1. Presentation on:
By- Divya Deep Yadav
Roll no.- 2021RPH3205
(Applied physics)
THERMOGRAVIMETRY
ANALYSIS (TGA)
2. CONTENTS
Thermal Analysis
Different thermal analytical methods
Thermogravimetry
Types of Thermogravimetry
Principle
Description
Recording of result
Information obtained from a TG curve
Factors affecting a TG curve
Instrumentation
Applications
3. THERMAL ANALYSIS
The term “thermal analysis” incorporates those techniques in
which some physical parameters of the system is determined
and/or recorded as a function of temperature.
When matter is heated it undergoes certain physical and
chemical changes. These changes that take place when an
unknown sample is heated provide us with information that
enables us to identify the material.
Based on the above definition, the various techniques of
thermal analysis are summarised in the table:
4. S.
No
NAME OF THE
TECHNIQUE
ABBREVIATI
ON OF THE
TECHNIQUE
INSTRUMENT
EMPLOYED
PARAMETE
R
MEASURED
GRAPH
1. THERMOGARVIME
TRY
TG Thermobalance Mass Mass vs.
Temperature
or Time
2. DERIVATIVE
THERMOGRAVIME
TRY
DTG Thermobalance dm/dt dm/dt vs.
Temperature
3. DIFFERENTIAL
THERMAL
ANALYSIS
DTA DTA
Apparatus
ΔT ΔT vs.
Temperature
4. DIFFERENTIAL
SCANNING
CALORIMETRY
DSC Calorimeter dH/dt dH/dt vs.
Temperature
5. THERMOMETRIC
TITRIMETRY
- Calorimeter Temperatur
e
Temperature
vs. Titrant
Volume
DIFFERENT THERMAL ANALYTICAL
TECHNIQUES
5. THERMOGRAVIMETRY
General Definition
It is a method of thermal analysis in which a
physical property of substance is measured as a
function of temperature whilst the substance is
subjected to a controlled temperature
programmer.
An Internationally accepted definition of
thermogravimetry is as follows:
"It is a technique where by weight of substance in
an environment heated or cooled at a controlled
rate, is recorded as a function of time or
temperature.”
6. TYPES OF THERMOGRAVIMETRY
There are three types of Thermogravimetry:
Isothermal / Static Thermogravimetry
Quasistatic Thermogravimetry
Dynamic Thermogravimetry
1. Isothermal/ Static Thermogravimetry: In this technique the sample
weight is recorded as a function of time at constant temperature.
2. Quasistatic Thermogravimetry: In this technique the sample is
heated to constant weight at each of the series of increasing
temperature.
3. Dynamic Thermogravimetry: In this technique a sample is heated
in an environment whose temperature is changing in predetermine
manner generally at linear rate.
Most of the studies are generally carried out with dynamic
thermogravimetry. Therefore it is generally referred to as
thermogravimetry.
7. PRINCIPLE
The principle of thermogravimetry is based on the simple fact that the
sample is weighed continuously as it is being heated to elevated
temperatures and changes in the mass of a sample are studied.
Changes in temperature affect the sample. Not all thermal changes/events
bring a change in mass of sample i.e. melting, crystallization but some
thermal events i.e. desorption, absorption, sublimation, vaporization,
oxidation, reduction and decomposition bring a drastic change in mass of
sample.
It is used in analysis of volatile products, gaseous products lost during the
reaction in thermoplastics, thermosets, elastomers, composites, films,
fibers, coatings, paints, etc.
8. DESCRIPTION:
It is a technique which is studied under thermal
analysis and is employed for detection of such type of
materials which undergo mass change (gain or loss)
when subjected to thermal events viz. decomposition,
oxidation, reduction, etc.
For this reason, it is very significant to optimize those
conditions/factors on which the change of mass of
sample depend throughout the operation/experiment.
9. RECORDING OF RESULT:
The instrument used for themogravimetry is a programmed precision
balance for rise in temperature known as Thermobalance.
Results are displayed by a plot of mass change versus temperature or time
and are known as Thermogravimetric curves or TG curves.
TG curves are normally plotted with the mass change (Dm) in percentage
on the y-axis and temperature (T) or time (t) on the x-axis.
A typical TG curve has been shown (Figure 1).
Fig.1.Characteristics of a
single-stage mass-loss
curve
10. There are two temperatures in the reaction,
Ti (procedural decomposition temp.) representing the
lowest temperature at which the onset of a mass
change is seen
Tf (final temp.) representing the lowest temperature at
which the process has been completed respectively.
