Abstract
Films formed on Alloy C22 and on unalloyed chromium and molybdenum in 1M NaCl and 1M HCl were investigated in situ by surface enhanced Raman spectroscopy (SERS). The films formed on all metals were dependent on pH, temperature and potential. Alloy C22's films were similar to those of chromium, especially in 1M NaCl. At low potentials in 1M NaCl the passive films consisted largely of Cr(OH)3. A second Cr compound, possibly Cr2O3, formed at higher potentials. In addition, Cr(VI) formed within Cr's passive film at transpassive potentials at room temperature. SERS indicated the presence of Cr (VI) in Alloy C22's passive film at transpassive potentials only at high temperature. There was no evidence of molybdenum compounds in the films formed in 1M NaCl. In 1M HCl, the passive films of Cr and Alloy C22 consisted mostly of amorphous Cr(III) oxide. A molybdenum compound was part of Alloy C22's film in 1M HCl and in 1MNaCl at high temperature.
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