Thermal Methods

Many Type of Thermal methods covered with application in this file.

1. CHEMICAL ANALYTICAL TECHNIQUES
2CHOE01

TERM ASSIGNMENT 1
THERMAL METHODS


Submitted To: Dr. Amita Chaudhary
Dr. Neha Patni

Submitted By:
Chinmay Patel (18bcl020)
Jeelkumar Patel (18bcl039)
Shivam Patel (18bcl077)
Shrey Patel (18bcl078)

2. Introduction and History
(Shivam Patel – 18BCL077)

HISTORY: -
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For thousands of years man has been slowly learning how to regulate fire to yield the degree
of heat required for individual purposes. No method of temperature measurement was available
to him, however, until early in the seventeenth century and then only up to about 300°C, and
the measurement of higher temperatures had to await the discovery and use of platinum.

In a Special Issue of Thermochimica Acta devoted to the history of thermal analysis Dr. R. C.
Mackenzie, of the Macaulay Institute for Soil Research in Aberdeen, has presented two most
interesting papers that together form a monumental and scholarly survey of the whole subject
from the earliest times to the present day

The first of many applications of platinum in the measurement of higher temperatures was due
to Guyton de Morveau who designed a pyrometer in 1803 that employed a platinum rod
supported in a refractory groove with its free end in contact with the short arm of a bent lever,
the longer arm serving as a pointer moving over a graduated scale, all made in platinum. Some
years later, in 1821, Professor J. F. Daniell, of King’s College, London, devised an improved
form that overcame the deficiencies of de Morveau’s instrument and in which the temperature
was determined by the difference in expansion of a platinum rod and an earthenware tube.

Neither of these instruments was capable of measuring really high temperatures, nor were they
of appreciable accuracy. A discovery was now made, however, as Dr. Mackenzie clearly brings
out, that was to lead to one of the two reliable and accurate methods of temperature
measurement that are still in extensive use in both the manufacturing industry and scientific
research.

It was in Berlin in 1821 that Thomas Johann Seebeck described the deflection of a magnetic
needle caused by the electric current generated when one of the junctions of two dissimilar
metals was heated. While it did not occur to Seebeck to make use of his discovery for the

3. measurement of temperature, this invaluable effect was employed five years later by Antoine
César Becquerel who decided that the most suitable combination of metals was a circuit
consisting of platinum and palladium. With this combination he was able to arrive at the
determination of temperatures up to 1350°C by extrapolation.

An iron-platinum thermocouple was then used by Professor C. S. M. Pouille of Paris, while
Henri Regnault, making use of the same couple, found such irregularities that he roundly
condemned the whole idea of the thermoelectric method, his troubles arising, of course, from
the use of iron as one element. Later, in 1862, Becquerel’s son Edmond, again using platinum
and palladium “as these two metals are not altered by the action of heat”, succeeded in
rehabilitating the reputation of the thermocouple, but it was not until 1872 that Professor Peter
Tait of Edinburgh, using platinum against iridium-platinum, devised a sound relationship
between e.m.f. and temperature, so making possible the development of accurate pyrometry.

But the successful practical use of the thermocouple was mainly due to the work of Henri Le
Chatelier, Professor of Metallurgy at the École des Mines in Paris, who in 1885 concluded that
platinum against rhodium-platinum gave the most consistent results.

Dr. Mackenzie’s fascinating account of the history of these and other developments, including
the later work of Roberts-Austen and the concept of the platinum resistance thermometer
proposed by Sir William Siemens in 1871, will be of immense interest to all physicists and
metallurgists concerned in any way with the control and measurement of temperature.


Introduction: -

Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal
analysis in which the mass of a sample is measured over time as the temperature changes. This
measurement provides information about physical phenomena, such as phase transitions,
absorption, adsorption and desorption; as well as chemical phenomena including
chemisorption’s, thermal decomposition, and solid-gas reactions (e.g., oxidation or reduction).

