U.S. patent application number 10/131209 was filed with the patent office on 2002-12-26 for magnesium-based hydrogen storage alloys.
This patent application is currently assigned to JAPAN METALS AND CHEMICALS CO., LTD., JAPAN METALS AND CHEMICALS CO., LTD.. Invention is credited to Hayami, Noboru, Osawa, Masahito, Terashita, Naoyoshi, Tomioka, Hidenori, Tsunokake, Shigeru.
Application Number | 20020197181 10/131209 |
Document ID | / |
Family ID | 18977226 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197181 |
Kind Code |
A1 |
Osawa, Masahito ; et
al. |
December 26, 2002 |
Magnesium-based hydrogen storage alloys
Abstract
Magnesium-based hydrogen storage alloys comprise a metallic
magnesium (Mg) and a magnesium-containing intermetallic compound
(Mg.sub.xM.sub.y wherein y is 1-x) and contain not less than 60
mass % of magnesium in total, and have a phase of a primarily
crystallized magnesium-containing intermetallic compound in its
solidification structure.
Inventors: |
Osawa, Masahito; (Ibaraki,
JP) ; Tomioka, Hidenori; (Tokyo, JP) ;
Terashita, Naoyoshi; (Ibaraki, JP) ; Hayami,
Noboru; (Tokyo, JP) ; Tsunokake, Shigeru;
(Tokyo, JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
JAPAN METALS AND CHEMICALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
18977226 |
Appl. No.: |
10/131209 |
Filed: |
April 25, 2002 |
Current U.S.
Class: |
420/402 ;
148/420; 420/900 |
Current CPC
Class: |
C22C 23/00 20130101;
C22C 23/06 20130101; H01M 4/383 20130101; Y02E 60/10 20130101; C22C
23/02 20130101 |
Class at
Publication: |
420/402 ;
148/420; 420/900 |
International
Class: |
C22C 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2001 |
JP |
2001-128555 |
Claims
What is claimed is:
1. Magnesium-based hydrogen storage alloys comprising a metallic
magnesium (Mg) and a magnesium-containing intermetallic compound
(Mg.sub.xM.sub.y wherein y is 1-x) and containing not less than 60
mass% of magnesium in total, and having a phase of an primary
crystallized magnesium-containing intermetallic compound in its
solidification structure.
2. Magnesium-based hydrogen storage alloys according to claim 1,
wherein an alloying element constituting the magnesium-containing
intermetallic compound is at least one element selected from the
group consisting of Al, Si, Ca, Co, Ni, Cu, Sr, Y, Pd, Sn, Ba and
Ln (lanthanide elements).
3. Magnesium-based hydrogen storage alloys according to claim 1 or
2, wherein the alloys are initially activated at a temperature of
not higher than 300.degree. C. under a hydrogen pressure condition
of not more than 3 MPa.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to hydrogen storage alloys useful as
a material for transportation and storage of hydrogen, and more
particularly to magnesium-based hydrogen storage alloys having a
large hydrogen storage quantity at a lower temperature under a
lower pressure.
[0003] 2. Description of Related Art
[0004] Recently, a hydrogen energy is expected as a petroleum
alternative energy. However, there are left many problems to be
solved such as infrastructure building, safety and the like for
putting the hydrogen energy into practice.
[0005] When hydrogen is filled into a high-pressure steel bottle, a
volume can be compressed to about {fraction (1/150)} or to about
{fraction (1/800)} at a liquefied state. On the other hand,
hydrogen storage alloys can occlude (absorb) a gaseous hydrogen
therein and store as a solid, so that a volume of hydrogen can be
apparently compressed to about {fraction (1/1000)}. Furthermore,
the hydrogen stored in the hydrogen storage alloys is simple in the
handling as compared with a liquid hydrogen or a high pressure
hydrogen gas. Therefore, there is a great merit in practical use
when hydrogen is transported and stored by using the hydrogen
storage alloys, and it is advantageous in the safety because it is
not required to handle hydrogen as a high pressure gas or a
liquid.
[0006] And also, hydrogen can be absorbed or desorbed only by
adjusting a temperature or a pressure in the hydrogen storage
alloys, so that it is possible to build a cheap hydrogen storage
equipment by using the hydrogen storage alloys and it is attempted
to reduce energy cost.
[0007] From the above reasons, or from a viewpoint of a future
energy agenda, it is urgently demanded to develop hydrogen storage
alloys for transporting and storing hydrogen in a high
performance.
