Equilibrium involving selected LaNi/sub x/ and LaCo/sub 5-x/M/sub x/ hydrides: phase transformations and related studies
Phase transformations of LaNi/sub 5/, La/sub 2/Ni/sub 3/, LaNi, and La/sub 7/Ni/sub 3/ at H/sub 2/ pressures and temperatures up to 700 atm and 550/sup 0/C are investigated for the first time. At 525/sup 0/C and pressures less than 60 atm LaNi/sub 5/ exists as ..cap alpha.. phase LaNi/sub 5/. Higher pressures cause the formation of phase f nominal composition LaNiH/sub approx. 3.5/ together with LaNi/sub 13/H/sub approx. 3.5/ or Ni. LaNi at 525/sup 0/C and intermediate pressures less than 9 atm exists as LaH/sub 3-x/ and LaNi/sub 5/. At higher pressures only the LaNiH/sub approx. 3.5/ phases are observed. Desorption isotherms for the first order transition from these high pressure phases into the low pressure phases are obtained for the starting materials LaNi/sub 5/ and LaNi. Kinetic results for the LaNi phase transformation are also obtained and a mechanism suggested. Equipment designed for conduction of these experiments is described. Also the complications due to the non-ideality of H/sub 2/ gas under such conditions are considered. The hydriding characteristics of LaCo/sub 4/ /sub 4/Al/sub 0/ /sub 6/ and LaCo/sub 4/ /sub 4/Ga/sub 0/ /sub 6/ are examined in order to determine the effect of substitutions upon the high pressure phase LaCo/sub 5/H/sub 9/. As contracted with LaCo/sub 5/H/sub z/ at pressures of order 100 atm, the substitution of Al and Ga increases the hydrogen storage capacity. During studies of the effect of O/sub 2/ upon the metal hydride LaCo/sub 5/H/sub z/, three reactions are observed: (1) H/sub 2/O formation by the metal hydride with a first order type dependence upon z, (2) H/sub 2/ gas phase reaction with O/sub 2/, and (3) at temperatures greater than 40/sup 0/C, a matrix oxidation reaction. Results of a study are presented which determines the superconducting T/sub c/ of several A15 type metal hydrides (Nb/sub 3/Au/sub 0/ /sub 75/Ir/sub 0/ /sub 25/H/sub z/ and Nb/sub 3/Au/sub 1-x/Ge/sub x/H/sub z/). T/sub c/ is observed to decrease with H content.
- Research Organization:
- California Univ., San Diego (USA)
- OSTI ID:
- 6171217
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
080201* -- Hydrogen-- Chemisorption Storage
36 MATERIALS SCIENCE
360204 -- Ceramics
Cermets
& Refractories-- Physical Properties
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
ALUMINIUM ALLOYS
CHEMICAL REACTIONS
COBALT ALLOYS
COBALT COMPOUNDS
COBALT HYDRIDES
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
GALLIUM ALLOYS
GERMANIUM COMPOUNDS
GERMANIUM HYDRIDES
GOLD COMPOUNDS
GOLD HYDRIDES
HYDRIDATION
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
INTERMETALLIC COMPOUNDS
IRIDIUM COMPOUNDS
IRIDIUM HYDRIDES
LANTHANUM ALLOYS
LANTHANUM COMPOUNDS
LANTHANUM HYDRIDES
NICKEL ALLOYS
NIOBIUM COMPOUNDS
NIOBIUM HYDRIDES
NONMETALS
OXIDATION
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
RARE EARTH ALLOYS
RARE EARTH COMPOUNDS
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS