Hydrogen storage material

A hydrogen storage material comprising a composite material comprising a matrix of an alloy consisting essentially of iron and titanium in an iron/titanium atomic ratio of 1/1.04-1.40, and dispersed therein as separate phases, a metallic oxide composed of iron, titanium and oxygen.

This invention relates to a hydrogen storage material. More specifically, 
this invention relates to a hydrogen storage material comprising iron, 
titanium and iron-titanium oxide capable of absorbing a large quantity of 
hydrogen at room temperature and of releasing a large quantity of the 
absorbed hydrogen at room temperature. 
It has been suggested recently to utilize intermetallic compounds capable 
of storing hydrogen in almost equal or higher densities to or than liquid 
hydrogen in storing or transporting hydrogen. For example, iron-titanium, 
lanthanum-nickel, Mischmetal-nickel, calcium-nickel, titanium-manganese, 
magnesium-nickel, and magnesium-copper are known as such intermetallic 
compounds. 
The lanthanum-nickel and Mischmetal-nickel intermetallic compounds can be 
easily converted to hydrides, but have the defect that they are difficult 
to produce and are susceptible to oxidation. 
The titanium-manganese intermetallic compound can be easily converted to a 
hydride, but has the defect that in releasing hydrogen, a large amount of 
hydrogen remains at atmospheric pressure and room temperature. 
The magnesium-nickel intermetallic compound and magnesium alloys containing 
this intermetallic compound have the advantage of being able to store a 
large amount of hydrogen per unit weight, but suffer from the defect that 
to release hydrogen at atmospheric pressure to several atmospheres, they 
have to be heated to a temperature of at least 300.degree. C. to increase 
their dissociation equilibrium pressure to the aforesaid pressures. 
The iron-titanium intermetallic compound (FeTi), on the other hand, is 
considered to be most promising as a hydrogen storage material because it 
has superior hydrogen storing characteristics and is relatively 
inexpensive. However, it suffers from the disadvantage that its activation 
for hydrogen absorption is difficult and the hydrogen absorbing 
equilibrium pressure at room temperature is fairly high. For example, to 
activate FeTi, it must be pulverized to fine particles, for example those 
having a particle diameter smaller than 100 mesh (Tyler's mesh) and then 
heated to a temperature of as high as 200.degree. to 400.degree. C. in 
hydrogen under a pressure of several tens of atmospheres. 
In order to facilitate the activation of FeTi and lower the hydrogen 
absorbing pressure at the time of hydride formation, it has been known to 
substitute niobium, manganese or titanium for a part of Fe In FeTi. To 
eliminate the aforesaid defects of FeTi by using an intermetallic compound 
containing niobium, it is necessary to substitute niobium for several % by 
weight of Fe. Hence, the resulting compound is expensive and is 
economically disadvantageous. Intermetallic compounds having manganese or 
titanium substituted for a part of Fe cause a large amount of hydrogen to 
remain therein, and therefore, the amount of hydrogen they can release is 
reduced. 
It is an object of this invention therefore to provide a hydrogen storage 
material which eliminates the aforesaid defects of conventional 
intermetallic compounds and can withstand practical use. 
Another object of this invention is to provide a hydrogen storage material 
which does not require activating treatment, has a high rate of hydrogen 
absorption and a low hydrogen absorbing equilibrium pressure and which can 
store and release hydrogen in great quantities at room temperature. 
Still another object of this invention is to provide a low-cost hydrogen 
storage material. 
Other objects and advantages of this invention will become apparent from 
the following description. 
According to this invention, these objects and advantages can be achieved 
by a hydrogen storage material comprising a composite material comprising 
a matrix of an alloy consisting essentially of iron and titanium in an 
iron/titanium atomic ratio of 1/1.04-1.40, and dispersed therein as 
separate phases, a metallic oxide composed of iron, titanium and oxygen. 
Thus, the hydrogen storage material of this invention comprises a composite 
material comprising 
(1) a matrix of an alloy consisting essentially of iron and titanium in an 
iron/titanium atomic ratio of 1/1.04-1.40, and 
(2) dispersed therein as separate phases, a metallic oxide comprising iron, 
titanium and oxygen. 
