Thermal Analysis

SUBMITTED BY:

HARSHALA DHENDE FIRST YEAR M.PHARM SEM-I (DEPT. OF PHARMACEUTICS)

Guided By:Mr. Mukesh T. Mohite

A SEMINAR ONDIFFERNTIAL THERMAL ANALYSIS (DTA)DR. D.Y.PATIL COLLEGE OF PHARMACY, AKURDI, PUNE1

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Outline..What is Thermal Analysis?

Types of thermal analysis techniques

DTA(DIFFERENTIAL THERMAL ANALYSIS)

Principle involved

Instrumentation

Advantages and disadvantages

Applications

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What is Thermal analysis?

Definition of Thermal Analysis (TA): Thermal Analysis (TA)is a group of techniques that study the properties of materials as they change with temperature.

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When a material is heated its structural and chemical composition can undergo changes such as fusion, melting, crystallization, oxidation, transition, decomposition, expansion and sintering.

Using Thermal Analysis such changes can be monitored in every atmosphere of interest. The obtained information is very useful in both quality control and problem solving.

In practice thermal analysis gives properties like; enthalpy, thermal capacity, mass changes and the coefficient of heat expansion. 4

Thermal analysis includes different methods. These are distinguished from one another by the property which is measured;

Thermo gravimetric analysis (TGA): mass

Differential thermal analysis (DTA): temperature difference

Differential scanning calorimetric (DSC): heat difference

Pressurized TGA (PTGA): mass changes as function of pressure.s Thermo mechanical analysis (TMA): deformations and dimension

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7. Dilatometer (DIL): volume

8. Evolved gas analysis (EGA): gaseous decomposition products

Often different properties may be measured at the same time: TGA-DTA, TGA-EGA 6

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DIFFERENTIAL THERMAL ANALYSIS(DTA)

INTRODUCTIONDifferential thermal analysis(DTA) is a thermo analytical technique similar to differential scanning calorimetric.

In DTA ,the material under study and an inert reference are made to undergo identical thermal cycles ,while recording any temperature difference between sample and reference.

This differential temperature is then plotted again time or, or against temperature.

The curve plotted is called as DTA curve or thermo gram.

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Changes in the sample either endothermic or exothermic,can be detected relative to the inert reference.

Thus a DTA curve provides data on the transformation that have occurred such as glass transition, crystallization, melting and sublimation.

The area under DTA peak is the enthalpy change and is not affected by the heat capacity of the sample.

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Fig. no 1

Fig. no 2 differential thermogram showing types of changes encountered with polymeric material

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In DTA both the test sample and inert reference material (alumina) controlled heating or cooling programming.

If zero temperature difference b/t sample and reference material then sample doe not undergo any chemical and physical changes.

If any reaction takes place temperature difference will occur between sample and reference material.

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Principle of DTA.

A technique in which the temperature difference between a substance and reference material is measured as function of temperature, while the substance and reference are subjected to controlled temperature programmed.

The difference in the temp is called as differential temperature and is plotted against temp or function of time.

Physical changes usually result in endothermic peaks, whereas chemical reaction those of an oxidative nature show exothermic peak.

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Endothermic reaction(absorption of heat) includes sublimation and gives downward peak.Exothermic reaction(liberation of heat) includes oxidation, polymerization and gives upward peak.

fig no.3 exothermic and endothermic reactions.14

Factors causing change in heat/temperature:Physical: Adsorption(exothermic)

Desorption(endothermic)

A change in crystal structure (endo or exothermic)

Crystallization (exothermic)

Melting(endothermic)

Vaporization (endothermic)

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Chemical :-

Oxidation (exothermic)

Reduction (endothermic)

Break down reactions (endo or exothermic)

Chemisorptions (exothermic)

Solid state reactions (endo or exothermic)

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INSTRUMENTATIONA DTA consists of a , 1. sample holder 2. thermocouples 3. a furnace; 4. a temperature programmer 5. and a recording system.

