Differential Thermal Analysis (DTA) is a thermal analysis technique used to measure temperature differences between a sample and a reference material to study material properties as they change with temperature. The technique can detect endothermic and exothermic changes, enabling identification of material phases and transitions, and is widely used across various industries for assessing material stability and purity. Key components of a DTA system include a sample holder, furnace, temperature controllers, and differential temperature sensors, each influencing the accuracy and resolution of the analysis.

1. Differential Thermal Analysis
(DTA) and Derivative
Differential Thermal Analysis
(DDTA)

2. THERMALANALYSIS TECHNIQUES
• Thermal analysis comprises a group of techniques where
the properties of material are studied as they change
with temperature .
• To determine the thermo-physical properties several
methods are commonly used:
• Differential thermal analysis (DTA), differential scanning
calorimetry (DSC), thermo gravimetric analysis (TGA),
dilatometry (DIL), evolved gas analysis (EGA), dynamic
mechanical analysis (DMA), dielectric analyze (DEA) etc.

3. DTA :
• DTA may be defined formally as a technique for
recording the difference in temperature
between a substance and a reference material
against either time or temperature .
• As the two specimens are subjected to identical
temperature regimes in an environment heated
or cooled at a controlled rate.
• This is a comparison method .

4. • Analytical method for recording the difference in
temperature between a substance and a reference
material as a function of temperature or time .
• Any transformation – change in specific heat can be
detected by DTA .
• In DTA both test sample and an inert reference material
(alumina)are controlled by heating or cooling
programming.
• If zero temperature difference between sample and
reference material – sample does not undergo any
chemical or physical change .

5. Principle :
• This technique is simple .
• The basic principle is :
• It involves the technique of recording the temperature
difference (ΔT) between the test sample and an inert
reference sample under controlled and identical
conditions of heating or cooling is recorded
continuously as a function of temperature or time, thus
the heat absorbed or emitted by a chemical system is
determined.

6. • If any reaction takes place in the sample, then the
temperature difference will occur between the
sample and the reference material
• In an endothermic change (such as melting or
dehydration of the sample) the temperature of the
sample is lower than that of the reference material
(i.e) ΔT = ‒ ve (for endothermic process)
• In an exothermic change or process the sample
temperature is higher than that of the reference
material. (i.e) ΔT = + ve (exothermic process)

9. • The difference in temperature ΔT between the
sample temperature and the reference temperature
T, (ΔT = Ts - Tr) is then monitored and plotted against
sample temperature to give a differential thermo
gram.
• A DTA curve can be used as a finger print for
identification purposes.
• The shape and the size of the peak give information
about the nature of the test sample.

10. • Sharp endothermic peaks indicate phase changes
(such as melting, fusion etc.) transition from one
crystalline form to another crystalline form.
• Broad endothermic peaks are obtained from
dehydration reactions.
• Chemical reactions like oxidative reactions are
exothermic reactions.
• The origin of the temperature difference in the
sample lies in the energy difference between the
products and reactants .

11. • This energy is manifested as enthalpic change either
exothermic or endothermic .
• The area under a DTA peak can be to the enthalpy
change and is not affected by the heat capacity of
the sample.

12. 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)

13. Chemical:
• Oxidation (exothermic)
• Reduction (endothermic)
• Break down reactions (endo – or
exothermic)
• Chemisorption (exothermic)
• Solid state reactions (endo – or exothermic)

15. INSTRUMENTATION:
Sample holder:
• This is used to contain the sample as well as
reference material.
Material – criteria for selecting material are
• Cost, ease of fabrication and inertness towards
the reactants and products in the temperature
range of interest.

16. • Metallic - aluminium, nickel, stainless steel,
platinum ( generally employed), and its alloys.
• Gives sharp exotherms and flat endotherms.
• Non metallic - glass, ceramic, vitreous silica or
sintered alumina.
• Gives flat exotherms and sharp endotherms.

17. Geometry – cylindrical geometry is used.
• Types of sample holders:
• Sample holders with dimples in which
thermocouples junctions are inserted. The dimples
are called thermocouple wells .
• It has better contact between sample holder and
thermocouple junction.
• These are common.

19. Furnace:
• This is device for heating the sample.
• Its actually a oven enclosed in furnace.
• In DTA apparatus, tubular furnace is preferred for its
good temp regulation and programming.
• This is constructed material ( wire or ribbon) wound
on a refractory tube.
• These are fairly inexpensive .

21. Temperature controller and recorder:
• Temperature controller:
• Three basic element required to control
temperature are sensor, control element and heater
• Two methods:
On – off control :
• If the sensor signal indicates that the temp has
become greater than the set point, the heater is
turned off .

22. • Not widely used in DTA
• Inexpensive
Proportional control :
• Heat in put to the system is progressively reduced as
the temperature approaches the desired value .
• These are widely used in DTA instruments .
• But in expensive DTA instrument elegant electronic
controllers are used .

24. Temperature programming :
• A time dependent temperature cycling of
furnace is required to produce a desired rate of
heating or cooling and to maintain the
temperature at any desired value.
• A temperature programmer is employed which
transmits certain time based instructions to
control unit.

25. Recorder:
• The signals obtained from the sensors are recorded by
the recorder. And record the DTA curve.
• Two types
Deflection type:
• The recording pen is moved directly by the input signal.
Null type:
• The input signal is compared with a reference or
standard signal and the difference is amplified and used
to adjust the reference signal through a servo motor until
it matches the input signal .

