Studies on the ionization produced by metallic salts in flames II. Reactions governed by ionic equilibria in coal-gas/air flames containing alkali metal salts

Abstract

The ionization produced by adding alkali metal salts to coal-gas/air flames has been studied by measuring the attenuation of 3 cm. waves, this attenuation arising from free electrons. In a previous paper (Belcher & Sugden 1950) the coefficient relating attenuation to electron population has been determined and is used in applying the present results to the problems of chemical equilibrium involving ions in the flames. An examination has been made of the degree of equilibrium obtained in a number of chemical reactions in the flame by varying the electron content, the amount of added alkali metal salt, and its nature. Flame temperatures were measured by the sodium line-reversal method, considered to be the most suitable for the purpose. In the case of potassium bicarbonate the results are compatible with chemical equilibrium of the ions if suitable account is taken of other equilibrated reactions involving potassium hydroxide, oxide and hydroxyl ions. Some evidence of disequilibrium has been observed when potassium halides are added, where both formation of negative halide ion and halogen acid affect the electron content. This appears to be connected with concentrations of hydrogen atoms and hydroxyl groups (chain centres) which diverge from the values expected at equilibrium. Addition of extra free halogen confirms the anomalies. In the case of the chlorides and fluorides, the halogen appears to be completely removed as halogen acid. A comparison of the alkali chlorides on the whole supports the use of the Saha equation relating equilibrium ionization and flame temperature, providing account is taken of side reactions.