The key feature is the existence of two thermocouples connected to a voltmeter.

One thermocouple is placed in an inert material such asaluminum oxide, while the other is placed in a sample of the material under study.

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1. Sample holder: The sample holder and reference cells are made up of aluminum. 2. Sensors/thermocouples: Platinum or chromyl thermocouples one for sample and one for reference material is joined to differential temperature controller. 3. Furnace: alumina block containing sample and reference cells.

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4. Temperature controller: controls temperature program and furnace atmosphere 5. Recording system: It is a system where the change in the temperature i.e. differential temperature is recorded and the enthalpy is recorded

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Fig. no. 4 Instrumentation

WorkingWe need to take two aluminum containers for keeping the sample as well as reference in them.

Thermocouples are connected to each of the material for measuring their temperature, and heat is applied to them under cautiously regulated conditions.

Now, if it is seen that the sample material has gone through certain chemical reaction or physical transformation, its temperature will change significantly due to the change in its enthalpy' or heat content.

However, the temperature of the reference material will remain unchanged.21

Working principle .

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Interpretation of DTA curve..

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Factors affect results in DTA.

There are so many factors that affects the DTA curve. They are divided into two;

24SamplecharacteristicsInstrumental factors

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Instrumental factors:25

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Sample characteristics factors..26

Lets see how these factors effect the DTA curve and the suggestions..

FactorsEffectSuggestions

1. Heating rateChange in the peak size and positionUse allow heating rate2. Location of thermocoupleIrreproducible curveStandardize thermocouple location3. Atmosphere around the sampleChange in the curveInert gas should be allowed to flow4. Amount of sampleChange in the peak size and positionStandardize sample mass5. Particle size of sampleIrreproducible curveUse small uniform particle6. Packing densityIrreproducible curveStandardize packing techniques7.Sample containerChange in peakStandardize container

Advantages: 1. Instruments can be used at a very high temperature 2. Instruments are highly sensitive 3. Flexibility in crucible volume/form 4. Characteristic transition or reaction temperature can be accurately determined

Disadvantages: 1. Reaction or transition estimations is only 20% to 50% DTA 2. Uncertainty in heats of fusion

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Applications of differential thermal analysisQualitative and Quantitative identification of Minerals: Detection of any minerals in sample.

Polymeric materials: DTA is useful for characterization of polymeric materials in the light of identification of thermo-physical, thermo-chemical ,thermo-mechanical, and thermo-elastic changes or transition.

Measurement of crystalline: Measurement of the mass fraction of crystalline material in semi- crystalline polymer.

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Producing phase diagrams and identifying phase conversions

Finding the change in enthalpy (H) in the entire procedure

Fingerprinting certain materials

Verifying decomposition temperatures of various organic composites

Exemplifying inorganic compounds

Analyzing a physical mixture of commercial polymers qualitatively

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Quantitative identification and purity assessment of material are accomplished by comparing the DTA curve of sample to that of a reference curve

Impurities may be detected by depression of the M.P.

DTA is widely used in the pharmaceutical]and food industries.

DTA may be used in cement chemistrymineralogical researchand in environmental studies.

DTA curves may also be used to date bone remainsor to study archaeological materialsUsing DTA one can obtain liquids & solidus lines of phase diagrams.

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References.. Differential thermal analysis (DTA) and differential scanning calorimetric (DSC) as a method of material investigation, Greg Klannik1, *, Josef Medved1 , Primo Mrvar1 1 , University of Ljubljana, Faculty of natural science and engineering, Department of materials and metallurgy, Akereva 12, SI-1000 Ljubljana, Slovenia.

Introduction to thermal Analysis Techniques and Applications, Edited by Michael E. Brown Chemistry Department, Rhodes University, Grahamstown, South Africa KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW page no.55-80

Handbook of differential thermal analysis and colorimetric, volume 1, by Patrick K.Gallaghaer, page no.52

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Principle of instrumental analysis, By Douglas A. Skoog and F. James Holler, 6th edition page no.62

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