DIFFERENTIAL THERMAL ANALYSIS (DTA)

Presented By

Mr. Shaise JacobFacultyDept. of Pharmaceutical AnalysisNirmala College of PharmacyMuvattupuzha, KeralaIndiaE mail - jacobshaise@gmail.com

Thermal Analysis Techniques

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

Types of thermal analysis

• TG (Thermogravimetric) analysis: weight

• DTA (Differential Thermal Analysis): temperature

• DSC (Differential ScanningCalorimetry): temperature

• In Differential Thermal Analysis, the temperature difference that develops

between a sample and an inert reference material is measured, when both are subjected

to identical heat - treatments.• The related technique of Differential

Scanning Calorimetry relies on differences in energy required to maintain the sample and reference at an identical temperature.

Thermogravimetry (TG)

• Thermogravimetry is the measurement of the mass of a sample as the temperature increases. This method is useful for determining sample purity and water, carbonate, and organic content; and for studying decomposition reactions.

INTRODUCTION

• This is a comparison method

• Analytical method for recording the difference in temperature (∆T) b/w a substance and an inert reference material as a function of temperature or time

• Any transformation – change in specific heat or an enthaply of transition can be detected by DTA

• In DTA both test sample & an inert reference material (alumina) – controlled heating or cooling programming

• If zero temperature difference b/w sample & reference material – sample does not undergo any chemical or physical change.

• If any reaction takes place temperature difference (∆T) will occur b/w sample & reference material

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

• in the study of clays where the structural similarity of different forms renders diffraction experiments difficult to interpret.

∆T VS Temp.

Sharp Endothermic – changes in crystallanity or fusionBroad endotherms - dehydration reactionPhysical changes usually result in endothermic curvesChemical reactions are exothermic

Apparatus

• The key features of a differential thermal analysis 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.

• 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

with the 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 chemical change

• If any reaction – difference in ∆T

Differential Thermal Analysisadvantages:

• instruments can be used at very high temperatures

• instruments are highly sensitive

• characteristic transition or reaction temperatures can be accurately determined

disadvantages:

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

DTA

Factors affect results in DTA

• Sample weight• Particle size• Heating rate• Atmospheric conditions• Conditions of sample packing into

dishes

Applications

• Quantitative identification and purity assessment of materials 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