The compatibility of metal electrodes in the oil fired MHD environment
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An important item in the development of the MHD generator is the development of a durable electrode. This paper investigates the compatibility of metal electrodes to the oil fired MHD environment by examining the degradation mechanisms of type 304 steel and SHOMAC® steel anodes and W-Cu and WC-Ag cathodes. For purpose of clarification, we wish to state that the cathode is the electrode that is bombarded by positive ions from the MHD plasma; the anode is bombarded by negative ions. It is shown that type 304 steel anode loss is due to both corrosion by current and abrasion by combustion gas flow, and can be predicted by using empirical equations, if only the surface temperature is given. Abrasion appears if the surface temperature is over about 700 K. General corrosion also occurs on both type 304 steel and SHOMAC steel anodes and is accompanied by the formation of solid oxide scales. On the other hand, W-Cu cathode loss is mostly by abrasion in the current region below about 0.3 A/cm2. However, above that current value, corrosion by current increases rapidly due to the generation of intensive arc spots.
KeywordsCorrosion Rate Cathode Material Weight Loss Rate Abrasion Loss Steel Anode
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