Pw. Morrison et al., IN-SITU FOURIER-TRANSFORM INFRARED CHARACTERIZATION OF THE EFFECT OF ELECTRICAL FIELDS ON THE FLAME SYNTHESIS OF TIO2 PARTICLES, Chemistry of materials, 9(12), 1997, pp. 2702-2708
Electric fields facilitate flame synthesis of powders with precisely c
ontrolled size and composition. Fourier transform infrared (FTIR) spec
troscopy 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 de 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 ha
ve the same temperature. Electric fields modestly increase the flame t
emperature. The FTIR measured mole fractions of HCl are in good agreem
ent with a mass balance indicating that all TiCl4 is converted to TiO2
by either direct hydrolysis or oxidation followed by hydrolysis of Cl
-2. The absorption spectrum of the TiO2 indicates that the particles s
catter like a collection of ellipsoids. In the absence of electric fie
lds, 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 field
s, however, that concentration decreases by 70% over the same distance
. Thus, FTIR spectroscopy is a powerful diagnostic tool that can provi
de in situ information of the temperature, composition, and particle c
haracteristics in the adverse environment of electrically modified fla
mes.