ME4331 – DSC Review
APR 29 , 2008
Jeung Hwan Choi
CALORIMETRY
Calorimetry
- The science of counting the heat of chemical reactions or physical changes.
- In constant-pressure calorimetry, the heat measured represents the enthalpy
change.
Differential Scanning Calorimetry
Differential Scanning Calorimetry (DSC) is a thermal analysis
method in which the difference in the amount of heat applied (or
removed) to increase (or decrease) the temperature of a sample
material and a reference material are measured as a function of
temperature.
- Höhne et al. (1996) Differential Scanning Calorimetry
- Perkin Elmer, Inc.
- Wikipedia.org
DIFFERENTIAL SCANNING CALORIMETER
- The DSC will maintain the temperatures of the sample and reference equal during
a scan (change of both materials from one temperature to another).
- The Pyris1 Differential Scanning Calorimeter allows the user to change the
temperature at a prescribed constant rate (linear temperature control).
sample
furnace
reference
furnace
- Höhne et al. (1996) Differential Scanning Calorimetry
- Perkin Elmer, Inc.
DSC – ENDOTHERMIC VS. EXOTHERMIC
- When the sample undergoes a physical transformation such as phase transitions,
more (or less) heat will need to flow to it than the reference to maintain both at the
same temperature.
- This noticeable difference results in the appearance of an upper or lower peak,
depending on whether the transformation is exothermic or endothermic.
- A solid sample melting to a liquid will
require more heat flowing to the sample
to increase its temperature at the same
rate as the reference, and is an example
of an endothermic process.
- If a liquid crystallizes into a solid during
a cooling scan, more heat would have to
be removed compared to the reference
and is an example of an exothermic
process.
- Höhne et al. (1996) Differential Scanning Calorimetry
- Perkin Elmer, Inc.
DSC – MELTING POINT
• Melting point measurement
heating rate
= 5 °C/min
- Melting point of a pure substance (i.e. ice) is the onset temperature
- Onset is determined from the intersection of the slopes of the base and
the rising curve
Reference : Höhne et al. Differential Scanning Calorimetry 1996
Perkin Elmer, Inc.
DSC outline – latent heat
DSC - LATENT HEAT
• Latent heat of fusion of ice
Reference : CRC Handbook of Chemistry and Physics 2007
DSC outline – latent heat
DSC - LATENT HEAT
• Latent heat measurement
Possible errors
heating rate
= 5 °C/min
- Weight value
- Evolution width
- Baseline error
(Instrument based)
- Baseline error
(sample based)
t
T
T2
1 Power Compensation
1 2 dH
1 2 dH dt
dT
h  
dt  

dT  
m T Heat (Cool )ing Rate
m t1 dt
m T1 dt dT
1
Reference : Höhne et al. Differential Scanning Calorimetry 1996
Perkin Elmer, Inc.
DSC outline – latent heat
DSC - BASELINE
• Selecting a baseline
Standard
(linear)
Horizontal
(from left)
Sigmoidal
Horizontal
(from right)
Linear baseline suffices for samples that :
- are small in weight / volume
- have a small specific transition energy
- undergo a slow scanning rate
Otherwise, sigmoidal baseline gives a good result
Reference : Höhne et al. Differential Scanning Calorimetry 1996
Perkin Elmer, Inc.
DSC outline – latent heat
DSC - SPECIFIC HEAT
• Specific heat of ice / water
Reference : CRC Handbook of Chemistry and Physics 2007
DSC outline – specific heat
DSC - SPECIFIC HEAT
• Specific heat measurement
Red :
with water
Blue :
empty
heating rate
= 5 °C/min
1 dH 1 dH dt
1 Power Compensation
cp  
 

 
m dT m dt dT m Heat (Cool )ing Rate
Reference : Höhne et al. Differential Scanning Calorimetry 1996
Perkin Elmer, Inc.
DSC outline – specific heat
Green :
specific heat
DSC – PHASE DIAGRAM
• System NaCl-H2O Phase Diagram
DSC outline – specific heat
DSC – PHASE DIAGRAM
• 1xNaCl Thermal Analysis
DSC outline – specific heat
DSC – PHASE DIAGRAM
• 5xNaCl Thermal Analysis
DSC outline – specific heat
DSC – PHASE DIAGRAM
• 10xNaCl Thermal Analysis
DSC outline – specific heat
DSC – PHASE DIAGRAM
• 23.3%(w/w) NaCl Thermal Analysis
DSC outline – specific heat
DSC – PHASE DIAGRAM
• NaCl+H2O Thermal Analysis
DSC outline – specific heat
DSC – PHASE DIAGRAM
• NaCl+H2O Thermal Analysis
DSC outline – specific heat
CRYOMICROSCOPY
• Visualization of freeze-thaw events
microscope
LN2 dewar
video text
overlay
cooling pump
computer interfaced
temperature controller
cryostage
Reference : Linkam Scientific Instruments
Cryomicroscopy - layout
CRYOMICROSCOPY
• Growth of Primary Ice
Video credits : Bumsoo Han
DSC outline – specific heat
CRYOMICROSCOPY
• Solidification of the Eutectic
Video credits : Bumsoo Han
DSC outline – specific heat
EUTECTIC SOLIDIFICATION
• Phase change behavior in salt solutions
(10xPBS)
pre-eutectic @ -26°C
Photo credits : Adam Grovender
ADD: 10xPBS eutectic (photo)
eutectic @ -26°C
(after supercooling)
DSC CAL
• Diamond DSC 5C/min calibrations :
- Baseline Curvature Calibrations
- Baseline Slope Calibrations
- Sample Temperature Calibrations
- Furnace Calibrations
- Heat Flow Calibrations
DSC CAL
• Diamond DSC 5C/min calibrations : Baseline Curvature
- minimize amplitude of curve for operating temp. range
Factory default
Coarse control : + 1
Fine control : + 3
DSC CAL
• Diamond DSC 5C/min calibrations : Baseline Curvature
- minimize amplitude of curve for operating temp. range
Factory default
Fine control : + 14
Fine control : + 10
Fine control : + 13
Fine control : + 15
Fine control : + 20
DSC CAL
• Diamond DSC 5C/min calibrations : Baseline Slope
- minimize slope of curve for operating temp. range
Factory default
FSlope : - 3
Slope : - 5
Slope : + 5
Slope : - 4
DSC CAL
• Diamond DSC 5C/min calibrations : Sample Temp. Cal.
- Correctly predict transition temperatures of standards
n-Decane : Expected = -29.66 , Measured = -31.73
Scyclohexane : Expected = -87.06 & 6.54 , Measured = -87.1 & 5.2
DSC CAL
• Diamond DSC 5C/min calibrations : Furnace Calibration
- 9-point temperature calibration between upper and lower temp. range
- matches platinum resistance thermometer and programmed temp.
-150.04 -125.01 -100.02 -75.02 -50.05 -24.93 -0.002 24.99 49.99 75.01 99.99
DSC CAL
• Diamond DSC 5C/min calibrations : Heat Flow Calibration
- match enthalpy values with known reference materials
n-Decane : H = 202.09 vs 201.19 +/- 0.5, -0.45%
T = -29.66 vs -29.66 +/- 0.04
DSC CAL
• Diamond DSC 5C/min calibrations : Heat Flow Calibration
- match enthalpy values with known reference materials
H2O : H = 333.8 vs 338.6 +/- 0.15, +1.07%
T = 0 vs -0.43 +/- 0.01
END OF SLIDES