DIFFERENTIAL THERMAL ANALYSIS (DTA)

1. DIFFERENTIALTHERMAL ANALYSIS
[DTA]

2. Definition of Thermal Analysis (TA):
Thermal Analysis (TA)is a group of techniques that study the
properties of materials as they change with temperature.
TYPES :
• TG (Thermogravimetric) analysis: weight
• DTA (Differential Thermal Analysis): temperature
• DSC (Differential Scanning Calourimetry):temperature
WHAT IS THERMAL ANALYSIS ?

3. Differential Thermal Analysis (DTA) :-
A technique in which the difference in
tempreture between the sample and referance
material is monitored against time or tempreture
while the tempreture of the sample, in a specified
atmosphere, is programmed.
WHAT IS DIFFERENTIALTHERMAL ANALYSIS ?

4. INTRODUCTION :
• This is a comparison method
• When a material is heated its structural and chemical composition can
undergo changes such as fusion, melting, crystallization, oxidation, transition,
decomposition, expansion and sintering.
• Using Thermal Analysis such changes can be monitored in every atmosphere
of interest. The obtained information is very useful in both quality control and
problem solving.
• 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, or against
temperature.

5. • The curve plotted is called as DTA curve or thermo gram.
• Changes in the sample either endothermic or exothermic,can be detected
relative to the inert reference.

6. PRINCIPAL :
• A technique in which the temperature difference 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 temp is called as differential temperature and is plotted
against temp or function of time.
• 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.

8. INSTRUMENTATON :
A DTA consists of a –
1. Sample holder
2. Thermocouples
3. A furnace;
4. A temperature programmer
5. A recording system.
 The key feature is the existence of two thermocouples connected to
a voltmeter.
 One thermo couple is placed in an inert material such as aluminum
oxide, while the other is placed in a sample of the material under
study.

9. 2.Sensors/thermocouples:
Platinum or chromyl thermocouples one for sample and one for
reference material is joined to differentialtemperaturecontroller.
3. Furnace:
alumina block containing sample and reference cells.
4.Temperature controller:
controls temperature program and furnace atmosphere.
5.Recordingsystem:
It is a system where the change in the temperature i.e. differential
temperature is recorded and the enthalpy is recorded
1.Sampleholder:
The sample holder and reference cells are made up of aluminum.

11. WORKING :
 We need to take two aluminum containers for keeping the sample as
well as reference in them.
 Thermocouples are connected to each of the material for measuring
their temperature, and heat is applied to them under cautiously
regulated conditions.
 Now, if it is seen that the sample material has gone through certain
chemical reaction or physical transformation, its temperature will
change significantly due to the change in its ‘enthalpy' or heat content.
 However, the temperature of the reference material will remain
unchanged.

12. FACTORS AFFECTING RESULT IN DTA :
There are so many factors that affects the DTA curve.They are
divided into two types as follows ;
SAMPLE CHARACTERISTICS
• TYPE - 1
INSTRUMENTAL FACTORS
• TYPE -2

13. INSTRUMENTAL FACTORS :
Furnace
temperature
Furnace size
and shape
Sample holder
material
Heating rate
Thermocouple
location

14. Sample characteristics factors :
Heat
capacity
Swelling
and
shrinking
of sample
Amount
of sample
Packing
density
Effect of
diluents

15. Factors Effect Suggestion
1.Heating factor Change in the peak size
and position
Use allow heating rate
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
Lets see how these factors affect the curve :

16. Advantages:
• Instruments can be used at very high temperatures.
• Instruments are highly sensitive.
• Characteristic transition or reaction temperatures can be accurately
determined.
Disadvantages:
• Uncertainty of heats of fusion, transition, or reaction estimations is
20-50%.

17. Applications of differential thermal 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 thermophysical, 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.
• Impurities may be detected by depression of the M.P.
• DTA is widely used in the pharmaceutical] and food industries.
• DTA may be used in cement chemistrymineralogical researchand
in environmental studies.