1. Differential Scanning Calorimetry
By : Dr. Kundan Tayade.

2. Calorimeter
A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity.
The world’s first ice-calorimeter, used in the winter of , by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black’s prior discovery of latent heat. These experiments mark the foundation of thermochemistry. The name calorimeter was made up by Antoine Lavoisier. In 1780, he used a guinea pig in his experiments with this device to measure heat production. The heat from the guinea pig's respiration melted snow surrounding the calorimeter, showing that respiratory gas exchange is a combustion, similar to a candle burning.

3. DSC: The Technique • Differential Scanning Calorimetry (DSC) measures
differential heat flows associated with transitions
in substance and reference materials linearly heated at a predetermined rate as a function of time and sample 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. Both in DSC and DTA sample and reference both are heated (or cooled) at constant temperature linearly at predetermined rate.
During a thermal event in the sample, the system will transfer heat to or from the sample pan to maintain the same temperature in reference and a sample pans
There are two basic types of DSC instruments: power compensation DSC and heat-flux DSC
Both differ fundamentally in their instrumentation.

5. Power Compensation DSC
sample
pan
DT = 0
inert gas
vacuum
individual
heaters
controller DP
reference
thermocouple
sample holder
Al or Pt pans
sensors
Pt resistance thermocouples
separate sensors and heaters for the sample and reference
furnace
separate blocks for sample and reference cells
temperature controller
differential thermal power is supplied to the heaters to maintain the temperature of the sample and reference at the program value

6. POWER COMPENSATED DSC:
Two control circuits are employed. One for avg.-temp. control and other for differential-temp. control.
power compensation DSC
In average-temp. control circuit , electrical signal is proportional to desired avg. temp. of sample and ref. holders as a function of time.
In differential –temp. circuit : sample and reference Signals from platinum resistance sensors are fed into differential amplifier. The amplifier output then adjusts power input into two furnaces in such a way that their temperature are kept identical.

7. Heat Flux DSC sample holder sample and reference are connected by
pan
inert gas
vacuum
heating
coil
reference
thermocouples
chromel wafer
constantan
chromel/alumel
wires
sample holder
sample and reference are connected by
a low-resistance heat flow path
Al or Pt pans placed on constantan disc
sensors
chromel®-constantan (a copper-nickel alloy usually consisting of 55% copper and 45% nickel) area thermocouples (differential heat flow)
chromel®-alumel thermocouples (sample temperature)
furnace
one block for both sample and reference cells
temperature controller
the temperature difference between the sample and reference is converted to differential thermal power, dDq/dt, which is supplied to the heaters to maintain the temperature of the sample and reference at the programmed value

8. HEAT FLUX DSC
Heat flows into both sample and reference material via electrically heated constantan thermoelectric disk.
Sample and reference is placed on constantan disc. Heat is transferred to it.
Heat flux DSC
The differential heat flow into two pans is directly proportional to difference in output of two thermocouple junctions .
Sample temperature is estimated by chromel/alumel junction under sample disk.

9. Modulated DSC
Heating and cell arrangement is same as in heat flux DSC.
With the help of Fourier Transform programmed, the overall
signal is mathematically Deconvoluted into two parts, 1) a
reversing heat flow signal 2) a non-reversing heat flow signal.
Usually step transitions such as glass transition appears only in the reversing heat flow signal and exothermic or endothermic events may appear in both signals.

10. What can DSC measure? Significance: Glass transitions
Melting and boiling points
Crystallization time and temperature
Percent crystallinity
Heats of fusion and reactions
Specific heat capacity
Oxidative/thermal stability
Rate and degree of cure
Reaction kinetics
Purity

11. DSC Thermogram Endothermic< >Exothermic - Heat Flow Temperature
Oxidation
Crystallisation
Cross -
Linking
Endothermic< >Exothermic
(Cure) -
Glass
Transition
Heat Flow
Melting
Temperature 6

12. WHY PURGE GAS? Purge gas should always be used during DSC experiments.
Provides dry , inert atmosphere
Ensures even heating
Helps sweep away any off gases that might
be released
Nitrogen
Most common
Increases Sensitivity
Typical flow rate of 50ml/min

13. Keeping the DSC Cell Clean!
One of the first steps to ensuring good data is to keep the DSC cell clean.
How do DSC cells get dirty?
Decomposing samples during DSC runs.
Samples spilling out of the pan.
Transfer from bottom of pan to sensor.

14. How do we keep DSC cells clean?
DO NOT DECOMPOSE SAMPLES IN THE DSC CELL!!!
Run TGA to determine the decomposition temperature
Stay below that temperature!
Make sure bottom of pans stay clean
Use lids
Use hermetic pans if necessary

15. CLEANING CELL: If the cell gets dirty. Clean w/ brush.
Brush gently both sensors and cell if
necessary.
Be careful with the thermocouple.
Blow out any remaining particles.

16. THANK YOU!