1. Differential Scanning Calorimetry

2. Definitions • A calorimeter measures the heat into or out of a sample.
differential calorimete
r measures the heat of a
sample relative to a reference. • A
differential scanning calorimeter
does all of the
above and heats the sample with a linear temperature
ramp. •
Endothermic
heat flows into the sample. •
Exothermic
heat flows out of the sample.

3. DSC: The Technique • Differential Scanning Calorimetry (DSC) measures
temperatures
and
heat flows
associated with transitions in
materials as a function of time and temperature in a
controlled atmosphere. •
These measurements provide
quantitative and qualitative
information about physical and chemical changes that
involve
endothermic or
exothermic
processes
, or
changes
in heat capacity .

4. What Can You Measure with DSC?
Qualitative analysis
Fingerprinting of minerals, clays, polymers
Sample purity
Melting points
Heat capacity, cp
Glass transition temperature, Tg
Crystallization temperature, Tc
Phase diagrams

5. Schematic of DSC Instrument
Reference
Sample T1 T2
Pt thermopile
Pt thermopile
Low mass
1 gram
heater
heater
N2 flow DW

6. Glass Transition Step in thermogram
Transition from disordered solid to liquid
Observed in glassy solids, e.g., polymers
Tg, glass transition temperature
Glass transition
dH/dt, mJ/s Tg
Temperature, K

7. Crystallization Sharp positive peak Disordered to ordered transition
Thermogram
Sharp positive peak
Disordered to ordered transition
Material can crystallize!
Observed in glassy solids, e.g., polymers
Tc, crystallization temperature
Crystallization
dH/dt, mJ/s Tc
Temperature, K

8. Melting Negative peak on thermogram Ordered to disordered transition
Tm, melting temperature
NB: melting happens to crystalline polymers; glassing happens to amorphous polymers
Melting
dH/dt, mJ/s Tm
Temperature, K

9. Analysis Sharp positive peak Disordered to ordered transition
Crystallization
Sharp positive peak
Disordered to ordered transition
Observed in glassy solids, e.g., polymers
Tc, crystallization temperature
dH/dt, mJ/s Tc
Temperature, K

10. DSC Thermogram > exothermic - Heat Flow Temperature 6
Oxidation
Crystallisation
Cross -
Linking
(Cure)
> exothermic -
Glass
Transition
Heat Flow
Melting
Temperature 6
Technical Group Talk

11. DSC: Main Sources of Errors
Calibration
Contamination
Sample preparation – how sample is loaded into a pan
Residual solvents and moisture.
Thermal lag
Heating/Cooling rates
Sample mass
Processing errors
Technical Group Talk

13. Other DSC techniques
These are three defferent types of DSC instruments.
power-compensated DSC
Heat-flux DSC
Modulated DSC

14. Power-compensated DSC
In this case, the sample and reference material are heated separately and continuously maintained at same temperature.
While both temperatures are increased or decreased linearly.
The differential power is recorded as a function of temperature and the peak area represents the energy of transition.
Isothermal condition i.e Ts=Tr is obtained by placing a platinum resistant thermometer in the sample with an identical sensors in the reference holder.
This DSC has lower sensitivity and capable of higher resolution than heat-flux DSC.

15. POWER-COMPENSATED DSC

16. Heat-flux DSC instrument
In this case, the difference in heat flow into the sample and reference is measured while the sample temperature is changed at a constant rate.
Both sample and reference are heated by a single heating unit.
The differential heat flow to the sample and reference is monitored by chromel-constantan area thermocouples.

17. HEAT-FLUX DSC

18. Modulated DSC Benefits
Increased Sensitivity for Detecting Weak (Glass) Transitions
Eliminates baseline curvature and drift
Increased Resolution Without Loss of Sensitivity
Two heating rates (average and instantaneous)
Ability to Separate Complex Thermal Events and Transitions Into Their Heat Capacity and Kinetic Components
Ability to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions
Downside
Slow data collection
Modulated DSC

19. MODULATED DSC Reversible Transitions Glass Transition Melting
Non-reversible
Crystallisation
Curing
Oxidation/degradation
Evaporation

20. Applications of DSC
Qualitative analysis:-It is a finger-printing of minerals,clays,polymers,etc.
Sample purity.
Melting point.
Heat capacity(Cp).
Glass transition(Tg).
Crystallization temperature(Tc).
Phase diagrams.

21. In food industry for characterisation of edible fats and oils.
The total time of analysis in DSC is 30minutes.
It is used for identification of optical isomers.
It is used for impurity studies in pharmaceutical industries.

22. It is used in polymer industry.
Specific heat,heat of fusion,heat of dehydration,decomposition of samples can be determined.
It is used to access the purity of any substances.
Example:-carnauba wax.

23. REFERENCES INSTRUMENTAL ANALYSIS SKOOG
INSTRUMENTAL METHODS OF CHEMICALANALYSIS
GURUDEEP.
R.CHATWAL,SHAM,K.ANAND.
INSTRUMENTAL METHODS OF ANALYSIS,7TH EDITION
WILLARD,MERRITT.

24. THANK YOU