JPH10195577A - Hydrogen storage alloy excellent in initial activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy increased in hydrogen absorbing and releasing rates, excellent in practical use, and having a superior initial activity. SOLUTION: This hydrogen storage alloy has a composition containing, by atom, 19-30% Ti, 0.5-10% Zr, 0.02-0.4% Hf, 30-44% Mn, 4-13% Cr, 7-17% V, 2-9% Ni, 0.1-3.5% Re (where Re represents a mixture consisting of one or >=2 elements among La, Ce, Pr, and Nd), and 1-10% oxygen and satisfying Ti(%)+Zr(%)+Hf(%)+Mn(%)+Cr(%)+V(%)+Ni(%)+Re(%) + oxygen (%) +(inevitable impurities) (%)=100%. Moreover, this hydrogen storage alloy has a structure where hydrogenation and oxidation treatment product phases are dispersedly distributed in matrix phases of Ti-Mn alloy and the hydrogenation and oxidation treatment product phases are constituted essentially of Re oxide and Re-Ni alloy and further has a structure where numerous cracks developing at the time of hydrogenation treatment are present and the hydrogenation and oxidation treatment product phases are exposed in the inner surface of the cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable, for example, as a heat absorbing / generating source of a heat pump, or for practical use as an electrode of a battery for storing and transporting hydrogen.
The present invention relates to a hydrogen storage alloy having a very high rate of hydrogen absorption and desorption and exhibiting excellent initial activation.

[0002]

2. Description of the Related Art Conventionally, a Ti-pump having the following composition range intended to be incorporated as a heat-absorbing and heat-generating source of a heat pump.
Mn-based hydrogen storage alloys are known. Atomic%, Ti: 27.5 to 31.5%, Zr: 1 to 5%, Mn: 38.5 to 44.5%, Cr: 7 to 13%, V: 10 to 16%, Ni: 1 ５5%, inevitable impurities: residual, crystal structure equivalent ratio: [Mn (%) + Cr (%) + V (%)
+ Ni (%)] / [Ti (%) + Zr (%)] = 2.0
A hydrogen storage alloy having a composition that satisfies 5 to 2.20.

[0003]

In recent years, hydrogen storage alloys have been used for increasing the output and performance of heat pumps and the like, which have been widely applied, and for further saving energy in practical use as electrodes of batteries. There is a strong demand, and it is strongly desired that the hydrogen storage alloy be capable of initial activation in a shorter time with a large effective hydrogen storage amount and a much faster hydrogen absorption and release rate. I have. However, the above-described conventional technique has a problem that it is difficult to sufficiently satisfy these requirements.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above-mentioned viewpoints, as a result of researching to improve the effective hydrogen storage amount, the hydrogen absorption / release rate and the initial activation of the hydrogen storage alloy, (a) First, in atomic%, Ti: 19 to 30% , Zr: 0.5 to 10%, Hf: 0.02 to 0.4%, Mn: 30 to 44%, Cr: 4 to 13%, V: 7 to 17%, Ni: 2 to 9%, Re : 0.1 to 3.5%, wherein Re represents a mixture of one or more of La, Ce, Pr and Nd, and the same applies hereinafter.) Oxygen: 1 to 10% Inevitable impurities: After ingoting and casting a Ti—Mn alloy having the remaining composition, an ingot of this alloy is subjected to a homogenizing heat treatment.
Re-N along the grain boundaries of the base phase of Ti-Mn alloy
Although it has a structure in which the dispersed phase of the i-type alloy is present, it is further hydrogenated under the condition of cooling after maintaining for a predetermined time at a predetermined temperature in a range of 400 to 700 ° C. in a hydrogen atmosphere following the homogenizing heat treatment. When the treatment is performed, the dispersed phase of the Re—Ni-based alloy formed by the homogenization heat treatment preferentially reacts with hydrogen in the atmosphere, and the main component is a hydride of Re [hereinafter, referred to as “H”.
Re hydride] and a hydrogenation product phase composed of a Re-Ni-based alloy, and the hydrogenation product phase exhibits a large thermal expansion as compared with the base phase of the Ti-Mn-based alloy. An infinite number of cracks are generated in the base phase starting from the hydrogenation product phase, and the hydrogenation product phase is exposed on the inner surfaces of the cracks. When the oxidation treatment is performed at a predetermined temperature within a range of 400 to 500 ° C. for a predetermined time, the Re hydride becomes a Re oxide, and as a result, Ti-M
The n-type alloy has a hydrogenation treatment product phase dispersed and distributed in a base phase of a Ti—Mn-based alloy as shown in a schematic structure enlarged schematic diagram exemplifying a representative structure in FIG. The phase is mainly composed of a Re—Ni-based alloy and a Re oxide, and further has numerous cracks, and has a structure in which the hydrogenated oxidation product phase is exposed on the inner surface of the crack.

