In Situ Fourier Transform Infrared Characterization of the Effect of Electrical Fields on the Flame Synthesis of TiO2Particles

Abstract

Electric fields facilitate flame synthesis of powders with precisely controlled size and composition. Fourier transform infrared (FTIR) spectroscopy is used for the first time to measure the effect of electric fields on the process temperature and composition during synthesis of titania powders by TiCl4 oxidation in a premixed methane−oxygen flame; flat electrodes apply a dc electric field to the flame. Emission and transmission FTIR spectra are taken at various flame heights. At each height, the FTIR measurements reveal that the particles and the gas have the same temperature. Electric fields modestly increase the flame temperature. The FTIR measured mole fractions of HCl are in good agreement with a mass balance indicating that all TiCl4 is converted to TiO2 by either direct hydrolysis or oxidation followed by hydrolysis of Cl2. The absorption spectrum of the TiO2 indicates that the particles scatter like a collection of ellipsoids. In the absence of electric fields, the particle mass concentration decreases by 20% from 0.3 to 1.3 cm above the burner by gas dilution. In the presence of electric fields, however, that concentration decreases by 70% over the same distance. Thus, FTIR spectroscopy is a powerful diagnostic tool that can provide in situ information of the temperature, composition, and particle characteristics in the adverse environment of electrically modified flames.