THE CHARACTERIZATION OF TI- AND CA-MH SYSTEMS IN THE HIGH-TEMPERATURECHEMICAL HEAT-PUMP FOR GAS-COOLED REACTOR APPLICATIONS

Ca-Ni, Ca-Mg, Ti-Cu and Ti-Cr alloy systems, which have high melting p oints and hopefully high hydrogen absorption capacities with a high he at of reactor, are prepared in the compositional range 5-79 wt.% secon dary additives. Absorption of hydrogen by these systems has been studi ed in the testing temperature range from 300 to 1200 degrees C. Ca-Ni compounds (10-78.5.wt.% Ni), which encompass the intermetallic compoun ds CaNi2 and CaNi3 in this range, are found to show a high hydrogen ab sorption, much more than 1.5 wt.% H-2 up to 600 degrees C. On the cont rary, Ca-Mg compounds (37.8-64.5 wt.% Mg) reveal good absorption and d issociation behaviors at temperatures from 320 to 400 degrees C under a hydrogen pressure of 0.5-2 Mpa and clear dependence of the absorptio n capacity on the composition ratio. Ti-52.4wt.% CU, with CuO ternary addition (5 wt.%) to enhance absorption rate, shows a very interesting behavior at 530 degrees C, i.e. secondary plateau at 0.02-0.1 MPa. Ti -5 wt.% Cr shows 3.5 wt.% H-2 absorption capacity at 300 and 500 degre es C at 0.1 MPa, but not such good dissociation is found at 300 degree s C. These data suggest that in Ca-Mg or Ca-Ni systems the hydrogen ab sorption capacity is determined by the amount of the secondary element ; the crystal structure appears to be of importance, and Ti-Cr systems are found to be possible for high temperature use as the MH material of the heat pump mentioned above.