The specific surface area is the surface area (㎡/g) of the substance per unit mass. It is one of the most important physical properties of ultra-fine powder materials, especially nano-powder materials. It is used to evaluate their activity, adsorption, catalysis and other properties. important physical properties. Therefore, in the research, manufacture and application of various ultrafine powder materials, it is very important to measure the specific surface area. The specific surface area of powder is related to many factors such as its particle size, particle size distribution, particle shape and surface roughness, and it is a comprehensive reflection of powder polydispersity.

There are many methods for determining the specific surface area of powder, such as air permeation method, BET adsorption method, infiltration heat method, mercury intrusion method, X-ray small angle scattering method, etc. In addition, it can also be determined according to the particle size distribution of the measured powder and the observed particle shape factor. Calculation. Among the above methods, the BET low-temperature nitrogen adsorption method is the most widely used classical method.

The BET adsorption method, which measures specific surface area, is based on the determination of the adsorption amount of the gas monolayer on the surface of the sample. The most widely used adsorbent is nitrogen, the measurement range is 1-1000m2/g, which is very suitable for the determination of nano-powder. It uses nitrogen as the adsorbate and helium or hydrogen as the carrier gas. The two gases are mixed in a certain proportion to reach the specified relative pressure, and then flow through the nano-powder material sample. When the sample tube is put into the liquid nitrogen (-196℃) vacuum flask, the powder material will physically adsorb the nitrogen in the mixed gas, but the carrier gas will not be adsorbed. At this time, an adsorption peak appeared in the chromatography workstation (gas sensor system). When the liquid nitrogen cup was removed, the powder sample returned to room temperature, and the adsorbed nitrogen gas was desorbed, and a desorption peak opposite to the adsorption peak appeared on the workstation. The area of the adsorption peak or desorption peak is proportional to the amount of nitrogen adsorbed on the surface of the sample, and it can also be considered to be proportional to the surface area of the nano-powder sample. Take a standard sample, such as powder material with a known specific surface area, or pure nitrogen gas with a known volume, and obtain a standard sample peak in the workstation. By comparing the standard peak and the desorption peak area of the sample to be tested, the final result can be obtained. specific surface area. Its advantages are: fast analysis speed, good accuracy and high resolution, especially for small and medium specific surface samples, such as nano silicon battery materials, nano metal powders, etc., the lower limit of specific surface analysis is low, and the repeatability is high.