JPH10195572A - Hydrogen storage alloy excellent in initial activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy having a high hydrogen absorbing and releasing rates and excellent in initial activation. SOLUTION: This hydrogen storage alloy is composed of a Ti-Mn alloy having a composition consisting of, by atom, 19-33% Ti, 1-10% Zr, 0.05-0.4% Hf, 32-45% Mn, 3-13% Cr, 10-22% V, 2-10% Ni, 0.1-3.5% La and/or Ce, and the balance inevitable impurities and also having a structure constituted of primary phases of Ti-Mn alloy, numerous cracks developing with (La and/or Ce)-Ni alloy phases as origins by hydrogenation treatment, and secondary (La and/or Ce)-Ni alloy phases fluidized and distributed along the cracks by dehydrogenation treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat pump incorporated in a heat pump, for example.
Alternatively, the present invention relates to a hydrogen storage alloy which has an extremely high hydrogen absorption and desorption rate and exhibits excellent initial activation when used for hydrogen storage and transport and practically as, for example, an electrode of a battery.

[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 conducting research to improve the hydrogen absorption / release rate and the initial activation of the hydrogen storage alloy, Ti: 19 to 33%, Zr: 1 to 10%, and Hf: 0.05 to 0.4% Mn: 32 to 45%, Cr: 3 to 13%, V: 10 to 22%, Ni: 2 to 10%, La and / or Ce [hereinafter, indicated by La (Ce) ]: 0.1 to 3.5%, unavoidable impurities: residual, and a main phase of a Ti-Mn-based alloy;
It was composed of countless cracks generated from the La (Ce) -Ni-based alloy phase in the hydrogenation treatment and regenerated La (Ce) -Ni-based alloy phases fluidized and distributed along the cracks in the dehydrogenation treatment. A hydrogen storage alloy composed of a Ti—Mn base alloy having a structure dissociates hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) by the catalytic action of the La (Ce) —Ni-based alloy phase, The dissociated hydrogen atoms are absorbed at a much higher rate than the Ti-Mn-based alloy main phase, and the release has an action by the reverse mechanism.
The system alloy phase is fluidized along countless cracks and is in a planar state.As a result, the working area is significantly enlarged. La (Ce) -Ni having a wide working area by absorbing and releasing hydrogen at a much higher speed than before, and by absorbing hydrogen atoms of the Ti-Mn-based alloy main phase during initial activation. The research results show that the increase in the effective hydrogen storage amount and the remarkable promotion of the initial activation can be achieved because the treatment is performed through the system alloy phase.

The present invention has been made on the basis of the above-mentioned research results. In atomic%, Ti: 19 to 33%, Zr: 1 to 10%, Hf: 0.05 to 0.4% Mn: 32 to 45%, Cr: 3 to 13%, V: 10 to 22%, Ni: 2 to 10%, La (Ce): 0.1 to 3.5%, unavoidable impurities: residual Having, and a main phase of Ti-Mn-based alloy,
It was composed of countless cracks generated from the La (Ce) -Ni-based alloy phase in the hydrogenation treatment and regenerated La (Ce) -Ni-based alloy phases fluidized and distributed along the cracks in the dehydrogenation treatment. A hydrogen storage alloy having a good initial activity and comprising a Ti—Mn base alloy having a structure.

[0006]

