ISSN:
1573-4889
Keywords:
Sulfidation
;
nickel-molybdenum
;
multilayered scale
;
MoS2
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The sulfidation behavior of Ni-Mo alloys containing up to 40 wt.% Mo was studied at $$P_{s_2 } $$ =0.01 atm. over the temperature range of 550–800°C. The alloys included two solid solutions (Ni-10Mo and Ni-20Mo), the single-phase intermetallic compound Ni4Mo(Ni-29Mo), and two alloys which were two-phase, Ni-30Mo and Ni-40Mo (Ni4Mo+Ni3Mo). The sulfidation of all alloys followed the parabolic rate law. The rate of sulfidation decreased with increasing amounts of Mo. Activation energies for sulfidation gave values of 39.1±1.0 kcal/mol. The sulfide scales were bilayered, consisting of an outer layer nickel sulfide (NiS1+x and Ni3S2) and an inner, complex layer of MoS2 plus intermetallic particles. The rate-controlling step of the sulfidation for the alloys was inward sulfur diffusion and/or outward nickel diffusion through the inner MoS2 layer. Neither selective sulfidation nor internal sulfidation were observed. No significant difference in the sulfidation kinetics, sulfide structure, and scale constitution could be noted between single-phase alloys and two-phase alloys. The location of the markers was the interface between the inner and outer layers, indicating that the inner layer formed by inward diffusion of sulfur, and the outer layer grew by outward nickel diffusion. The inability to form a continuous protective molybdenum sulfide layer is discussed in terms of the structure of MoS2 and changes caused by intercalation of Ni into the layered crystal structure. The decrease in sulfidation rate with increasing Mo was attributed to increasing amounts of the intermetallic compound. The increasing volume fraction of particles decreased the available diffusion area in the inner layer and provided a “blocking” effect.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00664798
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