Measurement of Small Volume Flame Temperatures by the Two-Line Atomic Fluorescence Method

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Abstract
Measurement of small volume temperatures of analytical flames by the two-line atomic fluorescence technique involving the use of direct-line Stokes and anti-Stokes fluorescence of indium and thallium has been examined. Spatial flame temperatures have been measured with a volume resolution of 0.3 mm by 2 mm by 5 mm in the flame. Theoretical and practical considerations of the method are given, particularly in terms of the limitation of using indium or thallium. The use of the two thallium lines (377.57 and 535.05 nm) was subject to fewer random errors than the use of the two indium lines (410.18 and 451.13 nm) for the range of temperatures studied. However, thallium lines are restricted to the measurement of temperatures above about 2000°K (for the air-acetylene and nitrous oxide-acetylene flames); for temperatures below about 2000°K, the fluorescence irradiance ratio could not be measured with sufficient signal/noise ratio due to the low intensity of the anti-Stokes fluorescence line. In the present experiment, indium lines were used for the measurement of a wide range of “low” flame temperatures (approximately 700 to 2600°K) owing to the better signal/noise ratios for both lines; indium lines were also preferable for the air-acetylene flame, even though the error produced by the random uncertainty in the fluorescence ratio was larger than for thallium. The present method has been successfully applied to the measurement of the spatial temperature profiles of analytical flames, such as argon-hydrogen(-entrained air), argon-oxygen-hydrogen, air-acetylene, and nitrous oxide-acetylene.