The document discusses Differential Thermal Analysis (DTA), covering its principles, characteristics of DTA curves, instrumentation, factors affecting DTA curves, and applications. DTA compares the temperature of a sample with a reference material to analyze physical and chemical changes during heating. The technique has significant applications in identifying compositions, studying thermal stabilities, and examining reactions in materials.

1. USMAN ALI 1

2. PRESENETED BY
USMAN ALI &
UMAR RAFIQUE
TO
Sir. AJMAL BHATTI Sb
Government College Gujranwala
2USMAN ALI

3. Differential
Thermal
Analysis
(DTA)
• Principle
• Characteristics
of DTA Curve
• Instrumentation
• Factors
Affecting DTA
Curve
• Interpretation of
DTA Curve
• Application
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4. Limitations Of TGA
 The Chemical or physical changes which are
not accompanied by the change in mass on
heating are not indicated in
thermogravimetric analysis
 During TG, Pure fusion reaction, crystalline
transition, glass transition, crystallization
and solid state reation with no volatile
product would not be indicated because they
provide no change in mass of the specimen.
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5. 1.Principle
Differential Thermal analysis is a technique in
which the temperature of the substance
under investigation is compared with the
temperature of a thermally inert material
such as a-alumina, and is recorded with
furnace temperature as the substance is
heated or cooled at a predetermined uniform
rate.
The principle of method consists in measuring
the change in temperature associated with
physical or chemical changes during the
gradual heating of the substance.
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6. Phenomena causing changes in
Temperature
Physical:
 Adsorption (exothermic)
 Desorption (endothermic)
 A change in crystal structure
(endo – or exothermic)
 Crystallization (exothermic)
 Melting (endothermic)
 Vaporization (endothermic)
 Sublimation (endothermic)
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7. Chemical:
 Oxidation (exothermic)
 Reduction (endothermic)
 Break down reactions
(endo – or exothermic)
 Chemisorption (exothermic)
 Solid state reactions
(endo – or exothermic)
 Generally speaking, phase transitions,
dehydration, reduction and some decomposition
reactions produce endothermic effects whereas
crystallization, oxidation and some
decomposition reaction produce exothermic
effects.
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8. Historical Aspects:
In 1899 Robert Austen
improved this technique
by introducing two
thermocouples, one
placed in sample and
other in the reference
block.
This technique was later
on modified by
Burgess(1909),
Norton(1939),
Grim(1951), Kerr(1948),
Kauffman(1950), Fold
Vari(1958).
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9. Characteristics Of DTA Curves
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10. Characteristics Of DTA Curves
Temperature of the sample is greater
for an exothermic reaction, than that of
reference, for endothermic the sample
temperature lags behind that of
reference
The peak temperature corresponds to
the maximum rate of heat of evolution.
It does not represent the maximum rate
of reaction nor the completion of the
exothermic process.
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11. Characteristics Of DTA Curves
 DTA curves are not only help in the
identification of materials but their peak
areas provide quantitative information
regarding mass of sample, heat of reactions
(Enthalpy change) and factors such as sample
geometry and thermal conductivity.
 If latter two factors are expressed by a factor
“K” called calibration factor, then peak area
can be expressed as:
Peak Area (A) = ±∆ H m K
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12. Instrumentation:
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13. Instrumentation:
1. Source of Uniform Heating:
 Nichrome (up to 1300 0C )
 Platinum and its alloys (up to 1750 0C )
 Molybdenum (up to 2000 0C )
2. Temperature Regulating System:
 Electronic Temperature Regulators
3. Specimen Holder:
 Pt, Ni, stainless steel, Ag and alloy such as Pt-
Rh
 Ceramic material: sintered alumina, silica
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14. Instrumentation:
4. Measurement of Temperature:
 Rare metal alloys Pt - Rh (Pt 10% - Rh 13%)
used as thermocouple
 W - Mo also used as thermocouple
5. Temperature Recording System:
Galvanometric Observation ( For few
samples)
Automatic pen
Ink electronic Recorder
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15. Factors Affecting DTA Curves:
DTA is a dynamic temperature technique.
Therefore, a large number of factors can affect.
These factors can be divided into the two
groups:
i) Instrumental factors
ii) Sample factors
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16. Factors Affecting DTA Curves:
Instrumental Factors:
Size and shape of sample holder
Sample holder material
Heating rate of sample
Sensitivity of recording system
Location of thermocouple in the sample
Atmosphere around sample
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17. Factors Affecting DTA Curves:
Sample characteristics:
Amount of sample
Particle size
Packing density
Heat capacity
Thermal conductivity
Degree of crystallinity
Dilutes of diluents
Swelling and shrinking of sample
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18. Factors Affecting DTA Curves:
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19. Interpretation of DTA Curve
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20. Applications
The important applications of DTA are:
Rapid identification of the composition
of mixed clays
Studying the thermal stabilities of
inorganic compounds
Critically examining in a specific
reaction whether a new compound is
actually formed or the product is
nothing but an unreacted original
substance 20USMAN ALI

21. Applications
DTA offers a wide spectrum of useful
investigations related to reaction
kinetics, polymerization, solvent -
retention, phase-transformations, solid-
phase reactions and curing or drying
properties of a product
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22. Thank
You !
USMAN ALI 22