U.S. patent application number 11/497449 was filed with the patent office on 2006-11-30 for mg-ni hydrogen storage composite having high storage capacity and excellent room temperature kinetics.
Invention is credited to Michael A. Fetcenko, Taihei Ouchi, Stanford R. Ovshinsky, Melanie Reinhout, Kwo Young.
Application Number | 20060266441 11/497449 |
Document ID | / |
Family ID | 34653166 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266441 |
Kind Code |
A1 |
Fetcenko; Michael A. ; et
al. |
November 30, 2006 |
Mg-Ni hydrogen storage composite having high storage capacity and
excellent room temperature kinetics
Abstract
A hydrogen storage alloy having an atomically engineered
microstructure that both physically and chemically absorbs
hydrogen. The atomically engineered microstructure has a
predominant volume of a first microstructure which provides for
chemically absorbed hydrogen and a volume of a second
microstructure which provides for physically absorbed hydrogen. The
volume of the second microstructure may be at least 5 volume % of
atomically engineered microstructure. The atomically engineered
microstructure may include porous micro-tubes in which the porosity
of the micro-tubes physically absorbs hydrogen. The micro-tubes may
be at least 5 volume % of the atomically engineered microstructure.
The micro-tubes may provide proton conduction channels within the
bulk of the hydrogen storage alloy and the proton conduction
channels may be at least 5 volume % of the atomically engineered
microstructure.
Inventors: |
Fetcenko; Michael A.;
(Rochester, MI) ; Young; Kwo; (Troy, MI) ;
Ouchi; Taihei; (Rochester, MI) ; Reinhout;
Melanie; (Shelby Twp, MI) ; Ovshinsky; Stanford
R.; (Bloomfield Hills, MI) |
Correspondence
Address: |
ENERGY CONVERSION DEVICES, INC.
2956 WATERVIEW DRIVE
ROCHESTER HILLS
MI
48309
US
|
Family ID: |
34653166 |
Appl. No.: |
11/497449 |
Filed: |
August 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10733702 |
Dec 11, 2003 |
|
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11497449 |
Aug 2, 2006 |
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Current U.S.
Class: |
148/403 ;
420/459; 420/900; 502/326; 502/328; 502/330 |
Current CPC
Class: |
Y10T 428/12944 20150115;
Y02E 60/10 20130101; H01M 4/383 20130101; H01M 10/345 20130101;
Y02E 60/32 20130101 |
Class at
Publication: |
148/403 ;
420/459; 420/900; 502/326; 502/328; 502/330 |
International
Class: |
C22C 45/04 20060101
C22C045/04 |
Claims
1. A hydrogen storage alloy comprising having an atomically
engineered microstructure that both physically and chemically
absorbs hydrogen.
2. The hydrogen storage alloy of claim 1, wherein said atomically
engineered microstructure has a predominant volume of a first
microstructure which provides for chemically absorbed hydrogen and
a volume of a second microstructure which provides for physically
absorbed hydrogen.
3. The hydrogen storage alloy of claim 2, wherein said volume of
said second microstructure comprises at least 5 volume % of said
atomically engineered microstructure.
4. The hydrogen storage alloy of claim 1, wherein said atomically
engineered microstructure includes porous micro-tubes, whereby the
porosity of said micro-tubes physically absorbs hydrogen.
5. The hydrogen storage alloy of claim 4, wherein said micro-tubes
comprise at least 5 volume % of said atomically engineered
microstructure.
6. The hydrogen storage alloy of claim 1, wherein said atomically
engineered microstructure includes micro-tubes, and said
micro-tubes provide proton conduction channels within the bulk of
said hydrogen storage alloy.
7. The hydrogen storage alloy of claim 6, wherein said proton
conduction channels comprise at least 5 volume % of said atomically
engineered microstructure.
Description
FILED OF THE INVENTION
[0001] The instant invention relates generally to hydrogen storage
materials and more specifically to a new composite hydrogen storage
material having heretofore unheard of properties. Specifically the
instant hydrogen storage material provides for a storage capacity
of up to 4.86 weight percent hydrogen with a high adsorption rate
at temperatures as low as 30.degree. C. and an absorption pressure
of less than about 150 PSI. The composite materials are light
weight and absorb at least 3 weight percent in less than two
minutes at 30.degree. C. More remarkably, the composite materials
also have the ability to fully desorb the stored hydrogen at
temperatures as low as 250.degree. C., an ability not heretofore
seen in materials with such a high total storage capacity. Even
more amazingly the same material can desorb 2.51 weight percent of
the stored hydrogen at 90.degree. C. and 1.2 weight percent at
30.degree. C. In addition these material are relatively inexpensive
and easy to produce.
BACKGROUND OF THE INVENTION
[0002] Growing energy needs have prompted specialists to take
cognizance of the fact that the traditional energy resources, such
as coal, petroleum or natural gas, are not inexhaustible, or at
least that they are becoming costlier all the time, and that it is
advisable to consider replacing them with hydrogen.
[0003] Hydrogen may be used, for example, as fuel for
internal-combustion engines in place of hydrocarbons. In this case
it has the advantage of eliminating atmospheric pollution through
the formation of oxides of carbon, nitrogen and sulfur upon
combustion of the hydrocarbons. Hydrogen may also be used to fuel
hydrogen-air fuel cells for production of the electricity needed
for electric motors.
[0004] One of the problems posed by the use of hydrogen is its
storage and transportation. A number of solutions have been
proposed:
[0005] Hydrogen may be stored under high pressure in steel
cylinders, but this approach has the drawback of requiring
hazardous and heavy containers which are difficult to handle (in
addition to having a low storage capacity of about 1% by weight).
Hydrogen may also be stored in cryogenic containers, but this
entails the disadvantages associated with the use of cryogenic
liquids; such as, for example, the high cost of the containers,
which also require careful handling. There are also "boil off"
losses of about 2-5% per day.
[0006] Another method of storing hydrogen is to store it in the
form of a hydride, which then is decomposed at the proper time to
furnish hydrogen. The hydrides of iron-titanium, lanthanum-nickel,
vanadium, and magnesium have been used in this manner, as described
in French Pat. No. 1,529,371.
[0007] Since the initial discovery that hydrogen could be stored in
a safe, compact solid state metal hydride form, researchers have
been trying to produce hydrogens storage materials which have
optimal properties. Generally, the ideal material properties that
these researchers have been attempting to achieve are: 1) a high
hydrogen storage capacity; 2) light weight materials; 3)adequate
hydrogen absorption/desorption temperatures; 4) adequate
absorption/desorption pressures; 5) fast absorption kinetics; and
6) a long absorption/desorption cycle life. In addition to these
material properties, ideal materials would be inexpensive and easy
to produce.
[0008] The MgH.sub.2--Mg system is the most appropriate of all
known metal-hydride and metal systems that can be used as
reversible hydrogen-storage systems because it has the highest
percentage by weight (7.65% by weight) of theoretical capacity for
hydrogen storage and hence the highest theoretical energy density
(2332 Wh/kg; Reilly & Sandrock, Spektrum der Wissenschaft,
April 1980, 53) per unit weight of storage material.
[0009] Although this property and the relatively low price of
magnesium make the MgH.sub.2--Mg seem the optimum hydrogen storage
system for transportation, for hydrogen-powered vehicles that is,
its unsatisfactory kinetics have prevented it from being used up to
the present time. It is known for instance that pure magnesium can
be hydrided only under drastic conditions, and then only very
slowly and incompletely. The dehydriding rate of the resulting
hydride is also unacceptable for a hydrogen storage material
(Genossar & Rudman, Z. f. Phys. Chem., Neue Folge 116, 215
[1979], and the literature cited therein).
[0010] Moreover, the hydrogen storage capacity of a magnesium
reserve diminishes during the charging/discharging cycles. This
phenomenon may be explained by a progressive poisoning of the
surface, which during charging renders the magnesium atoms located
in the interior of the reserve inaccessible to the hydrogen.
[0011] To expel the hydrogen in conventional magnesium or
magnesium/nickel reserve systems, temperatures of more than
250.degree. C. are required, with a large supply of energy at the
same time. The high temperature level and the high energy
requirement for expelling the hydrogen have the effect that, for
example, a motor vehicle with an internal combustion engine, cannot
exclusively be operated from these alloys. This occurs because the
energy contained in the exhaust gas, in the most favorable case
(full load), is sufficient for meeting only 50% of the hydrogen
requirement of the internal combustion engine from a magnesium or
magnesium/nickel alloy. Thus, the remaining hydrogen demand must be
taken from another hydride alloy. For example, this alloy can be
titanium/iron hydride (a typical low-temperature hydride store)
which can be operated at temperatures down to below 0.degree. C.
These low-temperature hydride alloys have the disadvantage of
having a low hydrogen storage capacity.
[0012] Storage materials have been developed in the past, which
have a relatively high storage capacity but from which hydrogen is
nevertheless expelled at temperatures of up to about 250.degree. C.
U.S. Pat. No. 4,160,014 describes a hydrogen storage material of
the formula
Ti.sub.[1-x]Zr.sub.[x]Mn.sub.[2-y-z]Cr.sub.[y]V.sub.[z], wherein
x=0.05 to 0.4, y=0 to 1 and z=0 to 0.4. Up to about 2% by weight of
hydrogen can be stored in such an alloy. In addition to this
relatively low storage capacity, these alloys also have the
disadvantage that the price of the alloy is very high when metallic
vanadium is used.
