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Gas adsorption method specific surface area test
The specific surface area tester F-Sorb 2400 is currently the only fully automated and intelligent specific surface area measuring instrument in China. It is jointly developed by Jinyi Spectrum Technology and the weapon system.It adheres to the high-standard and strict technical requirements of the weapon industry, based on the international classic ratio The theory and principle of surface area testing adopts the universal specific surface area testing method at home and abroad, in line with international specific surface area testing standards, significantly improves product stability and service life, the test results are more accurate, the operation is simple and fast, and the workload of testers is greatly reduced
There are a variety of specific surface area testing methods. Among them, the gas adsorption method is widely used in various industries at home and abroad because of its scientific testing principle, the reliability of the testing process, and the consistency of the test results, and gradually replaces other testing methods. , Become the most authoritative test method recognized. Many international standards organizations have listed the gas adsorption method as the specific surface area test standard, such as ASTM D3037 of the United States and ISO-9277 of the international ISO standards organization. There are many industry standards for specific surface area testing in China, the most representative of which is the national standard GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Matters by Gas Adsorption BET Method".
The principle of measuring specific surface area by gas adsorption method is based on the adsorption characteristics of gas on a solid surface. Under a certain pressure, the surface of the sample particle (adsorbent) under test has a reversible physical adsorption effect on gas molecules (adsorbate) at ultra low temperature There is a certain equilibrium adsorption amount corresponding to a certain pressure. By measuring this equilibrium adsorption amount, the specific surface area of ​​the sample to be measured is equivalently determined using a theoretical model. Due to the irregularity of the outer surface of the actual particle, strictly speaking, this method measures the total surface area of ​​the outer surface of the particle and the internal through holes that can be reached by the adsorbate molecules, as shown in the figure.
Nitrogen has become the most commonly used adsorbate due to its easy availability and good reversible adsorption characteristics. The specific surface area measured by this method is called the "equivalent" specific surface area. The concept of "equivalent" refers to: the surface area of ​​the sample is the number and maximum number of nitrogen molecules coated (adsorbed) by the close packing of its surface Characterized by the cross-sectional area. The equilibrium saturation adsorption capacity (V) of nitrogen molecules on the sample surface is actually measured, and the single layer saturation adsorption capacity (Vm) is calculated by different theoretical models, and then the number of molecules is obtained, and the nitrogen molecule equivalence is calculated using the surface close-packed hexagonal model The maximum cross-sectional area (Am), you can find the specific surface area of ​​the measured sample. Calculated as follows:
sg: specific surface area of ​​tested sample (m2 / g)
Vm: Saturated adsorption capacity of nitrogen molecules in a single layer (ml)
Am: equivalent maximum cross-sectional area of ​​nitrogen molecules (close-packed hexagonal theoretical value Am = 0.162 nm2)
W: Quality of the tested sample (g)
N: Avogadro's constant (6.02x1023)
Substituting the above data, the basic formula for calculating specific surface area by nitrogen adsorption method is obtained:
It can be seen from the above formula that the accurate determination of the single-layer saturated adsorption amount Vm on the sample surface is the key to the measurement of specific surface area.