JPH10195574A - Hydrogen storage alloy excellent in initial activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy having high 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, 30-44% Mn, 4-13% Cr, 7-17% V, 2-9% Ni, 0.1-3.5% La and/or Ce, and 1-10% oxygen and satisfying Ti(%)+Zr(%)+Mn(%)+ Cr(%)+V(%)+Ni(%) + (La and/or Ce) (%) +o xygen (%) + (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 oxides of La(Ce) and La(Ce)-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%, Mn: 30 to 44%, Cr: 4 to 13%, V: 7 to 17%, Ni: 2 to 9%, La and / or Ce [hereinafter, La (Ce) ]: 0.1 to 3.5%, oxygen: 1 to 10%, unavoidable impurities: residue A Ti-Mn alloy having the following composition is melted and cast, and then homogenized in an ingot of this alloy. Subject to chemical heat treatment,
La (C) along the grain boundaries of the base phase of the Ti—Mn alloy
e) The structure in which the dispersed phase of the -Ni alloy is present, but after the homogenizing heat treatment, the condition of cooling after holding for a predetermined time at a predetermined temperature in the range of 400 to 700 ° C in a hydrogen atmosphere is set. , The dispersed phase of the La (Ce) -Ni-based alloy formed by the homogenizing heat treatment reacts preferentially with hydrogen in the atmosphere, and the main component is La (C).
e) hydride [hereinafter referred to as La (Ce) hydride]
And a hydrogenation product phase composed of a La (Ce) -Ni-based alloy, and the hydrogenation product phase is Ti-M
Since the thermal expansion is larger than that of the base phase of the n-based alloy, countless cracks are generated in the base phase starting from the hydrogenation product phase. When the phase is exposed, and subsequently, for example, in an oxidizing atmosphere, an oxidation treatment is performed at a predetermined temperature within a range of 400 to 500 ° C. for a predetermined time to obtain the above La (C).
e) The hydride becomes La (Ce) oxide, resulting in T
In the i-Mn-based alloy, as shown in a schematic microscopic enlarged schematic diagram illustrating a representative structure in FIG. 1, a hydrogen-oxidation treatment product phase is dispersed and distributed in a base phase of the Ti-Mn-based alloy, and the hydrogen-oxidation treatment is performed. The main component of the product phase is La (Ce) -Ni alloy and La
(Ce) oxide, and there are countless cracks,
In addition, the crack inner surface has a structure in which the hydrooxidation product phase is exposed.

(B) In the Ti-Mn-based alloy of (a), the content of L
a (Ce) -Ni-based alloy and La (Ce) oxide
Although it absorbs at a much faster rate than the conventional hydrogen storage alloy shown in FIG. 3 and releases it by the reverse mechanism, the hydrooxidation product phase is largely exposed to the myriad crack inner surfaces. As a result, the area of action is increased, and as a result, hydrogen absorption and release at a much higher rate than the hydrogen absorption and release rates in the conventional hydrogen storage alloy described above, and further, at the time of initial activation Since the absorption rate of hydrogen atoms in the base phase is remarkably increased because it is performed over a wide working area, remarkable promotion of initial activation can be achieved. The research results shown in (a) and (b) above were obtained.

The present invention has been made on the basis of the above research results. In atomic%, Ti: 19 to 30%, Zr: 0.5 to 10%, Mn: 30 to 44%, Cr: : 4 to 13%, V: 7 to 17%, Ni: 2 to 9%, La (Ce): 0.1 to 3.5%, oxygen: 1 to 10%, unavoidable impurities: remaining In addition, the hydrogenated oxidation treatment product phase is dispersed and distributed in the base phase of the Ti—Mn alloy, and the main component of the hydrogenated oxidation treatment product phase is an oxide of La (Ce) and La (Ce).
e) Hydrogen having a structure composed of an -Ni-based alloy, further having an infinite number of cracks generated during the hydrogenation treatment, and having a structure in which the hydrogenated oxidation treatment product phase is exposed on the inner surface of the crack. Storage alloy.

[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, Mn, V, La, and Ce, and misch metal, they were melted in an Ar atmosphere to prepare alloy melts having the compositions shown in Table 1, and cast into water-cooled copper molds to form ingots. 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. Are dispersed and distributed in the matrix phase of the Ti—Mn-based alloy represented by the following formula. The hydrogen reaction product phase is mainly composed of La (Ce) oxide and La (C
e) having a structure composed of a -Ni-based alloy, in addition to the numerous cracks generated during the formation of the above-mentioned hydro-oxidation product phase, and the above-mentioned hydro-oxidation product phase on the inner surface of the crack; A hydrogen storage alloy of the present invention having an exposed structure is obtained. When this alloy is incorporated as, for example, an endothermic source of a heat pump or practically used as an electrode of a battery for hydrogen storage, transportation, or the like, it is very effective. It is a hydrogen storage alloy that has a hydrogen storage capacity, has an extremely fast hydrogen absorption and release rate, and exhibits excellent initial activation. 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.
In the case where the content is less than 0.5 or the content of Ti is more than 30%, the plat-pressure of the low-temperature curve and the high-temperature curve in the pressure composition isotherm is increased. Is 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 is less than 19%, the pressure composition isotherm Since the plate pressures of the low-temperature curve and the high-temperature curve are remarkably reduced and a desired large effective hydrogen storage amount cannot be secured, the content ratios of Ti: 19 to 30% and Zr: 0. 5-1
0%, and desirably, Ti: 23 to 29, respectively.
%, Zr: 1 to 5%.