[0013] Moreover, U.S. Pat. No. 4,111,689 has disclosed a storage
alloy which comprises 31 to 46% by weight of titanium, 5 to 33% by
weight of vanadium and 36 to 53% by weight of iron and/or
manganese. Although alloys of this type have a greater storage
capacity for hydrogen than the alloy according to U.S. Pat. No.
4,160,014, hereby incorporated by reference, they have the
disadvantage that temperatures of at least 250.degree. C. are
necessary in order to completely expel the hydrogen. At
temperatures of up to about 100.degree. C., about 80% of the
hydrogen content can be discharged in the best case. However, a
high discharge capacity, particularly at low temperatures, is
frequently necessary in industry because the heat required for
liberating the hydrogen from the hydride stores is often available
only at a low temperature level.
[0014] In contrast to other metals or metal alloys, especially such
metal alloys which contain titanium or lanthanum, magnesium is
preferred for the storage of hydrogen not only because of its lower
material costs, but above all, because of its lower specific weight
as a storage material. However, the hydriding
Mg+H.sub.2.fwdarw.MgH.sub.2 is, in general, more difficult to
achieve with magnesium, inasmuch as the surface of the magnesium
will rapidly oxidize in air so as to form stable MgO and/or
Mg(OH).sub.2 surface layers. These layers inhibit the dissociation
of hydrogen molecules, as well as the absorption of produced
hydrogen atoms and their diffusion from the surface of the
granulate particles into the magnesium storage mass.
[0015] Intensive efforts have been devoted in recent years to
improve the hydriding ability of magnesium by doping or alloying it
with such individual foreign metals as aluminum (Douglass, Metall.
Trans. 6a, 2179 [1975]) indium (Mintz, Gavra, & Hadari, J.
Inorg. Nucl. Chem. 40, 765 [1978]), or iron (Welter & Rudman,
Scripta Metallurgica 16, 285 [1982]), with various foreign metals
(German Offenlegungsschriften 2 846 672 and 2 846 673), or with
intermetallic compounds like Mg.sub.2 Ni or Mg.sub.2Cu (Wiswall,
Top Appl. Phys. 29, 201 [1978] and Genossar & Rudman, op. cit.)
and LaNi.sub.5 (Tanguy et al., Mater. Res. Bull. 11, 1441
[1976]).
[0016] Although these attempts did improve the kinetics somewhat,
certain essential disadvantages have not yet been eliminated from
the resulting systems. The preliminary hydriding of magnesium doped
with a foreign metal or intermetallic compound still demands
drastic reaction conditions, and the system kinetics will be
satisfactory and the reversible hydrogen content high only after
many cycles of hydriding and dehydriding. Considerable percentages
of foreign metal or of expensive intermetallic compound are also
necessary to improve kinetic properties. Furthermore, the storage
capacity of such systems are generally far below what would
theoretically be expected for MgH.sub.2.
[0017] It is known that the storage quality of magnesium and
magnesium alloys can also be enhanced by the addition of materials
which may help to break up stable oxides of magnesium. For example,
such an alloy is Mg.sub.2Ni, in which the Ni appears to form
unstable oxides. In this alloy, thermodynamic examinations
indicated that the surface reaction
Mg.sub.2Ni+O.sub.2.fwdarw.2MgO+Ni extended over nickel metal
inclusions which catalyze the hydrogen dissociation-absorption
reaction. Reference may be had to A. Seiler et al., Journal of
Less-Common Metals 73, 1980, pages 193 et seq.
[0018] One possibility for the catalysis of the hydrogen
dissociation-absorption reaction on the surface of magnesium lies
also in the formation of a two-phase alloy, wherein the one phase
is a hydride former, and the other phase is a catalyst. Thus, it is
known to employ galvanically-nickeled magnesium as a hydrogen
storage, referring to F. G. Eisenberg et al. Journal of Less-Common
Metals 74, 1980, pages 323 et seq. However, there were encountered
problems during the adhesion and the distribution of the nickel
over the magnesium surface.
[0019] In order to obtain an extremely dense and good adherent
catalyst phase under the formation alone of equilibrium phases, it
is also known that for the storage of hydrogen there can be
employed an eutectic mixture of magnesium as a hydride-forming
phase in conjunction with magnesium copper (Mg.sub.2Cu), referring
to J. Genossar et al., Zeitschrift fur Physikalische Chemie Neue
Folge 116, 1979, pages 215 et seq. The storage capacity per volume
of material which is achieved through this magnesium-containing
granulate does not, however, meet any high demands because of the
quantity of magnesium copper which is required for the eutectic
mixture.
[0020] The scientists of this era looked at various materials and
postulated that a particular crystalline structure is required for
hydrogen storage, see, for example, "Hydrogen Storage in Metal
Hydride", Scientific American, Vol. 242, No. 2, pp. 118-129,
February, 1980. It was found that it is possible to overcome many
of the disadvantages of the prior art materials by utilizing a
different class of materials, disordered hydrogen storage
materials. For example, U.S. Pat. No. 4,265,720 to Guenter Winstel
for "Storage Materials for Hydrogen" describes a hydrogen storage
body of amorphous or finely crystalline silicon. The silicon is
preferably a thin film in combination with a suitable catalyst and
on a substrate.
[0021] Laid-open Japanese Patent Application No. 55-167401,
"Hydrogen Storage Material," in the name of Matsumato et al,
discloses bi or tri-element hydrogen storage materials of at least
50 volume percent amorphous structure. The first element is chosen
from the group Ca, Mg, Ti, Zr, Hf, V, Nb, Ta, Y and lanthanides,
and the second from the group Al, Cr, Fe, Co, Ni, Cu, Mn and Si. A
third element from the group B, C, P and Ge can optionally be
present. According to the teaching of No. 55-167401, the amorphous
structure is needed to overcome the problem of the unfavorably high
desorption temperature characteristic of most crystalline systems.
A high desorption temperature (above, for example, 150.degree. C.)
severely limits the uses to which the system may be put.
[0022] According to Matsumoto et al, the material of at least 50%
amorphous structure will be able to desorb at least some hydrogen
at relatively low temperatures because the bonding energies of the
individual atoms are not uniform, as is the case with crystalline
material, but are distributed over a wide range.
[0023] Matsumoto et al claims a material of at least 50% amorphous
structure. While Matsumoto et al does not provide any further
teaching about the meaning of the term "amorphous," the
scientifically accepted definition of the term encompasses a
maximum short range order of about 20 Angstroms or less.
[0024] The use by Matsumato et al of amorphous structure materials
to achieve better desorption kinetics due to the non-flat
hysteresis curve is an inadequate and partial solution. The other
problems found in crystalline hydrogen storage materials,
particularly low useful hydrogen storage capacity at moderate
temperature, remain.
[0025] However, even better hydrogen storage results, i.e., long
cycle life, good physical strength, low absorption/desorption
temperatures and pressures, reversibility, and resistance to
chemical poisoning, may be realized if full advantage is taken of
modification of disordered metastable hydrogen storage materials.
Modification of disordered structurally metastable hydrogen storage
materials is described in U.S. Pat. No. 4,431,561 to Stanford R.
Ovshinsky et al. for "Hydrogen Storage Materials and Method of
Making the Same". As described therein, disordered hydrogen storage
materials, characterized by a chemically modified,
thermodynamically metastable structure, can be tailor-made to
possess all the hydrogen storage characteristics desirable for a
wide range of commercial applications. The modified hydrogen
storage material can be made to have greater hydrogen storage
capacity than do the single phase crystalline host materials. The
bonding strengths between the hydrogen and the storage sites in
these modified materials can be tailored to provide a spectrum of
bonding possibilities thereby to obtain desired absorption and
desorption characteristics. Disordered hydrogen storage materials
having a chemically modified, thermodynamically metastable
structure also have a greatly increased density of catalytically
active sites for improved hydrogen storage kinetics and increased
resistance to poisoning.
[0026] The synergistic combination of selected modifiers
incorporated in a selected host matrix provides a degree and
quality of structural and chemical modification that stabilizes
chemical, physical, and electronic structures and conformations
amenable to hydrogen storage.
[0027] The framework for the modified hydrogen storage materials is
a lightweight host matrix. The host matrix is structurally modified
with selected modifier elements to provide a disordered material
with local chemical environments which result in the required
hydrogen storage properties.
[0028] Another advantage of the host matrix described by Ovshinsky,
et al. is that it can be modified in a substantially continuous
range of varying percentages of modifier elements. This ability
allows the host matrix to be manipulated by modifiers to
tailor-make or engineer hydrogen storage materials with
characteristics suitable for particular applications. This is in
contrast to multi-component single phase host crystalline materials
which generally have a very limited range of stoichiometry
available. A continuous range of control of chemical and structural
modification of the thermodynamics and kinetics of such crystalline
materials therefore is not possible.
[0029] A still further advantage of these disordered hydrogen
storage materials is that they are much more resistant to
poisoning. As stated before, these materials have a much greater
density of catalytically active sites. Thus, a certain number of
such sites can be sacrificed to the effects of poisonous species,
while the large number of non-poisoned active sites still remain to
continue to provide the desired hydrogen storage kinetics.
[0030] Another advantage of these disordered materials is that they
can be designed to be mechanically more flexible than single phase
crystalline materials. The disordered materials are thus capable of
more distortion during expansion and contraction allowing for
greater mechanical stability during the absorption and desorption
cycles.
[0031] One drawback to these disordered materials is that, in the
past, some of the Mg based alloys have been difficult to produce.
