Palitha Jayaweera

Stable High Conductivity Ceria/Bismuth Oxide Bilayered Electrolytes

The authors have developed a high conductivity bilayered ceria/bismuth oxide anolyte/electrolyte that uses the Po{sub 2} gradient to obtain stability at the anolyte-electrolyte interface and reduced electronic conduction due to the electrolyte region. Results in terms of solid oxide fuel cell (SOFC) performance and stability are presented. These results include a 90 to 160 mV increase in open-circuit potential, depending on temperature, with the bilayered structure as compared to SOFCs fabricated from a single ceria layer. An open-circuit potential of >1.0 V was obtained at 500 C with the bilayered structure. This increase in open-circuit potential is obtained without any measurable increase in cell resistance and is stable for over 1,400 h of testing, under both open-circuit and maximum power conditions. Moreover, SOFCs fabricated from the bilayered structure result in a 33% greater power density as compared to cells with a single ceria electrolyte layer.

Corrosion-resistant metallic coatings for applications in highly aggressive environments

Surface modification to improve the corrosion resistance of low-cost alloys is an economically attractive alternative to the use of expensive corrosion-resistant alloys. A low-grade steel surface modified by a suitable metallic diffusion coating can provide excellent corrosion resistance similar to that obtained with an expensive super alloy. We have used the fluidized bed reactor chemical vapor deposition (FBR-CVD) technique for the preparation of diffusion coatings containing Cr, Ni, Si and Ti on carbon and low-grade stainless steels. Several formulations of diffusion coatings on 409 SS have shown corrosion resistance similar to that of alloys AL6XN® or AL29-4C® in chemical heat pump applications. In this paper, we describe the preparation, characterization, and performance evaluation of a number of corrosion-resistant metallic diffusion coatings.

Electrocatalytic reduction of NOx on La1−xAxB1−yB′yO3−δ: evidence of electrically enhanced activity

Abstract Solid-state electrochemical cells can be used to sense and reduce NO x from combustion exhaust gases. In the reduction process the products are N 2 and O 2 . For these cells to be effective in fuel-lean combustion exhaust, cathode materials with high selectivity for NO vs. O 2 are necessary. Numerous compositions of La 1− x A x B 1− y B′ y O 3− δ (where A is Sr or Ba; and B and B′ are transition metals) were investigated for heterogeneous catalytic activity and selectivity for NO reduction using temperature programmed reaction (TPR). Ceramic cells using these materials as cathodes were fabricated and used to electrocatalytically reduce NO in NO/He and simulated exhaust atmospheres. An enhanced electrocatalytic three-way activity for NO x reduction was demonstrated that increases the window of operation into fuel-lean conditions.

Design and performance of wireless sensors for structural health monitoring

Wireless sensors can be realized by integrating a sensor with a passive commercial radio-frequency identification (RFID) chip. When activated, the chip responds with a digitally encoded signal that not only identifies the sensor but also contains information about the sensor state. Two devices have been developed to date: a temperature-threshold indicator and a chloride-threshold indicator. This paper discusses basic concepts, design issues, and preliminary performance.

Corrosion-resistant metallic coatings on low carbon steel

Abstract Corrosion resistant coatings of various metals and alloys such as Si, Ti, Ni, and TiNi were formed on steel rebars by fluidized bed chemical vapor deposition (FBR-CVD), paint-and-heat or FBR-plasma spray techniques. The paint-and-heat metallization and FBR-plasma spray are powder coating techniques that can be applied easily and economically on new components as well as on existing steel structures, such as bridges. These metallic powder coatings provide non-sacrificial, superior corrosion protection for a long time. TiNi (70:30 wt. %) coatings on steel rebars provided a 20 fold increase in corrosion resistance over uncoated steel. These metallic coatings can be used to prevent corrosion in many industrial applications.

Localized Corrosion of Alloy 22 in Sodium Chloride Solutions at Elevated Temperature

Abstract The localized corrosion behavior of Alloy 22 (UNS N06022) in acidified (pH = 3) sodium chloride (NaCl) brines at elevated temperature (80°C) and under potentiostatic and open-circuit condi...

Impedance Study of the Synergistic Effects of Coal Contaminants: Is Cl a Contaminant or a Performance Stabilizer?

Impedance spectroscopy and current-voltage measurements were used to study the synergistic effects of the coal gas contaminants As, P, S, and Cl at the parts per million level on the performance of the anode-supported Ni-yttria-stabilized zirconia (YSZ)/YSZ/ lanthanum strontium manganese solid oxide fuel cells (SOFCs) at 750°C. Three semicircles were differentiated in cell impedance spectra. The results indicate that the effects of the contaminants are synergistic, can be destructive or constructive, and are not a simple addition of individual contaminants. Adding H 2 S to As and P accelerated the performance degradation. The addition of H 2 S also increased the charge-transfer resistance, whereas the removal of H 2 S resulted in a substantial ohmic resistance increase. The presence of Cl could mitigate or prevent performance loss from an attack by As and P. Impedance spectra show that the presence of Cl species protected the electronic percolation and slowed the rate of the charge-transfer resistance increase. Therefore, the tolerance limit of SOFCs for each contaminant could be significantly increased with Cl species in the gas stream. It is speculated that Cl species could react with nickel phosphides and Ni-P alloy to form NiCl(g), resulting in the restructuring of the catalyst surface.

Fundamental Understanding of Crack Growth in Structural Components of Generation IV Supercritical Light Water Reactors

This work contributes to the design of safe and economical Generation-IV Super-Critical Water Reactors (SCWRs) by providing a basis for selecting structural materials to ensure the functionality of in-vessel components during the entire service life. During the second year of the project, we completed electrochemical characterization of the oxide film properties and investigation of crack initiation and propagation for candidate structural materials steels under supercritical conditions. We ranked candidate alloys against their susceptibility to environmentally assisted degradation based on the in situ data measure with an SRI-designed controlled distance electrochemistry (CDE) arrangement. A correlation between measurable oxide film properties and susceptibility of austenitic steels to environmentally assisted degradation was observed experimentally. One of the major practical results of the present work is the experimentally proven ability of the economical CDE technique to supply in situ data for ranking candidate structural materials for Generation-IV SCRs. A potential use of the CDE arrangement developed ar SRI for building in situ sensors monitoring water chemistry in the heat transport circuit of Generation-IV SCWRs was evaluated and proved to be feasible.