Thermogravimetric analysis (TGA) measures the change in mass of a sample as it is heated. In a TGA experiment, a sample is placed in a furnace that increases in temperature at a controlled rate while the sample mass is continuously monitored with a microbalance. A TGA curve plots the percentage mass change over time or temperature. TGA can be used to determine decomposition temperatures of materials, measure purity and stability, and study thermal decomposition mechanisms of organic, inorganic, and polymeric compounds.

1. THERMOGRAVIMET
RIC ANALYSIS
PARTH VISHNUBHAI NAYI
MSC SEM 2 (APPLIED PHYSICS)
ROLL NO. : 19

2. 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.
 Thermogravimetric analysis is method of thermal analysis in which changes in
physical and chemical properties of materials are measured as function of
increasing temperature rate or as a function of time.

3. PRINCIPLE
 In thermo-gravimetric analysis, the sample is heated in a given environment(air,
NO2, CO2,He,Ar,etc.) at controlled rate. The change in the weight of 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 thermo-gravimetric curve
or thermo-gram, this is the basic principle of TGA.

5. TGA CURVE
 TG curves are normally plotted with the mass change in percentage on y-axis and
temperature (T) or time (t) on the x-axis.
 There are two temperatures in the reaction, Ti (procedural decomposition temp.) and
Tf (final temp.) representing the lowest temperature at which the onset of a mass
change is seen and the lowest temperature at which the process has been completed
respectively.
 The reaction temperature and interval (Tf-Ti) depend on the experimental condition;
they do not have any fixed value.

7. Instrumentation of TGA
Fig: Instrumentation / Block Diagram of TGA

8. Instrumentation of TGA:
 Recording balance
 Sample holder
 Furnace
 Temperature programmer / controller
( thermocouple)
 Recorder

9. Recording balance
 MICROBALANCE:
 A microbalance is used record a change in mass of sample/ substance.
An ideal microbalance must possess following features:
 It should provide electronic to record the change in mass using recorder.
 It should have the capacity of auto weight
 It operating should be user friendly.
 Morden microbalances have the ability to be not affected by vibrations

10.  Recorder balance :
After the sample has been placed on microbalance , it is left for 10-15 min to stabilizer.
Recorder balances are of to types:
A. Deflection-type instruments and
B. Null- types instruments

11. A. Deflection balances
a) Beam types
b) Helical type
c) Cantilevered beam
d) Torsion wire

12. B. Null point balances:
It consist of sensor which detects the deviation from the null point and
restores the balance to its null points by means of restoring force.

13. SAMPLE HOLDER
 The sample holder to be studied is placed in sampled holder or crucible. It is
attached to weighing arm of microbalance.
 There are different types of crucibles used such as
a) Shallow pans (used for volatile substances)
b) Deep crucibles ( Industrial scale calcination)
c) Loosely covered crucibles( self generated atm. Studies )
d) Retort cups ( Boiling point studies )
 They are made up from platinum , aluminum, quartz or alumina and some other
materials like graphite , stainless steel , glass etc.

15. FURNACE
 The furnace should be designed in such way that is produces a linear heating
range.
 It should have a hot zone which can hold sample and crucible and its temperature
corresponds to the temperature of furnace.
 there are different combinations of microbalance and furnace available. The furnace
heating coil should be wound in such a way that there is no magnetic interaction
between coil and sample or there can apparent mass change.

16. TEMPERATURE
PROGRAMMER/CONTROLLER :
 Temperature measurement is done in no. of ways thermocouple is the most
common technique.
 The position of temperature measuring device relative to the sample is very
important.

17.  The Major Types :
 The Thermocouple is placed near the sample container and it has no contact with
the sample container. This isn’t a good arrangement where low-pressure are
employed.
 The sample is kept inside the sample holder but not in contact with it. This
arrangement is better than that of 1ST because it responds to small temperature
changes.
 The thermocouple is placed either in contact with sample or with container . This is
the best arrangement of sample temperature detection.

18. Temperature programmer/controller :
Thermocouple in a thermo-balance:

19. RECORDER
 The output from the microbalance and furnace are recorded using either chart
recorder.
 The recording system are mainly of 2-types
1. Time-base potentiometric strip chart recorder.
2. X-Y recorder.
 In some instrument , light galvanometer, photographic paper recorders or one
recorder with two or more pens are also used.
 In the X-Y recorder, we get curves having plot of weight directly against
temperatures.
 However , the percentage mass change against temperature or time would be more
useful.

20. FACTORS AFFECTING TGA
1. Instrumental factors:
a) 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.
b) Furnace atmosphere: The atmosphere inside the furnace surrounding the sample
has profound effect on the decomposition temperature of the sample. A pure N2
gas from a cylinder passed through the furnace which provides an insert
atmosphere.

21. 2. Sample characteristics:
a) Weight of sample: A small weight of sample is recommended using a small
weight eliminates the existence of temperature gradient throughout 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.

22. APPLICATIONS OF TGA
 TGA curve gives the information regarding chemical kinetics
 The atm. Of H2O present in the clay & soil can be determined.
 Solid state reactions.
 The determined of the composition of complex mixtures.
 TGA, we can determine the purity and thermal stability of both primary and
secondary standard.
 Thermal decomposition of organic , inorganic & polymerics compound’s can be
studied.
 Mechanics of polymer can be studied.

23. LIMITATIONS OF TGA
 TGA is applicable to solid compound’s only.
 As thermocouple is kept very close to sample but not in contact with the sample.
Therefore, exact temp. of the sample can not be detected.