U.S. patent application number 10/046072 was filed with the patent office on 2002-10-03 for high-capacity hydrogen storage alloy and method for producing the same.
This patent application is currently assigned to THE JAPAN STEEL WORKS, LTD.. Invention is credited to Ito, Hideaki, Kabutomori, Toshiki, Kubo, Kazuya, Takahashi, Toshio.
Application Number | 20020139456 10/046072 |
Document ID | / |
Family ID | 18876356 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139456 |
Kind Code |
A1 |
Kubo, Kazuya ; et
al. |
October 3, 2002 |
High-capacity hydrogen storage alloy and method for producing the
same
Abstract
A high-capacity hydrogen storage alloy has a crystal structure
containing a body-centered cubic structure as a single or main
phase and made of a composition represented by the general formula
Ti.sub.aCr.sub.bMo.sub.cFe- .sub.d, in which a is in a range of
from 25 to 45% by atomic weight, b is in a range of from 30 to 65%
by atomic weight, c is in a range of from 5 to 40% by atomic
weight, and d is in a range of from 0 to 15% by atomic weight. In
production of the alloy, a heat treatment is performed at a
temperature in a range of from 1,200 to 1,500.degree. C. for 1
minute to 24 hours and then cooling is performed at a speed equal
to or higher than the cooling speed obtained by water cooling.
Inventors: |
Kubo, Kazuya; (Hokkaido,
JP) ; Takahashi, Toshio; (Hokkaido, JP) ; Ito,
Hideaki; (Hokkaido, JP) ; Kabutomori, Toshiki;
(Tokyo, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Assignee: |
THE JAPAN STEEL WORKS, LTD.
|
Family ID: |
18876356 |
Appl. No.: |
10/046072 |
Filed: |
January 16, 2002 |
Current U.S.
Class: |
148/668 ;
148/423 |
Current CPC
Class: |
C22C 27/04 20130101;
C22C 14/00 20130101; C01B 3/0031 20130101; Y02E 60/10 20130101;
C22C 27/06 20130101; H01M 8/04216 20130101; H01M 8/04082 20130101;
Y02E 60/32 20130101; Y02P 70/50 20151101; Y02E 60/50 20130101; C01P
2002/70 20130101; H01M 4/383 20130101; C01P 2002/77 20130101 |
Class at
Publication: |
148/668 ;
148/423 |
International
Class: |
C22C 030/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 17, 2001 |
JP |
P. 2001-8788 |
Claims
What is claimed is:
1. A high-capacity hydrogen storage alloy comprising a crystal
structure containing a body-centered cubic structure as a single or
main phase and made of a composition represented by a general
formula Ti.sub.aCr.sub.bMo.sub.c: wherein a is in a range of from
25 to 45% by atomic weight, b is in a range of from 30 to 65% by
atomic weight, and c is in a range of from 5 to 40% by atomic
weight.
2. A high-capacity hydrogen storage alloy comprising a crystal
structure containing a body-centered cubic structure as a single or
main phase and made of a composition represented by a general
formula Ti.sub.aCr.sub.bMo.sub.cFe.sub.d: wherein a is in a range
of from 25 to 45% by atomic weight, b is in a range of from 30 to
65% by atomic weight, c is in a range of from 5 to 40% by atomic
weight, and d is not larger than 15% by atomic weight.
3. A high-capacity hydrogen storage alloy according to claim 1,
wherein a treatment that said hydrogen storage alloy is heated at a
temperature in a range of from 1,200 to 1,500.degree. C. for 1
minute to 24 hours and cooled at a cooling speed not less than the
speed of water cooling, has been performed.
4. A method for producing a high-capacity hydrogen storage alloy,
comprising the steps of: applying a heat treatment to a material
made of a composition defined in claim 1 to thereby heat said
material at a temperature in a range of from 1,200 to 1,500.degree.
