"Molten coal slag corrosion studies conducted on molybdenum at 1400°C used static and stirred slag experiments and electrical current experiments to parallel electrode conditions of slagging duct MHD generators. Crucibles containing molybdenum and slag were exposed to combustion-type gases in a tube furnace. Carbon monoxide-carbon dioxide gas mixtures controlled oxygen partial pressures at selected values between 10-11 and 10-3 atm. Metallograph and microprobe examination of polished sample sections defined corrosion characteristics.
At 1400°C, molybdenum metal is stable below 10-9 atm oxygen pressure. Molybdenum dioxide is stable at higher pressure, but volatile molybdenum trioxides prevent formation of stable oxide films in contact with gases. With a slag interlayer, molybdenum corrosion was lessened by slow diffusion processes (no gas-metal contact) and favorable thermodynamics. Still, iron alloyed with the molybdenum at low oxygen pressures and cathodic conditions, while molybdenum oxidation prevailed at higher oxygen pressures and anodic conditions. Dissolution into the slag of any molybdenum dioxide that formed was restricted by its solubility limit in the slag. Slag composition significantly affected corrosion. More iron oxide in the slag increased corrosion, as did the presence of potassium sulfate. Additions of carbon to the slag prevented molybdenum oxidation, but iron alloying and possible carburization occurred.
Under the test conditions, molybdenum electrodes undergo considerable attack as either the cathode or anode. However, the results cannot be applied to other conditions and molybdenum may be practical at lower temperatures or in refractory alloys. The test procedures developed can be used to screen electrode materials, identifying conditions of minimum attack. More elaborate tests are required to determine actual suitability of candidate materials"--Abstract, page ii.
Morris, Arthur E., 1935-
Kisslinger, Fred, 1919-2010
Anderson, H. U. (Harlan U.)
Materials Science and Engineering
M.S. in Metallurgical Engineering
University of Missouri--Rolla
xii, 123 pages
© 1979 Kenton Brian Wright, All rights reserved.
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Wright, Kenton Brian, "Molybdenum stability in coal slags at 1400⁰C: Corrosion properties for MHD electrode applications." (1979). Masters Theses. 3279.
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