5.2.1 Thermal analysis
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
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
Isobaric mass-change determination
Evolved gas detection
Evolved gas analysis
Emanation thermal analysis
Heating or cooling curve determination
Differential thermal analysis
Differential scanning calorimetry*
Dynamic thermomechanical measurement
Chapter 5 - 1
Acceptable abbreviation TG
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.
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.
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.
A plateau (AB, Fig.5.1) is that part of the TG curve where the mass is essentially constant.
Chapter 5 - 2
Fig. 5.1 Formalized TG Curve
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.
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.