Sample Preparation:

1
DIFFERENTIAL SCANNING CALORIMETRY
CPE/CEBC NSF-REU University of Kansas Summer
2004
Kate Wilbanks and Dr. Susan Stagg-Williams

• Helpful Hints
• If performing heat, cool, heat procedures, it
  may be beneficial to turn off the RCS after the
  cooling.
  
• To remove data/graphs from the control computer,
  hit Print Screen key, paste into Microsoft
  Paint and save to USB Removable Port or Zip Disk.

• Sample Preparation
• 1. Choose your pan non-hermetic, hermetic, or
  open.
  
• Non-hermetic Non-hermetic crimped pans provide
  better thermal contact between the sample, pan
  and constantan disc than open pans reduce
  thermal gradients in the sample minimize sample
  spills enable retention of sample for further
  study.
• Hermetic Hermetic pans offer the same
  advantages
  
• of non-hermetic pans. In addition, they provide
  an
  
• air-tight seal that can resist internal pressure
  up to
  
• 3 atm. They are good for volatile liquids,
  materials
  
• that sublime, aqueous solutions above 100C and
  
  
• materials in a self-generated atmosphere.
• Open Open pans are used when contact with the
  atmosphere or reaction gas is required. Hermetic
  pans can be used as open pans by putting a
  pinhole in it before sealing.
• 2. Prepare 1 70 mg of sample depending on
  measurement.
  
• 3. Press your pan.

• Sample Melting Point Procedure
• Equilibriate at 20C.
• Ramp 5C/min to 200C. (or about 50C above
  expected melting point.)
  

Objective Develop procedures for the TA Instr
uments DSC 2920.

Equipment The equipment used is the TA Inst
ruments DSC 2920 with RCS (Refrigerated Cooling
System) and Autosampler attachments. The Autos
ampler is not online. The RCS allows for a tem
perature range of -150C to 600C. Aluminum samp
le pans are used which prevent temperatures ab
ove 600C. Gases used are compressed air, helium
and carbon dioxide. The full Operators Manual
from TA Instruments is available on the control
computer.

• Sample Carbon Dioxide Desorption Procedure
• on this procedure, the gas must be manually
  changed
  
• Equilibriate at 20C. Air
• Ramp 10C/min to 350C. Air
• Isothermal 5 minutes. He
• Ramp 10C/min to 20C. He
• Isothermal 35 minutes. 30 minutes CO2, 5
  minutes He
  
• Ramp 10C/min to 350C. He
• Equilibriate at 20C. He or air

After the Experiment After the experiment is co
mplete, allow the experiment to cool or heat to
room temperature. The DSC should not be left
alone with the RCS on as it will continue to cool
at the earlier specified rate. When the DSC has
reached room temperature, the samples can be
removed from the sample dome.
To view and analyze the data, open Universal
Analysis(2) on the computer desktop. Find the
file and open to view peaks.
What it does The DSC determines the temperature
and heat flow associated with material
transitions as a function of time and
temperature. It also provides quantitative
qualitative data on endothermic (heat absorption)
and exothermic (heat evolution/desorption)
processes of materials during physical
transitions that are caused by phase changes,
melting or other heat-related changes.
Popular Uses The DSC is popularly used for po
lymer characterization. Four main characteristics
that can be determined for any sample by the DSC
are glass transition temperature, heat capacity,
melting point, and crystallization.
Results The results of the melting point proc
edure or standard heating procedure are simple t
o analyze the melting point is where the apex
of the peak lies on the x-axis Temperature (
C). The enthalpy of melting is the area under th
e curve.
How it works The sample pan and the blank ref
erence pan sit on a small slab of material with
a known (calibrated) heat resistance. Heat flows
into the two pans by conduction. The flow of heat
into the sample is larger because of its heat
capacity (Cp). The difference in flow dq/dt
induces a small temperature difference ?T across
the slab. This temperature difference is measured
using thermocouples. When a sudden change in the
heat capacity occurs the signal will respond and
exhibit a peak. From the integral of this peak
the enthalpy of melting can be determined, and
from its onset the melting temperature.
Figure 4 Press with non-hermetic dies installed.
The results of desorption procedure shown below
in Figure 5 are more complex. The four samples
analyzed are catalyst supports. It is expected
that the small exothermic peaks (circled in red)
are where the carbon dioxide desorbs. The
endothermic dip in the initial portion of each
run (blue arrow) is where an oxidation occurs.
The 10 Lanthana support has the largest peak
which indicates a large amount of heat given off
over a short period of time and is expected due
to its high basicity. Neither the 17.5 CeO2
support, nor the 18 CeO2 5 La2O3 support has an
exothermic peak this indicates that CO2 was not
significantly absorbed thus there is no
significant heat rise.
Future Use Future plans for the DSC include co
nnecting it to the mass spectrometer to confirm
the exothermic peaks during the desorption run
are CO2. The DSC and mass spectrometer would run
simultaneously with the exit gas (vacuum port)
from the DSC being analyzed by the mass spec. It
is hoped that where the exothermic peaks appear
(red circles in Figure 5 graphs), carbon dioxide
would appear in the mass spectrometer. In order
for this to work, the delay between the mass
spectrometer and DSC would need to be determined.
Typical desorption is determined by FT-IR, XRD or
TGA so this method will give an alternate
confirmation.
Running an Experiment After preparing your sa
mple and reference pans, you must load them into
the DSC. This must be done with great care
handling the pans roughly can create detrimental
deformations in the pans. Remove the 3 lids of
the sample dome the silver lid (top), cell
cover (middle), and bell jar (bottom). The
reference pan goes on the thermocouple further
away from the researcher close to the back
panel of the DSC. The sample pan goes on the
thermocouple closest to the researcher. The pans
should be flat on the surface to allow for good
thermal conditions. Replace the 3 lids of the
sample dome carefully. Dropping the bell jar can
ruin your sample. With the sample in place, th
e control software can now be opened TA
Advantage. The DSC must be turned on when TA
Advantage is opened. Open up the Procedure scr
een and save your information to the folder of
your choice you may need to create a new one.
Record the name mass (mg) of your sample. Conf
irm the file location where the run will be saved
is correct. Confirm your procedure. Sample pro
cedures are available and differ for different
measurements or your sample exposure needs. Apply
all changes.

• Safety Precautions
• Do not use hydrogen or any other explosive gas.
  
  
• Use of chlorine will damage the cell.
• If using samples that may emit harmful gases,
  vent samples near exhaust.
  
• After running any experiment, allow the DSC to
  return to room temperature before
  removing/changing sample.
  

ZrO2 calcined at 400C
17.5 CeO2 calcined at 700C ZrO2

• Available Resources
• Procedure for Melting Point/Standard Heat
  Measurement.
  
• Procedure for Carbon Dioxide Desorption
  Measurement.
  
• TA Instruments DSC 2920 Operators Manual.

• Before you Begin Experimentation
• Turn on control computer open up TA
  Controller.
  
• Confirm all connections are correct.
• Turn on DSC power, heater RCS.
• Confirm calibration.
• Start the purge gas at 10 psi 100 mL/min.
• Remove the 3 lids of the sample dome - silver
  lid (top), cell cover (middle), and bell jar
  (bottom).
  
• Prepare a sample.

Acknowledgements The National Science Foundatio
n Research Experiences for Undergraduates
Program
The University of Kansas
References TA Instruments DSC 2920 Operators M
anual http//www.psrc.usm.edu/macrog/dsc.htm htt
p//encyclopedia.thefreedictionary.com/Differentia
l20scanning20calorimeter http//www.deltalab.co
m/dsc.htm
Figure 5 Desorption Procedure Results