4. Thermogravimetric analyser
Thermogravimetric analysis (TGA) is conducted on an instrument referred to as a
thermogravimetric analyser. A thermogravimetric analyser continuously measures mass while
the temperature of a sample is changed over time. Mass, temperature, and time are considered
base measurements in thermogravimetric analysis while many additional measures may be
derived from these three base measurements.
A typical thermogravimetric analyser consists of a precision balance with a sample pan located
inside a furnace with a programmable control temperature. The temperature is generally
increased at a constant rate (or for some applications the temperature is controlled for a constant
mass loss) to incur a thermal reaction. The thermal reaction may occur under a variety of
atmospheres including: ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive
gases, carburizing gases, vapours of liquids or "self-generated atmosphere"; as well as a variety
of pressures including: a high vacuum, high pressure, constant pressure, or a controlled
pressure.
The thermogravimetric data collected from a thermal reaction is compiled into a plot of mass
or percentage of initial mass on the y axis versus either temperature or time on the x-axis. This
plot, which is often smoothed, is referred to as a TGA curve. The first derivative of the TGA
curve (the DTG curve) may be plotted to determine inflection points useful for in-depth
interpretations as well as differential thermal analysis.
A TGA can be used for materials characterization through analysis of characteristic
decomposition patterns. It is an especially useful technique for the study of polymeric
materials, including thermoplastics, thermosets, elastomers, composites, plastic films, fibers,
coatings, paints, and fuels.

Types of TGA
There are three types of thermogravimetry:
 Isothermal or static thermogravimetry: In this technique, the sample weight is
recorded as a function of time at constant temperature.
 Quasi Static thermogravimetry: In this technique, the sample temperature is raised
in sequential steps separated by isothermal intervals, during which the sample mass
reaches stability before the start of the next temperature ramp.

5.  Dynamic thermogravimetry: In this technique the sample is heated in an
environment whose temperature is changed in a linear manner.

TGA measures the amount of weight change of a material, either as a function of increasing
temperature, or isothermally as a function of time, in an atmosphere of nitrogen or air. TGA
consists of a sample pan that is supported by a precision balance. The pan resides in a furnace
and is heated or cooled during the experiment and the mass of the sample is monitored during
the experiment. The balance can register weight changes of down to 1 µg.
TGA determines temperature and weight change of decomposition reactions, which allows
quantitative composition analysis. May be used to determine water/solvent content, either in
the form as solvates or as loosely bound molecules on the particle surface. TGA can be used to
measure evaporation rates, such as to measure the volatile emissions of liquid mixtures.
Technical info
Instruments TGA/SDTA 851e from Mettler Toledo
Temperature range RT-1100 °C
Resolution 1 ug
Default parameters Protective gas: Air, 20 ml/min
Sample amount 5-10 mg

7. Principle and Instrumentation of various methods
(Chinmay Patel- 18BCL020)

i) Thermogravimetry Analysis
ii) Differential Analysis
iii) Differential Scanning Calorimetry


Name Abbreviation Instrument Parameter measured Graph
Thermogravimetric TGA Thermobalance Mass Mass vs Temp or
time
Differential Analyses DTA DTA apparatus Change in temp Change in temp vs
time
Differential Scanning
Calorimetry
DSC Calorimeter dH. dt dH/dt vs temp


THERMOGRAVIMETRIC ANALYSIS
Principle of TGA operation:
“It is a technique whereby the weight of the substance, in an environment heated or cooled at
a controlled rate, is recorded as a function of time or temperature.”

A TGA analysis is performed by gradually raising the temperature of a sample in a furnace as
its weight is measured on an analytical balance that remains outside of the furnace. In TGA,
mass loss is observed if a thermal event involves loss of volatile component. Chemical
reactions, such as combustion, involve mass losses, whereas physical changes, such as melting
do not. The weight of the sample is plotted against temperature or tine to illustrate thermal
transitions in the material – such as loss of solvent and plasticizer in polymers, water of
hydration in inorganic materials and decomposition of the material.

8. In simple words,
The sample is heated in given environment at controlled rate. The change in weight of the
substance is recorded as a function of temperature or time. The temperature is increased at a
constant rate for a known initial weight of the substance and the changes in the weights are
recorded as a function of temperature at different time interval. The plot of weight change
against temperature is called TGA curve or thermogram.

