JPS62294143A - Manufacture of metallic alloy for hydrogen storage - Google Patents

Abstract

PURPOSE:To easily and inexpensively manufacture a metallic alloy for hydrogen storage represented by a specific rational formula, by heating specific proportions of ferrozirconium, iron, and chromium in a melting furnace to melt them and then by cooling the above down to room temp. CONSTITUTION:In manufacturing a metallic alloy for hydrogen storage represented by a rational formula Zr(CrxFe1-x)2, ferrozirconium, iron, and chromium are weighed so that they come into weight ratios suited to the above (x) value preferably of about >0.2-0.8, which are formed into small lumps or small pieces, respectively, and alternately laminated into plural layers in a heat-resisting crucible. Subsequently, the above crucible is placed into a high vacuum-type high-frequency induction melting furnace to undergo heating so as to melt the alloy and single-phase substance of the above starting materials. After the above melting, the above molten alloy is cooled slowly in the air down to room., so that above-mentioned metallic alloy for hydrogen storage can be obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a hydrogen storage alloy, in particular Z, (C
, XF=r-x)2.

(Prior art) Hydrogen storage alloys have the property of absorbing hydrogen under temperature and pressure control and storing it as a metal hydride compound or releasing the stored hydrogen. It is seen as a promising hydrogen storage means for engines, fuel cells, etc., and as a heat pump, and recently, various hydrogen storage alloys have been proposed and are being put into practical use.

At present, the typical hydrogen storage alloys are:
There are three types: rare earth alloys and T-based alloys, and M9-based alloys.

Although rare earth alloys such as L and Ni have excellent storage capacity and reaction speed, they are very expensive, and to improve this, Mitsushi metal alloys are being researched. Ti-based alloys such as F, T, etc. have great advantages in terms of cost, and have low storage capacity and
Although the dissociation temperature is not so inferior, there are difficulties in the initial reaction (initial activation). Furthermore, although Mg-based alloys are excellent in terms of storage capacity and weight, they have the disadvantage of having a very high dissociation temperature that is difficult to control.

In addition to the above, research and development of materials such as alkali-based, aluminum-based, zirconium-based, and amorphous materials are being carried out at domestic and overseas research institutes and private companies, but there is still no material that comprehensively surpasses the above three types of alloys. unknown.

Generally, the items required when using hydrogen storage alloys are:
There are storage capacity, dissociation pressure temperature, storage-release reaction rate, activation difficulty, weight, cost, etc., and when considering each of the above alloy groups, each has its advantages and disadvantages.

On the other hand, the applicant has filed an earlier application (Japanese Patent Application No. 60-23511).
In No. 8), a zirconium-based hydrogen storage alloy having a composition in the range of 0, 15≦X≦0.8 expressed by the characteristic formula Z-(C-F-1-X)2 was used.

This zirconium-based hydrogen storage alloy exhibits good properties in terms of storage capacity, dissociation pressure temperature, storage/release reaction rate, and activation difficulty.

As described in the specification of the above-mentioned application, when producing the above-mentioned zirconium-based hydrogen storage alloy, Z.

, C,,F, are used as a single-phase material (pure metal), and weighed so as to have a predetermined mixing ratio according to the value of X, and the weighed Z, , and C, , and F. It has been manufactured by melting and cooling to a low temperature in an inert gas atmosphere using a normal alloy manufacturing method (for example, arc melting method, etc.).

(Problems to be Solved by the Invention) As mentioned above, a zirconium-based hydrogen storage alloy represented by the characteristic formula Z-(CrXF-1-X)2 is a single-phase raw material metal of Zr, C1, and F. In the case of manufacturing using a high-purity 2. Since the single-phase material is very expensive, the raw material cost of the hydrogen storage alloy becomes expensive, and there is a problem that it becomes difficult to manufacture the hydrogen storage alloy at a low cost.

Also, the melting point of Z, (1856°C) is the melting point of C,, (18
75℃), the temperature of the molten metal during melting reaches a high temperature of approximately 1900℃, and the molten metal container (crucible, etc.) of the melting furnace has a heat resistance temperature of 1900℃ or higher. Although it is possible to use a high-volume water-cooled copper crucible, when using the widely used magnesia-based crucible or calcia-based crucible, pure Zr undergoes a violent oxidation reaction when heated, so the oxides of the crucible material are There is a problem in that it tends to react with oxygen, etc. inside and generate impurities.

In addition, when producing hydrogen storage alloys, the raw materials must be divided into small lumps in order to prevent uneven distribution of the raw materials and promote dissolution, but it takes a lot of effort to break them into small lumps. In addition to this, there are problems in that the fine powder of pure Z1 generated at that time spontaneously ignites in the air, and various considerations must be taken in handling.

