Sulfidation behavior of rhenium and cobalt-rhenium alloys
- Certified Alloy Products, Inc., Long Beach, CA (United States)
- Univ. of Arizona, Tucson, AZ (United States). Arizona Materials Lab.
The sulfidation behavior of Re and three Co-Re alloys, 15, 30, and 45 w/o, was studied over the temperature range 700--800 C at sulfur pressures of 10{sup {minus}4} and 10{sup {minus}2} atm. The kinetics of sulfidation followed the parabolic rate law and the activation energies for all alloys were similar to that of pure cobalt. A positive rate dependency on sulfur pressure was observed and Pt markers were located at the metal-scale interface, both observations clearly suggesting that outward cation diffusion through a P-type sulfide scale occurred. Two dominant sulfides, Co{sub 9}S{sub 8} and ReS{sub 2}, formed. Weight gains decreased for a given set of conditions with increasing rhenium content. An order of magnitude decrease in the sulfidation rate occurred as the rhenium content increased from 15 to 45 w/o. Preferential sulfidation of cobalt initially occurred, causing a rhenium-enriched zone to form in the substrate beneath the cobalt-sulfide scale. The initial sulfide to form was Co{sub 3}S{sub 4}, but, subsequently, Co{sub 9}S{sub 8} became the dominant sulfide, forming beneath the outer Co{sub 3}S{sub 4} layer. ReS{sub 2} formed at lower cobalt levels. Pure Re was also studied, the sulfidation rate being about 10{sup 4} times slower than that of cobalt. The decreasing rate of sulfidation with increasing Re content is attributed primarily to slower cobalt diffusion outward through the Re-enriched substrate, a phenomenon similar to that observed by C. Wagner for the oxidation of Ni-Pt alloys.
- OSTI ID:
- 684331
- Journal Information:
- Oxidation of Metals, Journal Name: Oxidation of Metals Journal Issue: 5-6 Vol. 52; ISSN OXMEAF; ISSN 0030-770X
- Country of Publication:
- United States
- Language:
- English
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