DIFFERENTIAL SCANNING CALORIMETRY(DSC)

DIFFERENTIAL SCANNING CALORIMETRY(DSC)

1. Differential scanning calorimetry (dsc)

2. Instrumentation

3. 1)Heat-flux dsc instruments In heat-flux DSC ,the difference in heat flow in to the sample and referenced is measured while the sample temperature is changed at a constant rate. Both reference and sample are heated by a single heating unit. Heat flow in to the both sample and referece is via an electrically heated constant thermoelectric disk. The different heat flow in to the two pans is directly propotional to the difference in output of the two thermocouple junction.in heat-flux DSC ,we can write the total heat flow dH/dt=Cp dT/dt+f(T,t) Where H is a enthalpy in J mol -1 ,Cp is the specific heat capacity (heat capacity per mole)in J K -1 mol -1 , and f(T,t) is the kinetic response of sample in J mol -1

4. 2)Power-compensated DSC Intruments Temperature of sample and reference are kept equal to each other while both temp. are increased and decreased linearly. Independent two heating unit are employed . These unit are quit small ,allowing for rapid rates of heating and cooling,and equilibration. The sample and holders have platinum resistance thermometer to continuously monitor the temperature of the materials. Both sample and reference are maintained at the programmed tepm. By aaplying the power to the both.instruments record the power difference needed to maintained the sample and reference at the same temp. as a function of programmed temp. Power-compensated dsc has lower sensitive than heat-flux dsc ,but its response time is more rapid. This makes pcdsc well suited for kinetic studies in the fast equilibration to new temp.setting are needed. This is also capable for higher resolution than heat-flux dsc..

5. Endothermic and exothermic effect When the sample absobs energy, the enthalpy change is said to be enothermic processes such as melting , vaporization, and gelatinization are endothermic. When the sample releases energy, the prosess is said to be exothermic. Prosesses such as crystallization and Gelation are exothermic

6. Parameters to control Initial and final temperature Heating or cooling rate Amount of sample Thermal history of sample Type of gas: O2, N2, air Gas flow rate

7. DSC application Glass transition Melting Point Crystallization time and temperature Heat of melting and Crystallization Percent Crystallinity Oxydative stabilities Compositional analysis Heat capacity Purities Thermal stability Polymorphisam

8. Thank you !!!