Effect of water vapour partial pressure on the chromia (Cr₂O₃)-based scale stability

Abstract

The kinetics of the Cr2O3-based scale oxidation and volatilization were studied in the presence of water vapour (H2O). A commercial Cr2O3-based scale forming Type 310S stainless steel was examined at the ambient pressure (0.1 MPa) and 550 ºC in relatively low and high H2O containing environments of air-10% H2O and air-70% H2O, respectively. The increase in the partial pressure of H2O (pH2O) from 10% to 70% resulted in transition of the oxidation and volatilization kinetics from the parabolic rate law in air-10% H2O to the paralinear rate law in air-70% H2O. The kinetics transition was attributed to the increase in the Cr loss rate from the base scale after coupons exposure in air-70% H2O. The significant role of Mn alloying element in the base scale protectiveness was discussed in the context of the Cr2O3-based scale stability.

Characterization of metallic interconnects extracted from Solid Oxide Fuel Cell stacks operated up to 20,000 h in real life conditions: The fuel side

“…S3) which, according to literature, are connected to g-Fe 2 O 3 [49]. In addition, two peaks at 670 and 542 cm À1 could imply the presence of Fe 3 O 4 [38,39] (Fig. S3).…”

“…However, another phenomenon has to be addressed when describing the possible mechanism connected to the variation of the water vapor, namely the chromium volatilization. As already mentioned, the presence of Mn x O y at the interface with the fuel stream was only detected by Mahboubi et al [38] and more recently by Chandra-Ambhorn et al [39]. If we consider the reactions 3 and 4 from Ref.…”

“…4, dark green line) point out an increase of the intensity of the peaks related to the Mn x O y corresponding to thickening of the layer. Mahboubi et al [38] recently found such manganese oxides and hypothesized a formation mechanism that implies strong changes in the water vapor content of the atmosphere. Beside the fact that these experiments were performed at differing conditions (i.e., T 550 C and air/H 2 O mixture) the TGO nature is confirmed as expected by the dominant effect of water vapor.…”

“…Moreover, the stack is operated in co-flow between the fuel and the oxidant stream with a logical increase in temperature of both gases from the inlet and outlet manifolds. According to literature studies, water vapor partial pressure (pH 2 O) and temperature can indeed significantly change the TGO growth, promoting kinetics that are faster than those occurring in air or dry oxygen [32,38,40].…”