JPH10195570A - 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 and excellent in initial activation. SOLUTION: This hydrogen storage alloy is composed of a Ti-Ni alloy having a composition consisting of, by atom, 19-33% Ti, 1-10% Zr, 32-45% Mn, 3-13% Cr, 10-22% V, 2-10% Ni, 0.1-3.5% Re (where Re represents a mixture consisting of one or >=2 elements among La, Ce, Pr, and Nd), and the balance inevitable impurities and also having a structure constituted of primary phases of Ti-Mn alloy, numerous cracks developing with Re-Ni alloy phases as origins by hydrogenation treatment, and secondary Re-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 viewpoint, the effective hydrogen storage capacity of the hydrogen storage alloy
The hydrogen absorption and release rates and the initial activation
As a result of extensive research, Ti: 19 to 33%, Zr: 1 to 10%, Mn: 32 to 45%, Cr: 3 to 13%, V: 10 to 22%, Ni: 2 to 2 10%, Re: 0.1 to 3.5%, (where Re represents one or more of La, Ce, Pr, and Nd, the same applies hereinafter) Inevitable impurities: residue And a main phase of a Ti-Mn-based alloy,
Generated starting from Re-Ni alloy phase in hydrogenation treatment
Countless cracks and fluidization along the cracks in the dehydrogenation process
It has a structure composed of a recycled Re-Ni-based alloy phase
A hydrogen storage alloy made of a Ti-Mn-based alloy
-Hydrogen molecules in the atmosphere due to the catalytic action of the Ni-based alloy phase
(H _Two) Is dissociated into hydrogen atoms (H) and dissociated
Hydrogen atoms are much faster than Ti-Mn alloy-based phases
Absorption at a rate, and release also works by the opposite mechanism.
However, the Re-Ni alloy phase flows along innumerable cracks.
And the surface is in a state of being planarized.
Since the product is significantly expanded, the above conventional hydrogen
One step compared to hydrogen absorption and release rates in storage alloys
Hydrogen absorption and desorption at high speed.
Of Ti-Mn-based alloy main phase during initial activation
Re-N which has a large area of action by atomizing the absorption of atoms
Effective hydrogen storage because it is performed through the i-based alloy phase
Increased amount and significant acceleration of initial activation
The research result was obtained.

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%, Mn: 32 to 45%, Cr: 3 -13%, V: 10-22%, Ni: 2-10%, Re: 0.1-3.5%, unavoidable impurities: residual, and the main phase of Ti-Mn alloy When,
Ti-Mn having a structure composed of countless cracks generated from the Re-Ni alloy phase in the hydrogenation treatment and regenerated Re-Ni alloy phases fluidized and distributed along the cracks in the dehydrogenation treatment A hydrogen storage alloy having a good initial activity and comprising a base alloy.

[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 carried out under the condition of cooling after holding at a predetermined temperature in the range of 50 to 1050 ° C. for a predetermined time, the main phase of the Ti—Mn alloy and the Re— dispersed and distributed along the crystal grain boundaries of the main phase. Although it has a two-phase structure of a Ni-based alloy phase,
Further, following the homogenizing heat treatment, if hydrogenation treatment is performed under cooling conditions in a pressurized hydrogen atmosphere at a predetermined temperature in a range of 200 to 950 ° C. for a predetermined time, and then the Re-Ni formed by the homogenization heat treatment is cooled. The system-based alloy phase reacts preferentially with hydrogen in the atmosphere to form a hydrogenation product phase mainly composed of Re hydride and a Re-Ni-based intermetallic compound,
Since the hydrogen reaction product phase shows a large thermal expansion as compared with the Ti-Mn-based alloy main phase, innumerable cracks are generated in the main phase starting from the hydrogen reaction product phase. Is a state in which the hydrogen reaction product phase is exposed. Further, while performing the dehydrogenation treatment to a predetermined degree of vacuum while maintaining the predetermined temperature in the range of 500 to 950 ° C., the hydrogenation The Re hydride in the hydrogen reaction product phase generated by the treatment becomes Re, and this Re reacts with the co-existing Re-Ni-based intermetallic compound to form the Re-Ni-based alloy phase before the hydrogenation treatment. It is played, but this Re
At the time of re-forming the Ni-based alloy phase, it is fluidized, so that it flows and distributes in a plane along the crack, and the resulting Ti-Mn-based alloy has a schematic structure enlarged reproduction of FIG. As shown in the figure, regeneration of the main phase of the Ti-Mn-based alloy, countless cracks generated from the Re-Ni-based alloy phase in the hydrogenation treatment, and fluidization distribution along the cracks in the dehydrogenation treatment. It has a structure composed of the Re-Ni-based alloy phase.

