Oxidation of Metals

, Volume 31, Issue 3–4, pp 237–263 | Cite as

High-temperature sulfidation behavior of Ni-Nb alloys

  • M. F. Chen
  • D. L. Douglass
  • F. Gesmundo
Article

Abstract

The sulfidation properties of Ni-Nb alloys containing additions of niobium up to 40 wt.% have been studied at\(P_{S_2 } = 0.01\) atm over the temperature range 550-700 °C. The sulfidation reactions followed the parabolic rate law; the sulfidation rates decreased with increasing amounts of niobium. An Arrhenius plot of the rate constants gave activation energies of 25.0+3.5 kcal/ mole. The scales formed on Ni-Nb alloys were multilayered, generally consisting of an outer layer of nickel sulfide ( NiS1+x and Ni3S2) and an inner complex layer of NiNb3S6 plus NbS2. The position of the original metal surface was notedy platinum-wire marker experiments to be the interface between the inner andouter layers. The location of the marker indicates that the outer layer, generally greater in thickness than the inner layer, grew by outward diffusion of the nickel cations, and the inner layer formed probably by the inward diffusion of sulfur. Neither preferential sulfidation nor internal sulfidation was observed. The development of the scale structures from the transient stage to steady state was also studied.

Key words

sulfidation nickel-niobium multilayered scale NbS2 NiNb3S6 

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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • M. F. Chen
    • 1
  • D. L. Douglass
    • 1
  • F. Gesmundo
    • 2
  1. 1.Department of Materials Science and Engineering, School of Engineering and Applied ScienceUniversity of CaliforniaLos Angeles
  2. 2.Instituto di Chimica, Facolta di IngegneriaUniversità di GenovaGenovaItaly

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