“…. 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.
GAS IN
WEIGHT
BALANCE
CONTROLLER
GAS-TIGHT
ENCLOSURE
SAMPLE
HEATER
SAMPLE TEMP.
POWER
FURNACE TEMP.
TEMPERATURE PROGRAMMER
Mass (%) in green, rate of mass loss (%/°C) in blue.
EXCHANGE OF GASES:
REACTING GASES IN,
PRODUCTS OUT
CONVECTION
THROUGH
SURROUNDING
ATMOSPHERE
RADIATION FROM
FURNACE WALL
CONDUCTION
THROUGH SAMPLE
PAN AND
INSTRUMENT
INDICATION OF SAMPLE
TEMPERATURE
A) INSTRUMENTAL
B) SAMPLE-RELATED
• heating rate
• mass
• furnace atmosphere and flow-rate
• particle size
• geometry of pan and furnace
• sample history/pre-treatment
• material of pan
• packing
• thermal conductivity
• heat of reaction
For a given instrument, careful standardisation of experimental
procedures leads to highly reproducible results.
10 mg samples of PTFE, heated at 2.5, 5, 10 and 20 °C/min in nitrogen
CaC2CO4.H2O in air and nitrogen
A) MASS
NOISY OR ERRATIC RECORDS
• Classical buoyancy
CAN ARISE FROM:
• Effect temp. on balance
• static
• convection and/or turbulence
• vibration
• viscous drag on suspension
• pressure pulses in lab.
These are lumped together as the “buoyancy”
• uneven gas flow
correction, and if significant, can be allowed
for by a blank run
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.
a = PVC, b= nylon-6, c = LDPE, d= PTFE
PROCESS
Ad- or absorption
WEIGHT GAIN
WEIGHT LOSS

Desorption, drying

Dehydration, desolvation

Sublimation

Vaporisation

Decomposition

Solid-solid reactions (some)

Solid-gas reactions


Magnetic transitions


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).