A sample iron molybdenum alloy with 3.4 wt.-% (2 at.-%) molybdenum, and pure iron, are exposed to hydrogen sulfide saturated saline solution for up to 56 d. In addition, their behaviour under anodic polarization in the same electrolyte is investigated. The initially fast dissolution of the iron molybdenum alloy slows down significantly over time, while iron cor-1 rodes with a constant rate. The observed slow down of the corrosion rate can be described well with an exponential decay of the instantaneous corrosion rate with a time constant of (0.15 ± 0.03) d −1 , which implies stop in corrosion in practical terms after ≈2 w. Relationships are discussed between the instantaneous corrosion rate, and the time-averaged integral corrosion rate. Dissolution under anodic polarization of the iron molybdenum alloy is slower than for pure iron. While at certain times, pyrite, FeS 2 , is found as corrosion product, the main corrosion product is mackinawite, FeS. The latter likely contains a certain fraction of molybdenum in case of the iron molybdenum alloy. On iron molybdenum, corrosion products forming a sealing layer are observed, which slow down further corrosion. The corrosion products on iron molybdenum show better adhesion to the base material surface.
Abstract. Solid oxide fuel cells directly convert the chemical energy of a fuel into electricity. To enhance the efficiency of the fuel cells, the thickness of the gastight solid electrolyte membranes should be as thin as possible.Y203-stabilised ZrO 2 (YSZ) electrolyte films were prepared by reactive sputtering deposition using Zr/Y targets in Ar/O 2 atmospheres. The films were 5 -8 p.m thin and were deposited onto anode substrates made of a NiO/YSZ composite. After deposition of a cathode with the composition Lao.65Sr0 ~5MnO3 the electrochemical properties of such a fuel cell were tested under operating conditions at temperatures between 600 ~ and 850 ~ Current-voltage curves were recorded and impedance measurements were performed to calculate apparent activation energies from the fitted resistance data. The conductivity of the YSZ films varied between 4.6.10-6S/cm and 2.2.10 .5 S/cm at 400 ~ and the fuel cell gave a reasonable power density of 0.4 W/cm 2 at 0.7 V and 790 ~ using H~ with 3 % H=O as fuel gas. The gas compositions were varied to distinguish the electrochemical processes of the anode and cathode in the impedance spectra.
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