[0007] In the above Ti-Mn alloy,
The Re-Ni-based alloy phase that constitutes 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 the Ti-Mn-based alloy-based phase. Absorbs at a much faster rate than
Absorption of hydrogen atoms in the main phase is mainly due to the regenerated Re-
The release is performed through the Ni-based alloy phase, and the release has an action by the reverse mechanism. However, the regenerated Re-Ni-based alloy phase is fluidized along countless cracks and is in a planarized state. As a result, since the working area is significantly increased, hydrogen absorption and release at a much higher rate than the hydrogen absorption and release rates of the above-mentioned conventional hydrogen storage alloy become possible. Ti-M
Since the absorption of hydrogen atoms of the n-based alloy main phase is also performed via the regenerated Re-Ni-based alloy phase having a large area of action, the initial activation can be remarkably promoted.

In general, when a hydrogen storage alloy is applied as, for example, an endothermic source of a heat pump, it is necessary to repeat hydrogen absorption and release several times with respect to the heat pump in which the hydrogen storage alloy is incorporated. 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) was measured (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) Mn, Cr, V, and Ni Furthermore, in order to increase the effective hydrogen storage capacity, in addition to the partial replacement of Ti with Zr as described above, Mn includes Cr, V and N.
Partial replacement by i is essential, and in other words,
If the Ti is not partially replaced by a predetermined amount of Zr, or if at least one of the replacing elements Cr, V and Ni is not contained, M
If partial replacement of each of n with predetermined amounts of Cr, V, and Ni is not performed, a desired large effective hydrogen storage amount cannot be secured.
n, Cr, V and Ni: less than 2%;
n: 45%, Cr: 13%, V: 22% and Ni: 1
If it exceeds 0%, the gradient of plateau and the hysteresis in the pressure composition isotherm become large, and therefore, the content ratio is set to Mn: 32 to 45, respectively.
%, Cr: 3 to 13%, V: 10 to 22%, and Ni:
It was determined as 2 to 10%.

(C) Re These components are, as described above, a reclaimed Re-Ni-based alloy having the function of dissociating and absorbing hydrogen in the atmosphere at a higher speed than the main phase, and recombining and releasing into the atmosphere. It is an indispensable component for forming a phase. Therefore, if the ratio is less than 0.1%, the generation ratio of the recycled Re-Ni-based alloy phase is too small, and the above-described function of the phase is sufficiently exhibited. On the other hand, if the proportion exceeds 3.5%, the proportion of the regenerated Re-Ni-based alloy phase having a small hydrogen storage capacity becomes too large, and the hydrogen storage capacity of the entire alloy decreases. , The ratio is determined to be 0.1 to 3.5%, preferably 0.5 to 3.0%.

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, Mn, Cr, V, Ni, and Re,
Dissolved in an Ar atmosphere to prepare a Ti-Mn-based alloy melt having the composition shown in Table 1 and cast it into a water-cooled copper mold to form an ingot. The homogenization heat treatment was performed at the indicated temperature for 20 hours, and then the heat treatment was performed in the same manner as in Table 2.
In a hydrogen atmosphere at a predetermined pressure as shown in Table 1, after holding at room temperature for 1 hour, heating was started to heat to a predetermined temperature as shown in Table 2, and a hydrogenation treatment was performed at this temperature for 30 minutes. In the main phase of the Ti—Mn-based alloy formed by the homogenizing heat treatment, R is distributed and distributed along the crystal grain boundaries.
The e-Ni-based alloy phase is a hydrogen reaction product phase mainly composed of Re hydride and a Re-Ni-based intermetallic compound (innumerable cracks are generated starting from the hydrogen reaction product phase as a starting point). Subsequently, 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 subjected to Re-treatment.
-Regenerate into a Ni-based alloy phase (during this dehydrogenation treatment, the reactants are fluidized, so the regenerated Re-Ni-based alloy phase has numerous cracks as shown in the structure of the alloy of the present invention in FIG. 1). The hydrogen storage alloys 1 to 16 of the present invention (hereinafter, alloys 1 to 6 of the present invention)
16).

