2. THERMOGRAVIMETRIC ANALYSIS (TGA)
Thermogravimetric analysis measure the mass of a
sample in a specified atmosphere as the temperature of
the sample is programmed.
The output from a TGA experiment is a plot of mass vs
temperature. The TGA plot is called a thermal curve.
Weight is plotted along the y-axis and the temperature
along the x-axis
3. CONTINUE…….
The change in weight of a sample as the temperature
changes tells us several thing
First loss of weight indicates decomposition or
evaporation of the sample .A gain weight can indicate
adsorption by the sample of a component in the
atmosphere
Second the temperature at which no weight change take
place or determined which indicate the temperature
stability of the material
4. CONTINUE……
For example :
If pure calcium carbonate (CaCO3) is heated to
850◦C , it loses 44% of its weight
CaCO3 → CaO + CO2
5.
6. The formation of C02 can be verified by having the
evolved gas analyzed by MS or by IR spectroscopy
The CaO can be confirmed by analysis of the
residue by XRD or other technique
8. CONTINUE…..
Modern TGA equipment has a sensitive balance
usually microbalance for continuously measuring
sample weight , a furnace surrounding a sample
holder , and a purge gas system for providing inert
or reactive atmosphere. A computer generally
controls the furnace and the data is collected and
processed by computer
9. Modern analytical microbalance of several different
designs are commercially available
Torsion balance
Spring balance
Electro balance
10. TGA balance are available for sample masses from 1 to
1000mg .There are specialized high capacity TGA
system available that can accommodate samples of upto
100gram at system that can handle microgram quantities
of sample
And sample size for TGA is very small
A sample must be homogenous
The balance itself must be thermally isolated from
furnace
11. CONFIGURATION OF FURNACE
The horizontal
configuration was
design to minimize
buoyancy effect
Vertical configuration
suffer from buoyancy
effect
Horizontal furnace Vertical furnace
12. The furnace surrounds the sample and sample holder
Modern instruments can be heated and cooled rapidly
the sample
Instrument that heat at rate of up to 1000C/min are
available
Another instrument can heat at rate upto 200◦ C/min
from room temperature to about 1200◦C
But furnace also available for higher temperaure like
1500◦C ,1700◦C or 2400◦C but these furnace are
usefull for studying refractory material and engineering
materials
13. Sample holder and any instrument parts inside the
furnace such as thermocouple that used for measuring
the temperature that must be able to withstand high
temperature and be inert at these high temperature
Quartz platinum and various ceramics are used for the
sample holder and other parts
The sample is place in a small pan made of Pt quartz or
ceramic
14. ANALYTICAL APPLICATIONS OF TGA
1- Determination of correct drying temperature for
precipitates used in gravimetric analysis.
2- Identification of the gases given off while a
sample temperature is increase.
3- The composition of the residues can be determine
using such as XRD , XRF
15. 4- TGA is very important in determining the upper use
temperature of materials such as polymers by
identifying the temperature at which oxidative
degradation occurs on heating in air
16. 5- TGA can be used for the identification of compounds
presents in a mixture of materials
17. The uppermost curve is the weight loss curve for
pure compound A. The next lower curve is the
weight loss curve for pure compound B. The bottom
curve is the weight loss curve is the mixture of A
and B.
