DIFFERENTIAL THERMAL ANALYSIS & DIFFERENTIAL SCANNING CALORIMETRY

1. DIFFERENTIAL THERMAL
ANALYSIS
&
DIFFERENTIAL SCANNING
CALORIMETRY
Prachi Pathak

2. • Differential Thermal Analysis (DTA)
• The temperature difference between a sample and
an inert reference material, DT = TS - TR, is
measured as both are subjected to identical heat
treatments.
• Differential Scanning Calorimetry (DSC)
• The sample and reference are maintained at the
same temperature, even during a thermal event (in
the sample)
• The energy required to maintain zero temperature
differential between the sample and the reference,
dDq/dt, is measured

3. DTA
• Sample and Reference Placed in Heater
• Constant Heating Rate
– Initial Temp
– Final Temp
– Heating Rate (°C/min)
• Data
– Temp of Sample vs Time (or Temp)
– Temp of Reference vs Time (or Temp)
– Reference should be inert
• Measures
– Heat of crystallization
– Glass Transition Temperature

4. Differential Thermal Analysis
• DTA involves heating or cooling a test sample and an
inert reference under identical conditions, while
recording any temperature difference between the
sample and reference.
• This differential temperature is then plotted against
time, or against temperature.
• Changes in the sample which lead to the absorption
or evolution of heat can be detected relative to the
inert reference.

5. TGA+ DTA

6. • <10 mg of sample (s) and inert reference (r) are
contained in Al pans each with thermocouple, held in
heating block.
• There is a constant temperature difference T between
s and r since they have different heat capacities. But
when the sample undergoes an endo (exo) thermic
changes in T becomes different.
• If the test sample generates heat, its temperature will
be higher than the reference sample.
•If the sample absorbs heat, its temperature will be
lower than the reference sample.
DTA

7. DTA

8. • Modern instrumentation used for thermal analysis
usually consists of four parts:
1) sample/sample holder
2) Thermocouples: sensors to detect/measure a
property of the sample and the temperature
3) Furnace: an enclosure within which the
experimental parameters may be controlled
4) a computer to control data collection and
processing
DTA power compensated DTA

9. Instrumentation
• sample holder
sample and reference cells (Al)
• Sensors
Platinum/Rhodium or
chromel/alumel thermocouples one
for the sample and one for the
reference joined to differential
temperature controller
• Furnace
alumina block containing sample
and reference cells
• Temperature controller
controls for temperature program
and furnace atmosphere
sample
pan
inert gas
vacuum
reference
pan
heating
coil
alumina block
Pt/Rh or chromel/alumel
thermocouples

10. Differential Thermal Analysis
Advantages:
• instruments can be used at
very high temperatures
• instruments are highly
sensitive
• flexibility in crucible
volume/form
• characteristic transition or
reaction temperatures can
be accurately determined
Disadvantages:
• uncertainty of heat of
fusion, transition, or
reaction estimations is 20-
50%
DTA

11. Some uses of DTA
1. To construct phase diagrams and study phase transitions
2. To find H
Peak areas depend upon sample mass, m, enthalpy change H of the
process, and geometric and conductivity factors such as heating rate 
and particle size.
peak area  H  m
(cm2) (Jg-1) ( g)

12. 
T
3. To fingerprint substances
DTA of (a) butter and (b) margarine
temp 
a
b
4. To determine M.Pt., B.Pt., decomposition temperatures of
organic compounds
DTA of benzoic acid
A ambient pressure;
B 200 lb in-2 pressure

13. Differential Scanning Calorimetry

14. Differential Scanning Calorimetry
DSC is a thermal analysis method where differences in
heat flow into a substance and a reference are
measured as a function of sample temperature, while
both are subjected to a controlled temperature
program.

15. The basic difference between DTA and DSC
DSC- calorimetric method, energy differences measured.
DTA- temperature differences measured.
The applications of both techniques are similar, but DSC is
now more popular.
DTA is used for higher temperature and qualitative
applications.
DSC is used for calorimetric determinations, sample
purity determinations and kinetics.
Differential Scanning Calorimetry

16. • DSC differs fundamentally from DTA in that the
sample and reference are both maintained at the
temperature predetermined by the program.
• 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 sample pans.
• Two basic types of DSC instruments: power
compensation and heat-flux
Differential Scanning Calorimetry
power compensation DSC heat flux DSC

17. Two major types of DSC instruments are
available
Heat flux device – more popular; more stable
baseline and more durable cell.
Difference in heat flow into s and r is
measured with (linear) change in sample
temperature.
Power compensation device – better
resolution; faster heating and cooling rates.
s and r heated by separate heaters to keep
same temperature, as T is changed linearly.

18. Power Compensation DSC
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.
sample
pan
T = 0
inert gas
vacuum
inert gas
vacuum
individual
heaters
controller P
reference
pan
thermocouple

19. 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 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
program value
Heat Flux DSC
sample
pan
inert gas
vacuum
heating
coil
reference
pan
thermocouples
chromel wafer
constantan
chromel/alumel
wires

20. Differential Scanning Calorimetry – Principle
of Operation
• A sample is placed inside a crucible which is then
placed inside the furnace of the DSC system along
with a reference pan which is normally empty
(inert gas may be used).
• By applying a controlled temperature program
(isothermal, heating or cooling at constant rates),
phase changes can be characterized and/or the
specific heat of a material can be determined.
• Heat flow quantities are calculated based on
calibrated heat flow characteristics of the cell.

21. Differential Scanning Calorimetry –
Equipment
• Two pans
• Heat transfer disk (almost always made of
Constantan – an alloy of 60% Cu and 40% Ni
• a differential detector
• a signal amplifier
• a furnace
• a temperature controller
• a gas control device
• a data acquisition device
CHM 342
- Sample Reference
Gas
control
Furnace
controller
four
Data
acquisition
Microvolt
amplifier
Detectors
Furnace

22. Endothermic and exothermic effects
According to the thermal transformation, an
endothermic or exothermic effect is recorded.
In the case of an endothermic effect, it is needed
to provide heat to the system for its
transformation(sample absorbs energy). This will
result in a decrease of the temperature in the
system during the transformation(sample
releases energy).
In the case of an exothermic effect, the system
provides heat during its transformation. This
results in an increase of the temperature in the
system.

23. - common endothermic effects:
- melting, sublimation
- first order and second order phase transitions
- evaporation, dehydration
- denaturation (protein)
- gelatinization (starch with water)
- common exothermic effects
- Crystallization, Gelation (gel formation)
- Oxidation, combustion, Decomposition, ignition,
explosion
- Fermentation, Most of the chemical reactions,
Polymerization, reticulation

24. Endothermic and exothermic
effects• Heat Flux
24
EXO
ENDO
Time (sec)
Temperature (°C)
cooling
heating

25. Typical results from DSC
Analysis of a polymer shows
several features due to physical
and chemical changes,
including:
DSC of polymer

26. Summary of Pharmaceutically Relevant Information
Derived from DSC Analysis
• Melting points – crystalline materials
• Desolvation – adsorbed and bound solvents
• Glass transitions – amorphous materials
• Heats of transitions –melting, crystallisation
• Purity determination – contamination,
• crystalline/amorphous phase quantification
• Polymorphic transitions – polymorphs and
• pseudopolymorphs
• Processing conditions – environmental factors
• Compatibility – interactions between components
• Decomposition kinetics – chemical and thermal stability

27. Thank you!