Thermal
Analysis
Thermal analysis is versatile, generally applicable,
capable of high accuracy and adaptable to micro quantities. Included among the group are Differential Scanning Calorimetry (DSC), Differential Thermal
Analysis (DTA), Thermogravimetry (TG), Thermomechanical Analysis, Dynamic Mechanical Analysis and,
in some classification, temperature-resolved X-ray diffractometry
as well. Among them, TG is probably the
easiest to understand. A schematic diagram of this instrument follows.
The "tall" apparatus on
the right in the following photo shows an actual thermal balance, the model 92-16.18 from Setaram, that is used in our laboratory. Actually it combines thermogravimetry
with DTA, where the temperature difference between a sample and a reference,
inert substance is recorded as both are heated at the same rate. By this arrangement, TG and DTA scans of
the same sample can be undertaken simultaneously, up to the temperature limit
of 1,300¢XC. Such high temperature is
beyond the reach of DSC, to be discussed next, due to practical considerations
in the design of furnaces; indeed some special makes of TG/DTA can take samples
up to almost 2000oC.
In the above photo, the
stacked instrument on the left, with a silvery dewar on top, is our Setaram
low-temperature (heat-flux) Differential Scanning
Calorimeter. DSC may lay claim to
be the most powerful thermoanalytical technique,
since the materials property it measures directly is the heat exchanged by the
sample as the latter varies in temperature, or undergoes structural or chemical
changes. An instrument of
contemporary design can offer power sensitivity better than 10-7 W
with precisions > + 0.1% and 0.05 K attainable over a
temperature range down to LN2 at relatively low cost.
The second photo, below,
shows our recently installed "Diamond" (temperature-compensated) DSC,
procured from PerkinElmer. The
smaller device on the right is an UV source; photochemical processes can be
studied in this calorimeter as well.
The third photo is of the glove
box in our lab, with which sample preparation can proceed in a controlled
atmosphere.
Lastly, we discuss the interpretation
of thermoanalytical data.
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