PerkinElmer TGA 4000, Installation And Hardware Manual

Page: 59 / 88

TGA 4000 Hardware . 59
Sample Handling
The TGA 4000 measures the change in weight of a sample as a function of temperature or
time. The materials and techniques used to obtain data with a TGA 4000 are discussed
below.
Sample Preparation
The thermogravimetric analyzer 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.
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 TGA 4000 is able to operate in various gas atmospheres. The change
from one atmosphere to another should be rapid. The TGA 4000 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 has a flow rate of 40 ml/min. Since the equilibration time of the analyzer is
significant, it is recommended that the balance protective 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 flow rate of 20–40 ml/min is
recommended.
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.
NOTE: The flow rate for the system purge gas should be equal to or greater than that for
the sample purge gas.