Mechanism of selenium hydride atomization, fate of free atoms and temperature distribution in an argon shielded, highly fuel-rich, hydrogen-oxygen diffusion micro-flame studied by atomic absorption spectrometry

The mechanism of selenium hydride atomization and the fate of free atoms were investigated in a flame-in-gas-shield atomizer. The spatial distribution of free atoms was estimated from lateral absorbance profiles scanned at various observation heights. Spectroscopic temperature measurements based on atomic absorption at 196.1 and 204.0 nm Se lines were performed at an oxygen flow rate of 20 ml min(-1). A maximum temperature of close to 1600 degreesC was found in the core of the micro-flame. Temperature decreased steeply with distance from the micro-flame to reach 900 and 600 degreesC, respectively, at observation heights of 5 and 10 mm. Mercury was employed as an analyte to study the physical processes controlling the distribution of analyte atoms. It was found that the hydride is completely atomized by interaction with a cloud of hydrogen radicals before the analyte passes from the zone 2 mm above the top of the atomizer. Free analyte atoms form a cone that narrows with increasing observation height and disappear outside by reaction with molecular oxygen transported to the column of free atoms by local turbulence through the protecting gas shield. Possible ways of improving the performance of the protecting gas shield are suggested.