The efficiency of atomisation of sodium, potassium and lithium in the air—acetylene flame

Abstract

The efficiencies of atomisation (β) of Na, K and Li in the air—acetylene flame are found to be 0.98, 0.85 and 0.26 respectively. The β value for K is higher than previously determined values. For Na, the β value was obtained from a comparison of the flame profiles of Na atoms with those of Ag which is completely atomised. The β values for K and Li were measured by a relative atomic absorption method using Na as a reference element. The flame profiles of Na, K and Li indicate differing extents of compound formation which are in agreement with the measured β values. The principal compound formed is assumed to be the hydroxide; no evidence is found to support a significant extent of formation of any oxide or carbide. It is shown by analysing relative concentration data that the concentration of the alkali metal atom (M) is controlled by the equilibrium MOH + H ⇌⇌ M + H 2O. This is the same equilibrium as is found in hydrogen flames. Calculations of β from values of the free-energy change (Δ G) for the above equilibrium at 2400K give values which agree well with the experimental values.