In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

If the sample does not undergo any physical or chemical change. Then there will be no temperature difference between sample and reference. But a temperature difference will definitely occur if sample undergoes any change. For instance in an endothermic change such as melting or dehydration of the sample, the temperature of the sample will be lower than that of reference. On completion of the process the sample will again show zero difference of temperature as compared with reference. On the other hand if an exothermic reaction take place, the sample temperature will be higher than that of reference material.

If we plot a graph of difference of temp. Vs temp. of reference. The graph obtained is in the form of peaks. For endothermic peak will be in the downward and for exothermic the peak is In upward direction. The shape, size of the peaks gives lot, of information about the nature of the test sample. Endothermic curve is for physical change while exothermic is for chemical change. The oxidation reaction give exothermic curve, The melting or fusion are endothermic. Peak areas and peak heights are used for quantitative measurements.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

If the sample does not undergo any physical or chemical change. Then there will be no temperature difference between sample and reference. But a temperature difference will definitely occur if sample undergoes any change. For instance in an endothermic change such as melting or dehydration of the sample, the temperature of the sample will be lower than that of reference. On completion of the process the sample will again show zero difference of temperature as compared with reference. On the other hand if an exothermic reaction take place, the sample temperature will be higher than that of reference material.

If we plot a graph of difference of temp. Vs temp. of reference. The graph obtained is in the form of peaks. For endothermic peak will be in the downward and for exothermic the peak is In upward direction. The shape, size of the peaks gives lot, of information about the nature of the test sample. Endothermic curve is for physical change while exothermic is for chemical change. The oxidation reaction give exothermic curve, The melting or fusion are endothermic. Peak areas and peak heights are used for quantitative measurements.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

Following are the applications of DTA:

1) With the help of DTA, we can find out the effect of heat on Physical and chemical properties of sample.

2) DTA technique is used in fuel analysis, Polymers, ceramics, cements and in pharmaceutical fields.

3) The phenomenon is used to identify the products formed and also their quantitative estimation.

4) DTA gives information regarding transformation, fusion of the sample.

5) It is used for determination of M.P. and hence absolute purity of organic compound,

6) DTA phenomenon is used to find out thermal stability, fusion, phase changes, purity of variety of sample can be determined.

7) Moisture content in the sample can be determined.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

Following are the applications of DTA:

1) With the help of DTA, we can find out the effect of heat on Physical and chemical properties of sample.

2) DTA technique is used in fuel analysis, Polymers, ceramics, cements and in pharmaceutical fields.

3) The phenomenon is used to identify the products formed and also their quantitative estimation.

4) DTA gives information regarding transformation, fusion of the sample.

5) It is used for determination of M.P. and hence absolute purity of organic compound,

6) DTA phenomenon is used to find out thermal stability, fusion, phase changes, purity of variety of sample can be determined.

7) Moisture content in the sample can be determined.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

1) Furnace: It is operating from the temp. of 170-2800°C. The temperature varies 0.1-30°C per minute. The heating is done with heater coils or IR-radiations.

2) Two wells of equal size: One for reference and the other well (cavity) is for sample. The reference is usually Alumina. The reference and sample is placed in the wells.

3) Thermo couple: The temp. of reference and sample and the diff. between two temperature is measured with the help of thermocouples, which is combination of two metals

4) Amplifier: If the diff. of temp. is small, it is difficult to measure accurately then it is to be amplified with amplifier.

5) Atmosphere Control: The heating of sample and reference is done in presence of inert (purge) atmosphere. In other case the ref. or sample may react with the gases of atmosphere.

6) Recorder: Very sensitive recorders are used. It may be photographic light beam galvanometer or electronic potentiometer. A two point recorder records both the diff. temp. and reference material temp as a function of time or temp. ref. on the axis. Recorder will give graph, which on analysis we can have quantitative analysis and from the graph we can decide the change whether it is physical or chemical change.

In differential thermal analysis (DTA), the temperature difference between test sample and reference material (non-reactive generally alumina) is followed, while the two substances are subjected to identical and controlled heating or cooling. The thermal plot is temperature difference Vs the temperature of reference material.

1) Furnace: It is operating from the temp. of 170-2800°C. The temperature varies 0.1-30°C per minute. The heating is done with heater coils or IR-radiations.

2) Two wells of equal size: One for reference and the other well (cavity) is for sample. The reference is usually Alumina. The reference and sample is placed in the wells.

3) Thermo couple: The temp. of reference and sample and the diff. between two temperature is measured with the help of thermocouples, which is combination of two metals

4) Amplifier: If the diff. of temp. is small, it is difficult to measure accurately then it is to be amplified with amplifier.

