TABLE OF CONTENTS Many samples, on heating, release gases or vapour through desorption or decomposition. This release is accompanied by thermal effects and, obviously, mass-losses, which, themselves, can be detected by the appropriate thermal analysis technique, e.g. DTA or DSC and TG, respectively. The thermal analysis technique does not, however, identify the gas evolved and, for complex decompositions, such information is essential. It has thus become fairly routine to couple the basic techniques already described with a system for either detecting the evolution of gas (or gases) from the sample ( evolved gas detection, EGD) or, more satisfactorily, detecting and identifying the gases evolved ( evolved gas analysis, EGA) [1], [2], [3], [4]. The apparatus for EGA will obviously be more complex than that required for EGD. Gas-solid reactions can also be studied by determining the amounts of products formed or reactant gas consumed. A novel technique on this principle is pulsed (gas) thermal analysis [5] (see below).
In practice, the main techniques in current use for EGA are mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTIR). Because of the time intervals required between sampling, gas chromatography (GC) (see below) has declined in usage. If the evolved gas mixtures are so complex that preliminary separation is required. GC may be used for the separation coupled with MS or FTIR for the analysis.
The main thermal analysis technique with which EGA has been coupled is thermogravimetry (TG) and simultaneous techniques (see Chapter 7)...