C. for 1 minute to 24 hours; and cooling said material at a cooling
speed not less than the speed of water cooling after said heat
treatment.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a hydrogen storage alloy
used as a material for hydrogen storage, a hydrogen absorbing
material for thermal conversion, a hydrogen supply material for
fuel battery, a negative electrode material for nickel-hydrogen
battery, a material for hydrogen purification and recovery, a
hydrogen absorbing material for hydrogen gas actuator, or the like,
and particularly relates to a high-capacity hydrogen storage alloy
having excellent property at a temperature near the room
temperature, and a method for producing the high-capacity hydrogen
storage alloy.
[0002] Although a gas cylinder system and a liquid hydrogen system
have been heretofore used for storage and transportation of
hydrogen, a system using a hydrogen storage alloy has begun to be
noticed as an alternative to these systems. As well known, a
hydrogen storage alloy has a property of reversibly reacting with
hydrogen to absorb/release the hydrogen with incoming/outgoing of
reaction heat. This chemical reaction is used for attaining
practical application of a technique for storage and transportation
of hydrogen. Moreover, the reaction heat is used for promoting
development and practical application of a technique for
constructing a heat storage and heat transportation system or the
like. LaNi.sub.5, TiFe, TiMn.sub.1.5, or the like, is known well as
a representative hydrogen storage alloy.
[0003] For practical application of the hydrogen storage alloy to
various kinds of purposes, it is necessary to improve the property
of the hydrogen absorbing material more greatly. For example,
increase in hydrogen capacity, reduction in cost of raw materials,
improvement in plateau property, improvement in durability, etc are
the important issues. Especially, it has been known from long time
ago that metal of a body-centered cubic structure (hereinafter
referred to as "BCC") such as V, a TiVMn type alloy or a TiVCr type
alloy can absorb a great quantity of hydrogen compared with an
AB.sub.5 type or AB.sub.2 type alloy which has been already put
into practical use.
[0004] V, a TiVMn type alloy, a TiVCr type alloy, or the like,
capable of absorbing a large quantity of hydrogen, however, lacks
practical applicability because expensive V must be used so that a
hydrogen storage material using V increases raw material cost.
[0005] Although it is known that V or a TiVMn type or TiVCr type
alloy can absorb about 400 cc/g of hydrogen, there is also a
disadvantage that efficiency of the V or TiVMn type or TiVCr type
alloy is poor because the quantity of hydrogen allowed to be
absorbed/released effectively is about a half of the aforementioned
quantity so that the residual part of the alloy is chemically
combined with hydrogen and remains as a solid-soluble phase. In
addition, there are various difficulties to put the alloy into
practical use because the percentage of deterioration of the alloy
increases as absorption/release of hydrogen is repeated and because
equilibrium dissociation pressure decreases rapidly as the number
of hydrogen absorption/release cycles increases.
SUMMARY OF THE INVENTION
[0006] Basically, the present invention is to solve the
aforementioned problems and an object thereof is to provide a
hydrogen storage alloy which can absorb/release hydrogen
effectively at normal temperature without containing V and which
exhibits an excellent capacity of hydrogen absorption and an
rechargeable hydrogen capacity compared with a conventional
material and exhibits excellent durability.
[0007] To solve the aforementioned problems, according to a first
aspect of the prevent invention, there is provided a high-capacity
hydrogen storage alloy comprising a crystal structure containing a
body-centered cubic structure as a single or main phase and made of
a composition represented by the general formula
Ti.sub.aCr.sub.bMo.sub.c in which a is in a range of from 25 to 45%
by atomic weight, b is in a range of from 30 to 65% by atomic
weight, and c is in a range of from 5 to 40% by atomic weight.
[0008] According to a second aspect of the present invention, there
is provided a high-capacity hydrogen storage alloy comprising a
crystal structure containing a body-centered cubic structure as a
single or main phase and made of a composition represented by the
general formula Ti.sub.aCr.sub.bMo.sub.cFe.sub.d in which a is in a
range of from 25 to 45% by atomic weight, b is in a range of from
30 to 65% by atomic weight, c is in a range of from 5 to 40% by
atomic weight, and d is not larger than 15% by atomic weight.
