Real-Time Measurements of Deposit Formation from Sodium Sulfate-Seeded Flames

Abstract

The formation of deposits on substrates immersed in the exhaust gases of a sodium sulfate-seeded flame has been studied in real time using surface Raman scattering and interferometry. Deposits were produced on Pt/10% Rh or Incoloy 800 substrates maintained at 825 K by injecting solid Na₂SO₄ particles into a CH₄/O₂/N₂ flat-flame burner. For Na₂SO₄ deposits grown on inert substrates (Pt/10% Rh), the relationship between the sulfate Raman scattering signal and the interferometrically-determined deposit thickness was investigated. The composition of deposits produced from flames of varying stoichiometry was characterized by in situ Raman scattering. Na₂CO₃ was produced from fuel-rich flames, while Na₂SO₄ was produced from fuel-lean flames. Mixtures of Na₂CO₃ and Na₂SO₄ were obtained from flames of intermediate stoichiometry. For Na₂SO₄ deposits grown on reactive substrates (Incoloy 800), a rapid reaction occurred between the Na₂SO₄ deposit and the substrate, producing a salt film containing chromate anions (CrO₄ ⁻²).