Thermogravimetric analysis (TGA) is a technique that measures the weight changes that a material undergoes as a function of temperature or time under a controlled atmosphere. There are three main types of TGA: static, dynamic, and quasi-static. The basic principle is that a sample is heated at a controlled rate and the change in weight is recorded as a function of temperature or time. This produces a thermogravimetric curve or thermogram. TGA is used to determine characteristics such as thermal stability, decomposition temperature, and reaction kinetics of materials.

1. Thermogravimetric Analysis
Presented by - Dhakane Sumeet Sureshrao
M. Pharm Pharmaceutics
JSPM’s
Rajarshi Shahu College Of Pharmacy & Research, Pune
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2. Content
• Introduction
• Types
• Principle
• Instrumentation
• TGA curve
• Factor affecting TGA curve
• Application
• Advantages
• Disadvantages
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3. Introduction
Thermo - Thermal
Gravimetric - Measurement of weight
• It is thermo-analytical technique that measures weight
change of sample at given time and temperature.
• Definition-
TGA is a branch of thermal analysis which examine
mass change of a sample as function of temperature or time
as sample is subjected to controlled temperature program in
controlled atmosphere.
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4. • Types-
A) Static TGA-
In this type the sample under analysis is maintained
at a constant temperature for a period of time during which
any changes in weight are observed carefully.
B) Dynamic TGA -
In dynamic thermogravimetric analysis a sample is
subjected to conditions of predetermined, carefully
controlled continuous increase in temperature that is
invariably found to be linear with time.
C) Quasistatic TGA:-
In this technique sample is heated to a constant
weight at each of a series of increasing temperature
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5. Principle:-
• In thermogravimetric analysis, the sample is heated in a given
environment (air, N2, Co2, He, Ar, 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.
• The plot of weight change against temperature is called
thermogravimetric curve or thermogram.
• This is the basic principle of TGA.
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6. Instrumentation:-
• Essential requirements for an instrument
1) Balance
2) Sample Holder
3) Furnace
4) Temperature Measurement (Thermocouples)
5) Data recorder
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8. 1) Balance
A) Null-point Type :
- This Uses appropriate sensing-element (sensor) which
detects any slightest deviation of the balance
- Null-point mechanism provides a restoring force, directly
proportional to the change in weight, so it ensures sample
remain in same zone of furnace irrespective of mass
change.
- The weight change signal are differentiated electronically
to obtain a Thermogravimetric curve
Null
detector
Restoring Force
Weight Change 8

9. B) Deflection Type:
- Based on either a conventional analytical balance
- It may be helical spring, cantilever, beam and torsion type
analytical balance
- The deviations in weight change are directly recorded as
Data for Thermogram
Fig – Types of deflection balance 9

10. 2) Sample Holders
• Made up of Stainless steel, Quartz, Platinum or Alloy
• May be shallow or Crucible Shaped
• Selection of holder depend on - nature of sample
- weight of sample
- Temp range to be used
• This plays an important role in result of TGA
• Pan volumes of 20, 50, 100, and 250 μL are common
• Sample to be studied is places in it and attached to
balance
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11. 3) Furnace
• Furnace surrounds the sample and sample holder
• should be capable of producing a wide range of
temperature programs accurately
• Nichrome (1100℃),
Platinum, Alloy of platinum and rhodium (1500℃),
Tungsten molybdenum (1750℃), is used as material for
furnace.
• Temperature control of the furnace is achieved via a
thermocouple mounted very close to the furnace-winding.
• High size furnace yield larger hot zone whereas small size
may not.
• Temperature controlling with small size furnace may not
possible
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12. 4) Temperature measurement
• Thermocouple is a sensor that measure temperature. This
thermocouple used in TGA to analyze temperature.
• Chromel, Tungsten, rhenium thermocouples may used.
• Position of thermocouple play important role in
temperature measurement.
• Thermocouple in contact with sample or sample holder are
preferred.
• Made as small as possible and placed close to sample,
sometimes it placed at bottom of pan
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13. 5) Data Recorder
• Computer workstation in used to control, collect, and
process data for any thermal analysis technique.
• The data received from the sensors accurately converted
and processed to produce the TG curve
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14. TG Curve
• Result from above process is recorded as plot of Weight
Change VS Temperature or Time
• This is Referred as TG Curve
• In Static TGA Graph will be of Weight VS Time
• In Dynamic TGA Graph will be of Weight VS Temperature
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A A’
B’ B
• Horizontal Position indicate that there is no weight change.
• From this we can know about thermal stability of compound (no
change in properties).
• Curve A to A’ is perfectly horizontal so it will stable up to Ti °C.
• Curved portion (A’ to B’ ) indicate Weight loss
Ti Tf

16. • Procedural Decomposition Temperature (pdt)-
• It is lowest Temperature at which cumulative mass change
reaches a magnitude that thermocouple can detect.
• Indicated by Ti
• Final Temperature :-
• Is temperature at which cumulative weight change reaches
to maximum value, corresponding to complete reaction
• Indicated by Tf
• Reaction Interval :-
• Difference between Tf - Ti is defined as reaction Interval
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17. Factor Affecting TG curve
A) Instrumental Factor
1) heating Rate -
- If substance heated at faster rate it my decompose
. hence appropriate heating rate should used
2) Furnace Atmosphere :–
- atmosphere in Furnace Causes irregularities in curve
3) Sample holder :-
- Shape and size of Holder affect the heating rate of
. .sample so it may affect TG curve
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18. B) Sample Related Factor
1) Weight -
- smaller weight of sample give accurate result while
. Large amount causes deviation
2) Particle Size :–
- small particle size sample decompose at lower temp.
3) Compactness of sample :-
- Compressed sample decompose at higher temperature
. .so it may affect nature TG curve
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19. Application
• TG curve can used for identification or quality control
• To study of kinetics of reaction rate.
• To study thermal stability.
• To study sublimation behavior of various substance.
• To study catalyst - change in chemical state of catalyst is
determined
• Used for purity determination of primary and secondary
standard
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20. Advantages
• Accurate method
• Easy to use
• Minimal sample preparation
• Convenient and time saving technique
• Instrument can be used at very higher temperature
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21. Disadvantages
• Only Solid sample can be analyzed
• It is destructive Technique.
• Limited sample quantity
• Melting or Crystal change can not be analyzed in TGA
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•References –
Gurudeep R. Chatwal, Sham K. Anand, Himalaya publishing house, 2002,
Instrumental Method Of Chemical Analysis, 5th Ed. Page No 2.701.
D.A. Skoog Et al., Principal of Instrumental Analysis, 6th Ed, Harcourt
Publishers, 2001. Page No 892
Alexander, Kenneth, Riga, Alan, Haines, Peter, 2005/01/01,
Thermoanalytical Instrumentation and Applications, Ewing's Analytical
Instrumentation Handbook

23. Thank You
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