D A
NALYZE
S
AMPLES WITH A
T
OTAL
S
URFACE
A
REA OF
1.0
M
2
OR
L
ESS
The unique balanced measurement method used in the Gemini permits small amounts of surface
area to be measured with nitrogen gas that otherwise would be measurable only with krypton. Low
surface area samples often displace many times more nitrogen than they adsorb, especially if
composed of low-density materials of large particle size. The standard, built-in, helium free-space
difference measurement and mathematical compensation routine typically removes the effects of
more than 99% of this sample displacement, but the small amount remaining uncompensated can
still be significant.
A technique for adding a compensating volume with negligible surface area into the balance tube
has been developed. It can reduce the size of the initial imbalance to low levels and allow precise
measurement of adsorbed gas.
This technique can be performed by the following methods:
n
Using glass beads in the balance tube
n
Using filler rods in the sample and balance tubes
Some users find that a combination of the two methods — using glass beads and filler rods —
produces even better results. This, however, will depend on the type of sample being analyzed.
Filler rods and glass beads are included in the accessories kit. Either straight-wall or bulb sample
tubes may be used.
U
SING
G
LASS
B
EADS
This method typically produces the best results.
1. Place an appropriate quantity of sample in a clean sample tube.
2. Load a second sample tube of the same size with glass beads that have a total volume
approximately the same as the sample volume.
a. Determine the volume (v) of the sample in cm
3
:
where
m
=
mass of sample (g)
ρ
=
density of sample (g/cm
3
); if density is unknown, refer to your labor-
atory handbook.
D Analyze Samples with a Total Surface Area of 1.0
m2 or Less
Gemini VII Keypad Operator Manual
239-42801-01 (Rev E) — July 2021
D - 1
