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THERMAL METHODS OF ANALYSIS Dr Ashwini Wadegaonkar

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Page 1: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

THERMAL METHODS OF

ANALYSIS

Dr Ashwini Wadegaonkar

Page 2: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Unit 2: Thermal methods of analysis

Principle of thermal analysis

Classification of thermal techniques

Principle, instrumentation and applications of TGA

and DTA

Factors affecting the thermal analysis

Numerical problem

Page 3: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Thermal analysis

A group of techniques in which a property of the

sample is monitored against time or temperature

while the temperature of the sample, in a specified

atmosphere, is programmed.

Page 4: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Introduction

Thermal methods of analysis include a group oftechniques in which change in physical property of amaterial is measured as a function of temperature whilethe substance is subjected to a controlled temperatureprogramme.

In modern era the new materials are studied withrespect to – composition, stability, chemical reactionsand dynamic properties.

Thermal methods are useful for these kind of analysis.

These methods also provide information about thestructure, composition, purity and the temperaturephase change of a material.

Page 5: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Principle of thermal analysis

Thermal Analysis includes all the methods of measuring the

sample properties while the sample temperature is program-

controlled.

Page 6: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Thermal Analysis instrument includes the followings:

Detection Unit: Furnace, sample and reference

holder, and sensor, heat and cool the sample in the

furnace, and detects the sample temperature and

property.

Temperature Control Unit: Controls the furnace

temperature.

Data Recording Unit: Records the signals of sensor

and sample temperature, and analyzes them.

Page 7: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Temperature control, data recording and analysis

are all computer-controlled.

The combination of the furnace and sensor enables

the various types of the measurement techniques.

This computer can be connected to the several

instruments which has the other types of

measurement techniques, enables the simultaneous

measurement and analysis.

Page 8: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Classification of thermal techniques

Page 9: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA and DTA

Principle, instrumentation and applications

TGA – Thermogravimetry analysis

DTA – Differential Thermal Analysis

Page 10: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Principle

The substance under study is either heated or cooled at acontrolled rate and the weight of the substance isrecorded as a function of time and temperature.

If the temperature varies during the study, then the weightis plotted as function of temperature.

If the temperature is kept constant , the weight is plottedas a function of time.

The change in weight is used for quantitative analysisand the temperature at which the change in weighttakes place can be used for qualitative analysis

Page 11: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Types of TGA –

1. Isothermal or static thermogravimetry

2. Quasistatic thermogravimetry

3. Dynamic thermogravimetry

Page 12: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Instrumentation

The apparatus that simultaneously heats the sample and

monitors its weight is called a thermobalance.

Page 13: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Important features of thermobalance –- It should be capable of continuously registering the weight change of the sample

studied

- The furnace should reach the maximum desired temperature – at least 15000C ormore

- The rate of heating should be linear and reproducible

- The sample holder should be in the hot zone of the furnace and this zone should beof uniform temperature.

- There should be a provision to carry out heating in a variety of controlledatmospheres and in vaccume

- The balance should be protected from the effect of corrosive gases

- The temperature and the change in weight must be measured accurately as possible

- The balance must be sensitive enough to study small changes in the weight of thesample.

- It must have the facility for rapid heating and cooling of the furnace so that largenumber of analyses could be carried out in short time.

Page 14: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Thermogravimetric curve

Page 15: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Factors affecting Thermogravimetry

Instrumental factors

Characteristics of the sample

Page 16: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Factors affecting Thermogravimetry

Instrumental factors

1. Heating rate

2. Furnace atmosphere – static air, dynamic air, inert atmosphere

3. Sample holder

Characteristics of the sample

Weight of the sample

Particle size of the sample

Heat of reaction

Compactness of the sample

Source of the sample

Page 17: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

TGA – Thermogravimetry analysis

Applications –

The determination of purity and thermal stability ofboth primary and secondary standards used involumetric analysis

Determination of correct drying temperatures and thesuitability of various weighing forms for gravimetricanalysis

Determination of composition of complex mixtures

Determination of suitable ignition temperature

Direct application to analytical problems

Page 18: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

DTA – Differential Thermal Analysis

Principle

It is the analytical technique in which the temperaturedifference between the sample and a non reactivereference material is monitored when the twosubstances are subjected to an identical heatingprogramme.

The thermal curve is a plot of the difference between intemperature between the sample and the reference asa function of the temperature difference between thesample and the reference material when the sampledoes not undergo any chemical or physical change andthe reference material.

Page 19: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

DTA – Differential Thermal Analysis

DTA curve

Page 20: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

If the change is endothermic, the sample temperature islower than the reference material.

Conventionally exotherms are plotted upwards whereasendotherms are plotted downwards.

Both the shape and size of the peaks give a largeamount of information about the nature of the sample.

Sharp endothermic peaks signify the changes incrystallanity or fusion processes whereas broadendothermic peaks arise from dehydration reactions.

Physical changes usually result in endothermic peakswhile oxidative chemical reactions show exothermicpeaks.

Page 21: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

DTA – Differential Thermal Analysis

Instrumentation

Page 22: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

DTA – Differential Thermal Analysis

Sample cell

Furnace

Temperature programmer and controller

Amplifier and recorder

Page 23: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

DTA – Differential Thermal Analysis

Applications

It provides information about the temperature of transitions

It can be used to study the process in which heat is absorbed or evolved.

The thermal curves can be used in qualitative analysis

It is used to determine specific heat of substances

It is used to detect energy changes occurring during melting and polymorphic transitions. This technique is useful in constructing phase diagrams of systems.

It is used to determine directly the melting point of a substance and hence check the purity of compounds.

Thus can be used for the quality control of a large number of substance like cement, soil, glass, catalysts, explosives and polymers.

Page 24: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Comparison of TGA and DTA techniques

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Page 25: THERMAL METHODS OF ANALYSIS · 2020. 6. 7. · DTA –Differential Thermal Analysis Principle It is the analytical technique in which the temperature difference between the sample

Factors affecting the thermal analysis

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