protrudes, and the powder is easily scattered. This not only reduces the quality of the sample, but the powder will also enter the vacuum measurement system such as a pressure gauge, which reduces the vacuum of the system and is more troublesome to remove. In order to prevent this from happening, you can dry the sample in advance, control the degassing and heating rate not too fast, and you can also install a filter above the sample in case.


Three Dimensional Packaging Machine

Auto Packing Machine ,Small Packing Machine,Semi Automatic Packing Machine,Automated Packaging Machine

Guangzhou Jiluo Machinery Manufacturing Co.,Ltd , https://www.gzjiluo.com

Posted on