thermal analysis

1. THERMAL METHODS OF ANALYSIS
Mr. Ganesh B. Nigade,
Assistant Professor,
PDEA’s S. G. R. S. College of Pharmacy,
Saswad.
Mob:- 9960743549
E mail:- ganeshpharma2984@gmail.com

2. CONTENTS
 Introduction
 Types of Different Thermal Analysis
 TGA
 Principle
 Instrumentation
 Application
 DTA
 Principle
 Instrumentation
 Application
 DSC
 Principle
 Instrumentation
 Application
 Factor affecting to Thermal analysis
 References

3. INTRODUCTION
 THERMAL ANALYSIS –
Techniques in which a physical (thermal) property of a
substance is measured as a function of
temperature while the substance is subjected to a
controlled temperature variation.1
THERMAL ANALYSIS means the analysis of a
change in a property of a sample, which is related
to an imposed temperature alteration.2

4.  There is difference between “thermoanalytical
techniques” and “thermoanalytical methods”.
 The techniques are characterized by the suffix
“-metry”, while the more comprehensive methods,
which include the evaluation and interpretation of
the measured property values, are indicated by
adding “analysis”.
 Measurements are usually continuous and the
heating rate is often, but not necessarily, linear
with time.
 The results of such measurements are thermal
analysis curves and the features of these curves
(peaks, discontinuities, changes of slope, etc.) are
related to thermal events in the sample.

5. THERMAL EVENT

6. When matter is heated, it undergoes
ƒ
1) Physical Changes:- Phase change such as melting
Vaporization, crystallization, transition between
crystal structures, change in microstructures in
metal alloy & polymers,
2) Chemical Changes:- iclude reaction to form new
products, oxidation, decomposition, dehydtation,
corrosion

7. TYPES OF DIFFERENT THERMAL ANALYSIS
Properties Techniques Methods Abbreviations
Mass Thermogravimetry Thermogravimetric
Analysis
TGA
Pressure Thermomanometry Thermomanometric
Analysis
TMA
Electric Properties Thermoelectrometry Thermoelectric Analysis TEA
Optical Properties Thermooptometry Thermooptometric
Analysis
TOA
Dimensions or
Mechanical
Properties
Thermomechanometry Thermomechanical
Analysis
TMA
Temperature Thermometry Heating & Cooling Curve
Analysis
--
Temperature
Difference
Differential Thermometry Differential Thermal
Analysis
DTA
Heat flow
Difference
Differential Scanning
Calorimetry
-- DSC

8. THERMOGRAVIMETRIC ANALYSIS (TGA)
Principle:-
The mass of a sample in a controlled atmosphere is
recorded continuously as a function of temperature or
time as the temperature of the sample is increased
(usually linearly with time).
 Measurements of changes in sample mass with temperature.
 The temperature is increased at constant rate for known initial
weight of substance & change in weight are recorded as function
of temperature at different interval of time.
 Note that mass is a measure of the amount of matter in a sample,
whereas weight refers to the effect of the gravitational force on a
mass.
 A plot of mass or mass percentage as a function of time is called
a thermogram or a thermal decomposition curve.

9. INSTRUMENTATION
1. Thermobalance
2. Furnace
3. Sample Holder
4. Temperature
measurement
5. Computer-Data
acquisition ,
processing &
control system

10. THERMOBALANCE
 The usual range of thermobalance, is from 1 to 1000
mg, with usual sample weighing between 5 to 20
mg.
 It provide electronic signal to record the change in
mass.
Types of Thermobalance
 1) Null Point type balance
 2) Deflection type balance

11. VARIOUS POSITION OF BALANCE IN FURNACE

12. FURNACE
 Furnaces for TGA cover the range from ambient
temperature to l000°C,although some can be used
for temperatures up to 1600°C.
 Heating rates can often be selected from 0.1°C/min
to 100°C/min.
 Some units can heat as rapidly as 200°C/min.
 Insulation and cooling of the exterior of the furnace
is required to avoid heat transfer to the balance.
 Nitrogen or argon is usually used to purge the
furnace and prevent oxidation of the sample.

13. SAMPLE HOLDER
 Samples are typically contained in sample pans
made of platinum, aluminum, or alumina.
 Platinum is most often used because of its
inertness and ease of cleaning.

14. TEMPERATURE MEASUREMENT
 Thermocouple-
Wires- Platinum,
Rhodium, Chromium, Nickel
 Resistance Thermometers-
The electrical resistances of metallic conductors increase with
rising temperature

15. TG CURVE
Type (i) curves: The sample undergoes no
decomposition with loss of volatile
products over the temperature range
shown.
Type (ii) curves: The rapid initial mass-loss
observed is characteristic of desorption
or drying.
Type (iii) curves: represent decomposition of
the sample in a single stage.
Type (iv) curves: indicate multi-stage
decomposition with relatively stable
intermediates.
Type (v) curves: represent multi-stage
decomposition, but in this example stable
intermediates are not formed.
Type (vi) curves: show a gain in mass as a
result of reaction of the sample with the
surrounding atmosphere.
Type (vii) curves: are not often encountered.
The product of an oxidation reaction
decomposes again at higher
temperatures

16. APPLICATIONS
 Determination of purity & thermal stability of primary
& secondary standards.
 Determination of composition of complex mixture &
decomposition
 For study of sublimation behavior of compound
 To study reaction kinetics
 Determination of Dehydration / Desolvation

17. DIFFERENTIAL THERMAL ANALYSIS
Principle:-
Differential thermal analysis (DTA) is a technique in which
the difference in temperature between a substance
and a reference material is measured as a function
of temperature while the substance and reference
material are subjected to a controlled temperature
program.
The differential temperature is plotted against temperature
or time is called DTA curve.
Both sample & reference material heated in controlled
condition.
If any reaction (physical or Chemical changes ) takes
place temperature difference (∆T) will occur between
sample & reference material.

