Oxide Scale Morphology and Chromium Evaporation Characteristics of Alloys for Balance of Plant Applications in Solid Oxide Fuel Cells

This article compares chromium evaporation characteristics of chromia- and alumina-forming alloys at high temperatures [1123 K and 1223 K (800 °C to 950 °C)] in humid air (3 and 12 pct H2O) and presents a mechanistic understanding of variation in chromium evaporation on the basis of their oxide scale morphologies. For this study, an alloy from each of the distinct chromia-forming, alumina-forming, and chromia-alumina transition characteristics was selected (i.e., an alumina-forming alloy (Aluchrom YHf), a chromia-forming alloy (AISI 310S-austentic stainless steel), and an alloy that undergoes transition from chromia to alumina formation (Nicrofer6025 HT)). For generating baseline chromium evaporation data, pure chromium oxide was also tested. The chromium evaporation rate decreased in the order pure chromium oxide > AISI 310S > Nicrofer6025 HT > Aluchrom YHf. Surface morphologies, cross sections, and chemical characteristics of oxide scales were examined by scanning electron microscopy and energy dispersive X-ray spectroscopy and focused ion beam. The variation in chromium evaporation of different alloys is explained on the basis of physical and chemical characteristics of the oxide scales.