[0008] As the conventionally discovered hydrogen storage alloys,
there are mainly known binary intermetallic compounds of AB.sub.5
type such as LaNi.sub.5 or the like, AB.sub.2 type such as
ZrMn.sub.2 or the like, AB type such as TiFe or the like, and
A.sub.2B type such as Mg.sub.2Ni or the like. Among them, a
hydrogen storage quantity of the hydrogen storage alloys other than
Mg.sub.2Ni is as small as about 1.4 mass % in LaNi.sub.5, about 1.7
mass % in ZrMn.sub.2, and about 1.8 mass % in TiFe based on the
weight of the alloys, which is mainly composed of a relatively
heavy element such as a rare earth element or Zr, so that it is
difficult to increase the hydrogen storage quantity per the weight,
and V and the like are expensive and are costly less in the
merit.
[0009] On the other hand, Mg.sub.2Ni as a typical example of
A.sub.2B type alloy is about 3.6 mass % in the hydrogen storage
quantity, which is considerably larger than that of the other
alloys. However, it is demanded to develop a hydrogen storage
alloys with a higher capacity. Particularly, hydrogen storage
alloys mainly composed of magnesium are known to have a very large
hydrogen storage performance. Moreover, a hydrogen storage quantity
of magnesium metal itself (H.sub.2/(H.sub.2+Mg)) reaches 7.6 mass
%.
[0010] However, the magnesium-based hydrogen storage alloys are not
put into a practical use up to the present time. Because, it is
considered to be difficult to initially activate the magnesium
alloys. That is, magnesium is easy to absorb hydrogen and to form a
stable hydride, so that it is required to maintain at high
temperature and high pressure state of 350-450.degree. C. and 10-20
MPa for absorbing and desorbing hydrogen, which becomes difficult
to put into the practical use as a hydrogen storage alloy.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an object of the invention to provide
magnesium-based hydrogen storage alloys capable of easily absorbing
and desorbing a greater quantity of hydrogen at practical
conditions (low temperature and low pressure).
[0012] The inventors have made various studies for solving the
above problems inherent to the conventional magnesium-based
hydrogen storage alloys to achieve the above object, and found that
there is a constant relationship between an initial activation
property and a metal structure, and as a result, the invention has
been accomplished adding a metallographical consideration.
[0013] That is, the invention,,lies in a magnesium-based hydrogen
storage alloys comprising a metallic magnesium (Mg) and a
magnesium-containing intermetallic compound (Mg.sub.xM.sub.y
wherein y is 1-x) and containing not less than 60 mass % of
magnesium in total, and having a phase of a primarily crystallized
magnesium-containing intermetallic compound in its solidification
structure. In this case, it is favorable that an amount of metallic
magnesium occupied in total magnesium (.gtoreq.60 mass %) is about
7-45 mass % and the remainder is magnesium in the
magnesium-containing intermetallic compound. Furthermore, it is
favorable that an amount of magnesium in the intermetallic compound
is about 16-63 mass %.
[0014] In the invention, an alloying element constituting the
magnesium-containing intermetallic compound is preferable to be at
least one element selected from the group consisting of Al, Si, Ca,
Co, Ni, Cu, Sr, Y, Pd, Sn, Ba and Ln (lanthanide elements). And
also, it is favorable to be initially activated at a temperature of
not higher than 300.degree. C. under a hydrogen pressure condition
of not more than 3 MPa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram of a Mg--Ni series metal.
[0016] FIG. 2 is a photograph of the metal structure of a Mg--Ni
hydrogen storage alloy according to the invention.
[0017] FIG. 3 is a photograph of metal structure of a Mg--Ni
hydrogen storage alloy according to the comparative example.
DETAILED DESCRIPTION OF THE INVENTION
[0018] As mentioned above, the alloys mainly composed of magnesium
are characterized by having a large hydrogen storing quantity but
has a drawback that an initial activation property capable of
absorbing and desorbing hydrogen is poor.
[0019] This drawback is considered due to the fact that the
metallic magnesium phase itself is poor in the catalytic action
through the dissociation of a hydrogen gas molecule and that the
diffusion rate of hydrogen in a magnesium hydride produced on the
surface of the hydrogenation is slow, the hydrogenation is not
proceeded into the inside of the substrate.
[0020] Based on the above knowledge, the invention improves the
initial activation property by controlling the solidification
structure of magnesium or magnesium-containing intermetallic
compound while maintaining a large hydrogen storage property
inherent to magnesium. The thus developed magnesium-based hydrogen
storage alloys according to the invention are magnesium
(hereinafter referred to as Mg) as an essential component and
contains Mg-containing intermetallic compound capable of occluding
hydrogen.
[0021] As an alloying element forming the intermetallic compound by
bonding to Mg (hereinafter abbreviated as M), use may be made of at
least one element selected from the group consisting of Ln
(lanthanide elements), Ni, Ca, Al, Ba, Cu, Pd, Si, Sr, Y and Sn.