(B) In the Ti-Mn-based alloy of (a), the R
The e-Ni-based alloy and the Re oxide absorb at a much faster rate than the conventional hydrogen storage alloy shown in FIG. 3, and release shows an action by the reverse mechanism. The material phase is in a state where much is exposed on the myriad of crack inner surfaces, and as a result, the action area is expanded, so that the speed is much faster than the hydrogen absorption and desorption rate in the conventional hydrogen storage alloy. Hydrogen is absorbed and released, and the absorption rate of hydrogen atoms in the base phase at the time of initial activation is remarkably increased because of the large active area, so that initial activation can be promoted well. The research results shown in (a) and (b) above were obtained.

The present invention has been made on the basis of the results of the above-mentioned research, and in terms of atomic%, Ti: 19 to 30%, Zr: 0.5 to 10%, Hf: 0.02 to 0. 4%, Mn: 30 to 44%, Cr: 4 to 13%, V: 7 to 17%, Ni: 2 to 9% Re: 0.1 to 3.5%, Oxygen: 1 to 10%, inevitable impurities : Having the remaining composition, and a hydrogenation oxidation treatment product phase being dispersed and distributed in the base phase of the Ti—Mn alloy, the main component of the hydrogenation oxidation treatment product phase is an oxide of Re, A hydrogen storage alloy having a structure composed of a Ni-based alloy, further having innumerable cracks generated during the hydrogenation treatment, and having a structure in which the hydrogenation oxidation treatment product phase is exposed on the inner surface of the crack; It is characterized by the following.

[0007]

Embodiments of the present invention will be described below. In a normal high-frequency induction melting furnace, Ni, Zr, each having a purity of 99.9% or more as raw materials are used.
Using Ti, Hf, Mn, V, and Re, and misch metal, they are melted in an Ar atmosphere to prepare alloy melts having the compositions shown in Table 1, and cast into a water-cooled copper mold to form an ingot. The ingot is subjected to a homogenizing heat treatment in a vacuum atmosphere at a predetermined temperature in the range of 950 to 1050 ° C. for 20 hours, and then the ingot is heated to 1 to 1.2 ° C.
In a hydrogen atmosphere of a predetermined pressure within the range of the atmospheric pressure, the temperature is first maintained at room temperature for 1 hour, then, the temperature is raised to a predetermined temperature within the range of 400 to 700 ° C., and the temperature is maintained for 1 hour. When hydrogenation treatment is performed under the condition of forced air cooling by Ar gas and oxidation treatment is further performed at 450 ° C. for one hour in the air, the schematic structure enlarged schematic diagram illustrating a representative structure in FIG. The hydrogen oxidation treatment product phase is dispersed and distributed in the base phase of the Ti-Mn-based alloy represented by the following formula, and the hydrogen anti-product phase is mainly composed of an oxide of Re and a Re-Ni-based alloy. The hydrogen storage alloy according to the present invention, further comprising innumerable cracks generated during the formation of the hydrooxidation product phase, and having a structure in which the hydrogenation oxidation product phase is exposed on the inner surface of the crack. This alloy can be used, for example, Incorporation as a heat-absorbing and heat-generating source, or for practical use as a hydrogen storage / transportation / battery electrode, etc., it has a large effective hydrogen storage capacity, extremely fast hydrogen absorption and desorption rates, and excellent initial activation It becomes an effective hydrogen storage alloy. In general, when a hydrogen storage alloy is used as a heat absorbing / generating source of a heat pump, for example, when the hydrogen absorption / desorption is repeated several times with respect to the heat pump into which the hydrogen storage alloy is incorporated, the hydrogen storage amount is increased. Is gradually increased to a certain value, and initial activation is performed, and the apparatus is put to practical use with the initial activation performed. The number of repetitions, hydrogen pressure, and the like required for activation vary depending on the alloy composition.