Instrumentation for TGA operation:
The principle for TGA is based on the simple fact that the sample weighed continuously as it
is being heated to elevated temperatures. Hence, the following are the instruments required:
i) The balance
ii) Furnace
iii) Furnace temperature controller
iv) Recorder

The Balance:
It is the most important component of the Thermobalance. A good balance must fulfil the
following requirements:
i) Its accuracy, sensitivity, reproducibility and capacity should be similar to those of
analytical balances.
ii) It should have an adequate range of automatic weight adjustments.
iii) It should have a degree of mechanical and electronic stability.
iv) It should have a rapid response to weight changes.
v) It should be unaffected by vibration.
vi) The balance should be simple to operate and versatile.

9. Recorded balances are mainly of two types:
(a) Deflection type instruments
- Beam type
- Helical type
- The cantilevered beam
- Torsion wire
(b) Null-type instruments

10. Sample Holders:
The geometry, size and material of the sample holder (crucible) have an important effect on
the shape of TG curve. The size and shape depend on the nature, weight and the maximum
temperature range to be employed.
The materials for construction of the sample holders are glass, quartz, alumina, stainless steel,
platinum, graphite etc.
Sample holders are of the following types:
i) Shallow Pans:
These are generally used for samples where it is necessary to eliminate diffusion
rate as the rate controlling rate step. As volatile material is produced throughout the
sample mass, it should diffuse to the surface instantly to escape and be registered
as a weight loss.

ii) Deep crucibles:
These are employed in such cases where side reaction or partial equilibrium is to be
desired. These crucibles are used in the study of the industrial scale calcinations.
These are also used in the surface area measurements.

iii) Retort cups:
These are useful in boiling point studies. The retort provides the single plate of
reflux essential for a simple boiling point determination.

The Furnace:
The furnace and the control system should be designed to produce a linear heating rate over
the whole working temperature range of furnace. The choice of the furnace heating element
and type of furnace depend upon the temperature range of the furnace.
The size of the furnace is an important factor. For example, a main advantage of low mass
furnace is that it cools very quickly but its linear temperature rises is very difficult to control.
On the other hand, a high mass furnace may hold an isothermal temperature but it requires
comparatively more time to achieve the required temperature.

11. It becomes easier to obtain a larger uniform hot zone in the high mass furnace. With the small
mass furnace, it becomes difficult.

Recorder
The recording systems are mainly of two types:
(a) Time-base potentiometric strip chart recorder.
(b) X-Y recorders
In some instruments, light-beam-galvanometer, photographic paper recorders or one recorder
with two or more pens are used. One main advantage of these recorders is that one can check
the heating rate of the furnace for linearity.
In X-Y recorders we get curves having plot of weights directly against temperature.
The normal mode of recording data for thermogravimetry is the weight change vs temp or time.


Differential Thermal Analysis (DTA)
Principle of DTA:
The basic principle involved in the DTA is 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.
Thus, a differential thermogram consists of a record of the differences in sample and reference
temperature or furnace temperature. An ideal DTA curve is in which there is an exothermic
peak and an endothermic peak. Both the shape and size of the peak may furnish good
information about the nature of the test sample.

12. Instrumentation for DTA operation:
A large number of different types of instruments are available. However, a typical DTA
apparatus is shown in the image below.


The various components of DTA apparatus are as follows:
i) Furnace
ii) Sample Holder
iii) DC amplifier
iv) Differential Temperature Detector
v) Furnace Temperature programmer
vi) Recorder
vii) Control equipment

13. Sample Holders:
Metallic and non-metallic materials are used for the fabrication of sample holders. Metallic
generally include nickel, stainless steel, platinum and its alloys. Non-metallic materials include
glass, vitreous silica or sintered alumina. Metallic holders give rise to sharp exotherms and flat
endotherms whereas non-metallic holders yield relatively sharp endotherms and flat
exotherms.
Generally, sample holders are made up of platinum are used.
A cylindrical geometry is used around the thermocouple junctions as spherical faces problems
in its fabrication.

Furnace:
In DTA operation, a tubular furnace is preferred. This is constructed with an appropriate
material wound on a refractory tube. These furnaces possess the desired characteristics for good
temperature regulation and programming. These are fairly inexpensive. The choice of
resistance material as well as that of refractory is decided from the intended maximum
temperatures of the operation.
Another important characteristic of the furnace is its dimension which mainly depends upon
the length of the uniform temperate zone required.

