JP3490871B2 - Hydrogen storage alloy particles and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to particles of a hydrogen storage alloy having a surface layer containing an intermetallic compound phase having a high reaction rate with hydrogen.

[0002]

2. Description of the Related Art Hydrogen storage alloys are used as electrode materials for nickel-hydrogen batteries, as well as for storing and transporting hydrogen, storing heat,
It is applied to heat utilization systems such as heat pumps.
For example, when a hydrogen storage alloy is used for a heat utilization system of a heat pump, hydrogen is repeatedly stored and released several times per hour, and thus the reaction rate between the alloy and hydrogen is a major factor that determines the performance of the alloy. It will be one. Therefore, increasing the reaction rate with hydrogen greatly contributes to improving the characteristics of the hydrogen storage alloy.

Hydrogen storage alloys used in heat utilization systems are usually in powder form. Therefore, in order to increase the hydrogenation reaction rate of the hydrogen storage alloy, it is effective to form an alloy phase having a faster reaction rate than the core portion on the surface of the particles. Until now, the surface of hydrogen storage alloy powder has been modified by chemical treatment, or mechanical alloying treatment has been performed to fix hydride powder with a high hydrogenation reaction rate to the surface of the base particles. It is being appreciated.

[0004]

However, in the conventional surface treatment method, since the hydrogen storage alloy is added to the alloy system different from the matrix phase, it is difficult to control the surface state and complicated steps are required. I need. Even in the hydrogen storage alloy produced in this manner, the effect of improving the reaction rate with hydrogen is actually only about several percent.

By the way, some hydrogen storage alloys are known to have a phase having a fast reaction rate in the alloy itself. For example, LaNi such as LaNi _{3.5 to} LaNi ₅
In the —Ni-based hydrogen storage alloy, there is a La ₅ Ni ₁₉ phase having a Ce ₅ Co ₁₉ type crystal structure, and this phase is LaNi ₃
It is known that the reaction rate with hydrogen is higher than that of the phase, the LaNi ₅ phase, and the like. The inventors believe that it is possible to selectively form a phase having a Ce ₅ Co ₁₉ type crystal structure such as a La ₅ Ni ₁₉ phase in the surface layer portion of the grain by controlling the structure, The present invention has been accomplished. An object of the present invention is to provide particles of a hydrogen storage alloy in which a phase having a fast reaction rate with hydrogen is formed in the surface layer portion by controlling the structure by heat treatment.

[0006]

The particles of the hydrogen storage alloy according to the present invention have a composition of the general formula AB _x ( where x is 3.5 to 5 ) .
C having the composition represented by the general formula A ₅ B ₁₉ in the surface layer portion.
It is characterized by having a phase of an e ₅ Co ₁₉ type crystal structure .
A is at least one element selected from the group consisting of La, Ce, Nd, Pr, Y, Sm and Gd, and B is N
i, Co, Cr, Mn, Al, V, Fe, In, Si,
It is at least one element selected from the group consisting of Ge and Sn. The composition is represented by the general formula A ₅ B ₁₉ (where A is L
a, Ce, Nd, Pr, Y, Sm and at least one element selected from the group consisting of Gd, B is Ni, C
o, Cr, Mn, Al, V, Fe, In, Si, Ge and Sn) and has a phase of Ce ₅ Co ₁₉ type crystal structure in the surface layer portion. The particles of the hydrogen-absorbing alloy are obtained by adding the powder of the hydrogen-absorbing alloy having the composition represented by the general formula AB _x (where x is 3.5 to 5) to C
It can be produced by heating to a temperature at which the phase of the e ₅ Co ₁₉ type crystal structure can exist as a stable equilibrium phase and then cooling at a cooling rate of 10 ° C./min or more.

[0007]

Functions: The phases of the Ce ₅ Co ₁₉ type crystal structure are AB ₃ type and AB type.
Compared with crystal phases such as ₄ type and AB ₅ type, it has a property that the reaction rate with hydrogen is faster. Therefore, the Ce ₅
The particles of the hydrogen storage alloy having the phase of Co ₁₉ type crystal structure promote the reaction with hydrogen. In addition, if the phase of Ce ₅ Co ₁₉ type crystal structure is present in an amount of about 50% by volume or more in the portion at least about 50 nm from the surface, the reaction promoting effect of the hydrogenation reaction can be enjoyed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION First, preparation of particles of a hydrogen storage alloy according to the present invention will be described. For example, LaNi _4.5
In the case of the hydrogen storage alloy of, 900 ° C-
It is known that an intermetallic compound phase of La ₅ Ni ₁₉ exists in the temperature range of 1000 ° C. The crystal structure of this La ₅ Ni ₁₉ phase is shown in FIG. This phase is hexagonal C
It has an e ₅ Co ₁₉ type structure and contains a large number of stacking faults on the bottom surface. Due to the existence of these stacking faults, the reaction rate with hydrogen is faster than that of the LaNi ₅ phase.