A hydrogen storage material composed of a metallic matrix of iron and 
titanium in an atomic ratio of 1:1 and a metallic oxide composed of iron, 
titanium and oxygen present therein is known [Proc. 11th Intersociety 
Energy Conversion Engineering Conference, AIChE, 965 (1976)]. This article 
states that since FeTi having an iron/titanium atomic ratio of 1/1 has a 
strong affinity for hydrogen in the molten state and takes oxygen from air 
or from common oxide crucibles to form an oxygen stabilized phase having 
the composition Fe.sub.7 Ti.sub.10 O.sub.3, its maximum H-level, that is 
the amount of hydrogen stored, is decreased, and therefore that for 
production of FeTi particles, consideration must be given to means for 
preparing FeTi with 0 contents as low as practical within reasonable 
economic constraints. 
Thus, as seen in the aforesaid literature reference, in an intermetallic 
compound of iron and titanium in an atomic ratio of 1:1 (actually since it 
reacts with oxygen to form Fe.sub.7 Ti.sub.10 O.sub.3, iron is evidently 
somewhat in excess of titanium in the resulting alloy matrix), the absence 
of oxide was desirable and recommended in order to use it as a hydrogen 
storage material. In view of this conventional technique, the fact 
elucidated by the present inventors is unexpected and surprising. 
The present invention, in its broadest concept, provides a composite 
material having a metallic matrix consisting essentially of iron and 
titanium with an iron/titanium atomic ratio of 1/1.04-1.40. 
This metallic matrix can be expressed by the following formula 
EQU FeTi.sub.x 
wherein x is 1.04 to 1.40. If x is less than 1.04, the composite material 
exhibits much the same properties as a composite material having a 
metallic matrix with an iron/titanium atomic ratio of 1:1 to a value in 
which iron is more than titanium, and is undesirable as a hydrogen storage 
material. If x is larger than 1.40, the amount of residual hydrogen is 
large, and the amount of hydrogen released is small. Hence, the resulting 
composite material is not suitable as a hydrogen storage material. 
The metallic matrix in accordance with this invention forms a single FeTi 
phase when the x is in the range of 1.04 to about 1.1. When x exceeds 
about 1.1, a phase of a solid solution of Ti forms and a mixture of the 
FeTi phase and the solid solution phase results. 
The metallic matrix in accordance with this invention may be a single FeTi 
phase, or a mixed phase of the FeTi phase and the solid solution phase 
mentioned above. There is a general tendency that as the metallic matrix 
increases in the proportion of the solid solution phase, the rate of 
hydrogen absorption increases and the amount of remaining hydrogen in 
releasing hydrogen increases. Investigations of the present inventors have 
shown that even when the proportion of the solid solution phase of the 
metallic matrix increases, so long as the iron/titanium atomic ratio is 
within the aforesaid range (x=1.04 to 1.40), the hydrogen storage material 
of this invention can store hydrogen which can be released in a great 
amount. 
The composite material in accordance with this invention contains a 
metallic oxide composed of iron, titanium and oxygen dispersed as separate 
phases in the aforesaid metallic matrix in which titanium is in excess of 
iron. The composite material in accordance with this invention is produced 
by an arc-melting method to be described below. In the step of cooling the 
melt in the manufacturing process, the aforesaid metallic oxide is 
spontaneously and uniformly dispersed as fine separated phases as islands 
in the metallic matrix. The structural characteristic of the present 
invention is that the metallic oxide is dispersed as islands in the sea of 
the metallic matrix. The proportion of the metallic oxide dispersed is 
preferably 0.5 to 28% by weight, more preferably 1.5 to 9% by weight, 
based on the weight of the entire composite material. Electron probe X-ray 
microanalysis has shown that the aforesaid metallic oxide in accordance 
with this invention has an iron/titanium/oxygen atomic ratio of 
1/1.4-2.5/0.4-0.6. 
Specifically, investigations of the present inventors have shown that the 
concentration of titanium in the metallic oxide dispersed in the metallic 
matrix seems to increase gradually with increasing ratio of titanium to 
iron (namely, with increasing x), and therefore that in the hydrogen 
storage material of this invention, the metallic oxide is not limited to a 
specified single composition only. For example, empirical formulae 
Fe.sub.7 Ti.sub.11 O.sub.4, Fe.sub.5 Ti.sub.10 O.sub.3, Fe.sub.6 Ti.sub.11 
O.sub.3, Fe.sub.7 Ti.sub.13 O.sub.3, and Fe.sub.7 Ti.sub.10 O.sub.3 can be 
assigned to such a metallic oxide. 