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: hydrogen absorption under the condition of 1 hour and hydrogen crushing consisting of hydrogen release by vacuum evacuation were performed to obtain 200me.
A powder having a particle size of sh or less was used, and measurement was performed using this powder under the following conditions.

(A) The powder is sealed in a container immersed in a bath (oil or water), and while the temperature of the bath is maintained at 200 ° C., the valves Vb are closed, and the valves Va and Vc are opened and the hydrogen cylinder is opened. , Pressurized hydrogen is introduced into the system, and when the pressure in the system is reduced to 30 atm, the valve Va is closed, and the system is allowed to stand until the pressure in the system drops to a constant pressure (complete absorption of hydrogen by the powder). (B) The pressure in the system is maintained at a constant pressure (approximately 2
When the pressure drops to about 0 atm), the valve Vb is opened, the system is evacuated to a vacuum atmosphere of 10 ^-2 torr by a vacuum pump, the bath temperature is set to 20 ° C, the valves Vb and Vc are closed, and the valve Va is open. Then, hydrogen was introduced into the system except for the container, and when the pressure reached 30 atm, the valve Va was closed and the valve Vc was opened. In this state, the pressure drop with respect to time in the system was measured. From the pressure drop curve of the above, the hydrogen storage amount at the time when the hydrogen storage amount of the powder becomes 80% and the time required up to that time are obtained, and (hydrogen storage amount at 80% storage) ÷ (80% hydrogen storage amount Was calculated, and this value was used as the hydrogen absorption rate.

The hydrogen release rate is the state after the above-described 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 valve Vb: closed, valve Vc:
In the open state, the pressure rise with respect to time in the system was measured, and from the resulting pressure rise curve, the amount of hydrogen released from the powder was 8%.
The amount of hydrogen released at 0% and the time required up to that time are obtained, and (hydrogen released at 80% release) / (time required for 80% hydrogen release) is calculated. Speed. The results are shown in Tables 4 and 5.

Next, the above alloys 1 to 16 of the present invention and the conventional alloy are coarsely pulverized by a jaw crusher into coarse particles having a diameter of 2 mm or less, and further finely pulverized by 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 invention 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 into coarse particles having a diameter of 2 mm or less. Subsequently, the alloys 1 to 16 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.

Next, the battery was charged at a charging rate of 0.20.
C, discharge rate: 0.20C, charge amount: 1 of negative electrode capacity
The charge and discharge were performed under the condition of 35%, and the charge and discharge were counted as one charge and discharge, and the charge and discharge were repeated until the battery showed 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.

[0025]

[Table 3]

[0026]

According to the results shown in Table 3, the alloy of the present invention 1
Nos. 16 to 16 are the actions of the regenerated Re-Ni alloy phase, which is fluidized and distributed along an infinite number of cracks and has a wide area of action, and the Re-Ni alloy phase extends along the crystal grain boundaries. It is evident that the alloy exhibits a much higher hydrogen absorption and release rate than the conventional alloy having a dispersed distribution, and as a result, the initial activation is excellent.

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 high output, high performance, and energy saving.

[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%, Mn: 32 to 45%, Cr: 3 to 13%, V: 10 to 22%, Ni: 2 to 10% , Re: 0.1 to 3.5%, unavoidable impurities: residual, and a main phase of a Ti-Mn-based alloy;
Ti-Mn having a structure composed of countless cracks generated from the Re-Ni alloy phase in the hydrogenation treatment and regenerated Re-Ni alloy phases fluidized and distributed along the cracks in the dehydrogenation treatment A hydrogen storage alloy having a good initial activity, comprising a base alloy.