[0009] According to a third aspect of the present invention, there
is provided a method for producing a high-capacity hydrogen storage
alloy, comprising the steps of: applying a heat treatment to a
material made of a composition defined in claim 1 or 2 to thereby
heat the material at a temperature in a range of from 1,200 to
1,500.degree. C. for 1 minute to 24 hours; and cooling the material
at a cooling speed equal to or higher than the speed of water
cooling after the heat treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a hydrogen pressure-composition isothermal curve
(PCT curve) graph of a material obtained by applying a
water-cooling treatment to an alloy (material according to the
present invention) having a composition Ti.sub.36Cr.sub.53Mo.sub.11
(atomic ratio: TiCr.sub.1.5Mo.sub.0.3) after a heat treatment at
1,450.degree. C. for 1 minute;
[0011] FIG. 2 is a PCT curve graph of a material obtained by
applying a water-cooling treatment to an alloy (material according
to the present invention) having a composition
Ti.sub.36Cr.sub.53Mo.sub.11 (atomic ratio: TiCr.sub.1.5Mo.sub.0.3)
after a heat treatment at 1,450.degree. C. for 1 minute or at
1,300.degree. C. for 3 hours;
[0012] FIG. 3 is a PCT curve graph of a material obtained by
applying a water-cooling treatment to an alloy (material according
to the present invention) having a composition
Ti.sub.36Cr.sub.57Mo.sub.7 (atomic ratio: TiCr.sub.1.6Mo.sub.0.2)
after a heat treatment at 1,300.degree. C. for 3 hours;
[0013] FIG. 4 is a PCT curve graph of an alloy (conventional
material) of Ti.sub.36Cr.sub.53V.sub.11 (atomic ratio:
TiCr.sub.1.5V.sub.0.3) after repetition of hydrogen
absorption/release;
[0014] FIG. 5 is a PCT curve graph of an alloy (material according
to the present invention) of Ti.sub.36Cr.sub.53Mo.sub.11(atomic
ratio: TiCr.sub.1.5Mo.sub.0.3) after repetition of hydrogen
absorption/release;
[0015] FIG. 6 is a PCT curve graph of an alloy of
Ti.sub.36Cr.sub.53Mo.sub- .9V.sub.2 (atomic ratio:
TiCr.sub.1.5Mo.sub.0.25V.sub.0.05) after repetition of hydrogen
absorption/release;
[0016] FIG. 7 is a PCT curve graph of an alloy of
Ti.sub.36Cr.sub.53Mo.sub- .2V.sub.9 (atomic ratio:
TiCr.sub.1.5Mo.sub.0.05V.sub.0.25) after repetition of hydrogen
absorption/release;
[0017] FIG. 8 shows a result of X-ray diffraction measurement of an
alloy of Ti.sub.36Cr.sub.53Mo.sub.11-XV.sub.X (atomic ratio:
TiCr.sub.1.5Mo.sub.0.3-XV.sub.X ) after repetition of hydrogen
absorption/release;
[0018] FIG. 9 shows a result of X-ray diffraction measurement of an
alloy (material according to the present invention) of
Ti.sub.36Cr.sub.53Mo.sub- .11 (atomic ratio:
TiCr.sub.1.5Mo.sub.0.3);
[0019] FIG. 10 is a PCT curve graph of an alloy (material according
to the present invention) of Ti.sub.36Cr.sub.57Mo.sub.7 (atomic
ratio: TiCr.sub.1.6Mo.sub.0.2) containing a large quantity (3,250
ppm) of oxygen;
[0020] FIG. 11 is a PCT curve graph of an alloy (material according
to the present invention) of Ti.sub.36Cr.sub.57Mo.sub.7 (atomic
ratio: TiCr.sub.1.6Mo.sub.0.2) containing a small quantity (980
ppm) of oxygen.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The reason why the composition and producing condition are
determined in the present invention will be described below.
[0022] As described above, the present invention provides a crystal
structure containing a body-centered cubic structure (hereinafter
properly referred to as "BCC") as a single or main phase and made
of a ternary alloy containing Ti, Cr and Mo as constituent
elements, or a quarternary alloy further containing Fe as an
additive element in addition to Ti, Cr and Mo. If another crystal
structure is used, good plateau property cannot be obtained.
