The principle of determining the specific surface area by the gas adsorption method is based on the adsorption characteristics of the gas on the solid surface. Under a certain pressure, the surface of the sample particles (adsorbent) has reversible physical adsorption on the gas molecules (adsorbed matter) at ultra-low temperature, and There is a certain equilibrium adsorption amount corresponding to a certain pressure. By measuring the equilibrium adsorption amount, the specific surface area, pore volume, and pore size distribution of the sample to be tested are equivalently obtained by a theoretical model.
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High-purity nitrogen and liquid nitrogen (coolant) are the most commonly used adsorbents due to their easy availability and good reversible adsorption properties, and are widely used for the determination of specific surface area. For microporous samples with small pores and slow diffusion, such as molecular sieves and activated carbon samples; and samples with small specific surface area, such as natural ores, organic materials, etc., there are limitations in the adsorption of nitrogen gas, and argon can be selected. , carbon dioxide gas, helium gas, etc. do adsorption gas.
As an adsorbing gas, argon gas can be stably adsorbed on the surface of the material at 87K liquid argon temperature or 77K liquid nitrogen temperature, and is widely used in molecular sieve sample micropore testing. There are three main reasons for this:
1. The nitrogen molecule is a polar molecule and has a quadrupole distance, which enhances the interaction between the adsorbate molecules and the wall of the heterogeneous molecular sieve, which is prone to characteristic adsorption, which makes it difficult to identify molecular sieves with different pore sizes; The argon molecule is a spherical, non-polar monoatomic molecule that gives a more accurate micropore distribution.
2. For a defined pore width, nitrogen requires a lower P/P0 than argon. Therefore, argon gas is selected as the adsorption gas, and the micropore adsorption can be performed at a higher P/P0 point, which is beneficial to improve the test accuracy.
3. Argon gas can be selected at 87K liquid argon temperature adsorption to increase the temperature of the cold bath, which is beneficial to shorten the balance time and improve the test efficiency.
The limitation of argon gas adsorption gas test is that the capillary condensation disappears after the pore diameter is larger than 12 nm, so it can only be used for micropore test.
For activated carbon samples with more micropores, carbon dioxide can be selected as the adsorbate and adsorbed at the freezing point, which is mainly used for the test of saturated adsorption capacity of activated carbon. The adsorption point of carbon dioxide (273K) is much higher than that of argon and nitrogen (77K or 87K), which greatly increases the gas diffusion rate. Therefore, for activated carbon samples, carbon dioxide is selected for adsorption at freezing point, which has high efficiency, easy diffusion, and easy to obtain saturated adsorption capacity, and is more suitable for the test of saturated adsorption capacity of activated carbon. However, the saturated vapor pressure (3485.3 KPa) of the carbon dioxide freezing point is too high and can only be adsorbed in the microporous range, and the higher P/P0 pressure point cannot be achieved unless a high pressure adsorber is used.
For metal powders with a small specific surface area, organic materials and some natural ores can be selected from helium.
Bethed Instrument Technology (Beijing) Co., Ltd. is one of the earliest professional companies engaged in research, development, production and sales of nitrogen adsorption specific surface area instruments. It is a high-tech enterprise recognized by Beijing Zhongguancun Science and Technology Park.
At present, it has ten technical patents. It is the manufacturer with the most patented technology in the same industry in China. It has strong R&D and innovation capabilities, and many technical patents are specially used to improve the accuracy and stability of the instrument.
In 2012, it stood out among hundreds of thousands of companies, and was selected by the Ministry of Science and Technology as a technology-based SME technology innovation fund support enterprise. Special funds were invested in the research and development and update of instruments, thus launching a new generation of instruments to enable the development of enterprises to enter new Stage.
With hundreds of successful users, including many colleges and universities, research institutions and well-known companies, instrument sales have been leading for many years.
In 2009, the company passed the ISO9001 certification and has a complete sales, training and service system. It has an efficient and professional team to provide customers with quality equipment and first-class service.
The professional R&D team has been developed for 1 year, and many industry experts have participated in the international frontier design concept, integrated valve and pipeline design, full modular assembly, high vacuum and high stability, and superior performance compared to imported high-end equipment.
Professional and perfect after-sales service system, can provide 24-hour telephone consultation, 48-hour in-door service, Beijing, Shanghai, Guangzhou have service agencies to fully protect the normal operation of user equipment.