differential thermal analysis (dta) ppt
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DIFFERENTIAL THERMAL ANALYSIS (DTA) pptTRANSCRIPT
DIFFERENTIAL THERMAL ANALYSIS (DTA)
Presented By
Mr. Shaise JacobFacultyDept. of Pharmaceutical AnalysisNirmala College of PharmacyMuvattupuzha, KeralaIndiaE mail - [email protected]
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