氧化与老化机理.pdfVIP

CHAPTER 7 Oxidation and Reduction Mechanisms As was discussed in Chapter 5, the solubility of oxides, in general, decreases with the oxidation state. Monovalent alkali metal oxides are highly soluble, and most of the divalent oxides are sparsely soluble. Trivalent oxides such as alumina and hematite (Fe O ) exhibit very low solubility but are more soluble than quadrivalent oxides 2 3 containing titanium, lanthanides, and actinides. Fortunately, some of the metals have ¨ more than one oxidation state. For example, iron oxide is found as divalent wustite (FeO), as trivalent hematite (Fe O ), or as a combination of the two as magnetite (Fe O ). 2 3 3 4 Uranium oxide is found as U O and UO . Likewise, cerium is found as Ce O and CeO . 2 3 2 2 3 2 If one can reduce the oxides of higher oxidation states into lower ones and dissolve them in acidic aqueous solution, one may be able to produce CBPCs of these oxides. As was mentioned in Chapter 2, attempts to reduce oxides in forming phosphate glues were reported in the early literature. For example, Fedorov et al. [1] used a mixture of copper oxide (CuO) and metallic copper and developed a phosphate bonding agent for metals, where metal copper must have acted as the reductant. They also cite formation of phosphate glues with ZrO2 and with CaZrO3 in combination with Ni, Cr, and Ti. Some hazardous metals such as chromium (Cr) and radioactive fission products such as technetium (Tc) exhibit exactly opposite solubility characteristics as compared to the metals discussed above. These metals in