Embodiments of the present invention will be described below. First, a Ti-Mn-based alloy having the above composition is melted and cast, and then the ingot of this Ti-Mn-based alloy is placed in a vacuum or in a non-oxidizing atmosphere of an inert gas.
When a homogenizing heat treatment is performed under the condition of cooling after holding at a predetermined temperature within a range of 50 to 1050 ° C. for a predetermined time, La (dispersed and distributed along the main phase of the Ti—Mn alloy and the crystal grain boundaries of the main phase). Although it has a two-phase structure of Ce) -Ni alloy phase, it is further cooled in a pressurized hydrogen atmosphere at a predetermined temperature in a range of 200 to 950 ° C. for a predetermined time after the homogenization heat treatment, followed by cooling. When the hydrogenation treatment is performed, the La (Ce) -Ni-based alloy phase formed by the homogenization heat treatment preferentially reacts with hydrogen in the atmosphere, and the main components are La (Ce) hydride and La (Ce). -Ni-based intermetallic compound and a hydrogen reaction product phase, and the hydrogen reaction product phase shows a larger thermal expansion than the Ti-Mn-based alloy main phase, so that the hydrogen reaction product phase Countless cracks starting from the product phase Occurs, this crack the inner surface in a state in which the hydrogen reaction product phase is exposed, 5 have further subsequent
When the dehydrogenation process is performed by evacuation to a predetermined degree of vacuum while maintaining a predetermined temperature in the range of 00 to 950 ° C., La (C) in the hydrogen reaction product phase generated by the hydrogenation process is obtained.
e) The hydride becomes La (Ce) and this La (Ce)
Reacts with the coexisting La (Ce) -Ni-based intermetallic compound to regenerate the La (Ce) -Ni-based alloy phase before the hydrogenation treatment. At the time of reforming, it is fluidized, so that it flows and distributes in a plane along the crack, and the resulting Ti-
As shown in the schematic microstructure enlarged view of FIG. 1, the Mn-based alloy has a main phase of the Ti—Mn-based alloy and La in the hydrogenation treatment.
It has an infinite number of cracks generated starting from the (Ce) -Ni-based alloy phase and a structure composed of a regenerated La (Ce) -Ni-based alloy phase fluidized and distributed along the cracks by the dehydrogenation treatment. Become.

[0007] In the above Ti-Mn alloy,
The La (Ce) -Ni alloy phase constituting this dissociates the hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) by the catalytic action of the phase, and converts the dissociated hydrogen atoms into Ti-M
It absorbs at a much faster rate than the main phase of the n-based alloy, and therefore, the absorption of hydrogen atoms in the main phase is mainly performed through the regenerated La (Ce) -Ni-based alloy phase, and the release is performed in reverse. Has the function of
The (Ce) -Ni-based alloy phase is fluidized along countless cracks and is in a planar state. As a result, the working area is significantly increased. Hydrogen absorption and desorption can be performed at a much higher rate than the absorption and desorption rates, and the absorption of hydrogen atoms of the Ti-Mn-based alloy main phase during the initial activation is also planarized to have a wide active area. La (C
e) Since it is carried out through the -Ni-based alloy phase, remarkable promotion of initial activation can be achieved. In general,
When a hydrogen storage alloy is used as a heat absorbing / generating source of a heat pump, for example, the heat storage alloy incorporating the hydrogen storage alloy is used.
Repeated hydrogen absorption and release several times
Initial activation is performed so that the hydrogen storage amount gradually increases and eventually becomes a constant value, and the apparatus is put to practical use with the initial activation being 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.) (See FIG. 2).

Next, the reason why the composition of the Ti—Mn alloy constituting the hydrogen storage alloy of the present invention 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 of Ti is less than 1% or the content of Ti is more than 33.0%, the low-temperature side curve and the high-temperature side curve in the pressure composition isotherm are calculated. If the pressure becomes too high to achieve the desired increase in the effective hydrogen storage capacity, and if the substitution ratio exceeds 10% or the Ti content ratio is less than 19.0%, the pressure composition Since the plate pressure of the low-temperature curve and the high-temperature curve in the isotherm is remarkably reduced, and a desired large effective hydrogen storage amount cannot be secured, the content ratio is set to Ti: 19.0 to 33.0 respectively. 0%, Z
r: 1 to 10%.

(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 5%, 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.
It was determined to be 5 to 0.4%.

(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 That is, if partial replacement of Mn with predetermined amounts of Cr, V and Ni is not performed, a desired large effective hydrogen storage amount cannot be secured. , V and Ni: less than 2%,
Mn: 45%, Cr: 13%, V: 22% and N
When i exceeds 10%, the slope and hysteresis of the plate in the pressure composition isotherm become large.
45%, Cr: 3 to 13%, V: 10 to 22%, and Ni: 2 to 10%.

