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Differential thermal analysis and differential scanning calorimetry. : 

Differential thermal analysis and differential scanning calorimetry. Aju S. Sam 1st yr. M.Pharm Nehru College of Pharmacy.

Thermal methods of analysis : 

Thermal methods of analysis Technique in which some physical parameters of the system is determined and recorded as a function of temperature.

Differential thermal analysis (dta) : 

Differential thermal analysis (dta) Introduction: Records the difference in temperature between a substance and a reference material against time or temperature . Thermal changes due to fusion, crystalline structure inversions, boiling, decomposition, oxidation, reduction, destruction of crystalline lattice structure etc. are generally accompanied by rise or fall in temperature. phase transitions, dehydration, reduction produce endothermic effects. crystallization, oxidation produce exothermic effects.

Slide 4: 

DTA curve: Endotherms are plotted downwards and exotherms upwards. The temperature of the sample is greater for an exothermic reaction, than that of the reference; for endotherms the sample temperature lags behind that of the reference. Area of the peak is proportional to the amount of reacting material.

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Factors Affecting DTA Curve:

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Instrumentation: Furnace Assembly Sample and reference holder with temperature detector Temperature programmer Amplifier and recorder Atmosphere control equipment for furnace and sample holder

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Applications: Identification of substances Identification of products Melting points Quantitative analysis Quality control Analysis of biological materials Inorganic and Organic chemistry.

Differential scanning calorimetry(dsc) : 

Differential scanning calorimetry(dsc)

Slide 9: 

Introduction: Advantage of keeping the sample and reference at the same temperature and heat flow into sample and reference is measured. Achieved by placing separate heating devices in the sample and reference chambers. In DSC the heat flow is measure and plotted against temperature of furnace or time to get a thermogram. Curve obtained in DSC is between dH/dt in mJ s-1 or mcal s-1 as a function of time or temperature.

Slide 10: 

DSC curve: The area under the peak is directly proportional to the heat evolved or absorbed by the reaction, and the height of the curve is directly proportional to the rate of reaction.

Slide 11: 

Factors affecting DSC curve: Instrumental factors: a) Furnace heating rate. b) Recording or chart speed c) furnace atmosphere d) Geometry of sample holder/ location of sensors e) Sensitivity of recording mechanism. f) Composition of sample container. 2. Sample Characteristics: a) Amount of sample b) Solubility of evolved gases in sample. c) Particle size d) Heat of reaction e) Sample packing f) Nature of sample g) Thermal conductivity.

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Slide 13: 

Types of DSC instruments:

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Parameters measured by DSC: Melting and boiling points Crystallisation time and temperature Percent crystallinity Heats of fusion and reactions Specific heat capacity Oxidative/thermal stability Rate and degree of cure Reaction kinetics Purity

references : 

references H.H.Willard , L.L.Merrit Jr., J.A. Dean , F.A.Settle Jr., Instrumental Method of Analysis, Wadsworth Publishing company , USA, 1986. Skoog, Douglas A., F. James Holler and Timothy Nieman, Principles of Instrumental Analysis. Fifth Edition. New York. 1998. Gurdeep R Chatwal, Sham K. Anand., Instrumental Methods of Chemical Analysis. Fifth edition.2007

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