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The specific surface area of ​​the calibrated coal is calculated based on the amount of adsorbed gas, and the amount of adsorbed gas should be obtained by subtracting the volume of the unadsorbed gas from the volume of the gas passed in. The volume of unadsorbed gas is the equivalent dead volume. It is defined as follows: at a certain room temperature, a certain temperature of liquid nitrogen, and a fixed mark scale immersed in liquid nitrogen in the sample tube. Under a certain adsorption equilibrium pressure, the volume of unadsorbed gas in the sample tube (standard state: 273K and 1013hPa volume).
The particle size of the coal sample should not be too fine to avoid the loss of air flow during the degassing process, but it should not be too large, otherwise it is difficult to fit into the sample tube. Before measuring the specific surface area, the coal sample must be degassed and dried to remove the gas and water adsorbed by the coal. The degassed and dried process is generally dried at a vacuum of 1.33x10-2Pa at a temperature of 110 ℃ for 16h. It is considered that under such conditions The surface of the coal is free of water (or other gas adsorption), and then the sample is cooled to room temperature under anaerobic conditions for use.
It is not that the larger the specific surface area analyzer, the better the powder quality. For example, in the case where powder sphericity is required, the larger the specific surface of the powder material, the worse the sphericity. Specific surface area and particle size (the particle size is generally expressed by median diameter or mesh number) are two concepts and are not necessarily related. Two products with the same mesh number do not mean that they have the same specific surface area.
If the test process is not fully automated, then the tester cannot leave at all times, and must be highly concentrated, observe the dashboard, control the knob, and a little care will lead to the failure of the test process,
The system is evacuated above 1.33Xl0-2Pa, and after leak detection, the s1 and s2 are closed: the piston. Put the container with liquid nitrogen on the sample tube, so that the sample tube is immersed in liquid nitrogen to a fixed scale.