Differential Scanning Calorimetry (DSC) Basic Theory & Applications Training ©2009 TA Instruments Agenda (cid:1) Understanding DSC (cid:1) Experimental Design (cid:1) Calibration (cid:1) Optimization of DSC Conditions (cid:1) Interpretation of Undesirable Events in DSC Data (cid:1) Applications DSC Training Course 1 2900 Series DSC’s DSC 2010 DSC 2910 DSC 2920 DSC Training Course First Generation Q Series™ DSCs Q1000 Q100 Q10 DSC Training Course 2 Second Generation Q-Series™ DSCs Q2000 Q200 AutoQ20 Q2000 is top-of-the-line, research grade with all options Q200 is research grade and expandable Q20 is a basic DSC – Available as an Auto Q20 & also Q20P DSC Training Course Understanding DSC - Agenda (cid:1) What does a DSC measure? (cid:1) How does a DSC make that measurement? (cid:1) How is a Tzero™ DSC different? (cid:1) Tzero Results (cid:1) Advanced Tzero DSC Training Course 3 Agenda (cid:1) What does a DSC measure? (cid:1) How does a DSC make that measurement? (cid:1) How is a Tzero™ DSC different? (cid:1) Tzero Results (cid:1) Advanced Tzero DSC Training Course What 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 temperature DSC Training Course 4 Endothermic Heat Flow 0.1 (cid:1) Heat flows into the sample as a result of either (cid:1) Heat capacity (heating) 0.0 (cid:1) Glass Transition (Tg) (cid:1) Melting -0.1 (cid:1) Evaporation W/g) (cid:1) Other endothermic processes Flow ( -0.2 Heat -0.3 -0.4 Endothermic 0 25 50 75 100 125 150 Exo Up Temperature (°C) DSC Training Course Exothermic Heat Flow Exothermic 0.1 W/g) w ( Flo Heat (cid:1) Heat flows out of the sample as a result of either 0.0 (cid:1) Heat capacity (cooling) (cid:1) Crystallization (cid:1) Curing (cid:1) Oxidation (cid:1) Other exothermic processes -0.1 0 20 40 60 80 100 120 140 160 Exo Up Temperature (°C) DSC Training Course 5 Temperature (cid:1) What temperature is being measured and displayed by the DSC? Sensor Temp: used by most DSCs. It is measured at the (cid:1) sample platform with a thermocouple, thermopile or PRT. Sample Platform Chromel Area Detector Reference Platform Constantan Body Thin Wall Tube Base Surface Constantan Wire Chromel Wire Chromel Wire DSC Training Course Temperature (cid:1) What temperature is being measured and displayed by the DSC? Pan Temp: calculated by TA Q1000/2000 based on pan (cid:1) material and shape (cid:1) Uses weight of pan, resistance of pan, & thermoconductivity of purge gas What about sample temperature? (cid:1) (cid:1) The actual temperature of the sample is never measured by DSC DSC Training Course 6 Temperature (cid:1) What temperatures are not typically being displayed? Program Temp: the set-point temperature is usually not (cid:1) recorded. It is used to control furnace temperature Furnace Temp: usually not recorded. It creates the (cid:1) temperature environment of the sample and reference DSC Training Course Understanding DSC Signals Heat Flow (cid:1) Relative Heat Flow: measured by all DSCs except TA Q1000/2000. The absolute value of the signal is not relevant, only absolute changes are used. (cid:1) Absolute Heat Flow: used by Q1000/2000. Dividing the signal by the measured heating rate converts the heat flow signal into a heat capacity signal DSC Training Course 7 DSC Heat Flow dH Cp = Sample Heat Capacity = DSC heat flow signal dt = Sample Specific Heat x Sample Weight dH dT = Cp + f (T, t) dt dt dT f(T,t) = Heat flow that is function of time = Heating Rate dt at an absolute temperature (kinetic) DSC Training Course Agenda (cid:1) What does a DSC measure? (cid:1) How does a DSC make that measurement? (cid:1) How is a Tzero™ DSC different? (cid:1) Tzero Results (cid:1) Advanced Tzero DSC Training Course 8 How does a DSC Measure Heat Flow? (cid:1) DSC comprises two nominally identical calorimeters in a common enclosure that are assumed to be identical. (cid:1) Advantages of a twin calorimeter: Noise reduction by cancellation of common mode noise. (cid:1) Simplified heat flow rate measurement. (cid:1) Cancellation of calorimeter and pan heat capacities. (cid:1) Cancellation of heat leakages. (cid:1) DSC Training Course Heat Flux DSC Cell Schematic 2900 Series DSC Reference Pan Sample Pan Dynamic Sample Chamber Lid Gas Purge Inlet Thermoelectric Disc (Constantan) Chromel Chromel Disc Disc Heating Block Chromel Wire Thermocouple Alumel Wire Junction DSC Training Course 9 Perfectly Symmetrical? (cid:1) The heat flow rate of an empty perfectly symmetrical twin calorimeter should be zero. (cid:1) However, it almost never is because the DSC is rarely symmetrical as assumed. (cid:1) The asymmetry is the inevitable result of manufacturing tolerances and is unavoidable. For example, thermal resistance of the Tzero DSC cell is determined by the wall thickness of the “top hat”which is .005”(0.13mm). To achieve 1% thermal resistance imbalance would require manufacturing tolerance of .00005”(.00127mm). DSC Training Course Conventional DSC Measurements 2900 Series Heat Flow Heat Balance Equations Measurement Model T −T T −T q = fs s q = fr r qs qr s R r R s r Conventional DSC Heat Ts Tr Flow Rate Measurement R R q = q −q s r s r T −T −∆T q = r s = R R T T fs fr This 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 flows. DSC Training Course 10