[0023] Here, the component percentage of Ti is selected to be in a
range of from 25 to 45% by atomic weight (hereinafter properly
referred to as "at %") . If the component percentage of Ti is
smaller than 25 at %, the resulting alloy can be hardly initially
activated and the hydrogen absorption capacity of the alloy is
lowered to thereby make the practical use of the alloy impossible.
If the component percentage of Ti is larger than 45 at %, the
plateau property is worsened. Accordingly, the component-percentage
of Ti is selected to be in the aforementioned range. For the same
reason as described above, it is preferable that the lower limit
and the upper limit are 30 at % and 40 at % respectively.
[0024] Next, the component percentage of Cr is selected to be in a
range of from 30 to 65 at %. If the component percentage of Cr is
smaller than 30 at %, plateau property is worsened. On the other
hand, if the component percentage of Cr is larger than 65 at %, the
capacity of each of the hydrogen absorption and release is lowered.
Accordingly, the component percentage of Cr is selected to be in
the aforementioned range. For the same reason as described above,
it is further preferable that the lower limit and the upper limit
are 47 at % and 57 at % respectively.
[0025] Mo is added as an element substituted for a part of Cr. The
tendency of the change of PCT property after repetition of hydrogen
absorption/release varies widely in accordance with the quantity of
Mo substituted for a part of Cr. As shown in FIG. 4, in an alloy
(conventional material: Ti.sub.36at %Cr.sub.53at %V.sub.11at %)
obtained by adding V to a Ti--Cr binary alloy, absorption/release
pressure decreases largely in accordance with the repetition of
absorption/release (see FIG. 4). In an alloy (material according to
the present invention: Ti.sub.36at %Cr.sub.53at %Mo.sub.11at %)
obtained by adding only Mo to the Ti--Cr binary alloy, however,
reduction in pressure is small (see FIG. 5) When the Mo and V
contents of a TiCrMoV quarternary alloy are changed as a reference
example, it is understood that the change of pressure decreases as
the quantity of addition of Mo increases (see FIGS. 6 and 7).
Particularly when the quantity of addition of Mo is large, the
change of release pressure accompanying the repetition of hydrogen
absorption/release is so small that the alloy becomes very easy to
be handled when it is applied to a system. When the structural
change of the alloy is measured by X-ray diffraction after hydrogen
absorption/release is repeated by 500 times, it is found that the
X-ray diffraction peak becomes higher as the quantity of addition
of Mo increases (see FIG. 8). This means that, as the quantity of
Mo in the composition increases, the crystallinity of the alloy is
kept high even after repetition of hydrogen absorption/release.
That is, it is found that the material according to the present
invention exhibits good property also in durability against
repetition of hydrogen absorption/release because the BCC structure
is stabilized by addition of Mo.
[0026] Taking durability against repetition of hydrogen
absorption/release into account, the TiCrMo type alloy, which is a
material obtained by addition of Mo according to the present
invention, is an alloy small in the change of equilibrium
dissociation pressure owing to repetition of hydrogen
absorption/release and very easy to be handled in comparison with a
TiCrV type alloy used in the related art. However, if the quantity
of addition of Mo is larger than 40 at %, the maximum hydrogen
absorption capacity decreases remarkably. On the other hand, if the
quantity of addition of Mo is smaller than 5 at %, the BCC
structure of the alloy is hardly stabilized. Accordingly, the
quantity of Mo is selected to be in a range of from 5 to 40 at %.
For the same reason as described above, it is further preferable
that the lower limit and the upper limit are 7 at % and 10 at %
respectively.
[0027] Further, in order to adjust the equilibrium dissociation
pressure, Fe may be added as occasion demands. However, if the
quantity of addition of Fe is larger than 15 at %, the BCC
structure of the alloy is not stabilized. Accordingly, the quantity
of Fe is selected to be not larger than 15 at %. For the same
reason as described above, it is further preferable that the upper
limit is 7 at %.
