Thermogravimetric Analysis Theory, Operation, Calibration and Data Interpretation

1. Thermogravimetric AnalysisTheory, Operation, Calibration and Data Interpretation Prepared by Kadine Mohomed, Ph.D Thermal Applications Chemist TA Instruments

2. Agenda:TGA Theory, Operation and Calibration • Definitions and review of instrument • Balance, furnace and heat exchanger review • Mass and temperature calibration • Purge gas considerations • Baseline considerations • Sample preparation and pan selection • Method development

3. TGA: The Technique • Thermogravimetric Analysis (TGA) measures the amount and rate of change in the weight of a material as a function of temperature or time in a controlled atmosphere. • Measurements are used primarily to determine the composition of materials and to predict their thermal stability at temperatures up to 1000°C. • The technique can characterize materials that exhibit weight loss or gain due to decomposition, oxidation, or dehydration.

4. What TGA Can Tell You • Thermal Stability of Materials • Oxidative Stability of Materials • Composition of Multi-component Systems • Estimated Lifetime of a Product • Decomposition Kinetics of Materials • The Effect of Reactive or Corrosive Atmospheres on Materials • Moisture and Volatiles Content of Materials

5. Calcium Oxalate Example

6. Mechanisms of Weight Change in TGA • Weight Loss: • Decomposition: The breaking apart of chemical bonds. • Evaporation: The loss of volatiles with elevated temperature. • Reduction: Interaction of sample to a reducing atmosphere (hydrogen, ammonia, etc). • Desorption. • Weight Gain: • Oxidation: Interaction of the sample with an oxidizing atmosphere. • Absorption. All of these are kinetic processes (i.e. there is a rate at which they occur).

7. Features of the Q500/ Q50 TGA The Q500 is a research grade thermogravimetric analyzer, whose leading performance arises from a responsive low-mass furnace; sensitive thermobalance, and efficient horizontal purge gas system (with mass flow control). Its convenience, expandability and powerful, results-oriented software make the Q500 perfect for the multi-user laboratory where a wide variety of TGA applications are conducted and where future expansion of analytical work is anticipated.

8. Photodiodes Infrared LED Meter movement Balance arm Tare pan Sample platform Thermocouple Sample pan Furnace assembly Purge gas outlet Heater Elevator base Purge gas inlet Sample pan holder Features of the Q500 TGA 1. Q Series Two Point Mass Adjustment • 200mg range • 1000mg. range • *No need to do a mass recalibration • when switching from regular Pt pans to • Pt pans with Al hermetic pans. • *Mass Loss Reference Materials • Materials with nominal 2%, 50% and 98% mass loss are available for verification of TGA weight calibration. • 2. Curie Point Transition Temperature • Calibration • ASTM 1582 • *Curie Temperature Reference Materials: • TA Instruments is the exclusive worldwide distributor for a set of six certified and traceable Curie temperature materials developed by ICTAC

9. Q50/Q500 Features and Options FeatureQ500Q50 Furnace – low mass Standard Standard Furnace – EGA Option Option Temperature Range RT-1000°C RT-1000°C MFC / GSA Standard Option Autosampler Option NA Hi-Res TGA™ Option NA Modulated™ TGA Option NA Touch-screen display Standard NA TGA / MS operation Option Option TGA / FTIR operation 3rd Party 3rd Party NA = Not Available

10. Standard Furnace Low mass Used for Hi-Res Runs Cools down in <20min EGA Furnace Higher Mass Used for EGA runs due to quartz liner Cools down in ~40min TGA Furnaces

11. TGA: Purge Gas Flow 40ml/min 10ml/min 90ml/min 60ml/min EGA Furnace Standard Furnace

12. Standard Furnace

13. Balance Purge Quartz Liner Sample Thermocouple Sample Pan Off-Gases Purge Gas In Furnace Core EGA Furnace Schematic Low internal Volume ~15ml

14. TGA: How the balance works • The balance operates on a null-balance principle. At the zero, or “null” position equal amounts of light shine on the 2 photodiodes. • If the balance moves out of the null position an unequal amount of light shines on the 2 photodiodes. Current is then applied to the meter movement to return the balance to the null position. • The amount of current applied is proportional to the weight loss or gain.

15. TGA: Q Series MFC and GSA MFC and GSA standard on Q500 and optional on Q50

16. TGA: Q-Series Purge Gas Plumbing • Instruments w/o MFC • The gas 1 port purges the sample area only. • The gas 2 port purges the balance area only. • Instruments w/ MFC • The gas 1 port purges both sample and balance areas. • The gas 2 port is used when a different purge gas is required or gas switching is used. • Selection of gas on NOTES page is critical for proper use of MFC calibration tables.

17. Heat Exchanger – Cleaning • Check cleanliness (no algae growth) once every 3-6 months. • To clean dump old water, fill with new and add conditioner (algae growth suppressor) if available. • For Q series, after filling, in software choose “Control \ Prime Exchanger”. • For 2xxx, after filling, continue starting a dummy run until error 119 (heat exchanger – no flow) goes away.

