Exploring the Effect of Silicon on the High Temperature Corrosion of Lean FeCrAl Alloys in Humid Air

A new approach to reduce the chromium and aluminium concentrations in FeCrAl alloys without significantly impairing corrosion resistance is to alloy with 1–2 wt.% silicon. This paper investigates the “silicon effect” on oxidation by comparing the oxidation behavior and scale microstructure of two FeCrAl alloys, one alloyed with silicon and the other not, in dry and wet air at 600 °C and 800 °C. Both alloys formed thin protective oxide scales and the Cr-evaporation rates were small. In wet air at 800 °C the Si-alloyed FeCrAl formed an oxide scale containing mullite and tridymite together with α- and γ-alumina. It is suggested that the reported improvement of the corrosion resistance of Al- and Cr-lean FeCrAl’s by silicon alloying is caused by the appearance of Si-rich phases in the scale.

Fabrication of Mn–Co–Ni-coated layer on AISI 304 stainless steel for protection of Cr evaporation by electroplating process

Purpose This study aims to improve the oxidation resistance of SS304 stainless steel by fabrication of Mn–Co–Ni-coated layer. Mn–Co–Ni coating with the thickness ranging from 1.76 to 8.50 micron were prepared by electroplating process on SS304 stainless steel, focusing on the plating time which play significant roles on the performance of the film thickness and crystallize size. Design/methodology/approach Mn–Co–Ni coating layer was applied on AISI 304 stainless steel using electroplating process with solution consisted of cobalt sulfate (CoSO4), manganese sulfate (MnSO4) and nickel sulfate (NiSO4). Variation of Mn–Co–Ni coating, the morphology of the film and oxidation kinetics were investigated by using scanning electron microscopy and x-ray diffraction analysis. Furthermore, the sample with coating layer was tested by oxidation and Cr evaporation test. Findings From the formation parameter due to plating time for the conversion coating, it was found that plating time plays significant roles in the performance of the coating thickness and crystallize size. The crystallize size has an inverse relation to the full width at half maximum of diffraction peak. Film thickness higher than 6.07 micron causes a decrease in oxidation resistance and an increase of Cr evaporation from SS304 stainless steel. In this study, the Mn–Co–Ni coating with a thickness lower than 3.77 micron showed coating protection of oxidation better than SS304 substrate. Originality/value The effect of coating thickness was investigated to understand the properties of the coating. Furthermore, oxidation and Cr evaporation test were applied to evaluate the oxidation resistance of the coating layer.

Protective Ceramic Coatings for Solid Oxide Fuel Cell (SOFC) Balance-of-Plant Components

Solid oxide fuel cells (SOFCs) have the potential to meet the growing need for electrical power generation if the cost per megawatt can be further reduced. Currently, SOFC stacks are replaced too frequently to be cost competitive. SOFC service life can be extended by preventing chromium- (Cr-) bearing species from evaporating from the interior surfaces of balance of plant (BOP) components and poisoning the cathode to increase the lifetime. We have developed yttria-stabilized zirconia (YSZ) and aluminum oxide- (Al2O3-) modified sol-gel paints or inks for coating BOP components. 430 stainless steel (430SS) substrates with three surface conditions were coated with the 0.8–1.5 µm thick YSZ and Al2O3 paints. The coated 430SS samples were tested for thermal cycling resistance, thermal soak, and Cr evaporation. Thermal soak and thermal cycling test results show promise for the YSZ-coated 430SS substrates. The Cr evaporation test of a coated substrate showed a 51% reduction in Cr generation, when compared with a bare substrate.