[0028] The adjustment of the equilibrium dissociation pressure
maybe performed by changing the Ti/Cr ratio in the composition.
[0029] It has been also already found that hydrogenation property
is worsened remarkably when the oxygen content of a TiCrV type BCC
alloy is large. When the oxygen content increases, the influence of
increase in equilibrium dissociation pressure, great reduction in
hydrogen absorption capacity, deterioration in plateau property,
etc. is observed remarkably. In a TiCrMo type BCC alloy, however, a
large and flat plateau portion is exhibited even though the oxygen
content is relatively large. FIGS. 10 and 11 show the difference in
hydrogenation property between a TiCrMo alloy containing a large
quantity of oxygen and a TiCrMo alloy containing a small quantity
of oxygen for reference. As shown in FIGS. 10 and 11, equilibrium
dissociation pressure varies and the plateau width thereof varies
slightly in accordance with the oxygen content. In each of FIGS. 10
and 11, however, a relatively large plateau portion is obtained.
That is, it would be said that the TiCrMo alloy is not affected by
oxygen compared with the TiCrV alloy.
[0030] As described above, also in a TiCrMo alloy or a TiCrMoFe
alloy, property of a flat and large plateau portion is obtained
similarly to that in the TiCrV alloy if the TiCrMo or TiCrMoFe
alloy has a predetermined composition and contains a BCC structure
as a single or main phase (see FIG. 1). It is, however, preferable
that a heat treatment for production of the alloy is performed at a
temperature in a range of from 1,200 to 1,500.degree. C. and that
the cooling speed after the heat treatment is equal to or higher
than the speed obtained by water cooling. It has been already
confirmed that a solution treatment can be made sufficiently to
obtain good hydrogenation property if the heat treating time is not
shorter than 1 minute upon production of the alloy (see FIG. 1). In
comparison between an alloy heat-treated at 1,300.degree. C. for 3
hours and an alloy heat-treated at 1,450.degree. C. for 1 minute
according to the present invention, each alloy exhibits
substantially equal property. Accordingly, it is found that
excellent hydrogenation property can be exhibited even in the case
where the heat treatment is carried out for about 1 minute (see
FIG. 2). In accordance with compositions, however, the BCC
structure may be unable to be obtained in the heat treatment at
about 1,200.degree. C., so that hydrogenation property may be
worsened. In a composition shown in FIG. 3, different phases are
precipitated even in the heat treatment at 1300.degree. C., so that
property is worsened. It is, therefore, necessary to perform the
heat treatment suitably in the heat treatment range described in
the Scope of Claim for a patent, in accordance with the
composition.
[0031] It is found from the above results that a BCC single phase
is exhibited by each of almost all the compositions in the heat
treatment condition in which the heat-treating temperature is in
the range defined according to the present invention, that is, in a
range of from 1,200 to 1,500.degree. C., and that the BCC single
phase can be obtained sufficiently even in the case where the
heat-treating time is about 1 minute. To obtain better property, it
is preferable that a solution treatment is carried out at a
temperature as high as possible but within the range not to melt
the alloy in the heat treatment. Further, the alloy can be made
sufficiently soluble even in the case where the heat-treating time
is selected to be as short as possible in accordance with the ingot
size of the alloy. To obtain the BCC single phase structure, it is
preferable that a cooling method using a cooling speed as high as
possible is used after the heat treatment. However, even in the
case where the BCC single phase cannot be obtained perfectly, there
is no large deterioration of property. FIG. 9 shows a result of
X-ray diffraction measurement of Ti.sub.35.7at %Cr.sub.53.6at
%Mo.sub.10.7at % (which is equivalent to TiCr.sub.1.5Mo.sub.0.3 in
quantitative ratio and which is the same alloy composition as shown
in FIG. 1). In FIG. 9, different phase peaks are observed in
respective neighbors of 37.degree., 62.degree. and 75.degree. but
hydrogenation property is good as shown in FIG. 1.