Particularly those materials that did not form solutions in the
melt. Also, the most promising materials (i.e. magnesium based
materials) were extremely difficult to make in bulk form. That is,
while thin-film sputtering techniques could make small quantities
of these disordered alloys, there was no bulk preparation
technique.
[0032] Then in the mid 1980's, two groups developed mechanical
alloying techniques to produce bulk disordered magnesium alloy
hydrogen storage materials. Mechanical alloying was found to
facilitate the alloying of elements with vastly different vapor
pressures and melting points (such as Mg with Fe or Ti etc.),
especially when no stable intermetallic phases exist. Conventional
techniques like induction melting have been found to be inadequate
for such purposes.
[0033] The first of the two groups was a team of French scientists
which investigated mechanical alloying of materials of the Mg--Ni
system and their hydrogen storage properties. See Senegas, et al.,
"Phase Characterization and Hydrogen Diffusion Study in the
Mg--Ni--H System", Journal of the Less-Common Metals, Vol. 129,
1987, pp. 317-326 (binary mechanical alloys of Mg and Ni
incorporating 0, 10, 25 and 55 wt. % Ni); and also, Song, et al.
"Hydriding and Dehydriding Characteristics of Mechanically Alloyed
Mixtures Mg-wt. % Ni (x=5, 10, 25 and 55)", Journal of the
Less-Common Metals, Vol. 131, 1987, pp. 71-79 (binary mechanical
alloys of Mg and Ni incorporating 5, 10, 25 and 55 wt. % Ni).
[0034] The second of the two groups was a team of Russian
scientists which investigated the hydrogen storage properties of
binary mechanical alloys of magnesium and other metals. See Ivanov,
et al., "Mechanical Alloys of Magnesium--New Materials For Hydrogen
Energy", Doklady Physical Chemistry (English Translation) vol.
286:1-3, 1986, pp. 55-57, (binary mechanical alloys of Mg with Ni,
Ce, Nb, Ti, Fe, Co, Si and C); also, Ivanov, et al. "Magnesium
Mechanical Alloys for Hydrogen Storage", Journal of the Less-Common
Metals, vol. 131, 1987, pp. 25-29 (binary mechanical alloys of Mg
with Ni, Fe, Co, Nb and Ti); and Stepanov, et al., "Hydriding
Properties of Mechanical Alloys of Mg--Ni", Journal of the
Less-Common Metals, vol. 131, 1987, pp. 89-97 (binary mechanical
alloys of the Mg--Ni system). See also the collaborative work
between the French and Russian groups, Konstanchuk, et al., "The
Hydriding Properties of a Mechanical Alloy With Composition Mg-25%
Fe", Journal of the Less-Common Metals, vol. 131,1987, pp. 181-189
(binary mechanical alloy of Mg and 25 wt. % Fe).
[0035] Later, in the late 1980's and early 1990's, a Bulgarian
group of scientists (sometimes in collaboration with the Russian
group of scientists) investigated the hydrogen storage properties
of mechanical alloys of magnesium and metal oxides. See
Khrussanova, et al., "Hydriding Kinetics of Mixtures Containing
Some 3d-Transition Metal Oxides and Magnesium", Zeitschrift fur
Physikalische Chemie Neue Folge, Munchen, vol. 164, 1989, pp.
1261-1266 (comparing binary mixtures and mechanical alloys of Mg
with TiO.sub.2, V.sub.2O.sub.5, and Cr.sub.2O.sub.3); and Peshev,
et al., "Surface Composition of Mg--TiO.sub.2 Mixtures for Hydrogen
Storage, Prepared by Different Methods", Materials Research
Bulletin, vol. 24, 1989, pp. 207-212 (comparing conventional
mixtures and mechanical alloys of Mg and TiO.sub.2). See also,
Khrussanova, et al., "On the Hydriding of a Mechanically Alloyed
Mg(90%)--V.sub.2O.sub.5 (10%) Mixture", International Journal of
Hydrogen Energy, vol. 15, No. 11, 1990, pp. 799-805 (investigating
the hydrogen storage properties of a binary mechanical alloy of Mg
and V.sub.2O.sub.5); and Khrussanova, et al., "Hydriding of
Mechanically Alloyed Mixtures of Magnesium With MnO.sub.2,
Fe.sub.2O.sub.3, and NiO", Materials Research Bulletin, vol. 26,
1991, pp. 561-567 (investigating the hydrogen storage properties of
a binary mechanical alloys of Mg with and MnO.sub.2,
Fe.sub.2O.sub.3, and NiO). Finally, see also, Khrussanova, et al.,
"The Effect of the d-Electron Concentration on the Absorption
Capacity of Some Systems for Hydrogen Storage", Materials Research
Bulletin, vol. 26, 1991, pp. 1291-1298 (investigating d-electron
concentration effects on the hydrogen storage properties of
materials, including mechanical alloys of Mg and 3-d metal oxides);
and Mitov, et al., "A Mossbauer Study of a Hydrided Mechanically
Alloyed Mixture of Magnesium and Iron(III) Oxide", Materials
Research Bulletin, vol. 27, 1992, pp. 905-910 (Investigating the
hydrogen storage properties of a binary mechanical alloy of Mg and
Fe.sub.2O.sub.3).
[0036] More recently, a group of Chinese scientists have
investigated the hydrogen storage properties of some mechanical
alloys of Mg with other metals. See, Yang, et al., "The Thermal
Stability of Amorphous Hydride Mg.sub.50Ni.sub.50H.sub.54 and
Mg.sub.30Ni.sub.70H.sub.45" , Zeitschrift fur Physikalische Chemie,
Munchen, vol. 183, 1994, pp. 141-147 (Investigating the hydrogen
storage properties of the mechanical alloys Mg.sub.50Ni.sub.50 and
Mg.sub.30Ni.sub.70); and Lei, et al., "Electrochemical Behavior of
Some Mechanically Alloyed Mg--Ni-based Amorphous Hydrogen Storage
Alloys", Zeitschrift fur Physikalische Chemie, Munchen, vol.
183,1994, pp. 379-384 (investigating the electrochemical [i,.e
Ni--MH battery] properties of some mechanical alloys of Mg--Ni with
Co, Si, Al, and Co--Si).
[0037] Short-range, or local, order is elaborated on in U.S. Pat.
No. 4,520,039 to Ovshinsky, entitled Compositionally Varied
Materials and Method for Synthesizing the Materials, the contents
of which are incorporated by reference. This patent disclosed that
disordered materials do not require any periodic local order and
how spatial and orientational placement of similar or dissimilar
atoms or groups of atoms is possible with such increased precision
and control of the local configurations that it is possible to
produce qualitatively new phenomena. In addition, this patent
discusses that the atoms used need not be restricted to "d band" or
"f band" atoms, but can be any atom in which the controlled aspects
of the interaction with the local environment and/or orbital
overlap plays a significant role physically, electronically, or
chemically so as to affect physical properties and hence the
functions of the materials. The elements of these materials offer a
variety of bonding possibilities due to the multidirectionality of
d-orbitals. The multidirectionality ("porcupine effect") of
d-orbitals provides for a tremendous increase in density and hence
active storage sites. These techniques result in means of
synthesizing new materials which are disordered in several
different senses simultaneously.
[0038] Ovshinsky had previously shown that the number of surface
sites could be significantly increased by making an amorphous film
in which the bulk thereof resembled the surface of the desired
relatively pure materials. Ovshinsky also utilized multiple
elements to provide additional bonding and local environmental
order which allowed the material to attain the required
electrochemical characteristics. As Ovshinsky explained in
Principles and Applications of Amorphicity, Structural Change, and
Optical Information Encoding, 42 Journal De Physique at C4-1096
(October 1981): [0039] Amorphicity is a generic term referring to
lack of X-ray diffraction evidence of long-range periodicity and is
not a sufficient description of a material. To understand amorphous
materials, there are several important factors to be considered:
the type of chemical bonding, the number of bonds generated by the
local order, that is its coordination, and the influence of the
entire local environment, both chemical and geometrical, upon the
resulting varied configurations. Amorphicity is not determined by
random packing of atoms viewed as hard spheres nor is the amorphous
solid merely a host with atoms imbedded at random. Amorphous
materials should be viewed as being composed of an interactive
matrix whose electronic configurations are generated by free energy
forces and they can be specifically defined by the chemical nature
and coordination of the constituent atoms. Utilizing multi-orbital
elements and various preparation techniques, one can outwit the
normal relaxations that reflect equilibrium conditions and, due to
the three-dimensional freedom of the amorphous state, make entirely
new types of amorphous materials--chemically modified materials . .
.
[0040] Once amorphicity was understood as a means of introducing
surface sites in a film, it was possible to produce "disorder" that
takes into account the entire spectrum of effects such as porosity,
topology, crystallites, characteristics of sites, and distances
between sites. Thus, rather than searching for material changes
that would yield ordered materials having a maximum number of
accidently occurring surface bonding and surface irregularities,
Ovshinsky and his team at ECD began constructing "disordered"
materials where the desired irregularities were tailor made. See,
U.S. Pat. No. 4,623,597, the disclosure of which is incorporated by
reference.
[0041] The term "disordered", as used herein to refer to
electrochemical electrode materials, corresponds to the meaning of
the term as used in the literature, such as the following: [0042] A
disordered semiconductor can exist in several structural states.
This structural factor constitutes a new variable with which the
physical properties of the [material] . . . can be controlled.