In the hydrogen storage alloy of the present invention, JIS
The measurement of the effective hydrogen storage capacity according to the standard is as follows: (50 ° C.
Equilibrium storage pressure: hydrogen storage capacity at 11 atm)-(-5 ° C)
(Equilibrium release pressure of hydrogen at 1 atm) was measured (see FIG. 4).

Next, in the hydrogen storage alloy of the present invention,
The reason why the composition of the Ti—Mn-based alloy constituting the alloy is limited as described above will be described. (A) Ti and Zr In order to increase the effective hydrogen storage capacity, it is necessary to replace a part of Ti with Zr.
When the content of Ti is less than 0.5% or the content of Ti is more than 30%, the low-temperature side curve and the high-temperature side curve in the pressure composition isotherm are plotted. If the pressure becomes too high to achieve the desired increase in the effective hydrogen storage capacity, on the other hand, if the substitution ratio exceeds 10% or the Ti content ratio becomes less than 19%, the pressure composition isotherm , The plate-pressure of the low-temperature curve and the high-temperature curve significantly decreased, and it was not possible to secure a desired large effective hydrogen storage amount, so that the content ratios were 19 to 30% for Ti and 0 for Zr, respectively. .5-
10%, desirably, Ti: 23 to 29%, Z
r: 1 to 5%.

(B) Hf The Hf component has a function of forming a base phase of the Ti—Mn alloy together with the Zr component to sufficiently exert the above-mentioned action brought about by the Zr component. .0
If it is less than 2%, the desired effect cannot be exerted. On the other hand, if the content exceeds 0.4%, the above-mentioned action by Zr will be impaired.
2 to 0.4%, desirably 0.04 to 0.2%
And

(C) Mn, Cr, V, and Ni Further, as described above, in addition to the partial replacement of Ti by Zr, the partial replacement of Mn by Cr, V and Ni Is indispensable. In other words, when partial replacement of Ti with a predetermined amount of Zr is not performed, or when at least one of Cr, V, and Ni as replacement elements is not contained, it is needless to say that If the partial replacement of Mn with a predetermined amount of each of Cr, V and Ni is not carried out, it is impossible to secure a desired large effective hydrogen storage amount. %, Cr: 4%, V: 7% and Ni:
Less than 2%, Mn: 44%, Cr: 13
%, V: 17% and Ni: 9%, respectively,
This is because the plate slope and hysteresis in the pressure composition isotherm increase. Therefore, the content ratios of Mn: 30 to 44%, Cr: 4 to 13%,
V: 7 to 17% and Ni: 2 to 9%, desirably, Mn: 33 to 40%, Cr: 7 to 11%, V: 9 to
15% and Ni: 3 to 7%.

