Isothermal oxidation of tetragonal PbO in air produced multiphase assemblages with apparent equilibrium compositions which varied linearly with temperature from PbO1.548 at 286°C to PbO1.333 at 351°C. Oxidation at each temperature was relatively rapid to PbO1.40 and very slow from PbO1.40 to apparent equilibrium values. Pseudocubic PbO1+x, with compositions between PbO1.41 and PbO1.57, was indexed on a cubic unit cell at the lower O/Pb ratios and on a tetragonal unit cell at the higher ratios. Linear changes in lattice parameters and deviation from cubic symmetry accompanied reversible oxidation and reduction of the phase. Pseudocubic PbO1+x was reduced irreversibly to Pb3O4 below the composition PbO1.41. Hexagonal PbO1+x, with compositions between PbO1.333 and PbO1.41, developed to a maximum of 60% at intermediate temperatures. The hexagonal phase oxidized irreversibly to pseudocubic PbO1+x at lower temperatures and reduced irreversibly to Pb3O4 at higher temperatures. The extent of oxidation at a given temperature was greater in PbO with a mean diameter of 0.52 μm than in PbO with a mean diameter of 2.89 μm, indicating a metastable assemblage. Linear variation of oxidation limits with temperature across the composition boundary between the PbO1+x phases suggests that the free energies are equal at PbO1.41, with the lower limit of pseudocubic PbO1+x determined by tolerance of the structure for oxygen vacancies. Copyright © 1973, Wiley Blackwell. All rights reserved


Materials Science and Engineering

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1551-2916; 0002-7820

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Article - Journal

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© 2023 Wiley, All rights reserved.

Publication Date

01 Jan 1973