Furthermore, structural disorder opens up the possibility to
prepare in a metastable state new compositions and mixtures that
far exceed the limits of thermodynamic equilibrium. Hence, we note
the following as a further distinguishing feature. In many
disordered [materials] . . . it is possible to control the
short-range order parameter and thereby achieve drastic changes in
the physical properties of these materials, including forcing new
coordination numbers for elements . . .
[0043] S. R. Ovshinsky, The Shape of Disorder, 32 Journal of
Non-Crystalline Solids at 22 (1979) (emphasis added).
[0044] The "short-range order" of these disordered materials are
further explained by Ovshinsky in The Chemical Basis of
Amorphicity: Structure and Function, 26:8-9 Rev. Roum. Phys. at
893-903 (1981): [0045] [S]hort-range order is not conserved . . .
Indeed, when crystalline symmetry is destroyed, it becomes
impossible to retain the same short-range order. The reason for
this is that the short-range order is controlled by the force
fields of the electron orbitals therefore the environment must be
fundamentally different in corresponding crystalline and amorphous
solids. In other words, it is the interaction of the local chemical
bonds with their surrounding environment which determines the
electrical, chemical, and physical properties of the material, and
these can never be the same in amorphous materials as they are in
crystalline materials . . . The orbital relationships that can
exist in three-dimensional space in amorphous but not crystalline
materials are the basis for new geometries, many of which are
inherently anti-crystalline in nature. Distortion of bonds and
displacement of atoms can be an adequate reason to cause
amorphicity in single component materials. But to sufficiently
understand the amorphicity, one must understand the
three-dimensional relationships inherent in the amorphous state,
for it is they which generate internal topology incompatible with
the translational symmetry of the crystalline lattice . . . What is
important in the amorphous state is the fact that one can make an
infinity of materials that do not have any crystalline
counterparts, and that even the ones that do are similar primarily
in chemical composition. The spatial and energetic relationships of
these atoms can be entirely different in the amorphous and
crystalline forms, even though their chemical elements can be the
same . . .
[0046] Based on these principles of disordered materials, described
above, three families of extremely efficient electrochemical
hydrogen storage negative electrode materials were formulated.
These families of negative electrode materials, individually and
collectively, will be referred to hereinafter as "Ovonic." One of
the families is the La--Ni-type negative electrode materials which
have recently been heavily modified through the addition of rare
earth elements such as Ce, Pr, and Nd and other metals such as Mn,
Al, and Co to become disordered multicomponent alloys, i.e.,
"Ovonic". The second of these families is the Ti--Ni-type negative
electrode materials which were introduced and developed by the
assignee of the subject invention and have been heavily modified
through the addition of transition metals such as Zr and V and
other metallic modifier elements such as Mn, Cr, Al, Fe, etc. to be
disordered, multicomponent alloys, i.e., "Ovonic." The third of
these families are the disordered, multicomponent MgNi-type
negative electrode materials described in U.S. Pat. Nos. 5,506,069;
5,616,432; and 5,554,456 (the disclosures of which are hereby
incorporated by reference).
[0047] Based on the principles expressed in Ovshinsky's '597
Patent, the Ovonic Ti--V--Zr--Ni type active materials are
disclosed in U.S. Pat. No. 4,551,400 to Sapru, Fetcenko, et al.
("the '400 Patent"), the disclosure of which is incorporated by
reference. This second family of Ovonic materials reversibly form
hydrides in order to store hydrogen. All the materials used in the
'400 Patent utilize a Ti--V--Ni composition, where at least Ti, V,
and Ni are present with at least one or more of Cr, Zr, and Al. The
materials of the '400 Patent are generally multiphase
polycrystalline materials, which may contain, but are not limited
to, one or more phases of Ti--V--Zr--Ni material with C.sub. 14 and
C.sub. 15 type crystal structures. Other Ovonic Ti--V--Zr--Ni
alloys are described in commonly assigned U.S. Pat. No. 4,728,586
("the '586 Patent"), titled Enhanced Charge Retention
Electrochemical Hydrogen Storage Alloys and an Enhanced Charge
Retention Electrochemical Cell, the disclosure of which is
incorporated by reference.
[0048] The characteristic surface roughness of the metal
electrolyte interface is a result of the disordered nature of the
material as disclosed in commonly assigned U.S. Pat. No. 4,716,088
to Reichman, Venkatesan, Fetcenko, Jeffries, Stahl, and Bennet, the
disclosure of which is incorporated by reference. Since all of the
constituent elements, as well as many alloys and phases thereof,
are present throughout the metal, they are also represented at the
surfaces and at cracks which form in the metal/electrolyte
interface. Thus, the characteristic surface roughness is
descriptive of the interaction of the physical and chemical
properties of the host metals as well as of the alloys and
crystallographic phases of the alloys, in an alkaline environment.
The microscopic chemical, physical, and crystallographic parameters
of the individual phases within the hydrogen storage alloy material
are important in determining its macroscopic electrochemical
characteristics.
[0049] In addition to the physical nature of its roughened surface,
it has been observed that V--Ti--Zr--Ni type alloys tend to reach a
steady state surface condition and particle size. This steady state
surface condition is characterized by a relatively high
concentration of metallic nickel. These observations are consistent
with a relatively high rate of removal through precipitation of the
oxides of titanium and zirconium from the surface and a much lower
rate of nickel solubilization. The resultant surface has a higher
concentration of nickel than would be expected from the bulk
composition of the negative hydrogen storage electrode. Nickel in
the metallic state is electrically conductive and catalytic,
imparting these properties to the surface. As a result, the surface
of the negative hydrogen storage electrode is more catalytic and
conductive than if the surface contained a higher concentration of
insulating oxides.
[0050] The surface of the negative electrode, which has a
conductive and catalytic component--the metallic nickel--interacts
with metal hydride alloys in catalyzing the electrochemical charge
and discharge reaction steps, as well as promoting fast gas
recombination.
[0051] Finally, in U.S. Pat. Nos. 5,616,432 ('432 patent) inventors
of Ovonic Battery Company produced Mg--Ni--Co--Mn alloys similar to
the base alloys of the present inventive composite hydrogen storage
material. The storage capacity of these alloys was limited to about
2.7 weight percent and none of the stored hydrogen was desorbed
from the alloy at 30.degree. C. FIG. 1 plots the PCT curve of the
'432 patents thin film alloy (reference symbol .DELTA.) with that
of the present composite hydrogen storage material (reference
symbol .diamond-solid.). As can be seen, the hydrogen storage
composite materials of the present invention adsorb more than 4
weight percent of hydrogen, and what is even more remarkable is
that this hydrogen can be desorbed at a temperature of 30.degree.
C.
[0052] Thus until the advent of the present invention, no prior art
material was capable of simultaneously meeting the desired material
properties of: 1) a high hydrogen storage capacity; 2) light weight
materials; 3)adequate hydrogen absorption/desorption temperatures;
4) adequate absorption/desorption pressures; 5) fast absorption
kinetics; and 6) a long absorption/desorption cycle life, all in an
inexpensive and easy to produce material.
SUMMARY OF THE INVENTION
[0053] The present invention is a Mg--Ni composite material having
an Mg--Ni based alloy; and a coating of a catalytically active
metal deposited on at least a portion of a surface of the Mg--Ni
based alloy. The coating is less than about 200 angstroms thick and
the composite material provides for a storage capacity of up to
4.86 weight percent hydrogen with a high adsorption rate at
temperatures as low as 30.degree. C. and an absorption pressure of
less than about 150 PSI. More remarkably, the composite materials
also have the ability to fully desorb the stored hydrogen at
temperatures as low as 250.degree. C., an ability not heretofore
seen in materials with such a high total storage capacity. Even
more amazingly the same material can desorb 2.51 weight percent of
the stored hydrogen at 90.degree. C. and 1.2 weight percent at
30.degree. C. In addition these material are relatively inexpensive
and easy to produce.
[0054] The catalytically active metal deposited on at least a
portion of a surface of said Mg--Ni based alloy is more preferably
less than about 150 angstroms thick and most preferably less than
about 100 angstroms thick. The coating of catalytically active
metal is preferably formed from at least one metal selected from
the group consisting of iron, palladium, platinum, iridium, gold,
and mixtures or alloys thereof. Iron, and palladium are the most
preferred catalytic coatings.
[0055] The base alloy preferably has a two phase amorphous
structure. The Mg--Ni based alloy has a magnesium content which
ranges from 40 to 65 atomic percent of the alloy and more
preferably from 45 to 65 atomic percent of the alloy. The nickel
content ranges from 25 to 45 atomic percent of the base alloy and
preferably the nickel content is from 30 to 40 atomic percent. The
Mg--Ni based alloy further contains manganese and cobalt. The
cobalt content is between 1 and 10 atomic percent of the alloy and
preferably between 2 and 6 atomic percent of the alloy. The
manganese content is between 1 and 10 atomic percent of the alloy
and preferably between 3 and 8 atomic percent of the alloy.
[0056] The Mg--Ni based alloy may further contain at least one
element from the group consisting of Fe, Al, Zr, Zn, Cu, Ag, Cu, B,
La, Ru, Re, Li, Cr, Pd, Si, V, Sr Misch Metal and mixtures or
alloys thereof incorporated into the alloy in quantities totaling
less than about 5 atomic percent of the alloy for all inclusions
and each individual element is incorporated into said alloy in
quantities less than about 3 atomic percent.
