Techniques in which a physical property of a substance is measured as a function of
temperature whilst the substance is subjected to a controlled temperature programme.
In addition to being more accurate, this definition has the advantage that it can be adapted
to define any thermoanalytical technique by alteration of only a few words in each instance.
It follows from the above definition that some techniques, such as X-ray diffraction or IR
spectroscopy, can, when used in a specific manner, yield thermoanalytical information:
these individual cases are not discussed further.
5.2.2 Individual thermoanalytical techniques
Classification
In the light of the new definition some one hundred techniques known to the Committee
have been assessed and those previously defined, those that have come into prominence in
the interim and those showing prospect of future development were classified to bring out
interrelationships. The arrangement finally adopted for the defined techniques (Table 5.1)
incorporate additional physical properties and/or techniques as necessary: various modes of
certain techniques can also be distinguished.
TABLE 5.1. Classification of Thermoanalytical Techniques
Physical Acceptable
Property Derived Technique(s) abbreviation
Mass Thermogravimetry TG
Isobaric mass-change determination
Evolved gas detection EGD
Evolved gas analysis EGA
Emanation thermal analysis
Thermoparticulate analysis
Temperature Heating or cooling curve determination
Differential thermal analysis DTA
Enthalpy Differential scanning calorimetry* DSC
Dimensions Thermodilatometry
Mechanical charcs. Thermomechanical measurement
Dynamic thermomechanical measurement
Acoustic charcs. Thermosonimetry
Chapter 5 - 2
Thermoacoustimetry
Optical charcs. Thermoptometry
Electrical charcs. Thermoelectrometry
Magnetic charcs. Thermomagnetometry *The confusion that has arisen about this term is resolved by separating two modes (Powercompensation
DSC and Heat-flux DSC) as described in the definition given in the text.
The definitions and conventions of the individual techniques in the order introduced in
Table 5.1 are given as follows.
Some relevant terms especially used at TG and the DTA techniques are also included.
Thermogravimetry (TG)
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.
The record is the thermogravimetric or TG curve; the mass should be plotted on the
ordinate decreasing downwards and temperature (T) or time (t) on the abscissa increasing
from left to right.
Thermobalance
A thermobalance is used for weighing a sample continuously while it is being heated or
cooled.
Heating Rate
The heating rate is the rate of temperature increase, which is customarily quoted in degrees
per minute (on the Celsius or Kelvin scales). The heating or cooling rate is said to be
constant when the temperature/time curve is linear.
Plateau
A plateau (AB, Fig.5.1) is that part of the TG curve where the mass is essentially constant.
Chapter 5 - 3
Initial Temperature
The initial temperature, Ti, (B, Fig. 5.1) is that temperature (on the Celsius or Kelvin scale)
at which the cumulative-mass change reaches a magnitude that the thermobalance can
detect.
Final Temperature
The final temperature, Tf, (C, Fig. 5.1), is that temperature (on the Celsius or Kelvin scale)
at which the cumulative mass change reaches a maximum.
Reaction Interval
The reaction interval is the temperature difference between Tf and Ti as defined above.
Isobaric Mass-change Determination
A technique in which the equilibrium mass of a substance at constant partial pressure of the
volatile product(s) is measured as a function of temperature whilst the substance is
subjected to a controlled temperature programme.
The record is the isobaric mass-change curve; the mass should be plotted on the ordinate
decreasing downwards and temperature on the abscissa increasing from left to right.
Note: Throughout this section substance is to be understood in the sense of substance
and/or its reaction products.
Fig. 5.1 Formalized TG Curve
Chapter 5 - 4
Evolved Gas Detection (EGD)
A technique in which the evolution of gas from a substance is detected as a function of
temperature whilst the substance is subjected to a controlled temperature programme.
Evolved Gas Analysis (EGA)
A technique in which the nature and/or amount of volatile product(s) released by a
substance are/is measured as a function of temperature whilst the substance is subjected to a
controlled temperature programme. The method of analysis should always be clearly
stated.
Emanation Thermal Analysis
A technique in which the release of radio-active emanation from a substance is measured as
a function of temperature whilst the substance is subjected to a controlled temperature
programme.
Thermoparticulate Analysis
A technique in which the release of particulate matter from a substance is measured as a
function of temperature whilst the substance is subjected to a controlled temperature