Recently, the competition in the surface tester market has become more and more fierce. Many users have been widely confused by the widely distributed network messages. In order to facilitate users to choose high quality and low price ratio surface meters, as an instrument manufacturer, it is responsible for the user. Principles, a brief introduction to several issues and considerations that need to be learned during the purchase of specific surface and pore size distribution analyzers:
First, the wide application of specific surface meters
Catalyst, widely used in petrochemical, chemical, pharmaceutical, food, agricultural, fine chemical and other fields of adsorbents, such as activated carbon, molecular sieves, activated alumina, etc., widely used in environmental protection; pigments, inorganic pigments, calcium carbonate, zinc oxide, Silica, mineral powder, etc.; ceramic material, alumina, zirconia, yttria, silicon nitride, silicon carbide, etc.; carbon black, white carbon black, nano calcium carbonate and other reinforcing agents for rubber and plastic materials; New battery materials, such as lithium cobalt oxide, lithium manganate, graphite and other electrode materials; luminescent rare earth powder materials; magnetic powder materials, such as ferroferric oxide, ferrite, etc.; nano-powder materials, including nano-ceramic materials, nano-metals Materials, nano silver powder, iron powder, copper powder, tungsten powder, nickel powder, etc.; other, such as microfiber, porous fabric, composite materials, sediments, suspended solids, etc.
Second, the specific surface and aperture analyzer classification
Continuous flow chromatography: A method of determining the amount of nitrogen adsorption on the surface of a powder using a thermal conductivity detector in a gas chromatograph. Nitrogen is used as the adsorbate, helium is the carrier gas, and the two gases are mixed in a specified ratio to reach a certain partial pressure of nitrogen. The mixed gas is passed through the sample tube containing the powder sample, and the nitrogen molecule is sampled at the liquid nitrogen temperature. The surface is physically adsorbed, and the helium gas is not adsorbed. At this time, the concentration of nitrogen in the gas stream is reduced, and an electric signal is generated at the output end of the thermal conductivity detector to form a nitrogen adsorption peak. When the sample tube is returned to room temperature, the adsorbed nitrogen on the surface of the sample is completely desorbed to form a desorption peak. The size of the peak area of ​​the absorption (desorption) is proportional to the amount of nitrogen adsorption on the surface of the sample. This method can realize the direct comparison method for rapid determination of specific surface, BET specific surface measurement and mesoporous pore size distribution measurement. At present, domestic dynamic instruments tend to be multi-functional, and in the case of basically the same instrument structure, as long as the software is fully functional, It can realize both the measurement surface and the pore size distribution, and it can also be automated.
Static capacity method: The measurement of nitrogen adsorption is different from the dynamic method. In a closed vacuum system, it precisely changes the nitrogen pressure on the surface of the powder sample, gradually changing from 0 to nearly 1 atmosphere, and measuring with a high-precision pressure sensor. The pressure change before and after the sample is adsorbed, and then the adsorption amount or desorption amount of the gas is calculated according to the gas state equation. After measuring the nitrogen adsorption amount, the BET specific surface and pore size distribution can be obtained according to the theoretical formula of nitrogen adsorption. The key factors of static capacity test technology are pressure sensor accuracy, dead volume measurement accuracy, vacuum tightness, sample temperature and coolant level change, and sample chamber temperature field correction. In Europe and the United States and other developed countries, basically adopt static capacity nitrogen adsorption instrument.
Third, choose the precautions than the surface meter
1. The development process of nitrogen adsorption specific surface and pore size analyzer in China can be summarized into three stages: dynamic direct contrast method surface measuring instrument → dynamic specific surface and pore size distribution measuring instrument → static volume ratio surface and pore size distribution measuring instrument, From easy to difficult, from low to high, from simple to complex, the technical content is continuously improved, the functions are continuously improved, and the performance is constantly approaching the international advanced level;
2. The above three types of instruments also have their existence value: the dynamic direct comparison method is simpler and faster than the surface measuring instrument, and is suitable for rapid measurement of specific surface and determination of materials with the same adsorption characteristics as standard samples; dynamic specific surface and The pore size distribution analyzer realizes the measurement of the BET specific surface, which is in line with international standards, and its function can be extended to the measurement of the mesoporous pore size distribution. However, it is not yet possible to determine the complete adsorption/desorption isotherm curve, which is limited by the dynamic chromatography itself. The measurement range and accuracy of the pore size distribution are not ideal. The successful development of the static volume method than the surface and pore size distribution analyzer is an important indicator that the surface and pore size distribution instrument in China is close to the international advanced level. It has complete functions and advanced methods. Consistent with the international development direction, the accuracy, scope, stability and automation of the measurement are significantly higher than the dynamic chromatography method, which is of great significance for improving the test level in China.
3. The user has highly praised and warmly welcomed the success of the domestic static capacity method than the surface and pore size distribution measuring instrument. Especially in colleges and universities, the requirements of teaching and scientific research are relatively high. In recent years, Peking University (Shenzhen Graduate School) Nearly 20 units including Beijing University of Traditional Chinese Medicine, East China University of Science and Technology, Wuhan University, Xinjiang University, Jiangnan University, Weinan Normal University, Sichuan Nuclear Fuel Company, etc., purchased domestic static capacity ratio surface and aperture analyzers, and their performance Very satisfied with the quality, many schools are also planning;
4. Conclusion: The domestic static capacity method has complete functions, advanced methods and international standards, high test accuracy and good repeatability. It is the closest to the international advanced level and cost-effective. It is the most suitable instrument for Chinese universities. .
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