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Oxidation of Metals

, Volume 28, Issue 5–6, pp 309–328 | Cite as

The transition from internal oxidation to continuous-film formation during oxidation of dilute Ni-Si alloys

  • D. L. Douglass
  • P. Nanni
  • C. De Asmundis
  • C. Bottino
Article

Abstract

The oxidation of Ni-2.05Si and Ni-4.45Si was studied in oxygen over the range of 600°–1000°C for 18 hr. The oxidation kinetics did not follow a parabolic rate law, bur rather a power law of the form (Δw)n=kt was followed. The value of n ranged from 2.7 to 4.9 for Ni-2.05Si and from 3.0 to 6.4 for Ni-4.45Si. The low-silicon alloy exhibited extensive internal oxidation, whereas the higher-silicon alloy did not internally oxidize. In general, NiO containing little or no silicon formed as an exterior layer on both alloys. The internal oxidation zone in Ni-2.05Si was highly irregular in thickness, and in some areas there was no internal oxidation. The higher-silicon alloy formed a continuous layer of a silicon-rich oxide. X-ray diffraction did not detect silica (amorphous), and no evidence of Ni2SiO4 was observed, although EDAX analysis suggests that small amounts of the silicate might have formed. Theaverage thickness of the internal oxidation zone was found to agree well with calculated values based on oxygen solubility and diffusivity data. No enrichment of silicon occurred in the internal oxidation zone. Calculated values, 0.033 and 0.038 (depending on the model used), of the mole fraction of silicon required for the transition from internal oxidation to continuous silica film formation agreed well with experimental data obtained in both this study and with others reported in the literature.

Key words

Ni-Si alloys internal oxidation silica transition 

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Copyright information

© Plenum Publishing Corporation 1987

Authors and Affiliations

  • D. L. Douglass
    • 1
  • P. Nanni
    • 2
  • C. De Asmundis
    • 3
  • C. Bottino
    • 3
  1. 1.Department of Materials Science and Engineering, School of Engineering and Applied ScienceUniversity of CaliforniaLos Angeles
  2. 2.Facoltà di IngegneriaUniversità di GenovaGenovaItaly
  3. 3.Istuto di Chimica Fisica Applicata dei MaterialiConsiglio Nazionale delle RichercheGenovaItaly

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