Hydrogen defects in #alpha#-Al_2O_3 and water weakening of sapphire and alumina ceramics between 600 and 1000 deg C-I. Infrared characterization of defects

摘要

Hydrogen impurities in materials influence theirproperties, including flow strength, #alpha#-Al_2O_3 singlecrystals and polycrystalline ceramics were annealed m supercriticalwater between 850 and l025 deg C, under pressures in the range1500-2000 MPa. A few specimens were further subjected toplastic deformation. Hydrogen penetration was examined usinginfrared absorption measurements of O-H bond vibrations, whichrevealed two kinds of hydrogen defects In single crystals, defectsare characterized by sharp O-H absorption bands assigned tointerstitial protons. Hydrogen impurities of hydrothermallyannealed ceramics and of all hydrothermally deformed specimensare characterized by broad O-H bands assigned to molecular water.The grain boundaries of hydrothermally annealed ceramics areseverely damaged. The kinetics of hydrogen penetration isconsistent with diffusion data.