13
III. SAMPLE PREPARATION
Switch on the power to the unit using the mains on/off switch. Allow at least 15 minutes for the
pressure transducer to warm up and stabilize, during which time you can prepare your first sample.
Purging Method
To purge contaminating vapors and atmospheric gases from the sample (and the system) attach a
length of flexible plastic tubing to the hose barb connector on the right side of the
MULTIPYCNOMETER and immerse the other end of the tubing into a beaker of water. Then
perform the following steps.
1. Weigh accurately the clean, dry sample cell (cup). Record its (tare) weight, W
1
.
2. Fill the sample cell (cup) to just below the slot/hole with dry sample. If the sample has been
heated, ensure it has been cooled to room temperature (preferably in a desiccator) before
proceeding. Record the total weight of cell plus sample, W
2
.
3. Insert the cell with sample into the cell holder and replace the cover.
4. Close the “GAS FLOW IN” ON/OFF toggle valve and open the "VENT" toggle valve. Turn
the selector valve to "CELL".
5. Open the "VENT” RATE needle valve fully counter-clockwise.
6. Turn the "GAS FLOW IN” RATE needle valve fully clockwise. Do not over tighten it. Open
the “GAS FLOW IN” ON/OFF toggle valve.
7. Adjust the "GAS FLOW IN” RATE needle valve to give a slow rate of bubbling (1-2
bubbles per second) in the beaker of water then remove the tubing from the water.
8. After 5-10 minutes of flow, close the “GAS FLOW IN” ON/OFF toggle valve.
9. See Section IV for analyzing the sample (volume measurement).
Vacuum Method
If you prefer to decontaminate your sample with vacuum, use the following procedure.
1. Close the “GAS FLOW IN” ON/OFF toggle valve and open the "VENT" toggle valve. Turn
the Selector Valve to "CELL". Gently close the "VENT RATE" fully clockwise; do not over
tighten it.
2. Attach vacuum tubing between the hose-barb connection on the right side and a vacuum
pump. Switch on the pump.
3. Very slowly open the "VENT” RATE needle valve. If it is opened too rapidly, powder can
be pulled out of the cell holder. Wait at least 10 minutes for the system to be evacuated.
4. To repressurize the system, close the "VENT” toggle valve, switch off the pump and remove
the vacuum tubing. Open the “GAS FLOW IN” toggle valve, then slowly open the "GAS
FLOW IN" RATE needle valve to admit analysis gas until the system is returned to ambient
pressure.
To Next Page
Loading...