In the most preferred embodiment, the composite material of this invention 
comprises a metallic matrix consisting essentially of iron and titanium 
with a Ti/Fe atomic ratio of 1.04-1.40/1, preferably 1.08-1.30/1, and 
dispersed uniformly therein as separated phases 0.5 to 28% by weight, 
preferably 1.5 to 9% by weight, of a metallic oxide. 
Advantageously, the composite material of this invention can be produced 
very easily by an arc-melting method. Specifically, it can be produced, 
for example, by subjecting a predetermined amount of precisely weighed 
sponge titanium, titanium foil, electrolytic iron and ferric oxide to 
arc-melting in an atmosphere of an inert gas such as argon or helium, 
cooling the product and pulverizing the resulting ingot. Desirably, ferric 
oxide is powdery, and is melted while it is enveloped with titanium foil. 
Pulverization of the ingot can be carried out in the air. If it is 
pulverized to a particle size smaller than about 80 Tyler's mesh, 
especially smaller than about 100 Tyler's mesh, it can be used as a 
hydrogen storage material.

FIG. 1 of the accompanying drawings show hydrogen absorption curves of 
composite materials of this invention obtained by pulverizing ingots 
produced by arc-melting to a size smaller than 100 Tyler's mesh. Referring 
to FIG. 1, curve 2 is a hydrogen absorption curve of a composite material 
of this invention comprising a metallic material having the composition 
FeTi.sub.1.13 and dispersed therein 1.9% by weight, based on the weight of 
the entire composite material, of an oxide composed of iron, titanium and 
oxygen. As stated hereinabove, the composite material of this invention is 
not limited to a metallic oxide having one specified composition, but may 
include metallic oxides having an iron:titanium:oxygen atomic ratio within 
the aforesaid range. In FIG. 1 and other drawings accompanying the 
application, the metallic oxide is given as having the composition 
Fe.sub.7 Ti.sub.10 O.sub.3 for the sake of convenience in order to specify 
the weight proportion of the included metallic oxide. According to this 
method of expression, the curve 2 in FIG. 1 is expressed as FeTi.sub.1.13 
-1.9Fe.sub.7 Ti.sub.10 O.sub.3. Curve 3 is a hydrogen absorption curve of 
FeTi.sub. 1.13 -8.8Fe.sub.7 Ti.sub.10 O.sub.3. Curves 1 and 4 are 
respectively hydrogen absorption curves of FeTi.sub.1.13 and FeTi given 
for the sake of comparison. These hydrogen absorption curves are prepared 
by setting the respective composite materials in a pressure reactor, 
evacuating the reactor to a pressure of 2.times.10.sup.-6 mmHg, and 
introducing hydrogen gas of 99.99999% purity at 25.degree. C. at 60 
atmospheres. In FIG. 1, the abscissa represents the time (minutes) elapsed 
after the introduction of hydrogen at 60 atmospheres, and the ordinate, 
the number of hydrogen atoms absorbed based on the total number of iron 
and titanium atoms contained in the composite material. 
It is seen from FIG. 1 that FeTi having an iron/titanium atomic ratio of 
1/1 (curve 4) does not substantially begin to absorb hydrogen even after a 
lapse of 1000 minutes. In order for such FeTi to begin hydrogen absorption 
at 25.degree. C. and 60 atmospheres (for example, within 10 minutes), it 
must be first subjected to activating treatment in hydrogen at 50 
atmospheres at about 200.degree. C. 
FeTi.sub.1.13 having more titanium than iron (curve 1) exhibits the 
property of absorbing hydrogen even when it is not subjected to activating 
treatment, the time required for substantially initiating hydrogen 
absorption is still long, and is about 500 minutes. 
In contrast, FeTi.sub.1.13 -1.9Fe.sub.7 Ti.sub.10 O.sub.3 (curve 2) and 
FeTi.sub.1.13 -8.8Fe.sub.7 Ti.sub.10 O.sub.3 (curve 3) of the present 
invention without activating treatment begin substantial hydrogen 
absorption faster than FeTi and FeTi.sub.1.13. It is particularly 
surprising to note that a composite material having a large content of 
oxide (curve 3) begins hydrogen absorption faster. By repeating several 
times a cycle of absorbing hydrogen in this manner and then releasing 
hydrogen, the rate of absorbing hydrogen becomes so fast that hydrogen can 
be absorbed to saturation within 10 minutes. 
