Porosimetry of a Silica Alumina Powder

1. Starting the porosimeter

1. Start the porosimeter and allow it to stabilize.
2. Weigh the plastic tube holder, sample tube, glass insert, and plastic valve that screws into the top of the tube.
3. Then load the sample in the tube and re-weigh. When loading, try to get at least 20 m² of total surface area in the tube. Look up a typical surface area range for the type of solid you are using. However, never use less than 50 mg of sample.
4. Using the software for the porosimeter, initialize a new sample by clicking 'File' followed by 'New Sample' and select the appropriate method. Enter both weights (apparatus and apparatus + sample) into the program and rename the sample.
5. Load the sample and O-ring into the degas port and adjust the degas conditions as needed. The following program should be followed: the sample should first be heated and evacuated to 12 μm of Hg at a low temperature (90 °C) during the 'Evacuation Phase'. Then, ramp to the desired final temperature (usually 300 °C for inorganic materials and carbons) and hold for the desired time (the "Heating Phase").
6. Load the sample tube and O-ring into the sample port. Push upwards on the tube slightly before turning the nut to engage the pin that opens the plastic valve can engage. Make sure to hold the tube vertically.
7. Place a heating mantle under the bulb holding the sample tube, and support the heating mantle with a lab jack. Do not wiggle the bulb - hold the mantle firmly.
8. Show the degas schematic by clicking under "Degas" and selecting "Show degas schematic". Select "Unit 1", then "Start Degas." Click "Browse" to select your sample file(s), then "Start". The degas phase removes all traces of water and CO₂ from the sample before the adsorption experiment. N₂ cannot displace both water and CO₂! Once the desired pressure and temperature have been reached, degas steps can be skipped.
9. When the degas phase reaches the "cool down" step, lower the heating mantle and let the sample tube cool to room temperature.
10. Backfill the sample with helium. If the pressure does not approach 800 mm Hg, then the sample tube may have popped out of the fitting. If necessary, hold in place with your hands.
11. Once degassing is complete, weigh the sample and apparatus and edit the mass in the sample file.

2. Porosimetry measurement

1. Fill the porosimeter's Dewar flask with liquid N₂.
2. Put the plastic jacket on the sample tube, and load the sample and O-ring in the port above the Dewar flask. Attach the plastic insulating cover on the Dewar near the sample port.
3. Click 'Unit 1', then 'Sample Analysis'. Browse for the degassed sample file, then click 'Start' to begin taking measurements.
4. Ensure the initial evacuation completes successfully. If that fails, try re-setting the tube in the port (check the O-ring and re-tighten the nut). Measurements will be collected automatically over several hours. Results can be downloaded into an Excel spreadsheet.