JPS5928624B2 - Manufacturing method for hydrogen storage alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides hydrogen storage alloys, particularly MmNi 5-
Regarding the manufacturing method of xMnx alloys, in detail for hydrogen storage alloys, the present invention provides a method for manufacturing alloys with small pressure changes in the equilibrium pressure at a flat part of the hydrogen storage dissociation equilibrium pressure at a constant temperature, the so-called plateau region. .

It is known that certain metals or alloys react quantitatively with hydrogen to form metal hydrides under certain conditions.

Since this reaction is reversible, its application to various systems has been put into practical use or is being studied.

One of the important properties for using these metal hydrides is the hydrogen storage dissociation equilibrium pressure property at a constant temperature.
In particular, it is required that the plateau region be flat and the pressure change be small.

MmNi 5-xMnx alloy has been developed as this alloy, but this alloy has conventionally been produced by directly melting the component metals in an argon arc furnace, high-frequency furnace, etc., and then rapidly cooling them in a water-cooled crucible. Since the phase change of a solid occurs rapidly, it solidifies with an unstable lattice spacing, resulting in a large pressure change in the plateau region.

The purpose of the present invention is to solve the above-mentioned conventional drawbacks, and the gist thereof is to heat a MmN i 5- x Mnx alloy at a temperature of 700° C. to 1000° C., which is lower than the melting temperature, and then cool it.

In the present invention, it is mainly composed of nickel, manganese and Mitsushi metal, and its composition is MmN i 5
- Alloys represented by x Mn x, where X is in the range of 0.2 to 2.0, are targeted.

This alloy can be obtained relatively inexpensively and has a large hydrogen storage capacity, but it is known that as the cerium content, which is one of the components of Mitsushi metal, increases, the gradient in the plateau region becomes larger.

Also, as the amount of manganese increases, MmNi5-x
When X of Mnx exceeds 0.2, the slope of the plateau region also increases.

Therefore, when carrying out the present invention, cerium constitutes 50% or more of Mitsushi metal, and X of Mnx is 0.2.
It is particularly effective for alloys with the above-mentioned values.

The MmNi5-XMnX-based hydrogen storage alloy can be prepared by first melting the component metals using an argon arc furnace or the like, as is well known, to form an alloy.

Next, the alloy is heated in a vacuum or in an inert gas atmosphere such as argon in an electric furnace using a siliconite or nichrome heating element at a temperature of 700°C to 1000°C, and then cooled to produce a hydrogen storage alloy. It makes them manufacture.

It has been found that when heating the MmN i 5- x Mx alloy at a temperature of 1000'C or less, which is lower than its melting temperature of about 1330C, good results can be obtained without using special operations or equipment.

It is assumed that when the temperature exceeds 1000° C. and approaches the melting temperature, it becomes difficult to obtain the desired alloy due to the high vapor pressure of manganese.

On the other hand, if the heating temperature is less than 700° C., a long heating time is required, which is not practical.

The temperature is preferably 800°C or higher (G).

After heating, the alloy may be cooled by immediately immersing it in ice water or by slowly cooling it in air.

The hydrogen storage alloy obtained by the production method of the present invention is
Furthermore, since the interstitial distance of the crystals is uniform and the size of the crystal particles is constant, the pressure in the so-called plateau region of hydrogen absorption and dissociation equilibrium pressure is lower than that of conventional ones. Since the change is extremely small, it has the advantage of increasing the amount of hydrogen that can be absorbed and desorbed in practical use.
The reaction rate with hydrogen during activation treatment is high, the reaction completion time is short, and activation is extremely easy, which are extremely useful properties in practice as a hydrogen storage alloy.

Examples of the present invention will be shown below.

Commercially available Mitsushmetal (component is approximately 24% Rank Nuum)
After separating high-purity nickel and high-purity manganese to a composition of MmN i 4.5 Mn 6.5, they were placed in a water-cooled copper crucible and directly melted in an argon arc furnace. let

After repeating melting several times to homogenize the composition, it is taken out of the furnace and used as a raw material.

This lumpy raw material was placed in a quartz container, and after introducing argon gas into the container to sufficiently replace the inside of the container with gas, the pressure inside the container was reduced to 1 torr using a vacuum device.

This container was placed in an electric furnace previously maintained at 950° C., heated for 2 hours, and then taken out from the electric furnace and immediately cooled in ice water to produce a hydrogen storage alloy.

The results of X-ray diffraction of this alloy are shown in FIG.

This result can be compared to the X
When compared with the line diffraction pattern, it is clear that the diffraction pattern is sharper and the half width is smaller, indicating a homogeneous crystalline phase.

It is necessary to perform an activation treatment on the hydrogen storage alloy so that the alloy undergoes a quantitative hydrogen storage and release reaction.

This activation treatment was performed using Ml-11N14.5 Mn o, 5
This can be achieved by applying a pressure of 30 Ky/crfH degrees to the alloy at room temperature.

FIG. 2 shows the progress of the activation reaction of the alloy according to this example and the alloy of the comparative example.

It was confirmed that the time required for completing 100% reaction of the alloy of the example was reduced to about ⅓ compared to the alloy of the comparative example.

The hydrogen equilibrium pressure-hydride composition curve is shown in FIG.

At 30°C, MmNi4,5Mn□,5
The so-called plateau region of the alloy is at a hydrogen equilibrium pressure of 2.1-2.9at.
m was shown.

In the comparative example, the plateau region is 1, 1-7.0 atm
It was confirmed that the production method of the present invention produced a hydrogen storage alloy in which the pressure change in the plateau region was extremely small.

In addition, although the heating temperature of MmNi4.5Mn□,5 alloy having the same composition as above was set to 850°C and 750°C, and the heating time was changed stepwise, the effect was confirmed.

For comparison, in the above example in which the heating temperature was 950°C and the heating time was 2 hours, the value of was set to 100, and the same calculated value in other examples was used.
90% to 100% of the sample was rated A, 70% to 90% was rated B, and 50% to 70% was rated C.

The results are shown in Table 1.

[Brief explanation of the drawing]

Figures 1 to 3 compare examples and comparative examples according to the production method of the present invention, with Figure 1 being an X-ray diffraction diagram of the alloy, Figure 2 being an initial hydrogenation reaction rate diagram of the alloy, and Figure 3 being The figure is a hydrogen equilibrium pressure-hydride composition curve diagram of the alloy.

Claims (1)

[Claims] 1. An alloy mainly composed of nickel, manganese and Mitsushi metal, whose composition is represented by MmNi5-xMnx, and where X is in the range of 0.2 to 2.0, is heated at 700°
1. A method for producing a hydrogen storage alloy, which comprises heating at a temperature of 1000°C to 1000°C, and then cooling the alloy.