FIG. 2 of the accompanying drawings shows hydrogen absorption isothermal 
curves at 40.degree. C. (curves 2-a and 4-a), and hydrogen releasing 
isothermal curves (curves 2-b and 4-b). In FIG. 2, the abscissa represents 
the number of hydrogen atoms absorbed per total iron and titanium atoms 
contained in the composite material, and the ordinate, the hydrogen 
equilibrium pressure (atom. H.sub.2). Curves 2-a and 2-b refer to 
FeTi.sub.1.13 -1.9Fe.sub.7 Ti.sub.10 O.sub.3, and curves 4-a and 4-b, to 
FeTi for comparison. 
A comparison of curve 2-a with curve 4-a in FIG. 2 shows that the curve 2-a 
(the composite material of this invention) is located at a lower level, 
and therefore that the composite material in accordance with this 
invention can absorb hydrogen even at a low hydrogen pressure, and exhibit 
the property of absorbing a larger amount of hydrogen at the same hydrogen 
pressure. For example, when the hydrogen pressure is 10 atmospheres, FeTi 
(curve 4-a) scarcely absorbs hydrogen, but the composite material in 
accordance with this invention (curve 2-a) can absorb hydrogen at an 
atomic ratio of up to about 0.45. l The amount of hydrogen absorption at 
an atomic ratio of up to about 0.45 means that about 110 cc of hydrogen at 
1 atm. and 0.degree. C. is absorbed per gram of composite material. 
A comparison of curve 2-b with curve 4-b in FIG. 2 shows that the curve 2-b 
(the composite material in accordance with this invention) is located at a 
lower level. This means that the composite material in accordance with 
this invention releases hydrogen at a lower pressure than FeTi. The 
composite material in accordance with this invention releases nearly all 
of the absorbed hydrogen at a releasing pressure of 1 atmosphere, and 
there is substantially no remaining hydrogen. Hence, no problem resides 
with the releasing of hydrogen. If it is desired to take out hydrogen at a 
higher pressure from the composite material of this invention which has 
absorbed hydrogen, the temperature at the time of hydrogen releasing is 
slightly elevated. 
Table 1 below shows the maximum amount of the absorbed hydrogen which is 
released per gram of the composite material of this invention using the 
content of the metallic oxide as a parameter. The temperature for hydrogen 
releasing is 40.degree. C., and the atmosphere into which hydrogen is 
released is an open air atmosphere. The amount of hydrogen released is 
calculated for that at 0.degree. C. and 1 atm. 
TABLE 1 
______________________________________ 
Content of me- 
tallic oxide 
Amount of hydrogen released 
(y, wt. % as 
(cc/g) 
Fe.sub.7 Ti.sub.10 O.sub.3) 
FeTi.sub.1.08 --yFe.sub.7 Ti.sub.10 O.sub.3 
FeTi.sub.1.13 --yFe.sub.7 Ti.sub.10 O.sub.3 
______________________________________ 
0 201 190 
1.0 197 200 
1.9 192 183 
8.8 159 164 
16.8 158 148 
28.0 137 122 
______________________________________ 
It is seen from Table 1 that the composite material in accordance with this 
invention contains a metallic oxide having no hydrogen absorbing ability, 
the amount of hydrogen released per unit weight decreases with increasing 
content of the metallic oxide. Despite this tendency, the absolute amount 
of hydrogen released by the composite material of this invention is still 
large, and composite materials having a metallic oxide content of up to 
several % by weight release an amount of hydrogen which is comparable to 
intermetallic compounds free from oxides. 
As is clearly seen from the above description, the composite material 
suitable for use as a hydrogen storage material in accordance with this 
invention does not require any activating treatment such as 
high-temperature heat treatment prior to hydrogen absorption, and can 
rapidly absorb hydrogen at room temperature and easily release the 
absorbed hydrogen. The amount of hydrogen absorbed can reach the same 
level as the density of liquid hydrogen. The storage pressure may be not 
more than several tens of atmospheres and no special high-pressure 
container is required for storage. As is clearly seen from the constituent 
elements and the manufacturing method, the composite material in 
accordance with this invention is inexpensive, and is expected to be 
useful as a hydrogen storage material for use in large-sized hydrogen 
storage tanks. 
