Differential Thermal Analysis (DTA).ppt

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DIFFERENTIAL THERMALANALYSIS (DTA)

Presented By

Mr. Shaise Jacob

Faculty

Dept. of Pharmaceutical Analysis

Nirmala College of Pharmacy

Muvattupuzha, Kerala

India

E mail - [email protected]


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Types of thermal analysis

TG (Thermogravimetric) analysis:

weight

DTA (Differential Thermal Analysis):temperature

DSC (Differential ScanningCalorimetry):temperature


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In Differential Thermal Analysis, the

temperature difference that developsbetween a sample and an inert referencematerial is measured, when both are subjected

to identical heat - treatments. The related technique ofDifferential Scanning

Calorimetryrelies on differences in energyrequired to maintain the sample and reference

at an identical temperature.


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Thermogravimetry (TG)

Thermogravimetry is the measurement of themass of a sample as the temperature increases.This method is useful for determining samplepurity and water, carbonate, and organic

content; and for studying decompositionreactions.


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INTRODUCTION

This is a comparison method

Analytical method for recording thedifference in temperature (T) b/w asubstance and an inert reference material asa function of temperature or time

Any transformation change in specific heat

or an enthaply of transition can be detectedby DTA


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In DTA both test sample & an inert referencematerial (alumina) controlled heating orcooling programming

If zero temperature difference b/w sample &

reference material sample does notundergo any chemical or physical change.

If any reaction takes place temperaturedifference (T) will occur b/w sample &reference material


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A DTA curve can be used as a finger print foridentification purposes, for example,

in the study of clays where the structural

similarity of different forms renders diffractionexperiments difficult to interpret.


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T VS Temp.

Sharp Endothermic changes in crystallanity or fusionBroad endotherms - dehydration reaction

Physical changes usually result in endothermic curves

Chemical reactions are exothermic


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Apparatus

The key features of a differential thermalanalysis kit are as follows

1. Sample holder comprising thermocouples,sample containers and a ceramic or metallic

block.

2. Furnace.3. Temperature programmer.

4. Recording system.


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Heart of the analysis heating block

Identical pair of cavities for the sample, ref.material

Whole unit is set in an oven- control pressure

Thermocouple is place directly in contact withthe sample and another in contact with the

reference Temp.of the block is raised, the temperature of

the sample & reference follow

Zero temp. difference no physical or chemicalchange

If any reaction difference in T


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Differential Thermal Analysis

advantages:

instruments can be used at very hightemperatures

instruments are highly sensitive

characteristic transition or reactiontemperatures can be accuratelydetermined

disadvantages:

uncertainty of heats of fusion, transition,or reaction estimations is 20-50%

DTA


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Factors affect results in DTA

Sample weight

Particle size

Heating rate

Atmospheric conditions

Conditions of sample packing into dishes


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Applications

Quantitative identification and purityassessment of materials are accomplished bycomparing the DTA curve of sample to that ofa reference curve

Impurities may be detected by depression ofthe M.P


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Differential Thermal Analysis (DTA).ppt

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