DIFFERENTIAL THERMALANALYSIS (DTA) Prepared by:- Mr. Jiten B. Patel M.pharm(1st sem) B.M.C.P.
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 determinedDisadvantages: DTA• uncertainty of heats of fusion, transition, or reaction estimations is 20-50%
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