A SEARCH FOR A RAPID OXYGEN SENSOR USING HIGH-TEMPERATURE COMPLEX EUTECTIC THIN FILMS

THIS RESEARCH ADDRESSES THE NEED FOR OXYGEN SENSORS TO PROVIDE HIGHLY LOCALIZED, RAPID SENSING (ON THE MICRON SCALE) WHILE OPERATING IN A CORROSIVE ATMOSPHERE AT ELEVATED TEMPERATURE AND/OR PRESSURE. THE MATERIALS USED WILL BE IN THE FORM OF COMPLEX EUTECTIC THIN-FILMS. AN INTENSE LASER BEAM WILL BE USED TO SOLIDIFY DIRECTIONALLY EUTECTIC FILMS OF ZRO(2) WITH MO, ZRC, AND ZRN. TWO OF THESE THREE SYSTEMS (ZRO(2)-MO AND ZRO(2)-ZRC) ARE KNOWN TO FORM EUTECTIC-LIKE STRUCTURES. THEORETICAL MODELING BY H. E. CLINE (1979) PREDICTED THAT, FOR FILMS WITHIN A CRITICAL THICKNESS RANGE, THE MORPHOLOGY WILL BE LAMELLAR AND THAT THE LAMELLAE WILL FORM PERPENDICULAR TO THE SUBSTRATE. THE CONDITIONS FOR CHEMICAL STABILITY AND OXYGENPARTIAL PRESSURE FOR THE COEXISTENCE OF ZRO(2) WITH MO, ZRC,FOR ZRN WILL BE EXAMINED BY ANALYSIS OF THE THERMODYNAMIC FREE ENERGY OF FORMATION DATA, AND THESE, WHEN PLOTTED AGAINST TEMPERATURE (ELLINGHAM PLOTS), WILL ALLOW IDENTIFICATION OF ANY WINDOW OF PERMITTED COEXISTENCE OF ZRO(2) WITH MO, ZRC, OR ZRN. A HIGH TEMPERATURE, ATMOSPHERE-CONTROLLED, METAL STRIP-HEATER WILL BE USED TO PROBE QUICKLY FOR THESE COMPLEX EUTECTIC SYSTEMS. WITH THE INFORMATION THAT A EUTECTIC SYSTEM EXISTS FOR A DETERMINED OXYGEN PARTIAL PRESSURE, THE PROPER LASER SOURCE/DIRECTIONALSOLIDIFICATION CONDITIONS TO GROW WELL-ALIGNED LAMELLAR STRUCTURES WILL BE ESTABLISHED. OPTICAL AND SCANNING ELECTRON MICROGRAPHS OF THESE FILMS WILL BE MADE. THE PHASES WILL BE IDENTIFIED BY X-RAY ANALYSIS.