Performing A Single-Point Surface Area Measurement; Calibration - Micromeritics FlowSorb III 2305 Operator's Manual

FlowSorb III

Performing a Single-Point Surface Area Measurement

Calibration

The FlowSorb III should be calibrated at the start of each 8-hour operational
period. Calibration is accomplished by injecting a precise volume of a gas mix-
ture into the instrument through a septum using a syringe and needle. Side-port
needles are supplied to prolong septum life; sharp-edge needles should be
avoided. The septum requires periodic replacement, nevertheless. Replacement is
required more frequently when using the larger needle of the 10 mL syringe (ap-
proximately after 20 injections) than with the smaller needle of the 1 mL syringe
(approximately after 100 injections). Refer to Chapter 5 for ordering information.
A reference percentage potentiometer (small screwdriver adjustment on right panel)
may occasionally need to be adjusted when replacing a gas mixture of ap-
proximately 30% N
in gas composition, as well as to improve agreement of adsorption and desorption
results (refer to Appendix B for details). No adjustment is required when making
multipoint tests since adsorption data are not used.
As discussed in Appendix A, Theory, 1.0 cm
2
m of sample surface in the FlowSorb when employing a mixture of 30 mole %
N and 70 mole % He. Liquid nitrogen is used to set the adsorbing temperature
2
when ambient conditions are 22 °C and 760 mmHg. Procedurally the steps are
identical for other gases and conditions with the exception that another constant
is applicable and some electronic adjustments may be required (refer to Appendix
B, Other Gases and Compositions).
Small ambient temperature deviations from 22 °C are relatively insignificant, but
a calibration value differing considerably from 2.84 may be required in some lo-
calities far removed from sea-level elevations.
Perform the calibration as follows:
1. Insert empty sample tubes into two sample holders; install one at the Degas
position and one at the Test position.
2. Install a U-tube at the Cold Trap position.
3. Install a Dewar containing liquid nitrogen about the U-tube.
4. Depress the Det pushbutton.
6. Select the x1 or x10 pushbutton; the x1 setting is recommended for use with
the FlowSorb 2310.
7. Turn the Path knob to the Short or Long position (whichever is appropriate
for the sample to be analyzed subsequently).
Mar 2012
Performing a Single-Point Surface Area Measurement
/70% He with another supply to account for small differences
2
3
of nitrogen gas corresponds to 2.84
3-5