5) Atmosphere Control: The heating of sample and reference is done in presence of inert (purge) atmosphere. In other case the ref. or sample may react with the gases of atmosphere.

6) Recorder: Very sensitive recorders are used. It may be photographic light beam galvanometer or electronic potentiometer. A two point recorder records both the diff. temp. and reference material temp as a function of time or temp. ref. on the axis. Recorder will give graph, which on analysis we can have quantitative analysis and from the graph we can decide the change whether it is physical or chemical change.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Following are the applications of TGA:

1) With TGA we can have quantitative analysis. e.g. The thermal curve of 125.70 mg. of a substance contains mixture of \(Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\) (Mol. wt. = 146.12) and thermally stable salt had a loss in the mass of 6.98 mg. At Tonset 140°C. We can find out the % of Ca-oxalate. $$ Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\ \underrightarrow{140C} \ Ca{ C }_{ 2 }{ O }_{ 4 } + { H }_{ 2 }O\uparrow $$ This indicates 146.12 gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) will lose 18 gm of \( { H }_{ 2 }O\).

Therefore x gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) is loosing 6.98 gm of \({ H }_{ 2 }O\) $$ \therefore \ x\quad =\ \frac { 146.12\ \times \ 6.98 }{ 18 } \ =\ 56.7\ gm\ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O $$ That is \(\therefore \ x\ =\ \frac { 56.7\ \times \ 100 }{ 125.7 } \ =\ 45\ \% \ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\)

2) TGA curve gives the information regarding chemical kinetics.

3) As the Tonset is characteristic property so from Tonset, we can have qualitative analysis.

4) With the help of TGA curve, we can find out the energy of activation of the chemical reaction.

5) For any compound, the products formed at various temperatures can be found from TGA curve.

6) The amount of water present in the clay and soil can be determined.

7) Mechanism of polymer can be studied.

8) The correct drying and ignition temperature in gravimetry can be determined.

9) Thermal decomposition of organic, inorganic and polymeric compounds can be studied.

10) We can find out purity and thermal stability of primary and secondary standards can be determined in titrimetry.

Limitations:

1) TGA is applicable to solid compounds only.

2) As thermocouple is kept very close to sample but not in contact with the sample. Therefore exact temp. of the sample cannot be detected.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Following are the applications of TGA:

1) With TGA we can have quantitative analysis. e.g. The thermal curve of 125.70 mg. of a substance contains mixture of \(Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\) (Mol. wt. = 146.12) and thermally stable salt had a loss in the mass of 6.98 mg. At Tonset 140°C. We can find out the % of Ca-oxalate. $$ Ca{ C }_{ 2 }{ O }_{ 4 }.{ H }_{ 2 }O\ \underrightarrow{140C} \ Ca{ C }_{ 2 }{ O }_{ 4 } + { H }_{ 2 }O\uparrow $$ This indicates 146.12 gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) will lose 18 gm of \( { H }_{ 2 }O\).

Therefore x gm of \(Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\) is loosing 6.98 gm of \({ H }_{ 2 }O\) $$ \therefore \ x\quad =\ \frac { 146.12\ \times \ 6.98 }{ 18 } \ =\ 56.7\ gm\ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O $$ That is \(\therefore \ x\ =\ \frac { 56.7\ \times \ 100 }{ 125.7 } \ =\ 45\ \% \ of\ Ca{ C }_{ 2 }{ O }_{ 4 }\ { H }_{ 2 }O\)

2) TGA curve gives the information regarding chemical kinetics.

3) As the Tonset is characteristic property so from Tonset, we can have qualitative analysis.

4) With the help of TGA curve, we can find out the energy of activation of the chemical reaction.

5) For any compound, the products formed at various temperatures can be found from TGA curve.

6) The amount of water present in the clay and soil can be determined.

7) Mechanism of polymer can be studied.

8) The correct drying and ignition temperature in gravimetry can be determined.

9) Thermal decomposition of organic, inorganic and polymeric compounds can be studied.

10) We can find out purity and thermal stability of primary and secondary standards can be determined in titrimetry.

Limitations:

1) TGA is applicable to solid compounds only.

2) As thermocouple is kept very close to sample but not in contact with the sample. Therefore exact temp. of the sample cannot be detected.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The following are the factors:

1) Heating Rate: When the substance is heated to the faster rate, the temperature of the sample (decomposition) is higher, it means temperature changes and as thermogram depends on temperature so the thermogram changes.