The following Examples illustrate the present invention in greater detail. 
It should be understood however that the invention is not limited to these 
examples. 
EXAMPLE 1 
Electrolytic iron (46.93 parts by weight), 48.49 parts by weight of sponge 
titanium, 1.25 parts by weight of titanium foil (20 microns in thickness) 
and 3.3 parts by weight of powdery ferric oxide (the powdery ferric oxide 
was enveloped with the titanium foil) were put into a copper crucible 
cooled by water, and subjected to arc melting in an argon atmosphere to 
form an ingot having the composition FeTi.sub.1.13 -19Fe.sub.7 Ti.sub.10 
O.sub.3. 
The ingot was coarsely pulverized, and a specimen for electron probe X-ray 
microanalysis was prepared from the pulverized masses using a polishing 
paper and a polishing cloth in the same way as in the preparation of 
ordinary specimens for observation with an optical microscope. When the 
polishing cloth was used, polishing alumina powder having a size of 1 
micron and 0.05 microns respectively was used. 
The specimens were subjected to electron microprobe analysis at an 
acceleration voltage of 10 kV using Shimadzu EMX (an equipment made by 
Shimazu Seisakusho Co., Ltd.). The resulting chart and the photograph of 
the back scattered electron image obtained are shown in FIGS. 3-a and 3-b. 
In the chart of FIG. 3-a, the abscissa represents the scanning distance, 
and the ordinate, the intensity of characteristic X-rays of the individual 
elements shown in the drawing. In the photograph of FIG. 3-a, some 
relatively black spots are seen to be aligned in relatively straight rows. 
The chart of FIG. 3-a shows the results of electron microprobe analysis 
which was performed so as to scan the spots seen in FIG. 3-b. The three 
lines seen in FIG. 3-a relate to iron (Fe), titanium (Ti) and oxygen (O). 
It has been ascertained that the position at which the curve relating to 
oxygen goes down greatly shows a position between spots in the photograph, 
i.e. a position of the metallic matrix composed substantially of iron and 
titanium in the composite material of this invention. 
Accordingly, the spots in the photograph of FIG. 3-b, are separate phases 
of metallic oxide (in this photograph, many of them have a long diameter 
of about 10 to about 20 microns) dispersed in the metallic matrix in the 
composite material of this invention, and contain large amount of oxygen. 
To determine the iron, titanium and oxygen atomic ratio in the separated 
oxide phases which are seen as black spots in the photograph, pure iron 
and pure titanium (standard specimens) were subjected to electron 
microprobe analysis in the same way as above. The intensity of the 
standard specimens was taken as 100, and the intensities of iron and 
titanium specimens were determined. From the results, the weight 
percentages of iron and titanium contained in the oxide phases of the 
specimen were calculated, and the weight percent of oxygen was calculated 
by subtracting the weight percents of iron and titanium from 100. 
The results led to the confirmation that a specimen expressed as having the 
composition FeTi.sub.1.13 -19Fe.sub.7 Ti.sub.10 O.sub.3 actually have the 
approximate composition Fe.sub.7 Ti.sub.13 O.sub.3 and contains an oxide 
composed of iron, titanium and oxygen. 
Similarly, the following specimens were found to exist as oxides of the 
compositions indicated on the right side. 
______________________________________ 
FeTi-- 9.5Fe.sub.7 Ti.sub.10 O.sub.3 
Fe.sub.7 Ti.sub.11 O.sub.4 
FeTi.sub.1.08 --9.5Fe.sub.7 Ti.sub.10 O.sub.3 
Fe.sub.5 Ti.sub.10 O.sub.3 
FeTi.sub.1.08 --38Fe.sub.7 Ti.sub.10 O.sub.3 
Fe.sub.5 Ti.sub.10 O.sub.3 and 
Fe.sub.6 Ti.sub.11 O.sub.3. 
______________________________________ 
EXAMPLE 2 
Electrolytic iron (50.45 parts by weight), 47.97 parts by weight of sponge 
titanium, 1.25 parts by weight of titanium foil (thickness 20 microns) and 
0.33 part by weight of powdery ferric oxide (the powdery ferric oxide was 
enveloped with the titanium foil) were put into a copper crucible cooled 
by water, and subjected to arc melting in an atmosphere of argon to obtain 
an ingot having the composition FeTi.sub.1.13 -1.9Fe.sub.7 Ti.sub.10 
O.sub.3. 
