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
C. A. Sorrell, "Oxidation Of Tetragonal PbO In Air," Journal of the American Ceramic Society, vol. 56, no. 12, pp. 613 - 618, Wiley, Jan 1973.
The definitive version is available at https://doi.org/10.1111/j.1151-2916.1973.tb12437.x
Materials Science and Engineering
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01 Jan 1973