The reaction temperature and interval (Tf-Ti) depend
on the experimental condition; therefore, they do not
have any fixed value.
11. INFORMATION OBTAINED FROM A
TG CURVE:
Plateau: A plateau (AB, Fig.2.) is that part
of the TG curve where the mass is essentially
constant or there is no change in mass.
Procedural Decomposition Temperature:
The initial temperature, Ti, (B, Fig.2.) is
that temperature (in Celsius or Kelvin) at which the cumulative-
mass change reaches a magnitude that the Thermobalance
can detect.
Final Temperature: The final temperature, Tf, (C, Fig.3.), is that
temperature (in Celsius or Kelvin) at which the cumulative
mass change reaches a maximum.
Reaction Interval: The reaction interval is the temperature
difference between Tf and Ti.
12. It can be concluded that Thermogravimetry is
concerned with the change in weight of a material as
its temperature changes.
First, this determines the temperature at which the
material loses weight. This loss indicated
decomposition or evaporation of the sample.
Second, the temperature at which no weight loss takes
place is revealed, which indicates stability of the
material.
These temperature ranges are physical properties of
chemical compounds and can be used for their
identification.
14. INSTRUMENTAL FACTORS:
EFFECT OF FURNANCE ATMOSPHERE: the test samples are
generally heated in vaccum or in the presence of an inert gas, in
order to remove the gases formed during sample heating and also
to prevent the occurrence of any undesirable reactions. The
common atmospheres involved in thermogravimetry are as
follows:
1. Static air: In this type air from atmosphere is allowed to flow
through the furnace.
2. Dynamic air: In this type compressed air from a cylinder is
allowed to pass through the furnace at a measured flow rate.
3. Inert atmosphere: Nitrogen gas (oxygen free) is used as inert
environment.
15. HEATING RATE: If a substance is being heated at a fast
heating rate, the temperature of decomposition will be higher
than that obtained at a slower rate of heating. Eg.:- for
a 10% decomposition of polystyrene, the temperatures are :
375˚C for a heating rate of 1˚C / min and 394 ˚C for a
heating rate of 5˚C / min.
SAMPLE HOLDER: The geometry of the sample holder can
change the slope of TG curve. Sample holders range from flat
plates to deep crucibles of various capacities. Materials used
in their construction may vary from glass, alumina, and
ceramic compositions to various metals and metallic alloys.
When the atmosphere is solely the gas, the shape of crucible
has no effect on the slope of the curve. Generally shallow
dish is preferred as there is a rapid exchange of gases
between sample and the surrounding atmosphere.
16. SAMPLE CHARACTERISTICS:
Weight of the sample: If a large sample is used, there occurs a
deviation from linearity as the temperature rises, especially for an
exothermic reaction. Eg.: evolution of CO during decomposition of
calcium oxalate to CaCO3.
Sample particle size: With the particle size of smaller dimension
the decomposition takes place earlier, while with greater particle
size the decomposition proceeds only at higher temperatures.
Previous history of the sample: Eg.: TG studies showed that
Mg(OH)2 prepared by precipitation method has a different
temperature of decomposition from that of the naturally occurring
material. This factor shows that one should be sure about the
source or method of formation of the sample.
17. Heat of reaction: This effect was studied by
Newkirk. The heat of reaction alters the difference
between the sample temperature and the furnace
temperature. If the heat effect is exothermic or
endothermic, this will cause the sample temperature
to lead or lag behind the furnace temperature.
Compactness of the sample: A compressed sample
will decompose at higher temperatures than a loose
sample.
18. INSTRUMENTATION:
Components of Instrumentation: :
A. Recording balance
B. Sample Holder
C. Furnace
D. Furnace temperature programmer/Controller
E. Recorder
TG curves are recorded using a Thermobalance. It consists of an electronic microbalance, a furnace, a temperature
programmer and a recorder (instrument connected to Thermobalance to record the output/curves).
19. Applications
Thermal Stability
Material characterization
Compositional analysis
Used to analyze filler content in polymers; carbon black in
oils; ash and carbon in coals.
Kinetic Studies
Corrosion studies
Automatic Thermogravimetric Analysis
Evaluation of gravimetric precipitates
Evaluation of suitable standards
Testing of purity of samples
Curie point determination