In the case of the above-mentioned LaNi _4.5 hydrogen storage alloy, the temperature range in which the La ₅ Ni ₁₉ phase exists is known, but this La ₅ Ni ₁₉ phase is not described in the latest equilibrium diagram. It is a phase. Therefore, depending on the type of hydrogen storage alloy, the temperature range in which the La ₅ Ni ₁₉ phase exists may be unknown. In that case, in order to understand the temperature dependence of the phase state of the alloy, hydrogen of the desired composition should be used. It is necessary to prepare a powder sample of the storage alloy and perform a thermal analysis test. In the thermal analysis test, an alloy sample of several mmg to several tens of mmg and an α-Al ₂ O ₃ sample, which is a standard sample, are placed in a sample container,
Heating is performed at a temperature rising rate of 5 ° C. to 10 ° C./min in an inert gas such as Ar gas. When a phase transition occurs in an alloy sample,
A heat flow occurs due to the temperature gradient between the standard sample. By measuring this heat flow, La ₅ N
The temperature at which the i ₁₉ phase occurs can be known. Powder sample,
After heating to the formation temperature of the La ₅ Ni ₁₉ phase determined by thermal analysis, a heat treatment of quenching at a cooling rate of 10 ° C./min or more is performed to measure the hydrogenation characteristics. The rapid cooling is performed in order to maintain the La ₅ Ni ₁₉ phase existing in a certain temperature range at room temperature without changing the phase during the cooling, and it is preferable that the cooling rate is as fast as possible. The hydrogenation characteristic is measured using a Sibelts apparatus, and a P-C-T characteristic diagram is created based on the measurement result. Figure 2 shows LaNi
FIG. 4 shows a P-C-T characteristic diagram of _4.5 , and when the La ₅ Ni ₁₉ phase is present, the plateau region appears in two stages (see line (i)), whereas the La ₅ Ni ₁₉ phase is not present. Sometimes, the plateau region that appears is only one stage (see line (ii)). In the line (i), is the plateau region of LaNi _{4.5 and is} the plateau region of the La ₅ Ni ₁₉ phase.

[0010] In this manner, subjected to thermal analysis for several powder sample, by examining whether La ₅ Ni ₁₉ phase is formed in any sample, to determine the temperature range in which La ₅ Ni ₁₉ phase is formed be able to.

The hydrogen-absorbing alloy powder was charged into a heat treatment furnace, heated in a temperature range where the La ₅ Ni ₁₉ phase was formed, and cooled at a predetermined cooling rate, so that the surface layer portion was Ce ₅ Co.
Hydrogen storage alloy particles having a _19- type crystal structure are produced.
The heat treatment furnace is, for example, a heating chamber capable of creating an inert gas atmosphere after vacuuming the inside, a cooling chamber capable of creating an inert gas atmosphere, and the heating chamber and the cooling chamber are hermetically connected to each other. A transport path and a transfer means for moving the hydrogen storage alloy powder heated in the heating chamber from the heating chamber to the cooling chamber through the transfer path are used.

The hydrogen-absorbing alloy powder is evacuated to, for example, 10 ^-2 Torr or less, and then heated in an atmosphere (for example, Ar gas) inert to the hydrogen-absorbing alloy to obtain La ₅ N.
i ₁₉ Phase temperature range (hydrogen storage alloy is LaNi _4.5
In this case, the temperature is kept at 900 to 1000 ° C.) for a predetermined time. After the heating is completed, the hydrogen storage alloy powder is sent from the heating chamber to the cooling chamber through the transfer path by the transfer means. A gas (eg, Ar gas) inert to the hydrogen storage alloy is flown in the cooling chamber at a flow rate of, for example, about 5 m ³ / min, and the inert gas is agitated in the cooling chamber. The hydrogen storage alloy powder is blown by the fan to cool the hydrogen storage alloy powder.