26. Thermocouples :
• Thermocouple is an electrical device consisting
of two dissimilar electrical conductors forming
electrical junctions at different temperatures.
• Points to be considered while selecting a
thermocouple :
• Thermoelectric coefficient
• Temperature interval.
• Chemical compatibility with the sample .

27. • Chemical gaseous environment used and reproducibility
of the EMF vs. temperature curve as a function of
thermal cycling .
• Availability and cost
• Made of chromel P and alumel wires measure and control
temp up to 1100 degree C in air .
• Made from pure platinum and platinum – rhodium alloys
wires measure more than 11 .
• Made from refractory materials like tungsten and
rhenium in inert gas or vacuum for up to 2100 degree C .

28. Cooling system :
• The cooling system is considered separate from
the temperature programmer because in most
instrument cooling is completely independent
from heating .
• Its function is to maintain a suitable
atmosphere in the furnace and sample holder .

29. Differential temperature sensor
• To measure the temperature difference between
the sample and reference material) the sample
and reference holder are kept inside the furnace
and the temperature of the furnace and sample
holder is controlled by using furnace controller.
• Heart of the analysis – heating block Identical
pair of cavities for the sample, ref.material .

30. • Whole unit is set in an oven- control pressure .
• Thermocouple is place directly in contact with
the sample and another in contact with the
reference .
• Temp of the block is raised, the temperature of
the sample & reference follow Zero temp.
difference – no physical or chemical change .
• If any reaction – difference in ΔT.

31. FACTORS AFFECTING THE DTA
CURVE
The various factors affecting the DTA curve are
as follows:
• Environmental factors.
• Instrumental factors.
• Sample factors.

32. ENVIRONMENTAL FACTORS:
• The DTA technique is more sensitive to the gaseous
environment around the sample .
• Reaction of atmospheric gases with the sample may
also produce extra peaks in the curve.
• In DTA two types of gaseous environment are used
• Static gaseous atmosphere
• Dynamic gaseous atmosphere

33. Static gaseous atmosphere
• The atmosphere surrounding the sample is
changing in concentration chemically due to evolved
gases and physically due to convection currents
• Studies in it are imprecise.
Dynamic gaseous atmosphere
• The gases are swept past the sample in a
controlled way.
• Reliable and reproducible
• Sweep gases can be inert or reactive.
But should not contain any of the product gases .

34. INSTRUMENTAL FACTORS:
• Sample holder:
• The geometry and material with which it is made of
affects the DTA curve.
• If material has
High thermal conductivity – sharp exothermic peaks and
flat endothermic peaks are obtained.
• Eg. Metals
• Poor thermal conductivity - reverse is true.
• Eg. Ceramic
• the size of holder and the amount of sample should
be as small as possible for better resolution.

35. Differential temperature sensing devices:
• The thickness of thermocouple wires affect the
intensity of the peaks, shape of the peaks and the
baseline.
• If wires used are much thick
• More distortion of peak heights and peak
temperatures may take place.
• If thinner wires are used
• Less distortion of peak heights and peak
temperatures may take place.
• But the resistance is high and may be unstable in
impedance matching .

36. SAMPLE CHARACTERISTICS
Physical
• Packing density.
• Particle size
• Peak area decreases with increase in size.
• Peak T shifts to higher values with increase in size
• Completion T decreases with decrease in size.
• Degree of crystallinity.

37. • Amount of sample influence peak area.
• As wt of the sample increases peak intensity and
temperature.
• In order to maintain the heat capacity nearly
constant during heating, the sample is generally
mixed with diluents. Generally, diluents affects
the area, temperature and even resolution of
the DTA peaks.

38. Chemical:
• The chemical reactivity of the sample, the
sample holder, thermocouple material, the
ambient gaseous environment and added
diluents greatly alter the DTA peaks.
• Therefore, one should make every effort to
select these materials as inert chemically as
possible with the sample.

39. 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%.
• Sharp thermal changes are unable to predict.
• Precision not good.

40. APPLICATIONS:
• A DTA curve can be used only as a finger print
for identification purposes but usually the
applications of this method are the
determination of phase diagrams, heat change
measurements and decomposition in various
atmospheres.
• DTA is widely used in the pharmaceutical and
food industries.

41. • Used to study the characteristic of polymeric
material.
• This technique is used for testing the purity of the
drug sample and also to test the quality control of
number of substances like cement, soil, glass,etc.
• Used for the determination of heat of reaction,
specific heat and energy change occurring during
melting etc.

42. • Trend in ligand stability (thermal stability of the
ligands) gives the information about the ligands in
the coordination sphere.
• 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.
• DTA may be used in cement chemistry, mineralogical
research and in environmental studies.

43. • Impurities may be detected by depression of the M.P
• Quantitative identification and purity assessment of
materials are accomplished by comparing the DTA curve
of sample to that of a reference curve .
• DTA technique may also be used to study the thermal
stability of large no. of inorganic compound and
complexes .
• DTA techniques has been used to study oxalates ,metal
amine , carbonates and oxides .
• DTA investigation have been carried to help
identification , purity determination .

44. • Quantitative analysis include the evaluation of
kinetic parameter of polymers , explosives ,
pharmaceuticals , oils , fats and other organic
chemical .
• DTA may also be used for industrial controls , such as
for determination of the structural and chemical
changes occuring during sintering ,fusing and other
heat treatments .
• It is used for identifications of different types of
synthetic rubbers.

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