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DIFFERENTIAL
THERMAL
ANALYSIS (DTA)

Prepared by:-
Mr. Jiten B. Patel
M.pharm(1st sem)

B.M.C.P.

Thermal Analysis Techniques
• When a material is heated its structural and
chemical composition can undergo changes
such as fusion, melting, crystallization,
oxidation, decomposition, transition,
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.

Types of thermal analysis
• TG (Thermogravimetric) analysis:
weight

• DTA (Differential Thermal Analysis): temperature

• DSC (Differential ScanningCalorimetry):
temperature

• In Differential Thermal Analysis, the
temperature difference that develops
between a sample and an inert reference
material is measured, when both are subjected
to identical heat - treatments.
• The related technique of Differential Scanning
Calorimetry relies on differences in energy
required to maintain the sample and reference
at an identical temperature.

Thermogravimetry (TG)

• Thermogravimetry is the measurement of the
mass of a sample as the temperature increases.
This method is useful for determining sample
purity and water, carbonate, and organic
content; and for studying decomposition
reactions.

INTRODUCTION

• This is a comparison method

• Analytical method for recording the
difference in temperature (∆T) b/w a
substance and an inert reference material as
a function of temperature or time
• Any transformation – change in specific heat
or an enthaply of transition can be detected
by DTA

• In DTA both test sample & an inert reference
material (alumina) – controlled heating or
cooling programming
• If zero temperature difference b/w sample &
reference material – sample does not
undergo any chemical or physical change.
• If any reaction takes place temperature
difference (∆T) will occur b/w sample &
reference material

• A DTA curve can be used as a finger print for
identification purposes, for example,
• in the study of clays where the structural
similarity of different forms renders diffraction
experiments difficult to interpret.

∆T VS Temp.
Sharp Endothermic – changes in crystallanity or fusion
Broad endotherms - dehydration reaction
Physical changes usually result in endothermic curves
Chemical reactions are exothermic

Apparatus

• The key features of a differential thermal analysis
kit are as follows

1. Sample holder comprising thermocouples,
sample containers and a ceramic or metallic
block.
2. Furnace.
3. Temperature programmer.
4. Recording system.

• Heart of the analysis – heating block
• Identical pair of cavities for the sample, ref.
material
• 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 ∆T

Differential Thermal Analysis
Advantages:

• instruments can be used at very high
temperatures

• instruments are highly sensitive

• characteristic transition or reaction
temperatures can be accurately
determined

Disadvantages: DTA

• uncertainty of heats of fusion, transition,
or reaction estimations is 20-50%

Factors affect results in DTA

• Sample weight
• Particle size
• Heating rate
• Atmospheric conditions
• Conditions of sample packing into dishes

Applications

• Quantitative identification and purity
assessment of materials are accomplished by
comparing the DTA curve of sample to that of
a reference curve
• Impurities may be detected by depression of
the M.P

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DTA

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