The strength at which the gas is blown onto the hydrogen-absorbing alloy powder achieves the purpose of forming the La ₅ Ni ₁₉ phase on the surface layer of the particles when the cooling rate of the hydrogen-absorbing alloy is about 10 ° C./min or more. However, about 50 ° C./min or more is preferable, and about 100 ° C./min or more is more preferable.
The particle size of the hydrogen storage alloy is preferably about 100 μm, but there is no particular problem as long as it is within the range of about 30 to 200 μm.

[0014]

EXAMPLES Inventive Example 1 A raw metal powder compounded to have an atomic ratio of La: Ni of 1: 4.5 was press-molded and then melted in an arc furnace.
Then, it was allowed to cool and a LaNi _4.5 button-shaped ingot was produced. This ingot is crushed and the average particle size is about 100μ.
m test powder was obtained. 50 g of this test powder was placed in a sample container, heated in a heating furnace, held at a temperature of 950 ° C. for 8 hours, then transferred to a cooling chamber, and rapidly cooled by blowing Ar gas in the cooling chamber. Was applied.

Inventive Example 2 A raw metal powder compounded to have an atomic ratio of La: Ni of 1: 4.5 was press-molded, then melted by arc melting on a crucible equipped with a nozzle, and positioned below the nozzle. A sample powder having an average particle size of about 100 μm was obtained by the gas atomizing method in which the molten metal was ejected into the Ar gas flowing at high speed. 50 g of this test powder was placed in a sample container and heated in a heating furnace in the same manner as in Inventive Example 1 and held at a temperature of 950 ° C. for 8 hours, and then transferred to a cooling chamber, and in the cooling chamber. A quenching process was performed by spraying Ar gas.

Comparative Example 1 50 g of the test powder prepared in the same manner as in Inventive Example 1 was placed in a sample container and heated in a heating furnace and kept at a temperature of 950 ° C. for 8 hours. Furnace cooling treatment was performed therein.

Regarding the test powders that have been subjected to the above treatment,
The tissue state of the particles was observed by electron beam microanalysis (EPMA). Regarding the particles of Example 1 and Example 2, about 85% by volume of the portion from the surface to about 50 nm is La ₅ N.
It has been observed that i ₁₉ phase is accounted for. Further, about 80% by volume in the portion up to about 100 nm from the surface, about 75% by volume in the portion about 150 nm from the surface, La ₅ N respectively.
It is observed that the i ₁₉ phase occupies about 20 in the core part.
It was observed that the volume% was the La ₅ Ni ₁₉ phase. In addition, although it was observed that a small amount of La ₅ Ni ₁₉ phase was scattered in the particles of Comparative Example 1, the LaNi ₅ phase substantially occupied the whole.

The hydrogen absorption rate at various temperatures was measured for the test powder subjected to the above-mentioned treatment using a Sibelts apparatus. This measures the amount of absorbed hydrogen from the change in hydrogen pressure in a pressure vessel of known volume.
The hydrogen absorption rate when pressurized at a pressure of m was determined.

The measurement results are shown in FIG. In FIG. 3, the horizontal axis represents the value obtained by multiplying the reciprocal of the measured temperature (unit is absolute temperature) by 1000, and the vertical axis represents the amount of hydrogen gas absorbed by 1 g of the alloy in 1 minute in the standard state (1 atm. , 25 ° C.). It can be seen that the invention example 1 has a hydrogen absorption rate that is about 30% higher at any temperature than the comparative example 1. This is because the La ₅ Ni ₁₉ phase, which has a high reaction rate with hydrogen, exists in the surface layer of the particles. Inventive Example 2 is about 2 more than Inventive Example 1.
It is about 0% faster. This is due to the difference in the crystal grain size of the powder before the heat treatment, and the atomized alloy powder of Inventive Example 2 has crystal grains due to the rapid solidification effect as compared with the powder of Inventive Example 1 obtained by mechanical grinding after arc melting. This is because is miniaturized. Therefore, it can be said that it is more desirable to use the hydrogen storage alloy powder prepared by the gas atomization method.