(B) 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,
The slope and hysteresis of the plate in the pressure composition isotherm become large, and therefore, the content ratios thereof are Mn: 30 to 44%, Cr: 4 to 13%,
V: 7 to 17% and Ni: 2 to 9%, preferably Mn: 33 to 40%, Cr: 7 to 11,
V: 9 to 15% and Ni: 3 to 7%.

(C) La (Ce) As described above, these components have the effect of dissociating and absorbing hydrogen in the atmosphere at a higher speed than the main phase, and also recombining and releasing into the atmosphere. ) -Ni-based alloy phase is an indispensable component. Therefore, if the proportion is less than 0.1%, the generation rate of the La (Ce) -Ni-based alloy phase is too small, and the above-mentioned ratio is possessed. The effect cannot be fully exhibited, while the ratio is 3.5%
Is exceeded, the La (Ce) -N having a small hydrogen storage capacity is used.
Since the ratio of the i-based alloy phase becomes too large and the hydrogen storage amount of the entire alloy decreases, the ratio is set to 0.1 to
It was determined to be 3.5%, preferably 1 to 3.0%.

(G) Oxygen Oxygen is mainly composed of La which constitutes the product phase of the hydro-oxidation treatment.
Along with the (Ce) -Ni-based alloy, hydrogen molecules (H
₂ ) is dissociated into hydrogen atoms (H) and absorbed at a faster rate than the base phase, and the absorbed hydrogen atoms are diffused into the base phase. La (Ce) having the effect of recombining with
It is an indispensable component for oxide formation, but its proportion is 1%
If the ratio is less than the above, the formation of La (Ce) oxide is too small to exert the above-mentioned effects sufficiently, and the formation of cracks becomes insufficient. Since the proportion of the La (Ce) oxide becomes too large, the strength is reduced and the tendency to pulverization is promoted, so that the proportion is 1 to 10%, preferably 1.5 to 10%.
It was set at 7%.

The hydrogen storage alloy of the present invention can be converted into a powder having a predetermined particle size by ordinary mechanical pulverization, and can be heated to a predetermined temperature within a 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

[0014]

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, Mn, V, La, and Ce, and misch metal, melting in an Ar atmosphere to prepare alloy melts each having the composition shown in Table 1, and casting them in 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 La (C
e) A structure in which a hydrogenated oxidation treatment product phase composed of a -Ni-based alloy and La (Ce) oxide is exposed, and the hydrogenated oxidation treatment product is dispersed and distributed in a base phase of the Ti-Mn-based alloy. As shown in FIG. 3, the conventional alloy showed a structure composed of a base phase of a Ti—Mn-based alloy.

[0015]

[Table 1]

[0016]

[Table 2]

Next, the hydrogen absorption rate and the hydrogen release rate of the alloys 1 to 16 of the present invention and the conventional alloy were measured in accordance with JIS H7202 "Method for measuring hydrogenation rate of hydrogen storage alloy". 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 vessel 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.

[0019]

[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 powder was incorporated into a battery as an active material. 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.

[0021]

According to the results shown in Table 3, the alloy of the present invention 1
In No.-16, the La (Ce) of the hydro-oxidation treatment product phase exposed to the surface and the myriad of crack inner surfaces, thereby being exposed to the atmosphere with a large surface area as a whole.
Hydrogen in the atmosphere is dissociated into hydrogen atoms and absorbed through the Ni-based alloy and La (Ce) oxide, and the absorbed hydrogen diffuses into the base phase of the Ti-Mn-based alloy to store hydrogen. As described above, the La (Ce) -Ni-based alloy and the La (Ce) oxide having the extremely fast hydrogen absorption ability are distributed over a large surface area as a whole, so that the hydrogen absorption rate becomes relatively extremely fast, and Activation is remarkably promoted, and hydrogen is released at a high rate because of the reverse mechanism. On the other hand, in conventional alloys, hydrogen storage is performed by hydrogenation treatment. It is clear that the rate of hydrogen absorption and desorption has to be slow, and the initial activation is also slow, because no active crack formation is caused. As described above, in the hydrogen storage alloy of the present invention, the rate of hydrogen absorption and release is extremely high,
In addition, since it exhibits excellent initial activation in practical use, it greatly contributes to high output and high performance of various mechanical devices to which the hydrogen storage alloy is applied, and further to 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%, Mn: 30 to 44%, Cr: 4 to 13%, V: 7 to 17%, Ni: 2 to 2% 9%, La and / or Ce: 0.1-3.5%, Oxygen: 1-10% Inevitable impurities: Remaining, and have a hydrogen-oxidation treatment generated in the base phase of the Ti-Mn alloy. The material phase is dispersed and distributed, and the main component of the hydrooxidation treatment product phase is an oxide of La and / or Ce, and La and / or La.
Or having a structure composed of a Ce-Ni-based alloy, further having an infinite number of 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. A hydrogen storage alloy characterized by the following.