Effect of Al on high-temperature corrosion of Co-15a/oNb alloys in H[sub 2]-H[sub 2]O-H[sub 2]S environments

Journal Article · Tue Feb 01 04:00:00 EST 1994 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF01196646· OSTI ID:7045430

Shing, C C; Douglass, D L ^[1]

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1. Univ. of California, Los Angeles, CA (United States)

Co-15 at.% Nb alloys containing up to 15 at.% Al were corroded in gaseous H[sub 2]-H[sub 2]O-H[sub 2]S mixtures over the temperature range of 600-900[degree]C. The corrosion kinetics followed the parabolic rate law at all temperatures. Corrosion resistance improved with increasing Al content except at 900[degree]C. Duplex scales formed on alloys consisting of an outer layer of cobalt sulfide and a heterophasic inner layer. A small amount of Al[sub 2]O[sub 3] was found only on Co-15Nb-15Al. Contrary to what formed in Co-Nb binary alloys, neither NbS[sub 2] nor NbO[sub 2] were found in the inner layer of all alloys, but Nb[sub 3]S[sub 4] did form. The absence of NbS[sub 2] and NbO[sub 2] is due to the formation of stable Al[sub 2]O[sub 3] and Al[sub 2]S[sub 3] that effectively blocked the inward diffusion of oxygen and sulfur, respectively, and to the reduction of activity of Nb by Al additions in the alloys. Intercalation of ions in the empty hexagonal channels of Nb[sub 3]S[sub 4] is associated with the blockage of the transport of cobalt. An unknown phase (possibly Al[sub 0.5]NbS[sub 2]) was detected. Alloys corroded at 900[degree]C were abnormally fast and formed a scale containing CoNb[sub 3]S[sub 6] and Co. Pt markers were found at the interface between the inner and outer layers. 22 refs., 14 figs., 5 tabs.

• OSTI ID: 7045430
• Journal Information: Oxidation of Metals; (United States), Journal Name: Oxidation of Metals; (United States) Vol. 41:1-2; ISSN OXMEAF; ISSN 0030-770X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ALUMINIUM SULFIDES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COAL GASIFICATION PLANTS
COBALT ALLOYS
COBALT BASE ALLOYS
COMPILED DATA
CORROSION
CORROSIVE EFFECTS
DATA
DIFFUSION
ELEMENTS
FLUIDS
GASES
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
INDUSTRIAL PLANTS
INFORMATION
KINETICS
NIOBIUM ALLOYS
NIOBIUM COMPOUNDS
NIOBIUM SULFIDES
NONMETALS
NUMERICAL DATA
OXIDATION
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PETROLEUM REFINERIES
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SCALING
SULFIDATION
SULFIDES
SULFUR
SULFUR COMPOUNDS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
TRANSITION ELEMENT COMPOUNDS
VAPORS
WATER VAPOR