1. 1
2004 Training Seminars DSC
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.
Used by most DSC’s but not the Q1000

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 Q The absolute value of the signal is not relevant, only absolute changes are used.
Absolute Heat Flow: used by Q Dividing the signal by the measured heating rate converts the heat flow signal into a heat capacity signal
Absolute Heat Flow from Q1000 allows direct measurement of Cp

10. DSC Heat Flow

11. Tzero Heat Flow Equation
Besides the three temperatures (Ts, Tr, T0); what other values do we need to calculate Heat Flow?
Heat Flow
Sensor Model
How do we calculate these?
Tzero heat flow equation applicable for Q100 & Q1000. Uses 4 part equation using the C’s & R’s

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. More on Diagnostic Signals later
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

28. How to Get Better DSC Results2
2004 Training Seminars DSC
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 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 10-20°C/min
Only needed if you desire quantitative Cp from Direct Cp
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 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

51. Sample Pans Type of pan depends on- Sample form Volatilization
Temperature range
Use lightest, flattest pan possible
Always use reference pan of the same type as sample pan

52. Standard DSC Pans (Crimped)
Pan & lid weighs ~23mg, bottom of pan is flat
Used for solid non-volatile samples
Always use lid (see exceptions)
Lid improves thermal contact
Keeps sample from moving
Exceptions to using a lid
Running oxidative experiment
Running PCA experiment

53. Standard DSC Pans (Crimped)
Crimped pans are available in:
Aluminum - up to 600°C
Copper - up to 725°C (in N2)
Gold - up to 725°C
Standard Pans without lids
Graphite - up to 725°C (in N2)
Platinum - up to 725°C

54. Hermetic Pans (Sealed)
Pan & Lid weigh ~55mg, bottom of pan is not as flat as std pans
Used for liquid samples and samples with volatiles
Always use lid (same exceptions as before)
After sealing pans, should form dome

55. Hermetic Pans (Sealed)
Hermetic Pans are available in:
Aluminum – <600°C; <3 atm (300 kPa gage)
Alodined Aluminum - <600°C; <3 atm (300 kPa gage)
(For aqueous samples)
Gold – <725°C, <6 atm (600 kPa gage)
Specialized Sealed Pans
High Volume - 100µL; <250°C; 600 psig(4.1 MPa)
High Pressure - 35µL; <300°C; 1450 psig(10 MPa)
Note: 3 atm is approximately 44 psig

56. It Does Matter What Pan you use
Monohydrate Pharmaceutical sample
Green curve is hermetic sealed pan, while blue curve is vented pan. Sealed pan shows crystalline melt, while vented shows loss of H2O. Sample is a channel hydrate and loss of water causes collapse of crystalline structure to amorphous.

57. Sample Shape Keep sample thin
Cover as much as the bottom of pan as possible

58. Sample Shape Cut sample to make thin, don’t crush
If pellet, cut cross section

59. Sample Shape Cut sample to make thin, don’t crush
If pellet, cut cross section
If powder, spread evenly over the bottom of the pan

60. Using Sample Press When using crimped pans, don’t over crimp
Bottom of pan should remain flat after crimping
When using Hermetic pans, a little more pressure is needed
Hermetic pans are sealed by forming a cold wield on the Aluminum pans
Crimped Pans
Hermetic Pans
Not Sealed
Good Bad
Sealed

61. Sample Size Larger samples will increase sensitivity but…………….
Larger samples will decrease resolution
Goal is to have heat flow of mW going through a transition

62. Sample Size Sample size depends on what you are measuring
If running an extremely reactive sample (like an explosive) run very small samples (<1mg)
Pure organic materials, pharmaceuticals (1-5mg)
Polymers - ~10mg
Composites – 15-20mg

63. Effect of Sample Size on Indium Melt

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

65. Purge Gas Purge gas should always be used during DSC experiments
Provides dry,inert atmosphere
Ensures even heating
Helps sweep away any off gases that might be released
Nitrogen
Most common
Increases Sensitivity
Typical flow rate of 50ml/min

66. Purge Gas Helium Must be used with LNCS High Thermo-conductivity
Increases Resolution
Upper temp limited to 350°C
Typical flow rate of 25ml/min
Air or Oxygen
Used to view oxidative effects
Typical flow rate of 50ml/min

67. Sample Temperature Range
Rule of Thumb
Have 2-3 minutes of baseline before and after transitions of interest - if possible
DO NOT DECOMPOSE SAMPLES IN DSC CELL
Temperature range can affect choice of pans
Just because the instrument has a temperature range of –90°C to 550°C (with RCS) doesn’t mean you need to heat every sample to 550°!