These elements form an intermetallic compound of a general formula:
Mg.sub.xM.sub.y equilibrating with a Mg phase.
[0022] In the invention, the Mg.sub.xM.sub.y intermetallic compound
is used as a hydrogen storage alloy and formed by mixing the
Mg.sub.xM.sub.y intermetallic compound and metallic Mg at a given
composition ratio and melting and casting and alloying them. In
this case, a two phase comprising Mg phase and Mg.sub.xM.sub.y
intermetallic compound phase is produced accompanied with eutectic
reaction from a liquid phase during the solidification to form a
hydrogen storage alloy, but it is important to have a composition
precipitating a primary crystal of Mg-containing intermetallic
compound without initially precipitating Mg during the
solidification.
[0023] In general, Mg phase is precipitated as a primary crystal
during the solidification in alloys having a Mg content higher than
an eutectic point, while Mg.sub.xM.sub.y intermetallic compound
phase is precipitated as a primary crystal during the
solidification in alloys having a Mg content lower than an eutectic
point.
[0024] Although a phase diagram of Mg--Ni binary alloy is shown in
FIG. 1, when a total amount of Mg including metallic Mg of a matrix
portion is less than an eutectic point (Mg: 76.5 mass%), for
example, within a range of 60-76.4 mass %, a structure as shown in
a metallic structure photograph (.times.100 magnification) of FIG.
2, i.e. a structure wherein Mg.sub.xM.sub.y intermetallic compound
is precipitated as a primary crystal is produced during the
solidification. On the other hand, when the total amount of Mg
exceeds 77 mass %, a structure as shown in a metallic structure
photograph (.times.100 magnification) of FIG. 3, i.e. a structure
wherein the metallic Mg pointedly dispersed in the matrix portion
(mixed phase of Mg and Mg.sub.2Ni) is precipitated as a primary
crystal.
[0025] In the former case (FIG. 2), M element (other than Ni) is
easily activated in the first hydrogenation of Mg.sub.xM.sub.y
phase to decompose into a hydride of the M element or two phases of
M element and Mg hydride phase to thereby cause dismutation
reaction. The hydride of the M element or the M element produced by
this dismutation reaction provides a diffusion (introduction) path
of hydrogen in Mg phase and acts as a catalyst dissipating hydrogen
gas molecule into monoatom. For this end, the Mg-based hydrogen
storage alloy can be easily and initially activated to easily
occlude a great amount of hydrogen.
[0026] Moreover, when the M element is Ni, Mg.sub.2Ni intermetallic
compound itself produced is high in the catalytic performance and
reacts with hydrogen to directly form Mg.sub.2NiH.sub.4, which
forms a hydrogen diffusion path in the Mg phase, so that these
alloys are also easily and initially activated likewise the
aforementioned M element.
[0027] In the latter case (FIG. 3), when the Mg phase itself
solidified as a primary crystal is hydrogenated, a stable hydride
is formed on the surface. As a result, a hydrogen diffusion rate in
the Mg hydride becomes slow and hence hydrogenation does not
proceed into the inside, while the Mg phase itself is poor in the
catalytic action for the dissipation of hydrogen gas molecule and
the hydrogen diffusion path is not formed in the alloy, so that the
activation is considerably difficult. Therefore, hydrogen can not
be occluded to a theoretical occlusion quantity.
[0028] In the hydrogen storage alloys according to the invention,
the total amount of Mg including Mg of the intermetallic compound
is not less than 60 mass % from a viewpoint of obtaining a
theoretical hydrogen occlusion quantity of not less than 5 mass %.
The reason is described as follows. Considering a case that the
above Mg intermetallic compound is Mg.sub.xM.sub.y, when hydrogen
is stored in these alloys to hydrogenate Mg.sub.2Ni, there are
produced the following reaction formulae (1) and (2):
Mg.sub.2Ni+2H.sub.2.fwdarw.Mg.sub.2NiH.sub.4(4H/Mg.sub.2Ni=3.7 mass
%) (1)
Mg+H.sub.2.fwdarw.MgH2(2H/Mg=8.2 mass %) (2)
[0029] As seen from the formulae (1) and (2), when Mg.sub.2Ni and
Mg are hydrogenated, 2 mol of hydrogen atom bonds to Mg/mol
irrespectively of the form difference. That is, when Mg is 100 mass
%, the hydrogen occlusion quantity is 8.2 mass %, so that in order
to ensure a hydrogen occlusion quantity of 5.0 mass %, Mg content
is required to be not less than 60 mass % (5.0 mass %/8.2 mass
%.times.100.congruent.60%).
