JPH10195581A - 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% La and/or Ce, and 0.2-7% hydrogen and satisfying Ti(%)+ Zr(%)+Hf(%)+Mn(%)+Cr(%)+V(%)+Ni(%)+(La and/or Ce) (%) +hydrogen (%) + (inevitable impurities) (%)=100%. Moreover, this hydrogen storage alloy has a structure where hydrogen reaction product phases are dispersedly distributed in matrix phases of Ti-Mn alloy and the hydrogen reaction product phases are constituted essentially of hydride of La and/or Ce and (La and/or Ce)-Ni alloy and further has a structure where numerous cracks developing at the time of formation of the hydrogen reaction product phases are present and the hydrogen reaction 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 conducting research to improve the effective hydrogen storage amount, the hydrogen absorption / desorption 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%, La and // Ce [hereinafter referred to as La (Ce)]: 0.1 to 3.5%, hydrogen: 0.2 to 7, unavoidable impurities: residual, a Ti-Mn alloy having a composition of: When the ingot of this alloy is subjected to a homogenizing heat treatment after casting, La along the crystal grain boundary of the base phase of the Ti—Mn alloy is obtained.
It has a structure in which a dispersed phase of a (Ce) -Ni-based alloy is present. However, when the homogenizing heat treatment is followed by a hydrogenation treatment under a condition of cooling at a predetermined temperature in a hydrogen atmosphere for a predetermined time and then cooling. As shown in a schematic microscopic enlarged view illustrating a representative structure in FIG. 1, the dispersed phase of the La (Ce) —Ni-based alloy formed by the homogenization heat treatment reacts preferentially with hydrogen in the atmosphere, The main components are hydrides of La (Ce) [hereinafter referred to as hydrides of La (Ce)] and La (Ce).
e) It becomes a hydrogen reaction product phase composed of a -Ni-based alloy, and the hydrogen reaction product phase shows a large thermal expansion as compared with the base phase of the Ti-Mn-based alloy. Innumerable cracks are generated starting from the reaction product phase, and the hydrogen reaction product phase is exposed on the inner surface of the crack.

(B) In the Ti-Mn alloy of (a), La (C)
with e) -Ni system alloy, the hydrogen molecules in the atmosphere in the catalytic action possessed by this (H ₂₎ dissociates into hydrogen atom (H), a
The dissociated hydrogen atoms are absorbed at a much higher rate than the Ti-Mn-based matrix phase, and the release shows the action by the reverse mechanism. Since it is in an exposed state, and as a result, the working area is enlarged, the La (Ce) hydride also has an effect of promoting the progress of diffusion of absorbed hydrogen atoms and released hydrogen atoms. Hydrogen absorption and desorption become much faster than hydrogen absorption and desorption rates, and the absorption rate of hydrogen atoms in the above-mentioned base phase at the time of initial activation increases significantly over a wide working area. Remarkable promotion will 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-mentioned research results, 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%, La (Ce): 0.1 to 3.5%, Hydrogen: 0.2 to 7 %, Unavoidable impurities: residual, and the hydrogen reaction product phase is dispersed and distributed in the base phase of the Ti—Mn alloy, and the main component of the hydrogen reaction product phase is a hydride of La (Ce). And La (Ce) -Ni
A hydrogen storage having a structure composed of a base alloy, and further having a myriad of cracks generated during the formation of the hydrogen reaction product phase, and having a structure in which the hydrogen reaction product phase is exposed on the inner surface of the crack. The alloy has characteristics.

[0007]

Embodiments of the present invention will be described below. First, Ti-Mn having the above composition
After melting and casting the system alloy, the ingot of the Ti-Mn system alloy was held at a predetermined temperature within a range of 950 to 1050 ° C. in a vacuum or a non-oxidizing atmosphere of an inert gas for a predetermined time and then cooled. A homogenizing heat treatment is performed, and subsequently to the homogenizing heat treatment, at 200 to 950 ° C. in a hydrogen atmosphere under pressure.
When a hydrogenation treatment is performed under the condition of cooling after holding at a predetermined temperature within the range of the above for a predetermined time, a hydrogen reaction is generated in the base phase of the Ti—Mn-based alloy shown in a schematic enlarged enlarged schematic diagram illustrating a representative structure in FIG. The hydrogen reaction product phase has a structure composed of a hydride of La (Ce) and a La (Ce) -Ni-based alloy, and the hydrogen reaction product phase There are countless cracks that occurred during the formation of
The hydrogen storage alloy of the present invention having a structure in which the hydrogen reaction product phase is exposed is obtained on the inner surface of the crack, and this alloy is incorporated as, for example, an endothermic source of a heat pump, or used for hydrogen storage, transportation, and battery use. When practically used as an electrode or the like, a hydrogen storage alloy having a large effective hydrogen storage amount, an extremely fast hydrogen absorption and desorption rate, and excellent initial activation is obtained. 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, 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.
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. .
If it is less than 02%, 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: 33 to 40%, Cr: 7 to 11%,
V: 9 to 15% and Ni: 2 to 9%, desirably Mn: 30 to 44%, Cr: 4 to 13%, respectively
V: 7 to 17% and Ni: 3 to 7%.