Temperature Control:
In order to control temperature, the three basic elements are required. They are, sensor, control
element and heater.
The control element governs the rate of heat input required to match the heat loss from the
system. The location of the sensor with respect to the heater and mode of heat transfer measure
the time elapsed between sensing and variation in heat input.
There are two methods for controlling temperature:
(a) On-off control
- In this device, if the sensor-signal indicates that the temperature has become greater
than the set point, the heater is cut-off.

14. - This type of control is not used in DTA as it may result in electrical interference in
the measurement of signal.
- This type of control is inexpensive and can be used in thermogravimetry.
(b) Proportional control
- In on-off controllers there occurs fluctuations of temperatures around the set value.
These can be minimized if the heat-input to the system is progressively reduced as
the temperature approaches the desired value. Such a controller that anticipates the
approach to the set value is known as proportional controller.

Temperature programming:
In order to produce a desired rate of heating or cooling and to maintain a constant temperature
at any desired value, thermal apparatus requires a time-dependent temperature cycling of
furnace. This can be achieved by employing a temperature programmer which transmits a
certain time-based instruction to the control unit.
The simplest device is to use a variable speed motor driven autotransformer which gives a
power input to the furnace that is proportional to the rate of movement of the drive mechanism.

Recorder:
The signals obtained from the sensors can be recorded in which the signal trace is produced on
paper or film, by ink, heating stylus, electric writing or optical beam.
The mode of analog recording is of two types:
(a) Deflection type
- The recording pen is moved directly by input signal.
(b) Null type
- The input signal is compared with a reference signal and the difference is amplified
and used to adjust the reference signal through a servo motor until it matches the
input signal.

15. Differential Scanning Calorimetry
Principle of DSC operation:
DSC is used to measure enthalpy changes due to changes in the physical and chemical
properties of a material as a function of time or temperature.
It is a thermal method whereby the energy necessary to establish a zero difference between a
substance and a reference material is recorded as a function of time or temperature when both
are heated or cooled at a predetermined rate.
We can also say that, DSC relies on the measurement of the difference between the heat flow
vs temperature relation of the sample and the heat flow vs temperature relation of a standard.
There are many types of calorimeters and the criteria for their classification is as follows:
i) Ranges of temperature and pressure range
ii) Type of the test process
iii) Thermodynamic conditions
iv) Sample weight change during the measurement

Instrumentation for DSC:
A block diagram of a DSC instrument is shown below.

16. This instrument works on the temperature control of two similar specimen holder assembly. In
its left-half, there is a circuit for differential temperature control while in its right-half there is
a circuit for average temperature control.
In average temperature control circuit, an electrical signal, which is proportional to the dialled
temperature of the sample and reference holders, is generated through the programmer.
In the differential temperature control circuit, signals representing the temperatures of the
sample and the reference are compared. If no reaction is taking place in the sample, the
differential power input to the sample and reference heater is nearly zero. However, if the
reaction is taking place (ΔH is not zero) a differential power is fed to the heaters. A signal
proportional to this differential power along with the sign is transmitted to the recorder pen.
The integral of the peak so obtained gives the internal energy change of the sample.

17. Sampling Method For DSC
(Jeelkumar Patel- 18BCL039)
Differential Scanning Calorimetry (DSC) sample preparation is of extremely
importance for achieving optimum measurement quality. Sample preparation needed,
 Accurately-weighed samples (~3-20 mg, usually 3-5 mg for simple powders)
 Small sample pans (0.1mL) of inert or treated metals (Al, Pt, stainless)
 Several pan configurations should be used for the sample and the reference
 Material should completely cover the bottom of the pan to ensure good thermal
contact
 Avoid overfilling the pan to minimize thermal lag from the bulk of the material
to the sensor
 Small sample masses and low heating rates increase resolution, but at the
expense of sensitivity


Fig.1 DSC sampling

18. Characteristics of a good sample for DSC,
1) Sample Shape
2) Sample Pans
3) Sample weight

1) Sample Shape:
 It is recommended that the sample is as thin as possible and covers as
much of the pan bottom as possible.
 Samples in the form of cakes (as in case of polymers) must preferably
be cut rather than crushed to obtain a thin sample.
 Crushing the sample, whether in crystalline form or a polymer, induces
a stress, which can in turn affect the results.
 In most cases lids should always be used in order to more uniformly heat
the sample and to keep the sample in contact with the bottom of the pan.
 In case where oxidation properties of a sample are to be studied no lid
is used and the purge gas is usually oxygen as described in ASTM
Standard Test Methods E1858, Oxidative Induction Time or ASTM
E2009, Oxidation onset temperature.

