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Differential Scanning Calorimetry

Differential Scanning Calorimetry. Definitions. •. A. calorimeter. measures the heat into or out of a. sample. •. A. differential calorimete. r measures the heat of a. sample relative to a reference. •. A. differential scanning calorimeter. does all of the.

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Differential Scanning Calorimetry

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  1. Differential ScanningCalorimetry

  2. Definitions • A calorimeter measures the heat into or out of a sample. • A differential calorimete r measures the heat of a sample relative to a reference. • A differential scanning calorimeter does all of the above and heats the sample with a linear temperature ramp. • Endothermic heat flows into the sample. • Exothermic heat flows out of the sample.

  3. DSC: The Technique • Differential Scanning Calorimetry (DSC) measures the temperatures and heat flows associated with transitions in materials as a function of time and temperature in a controlled atmosphere. • These measurements provide quantitative and qualitative information about physical and chemical changes that endothermic exothermic processes changes involve or , or in heat capacity .

  4. What Can You Measure with DSC? • Qualitative analysis • Fingerprinting of minerals, clays, polymers • Sample purity • Melting points • Heat capacity, cp • Glass transition temperature, Tg • Crystallization temperature, Tc • Phase diagrams

  5. Schematic of DSC Instrument Reference Sample T1 T2 Pt thermopile Pt thermopile Low mass 1 gram heater heater N2 flow DW

  6. Glass Transition Thermogram • Step in thermogram • Transition from disordered solid to liquid • Observed in glassy solids, e.g., polymers • Tg, glass transition temperature Glass transition dH/dt, mJ/s Tg Temperature, K

  7. Crystallization Thermogram • Sharp positive peak • Disordered to ordered transition • Material can crystallize! • Observed in glassy solids, e.g., polymers • Tc, crystallization temperature Crystallization dH/dt, mJ/s Tc Temperature, K

  8. Melting Thermogram • Negative peak on thermogram • Ordered to disordered transition • Tm, melting temperature • NB: melting happens to crystalline polymers; glassing happens to amorphous polymers Melting dH/dt, mJ/s Tm Temperature, K

  9. Analysis Crystallization • Sharp positive peak • Disordered to ordered transition • Observed in glassy solids, e.g., polymers • Tc, crystallization temperature dH/dt, mJ/s Tc Temperature, K

  10. DSC Thermogram Oxidation Cross - Linking Crystallisation (Cure) > exothermic - Glass Transition Heat Flow Melting Temperature 6 Technical Group Talk

  11. DSC: Main Sources of Errors • Calibration • Contamination • Sample preparation – how sample is loaded into a pan • Residual solvents and moisture. • Thermal lag • Heating/Cooling rates • Sample mass • Processing errors Technical Group Talk

  12. Other DSC techniques These are three defferent types of DSC instruments. • power-compensated DSC • Heat-flux DSC • Modulated DSC

  13. Power-compensated DSC • In this case, the sample and reference material are heated separately and continuously maintained at same temperature. • While both temperatures are increased or decreased linearly. • The differential power is recorded as a function of temperature and the peak area represents the energy of transition. • Isothermal condition i.e Ts=Tr is obtained by placing a platinum resistant thermometer in the sample with an identical sensors in the reference holder. • This DSC has lower sensitivity and capable of higher resolution than heat-flux DSC.

  14. POWER-COMPENSATED DSC

  15. Heat-flux DSC instrument • In this case, the difference in heat flow into the sample and reference is measured while the sample temperature is changed at a constant rate. • Both sample and reference are heated by a single heating unit. • The differential heat flow to the sample and reference is monitored by chromel-constantan area thermocouples.

  16. HEAT-FLUX DSC

  17. Modulated DSC Benefits • Increased Sensitivity for Detecting Weak (Glass) Transitions • Eliminates baseline curvature and drift • Increased Resolution Without Loss of Sensitivity • Two heating rates (average and instantaneous) • Ability to Separate Complex Thermal Events and Transitions Into Their Heat Capacity and Kinetic Components • Ability to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions Downside • Slow data collection

  18. Reversible Transitions • Glass Transition • Melting • Non-reversible • Crystallisation • Curing • Oxidation/degradation • Evaporation • MODULATED DSC

  19. Applications of DSC • Qualitative analysis:-It is a finger-printing of minerals,clays,polymers,etc. • Sample purity. • Melting point. • Heat capacity(Cp). • Glass transition(Tg). • Crystallization temperature(Tc). • Phase diagrams.

  20. In food industry for characterisation of edible fats and oils. • The total time of analysis in DSC is 30minutes. • It is used for identification of optical isomers. • It is used for impurity studies in pharmaceutical industries.

  21. It is used in polymer industry. • Specific heat,heat of fusion,heat of dehydration,decomposition of samples can be determined. • It is used to access the purity of any substances. Example:-carnauba wax.

  22. REFERENCES • INSTRUMENTAL ANALYSIS SKOOG • INSTRUMENTAL METHODS OF CHEMICALANALYSIS GURUDEEP. R.CHATWAL,SHAM,K.ANAND. • INSTRUMENTAL METHODS OF ANALYSIS,7TH EDITION WILLARD,MERRITT.

  23. THANK YOU

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