Hydrogen defects in alpha-Al2O3 and water weakening of sapphire and alumina ceramics between 600 and 1000 degrees C - I. - Infrared characterization of defects

Hydrogen impurities in materials influence their properties, including flow strength, alpha-Al2O3 single crystals and polycrystalline ceramics were an nealed in supercritical water between 850 and 1025 degrees C, under pressur es in the range 1500-2000 MPa. A few specimens were further subjected to pl astic deformation. Hydrogen penetration was examined using infrared absorpt ion measurements of O-H bond vibrations, which revealed two kinds of hydrog en defects. In single crystals, defects are characterized by sharp O-H abso rption bands assigned to interstitial protons. Hydrogen impurities of hydro thermally annealed ceramics and of all hydrothermally deformed specimens ar e characterized by broad O-H bands assigned to molecular water. The grain b oundaries of hydrothermally annealed ceramics are severely damaged. The kin etics of hydrogen penetration is consistent with diffusion data. (C) 2000 A cta Metallurgica he. Published by Elsevier Science Ltd. All rights reserved .