2) Sample Pans:
 Lightest, flattest pans are known to have the least effect on the results
obtained from a DSC.
 Crimped pans on the other hand provided the highest sensitivity and
resolution.
 Hermetic pans are used where the sample is expected to have some
volatile content.
 These pans prevent evaporation.
 Two main reasons for the use of these pans are: The Tg of polymer or
amorphous material shifts with volatile content.
 Evaporation peaks look just like melting endotherm.
3) Sample Weight:
 Though 5 to 10 mg is considered to be an appropriate sample weight for
a DSC test, selection of the optimum weight is dependent on a number

19. of factors: the sample to be analyzed must be representative of the total
sample and the change in heat flow due to the transition of interest
should be in the range of 0.1-10mW.
 A recommendation for metal or chemical melting sample is less than
5mg.
 For polymer glass transition Tg or melting sample the mass should be
10mg.
 Polymer composites or blends the sample mass is greater than 10mg.
 The accuracy of the analytical balance used to measure the sample
weight should be accurate to ±1%.
 If the total mass of the sample + pan + lid is recorded before and after a
run, further deductions on the processes occurring can be made from any
change in mass.

DSC sample experimental conditions:
1) Start Temperature
2) End Temperature
3) Reference Pan
4) Heating Rate


1) Start Temperature:
 Generally, the baseline should have two minutes to completely stabilize
prior to the transition of interest.
 Therefore, at 10°C/min heating rate the run should start at least 20°C
below the transition onset temperature.
2) End Temperature:
 Allowing a two-minute baseline after the transition of interest is
considered appropriate in order to correctly select integration or analysis
limits.

20.  Care should be taken not to decompose samples in the DSC, it not only
affects the baseline performance but the cell life.
3) Reference Pan:
 A reference pan of the same type used to prepare the sample should be
used at all times.
 A material in the reference pan that has a transition in the temperature
range of interest should never be used.
4) Heating Rate:
 Heating the samples at low heating rates increases resolution by
providing more time at any temperature.
 Transitions due to kinetic processes (such as crystallization) are shifted
to lower temperature at highest cooling rates or higher temperatures at
high heating rates.
dH/dt=Cp*dT/dt+ƒ (T, t)
Where, dH/dt=heat flow measured by DSC
Cp=heat capacity or weight of the sample
dT/dt=heating rate
ƒ (T, t) =time dependent or kinetic component


Interpretation Graph
(Jeelkumar Patel- 18BCL039)

Endothermic: heat flows into the sample as a result of either heat capacity (heating) or some
endothermic process (glass transition, melting, evaporation, etc.)
Exothermic: heat flows out of the sample as a result of either heat capacity (cooling) or some
exothermic process (crystallization, cure, oxidation, etc.)
 An endothermic and exothermic peak are recorded on these curves (Fig.2), which result
from the temperature differences between a tested sample and a reference sample,

21. showing negative or positive deviations from the so called “baseline”, which is recorded
at the time when no transformations/ reactions occur in the sample.

Fig.2 DSC curves of heating and cooling cycles for pure metal: a – onset temperatures, b –
peak signals, c – peak temperatures
 The differences are caused by phase transformations and chemical reactions occurring
in the material.
 If the temperature of a tested sample during the phase transformation /chemical reaction
is lower than the reference temperature, the heat is absorbed. The situation is registered
as the endothermic peak.
 Conversely, when the sample temperature is higher and there is separation of the heat,
then this is marked as the exothermic effect on the DSC curve.







Fig.3 DSC Thermogram

22. Heat flows into the sample as a result of either heat flows out of the sample as a result of
either
 Heat capacity (heating)
 Heat capacity (cooling)
 Glass Transition (Tg)
 Crystallization
 Melting
 Curing
 Evaporation
 Oxidation
 Other endothermic processes
 Other exothermic processes

Glass Transition Temperature by DSC (Tg):
On further heating the polymer to a certain temperature, plot will shift downward suddenly,
like this:
This means there is more heat flow. There is an increase in the heat capacity of the polymer.
This happens because the polymer has just gone through the glass transition. Because of this
change in heat capacity that occurs at the glass transition, we can use DSC to measure a
polymer’s glass transition temperature.

