Oxidation of Metals

, Volume 32, Issue 1–2, pp 89–109 | Cite as

Analyses of the gaseous species in halide-activated cementation coating packs

  • Si -Cheng Kung
  • Robert A. Rapp
Article

Abstract

The partial pressures of equilibrium gaseous species in pack-cementation diffusion processes using pure condensed Al(l), Cr(s), and Si(s) metals activated by various halide salts under Ar or reducing environments which contain different amounts of hydrogen have been calculated. The analyses indicate that the presence of hydrogen gas in the system does not significantly alter the equilibrium partial pressures of gaseous species for a pack containing Al at unit activity. In general, the partial pressures of CrCl2 and SiCl2 are higher in a chloride-activated pack than in a fluoride-activated pack. Therefore, the codeposition of Cr or Si with Al is possible when a chloride salt is used as the activator with a masteralloy of composition dilute in Al. The addition of hydrogen to the gas phase decreases the partial pressure of Cl2 and thereby the partial pressures of CrCl2 and SiCl2. However, the presence of hydrogen and the formation of hydrogen halides and metal hydrides could increase the kinetics of the transporting processes, particularly for the coatings of Cr and Si. The study also indicates that the vapor pressures for the volatile chlorides of Fe are significantly higher than those for Ni or Co, so that displacement reactions leading to the loss of Fe from the substrate are expected for coating processes involving high halide activities.

Key words

cementation pack masteralloy activator halides hydrides thermodynamics diffusion coating 

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References

  1. 1.
    S. R. Levine and R. M. Caves,J. Electrochem. Soc. 121, 1051 (1974).Google Scholar
  2. 2.
    R. A. Rapp, D. Wang, and T. Weisert, InMetallurgical Coatings, M. Khobaib and R. Krutenat, eds. (TMS-AIME, Warrendale, 1987), p. 131.Google Scholar
  3. 3.
    L. L. Seigle, InSurface Engineering, R. Kossowsky and S. C. Singhal, eds. (Martinus Nijhoff Publishers, Boston, 1984).Google Scholar
  4. 4.
    L. L. Seigle, B. K. Gupta, R. Shankar, and A. K. Sarkhel, Kinetics of pack aluminization of nickel (NASA Contract Report 2939, prepared for Lewis Research Center under contract NGR-33-016-160, NASA Scientific and Technical Information Office, 1978).Google Scholar
  5. 5.
    D. C. Tu and L. L. Seigle,Thin Solid Films 95, 47 (1982).Google Scholar
  6. 6.
    R. Sivakumar and L. L. Seigle,Met. Trans. 13A, 495 (1982).Google Scholar
  7. 7.
    B. K. Gupta, A. K. Sarkhel, and L. L. Seigle,Thin Solid Films 39, 313 (1976).Google Scholar
  8. 8.
    B. K. Gupta and L. L. Seigle,Thin Solid Films 73, 365 (1980).Google Scholar
  9. 9.
    N. Kandasamy, F. J. Pennisi, and L. L. Seigle,Thin Solid Films 84, 17 (1981).Google Scholar
  10. 10.
    B. Nciri and L. Vandenbulke,J. Less-Common Metals,95, 55 (1983).Google Scholar
  11. 11.
    S. C. Kung and R. A. Rapp,J. Electrochem. Soc. 3, 731 (1987).Google Scholar
  12. 12.
    W. Johnson, K. Komarek, and E. Miller,Trans. Met. Soc., AIME 242, 1685 (1968).Google Scholar
  13. 13.
    G. Eriksson,Chem. Scr. 8, 100 (1975).Google Scholar
  14. 14.
    L. B. Pankratz, Thermodynamic Properties of Halides (Bureau of Mines, Bulletin 674, Dept. Interior, 1984).Google Scholar
  15. 15.
    I. Barin and O. Knacke,Thermochemical Properties of Inorganic Substances (Springer-Verlag, New York, 1973).Google Scholar
  16. 16.
    R. A. Kent and J. L. Margrave,J. Am. Chem. Soc.,87, 3583 (1965).Google Scholar
  17. 17.
    K. F. Zombov and J. L. Margrave,J. Chem. Phys.,47, 3122 (1967).Google Scholar
  18. 18.
    M. W. Chase, Jr., C. A. Davis, J. R. Downey, Jr., D. J. Frurip, R. A. McDonald, and A. N. Syverud,JANAF Thermochemical Tables, third ed. (National Bureau of Standards, 1985).Google Scholar

Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • Si -Cheng Kung
    • 1
  • Robert A. Rapp
    • 1
  1. 1.Department of Materials Science and EngineeringThe Ohio State UniversityColumbus

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