[0030] On the other hand, the upper limit of the total Mg amount is
an eutectic point composition as mentioned above. The upper limit
of Mg mass % in each alloying element (M) is shown in Table 1
together with a compound form.
1TABLE 1 Mg Mg Element content Compound Element content Compound Ni
77 Mg.sub.2Ni Sr 82 Mg.sub.17Sr.sub.2 Ca 84 Mg.sub.2Ca Y 74
Mg.sub.24Y.sub.5 Al 68 Mg.sub.17Al.sub.12 La 90 Mg.sub.12La Ba 88
Mg.sub.17Ba.sub.2 Si 98 Mg.sub.2Si Cu 70 Mg.sub.2Cu Sn 64
Mg.sub.2Sn Pd 73 Mg.sub.6Pd Note) Mg content is mass % of an
eutectic point composition.
EXAMPLE
[0031] A sample used in this example is prepared by adjusting
components as shown in Table 2, melting them in a high frequency
induction apparatus, and casting in a water-cooling iron mold.
Then, the hydrogen storage alloys prepared for test is pulverized
to a size of about several mesh and weighed by 2 g. The thus weight
sample is sufficiently evacuated at 300.degree. C. and kept at this
temperature under a hydrogen pressure of 3 MPa for 24 hours or 120
hours, during which a hydrogen storage quantity is calculated from
a pressure change to evaluate an initial activation property. The
evaluated results are shown in Table 2 together with compositions
of example alloys and comparative example alloys.
2 TABLE 2 Activation rate After After Metallic Composition 24 hours
120 hours Mg.sub.xM.sub.y magnesium (mass ratio) (mass %) (mass %)
(mass %) (mass %) Example 1 Mg.sub.65Al.sub.35 4.4 5.0 Mg 45 Al 35
20 Example 2 Mg.sub.70Si.sub.30 4.1 5.1 Mg 52 Si 30 18 Example 3
Mg.sub.70Ca.sub.30 4.2 5.1 Mg 36 Ca 30 34 Example 4
Mg.sub.70Ni.sub.30 4.9 5.3 Mg 25 Ni 30 45 Example 5
Mg.sub.60Cu.sub.40 4.0 5.0 Mg 31 Cu 40 29 Example 6
Mg.sub.75Sr.sub.25 4.2 5.3 Mg 59 Sr 25 16 Example 7
Mg.sub.70Y.sub.30 4.7 5.2 Mg 39 Y 30 31 Example 8
Mg.sub.65Pd.sub.35 4.6 5.1 Mg 48 Pd 35 17 Example 9
Mg.sub.60Sn.sub.40 4.0 5.0 Mg 16 Sn 40 44 Example 10
Mg.sub.70Ba.sub.30 4.1 5.0 Mg 45 Ba 30 25 Example 11
Mg.sub.70La.sub.30 4.3 5.0 Mg 63 La 30 7 Example 12
Mg.sub.70Ni.sub.20Ca.sub.10 4.6 5.2 Mg 29 Ni 20 41 Ca 10 Example 13
Mg.sub.70Ni.sub.10Ca.sub.10La.sub.10 4.5 5.1 Mg 41 Ni 10 29 Ca 10
La 10 Comparative Mg 0.1 0.7 Mg 100 -- -- 100 Example 1 Comparative
Mg.sub.78Ni.sub.22 0.2 1.0 Mg 18 Ni 22 60 Example 2
[0032] From the above test results, it has been confirmed that the
Mg intermetallic compound is precipitated as a primary crystal in
all alloys of Examples 1-13.
[0033] Moreover, in single Mg body of Comparative Example 1 and the
alloy of Comparative Example 2 having a composition of solidifying
Mg as a primary crystal, the theoretical hydrogen occlusion
quantity is large because the hydrogen occlusion quantity is
determined by the Mg content, but they can not be activated under
low temperature and low pressure conditions of 300.degree. C. and 3
MPa, so that the hydrogen occlusion quantity after 120 hours is
small. On the other hand, in the alloys of Examples 1-13, it is
possible to occlude hydrogen up to substantially an equilibrium
state after 120 hours under the above test conditions (300.degree.
C., 3 MPa). As a result, it can be seen that the alloys according
to the invention can be sufficiently activated even under practical
conditions while maintaining the high hydrogen storage performance
of Mg-based alloys.
[0034] As mentioned above, according to the invention, there can be
provided Mg-based hydrogen storage alloys having a high hydrogen
storage property suitable for transporting and storing hydrogen.
Furthermore, the invention facilitates the occlusion and discharge
of hydrogen under practical environment, so that it contributes to
minimize machines and equipments using such alloys and to decrease
the cost.
* * * * *