2004 Training Seminars DSC

1. 1 2004 Training SeminarsDSC Understanding DSC

2. Agenda • What does a DSC measure? • How does a DSC make that measurement? • How is a Tzero™ DSC different? • Tzero Calibration • Tzero Results • Advanced Tzero

3. 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

4. Endothermic Heat Flow • Heat Flow • Endothermic: heat flows into the sample as a result of either heat capacity (heating) or some endothermic process (glass transition, melting, evaporation, etc.)

5. Exothermic Heat Flow • Heat Flow • Exothermic: heat flows out of the sample as a result of either heat capacity (cooling) or some exothermic process (crystallization, cure, oxidation, etc.)

6. Temperature • 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 PRT.

7. Temperature • What temperature is being measured and displayed by the DSC? • Pan Temp: calculated by TA Q1000 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 DSC

8. Temperature • What other temperatures are not typically being displayed. • Program Temp: the set-point 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 reference

9. Understanding DSC Signals Heat Flow • Relative Heat Flow: measured by all DSCs except TA Q1000. The absolute value of the signal is not relevant, only absolute changes are used. • Absolute Heat Flow: used by Q1000. Dividing the signal by the measured heating rate converts the heat flow signal into a heat capacity signal

10. DSC Heat Flow

11. Tzero Heat Flow Equation Heat Flow Sensor Model Besides the three temperatures (Ts, Tr, T0); what other values do we need to calculate Heat Flow? How do we calculate these?

12. Measuring the C’s & R’s • Tzero™ Calibration calculates the C’s & R’s • Calibration is a misnomer, THIS IS NOT A CALIBRATION, but rather a measurement of the Capacitance (C) and Resistance (R) of each DSC cell • After determination of these values, they can be used in the Four Term Heat Flow Equation showed previously

13. Measuring the C’s & R’s • Preformed using Tzero™ Calibration Wizard • Run Empty Cell • Run Sapphire on both Sample & Reference side

14. Measuring the C’s & R’s Empty DSC constant heating rate Assume: Heat balance equations give sensor time constants

15. Measuring the C’s & R’s Repeat first experiment with sapphire disks on sample and reference (no pans) Assume: Use time constants to calculate heat capacities

16. Measuring the C’s & R’s Use time constants and heat capacities to calculate thermal resistances

17. A few words about the Cs and Rs • The curves should be smooth and continuous, without evidence of noise or artifacts • Capacitance values should increase with temperature (with a decreasing slope) • Resistance values should decrease with temperature (also with a decreasing slope) • It is not unusual for there to be a difference between the two sides, although often they are very close to identical

18. Good Tzero™ Calibration Run

19. Bad Tzero™ Calibration Run Can see that it is bad during Tzero™ cal run

20. Before Running Tzero™ Calibration • System should be dry • Dry the cell and the cooler heat exchanger using the cell/cooler conditioning template and the default conditions (2 hrs at 75°C) with the cooler off • Preferably enable the secondary purge • Do not exceed 75°C cell temperature with the cooler off, although the time can be extended indefinitely

21. Stabilization before Calibration • System must be stable before Tzero™ Calibration • Stabilization is achieved by cycling the baseline over the same temperature range and using the same heating rate as will be used for the subsequent calibration • Typical systems will stabilize after 3-4 cycles, 8 cycles recommended to ensure that the system has stabilized

22. Tzero™ Calibration Conditions • Normally, Heat Only calibration is all that is necessary • Heating Rate should be 20°C/min • Temperature Limits based on cooler type • RCS; –90 to 400°C • LNCS; –180 to 300°C • Use Diagnostic signals to improve troubleshooting capability

23. Enable and Select Diagnostic Signals Check this box!

24. Enable and Select Diagnostic Signals Select 1-8 for an RCS or all of them for an LNCS More on Diagnostic Signals later

25. Example of Typical Results Characteristics of the thermal resistances and heat capacities: Both curves should be smooth, with no steps, spikes or inflection points. Thermal resistances should always have negative slope that gradually decreases. Heat capacities should always have positive slope that gradually decreases. This cell is very well balanced. It is acceptable and usual to have larger differences between sample and reference.

26. Tzero™ vs Conventional Baseline

27. Indium with Q Series Heat Flow Signals Q1000 Q100 Q10

28. 2 2004 Training SeminarsDSC How to Get Better DSC Results

29. Agenda • Keeping your DSC cell clean • Calibration • Sample Preparation • Thermal Method

30. Agenda • Keeping your DSC cell clean • Calibration • Sample Preparation • Thermal Method

31. Keeping the DSC Cell Clean • One of the first steps to ensuring good data is to keep the DSC cell clean • How do DSC cells get dirty? • Decomposing samples during DSC runs • Samples spilling out of the pan • Transfer from bottom of pan to sensor

32. How do we keep DSC cells clean? • DO NOT DECOMPOSE SAMPLES IN THE DSC CELL!!! • Run TGA to determine the decomposition temperature • Stay below that temperature! • Make sure bottom of pans stay clean • Use lids • Use hermetic pans if necessary

33. TGA Gives Decomposition Temperature

34. Cleaning Cell • If the cell gets dirty • Clean w/ brush • Brush gently both sensors and cell if necessary • Be careful with the Tzero™ thermocouple • Blow out any remaining particles

35. Brushing the Sample Sensor

36. Calibration • Heat Flow (Cell Constant) (All DSC’s) • Temperature Calibration (All DSC’s) • Direct Cp (Q1000)

37. Heat Flow Calibration (Cell Constant) • Heat Flow Calibration of Differential Scanning Calorimeters – ASTM E-968 • Enthalpy Calibration • Performed using Calibration Wizard • One Run • Indium metal • Sample Weight 1-5mg • Pre-melt sample the first time you run it • Heating rate of 10°C/min • Dependent upon purge gas

38. Cell Constant • The cell constant is calculated as the ratio of the theoretical heat of fusion of a standard material, to the measured heat of fusion • Cell Constant should be 0.95-1.20 in N2

40. Calibration • Heat Flow (Cell Constant) (All DSC’s) • Temperature Calibration (All DSC’s) • Direct Cp (Q1000)

41. Temperature Calibration • Temperature Calibration of Differential Scanning Calorimeters – ASTM E-967 • Performed using Calibration Wizard • Indium Cell constant run also performs temperature calibration • Can do up to 5 standards • Pure metals typically used - In, Sn, Zn, Pb • We’ve found that on the Q series DSC’s one temperature calibration point is all that is usually needed

43. Calibration • Heat Flow (Cell Constant) (All DSC’s) • Temperature Calibration (All DSC’s) • Direct Cp (Q1000)

44. Direct Cp Calibration (Q1000 Only) • Required to measure the absolute value of Heat Capacity (Cp) with a single run • Reset previous calibration value to 1.0 • Run standard material (sapphire) in standard mode, @ 10-20°C/min Set to 1.0

45. Direct Cp Calibration • The heat capacity calibration constant, K, is calculated as the ratio of the theoretical heat capacity of a standard material, to the measured heat capacity of the material

46. Use sapphire encapsulated in pan Setup to do Cp Constant (Direct)

47. Direct Cp Calibration

48. Cp Constant (Direct) • Get data table from UA • Calculate Cp constant @ a single point or average values (see below)

49. Cp Constant (Direct) • Type new value into calibration table

50. Agenda • Keeping your DSC cell clean • Calibration • Sample Preparation • Thermal Method