As described above, for example, in LaNi _4.5 , since the La ₅ Ni ₁₉ phase of Ce ₅ Co ₁₉ type structure exists in the temperature range of about 900 to 1000 ° C., after sufficiently heating and holding in that temperature range, By quenching, L on the particle surface
It can be formed a ₅ Ni ₁₉ phase. The hydrogen storage alloy is not limited to LaNi _4.5 alloy, but La: Ni is 1: 3.5.
It is possible to form the La ₅ Ni ₁₉ phase having the Ce ₅ Co ₁₉ type structure in the range of 1: 5 to 1: 5. Further, not only the binary alloy of La and Ni, but La is Ce,
Substitute with Nd, Pr, Y, Sm or Gd, and replace Ni with C
Other binary hydrogen storage alloys substituted with o, Cr, Mn, Al, V, Fe, In, Si, Ge or Sn may be used.
Furthermore, not only binary alloys but also La, Ce, Nd, P
at least one element selected from the group consisting of r, Y, Sm, and Gd, and Ni, Co, Cr, Mn, Al, V, Fe,
A ternary or higher hydrogen storage alloy containing at least one element of the group consisting of In, Si, Ge and Sn in the range of 1: 3.5 to 1: 5 may be used.

[0021] Thus, the hydrogen storage alloy of the present invention have the general formula AB _x (where, x is from 3.5 to 5) a composition represented by the composition of the phases of Ce ₅ Co ₁₉ type crystal structure General formula A ₅ B ₁₉
, A is at least one element selected from the group consisting of La, Ce, Nd, Pr, Y, Sm and Gd, B is Ni, Co, Cr, Mn, Al, V, Fe,
It can be shown as at least one element selected from the group consisting of In, Si, Ge, and Sn.

In the particles of the hydrogen storage alloy of the present invention, at least about 50% by volume of the surface layer portion up to 50 nm from the surface is C.
The phase having the e ₅ Co ₁₉ type crystal structure can achieve the effect of promoting the reaction with hydrogen. In order to further enhance the reaction promoting effect with hydrogen, it is preferably about 60% by volume or more, more preferably about 70% or more.

[0023]

The particles of the hydrogen storage alloy of the present invention have the general formula
C represented by the general formula A ₅ B ₁₉ which is represented by AB _x ( where x is 3.5 to 5 ) and has a large reaction rate with hydrogen on the surface layer of the particle .
Since it forms a phase of e ₅ Co ₁₉ type crystal structure, it has a fast reaction rate with hydrogen in the absorption and desorption process of hydrogen, and it is used for applications such as heat pumps that absorb and desorb hydrogen several times per hour. It is particularly advantageous.

[Brief description of drawings]

FIG. 1 is a diagram showing a crystal structure of a La ₅ Ni ₁₉ phase.

FIG. 2 is a P-C-T characteristic diagram of LaNi _4.5 alloy.

FIG. 3 is a graph showing the relationship between temperature and hydrogen storage rate for the test powders of Examples and Comparative Examples.

Front page continuation (51) Int.Cl. ⁷ Identification symbol FI H01M 4/38 H01M 4/38 A (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Denki Co., Ltd. ( 58) Fields surveyed (Int.Cl. ⁷ , DB name) B22F 1/00-1/02 H01M 4/24-4/26, 4/38

Claims (3)

(57) [Claims] 1. The composition is the general formula AB _x ( However, x is 3 . 5-
5 ) And the composition of the surface layer is represented by the general formula A _Five B ₁₉ Represented by
Ce _Five Co ₁₉ Of hydrogen storage alloy having phase of crystal structure
As a child, A is La, Ce, Nd, Pr, Y, Sm
And at least one element selected from the group consisting of Gd
Element B is Ni, Co, Cr, Mn, Al, V, Fe,
A small amount selected from the group consisting of In, Si, Ge and Sn.
Hydrogen storage characterized by being at least one element
Gold particles. 2. Particles of hydrogen storage alloy are gas atomized
The hydrogen absorbing particles according to claim 1, which are particles prepared by a method.
Kura alloy particles. 3. The composition is the general formula AB _x ( However, x is 3 . 5-
5 ) And the composition of the surface layer is represented by the general formula A _Five B ₁₉ Represented by
Ce _Five Co ₁₉ Has a phase of a crystal structure (where A is L
Is it a group consisting of a, Ce, Nd, Pr, Y, Sm and Gd?
At least one element selected from B, Ni, C
o, Cr, Mn, Al, V, Fe, In, Si, Ge and
And at least one element selected from the group consisting of Sn
By the method of producing powder consisting of particles of hydrogen storage alloy
Yes, the general formula AB _x Of a hydrogen storage alloy with a composition represented by
Powder to Ce _Five Co ₁₉ Equilibrium phase with stable phase
And a cooling rate of 10 ° C / min or more.
Particles of hydrogen storage alloy, characterized by cooling at
A method for producing a powder consisting of.