thermalmethods6586575646543646455543646.ppt

thermal analysis

1. Thermal Methods of Analysis

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
ƒ1) 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 PropertiesThermooptometry 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 N
2
Sample characteristics
1) Sample particle size
2) Weight of sample

34. References
1. Douglas A. Skoog, Principles of Instrumental Analysis, 6
th

Edition, 894-904.
2. Michael E. Brown ,Introduction to Thermal Analysis
Techniques and Applications, 2
nd
Edition.
3. Gurdeep Chatwal , Instrumental methods of chemical
analysis : Analytical Chemistry.

35. THANK you