1. THERMAL ANALYSIS
By
T.SHIVAKUMAR,
, Kottam Institute of
Pharmacy,
Erravally ‘X’ Roads,
MBNR-Dist.AP.

2. Thermal methods of Analysis
 This is based on the concept of heating a sample
– followed by well-defined modified
procedures, such as : gravimetric
analysis, differential analysis and titrimetric
analysis.
 Some property of a system is measured as a
function of temperature.
 Thermal spectra or Thermograms

3. Conti….
 Thermo grams characterize a single or multi
component system in terms of :
 Thermodynamic properties, and
 physicochemical reaction kinetics.

4. Thermal Analysis is widely used …
Other Polymers
13% 21%
Chemicals
9%
Textiles Pharma
4% 9%
Aerospace
4% Petrochem
8%
Metals
5%
Auto Ag/Food
5% Government Academic 8%
7% 7%

5. Different Techniques
 Thermometric Titration (TT)
 Thermal Mechanical Analysis (TMA)
 Dynamic Mechanical Analysis (DMA)
 Differential Scanning Calorimetriy (DSC)
 Thermal Gravimetric Analysis (TGA)
 Differential Thermal Analysis (DTA)
 Temperature Programmed Desorption (TPD)

6. Principle
 Sample is heated at a constant heating rate
 Sample’s Property Measured
 Wt TGA
 Size TMA
 Heat Flow DSC
 Temp. DTA
 Heat of mixing TT
 Tem. at which TPD
gas is desorbed
at the surface.

7. What is DTA ?
 Involves the technique of recording the difference in
temperature between the Test and Reference material
time being constant for both.
 Hence the Differential Thermogram consists record of
difference in Temperatures.

8. Thermogram
A differential thermogram consists of a record of the
difference in sample and reference themperature(∆T)
plotted as a function of time t, sample
temperature(Ts), reference temperature(Tr) or furnace
temperature(Tf).
In most of the
cases, physical
changes give rise to
endothermic curves,
whereas chemical
reactions give rise to
exothermic peaks.

9. Factors affecting DTA curve
A] Environmental factors
B] Instrumental factors
i] Sample holder
ii] Differential temperature sensing device
iii] Furnace characteristics
iv] Temperature- programmer controller
v] Thermal Regime
vi] Recorder
C] Sample factors
1] Physical
2] Chemical

12. Instrumentation
 A differential thermal analyzer is composed of five
basic components, namely :
1} Furnace
2} Sample holder
3} temperature controller and recorder
4} thermocouple
5} Cooling device

13. 1} Furnace
 Tubular furnace is most commonly used because it
possess the desired characteristic for good
temperature regulation and programming.
 Dimension of the furnace is depends upon the
length of the uniform temperature zone desired.
 The choice of resistance material is depends on the
maximum temperature of the operation and gaseous
environment.
 Grooved muffled cores preferred.

14. 2} Sample holder
o Should having low cost, ease of fabrication and
inertness towards the sample.
o Metallic material: nickel, stainless steel, platinum
o Non-metallic material: glass, vitreous silica or sintered
alumina.
o Most commonly the shape of holder is cylindrical.
o The nature of physical constant between the sample,
thermocouple junction and the specimen holder affect
the DTA signals. So to maintain it, a sample holder
with dimples in which thermocouple junctions are
inserted (thermocouple wells) are used.

15. 3} Temperature controller and recorder
A] Temperature Controller
 In order to control temperature, the three basic
elements are required.
 These are sensor, control element and heater.
 The control element governs the rate of heat-input
required to match the heat loss from the system.
 The location of sensor with respect to the heater and
mode of heat transfer measure the time elapsed
between sensing and variation in heat input.

16. Conti…
B] Temperature programming
 It transmits a certain time-based instruction to the
control unit.
 By this device one can achieve linearity in the rate
of heating or cooling it is driven in a non-linear
fashion using a special cam-drive.
 Heating rates of 10-20 o C / mints are employed.
C] Recorder
 The signals obtained from the sensors can be
recorded in which the signal trace is produced on
paper or film, by ink, heating stylus, electric writing
or optical beam.