(D) La (Ce) As described above, these components dissociate and absorb hydrogen in the atmosphere at a much higher rate than the main phase, and recombined to release hydrogen into the atmosphere. Ce) -Ni is an indispensable component for forming a Ni-based alloy phase. Therefore, if its proportion is less than 0.1%, the recycled La (Ce)-
If the proportion of the Ni-based alloy phase is too small, the above-mentioned action of the Ni-based alloy phase cannot be sufficiently exerted. On the other hand, if the proportion exceeds 3.5%, the regenerated La having a small hydrogen storage capacity is not used.
Since the proportion of the (Ce) -Ni-based alloy phase becomes too large, the hydrogen storage capacity of the entire alloy decreases, so that the proportion is 0.1 to 3.5%, preferably 0.5 to 3. It was set to 0%.

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. The powder can also be obtained by hydrogenation and pulverization of hydrogen release by evacuation.

[0014]

Next, the hydrogen storage alloy of the present invention will be described in detail with reference to examples. In a normal high-frequency induction melting furnace,
As a raw material, T has a purity of 99.9% or more.
Using i, Zr, Hf, Mn, Cr, V, Ni, La, and Ce, dissolved in an Ar atmosphere,
2. A molten Ti—Mn alloy having the composition shown in FIG. 2 was prepared and cast into a water-cooled copper mold to form an ingot, and the ingot was kept in a vacuum atmosphere at a predetermined temperature shown in Table 1 for 20 hours. , And then in a hydrogen atmosphere at a predetermined pressure also shown in Table 2,
First, after holding at room temperature for 1 hour, the temperature was raised and heated to the predetermined temperature shown in Table 2 as well, subjected to a hydrogenation treatment at this temperature for 30 minutes, and formed by the above homogenization heat treatment. The La (Ce) -Ni alloy phase dispersed and distributed along the crystal grain boundaries in the main phase of the Ti-Mn alloy is changed to La
(Ce) A hydrogen reaction product phase mainly composed of a hydride and a La (Ce) -Ni-based intermetallic compound (innumerable cracks are generated starting from the hydrogen reaction product phase due to the formation of the hydrogen reaction product phase). While maintaining the hydrogenation temperature,
A vacuum dehydrogenation treatment is performed until the atmosphere reaches a degree of vacuum of 10 ^-5 torr, and the hydrogen reaction product phase is La (Ce).
-Regenerate into Ni-based alloy phase (During this dehydrogenation treatment, the reactants are fluidized, so that the regenerated La (Ce) -Ni-based alloy phase is as shown in the structure of the alloy of the present invention in FIG. Hydrogen storage alloys 1 to 16 of the present invention (hereinafter referred to as alloys of the present invention 1 to 16) were produced by flowing along innumerable cracks to form a planar distribution.

For the purpose of comparison, the composition of the molten Ti—Mn alloy is as shown in Table 2, and the conventional conditions are the same under the same conditions except that the hydrogenation treatment and the dehydrogenation treatment after the homogenization heat treatment are not performed. Hydrogen storage alloy (hereinafter referred to as conventional alloy)
Was manufactured.

[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".

First, as shown in the schematic explanatory view of FIG. 3, a hydrogen absorption rate measuring apparatus is described. Prior to measurement, alloys 1 to 16 of the present invention and a conventional alloy are sealed in a pressure vessel, and the hydrogen atmosphere pressure is measured. : 8 atm, heating temperature: 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. (A) The powder was sealed in a container immersed in a bath (oil or water), and the temperature of the bath was kept at 200 ° C.
b: Closed, valves Va and Vc: Open and pressurized hydrogen was introduced into the system from a hydrogen cylinder, and when the pressure in the system reached 30 atm, valve Va was closed and the pressure in the system dropped to a constant pressure (powder (The hydrogen absorption is completed), and the powder is initially activated. (B) When the pressure in the system drops to a constant pressure (about 20 atm), the valve Vb is opened and the system is opened by a vacuum pump. After a vacuum atmosphere of 10 ^-2 Torr, the bath temperature was set to 20 ° C., the valves Vb and Vc were closed and the valve Va was opened to introduce hydrogen into the system except for the container, and the pressure became 30 atm. At this time, the valve Va: closed and the valve Vc: open, the pressure drop with respect to time in the system was measured in this state, and the hydrogen storage amount at the time when the hydrogen storage amount of the powder became 80% was obtained from the resulting pressure drop curve. And the time required until then, (hydrogen occlusion amount at 80% occlusion) ÷ (80 Calculating the time) that takes in hydrogen storage capacity was the value as 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. Exhaust to 10 ^-2 Torr, then measure the pressure rise in the system with the valve Vb: closed and valve Vc: open,
From the resulting pressure rise curve, the hydrogen release amount of the powder was 80%.
The amount of hydrogen released at the time when became and the time required until then were calculated, and (the amount of hydrogen released at the time of 80% release) divided by (the time required for the release of 80% hydrogen) was calculated. did. Table 3 shows the results.

