Perkin-Elmer STA 6000, Installation And Hardware Manual

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58 . STA 6000 Installation and Hardware GuideSTA 6000 Installation and Hardware Guide
Sample Handling
The STA 6000 measures the change in temperature (relative to a reference) and weight of a
sample as a function of temperature and/or time. The materials and techniques used to
obtain data with an STA 6000 are discussed below.
Sample Preparation
The instrument analyzes solid samples in powder, crystal, or granular form. Although
quantitative accuracy will remain the same regardless of sample shape, the qualitative
appearance of a run may be affected by the sample configuration. The best sample form for
optimum performance is powder or fine granules. Solid materials can be sliced into small
pieces with a razor or knife.
If you are using the AS 8000 with the STA 6000, the sample size should be approximately
40 mg.
Sample Pans
The preferred sample pan is the self-centering, thin-walled, ceramic sample pan provided
with the instrument. The sample centers itself in the pan and the pan centers itself on the
sample holder. Three sample pans are provided in the Spares kit.
Other sample pans can also be used. The only requirement that the pans must meet is that
they do not react or melt within the temperature range of interest and that the sample does
not form alloys with the material of the sample pan.
Sample Atmosphere
It is important that the STA 6000 be able to operate in various gas atmospheres. The change
from one atmosphere to another should be quick. The STA 6000 has one purge gas inlet for
the system purge gas inlet and two sample purge gas inlets at the back of the analyzer. The
system purge gas should be a dry inert gas that flows through the microbalance chamber.
This keeps the environment of the balance constant, prevents absorption or desorption of
vapors, and protects the balance against gaseous products evolving from the samples. The
system purge gas flow rate is 40 ml/min. Since the equilibration time of the analyzer is
significant, it is recommended that the system purge gas be present at all times.
You can control the atmosphere in which the sample is run by using a sample reactive or
purge gas to displace or introduce reactive gases into the sample furnace. Recommended
purge gases are air, nitrogen, argon, oxygen, and helium. When changing from one purge
gas to another, always check the temperature calibration. A sample purge flow rate of
20–40 ml/min is recommended. A purge gas inlet pressure of 2–3 bar (30–45 psi) is suitable,
with a maximum pressure of 6.2 bar (90 psi).
The reaction gas enters the furnace/sample area directly, just below the sample, and flows
via the furnace wall to the sample. Thus, dead volume can be low resulting in a small gas
change time constant. The time constant depends on the flow rate.
The gas atmosphere should be pure (99.9% minimum), especially if you use nitrogen. There
should be no trace of oxygen as this could lead to unwanted reactions. The gas must be
dry. A size 1A cylinder equipped with a suitable regulator is recommended.