Development of a TG-FTIR system for investigations with condensable and corrosive gases

A thermogravimetric analyzer and a Fourier-transform infrared (FTIR) spectrometer were combined and redesigned for investigations with corrosive and condensable reactive gases. The standard gas inlet and outlet of the thermogravimetric analyzer were changed in order to heat the gas tubes, which are lead through the flanges, and avoid condensation in these parts of the system. Furthermore, all tubes upstream and downstream of the thermogravimetric analyzer were trace heated up to 180 °C. The gas measuring cell of the FTIR spectrometer was designed such that an optimum compromise between the small flow rates through the thermogravimetric analyzer and a short residence time of the gases in the gas measuring cell could be achieved. The gas supply allows the dosage of different gas compositions containing nitrogen, oxygen, water, NH₃, and NO₂, for example. The system was validated by analyzing the composition of a diesel particulate matter (PM) sample with a temperature-programmed desorption followed by oxidation (TPD/O) experiment, which showed good agreement with the established analysis methods. The reactivity of the PM sample was investigated by temperature-programmed oxidation (TPO) experiments with different reactive gas mixtures of oxygen, water, and NO₂ in nitrogen. By adding NO₂, the soot oxidation started at lower temperatures and the addition of water lead to a shift of the maxima of the carbon oxidation rates to lower temperatures. The ratio of formed CO₂ and CO was shifted to higher values by the addition of NO₂ and water whereby the influence of water was much more pronounced.