Next, the alloys 1 to 16 of the present invention and the conventional alloy are coarsely pulverized with a jaw crusher to coarse particles having a diameter of 2 mm or less, and further finely pulverized with a ball mill to obtain a particle size of 350. In the state of fine powder having a mesh size or less, based on JIS standards, (storage equilibrium pressure at 50 ° C .: hydrogen storage amount at 11 atm) − (equilibrium release pressure at −5 ° C .: hydrogen storage at 1 atm. Was measured and calculated to obtain an effective hydrogen storage amount. The results are shown in Table 3.

Further, for the purpose of evaluating the initial activation of the above-mentioned alloys 1 to 16 and the conventional alloy, first,
The alloys 1 to 16 of the present invention and the conventional alloy are coarsely pulverized using a jaw crusher to obtain coarse particles having a diameter of 2 mm or less. Subsequently, the alloys 1 to 23 of the present invention and the conventional alloy having the coarse particles are finely ground using a ball mill. Crushed to a particle size of 200 mesh or less,
In addition, polytetrafluoroethylene (P
TFE) and carboxymethylcellulose (CMC) as a thickener were added to form a paste, filled into a commercially available Ni plate having a porosity of 95%, dried, and pressed to obtain a plane size of 30 mm × 40 mm, thickness: 0.40
0.43 mm shape (the active material powder filling amount: about 1.8
g), and a Ni thin plate serving as a lead is attached to one side of the negative electrode by welding to form a negative electrode, while the positive electrode uses Ni (OH) ₂ as an active material, and uses polytetrafluoroethylene (B) as a binder. PTFE) and carboxymethylcellulose (CMC) as a thickener were added to form a paste, which was filled in the above foamed Ni plate, dried, and pressed to obtain a plane size: 30 mm × 40 mm, thickness: 0.71 ~
It is formed by attaching a Ni thin plate to one side of the 0.73 mm shape. Then, the positive electrode is disposed on both sides of the negative electrode with a separator plate made of a polypropylene-polyethylene copolymer interposed therebetween. In order to prevent the active material from falling off from the respective outer surfaces, they are integrated by sandwiching them with a protective plate made of vinyl chloride, and this is charged into a cell made of vinyl chloride.
A battery was manufactured by charging a 5% KOH aqueous solution. Then, the battery was charged and discharged under the conditions of a charge rate: 0.20 C, a discharge rate: 0.20 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.

[0023]

[Table 3]

[0024]

According to the results shown in Table 3, the alloy of the present invention 1
Nos. 16 to 16 are regenerated La (Ce) -N fluidized and distributed along innumerable cracks to have a wide working area.
Due to the action of the i-based alloy phase, the La-Ni-based alloy phase exhibits a much faster hydrogen absorption and desorption rate as compared to the conventional alloy in which the La-Ni-based alloy phase is dispersed and distributed along the crystal grain boundaries. It is clear that the initial activation is excellent. As described above, the hydrogen storage alloy of the present invention has a large effective hydrogen storage capacity, a very fast hydrogen absorption and desorption rate, and excellent initial activation in practical use. It greatly contributes to higher output, higher performance, and energy saving of various mechanical devices.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a pressure composition isotherm of the hydrogen storage alloy of the present invention.

FIG. 3 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 33%, Zr: 1 to 10%, Hf: 0.05 to 0.4% Mn: 32 to 45%, Cr: 3 to 13%, V: 10 -22%, Ni: 2-10%, La and / or Ce: 0.1-3.5%, unavoidable impurities: residual, and a main phase of a Ti-Mn alloy;
Innumerable cracks generated from the La and / or Ce-Ni-based alloy phase in the hydrogenation treatment and regenerated La and / or Ce fluidized and distributed along the cracks in the dehydrogenation treatment
-A hydrogen storage alloy having a good initial activity, comprising a Ti-Mn-based alloy having a structure composed of a Ni-based alloy phase.