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Passivity Mechanisms in Stainless Steels: Mo-N Synergism.
Rept. for Jun 85-Jun 86,
STATE UNIV OF NEW YORK AT STONY BROOK DEPT OF MATERIALS SCIENCE AND ENGINEERIN G
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Increasing the N content of a commercial grade 18-8 Stainless steel from 0.04 to 0.24 N was found to raise the breakdown potential from 200 mV to 304 vV in deaerated 0.1M HCl pH 1.2. In deaerated 0.5M H2SO4 0.5M NaCl pH 0.4 the 0.04 N alloy pitted at 448 mV. The 0.24 N alloy exhibited breakdown at 448 mV, a pitting inhibition potential at 540 mV, and a final pitting potential at 640 mV. Variable angle XPS studies of the passive film formed on the 0.24 N alloy at 0 mV after 10 seconds and 1 hour provided evidence of the role of N and SO4 in the initial stages of repassivation. The N was found to exist in three forms, namely CrN 397.1 eV at the metal-film interface, a complex of NH3 or NO 399.6 eV distributed throughout the passive film, and an ammonium salt 401.5 eV observed at the passive film-solution interface.
APPROVED FOR PUBLIC RELEASE