(C) Re These components are, as described above, a re-Ni-based alloy phase having an action of dissociating and absorbing hydrogen in the atmosphere at a much higher rate than the main phase, and recombining and releasing into the atmosphere. Therefore, if the ratio is less than 0.1%, the generation ratio of the Re-Ni-based alloy phase is too small, and the above-described action of the Re-Ni-based alloy phase can be sufficiently exhibited. On the other hand, if the proportion exceeds 3.5%, the proportion of the Re-Ni-based alloy phase having a small hydrogen storage capacity becomes too large, and the hydrogen storage amount of the entire alloy is reduced. 0.1 to 3.5%, preferably 1
３3%. Further, the above-mentioned Re-Ni alloy and R
In order to sufficiently exert the above-mentioned action of the e-hydroxide, it is necessary that the main component of Re is La and / or Ce. In this case, preferably, the proportion of La and / or Ce is 50% in proportion to Re. More preferably, Re is substantially La and / or Ce.
It is good to consist of.

(G) Oxygen Oxygen is mainly composed of Re-
Along with the Ni-based alloy, hydrogen molecules (H ₂ ) in the atmosphere are dissociated and absorbed into hydrogen atoms (H) at a faster speed than the base phase, and the absorbed hydrogen atoms are diffused into the base phase. It is an essential component for the formation of a Re oxide having an action of quickly recombining the hydrogen atoms diffused from the base phase into hydrogen molecules. If the proportion is less than 1%, the formation of the Re oxide is too small and the above-mentioned ratio is too small. Cannot sufficiently exhibit the effect of the invention, and the formation of cracks becomes insufficient. On the other hand, when the ratio exceeds 10%, the ratio of the Re oxide becomes relatively too large, and the strength decreases. Since the tendency to pulverization is promoted, the ratio is set to 1 to 10%, preferably 1.5 to 7%.

The hydrogen storage alloy of the present invention can be converted into powder having a predetermined particle size by ordinary mechanical pulverization, and can be heated to a predetermined temperature within the range of 10 to 200 ° C. in a pressurized hydrogen atmosphere. And powder by hydrogenation and pulverization of hydrogen release by vacuum evacuation, and the resulting powder has a structure as shown in a schematic structure enlarged schematic diagram illustrating a representative structure in FIG. Becomes

[0015]

EXAMPLES Next, the hydrogen storage alloy of the present invention will be specifically described with reference to examples. In a normal high-frequency induction melting furnace,
N, each having a purity of 99.9% or more as a raw material
Using i, Zr, Ti, Hf, Mn, V, and Re, and misch metal, melting in an Ar atmosphere to prepare alloy melts having the compositions shown in Table 1, respectively, and casting into a water-cooled copper mold. The ingot was subjected to a homogenizing heat treatment in a vacuum atmosphere at a predetermined temperature shown in Table 2 for 20 hours, and then at room temperature in a hydrogen atmosphere at a predetermined pressure shown in Table 2. After holding for 1 hour, the temperature was raised and heated to a predetermined temperature also shown in Table 2, held at this temperature for 1 hour, and then subjected to a hydrogenation treatment under the condition of forced air cooling with Ar gas. Hydrogen storage alloys 1 to 16 of the present invention (hereinafter referred to as alloys 1 to 16 of the present invention) were produced by subjecting 450 to oxidation treatment in the atmosphere under the condition of holding for 1 hour. For the purpose of comparison, a conventional hydrogen storage alloy (hereinafter referred to as a conventional alloy) was prepared under the same conditions except that the composition of the molten alloy was as shown in Table 1 and the hydrogenation treatment and the oxidation treatment after the homogenization heat treatment were not performed. Manufactured). The structure of the resulting hydrogen storage alloy was observed with a scanning electron microscope. As a result, each of the alloys 1 to 16 of the present invention had an infinite number of cracks as shown in FIG. Is Re-N
A hydro-oxidation treatment product phase composed of the i-based alloy and the Re oxide is exposed, and this hydro-oxidation treatment product is Ti-Mn
3 shows a structure dispersed and distributed in the base phase of the base alloy, and the conventional alloy shows a structure composed of the base phase of the Ti—Mn base alloy as shown in FIG. 3.