The ingot was pulverized to a particle diameter smaller than 100 mesh using 
an agate mortar in the air to form a hydrogen storage material in 
accordance with this invention. 
A predetermined amount of the pulverized material was charged into a 
pressure reactor, and the inside of the reactor was reduced in pressure to 
5.times.10.sup.-6 mmHg. Then, hydrogen having a purity of 99.99999% was 
introduced under a pressure of 60 atmospheres. The temperature was 
25.degree. C. The results are shown in curve 2 of FIG. 1, and curves 2-a 
and 2-b in FIG. 2. 
A composite material having the composition FeTi.sub.1.13 -8.8Fe.sub.7 
Ti.sub.10 O.sub.3 produced in the same way as the composite material 
FeTi.sub.1.13 -1.9Fe.sub.7 Ti.sub.10 O.sub.3, and intermetallic compounds 
having the compositions FeTi and FiTi.sub.1.13 were caused to absorb and 
release hydrogen in the same way as the composite material FeTi.sub.1.13 
-1.9Fe.sub.7 Ti.sub.10 O.sub.3. 
The results obtained with regard to the composite material FeTi.sub.1.13 
-8.8Fe.sub.7 Ti.sub.10 O.sub.3 are shown in curve 3 of FIG. 1. Curve 1 in 
FIG. 1 shows the results obtained with regard to FeTi.sub.1.13 
(comparison), and curve 4 of FIG. 1 and curves 4-a and 4-b of FIG. 2 show 
the results obtained with regard to FeTi(comparison). 
The abscissa of the absorption and releasing isothermal curves shown in 
FIG. 2 represents the amount of hydrogen which the composite material can 
release at 1 atm. at a given temperature (40.degree. C. in FIG. 2). Thus, 
the amount of hydrogen represented by the abscissa does not contain that 
of hydrogen which cannot be released at 1 atm. at that temperature. This 
indication of the abscissa is the same for all of the other absorption and 
releasing isothermal curves (FIGS. 7 to 12). 
EXAMPLE 3 
Composite materials of the following compositions were produced and 
pulverized to a particle size smaller than 100 mesh in the same way as in 
Example 2. 
(a) FeTi.sub.1.04 
(b) FeTi.sub.1.04 -2.9Fe.sub.7 Ti.sub.10 O.sub.3 
(c) FeTi.sub.1.04 -9.5Fe.sub.7 Ti.sub.10 O.sub.3 
The hydrogen absorbing speeds at 25.degree. C., and the absorption and 
releasing isothermal curves at 40.degree. C. of the finely pulverized 
composite materials are shown in FIGS. 4 and 7 as follows: 
______________________________________ 
FIG. 7 
Composition 
FIG. 4 absorption 
releasing 
______________________________________ 
(a) 5 5-a 5-b 
(b) 6 6-a 6-b 
(c) 7 7-a 7-b 
______________________________________ 
EXAMPLE 4 
Composite materials having the following compositions were produced and 
pulverized to a particle diameter smaller than 100 mesh in the same way as 
in Example 2. 
(d) FeTi.sub.1.22 
(e) FeTi.sub.1.22 -2.9Fe.sub.7 Ti.sub.10 O.sub.3 
(f) FeTi.sub.1.22 -9.5Fe.sub.7 Ti.sub.10 O.sub.3 
The hydrogen absorbing speeds at 25.degree. C. and the absorption and 
releasing isothermal curves at 40.degree. C. of the resulting fine powders 
of the composite materials are shown in FIGS. 5 and 8 as follows: 
______________________________________ 
FIG. 8 
Compostion FIG. 5 Absorption 
Releasing 
______________________________________ 
(d) 8 8-a 8-b 
(e) 9 9-a 9-b 
(f) 10 10-a 10-b 
______________________________________ 
EXAMPLE 5 
Composite materials having the following compositions were produced and 
pulverized to a particle diameter smaller than 100 mesh in the same way as 
in Example 2. 
