Micromeritics Gemini VII 2390a, Operator'S Manual

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Gemini VII Equipment Description
239-42828-01 - Dec 2012 1-5
Operation
The sample and balance tubes are immersed in a single liquid nitrogen bath which maintains isother-
mal conditions for both tubes. The analysis gas is then delivered to the sample tube by a servo valve
mechanism. The delivery rate of analysis gas flow into the balance tube is controlled by another servo
valve connected to a differential pressure transducer. This differential pressure transducer measures the
pressure imbalance between the sample and balance tubes, which is caused by the adsorption of the
analysis gas onto the sample. As the sample adsorbs analysis gas, the pressure drops in the sample
tube. The servo valve continuously restores the pressure balance between the two tubes by admitting
more gas into the sample tube. The end result is that the Gemini maintains a constant pressure of anal-
ysis gas over the sample while varying the rate of analysis gas delivery to match exactly the rate at
which the sample can adsorb the gas.
The Gemini provides rapid and accurate sample analysis. As many as 50 data points can be collected
and reported in the BET, Langmuir, or t-Method range. The 2390p model of the Gemini VII Series can
report discrete point adsorption isotherms consisting of up to 1,000 adsorption points and, with the
Gemini 2390
t
, up to 1,000 adsorption and desorption isotherm points.
The Gemini requires only pure nitrogen as the analysis gas, even for most low surface area samples.
The analyzer requires no flow regulator, gas mixer, or mixed gases to operate. Surface areas as low as
0.01 m
2
/g are easily determined with excellent precision using nitrogen gas as the adsorbate. Option-
ally, helium may be used to determine any slight differences in volume between the balance tube and
the sample tube (differential free space). The Gemini uses this information to automatically compen-
sate even for these small differences in calculating analysis results.
The design of the Gemini avoids many errors which may occur with other surface area analysis
equipment:
• Any free space associated with the sample tube is offset by an identical amount in the balance tube.
• Any thermal gradient in the coolant bath is the same for both the sample and balance tubes and
produces a net effect of zero.
• Non-ideal gas behavior occurs in both the sample and balance tubes, cancelling negative effects on
sample analysis.
• Gas-mixture separation, which may occur in flowing-gas systems due to thermal diffusion, cannot
occur because mixed gases are not used.
MP-Method reports   
DFT reports
  
Feature (continued) 2390a 2390p 2390t