Effect Of Water And Its Derived Impurities On Metal Oxides

Water, an ubiquitous impurity in all phases of materials processing, degrades the near-infrared transmission of metal halides and oxides. With the halides, one deals with both the oxygen and hydrogen impurities derived from H2O, while with the oxides, only the H-impurity. The electrolytic and thermal dissociation modes of H2O become significant at the much higher process temperature of the refractory metal oxides. Because of the high strength of the oxide ion as a Lewis base, halogen atoms are unable to abstract the proton of the H-impurity. However, they can displace by electron transfer the H-impurity as the unit OH, a pseudohalide. The limitation and application of the use of halogens to clean up H-impurities in metal oxides are demonstrated with the use of basic and acidic metal oxides.