[0057] The Mg--Ni composite material is capable of adsorbing at
least 3 weight percent hydrogen at a pressure of less than about
150 PSI and more preferably capable of adsorbing at least 3 weight
percent hydrogen at a pressure of less than about 50 PSI. The
Mg--Ni composite material absorbs 3 weight percent hydrogen in less
than two minutes at 30.degree. C. and absorbs 3.5 weight percent
hydrogen in less than 10 minutes at 30.degree. C.
BRIEF DESCRIPTION OF THE FIGURES
[0058] FIG. 1 plots the PCT curve of a prior art thin film alloy
with that of the present composite hydrogen storage material,
specifically shown is the increased storage capacity at 30 .degree.
C.;
[0059] FIG. 2 depicts the XRD plot and the corresponding hydrogen
desorption characteristics of composite materials of the present
invention formed by two different processes;
[0060] FIGS. 3A and 3B show cross-sectional micrographs of a melt
spun ribbon of a base alloy composition useful for the composite
material of the instant invention at 600.times. and 4000.times.,
respectively;
[0061] FIG. 4 shows another cross section micrograph of a melt spun
ribbon of a base alloy composition useful for the composite
material of the instant invention at 600.times., specifically shown
is the desired degree of uniformity of the melt spun ribbon;
[0062] FIG. 5 is a high resolution TEM micrograph of the a base
alloy composition useful for the composite material of the present
invention, specifically the TEM micrographs reveal some
three-dimensional micro-tube structures imbedded in the amorphous
bulk;
[0063] FIG. 6 depicts x-ray diffraction plots of different base
alloy materials made according to the production process of the
instant invention;
[0064] FIGS. 7A and 7B are x-ray diffraction plots of a base alloy
of the present invention after melt spinning, but before mechanical
alloying and after mechanical alloying respectively;
[0065] FIGS. 8A and 8B are bar graph plots of the amount of
hydrogen (in weight percent) desorbed from composite materials
produced from alloys of the instant invention coated with various
catalytic coatings on the y-axis, versus a different desorption
temperatures on the x-axis;
[0066] FIG. 9 is an illustrative drawing of the microstructure of a
composite material of the instant invention;
[0067] FIG. 10 plots the amount of hydrogen abortion in the first
90 minutes for composite materials using the base alloys AR003 (52%
Mg), AR026 (55% Mg), AR030 (58% Mg), and AR031 (Mg61%);
[0068] FIG. 11 shows the results of cycling a composite material of
the instant invention at 200.degree. C., and specifically plots the
absorption and desorption capacities versus cycle number;
[0069] FIG. 12 shows absorption curves for a composite material of
the instant invention having a base alloy composition of
Mg.sub.52Ni.sub.39Mn.sub.6Co.sub.3 with a 100 Angstrom palladium
coating thereon at 30.degree. C. and 60.degree. C.;
[0070] FIG. 13 shows the desorption curves for the same material as
in FIG. 12;
[0071] FIGS. 14 and 15 depict the PCT curves for adsorption and
desorption of hydrogen for the material of FIGS. 12 and 13 at
30.degree. C. and 50.degree. C., respectively, specifically these
figures show that the hysteresis between the hydrogen adsorption
and desorption is low;
[0072] FIG. 16 plots the absorption and desorption pressures of
various composite materials of the present invention versus
hydrogen content (PCT) measured at 200.degree. C.;
[0073] FIG. 17 plots the absorption and desorption plateau
pressures as a function of Mg content of the base alloy for the
various composite materials of FIG. 16;
[0074] FIG. 18 is an x-ray diffraction graph of base alloy
materials of the instant invention and specifically shows how use
of a graphite crucible introduces deleterious carbon contaminants
into the alloy material;
[0075] FIG. 19 plots hydrogen absorption versus time (hydrogen
absorption rates) for sample composite materials of the instant
invention which were prepared with and without glove box protection
(i.e. protection from oxygen contamination);
[0076] FIG. 20 plots the PCT curves at 90.degree. C. of composite
materials having a base alloy of AR003 produced by various alloy
grinding techniques;
[0077] FIG. 21 depicts a schematic representation of the surface of
a composite material of the present invention, and specifically
illustrates the possible detrimental effects of oxygen
contamination therein;
[0078] FIG. 22 is a plot of PCT absorption and desorption curves at
90.degree. C. for a composite material of the instant invention
having a base alloy of AR046 and for another composite material of
the instant invention formed from a AR046 base alloy in which 2 at.
% silver was partially substituted for nickel in the base alloy
(designated AR055), specifically the silver substituted base alloy
exhibits improved hydrogen desorption at 90.degree. C.; and
[0079] FIG. 23 plots the hydrogen absorption versus time (the
absorption rate) for various additives added to composite materials
of the instant invention produced with AR0025 base alloys.
DETAILED DESCRIPTION OF THE INVENTION
[0080] The Mg--Ni alloy composite materials of the instant
invention exhibit, for the first time ever, the ability to store
and release significant quantities of hydrogen at temperatures less
than about 100.degree. C. with good kinetics. Specifically, the
instant composite materials can store greater than about 3 weight
percent hydrogen at 30.degree. C. More preferably these materials
can store greater than about 3.5 weight percent hydrogen and most
preferably they can store more than about 4 weight percent hydrogen
at 30.degree. C. The base alloys are produced by melt spinning and
mechanical alloying and have an addition of a minute quantity of
palladium and/or iron on at least a portion of the surface of the
alloy to form the composite. As discussed hereinafter, the
conditions of the melt spinning and mechanical alloying of the base
alloy play a major role in creating the unique properties of the
instant composite materials.
[0081] The preferred composite materials of the instant invention
generally contain a base Mg--Ni alloy having a two phase amorphous
microstructure. The processes of producing these materials, which
will be described herein below, are key to producing Mg--Ni alloys
which have this two phase amorphous microstructure. That is, if the
processing is not correct, materials with a single phase structure
will form. This mixed phase structure has a Mg-rich phase and a
Ni-rich phase, the inventors have found that the composite
materials that have the best kinetics when the ratio of the Mg-rich
phase to Ni-rich phase in the base alloy is high. Specifically, it
is believed that the Mg-rich amorphous phase acts as a storage
phase and the Ni-rich phase acts as a catalytic phase to
disassociate the molecular hydrogen to atomic hydrogen, which is
then stored in the Mg-rich phase material. Thus, when making the
most preferred materials of the present invention, the processes
will preferably avoid the production of a single amorphous phase
material. It should be noted that by amorphous, it is meant that
the structure is predominantly amorphous. The structure may contain
some microcrystalline or nanocrystalline areas and still be
considered amorphous. Amorphous portions of the materials will be
defined herein as having no long-range order greater than about 20
Angstroms.
[0082] The base alloys of the composite materials of the instant
invention comprise mainly magnesium and nickel. Table 1 indicates
the alloy designation and nominal compositions for specific
examples of the base alloy according to the instant invention.
Nominal magnesium content ranges from 40 to 65 atomic percent of
the alloy and preferably the magnesium content ranges from 45 to 65
atomic percent of the alloy. The nickel content ranges from 25 to
45 atomic percent of the base alloy and preferably the nickel
content is from 30 to 40 atomic percent.
[0083] The base alloy preferably also contains manganese and cobalt
in quantities much lower than the content of Mg and Ni. The cobalt
content is kept as low as possible to reduce the cost of the alloy,
and still produce stable, high storage capacity alloys. With that
in mind, the cobalt content is between 1 and 10 atomic percent of
the alloy and preferably between 2 and 6 atomic percent. The
manganese content is between 1 and 10 atomic percent and preferably
between 3 and 8 atomic percent.
[0084] Finally, the alloy may also contain elements which help to
enhance achievement and stabilization of the amorphous structure of
the base alloy and increase the catalytic activity of the alloy,
thereby increasing the kinetics thereof. Such elements may include
Fe, Al, Zr, Zn, Cu, Ag, Cu, B, La, Ru, Re, Li, Cr, Pd, Si, V, Sr,
Misch Metal and mixtures or alloys thereof . These elements, if
present will be in quantities totaling less than about 5 atomic
percent, and each individual element will be included less than
about 3 atomic percent. Iron is a preferred additive.
[0085] The following describes the basic process of producing the
base alloys for the hydrogen storage composite materials of the
present invention. One kilogram of raw materials having a ratio of
ingredients to produce the desired composition is placed into a
boron nitride (BN) crucible within a melt spinning chamber. An
additional 50 grams of magnesium is added to compensate evaporative
losses of magnesium during melting/spinning. The temperature of
crucible is ramped up to 1050.degree. C. within 40 minutes. A boron
nitride rod which plugs a hole in the bottom of the crucible is
removed and liquid metal is forced out from the bottom of the
crucible toward a high speed, water-cooled Be--Cu alloy
melt-spinning wheel rotating at a linear speed of about 10 m/sec.
The alloy is quenched/solidified when it hits the wheel and the
ribbons of alloy material that are formed are collected from the
bottom of the chamber. After proper cooling for more than 12 hours,
the ribbons and flakes were collected and transferred under a
protective argon atmosphere to an attritor (Union Process Model
S-1) for mechanical alloying (MA). Two different MA processes were
used. The first was a 48 hour continuous grinding in an argon
atmosphere without any additives which yielded a mixed
microcrystalline and amorphous structure. The average crystallite
size was 45 angstrom determined by the full width at half maximum
from XRD peaks. The second process used small amount of graphite
and heptane as grinding aids. The carbon and heptane help to reduce
the amount of alloy powder which sticks to the walls of the
attritor and also reduces the oxygen contamination of the alloy
material. The grinding time was reduced to only two hours as
opposed to the 48 hours of the other method. The resulting
mircostructure from this second method is a polycrystalline
material with an average crystallite size of 285 angstrom. The XRD
of alloy materials from two processes and their corresponding
hydrogen desorption characteristics are shown in FIG. 2. Although
the total desorption amounts from both process were the same, the 2
hour mechanically alloyed sample did provide faster desorption
kinetics and was more economical to produce. Therefore, the second
method is more preferred.
