Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention pertains to granulating metal materials which are
capable of reacting with and absorbing hydrogen, and to conditioning or
actlvating the metal material to its s-tate in which i-t will readily react wi-th
and absorb hydrogen.
The storage of hydrogen in the form of a granular metal hydride has
several advantages over other storage methods such as cryogenic storage
of liquid hydrogen or pressurized storage of gaseous hydrogen. Primarily,
it is a safe, efficient method of storing hydrogen. The device for storing
hydrogen as a metal hydride is commonly referred to as a hydride reservoir,
10 which consists of a pressure vessel or container filled with a granular
metal material capable of being converted to a metal hydride. The container
is provided with a hydrogen gas connection and a means of handling the
thermal load encountered during hydriding (reaction with and absorption of
hydrogen) and dehydriding (decomposition of metal hydride and release of
hydrogen) .
Heretofore, the metal material which was to be utilized in the hydride
vessel or container was ground into small particles having a size of about
one millimeter or less using conventional reduction equipment capable of
handling very hard material. The granular metal material then requlred
20 condltioning before a practical forward rate of hydriding can be attained.
This conditioning involves an activation of the metal material to a state in
which it is capable of readily reacting with and absorbing hydrogen. The
conditioning involves heating the m-etal material, subjecting the material
to a vacuum to outgas the surface thereof, and flushing the vacuumed
material with hydrogen gas which apparently further cleans the particle
surfaces of the metal material and initiates a hydriding reaction. However,
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at the temperature at which the condltioning is accomplished, there is
relatively little hydrogen actually absorbed by the metal material. Never-
theless, it is evident Erom the changes occurring in the metal material that
a reaction does occur during the conditioning stage. Severe embrittlement
of the metal material occurs, and an appreciable breakdown in particle size
takes place (see publication BNL 50589, November 1976 from Brookhaven
~ational Laboratories) during the conditioning stage. Generally, the
conditioning stage must be repeated in cyclic fashion to obtain adequate
activation, i.e., a second cycle, and usually subsequent cycles, of
vacuuming the material and then flushing the material with hydrogen are
required following the initial vacuuming and flushing.
The principal objective of the present invention was to provide a
process for simultaneously granulating and conditioning the metal material,
whereby the reduction apparatus heretofore necessary in grinding the very
hard metal material is eliminated. Another objective was to achieve
activation more effectively and re efficiently.
The invention may be generally defined as a method for s~multa-
neously granulating a metal material selected from the group consisting of
titanium, nickel, rare earth metals, calcium, magnesium, iron-titanium
alloys, lanthanam-nickel alloys, calcium-nickel alloys, mischmetal-nickel
alloys, manganese-nickel alloys, manganese-iron-titanium alloys, and
mischmetal-calcium-nickel alloys, and conditioning or activating the metal
material, said method comprising the following steps:
(l) heating the metal material to a temperature within the range
of about 200F and about 1000F, said metal material having an average
particle siæe ~thin the range of about 1 centimeter to about 1 meter;
(2) treating the metal material with hydrogen at a hydrogen
partial pressure of between one atmosphere and about 50 atmospheres to
activate the metal material to a state in which it is capable of readily
reacting with and absorbing hydrogen when contacted with hydrogen at a
given temperature and pressure and of releasing hydrogen when either the
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temperature is increased above the given temperature, the pressure is reduced
below the given pressure or the temperature -Ls increased above the given
temperature and the pressure is concurrently reduced below the given
pressure; and
(3) concurrently subjecting the metal material to mechanlcal
impact sufficient to reduce its average particle size to less than about 1
centimeter.
In a preferred embodiment, the heating and hydrogen treatment
are performed within a rotary ball mill, with the ball mill being rotated
to subject the metal material to mechanical impact. The ball mill can
contain a plurality of balls made of a material which is substantially
harder than the metal material which is being heated and treated with
hydrogen.
The activating mechanism which occurs as the metal material is
treated with hydrogen also produces a profound change in the physical
properties of the metal material. The metal material tends to develop
stresses within the particles causing fractioning of the material along the
stress boundaries. The material becomes extremely fragile and can be broken
into fine particles with minimal mechanical impact.
When the metal material is broken into small particles in the
presence of hydrogen, the newly created surfaces oE the small particles have
not been contaminated with surface contaminants such as oxygen and water.
The small particles of metallic material readily react with hydrogen to form
the activated metallic hydride material which is capable of reversibly
absorbing large quantities of hydrogen. In contrast, when the metal material
is ground to small particle size on conventional reduction equipment, the
material must be subjected to a vacuum followed by heating in the presence
of hydrogen, with the vacuuming and hydrogen treatment being repeated
numerous times before the material is capable of reversibly absorbing its
maximum amount of hydrogen. In accordance with the present invention, the
same effect is achieved in the single activation which occurs simultaneously
with the particle reduction.
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A metal material selected from the group CQnSiSting of iron, titanium,
nickel, rare earth metals, calcium, magnesium, manganese, and mixtures
or alloys thereof is simultaneously granulated and ac-tivated to a state in
which it is capable of readily reacting with and absorbing hydrogen when
contacted with hydrogen at a given temperature and pressure and of
releasing hydrogen when either the temperature is increased above the
given temperature, the pressure is reduced below the given pressure, or
the temperature is increased above the given temperature and the pressure
is concurrently reduced below the given pressure. The activation and
10 particle size reduction is accomplished by heating the metal material
having a particle size greater than about 1 centimeter to a temperature of
at least about 200 F. The heated metal material is then treated with
hydrogen while concurrently being ~ubjected to mechanical impact sufficient
to reduce the average particle size of the material to less than about 1
centimeter. The hydrogen and mechanical impact treatment can, of course,
be started anytime during the period in which the material is being heated.
The duration oi the hydrogen and mechanical impact treatment depends on
the initial particle size of the metal material. Chunks of material up to
about 1 meter or more in diameter can be processed according to this
20 invention if appropriate means are provided for subjecting the chunk of
material to mechanical impact.
In a preferred embodiment of the invention, the metal material is
placed in a rotary ball mill. As the ball mill rotates, the material is heated
and treated with hydrogen. Alternatively, the material can be heated in a
separate heating means, with the heated material being fed to the ball
mill for treatment with the hydrogen. The rotation of the ball mill produces
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mechanical impact between particles of the material and between the
ma-terial and the internal surfaces of the ball mill. The ball mill may
also CQntain a plurality oE balls made of material which is subs-tantially
harder than the metal material which has been heated and treated with
hydrogen .
In the heat and hydrogen treatment, the metal material is heated
to a temperature of between about 200 F and 1000 F, and subjected to
hydrogen at a hydrogen partial pressure of between about 1 atmosphere
and 50 atmospheres. Just prior to the hydrogen treatment, the metal material
10 is advantageously subjected to a vacuum in order to outgas the surface of
the material. Flushing of the material with an inert gas such as argon can
also be effective in outgasing the material prior to the hydrogen treatment.
Whereas, this invention is described with respect to particular
embodiments, it is to be understood that changes may be made therein and
other embodiments constructed without departing from the novel inventive
concepts set forth in the claims which follow.
