Thermal gravimetric analysis (TGA) is an ideal tool for the characterization of all kinds of organic and inorganic solids and liquids. Thermodynamic transitions, thermal stability, decomposition and chemical reactions can be detected and quantified with high accuracy over a broad temperature range. However, this method does not provide details about the chemistry behind the processes under study. The combination of thermal analysis with infrared spectroscopy bridges this analytical gap. Fourier-Transform Infrared (FTIR) spectroscopy is a classical tool for the identification and quantification of gases. This technique is based on the interaction of infrared radiation with the vibrating dipole moments of molecules. FTIR yields a unique IR spectrum for each substance, except for homonuclear diatomic gases and pure metals.
In a simple case, only one type of gas molecule is evolved with an applied temperature increase in the TGA. The evolved gas is flowed into the FTIR and can be readily identified by searching its spectrum against a gas phase reference library. In a typical decomposition process, evolved fume is a mixture of gases. Different hardware and software approaches to identify the composition of complex gas mixtures will be presented with a thorough discussion of the following topics:
- Mixture analysis using library search
- TGA-IR at reduced pressure
- Spectra manipulation method for deconvoluting complex spectra (mixtures)
Examples of applications will include the identification of plasticizers in polymers, PVC undercoating analysis, decomposition of PETN explosive, NHF propellant, and others.