Compound Formation and Phase Equilibria in the System PbO-SiO2

Compound formation in the system PbO-SiO₂ was studied; the results are contrasted with those previously reported. Fifteen binary phases, 4 of which had not been reported, were prepared in the present study. The new phases include Pb₅Si₈O₂₁, an orthorhombic polymorph of PbSiO₃, Pb₃SiO₅, and a high-SiO₂ phase containing ∼ 60 mol% SiO₂. It was shown that Pb₃SiO₅ is thermodynamically stable relative to Pb₂SiO₄ and 4PbO.SiO₂ below 640±5°C. A revised phase equilibrium diagram is presented.