2) Heat of Reaction: It depends whether the reaction is exothermic or endothermic, it means heat changes so the thermogram changes.

3) Furnace Atmosphere: The nature of the surrounding atmosphere can have the effect on temperature of decomposition. e.g. instead of N₂ if CO₂ is used as surrounding atmosphere, the decomposition of CaCO3 take place at much higher temperature. $$ CaC{ O }_{ 3 }\quad \overset { \Delta }{ \longrightarrow } \quad CaO\quad +\quad C{ O }_{ 2 } $$ As the CO₂ is on R.H.S. so the reverse reaction takes place, so the nature of thermogram changes. It means whenever furnace atmosphere is enrich with one of the product of reaction the decomposition temp. changes and so the nature of thermogram changes

4) Geometry of Crucible: The geometry of crucible can change slope of TGA curve, usually flat shaped crucible is used, because the diffusion of gases evolved is easier.

5) Characteristics of Samples: Characteristic means amount of sample, particle size packing density, thermal conductivity of sample, the mode of preparation of sample and the atmosphere around it.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The following are the factors:

1) Heating Rate: When the substance is heated to the faster rate, the temperature of the sample (decomposition) is higher, it means temperature changes and as thermogram depends on temperature so the thermogram changes.

2) Heat of Reaction: It depends whether the reaction is exothermic or endothermic, it means heat changes so the thermogram changes.

3) Furnace Atmosphere: The nature of the surrounding atmosphere can have the effect on temperature of decomposition. e.g. instead of N₂ if CO₂ is used as surrounding atmosphere, the decomposition of CaCO3 take place at much higher temperature. $$ CaC{ O }_{ 3 }\quad \overset { \Delta }{ \longrightarrow } \quad CaO\quad +\quad C{ O }_{ 2 } $$ As the CO₂ is on R.H.S. so the reverse reaction takes place, so the nature of thermogram changes. It means whenever furnace atmosphere is enrich with one of the product of reaction the decomposition temp. changes and so the nature of thermogram changes

4) Geometry of Crucible: The geometry of crucible can change slope of TGA curve, usually flat shaped crucible is used, because the diffusion of gases evolved is easier.

5) Characteristics of Samples: Characteristic means amount of sample, particle size packing density, thermal conductivity of sample, the mode of preparation of sample and the atmosphere around it.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The instrumentation of TGA is consisting of the following components:

1) Balance: It must be highly sensitive analytical balance. It must be precise and accurate at experimental temp. The commonly used balance is "Cahn" electro balance. It functions as null type device by providing an electrical force to restore the beam to a predetermined position. When mass changes, the beam of the balance changes, a shutter fixed to the beam changes the amount of light reaching a photo tube (EMR), which causes a restoring force to be generated by passing a current through an electromagnet, that serves as the pivot for the balance beam. A permanent magnet above and below the pivot provides the magnetic attraction to the electromagnet. The force require to restore the beam is proportional to the current which is recorded.

2) Furnace or Heating Device: Here the sample is heated by resistance heaters, IR-radiations, Microwave radiations or heating can also be done by passing the hot vapors of liquids or solids. The furnace must be design in such a manner that heat produced is directly given to the sample. The rate of increase of temp must be 0.15 to 2 deg per minute. The heating should be done in such a manner so that the weighing system should not be affected.

3) Sample Holder: The sample holder should be made up of glass, quartz, stainless steel or pt. The size and shape depends on the weight and nature of the sample

4) Temperature measurement and control: The temperature measurement is done by thermo couples. It is placed very Close to the sample. The emf generated by thermocouple, when heated is incident and is applied on the X-axis of Data acquisition and Manipulation (computer).

5) Recorder: The electrical current obtained with EMR null detector is plotted on the Y-axis and emf. of the thermocouple on X-axis in data acquisition manipulation (Computer).

6) Control of Atmosphere: The results in tile thermo gravimetry depends on the atmosphere of sample see that the atmosphere should be inert gas called purge gas which may be Ar OR N₂.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

The instrumentation of TGA is consisting of the following components:

1) Balance: It must be highly sensitive analytical balance. It must be precise and accurate at experimental temp. The commonly used balance is "Cahn" electro balance. It functions as null type device by providing an electrical force to restore the beam to a predetermined position. When mass changes, the beam of the balance changes, a shutter fixed to the beam changes the amount of light reaching a photo tube (EMR), which causes a restoring force to be generated by passing a current through an electromagnet, that serves as the pivot for the balance beam. A permanent magnet above and below the pivot provides the magnetic attraction to the electromagnet. The force require to restore the beam is proportional to the current which is recorded.