(g) FeTi.sub.1.27 
(h) FeTi.sub.1.27 -2.9Fe.sub.7 Ti.sub.10 O.sub.3 
(i) FeTi.sub.1.27 -9.5Fe.sub.7 Ti.sub.10 O.sub.3 
The hydrogen absorbing speeds at 25.degree. C. and the absorption and 
releasing isothermal curves at 40.degree. C. of the fine powders of the 
composite materials are shown in FIGS. 6 and 9 as follows: 
______________________________________ 
FIG. 9 
Composition 
FIG. 6 Absorption 
Releasing 
______________________________________ 
(g) 11 11-a 11-b 
(h) 12 12-a 12-b 
(i) 13 13-a 13-b. 
______________________________________ 
EXAMPLE 6 
Composite materials having the following compositions were produced and 
pulverized to a particle diameter smaller than 100 mesh in the same way as 
in Example 2. 
(j) FeTi.sub.1.38 
(k) FeTi.sub.1.38 -2.9Fe.sub.7 Ti.sub.10 O.sub.3 
(l) FeTi.sub.1.38 -9.5Fe.sub.7 Ti.sub.10 O.sub.3 
The hydrogen absorption and releasing isothermal curves at 40.degree. C. of 
the resulting fine powdery composite materials are shown in FIG. 10 as 
follows: 
______________________________________ 
FIG. 10 
Composition Absorption 
Releasing 
______________________________________ 
(j) 14-a 14-b 
(k) 15-a 15-b 
(l) 16-a 16-b 
______________________________________ 
EXAMPLE 7 
Composite materials of the following compositions were produced and 
pulverized to a particle diameter smaller than 100 mesh in the same way as 
in Example 2. 
The hydrogen releasing isothermal curves at 40.degree. C. of the resulting 
fine powdery composite materials are shown in FIG. 11 as follows: 
______________________________________ 
Composition FIG. 11 
______________________________________ 
(m) FeTi.sub.1.08 17 
(n) FeTi.sub.1.08 --1Fe.sub.7 Ti.sub.10 O.sub.3 
18 
(o) FeTi.sub.1.08 --1.9Fe.sub.7 Ti.sub.10 O.sub.3 
19 
(p) FeTi.sub.1.08 --8.8Fe.sub.7 Ti.sub.10 O.sub.3 
20 
(q) FeTi.sub.1.08 --16Fe.sub.7 Ti.sub.10 O.sub.3 
21 
(r) FeTi.sub.1.08 --28Fe.sub.7 Ti.sub.10 O.sub.3 
22. 
______________________________________ 
EXAMPLE 8 
Composite materials having the following compositions were produced and 
pulverized to a particle diameter smaller than 100 mesh in the same way as 
in Example 2. 
The hydrogen releasing isothermal curves at 40.degree. C. of the resulting 
fine powdery composite materials are shown in FIG. 12 as follows: 
______________________________________ 
Compostion FIG. 12 
______________________________________ 
(s) FeTi.sub.1.3 23 
(t) FeTi.sub.1.13 --1Fe.sub.7 Ti.sub.10 O.sub.3 
24 
(u) FeTi.sub.1.13 --1.9Fe.sub.7 Ti.sub.10 O.sub.3 
25 
(v) FeTi.sub.1.13 --8.8Fe.sub.7 Ti.sub.10 O.sub.3 
26 
(w) FeTi.sub.1.13 --16Fe.sub.7 Ti.sub.10 O.sub.3 
27 
(x) FeTi.sub.1.13 --28Fe.sub.7 Ti.sub.10 O.sub.3 
28. 
______________________________________ 
As is clear from the above-given Examples, the composite materials of this 
invention comprising an alloy matrix of iron and titanium and dispersed 
therein as separate phases an oxide composed of iron, titanium and oxygen 
have a fast rate of hydrogen absorption at room temperature, and can 
absorb a large quantity of hydrogen, and release a large quantity of the 
absorbed hydrogen. Thus, they have superior properties as a hydrogen 
storage material. 
While it is necessary in customary practice to reduce the pressure of the 
inside of a pressure container having the hydrogen storage material of the 
invention therein to a high vacuum of, for example, about 
5.times.10.sup.-6 mmHg before hydrogen is introduced thereinto, 
investigations of the present inventors have shown that hydrogen 
absorption is possible in quite the same way as in the formation of a high 
vacuum from the outset by first forming a vacuum of 10.sup.-2 to 10.sup.-3 
mmHg (which vacuum is easily formable), then introducing hydrogen, again 
forming a vacuum of about 10.sup.-2 to 10.sup.-3 mmHg, and then 
introducing hydrogen under high pressure.