A detailed study of the system PbO‐Fe2O3, largely by X‐ray diffraction analysis, has been made. The results indicate the existence of three intermediate phases: (1) a phase (beta) extending from PbO·5Fe2O3 to PbO·6Fe2O3, (2) a phase (gamma) extending from PbO ‐ 2Fe2O3 to PbO ‐21/2Fe2O3, and (3) a phase (delta) 2PbO·– Fe2O3. Structures are proposed for the beta and gamma phases that explain their solubility limits, magnetic properties, and very great similarity in structure and in lattice dimensions.

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The effects of adsorbed H,O on the dielectric properties of ultrafine BaTiO, particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO, materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H,O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accompIished by washing as-received powders in isopropanol.

T h e effect of various gaseous atmospheres (nitrogen, hydrogen, and water vapor) on the fracture strength of single-crystal and polycrystalline A1203 was investigated. Sapphire specimens exposed to hydrogen and nitrogen at elevated temperatures and subsequently tested at room temperature did not become brittle or lose strength. Sapphire specimens exposed to moisture in a specific temperature range showed a definite impairment of strength in subsequent room-temperature bend tests. The strength was recovered when the moisture-exposed specimens were heated to 400OC. It is suggested that the loss of strength and the recovery are due to the formation and decomposition of a surface precipitate, presumably a hydrate of some type.Polycrystalline alumina (Lucalox) did not show any significant loss in strength when exposed to moisture.

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