Application of auger electron spectroscopy to the determination of the composition of passive films on type 316 SS

J. B. Lumsden, R. W. Staehle

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78 Scopus citations
Original languageEnglish (US)
Pages (from-to)1205-1208
Number of pages4
JournalScripta Metallurgica
Issue number12
StatePublished - Dec 1972

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The results presented in Figure l indicate that there is a depletion of Fe and Ni in the film relative to that in the substrate, but the film is somewhat enriched in Cr. No Si nor Mo enrichment was found in the film; indeed there was a depletion of these elements near the surface. This is inconsistant with the results of Rhodin (lO,ll) who, using a microchemical method on films isolated from the substrate, found that passive films on a similar alloy consisted of approximately 14% Si and 4.2% Mo byweight. It should be emphasized, however, that the results herein were for a well defined system with a controlled pH and with the substrate at a constant potential; whereas, those obtained by Rhodin were formed in a 60°C 5% HNO3 - 0.5% K2Cr207 solution with no applied potential. Also, recent AES results on mill-finished 316 without any subsequent surface treatment have indicated a Mo enrichment to about 14% compared to an alloy content of about 2% (12). No enrichment of Mo on the substrate surface was found in the results reported in this paper. One possible consideration for the depletion of Si and Mo near the surface in the results reported in this paper, is loss by evaporation; however, the vapor pressures of Si, Mo, and any possible compounds is so low as to preclude this as an explanation. Figure l also shows that nitrogen is present in the film. While nitrogen is normally found in the alloy at about 0.1%, that observed was probably picked up form the solution. This result is an indication of the sensitivity of the Auger technique to small quantities of environmental species which can be sparingly incorporated in the film. The concentration of the environmental species found in the film decreased as the substrate was approached. Since the sample was thoroughly washed immediately after removal from the solution first in tap water and then in distilled water, the possibility that sulfur and chlorine dried on the surface was eliminated. The origin of the C inside the film is uncertain. Two possible sources are: dissolved CO2 in the solution and diffusion from the substrate. The vacuum system was carbon free. From the uniform decay of the S and Cl Auger peak heights we have concluded that sputtering was reasonably uniform on the area of analysis. Were this not so one would expect a smeared-out distribution of S and Cl. Also an inspection of Figure l indicates that the substrate was reached between 20 and 30 minutes of sputtering time. This suggests a sputtering rate of about 2 A minute for the passive film. Acknowledgement We wish to acknowledge the support of the American Iron and Steel Institute under contract No. 61-244 and the Office of Naval Research under contract No. NOOOI4-67-A-0232-O006. References I. D.F. Stein, A. Joshi and R.P. Laforce, Trans. ASM 62, 776 (1969). 2. H.L. Marcus and P.W. Palmberg, Trans AIME 245, 1664 (1969). 3. R. Viswarathan, Met. Trans. 2, 809 (Ig71). 4. K.N. Goswami and R.W. Staehle, Electrochim Acta 16, 1895 (1971). 5. R.E. Weber and W.J. Peria, J. Appl. Phys. 38, 4355 (1967). 6. P.K. Rol, J.M. Fluit and J. Kistemaker, Ph~sica 26, lOOg (1960). 7. J.M. Schroeer, But1. Am. Phys. Soc. lO, 41 (1967). 8. C.A. Anderson, Intern. J. Mass Spectry. Ion Phys. 2, 61 (1969). 9. A.J. Socha, Sur. Sci. 25, 147 (1956). lO. T.N. Rhodin, Corrosion 12, 123t (1956). II. Ibid., p. 465t. 12. G.J. Barnes, A.W. Aldage and R.C. Jerner, J. Electrochem. Soc. llg, 684 (1972).

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