23. Crystallization Temperature by DSC (Tc):
After glass transition, the polymers have a lot of mobility. When they reach the right
temperature, they will give off enough energy to move into very ordered arrangements, which
is called crystals.






















After
crystallization
Given off
heat
Exothermic
Heater to sample pan
has not to put a lot of
heat into the polymer
in order to keep the
temperature rising at
the same rate as that
of the reference pan
This drop in the heat
flow as a big peak in
the plot of heat flow
versus temperature

24. Melting Temperature (Tm) by DSC:
If we heat our polymer past its Tc, eventually we’ll reach another thermal transition, called
melting. When we reach the polymer’s melting temperature Tm, the polymer crystals begin to
fall apart, that is they melt when the polymer crystals melt, they must absorb heat in order to
do so.















After
melting
Heat is
absorbed
Endothermic
Heater to sample pan has
to put a lot of heat into
the polymer in order to
both melt the crystals
and keep the
temperature rising at the
same rate as that of the
reference pan
This increase in the heat
flow as a big dig in the
plot of heat flow versus
temperature
After Melting

25. Comparison of TG-DSC for variety of physicochemical processes:


Fig.4 Comparison of TG-DSC

26. Applications and References
(Shrey Patel- 18BCL078)

Applications
-Thermal Stability: -
 A material which does not decompose under the influence of temperature can be called
Thermally stable. TGA is one of the ways to determine the thermal stability of material.
 The ASTM E2550 standards describes the thermal stability of a material as
“Temperature at which the material starts to decompose or react, along with the extent
of mass change determined using thermogravimetry”. And also “the absence of reaction
or decomposition is used as an indicator for thermal stability”.
 For Example: - Determination of thermal stability of
Aspirin.


The above graph shows the TGA curve of acetylsalicylic acid (Aspirin) when heated to
600
o
C in a nitrogen atmosphere.

Two mass-loss steps were detected through the TGA curve. Each step is evaluated
through the determination of:
 Characteristic temperature at which mass loss occurs.

27.  Extent of mass change occurring during the step.

Theoretically, three characteristics temperatures can be shown for mass-loss step: -
 Peak temperature of the DTG (which is the 1
st
derivative of TGA curve, i.e. dash-dotted
line).
 Extrapolated onset temperature according to the standard ISO 11358-1. It is the point
of intersection of the starting-mass baseline and tangent to the TGA curve at the point
of maximum gradient.
 Onset temperature according to ASTM E2550 that is the point in TGA curve where a
deflection is first observed from the established baseline prior to the thermal event.
In the example of Aspirin, the first mass-loss step occurs at the following characteristics
temperatures: -
 161
o
C (peak of the DTG curve)
 143
o
C (extrapolated onset temperature of TGA curve)
 102
o
C (onset temperature according to ASTM E2550). This third value is used for
evaluating the thermal stability of the tested acetylsalicylic acid sample. (Below graph
shows the exact 102
o
C temperature)

28. Some points regarding this experiment: -
 It is crucial to define the measurement conditions as the results are affected by the
heating rate, atmosphere (gas and flow rate), sample mass and the crucible type. And
for the same reason, the results for two samples can only be compared if the
measurements were carried out under identical conditions.
 The following measurement conditions are recommended:
1) Sample mass: Betweem1-10g (preferred 5g)
2) Heating rate: 10-20 K/min
3) Flow rate of atmosphere: 20 to 100 ml/min
In the example, the thermal stability is given at 102
o
C for a measurement of acetylsalicylic acid
in a dynamic nitrogen atmosphere.
-Corrosion: -
 Thermal corrosion or high temperature corrosion is a chemical interaction of a material
with the surrounding gas atmosphere as a result of heating.
 The formation of oxides of metals provides a protective layer preventing further
atmospheric attacks and thus allowing a material to be used for sustained periods at
both room and high temperatures under hostile conditions.
 Typically, corrosion studies is carried on by using TGA.