(D) La (Ce) As described above, these components dissociate and absorb hydrogen in the atmosphere at a much higher rate than the base phase, and have the effect of recombining and releasing into the atmosphere. ) -Ni-based alloy, and La (C) having an effect of promoting the diffusion of absorbed hydrogen into the base phase and the diffusion of hydrogen released from the base phase.
e) Although it is an indispensable component for the formation of hydride, if the proportion is less than 0.1%, the production rate of the La (Ce) -Ni-based alloy and the La (Ce) hydride is too small to obtain desired fast hydrogen. When the rate of absorption and release cannot be ensured, while the proportion exceeds 3.5%, the proportion of the dispersed phase having a small hydrogen storage amount becomes too large, and the hydrogen storage amount of the entire alloy decreases. Therefore, the ratio is set to 0.1 to 3.
5%, preferably 1-3%.

(E) Hydrogen Hydrogen is mainly composed of La (Ce) which constitutes a hydrogen reaction product phase.
The La (Ce) -Ni-based alloy, which also forms a hydride, also dissociates and absorbs hydrogen by the La (Ce) -Ni-based alloy, which forms a hydrogen reaction product, into the base phase at a high diffusion rate, while rapidly releasing hydrogen from the base phase. The La (Ce) -Ni alloy has an effect of diffusing into the alloy, but if the ratio is less than 0.2%, the ratio of La (Ce) hydride which exerts the effect is too small to sufficiently exert the effect. On the other hand, if the proportion exceeds 7%, the proportion of La (Ce) hydride becomes too large as compared with the La (Ce) -Ni-based alloy, and the proportion of La (Ce) -Ni-based alloy is relatively high. Since the amount of alloy decreases and the hydrogen absorption / desorption rate and the initial activation decrease, the ratio is set to 0.2 to 7%, preferably 2 to 7%.
6%.

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 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, examples of the hydrogen storage alloy of the present invention will be specifically described. In a normal high-frequency induction melting furnace, Ni, Zr, Hf, Ti, Mn, V, La, and C each having a purity of 99.9% or more as raw materials.
e. Further, using a misch metal, melting in an Ar atmosphere to prepare an alloy melt having the composition shown in Table 1, and casting it into a water-cooled copper mold to form an ingot. A homogenizing heat treatment is performed at a predetermined temperature in the range of 950 to 1050 ° C. for 20 hours, and then, in a hydrogen atmosphere at a predetermined pressure shown in Table 1, first at room temperature for 1 hour, and then The temperature was then increased to the predetermined temperature shown in Table 1, and maintained at this temperature for 1 hour, and then subjected to hydrogenation treatment under the condition of forced air cooling with Ar gas, whereby hydrogen storage alloys 1 to 5 of the present invention were obtained. 1
6 (hereinafter referred to as alloys 1 to 16 of the present invention). For the purpose of comparison, a conventional hydrogen storage alloy (hereinafter, referred to as “metal alloy”) was prepared under the same conditions except that the composition of the molten alloy was as shown in Table 1 and no hydrogenation treatment was performed after the homogenization heat treatment.
Conventional alloy). 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 numerous cracks as shown in FIG. Is L
A hydrogen reaction product phase composed of an a (Ce) -Ni-based alloy and a La (Ce) hydride is exposed, showing a structure in which the hydrogen reaction product is dispersed and distributed in a base phase of the Ti-Mn-based alloy. As shown in FIG. 3, the conventional alloy had a structure composed of a base phase of a Ti—Mn alloy.

[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, as for the apparatus for measuring the hydrogen absorption rate, as shown in the schematic explanatory view of FIG. 5, (a) a powder is sealed in a vessel immersed in a bath (oil or water), and the temperature of the bath is set to 200. ℃ while maintaining the valve V
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 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. 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 alloys 1 to 16 of the present invention and the conventional alloy, first, the alloys 1 to 16 of the present invention and the conventional alloy were coarsely pulverized using a jaw crusher to obtain a diameter: Then, the alloys 1 to 16 of the present invention and the above-mentioned conventional alloy were finely pulverized with a ball mill to a particle size of 200 mesh or less, and polytetrafluoroethylene as a binder was added thereto. (PTFE) and carboxymethylcellulose (CMC) as a thickener were added to form a paste, and then 95%
Filling a commercially available foamed Ni plate having a porosity of
Press, plane dimension: 30mm x 40mm, thickness: 0.40
０．４0.43 mm (filling amount of the active material powder: 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
-16, unlike the conventional alloys, the hydrogen reaction product phase exposed to the surface and the myriad of crack inner surfaces and thus exposed to the atmosphere with a large surface area as a whole was obtained.
Hydrogen in the atmosphere is dissociated into hydrogen atoms and absorbed through the a (Ce) -Ni alloy, and the absorbed hydrogen diffuses directly or through the La (Ce) hydride into the base phase of the Ti-Mn alloy. Hydrogen absorption is performed, but as described above, La (Ce) -Ni having extremely fast hydrogen absorption capacity is used.
Since the system alloy is distributed over a large surface area as a whole, the hydrogen absorption rate becomes relatively extremely high, and the initial activation is also greatly promoted, and the hydrogen release is also based on the reverse mechanism. Therefore, hydrogen is released at a high speed. 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 high output and high performance of various mechanical devices 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%, La and / or Ce: 0.1 to 3.5%, hydrogen: 0.2 to 7%, unavoidable impurities: remaining, and The hydrogen reaction product phase is dispersed and distributed in the base phase of the Ti—Mn-based alloy, and the hydrogen reaction product phase is mainly composed of La and / or Ce hydride, La and / or Ce.
-Has a structure composed of a Ni-based alloy, and further has a myriad of cracks generated during the formation of the hydrogen reaction product phase, and has a structure in which the hydrogen reaction product phase is exposed on the inner surface of the crack. A hydrogen storage alloy, characterized in that: