Differential Scanning Calorimetry (DSC)

1 1 2009 TA InstrumentsDifferential Scanning CalorimetryBasic Theory & Applications Training (DSC) DSC Training CourseAgenda Understanding DSC Experimental Design Calibration Optimization of DSC Conditions Interpretation of Undesirable Events in DSC Data Applications2 DSC Training Course2900 Series DSC sDSC 2010 DSC 2910 DSC 2920 DSC Training CourseQ1000Q100Q10 First Generation Q Series DSCs3 DSC Training CourseSecond Generation DSCsQ2000Q200 AutoQ20Q2000 is top of the line, research grade with all optionsQ200 is research grade and expandableQ20 is a basic DSC Available as an Auto Q20 & also Q20 PDSC Training CourseUnderstanding DSC.

2 Agenda What does a DSC measure? How does a DSC make that measurement? How is a Tzero DSC different? Tzero Results Advanced Tzero4 DSC Training CourseAgenda What does a DSC measure? How does a DSC make that measurement? How is a Tzero DSC different? Tzero Results Advanced TzeroDSC Training CourseWhat Does a DSC Measure?A DSC measures the difference in heat flow rate (mW = mJ/sec) between a sample and inert reference as a function of time and temperature5 DSC Training Course 0 .4 0 .3 0 .2 0 .10 .00 .1 Heat Flow (W/g)02 55 07 51 0 01 2 51 5 0T e m pe rature ( C )E xo U pEndothermic Heat Flow Heat flows intothe sample as a result of either Heat capacity (heating) Glass Transition (Tg) Melting Evaporation Other endothermic processesEndothermicDSC Training Course 0.

3 10 .00 .1 Heat Flow (W/g)02 04 060801 0 01 2 01 4016 0 Tem perature ( C )Exo U pExothermic Heat Flow Heat flows out ofthe sample as a result of either Heat capacity (cooling) Crystallization Curing Oxidation Other exothermic processesExothermic6 DSC Training CourseTemperature What temperature is being measured and displayed by the DSC? Sensor Temp: used by most DSCs. It is measured at the sample platform with a thermocouple, thermopile or BodyChromel WireChromel Area DetectorConstantan WireChromel WireBase SurfaceThin Wall TubeSample PlatformReference PlatformDSC Training CourseTemperature What temperature is being measured and displayed by the DSC?

4 Pan Temp: calculated by TA Q1000/2000 based on pan material and shape Uses weight of pan, resistance of pan, & thermoconductivity of purge gas What about sample temperature? The actual temperature of the sample is never measured by DSC7 DSC Training CourseTemperature What temperatures are not typically being displayed? Program Temp: the temperature is usually not recorded. It is used to control furnace temperature Furnace Temp: usually not recorded. It creates the temperature environment of the sample and referenceDSC Training CourseUnderstanding DSC SignalsHeat Flow Relative Heat Flow: measured by all DSCs except TA Q1000/2000.

5 The absolute value of the signal is not relevant, only absolute changes are used. Absolute Heat Flow: used by Q1000/2000. Dividing the signal by the measured heating rate converts the heat flow signal into a heat capacity signal8 DSC Training CourseDSC Heat Flowt)(T,dtdT Cp dtdHf+=signal flowheat DSC dtdH= Weight SampleHeat x Specific Sample CapacityHeat Sample Cp==Rate Heating dtdT=(kinetic) re temperatuabsolutean at timeoffunction is that flowHeat t)(T,=fDSC Training CourseAgenda What does a DSC measure? How does a DSC make that measurement?

6 How is a Tzero DSC different? Tzero Results Advanced Tzero9 DSC Training CourseHow does a DSC Measure Heat Flow? DSC comprises two nominally identical calorimeters in a common enclosure that are assumed to be identical. Advantages of a twin calorimeter: Noise reduction by cancellation of common mode noise. Simplified heat flow rate measurement. Cancellation of calorimeter and pan heat capacities. Cancellation of heat Training CourseHeat Flux DSC Cell Schematic2900 Series DSCD ynamic Sample ChamberReference PanSample PanLidGas Purge InletChromel DiscHeating BlockChromel DiscAlumel WireChromel WireThermocouple JunctionThermoelectric Disc (Constantan)10 DSC Training CoursePerfectly Symmetrical?

7 The heat flow rate of an empty perfectly symmetrical twin calorimeter should be zero. However, it almost never is because the DSC is rarely symmetrical as assumed. The asymmetry is the inevitable result of manufacturing tolerances and is example, thermal resistance of the Tzero DSC cell is determined by the wall thickness of the top hat which is .005 ( ). To achieve 1% thermal resistance imbalance would require manufacturing tolerance of .00005 (.00127mm).DSC Training CourseConventional DSC MeasurementsHeat FlowMeasurement ModelThis model assumes that the sample and reference calorimeter thermal resistances are identical, the temperature of the furnace at the sample and reference calorimeters are equal and does not include other known heat =rrfrrRTTq =Heat Balance Equationsrsqqq =RTRTTqsr = =Conventional DSC HeatFlow Rate Measurement2900 Series11 DSC Training CourseConventional DSC.

8 Assumptions The resistance between the sample sensor and the furnace equals the resistance between the reference sensor and the furnace Pan and calorimeter heat capacities are ignored Measured temperature equals sample temperature No heat exchange with the surroundingsDSC Training CourseConsequences of the Assumptions Whenever the heating rate of the sample and reference calorimeters is not identical, the measured heat flow is not the actual sample heat flow rate. This occurs during transitions in standard DSC and always during MDSC . Resolution suffers.

9 Sensitivity suffers. MDSC results are strongly period dependent, requiring long periods and slow heating rates. The heat flow baseline is usually curved and has large slope and Training CourseViolations of AssumptionsPan and calorimeter heat capacities are ignored Sample and reference heat capacities are assumed to be the same and to heat at the same rate. In general the sample and reference calorimeter heat capacities do not match contributing to empty DSC heat flow rate baseline. During transitions and MDSC experiments the sample and reference heating rates differ and the measured heat flow rate is incorrect because the sample and reference sensor and pan heat capacities store or release heat at different Training CourseExpanded Principle of OperationQ = Ts Tr + A + B + C RThermalResistanceImbalanceThermalCapaci tanceImbalanceHeatingRateImbalanceTfsTsR sTfrTrRrCsCrNot Being Measured w/ Conventional DSC13 DSC Training CourseAgenda What does a DSC measure?

10 How does a DSC make that measurement? How is a Tzero DSC different? Tzero Results Advanced TzeroDSC Training DSC SchematicSample & Reference PlatformsTzero Thermocouple14 DSC Training CourseConstantan BodyChromel WireChromel Area DetectorConstantan WireChromel WireBase SurfaceThin Wall TubeSample PlatformReference Heat Flow MeasurementTrTsRsCsCrRrToTfQ Series DSCDSC Training CourseTzero Heat Flow Measurement Rs Rr qs qr Cs Cr Tr T0 Ts Heat Flow Rate EquationsHeat FlowSensor ModelThe sample and reference calorimeter thermal resistances and heat capacities obtained from Tzero calibration are used in