29.  The above figure shows several heating cycles on a hanging steel sample.
 The steel sheet was heated at a rate of 5 K/min in a nitrogen atmosphere with 16%
oxygen. With each subsequent heating cycle oxidation decreases.
 In the beginning of test, oxidation of the sheet surface occurs and it can be observed on
the early onset and rapid mass heating for the first heating.
 After a couple of heating cycles, inner oxidation occurs, which is indicated by a slower,
diffusion-dependent mass increase

-Glass Transition:-

 To understand a material’s property, understanding of Glass transition is critical.
 It indicates the temperature at which a substance transforms from a glassy state to a
rubbery state or vice versa. The formation of such amorphous glasses is a universal
phenomenon observed in almost all materials.
 In the above figure, Glass transition temperatures of PS, PVC, PET and PVAC is shown
with complete graph of PET.
 The glass transition temperature provides information about molecular dynamics in the
supercooled melt.
 It defines the upper temperature limit for the use of solid amorphous materials and for
rubbery materials it is the lower temperature limit.
 It can be used to identify and compare materials and so is important for quality
assurance and failure analysis

30. -Specific Heat capacity:-

 Specific heat capacity of a material can be determined by DSC because of its ease of
use, short measurement times and mostly it provides adequate accuracy.
 The above figure represents DSC curve of Polystyrene at a heating rate of 10 K/min.
 Then after plotting graph of Specific heat capacity Vs. Temperature and the Specific
heat capacity at 50
o
C, 60
o
C and 70
o
C is shown in figure.
 Specific heat capacity is important for improving technical processes such as injection
molding, spray drying, and crystallization, and it is an important property for the safety
analysis of chemical processes and reactor construction.

-TGA in Automotive industry:-

31.  Due to the wide range of materials used in automotive industry, virtually all thermal
analysis techniques can be used in quality control and for research and development.
 For example, with adhesive, parameters such as gelation and the curing time as function
of temperature are important for optimizing performance of products.
 The main properties taken into consideration are the glass transition, composition,
expansion, the modulus and damping behavior.
 Composites can reduce vehicle weight and increases fuel economy so the use of
composites in automotive industry continues instead of metals.

-Sorption Analysis

 TGA is very useful in determining effects of moisture on material.
 Product stability, processability and mechanical stability can be influenced by moisture
and it is important to know how food products, powders or polymers react in a well-
defined humid environment.
 TGA Sorption-Analysis gives result regarding processing, self-life of products and
structural properties.
 To be specific it can be used to determine sorption enthalpies as well as calculate
isotherms, BET and GAB plots, and surface coverage behavior.

32. -Purity Determination: -

 DSC purity analysis of substances in drugs and foods is very important.
 In general, substances which may have some amount of impurity may produce
unexpected reactions, lose their efficiency, or create toxic compounds and in worst case
just a few percent of impurity can be toxic or even lethal.
 In the above figure, DCS curve of dimethyl terephthalate with 0-11% salicylic acid as
base horizontal on right side.
 Purity determination by DSC is based on the thermodynamics of an ideal eutectic
system.

-Polymer Crystallization: -

33.  Thermal analysis techniques are ideal for the study of crystallization behaviors, vital to
the optimization and processing of materials.
 DSC measures the heat flow produced in a sample when it is heated, cooled, or held
isothermally at constant temperature. This technique is widely used to investigate
exothermal events caused by crystallization or endothermal melting processes.
 Crystallization processes can also be investigated by thermomechanical analysis
(TMA), which measures dimensional changes in materials. TMA necessitates that
volume changes are also measured to estimate the percentage of crystallinity.

34. References
 Matthey, J. (2020). No Title. Johnson Matthey Technology Review. Retrieved from
https://www.technology.matthey.com/
 Wagner, M. (2017). No Title. In Thermal Analysis in Practice (p. 24). Schwerzenbach.
Retrieved from
https://www.hanserpublications.com/SampleChapters/9781569906439_978156990-
6439 SAMPLE CHAPTER Wagner.pdf
 No Title. (2016). Retrieved from https://www.mt.com/in/en/home.html
 Mettler toledo. (n.d.). No Title. Mettler Toledo, (2018). Retrieved from
https://www.azom.com/webinar.aspx?id=148
 Mettler toledo. (n.d.). No Title. Mettler Toledo, (2018). Retrieved from
https://www.azom.com/webinar.aspx?id=148
 Instrumental methods of chemical analysis by Gurdeep Chatwal and Sham Anand.
(2011)
 PPT on Thermal methods, uploaded on LMS (Nirma University) by Prof. Amita
Chaudhary.