, MODULE III
INSTRUMENTAL METHODS AND NANOMATERIALS
Thermal Methods of Analysis
Thermal method of analysis is the measurement of physical property of a substance or its
reaction product as a function of temperature as the substance is subjected to controlled
temperature programme. Two important thermal methods are
1. TGA
2. DTA
Thermo Gravimetric Analysis (TGA)
TGA is a thermal method of analysis in which the mass of the sample is measured as a
function of temperature when the temperature of the sample is increased linearly from room
temperature to 1200°C.
A sample on heating mass change occurs due to the physical and chemical changes
undergone by the substance.
This method gives an idea about quantitative as well as qualitative picture of the sample
under investigation. On heating mass of the sample changes due to physical changes like
vaporisation of moisture volatile component or due to the partial or complete loss of water of
crystallisation. It is also due to chemical changes like decomposition, dissociation of substance,
oxidation, reduction and combination with atmospheric gases.
Principle and method:
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, In order to explain the principle and method of TGA, let us consider the thermo gram
of the compound MX2.2H2O.
From the figure it is clear that from A to B, this compound is stable and there is no
weight change. At B the compound begins to loss its weight and the process is completed at C.
This is due to the evolution of 2 moles of water per each mole of the compound produces
anhydrous sample. From C to D, the compound is stable. So we get a horizontal weight level at
this region. At D, the compound again begins to lose weight due to the decomposition of MX2.
From E to F, again we get a horizontal weight level. This shows the stability of MO.
From the various regions of the curve, the thermal stability of initial compound, intermediate
compound and the final product can be obtained. It also gives an idea about the stoichiometry of
the compound at any given temperature.
Applications:
1. Qualitative Analysis
In order to explain the qualitative analysis, let us consider the thermogram of
CaC2O4.H2O.
CaC2O4.H2O is stable upto 100°C. So we get a horozontal region in this temperature region. On
inceasing the temperature above 100°C it loses the two mols of water per each mole of the
compound producing anhydrousCaC2O4.So the horizontal weight level changes.Anhydrous
CaC2O4is stable from 226°C - 346°C.So again we get a horizontal weight level. Above 346°C
evolution of CO takes place producing CaCO3.CaCO3 is stable from 420°C - 660°C. So
horizontal weight level obtained in this temperature region. Above 660°C decomposition of
CaCO3 takes place producing CaO and the process is completed at 840°C. CaO is stable from
840°C - 980°C. So we get a horizontal weight level in this temperature region.
2. Study of polymers
Thermo grams provide ready information about the decomposition pattern of various
polymers. Decomposition pattern is the characteristics of each type of polymer. So TGA helps
for the identification of polymers.
3. Quantitative analysis – Analysis of binary mixtures
Sree Buddha College of Engineering, Pattoor Page 2
INSTRUMENTAL METHODS AND NANOMATERIALS
Thermal Methods of Analysis
Thermal method of analysis is the measurement of physical property of a substance or its
reaction product as a function of temperature as the substance is subjected to controlled
temperature programme. Two important thermal methods are
1. TGA
2. DTA
Thermo Gravimetric Analysis (TGA)
TGA is a thermal method of analysis in which the mass of the sample is measured as a
function of temperature when the temperature of the sample is increased linearly from room
temperature to 1200°C.
A sample on heating mass change occurs due to the physical and chemical changes
undergone by the substance.
This method gives an idea about quantitative as well as qualitative picture of the sample
under investigation. On heating mass of the sample changes due to physical changes like
vaporisation of moisture volatile component or due to the partial or complete loss of water of
crystallisation. It is also due to chemical changes like decomposition, dissociation of substance,
oxidation, reduction and combination with atmospheric gases.
Principle and method:
Sree Buddha College of Engineering, Pattoor Page 1
, In order to explain the principle and method of TGA, let us consider the thermo gram
of the compound MX2.2H2O.
From the figure it is clear that from A to B, this compound is stable and there is no
weight change. At B the compound begins to loss its weight and the process is completed at C.
This is due to the evolution of 2 moles of water per each mole of the compound produces
anhydrous sample. From C to D, the compound is stable. So we get a horizontal weight level at
this region. At D, the compound again begins to lose weight due to the decomposition of MX2.
From E to F, again we get a horizontal weight level. This shows the stability of MO.
From the various regions of the curve, the thermal stability of initial compound, intermediate
compound and the final product can be obtained. It also gives an idea about the stoichiometry of
the compound at any given temperature.
Applications:
1. Qualitative Analysis
In order to explain the qualitative analysis, let us consider the thermogram of
CaC2O4.H2O.
CaC2O4.H2O is stable upto 100°C. So we get a horozontal region in this temperature region. On
inceasing the temperature above 100°C it loses the two mols of water per each mole of the
compound producing anhydrousCaC2O4.So the horizontal weight level changes.Anhydrous
CaC2O4is stable from 226°C - 346°C.So again we get a horizontal weight level. Above 346°C
evolution of CO takes place producing CaCO3.CaCO3 is stable from 420°C - 660°C. So
horizontal weight level obtained in this temperature region. Above 660°C decomposition of
CaCO3 takes place producing CaO and the process is completed at 840°C. CaO is stable from
840°C - 980°C. So we get a horizontal weight level in this temperature region.
2. Study of polymers
Thermo grams provide ready information about the decomposition pattern of various
polymers. Decomposition pattern is the characteristics of each type of polymer. So TGA helps
for the identification of polymers.
3. Quantitative analysis – Analysis of binary mixtures
Sree Buddha College of Engineering, Pattoor Page 2
