1. Thermogravimetry Duncan Price IPTME, Loughborough University © Copyright: D.M.Price@lboro.ac.uk (2006)

2. definitions “…. a technique in which the mass of a substance is measured as a function of temperature, while the substance is subjected to a controlled temperature programme.” “Controlled temperature programme” can mean: heating and/or cooling at a linear rate (by far commonest) isothermal measurements combinations of heating, cooling and isothermal stages other, more modern approaches, in which the temperature profile is modified according to the behaviour of the sample.

3. instrumentation GAS-TIGHT ENCLOSURE SAMPLE HEATER TEMPERATURE PROGRAMMER BALANCE CONTROLLER POWER FURNACE TEMP. SAMPLE TEMP. WEIGHT GAS IN

4. balance/furnace configurations

5. example curve Mass (%) in green, rate of mass loss (%/°C) in blue.

6. physical limitations on the heating process CONVECTION THROUGH SURROUNDING ATMOSPHERE CONDUCTION THROUGH SAMPLE PAN AND INSTRUMENT RADIATION FROM FURNACE WALL EXCHANGE OF GASES: REACTING GASES IN, PRODUCTS OUT INDICATION OF SAMPLE TEMPERATURE

7. factors that affect the results A) INSTRUMENTAL heating rate furnace atmosphere and flow-rate geometry of pan and furnace material of pan B) SAMPLE-RELATED mass particle size sample history/pre-treatment packing thermal conductivity heat of reaction For a given instrument, careful standardisation of experimental procedures leads to highly reproducible results.

8. effect of heating rate 10 mg samples of PTFE, heated at 2.5, 5, 10 and 20 °C/min in nitrogen

9. isoconversion kinetic treatment

10. lifetime prediction

11. effect of atmosphere CaC 2 CO 4.H 2 O in air and nitrogen

12. sources of error A) MASS Classical buoyancy Effect temp. on balance convection and/or turbulence viscous drag on suspension B) TEMPERATURE Temperature calibration difficult to carry out accurately. Many methods exist, but none totally satisfactory. Best accuracy from simultaneous TG-DTA or TG-DSC instrument. These are lumped together as the “buoyancy” correction, and if significant, can be allowed for by a blank run NOISY OR ERRATIC RECORDS CAN ARISE FROM: static vibration pressure pulses in lab. uneven gas flow

13. calibration MASS - Use standard weights. Use standard samples to check operation, but unwise to use them as weight standards. TEMPERATURE - Four approaches: Observe deflection on Temperature/time curve Curie-point standards Drop-weight methods In simultaneous-type units, use melting standards DO NOT use decomposition events to define temperature.

14. calibration using sample thermocouple

15. calibration using drop weight

16. calibration using curie point weight change/ mg temperature /°C 350 370 0.0 0.2 Nickel metal 3°C/min. in nitrogen

17. calibration using TG-DTA

18. polymer stability studies a = PVC, b= nylon-6, c = LDPE, d= PTFE

19. compositional analysis of filled rubber

20. composition of PVAc

21. LDPE/nylon film

22. sample controlled TG

23. comparison of temperature programmes

24. modulated temperature thermogravimetry

25. thermogravimetry-EGA by mass spectroscopy

26. simultaneous DSC/DTA-thermogravimetry TRTR ΔTΔT S R

27. simultaneous DSC-thermogravimetry

28. TGA-MS of PVC

29. thermogravimetry-EGA by FTIR

30. summary PROCESSWEIGHT GAINWEIGHT LOSS Ad- or absorption Desorption, drying Dehydration, desolvation Sublimation Vaporisation Decomposition Solid-solid reactions (some) Solid-gas reactions Magnetic transitions

31. recommended reading D. M. Price, D. J. Hourston & F. Dumont, “Thermogravimetry of Polymers”, R. A. Meyers (Ed.), Encyclopedia of Analytical Chemistry, John Wiley & Sons Ltd., Chichester (2000) pp. 8094-8105. G. R. Heal,”Thermogravimetry & Derivative Thermogravimetry”, in P.J. Haines (ed.) Principles of Thermal Analysis & Calorimetry, ch. 4, Royal Society of Chemistry, Cambridge (2002) pp. 10-54. C. M. Earnest (Ed.), Compostional Analysis by Thermogravimetry, ASTM STP 97, American Society for Testing and Materials (1988).