[0016]

[Table 1]

[0017]

[Table 2]

Next, with respect to the alloys 1 to 16 of the present invention and the conventional alloy, the hydrogen absorption rate and the hydrogen release rate were measured in accordance with JIS H7202 "Hydrogen storage alloy hydrogenation rate test measurement method". Prior to the measurement, the alloys 1 to 16 of the present invention and the conventional alloy were sealed in a pressure vessel, and the hydrogen atmosphere pressure was 8 atm and the heating temperature was 200.
C., holding time: 200 m after hydrogen crushing consisting of absorption of hydrogen under the condition of 1 hour and release of hydrogen by evacuation.
A powder having a particle size of esh or less was used, and measurement was performed using the powder under the following conditions.

First, regarding the hydrogen absorption rate, as shown in the schematic explanatory view of FIG. 5, (a) a powder was sealed in a container immersed in a bath (oil or water), and the temperature of the bath was set to 200.
C, the valves Vb: closed, valves Va and Vc:
When opened, pressurized hydrogen is introduced into the system from a hydrogen cylinder. When the pressure in the system reaches 30 atm, the valve Va is closed, and the system is left until the pressure in the system drops to a constant pressure (hydrogen absorption by powder is completed). (B) When the pressure in the system drops to a constant pressure (about 20 atm), the valve V
b: Open, set the system to a vacuum atmosphere of 10 ^-2 Torr with a vacuum pump, set the bath temperature to 20 ° C, and set the valves Vb and Vc:
Close, valve Va: open and introduce hydrogen into the system excluding the vessel,
When the pressure reaches 30 atm, valve Va: closed, valve V
c: Open, pressure drop with respect to time in the system was measured in this state, and from the resulting pressure drop curve, the hydrogen storage amount at the time when the hydrogen storage amount of the powder became 80% and the time required until then were calculated. Then, (hydrogen storage amount at 80% storage) ÷ (80%
The time required for hydrogen storage) was calculated, and this value was used as the hydrogen absorption rate. Regarding the hydrogen release rate, the state after the above-mentioned hydrogen absorption rate measurement, that is, the valves Va and Vb:
Closed, valve Vc: Open and the pressure in the system is constant (typically 20
(Atmospheric pressure), the bath temperature is set to an appropriate temperature for releasing hydrogen of powder in the range of 100 to 300 ° C., for example, 120 ° C., then the valve Vb is opened and the valve Vc is closed to remove the inside of the system. After exhausting to 10 ^-2 torr and then, with the valve Vb closed and the valve Vc open, the pressure rise over time in the system was measured and the resulting pressure rise curve showed that the hydrogen release of the powder was 80%. The amount of hydrogen released at the point of time and the time required up to that time were obtained, and (the amount of hydrogen released at the time of 80% release) / (the time required for the release of 80% hydrogen) was calculated. . Table 3 shows the results.

[0020]

[Table 3]

