AKTS advanced thermal analysis software

TG-EGA Systems (Evolved Gas Analysis, MS and/or FTIR) / Problems related to the identification of thermal decomposition of solids

Solid state kinetic analysis can be also used for the elaboration of the results obtained by hyphenated techniques such as TG-MS or TG-FTIR. The application of these techniques is widely recognized for the characterization of the degradation of solids [1].

One of the problems related to the measurement and analysis of material decomposition is the time lag observed between:

- the DTG- (or TG) signal due to the decomposition of the solids

and

- the MS or FTIR signal of the evolving gas (EGA signals).

In order to apply correctly the EGA signals for the description of the kinetics of the decomposition of solids, the interrelation between thermoanalytical and mass spectrometric curves in the TA-MS and/or TA-FTIR system has to be known. The proper description of the input signal DTG by the output signal (EGA) depends on the convective and diffusional mass transfer occurring in combined thermoanalyzer-EGA systems [2]. More generally, the difference between input and output signals depends on:

the carrier gas flow rate (residence time in the thermoanalyzer chamber and distance between thermoanalyzer and EGA system)
the back-mixing of the carrier gas in the thermoanalyzer chamber (mixed-flow volume and plug-flow volume)
the choice of the carrier gas (the diffusion of the evolved gas in the carrier gas)
the temperature (non-isothermal experiments progressively modify the diffusion of the evolved gas in the carrier gas)

[1] K.G.H. Raemaekers, J.C.J. Bart, Thermochim. Acta, 295 (1997) 1.
[2] B. Roduit, J. Baldyga, M. Maciejewski and A. Baiker, Thermochim. Acta, 295 (1997) 59.