6. Thermo gravimetric analysis (TGA)
It is an analysis, the mass of sample is recorded
continuously as its temperature is increased linearly from
ambient to high temperature.
Mass of material a functions of temperature.
Processes occurring without change in mass (e.g.- Physical
transitions ) cannot be studied by TG.
Reactant(s) Product(s) + Gas (a mass loss)
Gas + Reactant(s) Product(s) (a mass gain)
8. Best practices for Thermal Analysis
Removal of absorbed water by drying.
Use purge gas (N2or He) to remove corrosive off-gases
Use samples with narrow grain size distribution.
For measurement in vacuum, sample Grain size > 60
mesh
Calibration using the
- Curie Temperature.
-Standard compounds.
Keep the constant heating rate, same gas atmosphere
and crucible for the analysis.
9. Decomposition of CaCO3 at different
gas atmosphere
Effect of gas atmosphere and crucible on TG
Decomposition of CaCO3 using
different crucible
10. Three factors should be noted when you get a TG curve:
1. General shape.
2. The particular T at which changes in mass occur.
3. The magnitudes of the mass changes.
11. Differential Thermal Analysis(DTA)
Heat absorbed or emitted by sample is observed
by measuring the temperature difference between
that sample and reference compound as
temperature of both are increased.
ΔT =TS-Tr as function of Temperature.
ΔT ΔH
- Qualitative.
ΔT
Temperature of furnace
12. Differential Thermal Analysis (DTA)
Instrument
Endothermic - heat flows into the sample.
Exothermic - heat flows out of the sample.
13. Interpretation of DTA
ΔH = K * Peak area
K - can be determined by measuring the ΔH and peak area of know metals
14. Limitations of Differential Thermal Analysis
(DTA)
ΔT determined by DTA is not so accurate (2-3 ̊C).
Small change in ΔT cannot be determined and
quantified.
Due to heat variation between sample and reference
makes, it less sensitive.
To improve the above limitations change in the
methodology is required.
21. Application in Food Industry
Standard TGA results for Double mint chewing
gum sample
TGA auto stepwise results for Double mint
chewing gum sample
The correct combination of the gum formulation.
Elastomers, glycerin, softening agents, and carbonates, flavoring agents, poly
vinyl acetate
22. Application in determination of phase
transition
113 ̊ C
Rhombohedral to monoclinic
124 ̊C
Melting point
179 ̊C
Liquid phase transistion
446 ̊C
Boiling point
Sulfur element
23. To find the melting and Boiling point of
Materials
Benzoic acid
24.
25. OPEN FOR DISCUSSION
TG ?..
DTA ??
DSC ???ΔH ?
Calibration ?..
DTG
/DTA ???ΔT ?
sample ?
??....