Ionisation in Flames, with Special Regard to Aluminium

Abstract

The gas phase equilibria between aluminium metal, oxygen, and hydrogen, existing in a laminar, premixed hydrogen-oxygen flame, have been investigated by a quantitative study of the emission spectra from the metal and its monoxide. The stability of the monoxide was estimated by second and third law methods, and a thermochemical analysis was made to determine the nature of possible aluminium compounds containing both hydrogen and oxygen, which were believed to be the major species present. The measurements were carried out at flame temperatures above 2300 K, below which it was found that alumina particles were formed in the flame, when aluminium was added in the form of vapours of its isopropoxide. Also as a parallel topic, a study was made using a rotating electrostatic probe, of inhomogeneous distributions of charged species in the flame. The ionisation was produced by seeding the flame with both stable inert particles, and small evaporating crystals. The observations gave information on the relative particle gas velocities in the flames used, and the chemical origin of the ionisation detected in the region of the particles.