[0086] To produce the composite material of the present invention,
powder is discharged from the bottom of the attritor into a sealed
container and then transferred to a sifter to classify the powder
into various sizes. For the instant examples only powder passing
through a 200-mesh screen is used. Powder is pressed onto an
expanded Ni-substrate inside a glove box using a 30-ton pneumatic
press. The surfaces of the pressed sample are coated with a 100
.ANG. layer of a catalytic metal by thermal evaporation in an
Edward Auto 306 evaporator. The composite material sample is then
tested in a pressure-concentration-isotherm (PCT) apparatus to
determine its gas phase hydrogen absorption/desorption
characteristics.
[0087] FIGS. 3A and 3B show cross-sectional SEM micrographs of a
melt spun ribbon of a base alloy composition useful for the
composite material of the instant invention at 600.times. and
4000.times., respectively. This melt spun ribbon shows gross phase
segregation into large crystallites of the two phases within
portions of the ribbon. Specifically, in this example, the large
crystallites appear on the air side of a melt spun ribbon produced
on a chilled roller melt quenching apparatus. This gross
segregation presents itself as mottled areas in FIG. 2A and as the
snowflake shaped areas in FIG. 3B. FIG. 3B also shows a section of
the melt spun ribbon that does not show the growth of large
crystallites on the right hand side of the cross section.
[0088] FIG. 4 shows another cross section SEM micrograph of a melt
spun ribbon of an alloy composition of the instant invention at
600.times.. This ribbon shows no sign of the growth of large
crystallites of Mg-rich and Ni-rich phases. Thus the parameters of
the melt quenching (melt spinning) are important and should be set
so that few if any large crystallites are formed when the alloy
melt is quenched. The reason for the desire to eliminate the larger
crystallites is that the next step in the process of making the
base alloy materials is a mechanical grinding/alloying step in
which the melt spun ribbon materials are mechanically alloyed for
up to 72 hours to produce an amorphous material. The larger the
crystallites in the melt. spun ribbon, the longer the mechanical
alloying required to destroy these crystallites and form the
amorphous microstructure.
[0089] FIG. 5 is a high resolution TEM micrograph of an inventive
base alloy of the present invention. The TEM micrograph reveals
three-dimensional tube-like structures imbedded in the amorphous
bulk. These tube-like structures or micro-tubes have never been
reported in the prior art of mechanical alloyed materials. These
tube structures are believed to be the product of rolling up of
two-dimensional sheets during the mechanical alloying process in
the attritor. The morphology of these micro-tubes is similar to the
recently found nano-tube structures made from carbon. While the
actual function of these micro-tubes and their connection to the
material's hydrogen storage capacity is not clear at present time,
the inventors believe this special connecting tube structure may
have a positive contribution to the bulk hydrogen diffusion since
they offer a non-conventional network and may very well act as
proton conduction channels in the bulk alloy. It is further
believed that the enhanced hydrogen storage of the base alloys of
the inventive composite materials may be due to a combination of
chemically and physically adsorbed hydrogen. The Mg--Ni micro-tubes
appear to contain a degree of porosity which may allow
physi-adsorbed hydrogen which would be available (desorbed) at low
temperatures. The micro-tubes also contribute an extra degree of
disorder to the material of the present invention. In addition to
the tube structure discussed above, the electron diffraction
pattern of the material also indicates the co-existence of
microcrystalline and amorphous regions. It is this special
combination of various microstructures that makes the material
capable of reversibly storing a considerable amount of hydrogen at
relatively low temperatures and low working hydrogen pressures. The
micro-tubes appear as an inner core of Ni-rich material surrounded
by an outer sheathing of Mg-rich material.
[0090] Different base alloy materials were made according to the
production process of the instant invention. X-ray diffraction
plots of the different base alloys are shown as curves A-G in FIG.
6. It is significant to note that, as discussed above, the sample
having the most pronounced two-phase amorphous structure (curve D)
had the best performance of all the materials (especially
desorption kinetics). That is, the material having a dual amorphous
phase structure out performed similar alloys having a single
amorphous phase. Analysis shows that one of the two separate
amorphous components of the dual amorphous phase structure material
is enriched in Mg, while the other is enriched in Ni when compared
to each other. While not wishing to be bound by theory, it is
believed that the Ni-rich component may act as the catalytic phase,
while the Mg-rich component may be the storage phase.
[0091] FIGS. 7A and 7B are x-ray diffraction plots of a base alloy
(designated AR3-MS425) of the present invention after melt
spinning, but before mechanical alloying and after mechanical
alloying respectively. As can be seen, the as melt spun material is
crystalline having sharp peaks. After mechanical alloying, the
material becomes mostly amorphous showing very much widened peaks.
FIG. 7B also indicates that a dual amorphous phase material results
from the mechanical alloying.
[0092] Comparison of two different methods of alloy preparation
using the same chemical composition of the base alloy (one forming
a single phase amorphous structure and the other forming a two
phase structure) shows some interesting results. A single amorphous
phase structure material, having a nominal overall composition of
Mg.sub.49Ni.sub.41Mn.sub.7Co.sub.3 (atomic %) was produced. This
material (designated AR3-MS420) showed a hydrogen storage capacity
of 4.1 wt %. This number is quite good as far as capacity goes, but
the kinetics were slow, and to get the final capacity number in a
reasonable time, the temperature of the alloy had to be raised to
90.degree. C. While this is greater than the 30.degree. C. in which
the dual phase material can adsorb the hydrogen (discussed herein
below), it is still far below the 300.degree. C. required by other
Mg materials of the prior art. Thus even this single phase material
can be useful in situations where heat is available in the
80-100.degree. C. range and kinetics are not critical. In
comparison, the two phase material (designated AR3-MS425) had a
slightly higher maximum hydrogen storage capacity (4.3%) than the
AR3-MS420, but the absorption kinetics are greatly improved.
Specifically the entire 4.3% absorption took only a few minutes at
30.degree. C.
[0093] Turning now to another inventive alloy material having a
nominal overall composition of
Mg.sub.61Ni.sub.32.5Mn.sub.3Co.sub.2Fe.sub.1.5 (designated AR031),
this material had an incredible maximum hydrogen storage capacity
of 4.86 wt. % at an amazing temperature of 30.degree. C., and on
top of the high storage capacity, the absorption kinetics of the
material were quite good, absorbing the hydrogen within a matter of
minutes.
[0094] The instant inventors have found that iron seems to be a
better catalytic coating than even palladium. That is, while the
micro-thin palladium coating greatly enhances the absorption
kinetics of the base storage alloy, it does not increase the
desorption kinetics as greatly. However, iron increases not only
the absorption kinetics but also greatly increases the desorption
kinetics as well as reversible desorption capacity. FIG. 8A depicts
this increase in reversible desorption capacity. FIG. 8A is a bar
graph plot of the amount of hydrogen (in weight percent) desorbed
from composite materials produced from the AR031 base alloy (see
above) coated with various catalytic coatings on the y-axis, versus
a different desorption temperatures on the x-axis. The desorption
time is set at four hours in each case. As can be seen, the
composite material with the iron coating has the best reversible
desorption, i.e. 4.86 weight percent at 250.degree. C. and 2.27
weight percent at 90.degree. C. Furthermore, while iron and
palladium are the preferred catalytic material, a broader group
comprising iron, palladium, platinum, iridium, gold, and mixtures
or alloys thereof is deemed by the inventors to be useful in the
instant invention.
[0095] FIG. 8B is a bar graph plot of the amount of hydrogen (in
weight percent) desorbed from composite materials produced from
either the AR031 base alloy or another alloy AR026
(Mg.sub.55Ni.sub.36Mn.sub.6Co.sub.3) coated with various catalytic
coatings on the y-axis, versus a different desorption temperatures
on the x-axis. Amazingly, these composite materials can reversibly
desorb about 1.0 to 1.1 weight percent hydrogen even at
temperatures as low as 30.degree. C. This is unheard of for a
magnesium based system, and allows for instant startup of hydrogen
powered devices (i.e. fuel cells, hydrogen internal combustion
engines, etc.) without the need to instantaneously increase the
temperature of the hydride storage material to hundreds of
degrees.
[0096] The catalytic coating of palladium or iron should be as thin
as possible and still produced the desired enhancement of the
kinetics of the storage of hydrogen in the base alloy. Preferably
the coating is less than about 200 Angstroms and more preferably
less than about 150 Angstroms thick and most preferably less than
about 100 Angstroms thick. It should be noted that the coated
palladium constitutes less than about 0.05% of the composite
material and therefore could in no way contribute significantly to
the hydrogen storage capacity of the overall material. While, once
again, not wishing to be bound by theory, it is believed that the
coating acts catalytically to enhance the kinetics of the storage
material composite. Also, while the coating was evaporated onto the
base alloys of the present invention, it could also have been
coated onto the alloys by other techniques such as electroless
plating, electrolytic plating or chemical vapor deposition.
