Studies pertaining to hydrogen car development. Part A. The kinetics and mechanism of magnesium alloy-hydride formation and dissociation

Technical Report · Tue Oct 01 04:00:00 EDT 1974

OSTI ID:7287675

Douglass, D L

The reaction between high-pressure hydrogen and Mg-10Al to form MgH/sub 2/ in the range of 400 to 450/sup 0/C was found to be a diffusion-controlled process. Initially hydrogen dissolved rapidly into the metal particles, and MgH/sub 2/ generally nucleated homogeneously as spherical particles. Growth of the particles was controlled by hydrogen diffusion in the metal and the kinetics followed the Johnson-Mehl relationship. The particles were readily hydrided to 7 w/o hydrogen and were found to exhibit very little fragmentation. Dehydriding followed the same rate law and was found to be complete in 90 minutes at 300/sup 0/C, these conditions being favorable for the use of this hydride in vehicles combusting hydrogen. The reaction involving Mg-25Ni resulted in two hydrides, MgH/sub 2/ and Mg/sub 2/NiH/sub 4/, the former being more stable and forming first. The kinetics also followed the same rate law. Dehydriding occurred by dissociation of some of the Mg/sub 2/NiH/sub 4/ first, followed by complete dissociation of the remaining Mg/sub 2/NiH/sub 4/ and the MgH/sub 2/. The dehydriding curves showed two distinct regions corresponding to these steps. The alloy was two-phase; the second phase Mg/sub 2/Ni existed as eutectic plates which hydrided after the Mg matrix, and as primary plates which hydrided after the eutectic plates. The amount of the large primary Mg/sub 2/Ni plates was less in the machined particles than calculated from the lever law due to the brittle nature of the phase which enabled it to crack and drop out during machining. The Mg-25Ni alloy fragmented much more than the Mg-10Al alloy and also was found to dissociate slower at a given temperature. An analysis of numerus factors required of hydrides for use in vehicular applications showed that Mg-10Al was much better than Mg-25Ni and may be feasible with present-day technology.

• Research Organization: California Univ., Los Angeles (USA). School of Engineering and Applied Science
• OSTI ID: 7287675
• Report Number(s): PB-242130; UCLA-ENG-7489; DOT-TST-75-98
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
080201* -- Hydrogen-- Chemisorption Storage
33 ADVANCED PROPULSION SYSTEMS
330800 -- Emission Control-- Alternative Fuels
36 MATERIALS SCIENCE
360105 -- Metals & Alloys-- Corrosion & Erosion
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM HYDRIDES
AUTOMOBILES
CHEMICAL REACTION KINETICS
FUELS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN FUELS
HYDROGEN STORAGE
INTERMETALLIC COMPOUNDS
KINETICS
MAGNESIUM ALLOYS
MAGNESIUM COMPOUNDS
MAGNESIUM HYDRIDES
NICKEL ALLOYS
NICKEL COMPOUNDS
NICKEL HYDRIDES
REACTION KINETICS
SORPTIVE PROPERTIES
STORAGE
SYNTHETIC FUELS
TRANSITION ELEMENT COMPOUNDS
VEHICLES