Semester

Summer

Date of Graduation

2007

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Bruce S. Kang.

Abstract

The objective of this research was the development and long-term testing of cathode-interconnect contact materials for the solid-oxide fuel cell (SOFC). The research effort was focused on the utilization of silver and silver cerments. Silver is an attractive candidate contact material due to its high ductility, high conductivity, and low cost relative to other candidate SOFC contact materials. Furthermore, silver does not form non-conductive oxide scales in the SOFC cathode environment. One major concern about its usage is the volatility of silver at the SOFC operating temperature of around 800 °C. Samples were manufactured by depositing submicron size silver particles, bimetallic composites of silver and ceria, and strontium doped lanthanum manginite (LSM) using a screen printing process and placed in a simulated cathode environment (SCE). During the course of the long term exposure, mass loss measurements and microstructure changes of the surface of the sample were made using scanning electron microscopy (SEM).;Test results revealed significant bulk silver diffusion to the LSM cathode, which may defeat the purpose of using silver or silver cerments as contact material in the SOFC cathode chamber. Non-linear mass loss rates of the both the screen printed and foil silver samples were discovered, indicating a degree of evaporative instability in the silver. The LSM coating layer proved effective in reducing the evaporation of silver, while ceria actually increased the evaporation rate of the silver. Scanning electron microscopy showed that the LSM surface was highly stable at high temperature. Excessive bulk diffusion of the silver led to the entire silver layer diffusing into the LSM coating, leaving a void in the center of the sample.

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