[0097] It should be noted that the evaporated coating is on the
exterior of the pressed bulk sample and does not coat particles on
the interior of the bulk. This may not be the most useful way to
add the catalytic coating. FIG. 9 is an illustrative drawing of the
microstructure of a composite material of the instant invention as
envisioned by the inventors. The bulk base alloy consists of
magnesium rich hydrogen storage phases intermixed with nickel rich
catalytic phases. On the surface of bulk material is an ultra-thin
coating of the added catalytic material (i.e. Pd or Fe, ect.). The
ultra-thin coating is most likely not contiguous and is not to
scale in this illustrative depiction. In fact, cross-sectional SEM
photomicrographs do not show the 100-200 Angstrom catalytic coating
at all.
[0098] As alluded to above, the present method of adding the
catalytic material layer (evaporation onto the exterior of a
pressed bulk base alloy) may not be the best method of adding such
catalytic material to the composite. The inventors envision that in
addition to coating techniques, other techniques may be used to add
catalytic material to the bulk base alloy. For instance, the
inventors believe that the addition of catalytic particles, such as
catalytic iron nano-particles, to the base alloy during the last
minutes of mechanical alloying may embed the particles into the
surface of the particles of the base alloy. The particulate coated
base alloy may then be sintered causing the iron particles to be
distributed throughout the bulk of the composite material. Finally,
the inventors theorize that some combination of catalytic coating
and distributed catalytic particles may be the best form for the
composite materials of the present invention.
[0099] The amount of hydrogen abortion in the first 90 minutes were
recorded for AR003 (52% Mg), AR026 (55% Mg), AR030 (58% Mg), and
AR031 (Mg61%) and plotted in FIG. 10. The observed trend is that as
the magnesium content increases, the total storage capacity also
increases. However, the absorption rate decreases as
metal-to-hydrogen bond strength increases with the high Mg content.
Therefore, a balance between the amount of hydride former (Mg, for
example) and modifier (Ni, Co, etc.) is very important for the
general material performance, as well as the proper distribution of
these components
[0100] A mechanically alloyed sample of material having the base
alloy composition designated AR26 was produced by a two hour
grinding with heptane and graphite grinding aids. The base alloy
was pressed into an expanded metal substrate and then was coated
with 100 angstrom of Fe on both sides. The sample was put into a
PCT measurement apparatus and both the hydrogen adsorption and
desorption capacity at 200.degree. C. were measured as a function
of cycle number. The results of cycling at 200.degree. C. are shown
in FIG. 11 which plots the absorption and desorption capacities
versus cycle number. From the data, it can be seen that the
absorption capacity was not changed (2.8%) while desorption
capacity dropped slightly from a maximum of 2.6% to 2.4% after 400
cycles. The 200.degree. C. cycling temperature was chosen to hasten
the experimental measurements and does not reflect a restriction of
the useful temperature range for the tested sample.
[0101] As alluded to above, the instant composite materials have
very good low temperature kinetics. FIG. 12 shows absorption curves
for a composite material of the instant invention having a base
alloy composition of Mg.sub.52Ni.sub.39Mn.sub.6Co.sub.3 with a 100
Angstrom palladium coating thereon at 30.degree. C. (reference
symbol .smallcircle.) and 60.degree. C. (reference symbol
.box-solid.). The hydrogen absorption occurred at a pressure of
120-150 psi. As can be seen from these curves, this material has
very good kinetics (absorbing the majority of the hydrogen in a
matter of minutes) at relatively low temperatures and pressures.
That is, this composite material can absorb 3 weight percent
hydrogen in less than two minutes and 3.5 weight percent hydrogen
in less than 10 minutes at 30.degree. C. These are fantastic
results which have heretofore never been seen in the prior art.
FIG. 13 shows the desorption curves for the same alloy as in FIG.
8. This figure shows that the material can desorb the stored
hydrogen within a matter of minutes at 30.degree. C.
[0102] FIGS. 14 and 15 depict the PCT curves for adsorption and
desorption of hydrogen for the material of FIGS. 12 and 13 at
30.degree. C. and 50.degree. C., respectively. Perusal of these
figures shows that the hysteresis between the hydrogen adsorption
and desorption is low. This can be seen by comparing the pressure
differential between the adsorption and desorption curves of the
PCT plots at the midpoint of the composition range. The midpoint is
the point at about half of the maximum hydrogen storage
capacity.
[0103] A series of compositions with Mg contents varying from 42 to
62 atomic % were prepared. The PCT measured at 200.degree. C. for
some of the alloys is plotted in FIG. 16. The plot shows absorption
and desorption plateau pressures. The plateau pressure hystersis is
large compared to other hydrogen storage materials as Lavas phases
based AB.sub.2, or CaCu.sub.5-structure AB.sub.5 materials. FIG. 17
plots the absorption and desorption plateau pressures as a function
of Mg content of the base alloy for the various composite materials
of FIG. 16. This plot indicates that there is an optimal Mg content
at around 55% at which the absorption-desorption hystersis is
minimized.
[0104] In addition to the specifics on the melt quenching, the
composition of the crucible in which the alloy is melted is
important. FIG. 18 is an x-ray diffraction graph of materials of
the instant invention and specifically shows how use of a graphite
crucible (curves C and D) introduces carbon contaminants into the
alloy material. The carbon forms carbides which cannot be made
amorphous by mechanical alloying. However, the use of boron nitride
crucibles produces contaminants which can be made amorphous by
mechanical alloying (see curves A and B). The carbon contaminant is
a "malignant" contaminant and as such negatively influences the
properties of the composite material, whereas the boron nitride is
a "benign" contaminant and does not adversely influence the
properties of the hydrogen storage composite. Carbon enters the
alloy and takes hydrogen sites and as such the
reduction/elimination of carbon contamination allows for the
production of materials which have the storage capacity and
kinetics of the instant invention.
[0105] The magnetic susceptibility of samples having compositions
designated as AR003, AR026, and AR031, which were prepared by
grinding with and without the addition of graphite and heptane
grinding aids were measured. In both cases, grinding time was two
hours. The susceptibility results data was used to determine the
free nickel content percentage of the samples. The free nickel
content of the samples is listed in Table II. Samples ground with
graphite and heptane grinding aids showed higher percentage of free
nickel, which contributed to a more catalytic surface, thereby
helping hydrogen absorption.
[0106] In the inventors' original attritor setup, an overpressure
of argon was maintained in the attritor container throughout the
entire mechanical alloying process. Small amount of argon leaked
out from the collar holding the rotating shaft of the attritor. The
inventors believed that there might have been some air
back-streaming into the attritor as a result of this leakage. In an
attempt to reduce possible oxygen contamination, the inventors
constructed a glove box around the attritor and filled the glove
box with an argon atmosphere to protect the attritor. The hydrogen
absorption rates for samples prepared with and without glove box
protection are shown in FIG. 19. It can be seen that this added
protection was successful in reducing the oxygen contamination of
the mechanically alloyed materials. With reduction in oxygen
contamination, not only did the total storage capacity increase,
but the storage kinetics also increased. The calculated surface
reaction and bulk diffusion constant for the two samples are listed
in Table III. While the bulk diffusion constant improved by a
factor two with the reduction of oxygen contamination, the surface
hydrogenation kinetics increased by as much as seven times. This
clearly illustrates the importance of oxygen control during
processing.
[0107] In an attempt to reduce the grinding time required to make
the base alloy powder of the instant invention and thereby the
associated cost of production, the inventors used an air stream
crushing technique to break up the ribbons of the hydrogen storage
alloy. The technique used a high speed air stream impinging upon
coarse powder sitting in a cyclone-like container, the powder was
pulverized by crushing against each other and the powder was
collected from the container through a sieve. The temperature of
the impinging air stream is at least 5 to 10.degree. C. lower than
environment due to the expansion of the pressurized gas stream. The
powder thus obtained was labeled as the air stream sample. A
portion of the air stream sample powder was fed into the attritor
and ground for two hours with heptane and graphite grinding aids.
The PCT curves at 90.degree. C. are plotted in FIG. 20. A small
degradation in the hydrogen capacity is observed on air stream
sample due to oxygen in the air used. The inventors believe that
the results will be improved if a protective atmosphere such as
argon or nitrogen is used instead of air.
[0108] The possible detrimental effects of oxygen contamination are
illustrated in FIG. 21, which depicts a schematic representation of
the surface of a composite material of the present invention. The
surface oxide formed during powder processing, storage, or
transportation will hinder the hydrogen absorption through surface
catalysis (region 1 in FIG. 21). It will also obstruct hydrogen
atoms from recombining into hydrogen molecules at the surface
during hydrogen desorption. The second affected area is in the
grain boundary (as shown in region 2 in FIG. 21). The relatively
large size and electron affinity of the oxygen ion in the grain
boundary will stop hydrogen diffusion through the dangling bonds in
the grain boundary area and thus reduce the bulk diffusion of
hydrogen. Both the desorption and absorption kinetics will be
diminished substantially. The third negative effect of oxygen is in
the bulk region where useful hydrogen storage site are occupied or
interfered with by negatively charged oxygen. Therefore the
reversible storage capacity of hydrogen will be reduced (region 3
in FIG. 21).
