DTA: Introduction, Principle, Instrumentation, Application

1. Differential Thermal Analysis
(DTA)
Presented by:
Shobhit Srivastava
M.Pharm
1st year
Presented to:
Dr. Sujeet Kumar Gupta
Associate Professor
Hygia Institute of Pharmaceutical
Education & Research, Lucknow

2. Content
1. Thermal analysis
2. Methods of Thermal Analysis
3. Differential thermal analysis
a) Introduction
b) Principle
c) Instrumentation
d) Factor affecting curve of DTA
e) Advantage
f) Disadvantage
g) Application

3. Thermal Analysis
• Thermal analysis is defined as “series of techniques for
measuring the temperature dependency of a physical property of
a certain substance while varying the temperature of the
substance according to a specific program.”
• The substance referred to here includes reaction product.
• Physical properties include adsorption, sublimation, evaporation,
desorption etc. whereas chemical properties include
oxidation/reduction, crystallization, loss on drying etc.

4. Methods of Thermal Analysis
• TG (Thermogravimetric) analysis:
Technique where by the weight of a substance, in an environment
heated or cooled at a controlled rate, is recorded as a function of
time or temperature.
• DTA (Differential Thermal Analysis):
Technique involve recording of difference in temperature between a
sample and reference material against either time or temperature as
the two specimens are subjected to identical temperature regimen in
an environment heated or cooled at a controlled rate.

5. • DSC (Differential Scanning Colorimetry):
Technique in which the difference in the amount of heat required to
increase the temperature of a sample and reference are measured as
a function of time.

6. Differential Thermal Analysis (DTA)
Introduction
• Differential thermal analysis (DTA) is a thermo analytical
technique similar to differential scanning calorimetric.
• In DTA ,the material under study and an inert reference are made
to undergo identical thermal cycles, while recording any
temperature difference between sample and reference.
• This differential temperature is then plotted again time or against
temperature.
• The curve plotted is called as DTA curve or thermogram.

7. • Changes in the sample either endothermic or exothermic, can be
detected relative to the inert reference.
• Thus a DTA curve provides data on the transformation that have
occurred such as glass transition, crystallization, melting and
sublimation.
• The area under DTA peak is the enthalpy change and is not
affected by the heat capacity of the sample.
• In DTA both the test sample and inert reference material
(alumina) controlled heating or cooling programming.
• If zero temperature difference between sample and reference
material – then sample doe not undergo any chemical and
physical changes.
• If any reaction takes place temperature difference will occur
between sample and reference material.

8. Fig 1.Differential thermogram showing types of changes encountered with polymeric
materials.
+ Exothermic
∆T
Endothermic
Exothermic
Tg
Glass
transition
Melting
Crystallization
Oxidation
No
Oxidation
Decomposition
Temperature

9. Principle
• Monitoring of the temperature difference between a sample and
an inert reference as they are heated uniformly. Endothermic or
Exothermic changes in the sample lead to characteristic
deviation in temperature which can be used for qualitative and
quantitative analysis.
• A technique in which the temperature difference(∆T) between a
substance and reference material is measured as function of
temperature, while the substance and reference are subjected to
controlled temperature programmed.
• The difference in the temperature is called as differential
temperature and is plotted against temperature or function of
time.

10. • Physical changes usually result in endothermic peaks, whereas
chemical reaction those of an oxidative nature show exothermic
peak.
• Endothermic reaction (absorption of heat) includes sublimation
and gives downward peak.
• Exothermic reaction (liberation of heat) includes oxidation,
polymerization and gives upward peak.

11. Instrumentation
• A Differential Thermal Analysis
consists of:
1. Sample holder
2. Thermocouples
3. Furnace
4. Temperature Programmer
5. Recording system
• The key feature is the existence of two thermocouples connected
to a voltmeter.
• One thermocouple is placed in an inert material such as aluminum
oxide, while the other is placed in a sample of the material under
study.
Fig 2. Block Diagram of DTA

12. Fig 3. Schematic diagram of a typical instrument for DTA.

13. 1. Sample holder:
(a) Material:
• Low cost, ease of fabrication, inertness
• Metallic (e.g. Nickel, steel, Platinum )
• Non metallic (e.g. glass, silica, alumina)
(b) Geometry:
• Ideal spherical but due
to fabrication problem
cylindrically geometry
is used.