18. REFERENCE MATERIAL
 The reference material should have the following
characteristics:
(i) It should undergo no thermal events over the
operating temperature range.
(ii) It should not react with the sample holder or
thermocouple,
(iii) Both the thermal conductivity and the heat
capacity of the reference should be similar to those
of the sample.
For inorganic samples- Alumina, and carborundum,
SiC,
For organic compounds- octyl phthalate and silicone
oil.

19. INSTRUMENTATION
1. Furnace
2. Sample Holder
3. Temperature
measurement
4. Computer-Data
acquisition ,
processing &
control system

20. FURNACE
 Both sample & reference material match thermally
& arranged systematically with the furnace, so that
both are heated or cooled in identical manner.
 The metal block surrounding the well act as heat
sink.
 Temperature of the heat sink slowly increases by
using internal heater.
 Its temperature range from ambient temperature to
l600°C

21. SAMPLE HOLDERS
 Sample holder called crucible are made up of
metallic (Aluminum , Platinum) & ceramic (silica).
 Sample are usually 1- 10 mg for analysis.
 The dimension of two crucibles & cell well are as
nearly identical as possible.

22. TEMPERATURE MEASUREMENT
 Pair of thermocouples used in DTA.

23. DTA CURVE
 The initial decrease in T is due to the glass
transition. The glass transition temperature Tg
is the characteristic temperature at which
glassy amorphous polymers become flexible or
rubberlike.
 The two maxima are the result of exothermic
processes in which heat is evolved from the
sample, thus causing its temperature to rise.
 When heated to a characteristic temperature,
many amorphous polymers begin to crystallize
as microcrystals, giving off heat in the process.
Crystal formation is responsible for the first
exothermic peak
 The minimum labeled "melting" is the result
ofan endothermic process in which heat is
absorbed by the analyte.
 The second peak in the figure is endothermic
and involves melting of the microcrystals
formed in thc initial exothermic process. The
third peak is exothermic and is encountered
only if the heating is performed in the presence
of air or oxygen.
 The final negative change in ∆T results from
the endothermic decomposition of the polymer
to produce a variety of products.

24. APPLICATIONS
 DTA is a widely used tool for studying and characterizing
polymers. The types of physical and chemical changes in
polymeric materials that can be studied by DTA.
 DTA is also used in the ceramics and metals industry.
 DTA is used to study decomposition temperatures, phase
transitions, melting and crystallization points, and thermal
stability.
 An important use of DTA is for the generation of phase
diagrams and the study of phase transitions.
 The DTA method also provides a simple and accurate way of
determining the melting, boiling, and decomposition points of
organic compounds.

25. DIFFERENTIAL SCANNING CALORIMETRY
Principle:-
 Differential Scanning Calorimetry (DSC) is a Thermal
Analysis technique in which the heat flow rate (power) to
the sample is monitored against time or temperature
while the temperature of the sample, in a specified
atmosphere, is programmed.
 It is measure heat into or out of sample.
 Differences in heat flow occur with the occurrence of
two major events-
1) The heat capacity of the sample which increses with
temperature
2) Transitions occur

26. INSTRUMENTATION
1. Furnace
2. Sample Holder
3. Temperature
measurement
4. Computer-Data
acquisition ,
processing &
control system

27. INSTRUMENTATION
 Types of DSC
1) Power-compensated DSC
2) Heat-flux DSC
3) Modulated DSC

28. POWER-COMPENSATED DSC
 In power-compensated DSC, the temperatures of
the sample and reference are kept equal to each
other while both temperatures are increased or
decreased linearly. The power needed to maintain
the sample temperature equal to the reference
temperature is measured.

29. HEAT-FLUX DSC
 In heat-flux DSC, the difference in heat flow into the
sample and reference is measured while the
sample temperature is changed at a constant rate.
Both sample and reference are heated by a single
heating unit.

30. MODULATED DSC
 Modulated DSC (MDSC) uses the same heating
and cell arrangement as the heat-flux DSC method.
In MDSC, a sinusoidal function is superimposed on
the overall temperature program to produce a
micro heating and cooling cycle as the overall
temperature is steadily increased or decreased.

31. DSC CURVE

32. APPLICATIONS
 Glass Transition Temperatures :-
Determination of the glass transition temperature T, is one
of the most important applications of DSC. The physical
properties of a polymer undergo dramatic changes at
Tg, where the material goes from a glassy to a rubbery
state. At the glass transition, the polymer undergoes
changes in volume and expansion, heat flow and heat
capacity. The change in heat capacity is readily
measured by DSC.
 Crystallinity and Crystallization Rate:-
In most cases DSC is one of the easiest methods for
determining levels of crystallinity.
Reaction Kinetics:- Many chemical reactions, such as
polymer formation reactions, are exothermic and readily
monitored by DSC methods.

33. FACTOR AFFECTING TO THERMAL ANALYSIS
Instrumental
1) Furnace Heating rate-↑es heating rate , ↑es decomposition
2) Furnace atmosphere- pure intert gas like N2
Sample characteristics
1) Sample particle size
2) Weight of sample

34. REFERENCES
1. Douglas A. Skoog, Principles of Instrumental
Analysis, 6th Edition, 894-904.
2. Michael E. Brown ,Introduction to Thermal Analysis
Techniques and Applications, 2nd Edition.
3. Gurdeep Chatwal , Instrumental methods of
chemical analysis : Analytical Chemistry.

35. THANK YOU