Michael J. Martinez-Rodriguez

Impact of Corrosion Test Container Material in Molten Fluorides

The effects of crucible material choice on alloy corrosion rates in immersion tests in molten LiF–NaF–KF (46.5–11.5-42 mol. %) salt held at 850 °C for 500 hrs are described. Four crucible materials were studied. Molten salt exposures of Incoloy-800H in graphite, Ni, Incoloy-800H, and pyrolytic boron nitride (PyBN) crucibles all led to weight-loss in the Incoloy-800H coupons. Alloy weight loss was ~30 times higher in the graphite and Ni crucibles in comparison to the Incoloy-800H and PyBN crucibles. It is hypothesized galvanic coupling between the alloy coupons and crucible materials contributed to the higher corrosion rates. Alloy salt immersion in graphite and Ni crucibles had similar weight-loss hypothesized to occur due to the rate limiting out diffusion of Cr in the alloys to the surface where it reacts with and dissolves into the molten salt, followed by the reduction of Cr from solution at the molten salt and graphite/Ni interfaces. As a result, both the graphite and the Ni crucibles provided sinks for the Cr, in the formation of a Ni–Cr alloy in the case of the Ni crucible, and Cr carbide in the case of the graphite crucible.

Characterization of Microporous Layer in Carbon Paper GDL for PEM Fuel Cell

Department of Chemical Engineering University of South Carolina Columbia, SC 29208 Development of low-cost gas diffusion layers (GDL) with tailored properties is necessary to optimize fuel cell performance. Particularly in the cathode the water transport in the GDL depends strongly on the characteristics of the porous media used. In this study a custom series of Toray TGP-H-060, as described in Table 1, was selected for characterization. The techniques used for characterization consist of scanning electron microscopy (SEM) images taken from different views (MPL, substrate and cross-sections), pore size distribution (PSD) assessed by using mercury intrusion porosimetry [1], the MacMullin number [2], and polarization curves. Figure 1 shows the cross-sections images for the custom Toray series. The figure shows that the treatment in the substrate or MPL did not affect considerably the thickness of these layers. However, a merge between the substrate and the MPL can be observed instead of a defined and clear boundary. This correlates with the PSD shown in Figure 2 where the volume in the substrate is reduced when the MPL is present. The main peak around 0.05 μm corresponds to the MPL. Figure 3 shows the effect of the MPL and wet proofing in the MacMullin number. It can be observed that the addition of wet proofing increases the MacMullin number. However, the addition of the MPL decreases the MacMullin number. This can help explain the cell performance shown in Figure 4 at two humidity conditions when the wet proofing in the substrate is 10%. For both humidities the presence of the MPL decreases the cell performance but the increase in wet proofing in the MPL improves the performance. When the MPL is added to the GDL two significant negative effects occurs: decrease in the pore volume of substrate region (Fig. 2) and decrease in MacMullin number (Fig. 3). However, wet proofing the MPL shows no negative effects: Fig. 2 shows no noticeable effect in the pore volume and Fig. 3 shows just a little increase in the MacMullin number. Acknowledgements: This research was supported by the NSF Industrial/University Collaborative Research Center for Fuel Cells. The authors are grateful to Prof. Supapan Seraphin at Arizona Research Laboratory for the SEM images. References:

Dimensionless Analysis for Predicting Fe-Ni-Cr Alloy Corrosion in Molten Salt Systems for Concentrated Solar Power Systems

In high operating temperature concentrated solar power (CSP) systems, the use of molten salt heat transfer fluids causes corrosion of alloys in receivers and heat exchangers that decreases both hea...

The Effect of Low Concentrations of Tetrachloroethylene on the Performance of PEM Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells use components that are susceptible to contaminants in the fuel stream. To ensure fuel quality, standards are being set to regulate the amount of impurities allowable in fuel. The present study investigates the effect of chlorinated impurities on fuel cell systems using tetrachloroethylene (PCE) as a model compound for cleaning and degreasing agents. Concentrations between 0.05 parts per million (ppm) and 30 ppm were studied. We show how PCE causes rapid drop in cell performances for all concentrations including 0.05 ppm. At concentrations of 1 and 0.05 ppm, PCE poisoned the cell at a rate dependent on the dosage of the contaminant delivered to the cell. PCE appears to affect the cell when the cell potential was over potentials higher than approximately 0.2 V. No effects were observed at voltages around or below 0.2 V and the cells could be recovered from previous poisoning performed at higher potentials. Recoveries at those low voltages could be induced by changing the operating voltage or by purging the system. Poisoning did not appear to affect the membrane conductivity. Measurements with long-path length IR results suggested catalytic decomposition of the PCE by hydrogen over the anode catalyst.