0. Differential Scanning Calorimetry
Queens University Belfast
16/02/12

1. What is a DSC?
What is DSC?
Differential: measurement of the difference in heat flow
from sample and reference side
Scanning: the common operation mode is to run temperature or time scans   
Calorimeter: instrument to measure heat or heat flow.
Heat flow: a transmitted power measured in mW

2. DSC working principle Ice Air Ts Tr Hot Plate
Heat the hot plate from -20 °C to 30 °C,
What will happen to the ice?
How do Ts and Tr react?
How do the Ts and Tr relate to each other?

3. DSC working principle Tr Ts Tf Tf Temperature Time ∆T =Ts-Tr
DSC raw signal
-0.5
Time
or Tr Tf

4. DSC working principle ∆T =Ts-Tr DSC raw signal, -0.5 Time or Tr
-0.5 Tf
Heat flow (mW)
-10
DSC raw signal,
=∆T/Rth
Rth, thermal resistence of the system ∆H
DSC signal, 
Peak integral -> ∆H

5. Baseline slope
Time
or Tr
Heat flow F
(mW)
-10
Initial deflection
Where,
m is the sample mass
cp is the specific heat capacity
of the sample
 is the heating rate
A normal DSC curve is not horizontal, its baseline shows a slope.

6. Direction of DSC signal
ICTA and Anti-ICTA
ICTAC (International Confederation for Thermal Analysis and Calorimetry)
Direction of DSC signal
ICTA (∆T=Ts-Tr)
endothermic downwards,
exothermic upwards.
Anti-ICTA (∆T=Tr-Ts)
endothermic upwards,
exothermic downwards.

7. Endothermic and exothermic effects
When the sample absorbs energy, the enthalpy change is said to be endothermic. Processes such as melting and vaporization are endothermic.
Exothermic:
When the sample releases energy, the process is said to be exothermic. Processes such as crystallization and oxidation are exothermic.

8. Exothermic effect Tr Ts Temperature ∆T =Ts-Tr DSC raw signal Time
or Tr
Temperature Tr Ts
∆T =Ts-Tr
DSC raw signal

9. Schematic DSC curve of a polymer
1. initial startup deflection; 2. glass transition; 3. crystallization; 4. melting; 5. vaporization; 6. decomposition.

10. What is melting and crystallization?
Melting of Indium: °C, J/g (endothermic)
crystalline
amorphous
Crystallization of Indium: °C, J/g (exothermic)

11. Melting and Crystallization with DSC
Warum kalibrieren nur beim Heizen?

12. How to evaluate melting peaks
Pure materials:
- onset (independent of heating rate)
- Hf baseline: line, integral tangential
Impure materials:
- peak temperature (depends on )
- Hf baseline: line, tangential right purity analysis for eutectic systems (based on curve shape analysis)
Polymers
- peak temperature (depends on  and m)
- Hf baseline: line, spline, integral tangential

13. What is glass transition?
Glassy state
Glass transition
Rubbery state
amorphous solid,
rigid, brittle
liquid (non polymers)
rubber like (polymers)
Glass transition is cooperative molecular movement.

14. The glass transition with DSC
Temperature cp F
exotherm

15. Chemical reaction
A chemical reaction is a process that one or more substances (reactants) are converted to one or more new chemical substances (products) with different properties. e.g. oxidation, decomposition, polymerization etc.
Chemical reactions always involve a change in energy. Depending on whether the energy is absorbed or released during the process, they can be endothermic or exothermic.
Examples:
A freshly-cut apple turns brown;
A bicycle fender becomes rusty;
A copper penny turns green.

16. Chemical reaction
Homogeneous decomposition of dibenzoyl peroxide; peak temperature and peak shape depend on heating rate; peak area is independent of heating rate.

17. Where to use DSC? Material Properties Processing Polymers
Pharmaceuticals
Chemicals
Food
Cosmetics
Materials
Additives
Plasticizers
Impurities
Fillers
Processing
Thermal treatment
Mechanical stressing
Shaping
Storage and use
Material
Properties

18. DSC Resolution and Sensitivity
Multiple Thermocouples increase sensitivity and reduce noise
For Best Resolution: Low signal time constant e.g 1.7 s (20-μL Al crucible, N2 gas)
High baseline stability using chemically resistant ceramic substrate and relatively inert silver furnace

19. Sensor technology
Temperature gradients on the sensor lead to baseline deviation from zero
A single sensor temperature (T0) is measured.
Inhomogeneous temperature distribution of the sensor is not considered.

20. Sensor technology R S TS TR TS0 TR0
Inner ring of thermocouples measure TR and TS
Outer ring measures sensor temperatures at reference and samples sides, TS0 and TR0
Thermocouples act as thermal resistence, R.

21. Sensor technology R S TS TR TS0 TR0
Heat flow on the sample and reference sides are separately measured
N is the number of thermocouples (TC) per ring.
FRS5 sensor (56 TC): N = 14
HSS7 sensor (120 TC): N = 30

22. Noise and sensitivity

23. Noise and sensitivity

24. Resolution

25. Signal time constant Signal = RthCs, Cs = Cpan+ Csample+ Csensor
How long does the system take to equilibrate?
How fast does the signal come back to the baseline?
Small Signal better resolution
Signal = RthCs, Cs = Cpan+ Csample+ Csensor
FRS5 sensor (Rth  0.04 K/mW) & Al40 l (50 mg)
Cpan  50 mJ/K
Csample (10 mg, 1.5 J/gK)  15 mJ/K => Signal  3 s
Csensor  10 mJ/K
FRS5 sensor (Rth  0.04 K/mW) & Al20 l (20 mg)
Cpan  20 mJ/K => Signal  1.8 s

26. Signal time constant How to improve Signal?
Cs can be strongly influenced by the choice of the pan.
Recommendations for better resolution:
-> Al20 ul pan instead of Al40 ul pan
-> Al pans instead of alumina pans
Cs can be reduced by using smaller sample size
Signal can be further decreased by using He as purge gas.

27. Cooling behavior

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