[0032] As described above, a cooling method in which a cooling
speed as high as possible is obtained is preferably used for
cooling after the heat treatment. Therefore, a cooling speed equal
to or higher than the cooling speed obtained by water cooling is
used. An example of the cooling method includes quenching or roll
quenching using gas cooling or water cooling.
[0033] That is, in accordance with the present invention, hydrogen
can be absorbed/released effectively in various temperature ranges
by the operation of components Ti, Cr, Mo and Fe, and plateau
property is good. In addition, the alloy exhibits excellent
durability against hydrogen absorption/release and exhibits
excellent property particularly against the change of equilibrium
dissociation pressure. Accordingly, hydrogen storage/transportation
efficiency can be improved, so that the quantity of effective
hydrogen migration can be kept excellent even in the case where the
alloy is used for a long term.
EXAMPLES
[0034] Examples according to the present invention will be
described below in comparison with Comparative Examples.
[0035] Component materials Ti, Cr and Mo (Fe) were weighed and
mixed to achieve a target alloy. The mixture was received in a
crucible of a vacuum arc dissolving apparatus and arc-dissolved
under an atmosphere of high-purity Ar gas. Then, the mixture was
cooled to room temperature in the apparatus and solidified. The
alloy obtained thus was pulverized into a mesh size of from 50 to
200 in atmospheric air to thereby obtain samples to be measured. In
a stainless steel reactor in a pressure-composition isothermal
curve measuring apparatus, 5 g of each sample was enclosed.
[0036] A heat treatment was applied to the measurement sample in
the condition of a temperature range of from 1,200 to 1,500.degree.
C. for 1 minute to 24 hours. Then, the sample was cooled with
water.
[0037] An activating treatment was performed as a pre-treatment
before hydrogen absorption/release property of the sample was
measured. That is, the reactor was heated at 80.degree. C. for
about 1 hour while decompressed (to about 10.sup.-5 kgf/cm.sup.2)
and evaluated so that the reactor was degassed. Then, high-purity
hydrogen with pressure of 50 kgf/cm.sup.2 at 80.degree. C. was
imported into the reactor. Then, the reactor was cooled to
20.degree. C. By the aforementioned process, the sample began to
absorb hydrogen immediately. After 30 minutes, the absorption of
hydrogen was completed. The reactor was further evacuated while
heated to 80.degree. C. to thereby desorb hydrogen from the sample.
After these processes were repeated by a plurality of times, the
activating treatment was terminated.
[0038] Then, the hydrogen absorption/release property of each
sample was measured. That is, after the reactor temperature was
dropped to 20.degree. C. and kept at 20.degree. C., a predetermined
quantity of high-purity hydrogen was imported into the reactor.
After hydrogen was absorbed to the sample and the pressure in the
reactor was stabilized, the hydrogen pressure in the reactor was
measured, and the quantity of hydrogen-absorbed to the sample was
measured by a constant-volume method. After a predetermined
quantity of hydrogen was imported into the reactor again and the
pressure was stabilized, the hydrogen pressure and the hydrogen
absorption capacity were obtained. The aforementioned operation was
repeated until the pressure in the reactor reached 50 kgf/cm.sup.2.
Thus, hydrogen pressure-absorption capacity-isothermal curves were
obtained.
[0039] After hydrogen was absorbed to each sample until the
pressure reached 50 kgf/cm.sup.2 as described above, a
predetermined quantity of hydrogen was discharged from the reactor
while the reactor was kept at the aforementioned temperature of
20.degree. C. After the hydrogen pressure in the reactor was
stabilized, the pressure in the reactor and the quantity of
hydrogen desorbed from the sample were measured by a
constant-volume method. A predetermined quantity of hydrogen was
discharged from the reactor again. The aforementioned operation was
repeated until the pressure in the reactor reached 0.2
kgf/cm.sup.2. Thus, hydrogen pressure-release capacity-isothermal
curves were obtained in a hydrogen release process (FIGS. 1 to
3).
