CERAMIC/METAL ELEMENTS FOR MHD SIDEWALLS

THE COMBINED-CYCLE MAGNETOHYDRODYNAMIC (MHD) POWERPLANT HAS THE POTENTIAL OF BEING ONE OF THE MOST EFFICIENT, LEAST ENVIRONMENTALLY INTRUSIVE COAL-FUELED POWER SOURCES. AT PRESENT, COMPONENTS ARE BEING MANUFACTURED FOR THE PROOF-OF-CONCEPT 1,000 HOUR MHD GENERATOR TEST. THE PROJECTED LIFETIME OF THE GENERATOR IS 2,000 TO 3,000 HOURS. THE LIFE-LIMITING WALLS APPEAR TO BE THE INSULATING WALLS COMMONLY REFERRED TO AS THE SIDEWALLS. THEY ARE CONSTRUCTED FROM METALLIC WATER-COOLED BARS SEPARATED BY THIN BORON NITRIDE SPACERS. THE METAL, NORMALLY COVERED BY COAL SLAG, IS SUBJECT TO ELECTROCHEMICAL CORROSION CAUSED BY CURRENT LEAKAGE DRIVEN BY HIGH ELECTRIC FIELDS. BY REPLACING THE PLASMA- AND SLAG-EXPOSED METAL ELEMENTS WITH DIELECTRIC, CHEMICALLY STABLE CERAMIC, THE LIFE OF THE GENERATOR WILL BE SIGNIFICANTLY INCREASED. DEVELOPMENT OF THESE CERAMIC/METAL SIDEWALL ELEMENTS IS THE OBJECTIVE OF THIS WORK. THE PHASE I EFFORT CONSISTS OF DEVELOPMENT OF DESIGN STRATEGIES FOR LOW RESIDUAL STRESS IN CERAMIC-TO-METAL BRAZED JOINTS, EXPERIMENTAL VALIDATION OF THE DESIGN STRATEGIES, AND DESIGN AND CONSTRUCTION OF TWO SETS OF PROTOTYPE CERAMIC/METAL BARS. IN ADDITION, A THERMAL TEST FACILITY, IN WHICH THE PROTOTYPES ARE TO BE TESTED DURING THE PHASE II EFFORT, IS BEING DESIGNED IN PHASE I. IN PHASE II, THE PROTOTYPES WILL BE REFINED AND MADE IN STATISTICALLY SIGNIFICANT QUANTITIES, AND LIFE TESTED UNDER STEADY-STATE AS WELL AS THERMAL SHOCK CONDITIONS IN A SIMULATED MHD ENVIRONMENT.