Iron compounds in flames. Relative stabilities of Fe, FeO, FeOH and Fe(OH)2

Abstract

Spectrophotometric studies have been made of gas-phase Fe-containing species in fuel-rich premixed atmospheric-pressure laminar H₂+ N₂+ O₂ flames to which iron is added. The principal compound formed by Fe under the conditions of this work is shown to be FeOH, which is accompanied by lesser amounts of atomic iron, FeO and Fe(OH)₂. Standard zero-point enthalpy changes and equilibrium constants are determined for two important reactions: Fe + H₂O ⇌ FeOH + H; ΔH^°₀= 110 ± 20 kJ mol^–1, K= 66 exp(– 16 100 K/T); Fe + OH ⇌ FeO + H; ΔH^°₀= 22 ± 20 kJ mol^–1, K= 6.67 exp(– 3 160 K/T). The results give standard zero-point enthalpies of formation for FeOH(g) and FeO(g) from Fe(s), O₂(g) and H₂(g) of 69 ± 20 and 259 ± 20 kJ mol^–1 respectively.