Effects of Surface-Deposited Nanocrystalline Chromite Thin Films on the Performance of a Ferritic Interconnect Alloy

LaCrO 3 -based nanocrystalline thin films, substituted with Sr and Zn and coated onto a Fe-26 atom % Cr Ebrite alloy were evaluated at 750-900°C as potential enhancers of oxide properties in ferritic alloy interconnects of a solid oxide fuel cell. It was found that at 750°C the coatings provided ͑i͒ lower oxidation rates, ͑ii͒ increased electrical conductivity, ͑iii͒ protection during 24 h cycling and at least 2375 h of isothermal oxidation, and ͑iv͒ a fine-grained and uniform oxide microstructure. Although after oxidation at 850°C the grains grew substantially and the scale seemed to be overgrowing the film, conductivity and oxidation rates still matched that of the uncoated sample. Tensile tests showed that the coating improved scale adhesion after a 100 h oxidation at 850°C. At 900°C, the film was still capable of blocking 70% of the Cr that evaporated from an uncoated Ebrite substrate. Ferritic steels have in recent years been widely studied as possible interconnect materials in solid oxide fuel cell ͑SOFC͒ systems, where they provide the electrical connection between single cells and allow gas separation within the cell stack. 1,2 The choice of these steels is based on several factors, such as their low cost, compatible coefficient of thermal expansion ͑CTE͒ with the cell components, and their relatively slow growth rate and high conductivity of the oxide, namely, Cr 2 O 3 , that forms on their surfaces during operation. Although Cr 2 O 3 conductivity increases with temperature, these metallic interconnects are limited to operating temperatures in an intermediate regime of 600°C to no more than 800°C, due to fast growth rates of the Cr 2 O 3 3 and of Cr evaporation at higher temperatures. 4,5 When water vapor is present, the evaporation problem becomes severe, even within the 600-800°C temperature range. Alloy development 13-18 and coating applications 6,19-24 have been attempted to improve Cr 2 O 3 -forming alloys as interconnect materials. The former includes an earlier developed oxide-dispersionstrengthened ͑ODS͒ Plansee alloy 12,15,25 and a later Crofer alloy. Experimental Coating procedure.-The base alloy used for this work was a commercial ferritic stainless steel ͑Ebrite from Allegheny Ludlum Steel, in the form of a 1 mm thick sheet͒ with compositions shown in Oxidation.-Coated and uncoated samples were oxidized isothermally for 50 h in a Cahn thermal gravimetric balance in air at 750 or 850°C with a heating and cooling rate of 5°C/min. Cyclic oxidation was done in air at 5°C/min heating and cooling, and held for 24 h at 750°C during each cycle. A few specimens were held at 750 or 850°C for 100 h to evaluate the effectiveness of the coatings after longer term oxidation. One coated sample oxidized at 750°C was held for 1 month ͑713 h͒, removed for examination, and then placed back in the same furnace for another 2 months, for a total oxidation period of 2375 h. Tensile pull test, areal specific resistance, and Cr evaporation.-Oxidized samples were characterized using scanning electron microscopy ͑SEM͒, energy-dispersive spectroscopy ͑EDS͒, and * Electrochemical Society Active Member.

Signaling in Secret: Pay-for-Performance and the Incentive and Sorting Effects of Pay Secrecy

Key Findings: Pay secrecy adversely impacts individual task performance because it weakens the perception that an increase in performance will be accompanied by increase in pay; Pay secrecy is associated with a decrease in employee performance and retention in pay-for-performance systems, which measure performance using relative (i.e., peer-ranked) criteria rather than an absolute scale (see Figure 2 on page 5); High performing employees tend to be most sensitive to negative pay-for- performance perceptions; There are many signals embedded within HR policies and practices, which can influence employees’ perception of workplace uncertainty/inequity and impact their performance and turnover intentions; and When pay transparency is impractical, organizations may benefit from introducing partial pay openness to mitigate these effects on employee performance and retention

Oxidation Protective Coating onto Ferritic Interconnect by Nanocrystalline Perovskite Thin Films

Nanocrystalline chromite thin films were deposited on polished stainless steel (E-brite) substrates by spin coating suitable polymeric solutions onto the surface followed by annealing to develop the oxide film. These films had higher electrical conductivity as well as provide improved oxidation resistance compared to the normal Cr2O3 films, which occurred from oxidation of the alloy. This resulted in lower areal specific resistance (ASR) values for the chromite coated surfaces than those with the Cr2O 3 scale