17. 4} Thermocouple
 Thermocouples are the temperature sensors.
 It is made up from chromel p and alumel wires
are used to measure and control temperature
up to 1100 0C in air.
 For above 1100 0C one should use
thermocouple made from pure platinum &
platinum-rhodium alloy wires.

18. 5} Cooling device
 It is separate from the temperature programmer
because it is independent from heating.

19. DTA Analyzer

20. Methodology
o Insert a very thin thermocouple into a disposable
sample tube 2 mm in diameter and containing 0.1- 10
mg of sample,
o Another identical tube is either kept empty or filled
with a reference substance, such as
quartz, sand, alumina.
o The two tubes are simultaneously inserted into the
sample block and subsequently heated (or cooled) at
a uniform predetermined programmed rate

21. Requirements
 DTA—A few of the vital aspects are :
 Pre-treatment of the specimen,
 Particle size and packing of the specimen,
 Dilution of the specimen,
 Nature of the inert diluent,
 Crystalline substances must be powdered, and sieved
through 100-mesh sieve

22. Cont…
 Either to suppress an unwanted reaction (e.g.,
oxidation), or to explore the study of a reaction(e.g.,
gaseous reaction product)—the atmosphere should be
controlled adequately.

23. DTA Curve

24. 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.
Disadvantage:
 uncertainty of heats of fusion, transition, or
reaction estimations is 20-50%.

25. Applications of DTA
 Physical Chemistry
1. Heat of a Reaction
2. Specific Heat of substance like
Naphthalene.
3. Thermal Diffusivity of samples
 Analytical Chemistry
1. Identification of Products since no two
products have identical curves.
2. Determination of Melting point.

26. Applications 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 φ and particle size (included in a constant k for a
certain substance).
Usually the sample peak area is compared with a standard undergoing an
enthalpy change at a similar T (since the calibration constant depends on
T), under the same conditions,
e.g. indium MPt 156.4 C; ∆H fusion = 28.5 J g-1

27. 3. To fingerprint substances
4. To determine M.Pt., B.Pt., decomposition temperatures of organic
compounds .

28. 5. To characterize inorganic materials
The peak at 113 C corresponds to a solid-phase change from the rhombic to the
monoclinic form, while the peak at 124 C corresponds to the melting point of the
element.
Liquid sulphur is known to exist in at least three forms, and the peak at 179 C
apparently involves a transition among these.
The peak at 446 C corresponds to the boiling point of sulphur.

29. 6. To quantitatively analyze polymer mixtures
This is a thermogram of a physical mixture of seven commercial
polymers. Each peak corresponds to the characteristic melting point
of one of the components. Poly tetrafluoroethylene (PTFE) has an
additional low temperature peak, which arises from a crystalline
transition. Clearly, differential thermal methods can be useful for
qualitative analysis of polymer mixtures.

30. 7. To characterize polymers
Schematic DTA thermal curves for the totally amorphous polymer structure and
the semi crystalline polymer structure. Both show Tg ; only the semi-crystalline
polymer has a crystallization exotherm.

31. Cont…
 Quantitative analysis of Compounds
 Determination of Structural and Chemical changes
occurring during heat treatments.
 Quality Control of Cement, glass, textiles, soils,
explosives and resins.

32. Differential Scanning
Calorimetry

33. Definitions
• A calorimeter measures the heat into or out of a
sample.
• A differential calorimeter 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.

34. DSC: The Technique
• Differential Scanning Calorimetry (DSC) measures the
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.

