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Removal of residual chromium from aluminum oxide by containerless liquid-phase processing
Published online by Cambridge University Press: 03 March 2011
Abstract
Verneuil sapphire was purified of Cr3+ by containerless melting and processing at ca. 2550 K in argon, dry air, and pure oxygen. Recovered material was examined by laser induced fluorescence and Raman spectroscopy. The Cr3+ fluorescence intensity decreased in processed specimens at rates proportional to the chromium concentration and p(O2)0.21. The initial chromium concentration was ca. 5 ppm and decreased by factors of ca. 50, 3000, and 2 × 105 after processing for 300 s in argon, air, and oxygen, respectively. Evidence is presented that the Cr3+ was removed predominantly as CrO2(g) and not by conversion to other oxidation states of chromium in the condensed phase.
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