Thermogravimetric Analysis

1. Guided by:
Prof. D.P. Ambhore Sir
(M.Pharm)
Presented by:
Mr. Sanket Chordiya
(B.Pharm VII Sem.)
Seminar on
Thermo-Gravimetric Analysis
Paramhansa Ramakrishna Maunibaba Shikshan Sanstha’s
ANURADHA COLLEGE OF PHARMACY
ANURADHA NAGAR, SAKEGAON ROAD,
CHIKHLI. DIST- BULDANA (M.S.) 443201

2. Content
 Introduction
 Definition
 Types
 Principle
 Instrumentation
 Applications

3. Introduction
• The term “thermal analysis” incorporates those techniques in which
some physical parameter of the system is determined and recorded as
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.
• Types of Thermal Analysis:
I ) Thermo-gravimetric ( Change in Mass)
II) Differential Thermal Analysis (Change in Temperature)
III) Differential Scanning Calorimetry (Compensation of temperature)

4. Definition
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.”

5. Types Of 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 tempearture.
3. Dynamic Thermogravimetry : In this technique a sample
is heated in an environment whose temperature is
changing in predetermine manner generally at linear rate.

6. Principle
• In thermogravimetric analysis, the sample is heated in a given
environment (air, N2 , CO2 , He, etc.) at controlled rate.
• The change in the 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
weights are recorded as a function of temperature at different time
interval.
• This plot of weight change against temperature is called
thermogravimetric curve or thermogram, this is the basic principle of
TGA.

7. Example: TGA Curve for
AgNO3
The diagram indicates the
TGA curve for AgNO3 .
• The horizontal portion of the curve
indicates that, there is no change in
weight (AB &CD) and the portion BC
indicates that there is weight change.
• The weight of the substance (AgNO3 )
remains constant upto a temperature of
473°C indicating that AgNO3 is
thermally stable upto a temperature of
473°C.
• At this temperature it starts losing its
weight and this indicates that the
decomposition starts at this
temperature. It decomposes to NO2 , O2
and Ag.
• AgNO3 → Ag + NO2 + O2

8. Instrumentation/ Block Diagram of TGA

9. Instrumentation
The apparatus required for TGA analysis are
(a) A furnace which can be heated so that the temperature
gives linearity with time.
(b) A furnace controlled thermobalance
 A known weight of the sample is taken in a crucible(c), which is
enclosed by a furnace(F). The furnace(F) temperature is raised slowly,
the temperature of the sample and the corresponding weight are
taken.
 A platinum/platinum rhodium thermocouple is used to measure the
sample temperature, and the change in weights are found out by
finding the beam deflection on adding a known weight to the pan.(i.e)
the change in the weight are recorded from the beam deflection.
 Recorder: A recorder records the change in weight in y axis and w.r.to
temperature on the x-axis. We get a thermogram.

10. Sample Preparation
• Sample preparation has a significant effect in obtaining good data.
 It is suggested that maximizing the surface area of the sample in a
TGA pan improves resolution and reproducibility of weight loss
temperatures.
 The sample weight affects the accuracy of weight loss
measurements.
 Typically 10-20mg of sample is preferred in most applications.
Whereas, if the sample has volatiles 50-100mg of sample is
considered adequate.
 It is to be noted that most TGA instruments have baseline drift of
±0.025mg which is ±0.25% of a 10mg sample.

11. Experimental Conditions
• Heating Rate
 Samples are heated at a rate of 10 or 20°C/min in most cases.
 Lowering the heating rates is known to improve the resolution of
overlapping weight losses.
• Purge gas
Nitrogen is the most common gas used to purge samples in TGA due to
its inert nature. Whereas, helium provides the best baseline.
 Air is known to improve resolution because of a difference in the
oxidative stability of components in the sample.
 Vacuum may be used where the sample contains volatile components,
which helps improve separation from the onset of decomposition since
the volatiles come off at lower temperatures in vacuum. e.g. oil in a
rubber tire product.

12. Factors affecting the TG curve
The factors which may affect the TG curves are classified into two
main groups.
(1) Instrumental factors (2) Sample Characteristics
(1) Instrumental factors
(a) Furnace heating rate
(b) Furnace atmosphere
(2) Sample characteristics includes
(a) Weight of the sample
(b) Sample particle size

13. Instrumental factors
• Furnace Heating rate: The temperature at which the compound
(or sample) decompose depends upon the heating rate. When the
heating rate is high, the decomposition temperature is also high. A
heating rate of 3.5°C per minute is usually recommended for
reliable and reproducible TGA.
• Furnace atmosphere: The atmosphere inside the furnace
surrounding the sample has a profound effect on the decomposition
temperature of the sample. A pure N2 gas from a cylinder passed
through the furnace which provides an inert atmosphere.

14. Sample characteristics
(a)Weight of the sample: A small weight of the sample is
recommended using a small weight eliminates the
existence of temperature gradient throught the sample.
 (b) Particle size of the sample: The particle size of the
sample should be small and uniform. The use of large
particle or crystal may result in apparent, very rapid
weight loss during heating.

15. Application of TGA
TGA can be used to evaluate
the thermal stability of a material.
 TGA is used in the analysis
of ceramics and thermally stable
polymers.
 In an overview of thermal analysis
testing it is always preferable to do a
TGA experiment on unknown samples
before doing a DSC experiment
(especially for pharmaceuticals).
 From TGA, we can determine the
purity and thermal stability of both
primary and secondary standard.
For studying the sublimation behaviour
of various Substances.

16. Reference
• Gurdeep R. Chatwal, Sham K. Anand,
Instrumental Method Of Chemical Analysis, 5th
edition, Himalaya Publishing house,Page No.-
2.701.
• Sharma B.K. Goel Publishing House
“Instrumental Methods of Analysis” page No.-
234-237