35. Conventional DSC
Sample Empty
Metal Metal Metal Metal
1 2 1 2
Sample Reference
Temperature Temperature
Temperature
Difference =
Heat Flow
•A ―linear‖ heating profile even for isothermal methods

36. Thermal Analysis
Differential Scanning Calorimetry (DSC)

37. DSC Cell

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

39. DSC
Measure Transitions:
- Glass Transition Temperature (Tg)
- Melting Temperature (Tm)
- Crystallization Temperature (Tc)

40. Think First………Heat Later
1. Does the sample contain volatile components?
- 2 to 3% water/solvent can lower the glass
transition temperature (Tg) by up to 100oC.
- Evaporation creates endothermic peaks in
standard (non-hermetic) DSC pans and can be
suppressed with use of hermetic DSC pans.

41. 2. At what temperature does the sample decompose?
- Set the upper limit of the DSC experiment based on
decomposition temperature (TGA). No meaningful
DSC data can be obtained once decomposition
results in a 5% weight loss.
- Decomposition affect: the quality of the baseline
due to both endothermic and exothermic heat
flow, the quality of the baseline for future
experiments and can affect the useful lifetime of the
DSC cell due to corrosion.

42. 3. How does thermal history (temperature and time) affect
DSC results on my sample?
4. Identical materials can look totally different based on:
- Storage temperature and time.
- Cooling rate from a temperature above Tg or above the
melting point.
- Heating rate.
- Different kinds of experiments may need to be performed in
order to measure the current structure vs. comparing samples
to see if the materials are the same.

43. Amorphous Structure
 Glass Transition (Tg)
- Detectable by DSC due to a step increase in heat
capacity as the sample is heated to a temperature above
the glass transition temperature (Tg).
- Important transition because significant changes in
physical properties, reactivity and storage stability
occur at Tg.

44. Glass Transition (Tg)
 Reporting Tg as a single temp., it is necessary to state:
- What point in the step change (onset, midpoint or end) is
being measured.
- The experimental conditions used to measure Tg: heating
rate, sample weight.

45. Glass Transition (Tg)
 To increase sensitivity:
- Use >10mg samples.
- Quench cool sample from a temperature
above the melt to maximize amorphous
structure.

46. Tg sensitivity
Use >10oC/min heating rates.

47. Glass Transition (Tg)
 As a little as 2-3% water can lower Tg by up to 100oC.
- To measure an accurate Tg in a sample with a volatile
component by running sample in a hermetic (sealed) pan.
- Use a dry-box or dry-bag to prepare samples in hermetic
pans. This eliminates water absorption during preparation
and loss water during the measurement.

48. Crystalline Structure
 Crystalline structure in a sample is determined from the
presence of an endothermic melting peak.
 Important complimentary techniques to DSC include:
- Hot Stage Microscopy
- X-Ray Diffraction (XRD)
- Nuclear Magnetic Resonance (NMR)
- Infrared Spectroscopy

49. Crystalline Structure
 Factors which complicate DSC analysis:
- Endothermic peaks can be created by evaporation and
decomposition as well as melting.
- TGA should be done on all new samples prior to DSC to
determine volatile content and decomposition temperature.
- Dehydyration/Desolvation usually results in loss of crystalline
structure.
- Melting is a thermodynamic transition and therefore, the onset
of melting does not change significantly with heating rate.
- Decomposition is a kinetic (time-dependent) transition and
therefore, the onset temperature of the peak shifts to a
significantly higher temperature at higher heating rate.

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

51. Example DSC - PET
Sample : PET80PC20_MM 1min
Size : 23.4300 mg
1
Method: standard dsc heat -cool-heat
DSC
File: C:...DSCMelt Mixed 1PET80PC20_MM
Operator : SAC
Run Date : 05-Apr-2006 15 :34
1.001
Comment : 5/4/06 Tm
Instrument : DSC Q1000 V9.4 Build 287
1.5
245.24 C
1.0 Tc
Tg
Heat Flow (W/g)
137.58 C
20.30J/g 228.80 C
22.48J/g
79.70 C(I) 81.80 C
0.5
75.41 C
Cycle 1
144.72 C
0.0
-0.5
0 50 100 150 200 250 300
Exo Down Temperature ( C) Universal V4.2E TA Instruments

