IMPROVED REGENERATOR MATERIALS FOR CRYOCOOLERS

JAPANESE RESEARCHERS HAVE RECENTLY DEVELOPED ER-BASED ALLOYS THAT HAVE LARGE SPECIFIC HEATS BELOW 15K, AND HAVE DEMONSTRATED IMPROVED REGENERATOR PERFORMANCE USING THESE MATERIALS. THESE ALLOYS, HOWEVER, ARE VERY EXPENSIVE AND BRITTLE. THIS PROJECT FOCUSES ON INEXPENSIVE CERAMICS THAT HAVE MUCH LARGER (PEAK) SPECIFIC HEATS THAN THE ER-BASED ALLOYS. IN AN EFFORT TO OVERCOME THEIR LOW THERMAL CONDUCTIVITIES, THESE CERAMICS THEY WILL BE LOADED IN POWDER FROM INTO CESLUM AND THALLOUS HALIDES THAT HAVE METALLIC-LIKE THERMAL CONDUCTIVITIES. AN ADDITIONAL BENEFITOF THIS COMPOSITE APPROACH IS THAT THE GRAIN SIZE OF THE CERAMIC POWDER BROADENS THE SPECIFIC HEAT PEAK. THE POSITIONS OF THE SPECIFIC HEAT PEAKS CAN BE TEMPERATURE-SHIFTED BY DOPING, AND ONE FE-DOPED CASE WILL BE INVESTIGATED. (A SUBSTANTIAL DATABASE EXISTS ON THESE CERAMICS FROM PREVIOUS AIR FORCE PROGRAMS AIMED AT OTHER APPLICATIONS, INCLUDING A VARIETY OF DOPANT EFFECTS.) IN PHASE I, A MATRIX OF COMPOSITE SAMPLES WILL BE MADE WITH POWDER-GRAIN SIZES OF 0.02, 0.2, AND 2.0 MUM, AND THE THERMAL PROPERTIES OF THESE COMPOSITES WILL BE MEASURED FROM 4.2 TO 15K. THE HARDNESS OF THESE COMPOSITES WILL ALSOBE MEASURED, AND SPECIFIC COMPOSITES WILL BE RECOMMENDED FOR A PHASE II PROGRAM AIMED AT REGENERATOR AND CRYOCOOLER TESTINGS. JAPANESE RESEARCHERS HAVE RECENTLY DEVELOPED ER-BASED ALLOYS THAT HAVE LARGE SPECIFIC HEATS BELOW 15K, AND HAVE DEMONSTRATED IMPROVED REGENERATOR PERFORMANCE USING THESE MATERIALS. THESE ALLOYS, HOWEVER, ARE VERY EXPENSIVE AND BRITTLE. THIS PROJECT FOCUSES ON INEXPENSIVE CERAMICS THAT HAVE MUCH LARGER (PEAK) SPECIFIC HEATS THAN THE ER-BASED ALLOYS. IN AN EFFORT TO OVERCOME THEIR LOW THERMAL CONDUCTIVITIES, THESE CERAMICS THEY WILL BE LOADED IN POWDER FROM INTO CESLUM AND THALLOUS HALIDES THAT HAVE METALLIC-LIKE THERMAL CONDUCTIVITIES. AN ADDITIONAL BENEFITOF THIS COMPOSITE APPROACH IS THAT THE GRAIN SIZE OF THE CERAMIC POWDER BROADENS THE SPECIFIC HEAT PEAK. THE POSITIONS OF THE SPECIFIC HEAT PEAKS CAN BE TEMPERATURE-SHIFTED BY DOPING, AND ONE FE-DOPED CASE WILL BE INVESTIGATED. (A SUBSTANTIAL DATABASE EXISTS ON THESE CERAMICS FROM PREVIOUS AIR FORCE PROGRAMS AIMED AT OTHER APPLICATIONS, INCLUDING A VARIETY OF DOPANT EFFECTS.) IN PHASE I, A MATRIX OF COMPOSITE SAMPLES WILL BE MADE WITH POWDER-GRAIN SIZES OF 0.02, 0.2, AND 2.0 MUM, AND THE THERMAL PROPERTIES OF THESE COMPOSITES WILL BE MEASURED FROM 4.2 TO 15K. THE HARDNESS OF THESE COMPOSITES WILL ALSOBE MEASURED, AND SPECIFIC COMPOSITES WILL BE RECOMMENDED FOR A PHASE II PROGRAM AIMED AT REGENERATOR AND CRYOCOOLER TESTINGS.