SSA7000-BET instrument for measuring saturated vapor pressure and free space volume?

How does SSA7000-BET instrument measure saturated vapor pressure/Po?

When conducting physical adsorption analysis using this method, the saturation vapor pressure Po of liquid nitrogen is a necessary indicator for obtaining adsorption isotherms, which directly affects the accuracy of P/Po. The saturated vapor pressure is tested using a dedicated P0 tube, which is located near the sample tube and sealed at one end. During the test, it is ensured that the P0 tube and the sample tube are tested in the same liquid nitrogen environment. First, evacuate the P0 tube and then fill it with gas until it reaches saturation. At this point, the measured saturated gas pressure is the saturated vapor pressure.

How to measure the volume of free space?

Calculate the free space volume by inputting the adsorption capacity based on the testing or input method. Test method: Close the isolation valve between the manifold and sample tube, and place it at room temperature. Inject He into the manifold and measure the pressure after equilibrium. Open the isolation valve and measure the pressure after He diffuses into the sample tube and reaches equilibrium. Keep the isolation valve open, slowly raise the Dewar flask, and cool the sample tube to the same temperature. The internal pressure of the system decreases, and record the pressure value after reaching equilibrium. Based on the above process, combined with multiple pressure values such as system volume, system temperature, cold bath temperature, and test temperature, the volume value of the cold/hot free space is determined.