The sulfidation behavior of Co-Nb, Co-Mo binary alloys and Co-Mo alloys containing various ternary additions

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5943950

Gleeson, B M

Refractory metals, such as Mo and Nb, have the unique property of being extremely resistant to high-temperature sulfidation. However, in spite of this, studies on the addition of either Mo or Nb to the common-base metal Co, to improve its sulfidation resistance, are virtually nonexistent. This investigation involved studies of the effect of Mo and Nb additions on the sulfidation behavior of cobalt. Co-Nb alloys containing up to 30 wt.%Nb were studied over the temperature range 600-800{degree}C in a sulfur vapor pressure of 10{sup {minus}2} atm. Co-Mo alloys containing up to 40 wt.%Mo were studied over the temperature range 600-900{degree}C in both 10{sup {minus}2} and 10{sup {minus}4} atm sulfur vapor. The sulfidation behavior of ternary alloys has been studied also in which ternary additions of Cr,Al,Ti, and Mn have been added to Co-Mo binary alloys. The ternary alloys were studied over the temperature range 600 or 700{degree}C to 900{degree}C in a sulfur vapor pressure of 10{sup {minus}2} atm. The alloys were all multiphase, and the kinetics followed the parabolic rate law fairly well. Both Mo and Nb increased the sulfidation resistance of Co with increasing concentration. Mo was found to be more effective than Nb. For the ternary alloys, Al and Cr improved the sulfidation resistance of the Co-Mo binary alloy, whereas Mn had the opposite effect. The Ti-containing alloy underwent a mixed oxidation/sulfidation process, so that its kinetics were inapplicable. Scales that formed on the binary alloys were duplex, and on the ternary alloys they were usually triplex. In each case the outer layer was cobalt sulfide, and the inner layer was usually a complex, heterophasic mixture whose phases were often both temperature and composition dependent. For the ternary alloys, the intermediate layer consisted primarily of the ternary-element sulfide.

• Research Organization: California Univ., Los Angeles, CA (USA)
• OSTI ID: 5943950
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALLOY SYSTEMS
ALLOYS
ALUMINIUM ADDITIONS
ALUMINIUM ALLOYS
BINARY ALLOY SYSTEMS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMIUM ADDITIONS
CHROMIUM ALLOYS
COBALT ALLOYS
DIFFUSION
ELEMENTS
FLUIDS
GASES
HIGH TEMPERATURE
KINETICS
MANGANESE ADDITIONS
MANGANESE ALLOYS
METALLURGICAL EFFECTS
METALS
MOLYBDENUM
MOLYBDENUM ALLOYS
NIOBIUM
NIOBIUM ALLOYS
OXIDATION
REACTION KINETICS
SCALING
SULFIDATION
TERNARY ALLOY SYSTEMS
TITANIUM ADDITIONS
TITANIUM ALLOYS
TRANSITION ELEMENTS
VAPORS
VERY HIGH TEMPERATURE