[0040] Such hydrogen pressure-composition isothermal curves (PCT
curves) were plotted at various temperatures and the change of
equilibrium dissociation pressure in each PCT curve was plotted
with respect to 1/T (T represents the temperature expressed in K)
to thereby calculate heat .DELTA.H (kJ/molH.sub.2) of reaction of
the alloy. Results of the calculation were shown in Table 1.
[0041] Then, durability of each sample against repetition of
hydrogen absorption/release was measured. In a stainless steel
reactor in a durability evaluation testing apparatus, 2 g of each
sample was enclosed. The same activating treatment as described
above was applied and the reactor temperature was dropped to
20.degree. C. Then, the same processes as in the aforementioned
hydrogen absorption/release property measuring method were
repeated. Thus, the change of the hydrogen absorption capacity in
accordance with the number of repetition times was obtained by
comparison between PCT curves (FIGS. 4 to 7).
[0042] The reaction heat of the alloy sample in each of Example
according to the present invention exhibited a smaller value than
the reaction heat of the alloy sample in each of Comparative
Examples. Hence, it is preferable that the alloy according to the
present invention is used as a hydrogen supply material not for
heat pump but for fuel battery. As an example, the maximum capacity
of hydrogen absorption and the quantity of effective hydrogen
migration in TiCr.sub.1.5V.sub.0.3 (comparative material) and those
in TiCr.sub.1.5MO.sub.0.3 (material according to the present
invention) are shown in Table 2. As shown in Table 2, the ratio of
the quantity of effective hydrogen migration to the maximum
capacity of hydrogen absorption in the material according to the
present invention is large compared with that in the comparative
material. That is, the material according to the present invention
can utilize a great deal of hydrogen absorbing power in the alloy.
Moreover, because the material according to the present invention
is small in the maximum capacity of hydrogen absorption, it would
be said that the material according to the present invention is a
low-expansion alloy compared with the conventional material. This
brings increase in the percentage of alloy charged in a hydrogen
storage alloy tank and improvement in the handling property of the
tank. Accordingly, higher hydrogen storage density can be achieved
by use of the material according to the present invention.
1TABLE 1 Alloy Reaction Heat .DELTA.H (kJ/molH.sub.2) Alloy
Reaction Alloy Heat .vertline. .DELTA.H .vertline. Sample No.
Composition (kJ/molH.sub.2) Comparative Material 1
TiCr.sub.1.5V.sub.0.3 41.1081 2 TiCr.sub.1.4V.sub.0.4 41.7538
Material according to 3 TiCr.sub.1.5Mo.sub.0.3 25.2636 the
Invention 4 TiCr.sub.1.4Mo.sub.0.4 24.8324
[0043]
2TABLE 2 Maximum Hydrogen Capacity and Rechargeable Hydrogen
Capacity Maximum Rechargeable Hydrogen Hydrogen Capacity Capacity
Sample (cc/g) (cc/g) Comparative TiCr.sub.1.5V.sub.0.3 391 220
Material Material TiCr.sub.1.5Mo.sub.0.3 288 200 according to the
Invention
[0044] As described above, in the hydrogen storage alloy according
to the present invention, hydrogen can be absorbed/released
effectively in various temperature ranges by the operation of
components Ti, Cr, Mo and Fe in the alloy, and plateau property is
good. In addition, the alloy exhibits excellent durability against
hydrogen absorption/release and exhibits excellent property
particularly against the change of equilibrium dissociation
pressure. Accordingly, hydrogen storage/transportation efficiency
can be improved and the quantity of effective hydrogen migration
can be kept excellent even in the case where the alloy is used for
a long term.
[0045] As described above, the material according to the present
invention is inexpensive compared with the TiCrV type alloy which
is a material used in the related art, because V is not used in the
material according to the present invention. Moreover, the material
according to the present invention exhibits good hydrogenation
property which is equivalent to that of the TiCrV type alloy, and
there is little change of equilibrium dissociation pressure owing
to repetition of hydrogen absorption/release. That is, the material
according to the present invention is an alloy which is low in
expansion and low in alloy reaction heat and which has such good
property that the alloy can be handled easily.
* * * * *