14. 2. Furnace:
• Prefer a tubular furnace (wire or ribbon).
• Desired temperature regulation and programming.
• Inexpensive.
• Dimension, which depend mainly upon the length of the
uniform temperature zone.
• Made of Tungsten, Chromel, Nichrome v, Silicon carbide etc.
Where,
P = Power
L = Length
Km = Thermal conductivity coefficient
d1 = Diameter of heater coil round on the ceramic
d2 = Diameter of furnace cell
T1 & T2 = temperature of heating element & surface temperature of furnace shell

15. 3. Temperature controller:
(a) Temperature controller:
• Sensor
• Control element (rate of heat input require to match the heat
loss from the system)
• Heater
There are 2 methods for controlling temperature:
1. On-off control: If temperature greater than the set point then
heater cut off (not used in DTA).
2. Proportional control: Proportionally reduced the temperature
if temperature reached to desired value (used in DTA).
(b) Temperature programming:
Time dependent temperature cycling of the furnace.(maintain
constant temperature)

16. 4. Temperature Recorder:
Single trace is produce on paper or film, by ink, heating stylus,
electric writing or optical beam.
2 types of recorder are used in DTA:
(a) Deflection type: Pointer moved by input single
(1) Beam
(2) Cantilever
(3) Spring
(4) Torsion
Fig 4.Types of deflection recorder

17. (b) Null type: Input single is compared by the reference signal
and the difference is amplified.
5. Thermocouple:
Temperature sensor are thermocouple.
Made by Chromel & Alumel wire.

18. Factors affecting curve of Differential Thermal
Analysis
There are so many factors that affects the DTA curve. They are
divided into two
SAMPLE
CHARACTRISTIC
INSTRUMENTAL
FACTOR

19. Instrumental
Factors
Furnace
Temperature
Furnace Size
& Shape
Sample
Holder
Material
Heating
Rate
Thermocouple
location

20. Sample
Characteristics
Heat
Capacity
Swelling &
Shrinkage of
Sample
Amount of
Sample
Packing
Density
Effect of
Diluents

21. Table 1. Factor and their effect
Factor Effect Suggestions
1. Heating rate Change in the peak
size and position
Use allow heating rat
2. Location of
Thermocouple
Irreproducible curve Standardize
thermocouple location
3. Atmosphere around
the sample
Change in the curve Inert gas should be
allowed to flow
4. Amount of sample Change in the peak
size and position
Standardize sample
mass
5. Particle size of
Sample
Irreproducible curve Use small uniform
particle
6. Packing density Irreproducible curve Standardize packing
techniques
7.Sample container Change in peak Standardize container

22. Advantages:
1. Instruments can be used at a very high temperature.
2. Instruments are highly sensitive.
3. Flexibility in crucible volume/form.
4. Characteristic transition or reaction temperature can be
accurately determined.
Disadvantages:
1. Reaction or transition estimations is only 20% to 50% DTA.
2. Uncertainty in heats of fusion.

23. Application of Thermal Differential Analysis
 Qualitative and Quantitative identification of Minerals:
Detection of any minerals in sample.
 Polymeric materials:
DTA is useful for characterization of polymeric materials in the
light of identification of thermo-physical, thermo-chemical, thermo-
mechanical, and thermo-elastic changes or transition.
 Measurement of crystalline:
Measurement of the mass fraction of crystalline material in semi-
crystalline polymer.

24.  Producing phase diagrams and identifying phase conversions.
 Finding the change in enthalpy (ΔH) in the entire procedure.
 Fingerprinting of certain materials.
 Verifying decomposition temperatures of various organic
composites.
 Exemplifying inorganic compounds.
 Analyzing a physical mixture of commercial polymers
qualitatively.
 Quantitative identification and purity assessment of material are
accomplished by comparing the DTA curve of sample to that of
a reference curve.
 Impurities may be detected by depression of the melting point.

25.  DTA is widely used in the pharmaceutical and food industries.
 DTA may be used in cement chemistry mineralogical research
and in environmental studies.
 DTA curves may also be used to date bone remains or to study
archaeological materials Using DTA one can obtain liquids &
solidus lines of phase diagrams.

26. Reference:
1. Skoog Douglas A., Holler James F., Crouch Stanley R.,
“Instrumental Analysis”, Indian edition, 2007, published by
Cengage lerning india pvt. Ltd., New Delhi, page no.980-82.
2. Braun Robert D., “Introduction to Instrumental Analysis”,2004,
published by PharmMed Press, Hyderabad, page no.939-40.
3. Chatwal GR, Anand SK. Instrumental method of chemical
analysis. 5th ed. Mumbai: Himalaya publishing house; 2007. p.
2.719-2.738.

27. Thank you !!