18. TGA Performance Criteria • Baseline • Drift • Affected by TGA construction, balance quality, and buoyancy effect (minimized through proper construction techniques and purge gas control) • Sensitivity • Affected by TGA balance quality • Reproducibility • Affected by balance quality, temperature control, and construction quality • Temperature Accuracy • Affected by thermocouple placement, calibration stability, purge gas interaction

19. TGA Performance • TGA Performance is primarily a function of balance sensitivity and baseline stability • Balance sensitivity is optimized through design and construction techniques • Baseline stability is a function of instrument design, as well as purge gas control • TGA resolution is primarily a function of heating rate, but can be optimized using Hi-Res TGA

20. Quantifying TGA Baseline Performance Drift Unnormailzed Sample Mass Temperature or Time

21. Measuring Q500 TGA Baseline Performance Drift ~19 mg Q500, 20°C/min Ramp

22. TGA: Calibrations • Mass (Verify monthly) • Temperature (Verify monthly) • Platform (Perform if there is a problem picking up pans.) Q series instruments w/ MFC will also have options to calibrate the sample and balance MFC’s. These have been calibrated by TA Instruments and should not require further calibration. Contact TAI if a problem arises.

23. TGA: Mass Calibration Two point mass adjustment: 2050, 2950, Q50, Q500 • 100mg. (2XXX modules) or 200mg (Q series) range (use 100mg. weight) • 1000mg. range (use 1000mg. weight) • Q5000IR – 100mg • Run TGA weight calibration routine • Follow screen instructions to tare and masscalibrate using two calibration weights (if known,enter exact mass of calibration weights)

24. Mass Loss And Residue Validation 2.4 % 49.7 % 99.1 % 0.017% P/N 952540.901 TGA / SDT Mass Loss Reference Materials Kit $1,760 Mass Loss Reference Materials: Materials with nominal 2%, 50% and 98% mass loss are available for verification of TGA weight calibration.

25. Temperature Calibration: Curie Point Transition • Paramagnetic - a material that is susceptible to attraction by a magnet • Curie Point Temperature - that temperature where the material loses its magnetic susceptibility (defined as offset point) • Requires a magnet and well characterized transition materials • ASTM 1582 - Standard Practice for Calibration of Temperature Scale for Thermogravimetry

26. TGA: Temperature Calibration Vertical Balance Configuration - TGA 2050/2950/Q50/Q500 Tare Sample % Offset Furnace temp Attraction of Sample to Magnet Results in Initial Weight Gain Magnet

27. TGA: Temperature Calibration Important Points • Clear the ‘Temperature Table’ before performing the calibration runs (TGA only). • Choose method end condition of “Furnace Closed”. This prevents the potential of the furnace opening onto the magnet at the end of the run and damaging the TGA. • Start run and then put magnet under furnace. This allows capture of the weight increase (decrease) at the beginning. • Use of a small labjack is recommended for holding the magnet in place under the furnace.

28. Standards Can Be Run Simultaneously Alumel 157.00C Nickel 368.80C

29. Calcium Oxalate “Standard” Analysis • Although Calcium Oxalate is not generally accepted as a “Standard Material,” it does have practical utility for INTRA-laboratory use • Carefully control the experimental conditions; i.e. pan type, purge gases/flowrates, heating rate • Particularly control the amount (~5mg) and the particle size of the sample and how you position it in the pan • Perform multiple runs, enough to do a statistical analysis • Analyze the weight changes and peak temperatures and establish the performance of YOU and YOUR instrument • When performance issues come up, repeat the Calcium Oxalate analysis

30. Calcium Oxalate Decomposition • 1st Step CaC2O4•H2O (s) CaC2O4 (s) + H2O (g) Calcium Oxalate MonohydrateCalcium Oxalate • 2nd Step CaC2O4 (s) CaCO3 (s) + CO (g) Calcium Oxalate Calcium Carbonate • 3rd Step CaCO3 (s) CaO(s) + CO2 (g) Calcium Carbonate Calcium Oxide

31. Calcium Oxalate Repeatability Overlay of 8 runs, same conditions

32. Calcium Oxalate Repeatability

33. General Considerations(Experimental Effects)

34. TGA Curves are not ‘Fingerprint’ Curves • Pan material type, shape and size. • Ramp rate. • Purge gas. • Sample mass, volume/form and morphology. Because most events that occur in a TGA are kinetic in nature (meaning they are dependent on absolute temperature and time spent at that temperature), any experimental parameter that can effect the reaction rate will change the shape / transition temperatures of the curve. These things include:

35. Effect of Sample Size on Decomposition Temperature

36. Effect of Heating Rate on Decomposition Temperature

37. Mass Effect – Semi-crystalline PE

38. Shift in Onset with Ramp Rate

39. Typical Applications • Thermal Stability • Compositional Analysis • Oxidative Stability

40. Thermal Stability of Polymers

41. TGA of an Adhesive 25.18mg of an adhesive @ 10°C/min

42. Inset View Shows Strange Result Is this real?

43. Use time based derivative of temperature to plot the heating rate

44. Aberration in Heating Rate Usually means that the sample touched the thermocouple

45. Typical Applications • Thermal Stability • Compositional Analysis • Oxidative Stability

46. PET w/ Carbon Black Filler How much Carbon Black was in this sample?

47. PET

48. Comparison of Filled & Un-Filled PET

49. 100 (A) Polymer Air Carbon Black \\ \\ 0 100 "Light" Oil (B) Air Polymer WEIGHT (%) Carbon Black \\ \\ 0 100 Polymer + "Heavy" Oil (C) Air Carbon Black 0 TEMPERATURE (°C) Filled Polymer Analysis Inert filler Inert filler Inert filler

50. Kinetic Analysis • The rate at which a kinetic process proceeds depends not only on the temperature the specimen is at, but also the time it has spent at that temperature. • Typically kinetic analysis is concerned with obtaining parameters such as activation energy (Ea), reaction order (k), etc. and/or with generating predictive curves.