[0109] One additional aspect of the present invention which has not
been fully discussed, but which is very important, is the
equilibrium pressures of the present composite hydrogen storage
materials. The pressures used to adsorb the hydrogen into the
materials of the present invention are less than 150 PSI. Most of
the hydrogen can be adsorbed into the materials at less than about
50 PSI. In contrast, most other work on high capacity Mg based
hydrogen storage materials require pressures in the range of
1000-5000 PSI. With this greatly lowered pressure requirement, the
requirements for the materials of construction for hydrogen storage
beds and like systems is greatly reduced. Thus at 50-150 PSI, light
weight simple construction materials may be used (for example
rubber tubing as opposed to quarter inch stainless steel tubing may
be used) whereas in the range of 1000-5000 PSI, more expensive and
exotic materials must be used. This reduction in cost and
complexity of related systems and materials of construction are an
added benefit of the composite materials of the instant
invention.
[0110] One element proven to have positive contribution toward
hydrogen desorption is silver. When 2 at. % silver was partially
substituted for nickel in the base alloy designated AR046, the
resulting alloy (designated AR055) exhibits improved hydrogen
desorption at 90.degree. C. as can be seen from two PCT curves
illustrated in FIG. 22. This sample had a desorption plateau
pressure of around 0.003 MPa. It is believed that the relatively
large atomic size of silver may contribute greatly to disorder of
the polycrystalline sample and make the absorbed hydrogen easier to
remove from the lattice.
[0111] In an attempt to improve the hydrogen absorption rate of
AR025 materials, small amounts of additives (1.5 to 2. wt. %) were
added to the base alloy material by a shaker milling method. These
catalyst candidates include Cr.sub.2O.sub.3, V.sub.2O.sub.5, Pd,
RuO.sub.2.xH.sub.2O, PdO.xH.sub.2O, MgB.sub.2, LiBH.sub.4, and
Fe.sub.3O.sub.4. The shaker mill was run for 30 minutes to ensure
through mixing of the AR026 powder with the additives. The
resulting mixture was pressed into an expanded metal substrate and
tested in the gas phase reactor. The hydrogen absorption vs. time
(absorption rate) for each additive are plotted in FIG. 23. From
FIG. 23, it can be concluded that both Pd and RuO.sub.2.xH2O
improve hydrogen absorption kinetics substantially while maintain
high storage capacity. The PdO.xH.sub.2O also improves the
absorption kinetics but slightly reduces to the total storage
capacity.
[0112] Another potential application of these Mg-based hydrogen
storage composite materials outside of gas phase storage of
hydrogen is in nickel-metal hydride batteries (Ni--MH). A half-cell
test configuration was constructed using AR034 as the negative
electrode and a partially precharged sintered Ni(OH).sub.2
electrode as the counter electrode. The system was charged at a
rate of 100 mA/g for 12 hour (total capacity input was 1200 mAh/g).
Then the system was discharged and the total discharge capacity at
the third cycle was 692 mAh/g, which is equivalent to a gas phase
hydrogen reversible storage capacity of 2.58%. Thus the
electrochemical measurement confirmed the high hydrogen storage
potential that was observed from the gas phase measurements.
[0113] The drawings, discussion, descriptions, and examples of this
specification are merely illustrative of particular embodiments of
the invention and are not meant as limitations upon its practice.
It is the following claims, including all equivalents, that define
the scope of the invention. TABLE-US-00001 TABLE 1 In Atomic
Percent Alloy # Mg Ni Co Mn Fe Al Zr Cu Zn Ag B Other AR1 52 45 3
-- -- -- -- -- -- -- -- -- AR3 52 39 3 6 -- -- -- -- -- -- -- --
AR4 51.5 37 6 4 1.5 -- -- -- -- -- -- -- AR5 50 40 6 3 -- -- 1 --
-- -- -- -- AR6 51.5 37 3 4 1.5 3 -- -- -- -- -- -- AR7 51.5 37 6 4
-- -- -- 1.5 -- -- -- -- AR8 51.5 37 4 4 -- 2 -- 1.5 -- -- -- --
AR9 51.5 37 4 4 -- 2.5 1 -- -- -- -- -- AR10 51.5 37 4 3 1.5 2 -- 1
-- -- -- -- AR11 51.5 37 3 3 1 2 1 1.5 -- -- -- -- AR12 51.5 37 3 3
1 2 -- 1.5 1 -- -- -- AR13 51.5 37 3 3 1.5 3 -- -- 1 -- -- -- AR14
51.5 37 3 3 1 2 1 -- 1.5 -- -- -- AR15 51.5 36 3 3 1 2 1 1.5 1 --
-- -- AR16 51.5 36 4 4 1.5 -- -- -- -- -- 1 -- AR17 51.5 37 3 3 1.5
3 -- -- -- -- 1 -- AR18 51.5 35 4 4 1.5 -- -- -- -- -- 2 -- AR19 50
35 4 4 3 5 -- -- -- -- -- -- AR20 50 38 6 6 -- -- -- -- -- -- --
3%-La AR21 50 38 6 6 -- -- -- -- -- -- -- 3%-Ru AR22 50 38 6 6 --
-- -- -- -- -- -- 3%-Re AR23 51.5 33.5 4 4 -- -- -- 5 -- -- -- --
AR24 51.5 28.5 4 4 -- -- -- 10 -- -- -- -- AR25 51.5 28.5 4 4 3 --
-- 10 -- -- -- -- AR26 55 36 3 6 -- -- -- -- -- -- -- -- AR27 58 33
3 6 -- -- -- -- -- -- -- -- AR28 55 36 3 4.5 1.5 -- -- -- -- -- --
-- AR29 55 35 3 4.5 1.5 -- -- -- -- -- 1 -- AR30 58 32 3 4.5 1.5 --
-- -- -- -- 1 -- AR31 61 32.5 2 3 1.5 -- -- -- -- -- -- -- AR32 61
30 2 4.5 1.5 -- -- -- -- -- 1 -- AR33 55 30 3 12 -- -- -- -- -- --
-- -- AR34 55 24 3 18 -- -- -- -- -- -- -- -- AR35 55 29 10 6 -- --
-- -- -- -- -- -- AR36 55 23 16 6 -- -- -- -- -- -- -- -- AR37 47
44 3 6 -- -- -- -- -- -- -- -- AR38 42 49 3 6 -- -- -- -- -- -- --
-- AR39 51.4 38.6 3 6 -- -- -- -- -- -- -- 1%-Li AR40 51.4 38.6 3 6
-- -- -- -- -- -- -- 1%-Cr AR41 51.4 38.6 3 6 -- -- -- -- -- 1 --
-- AR42 51.4 38.6 3 6 -- -- -- -- -- -- -- 1% Pd AR43 55 36 3 5 --
1 -- -- -- -- -- -- AR44 55 36 3 4 -- 2 -- -- -- -- -- -- AR45 55
35 3 4 -- 2 -- -- -- -- 1 -- AR46 61 29 2 4.5 1.5 1 -- -- -- -- 1
-- AR47 61 28 2 4.5 1.5 2 -- -- -- -- 1 -- AR48 51.5 35 6 4 3.5 --
-- -- -- -- -- -- AR49 51.5 34 6 4 3.5 -- -- -- -- -- 1 -- AR50
51.5 32 6 4 3.5 1 -- 1 -- -- 1 -- AR51 50 38.5 6 4 1.5 -- -- -- --
-- -- -- AR52 48.5 40 6 4 1.5 -- -- -- -- -- -- -- AR53 43.4 43.9 3
6 2 -- -- -- -- -- -- Si--Cr--V AR54 51.5 37 6 4 1.5 1 -- -- -- --
1 -- AR55 61 27 2 4.5 1.5 1 -- -- -- 2 1 -- AR56 61 27 2 4.5 1.5 1
-- -- -- -- 1 2%-Sr AR57 61 27 2 4.5 1.5 1 -- -- -- -- 1 2%-MM AR58
61 27 2 4.5 1.5 1 -- -- 2 -- 1 -- AR59 61 27 2 4.5 1.5 1 2 -- -- --
1 -- AR60 61 27 2 4.5 1.5 1 -- 2 -- -- 1 -- AR61 48.5 37 9 4 1.5 --
-- -- -- -- -- -- AR62 46.5 42 6 4 1.5 -- -- -- -- -- -- -- AR63
44.5 44 6 4 1.5 -- -- -- -- -- -- -- AR64 48.5 38.5 6 4 3 -- -- --
-- -- -- -- AR65 48.5 36.5 6 4 3 1 -- -- -- -- 1 -- AR66 48.5 38 6
4 1.5 -- -- -- -- -- -- 2%-V AR67 59 27 2 4.5 1.5 1 -- -- -- 4 1 --
AR68 60 27 2 4.5 1.5 1 -- -- 1 2 1 -- AR69 59 27 2 4.5 1.5 1 -- --
2 2 1 -- AR70 58 27 2 4.5 1.5 1 -- -- 3 2 1 -- AR71 48.5 38 6 4 1.5
-- -- -- -- 2 -- -- AR72 48.5 40 4 4 1.5 -- -- -- -- 2 -- -- AR73
48.5 40 4 4 1.5 -- -- -- 2 -- -- -- AR74 48.5 37 4 4 1.5 -- -- -- 2
2 1 --
[0114] TABLE-US-00002 TABLE II Without heptane/ With heptane/ Base
Alloy # graphite grinding aids graphite grinding aids AR003 0.18%
0.34% AR026 0.27% 0.49% AR031 1.79% 2.81%
[0115] TABLE-US-00003 TABLE III Without glovebox With glovebox
proctection proctection Surface reaction 7 minutes 1 minute time
constant Bulk Diffusion 5.5 minutes 2.5 minutes time constant
* * * * *