Further, for the purpose of evaluating the initial activation of the alloys 1 to 16 of the present invention and the conventional alloy, as described in detail below, the alloy was powdered and incorporated as an active material into a battery. This is repeatedly charged and discharged until the capacity is reached, and 95% of the maximum discharge capacity is obtained.
The number of times of charge and discharge until a discharge capacity corresponding to ± 1% was shown was measured. That is, first, the conventional alloy is coarsely pulverized using a jaw crusher to obtain coarse particles having a diameter of 2 mm or less. Subsequently, the alloys 1 to 161 of the present invention and the coarsely pulverized conventional alloy are finely ground using a ball mill. Crushed 20
0 mesh or less, and after adding polytetrafluoroethylene (PTFE) as a binder and carboxymethylcellulose (CMC) as a thickener to form a paste, a commercially available product having a porosity of 95% Fill a porous Ni sintered plate, dry and pressurize, planar dimension: 3
A shape of 0 mm × 40 mm, thickness: 0.40 to 0.43 mm (the amount of the active material powder charged: about 1.8 g), and a Ni thin plate serving as a lead attached to one side of this by welding to form a negative electrode, On the other hand, for the positive electrode, Ni (OH) ₂ and CoO mixed in a ratio of 84:16 by weight as active materials were used, and polytetrafluoroethylene (PTF) was used as a binder.
E) and carboxymethylcellulose (CMC) as a thickener were added to form a paste, which was filled in the porous Ni sintered plate, dried, and pressed to obtain a planar dimension of 3
A shape of 0 mm × 40 mm, thickness: 0.71 to 0.73 mm was formed by attaching a Ni thin plate to one side of the shape, and then a polypropylene-polyethylene copolymer separator plate was provided on both sides of the negative electrode. The positive electrode is arranged via a protective plate made of vinyl chloride for the purpose of preventing the active material from falling off from the outer surface of each of the positive electrodes, and integrated into a vinyl chloride cell. A battery was manufactured by charging a 30% aqueous KOH solution as an electrolytic solution into the cell. Then, the battery was charged and discharged under the conditions of a charge rate: 0.15 C, a discharge rate: 0.15 C, a charged amount of electricity: 135% of the negative electrode capacity, and the charge and discharge were counted as one charge and discharge. The charging and discharging were repeated until the battery reached the maximum discharge capacity. Table 3 shows the number of times of charging and discharging required to show a discharge capacity of 95% of the maximum discharge capacity, and the initial activation was evaluated based on the number of times.

[0022]

According to the results shown in Table 3, the alloy of the present invention 1
In No. 16 to No. 16, through the Re-Ti-based alloy and Re oxide of the hydrogenated oxidation treatment product phase exposed to the surface and the myriad of crack inner surfaces and thereby exposed to the atmosphere with a large surface area as a whole, Hydrogen in the atmosphere is dissociated into hydrogen atoms and absorbed, and the absorbed hydrogen is
Hydrogen storage is performed by diffusing into the base phase of the base alloy, but as described above, the Re-Ni-based alloy and the Re oxide having an extremely fast hydrogen absorption capacity are distributed over a large surface area, so that the hydrogen absorption rate is Relatively fast,
In addition, the initial activation is remarkably promoted, and hydrogen is released at a high speed because of the reverse mechanism. On the other hand, in the conventional alloy, hydrogen storage is performed by hydrogen absorption. It is evident that the rate of hydrogen absorption and desorption has to be slower and the initial activation is slower as a result of the fact that the active crack formation by the activation treatment is not performed. As described above, the hydrogen storage alloy of the present invention has a very high rate of hydrogen absorption and desorption, and exhibits excellent initial activation in practical use. It greatly contributes to higher performance, higher performance and energy saving.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged enlarged view illustrating a representative structure of a hydrogen storage alloy of the present invention.

FIG. 2 is a schematic enlarged microstructure diagram illustrating a representative structure of the hydrogen storage alloy pulverized powder of the present invention.

FIG. 3 is a schematic enlarged schematic view illustrating a typical structure of a conventional hydrogen storage alloy.

FIG. 4 is a diagram showing a pressure composition isotherm of the hydrogen storage alloy of the present invention.

FIG. 5 is a schematic explanatory view of an apparatus used for measuring a hydrogen absorption / release rate of a hydrogen storage alloy.

Claims (1)

[Claims] 1. Atomic%, Ti: 19 to 30%, Zr: 0.5 to 10%, Hf: 0.02 to 0.4%, Mn: 30 to 44%, Cr: 4 to 13%, V: 7% to 17%, Ni: 2% to 9%, Re: 0.1% to 3.5%, Oxygen: 1% to 10% Inevitable impurities: remaining, and a Ti-Mn alloy base material The hydrooxidation product phase is dispersed and distributed in the phase, and the main component of the hydrooxidation product phase has a structure composed of an oxide of Re and a Re-Ni-based alloy, A hydrogen storage alloy, characterized by having a myriad of cracks generated at the time, and having a structure in which the hydrogenated product phase is exposed on the inner surface of the crack.