2) Furnace or Heating Device: Here the sample is heated by resistance heaters, IR-radiations, Microwave radiations or heating can also be done by passing the hot vapors of liquids or solids. The furnace must be design in such a manner that heat produced is directly given to the sample. The rate of increase of temp must be 0.15 to 2 deg per minute. The heating should be done in such a manner so that the weighing system should not be affected.

3) Sample Holder: The sample holder should be made up of glass, quartz, stainless steel or pt. The size and shape depends on the weight and nature of the sample

4) Temperature measurement and control: The temperature measurement is done by thermo couples. It is placed very Close to the sample. The emf generated by thermocouple, when heated is incident and is applied on the X-axis of Data acquisition and Manipulation (computer).

5) Recorder: The electrical current obtained with EMR null detector is plotted on the Y-axis and emf. of the thermocouple on X-axis in data acquisition manipulation (Computer).

6) Control of Atmosphere: The results in tile thermo gravimetry depends on the atmosphere of sample see that the atmosphere should be inert gas called purge gas which may be Ar OR N₂.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Only solid substances can be analyzed by this method.

In TGA following changes are possible: $$ 1)\ Reactants\ (S)\ \overset { \Delta }{ \longrightarrow } \ product\ (S)\ +\ gas $$ $$2)\ Reactants\ (S)\ +\ gas\ \ \overset { \Delta }{ \longrightarrow } \ \ product\ (S) $$

The second type of changes usually we do not perform in the laboratory. The first type of changes involves loss in the mass or weight. This loss may be due to gas which is obtained by decomposition of reactants on heating or this loss may be due to H₂O present with the reactants. This water is essential water. The essential water is water of crystallization or it is water of constituent’s.

e.g. i) The loss due to gas is $$ CaC{ O }_{ 3 }\ \overset { \Delta }{ \longrightarrow } \ CaO\ +\ C{ O }_{ 2 } $$

ii) The loss due to water of crystallization is $$ CuS{ O }_{ 4 }.5{ H }_{ 2 }O\ \overset { \Delta }{ \longrightarrow } \ CuS{ O }_{ 4 }.{ H }_{ 2 }O\ +\ 4{ H }_{ 2 }O $$

iii) The loss of water due to constituent is $$ 2Fe\left( OH \right) _{ 3 }\ \overset { \Delta }{ \longrightarrow } \ { Fe }_{ 2 }{ O }_{ 3 }\left( S \right) \ +\ 3{ H }_{ 2 }O $$

The graph is plotted mass Vs temperature or time. The graph thus obtained is known as Thermogram. Thermogram is characteristic curve for a given compound. In this graph the horizontal portion i.e. plateau indicate regions where there is no change in the weight while curved portion indicates the loss in the mass. The heating temperature varies from Ambient to 1500°C.

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Only solid substances can be analyzed by this method.

In TGA following changes are possible: $$ 1)\ Reactants\ (S)\ \overset { \Delta }{ \longrightarrow } \ product\ (S)\ +\ gas $$ $$2)\ Reactants\ (S)\ +\ gas\ \ \overset { \Delta }{ \longrightarrow } \ \ product\ (S) $$

The second type of changes usually we do not perform in the laboratory. The first type of changes involves loss in the mass or weight. This loss may be due to gas which is obtained by decomposition of reactants on heating or this loss may be due to H₂O present with the reactants. This water is essential water. The essential water is water of crystallization or it is water of constituent’s.

e.g. i) The loss due to gas is $$ CaC{ O }_{ 3 }\ \overset { \Delta }{ \longrightarrow } \ CaO\ +\ C{ O }_{ 2 } $$

ii) The loss due to water of crystallization is $$ CuS{ O }_{ 4 }.5{ H }_{ 2 }O\ \overset { \Delta }{ \longrightarrow } \ CuS{ O }_{ 4 }.{ H }_{ 2 }O\ +\ 4{ H }_{ 2 }O $$

iii) The loss of water due to constituent is $$ 2Fe\left( OH \right) _{ 3 }\ \overset { \Delta }{ \longrightarrow } \ { Fe }_{ 2 }{ O }_{ 3 }\left( S \right) \ +\ 3{ H }_{ 2 }O $$

The graph is plotted mass Vs temperature or time. The graph thus obtained is known as Thermogram. Thermogram is characteristic curve for a given compound. In this graph the horizontal portion i.e. plateau indicate regions where there is no change in the weight while curved portion indicates the loss in the mass. The heating temperature varies from Ambient to 1500°C.