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Polymer Chemistry
DSC Operation
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This is a Perkin Elmer DSC 6 Differential Scanning Calorimeter.On the
top of the DSC 6 is the lid of the furnace, in which the sample and reference
are heated. The calorimeter is computer-controlled. The thermogram resulting
from a run is shown on the computer screen.
Looking down on the furnace with the lid removed, we see the disks on
which the reference and sample are placed.
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A stream of nitrogen gas is directed inside the furnace to purge it of oxygen.
This will prevent oxidation of the sample during heating.
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The sample and reference are placed in two small aluminum pans and covered
with a lid. Each pan is closed by pressing in a crimper.
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The crimped pans containing the sample and the reference then are placed
in the appropriate spots in the furnace. Then the cover is placed back
on the furnace.
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| The furnace is heated and the temperature difference
between the sample and reference is monitored so that the DSC can keep the
temperatures the same. If an exothermic phase transition
occurs, the temperature of the sample will tend to surge ahead of the reference.
In this case the DSC doesn't need to furnish as much heat to the sample.
If an endothermic transition occurs, the DSC must furnish more heat to the
sample. The electrical power difference between the sample and reference
measures the heat flow (dQ/dt) in the sample. |
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A plot of heat flow vs. temperature change is called a thermogram. A thermogram
with an endothermic transition is shown below (endothermic is up on this heat
flow plot). DH (in J/g) is determined by dividing
the area under the curve by the mass of the sample. This is displayed on the
thermogram by the instrument.
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Partial support for this work was
provided by the National Science Foundation's Division of Undergraduate Education
through grants DUE #9950809 and DUE #9950296. Additional support was provided
by the Camille and Henry Dreyfus Foundation. PCOL faculty also acknowledge the
National Science Teachers Association which awarded the PCOL Faculty Consortium
the 1998 Gustav Ohaus Award for Innovation in College Science Teaching.
This page was last updated on February 10, 2001
whisnantdm@wofford.edu