68. Start-up Hook

69. Heating Rate Good starting point is 10°C/min
Faster heating rates increase sensitivity
but…………….
Faster heating rates decrease resolution
Good starting point is 10°C/min

70. Effect of Heating Rate
PMMA mg

71. Thermal History
The thermal history of a sample can and will affect the results
The cooling rate that the sample undergoes can affect :
Crystallinity of semi-crystalline materials
Enthalpic recovery at the glass transition
Run Heat-Cool Heat experiments to see effect of & eliminate thermal history
Heat at 10°C/min
Cool at 10°C/min

72. Heat-Cool-Heat of PET

73. Calculating % Crystallinity from the Latent Heat of Fusion6
2004 Training Seminars DSC
Calculating % Crystallinity from the Latent Heat of Fusion

74. Calculating % Crystallinity
Background
DSC or MDSC® measure the energy required (latent heat of fusion) to convert crystalline structure to amorphous structure at that temperature.
The heat of fusion is temperature dependent; i.e., it takes more heat to melt crystalline structure at higher temperatures.
The increase in the heat of fusion with temperature is due to the difference in the heat capacity curves for amorphous and crystalline material.
In order to correctly calculate % crystallinity from the heat of fusion requires a knowledge of how the heat of fusion changes with temperature.

75. Calculating % Crystallinity (cont.)
1- If 100% crystalline and amorphous material is available, create Cp and enthalpy plots from measured heat flow
Enthalpy plots are obtained by measuring the absolute integral of a Cp plot over some temperature range
All enthalpy plots are normalized to the same value (J/g) at a convenient temperature above the melting point where all samples should theoretically be the same because all have the same liquid structure (mobile amorphous)
See Figures 1-3

76. Enthalpy Plots Are Integrals of Heat Capacity Plots
Integrals of 100% Crystalline and 100% Amorphous Heat Capacity Curves Can Be Used to Create an Enthalpy Plot
Figure Drug 3.75mg MDSC® .159/60/1
Integrals of 100% Crystalline and 100% Amorphous Heat Capacity Curves Can Be Used to Create Relative Enthalpy Plot

77. Figure 2
Effect of the Temperature-Dependence of the Heat of Fusion on Crystallization and Melting Peak Areas for a Drug

78. The Enthalpy Plot Can Be Used to Calculate % Crystallinity
Illustrating the Temperature Dependence of the Heat of Fusion on the Monohydrate Form of the Drug
Figure 3

79. Calculating % Crystallinity (cont.)
For polymers, enthalpy values for 100% crystalline and 100% amorphous structure are available from ATHAS Databank as a function of temperature
See ATHAS Figures
Calculate % Crystallinity by dividing measured heat of fusion by the difference (*) in enthalpy for 100% crystalline and 100% amorphous structure at that temperature (Fig. 4)
% Crystallinity = 37/113*  33b 160ºC
*113 J/g = Heat of Fusion = (88323a – 66589a) J/mole 192a g/mole
a = values obtained from ATHAS Databank
note b; use of 140J/g for H = 26% Crystallinity

80. ATHAS – Page 1

81. ATHAS - Page 2
These are the Major Polymer
Categories for ATHAS

82. ATHAS – Page 3
Each Polymer Category has a Sub-listing

83. ATHAS – Page 4

84. ATHAS – Page 5 ---------------------- Specific Heat Capacity
Calculate g/mole from molecular structure which equals 192 g/mole for PET
Convert ºK to ºC
Specific Heat Capacity
Absolute Enthalpy

85. ATHAS – Page 6

86. Figure 4; % Crystallinity of PET @160 °C
Use of ATHAS Databank to Calculate % Crystallinity on 12.64mg Sample of Quench Cooled PET after Cold Crystallization
20°C/min