52. Influence of Sample Mass
0
Indium at Onset not
-2 10 C/minute influenced
Normalized Data 15mg by mass
10mg
4.0mg
-4
DSC Heat Flow (W/g)
1.7mg
1.0mg
0.6mg
-6
150 152 154 156 158 160 162 164 166
706 Temperature ( C)

53. Effect of Heating Rate
on Indium Melting Temperature
1
0
-1
Heat Flow (W/g)
-2
heating rates = 2, 5, 10, 20 C/min
-3
-4
-5
154 156 158 160 162 164 166 168 170
Temperature ( C)
6

54. 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

55. Sample Preparation : Shape
• Keep sample as thin as possible (to minimise thermal
gradients)
• Cover as much of the pan bottom as possible
• Samples should be cut rather than crushed to obtain a
thin sample (better and more uniform thermal contact
with pan)
99

56. Other DSC Techniques
Hyper-DSC
Based on principle that high heating rates give large broad transitions.
•Heating rates typically 400-500oC/min
•Need very small sample sizes (~nanograms)
Good for:
•A quick overview of new sample
•Picking out minute transition
Poor for:
•Accuracy: transitions can be shifted by as much as 40oC
•Repeatabiliy: Very sensitive to thermal lag.

57. Thermal Analysis
Differential Scanning Calorimetry (DSC)
DSC is a thermal method of analysis to study the thermal behaviour and thermal
properties of materials (typically polymers). The material is sealed in a sample pan
and subjected to a controlled temperature programme.
The resulting thermograph can yield much valuable information about the properties
of the material analysed.
 Main use of DSC: Material Identification (Tm and Hf) based on IS EN ISO
3146:2000; Method C2

58. Thermal Analysis
Differential Scanning Calorimetry (DSC)
Other uses of DSC:
% Crystallinity determination by DSC (based on IS EN ISO 3146:2000; Method C2).
Purity and Polymorphism analysis by DSC.
Thermal Stability of materials (e.g. – oxidative induction time (OiT) of materials) by
DSC.

59. Thermal Analysis
Differential Scanning Calorimetry (DSC)

60. Other DSC Techniques
Modulated DSC
•Composite heating profile:
•Determines heat capacity and separates heat flow into that due to
reversible and non-reversible events.
62 62
Modulate +/- 0.42 °C every 40 seconds
Ramp 4.00 °C/min to 290.00 °C
60 60
Typicaly:
Heating rates: 0 - 50C
Modulated Temperature (°C)
58 58
Temperature (°C)
Modulation:
Period: 60 second 56 56
Amplitude: +/-10C
54 54
Note that temperature is not decreasing during
Modulation i.e. no cooling
52 52
13.0 13.5 14.0 14.5 15.0
Time (min)

61. 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

62. Example MDSC
0.00 0.00
-0.02 -0.02 -0.02
-0.04 -0.04 -0.04
N onrev H eat Flow (W /g)
R ev H eat Flow (W /g)
H eat Flow (W /g)
-0.06 -0.06 -0.06
-0.08 -0.08 -0.08
-0.10 -0.10 -0.10
-0.12 -0.12 -0.12
-0.14 -0.14
-50 0 50 100 150 200 250
Exo Up Temperature (°C) Universal V4.2E TA Instruments

63. Reversible Transitions
•Glass Transition
•Melting
Non-reversible
•Crystallisation
•Curing
•Oxidation/degradation
•Evaporation
Technical Group Talk

64. Comparison of DSC & DTA
Aspect DSC DTA
1.Size of Sample 2-10 mg 50-20mg
2. Sensitivity A few joule/mol 0.5kJ/mol
3.Heating & Programmed Programmed
Cooling cycles Heating & Cooling heating
is possible.
4. Second order It can be observed It is not observed
phase transition with a sample of
200mg
5. Specfic heat Accurate Not accurate
measurement

65. References
1. Instrumental Methods of Chemical Analysis-
By, G.R. Chatwal & S.K. Anand.
2. Instrumental methods of analysis; seventh edition
by Willard. Merritt, Dean Seffle.
3. www. wikipedia.com