(Means for Solving the Problems) The method for producing a hydrogen storage alloy according to the present invention includes Zl(C,...
In manufacturing a hydrogen storage alloy represented by the characteristic formula F, -, )z, a single phase body of ferrozirconium, Cr, and a single phase body of F are used, and the composition ratio of C1 is Weigh ferrozirconium, Cr, and F8 so that the weight ratio corresponds to the value of
and F are heated and melted in a melting furnace, and after the molten M is cooled to room temperature.

The above ferrozirconium (zirconium iron alloy) is an inexpensive zirconium alloy that is used industrially as a deoxidizer, denitrifier, and special field additive. Contains in alloy form.

The single-phase Cr mentioned above is electrolytic chromium (purity 99.2%).
above), and the above F. Electrolytic iron (purity of 99.9% or more) can be used as the single-phase material.

The value of the above C1 composition ratio X is 0.2 < x≦0.8
A range of x is desirable; when x≦0.2, initial activation becomes difficult, and when x>0.8, sufficient plateau characteristics cannot be obtained under practical temperature conditions.

As the melting furnace, a vacuum type high frequency induction melting furnace and a heat-resistant melting crucible of 1700° C. or higher, such as a magnesia-based or calcia-based melting crucible, can be used. Then, in the melting crucible, ferrozirconium crushed into small lumps, C fragmented into small pieces, and F8 single phase material fragmented into small pieces in the same manner as the single phase material can be alternately laminated in multiple layers. desirable.

After melting in the melting furnace, it is desirable to slowly cool the material to room temperature in the atmosphere.

(Function) In the method for manufacturing a hydrogen storage alloy according to the present invention, Zr
Since ferrozirconium, which has a lower melting point than a single phase material (melting point 1600 to 1700°C), is used, in this case, F,
→Dissolution progresses in the order of ferrozirconium-C1, and although it locally reaches the melting point of Cr, the overall melting point is about 170%.
It can be melted at a relatively low temperature of about 0-1750°C.

In addition, although ferrozirconium contains 75 to 80% Z, it is a compound with F, so it is similar to a Zr single phase (it has the property of being violently oxidized when heated). Therefore, when heated, it is difficult to be oxidized by oxygen contained in the oxide in the crucible material, and no impurities are generated.

(Effects of the Invention) According to the method for producing a hydrogen storage alloy according to the present invention, as explained above, ferrozirconium, which is much cheaper than pure Z, C, , and Fo are used as raw materials for the hydrogen storage alloy. As a result, it is possible to produce a hydrogen storage alloy at about ⅓ the cost of production using conventional methods.

The melting point of ferrozirconium is low, and ferrozirconium does not react with oxygen atoms in the crucible material to produce impurities, so hydrogen storage alloys can be mass-produced using magnesia-based crucibles and high-frequency induction melting furnaces. I can do it.

Since ferrozirconium is a stable compound, it does not require special care when handling or melting, and is easily crushed, making it suitable for mass production of hydrogen storage alloys.

(Examples) Hereinafter, examples of the method for manufacturing a hydrogen storage alloy according to the present invention and the hydrogen storage alloy manufactured by the method will be described with reference to the drawings.

First, a method for manufacturing a zirconium-based hydrogen storage alloy having a composition in the range of 0, 2 < x≦0.8, which is expressed by the characteristic formula Z, (C,, F,, □) 2, will be described.

In the first step, as raw materials for manufacturing the hydrogen storage alloy, in this example, ferrozirconium containing 78.2% Z, electrolytic iron with a purity of 99.9%, and 99.9% purity. Using 2% electrolytic chromium, the above ferrozirconium is 0.5 to 1.0a! In addition to pulverizing the electrolytic iron and electrolytic chromium into small lumps of about 100 ml, the electrolytic iron and electrolytic chromium were also finely divided into small lumps or plates.

The small lumps of ferrozirconium, electrolytic iron, and electrolytic chromium were weighed so that the weight ratio corresponded to the value of X in the above-mentioned formula.

In the second step, high frequency power 20KW, frequency 3
Using a vacuum-type high-frequency induction melting furnace rated at KHz and a maximum melting amount of 5 kg, ferrozirconium, iron,
Several layers of chromium were laminated alternately in such a way that they were easily dissolved as a whole when a current was induced, and a total amount of 3 kg was loaded. However, the crucible can be used as long as it has a heat resistance of 1700° C. or higher, and the crucible was not heat-treated in advance.

In the third step, in order to remove oxygen and nitrogen from the furnace tank of the melting furnace, the inside of the furnace tank was evacuated to 10-3 to 10-'torr, and then a high frequency power source was turned on.

The initial power settings at this time were a high frequency voltage of 150 cm and a direct current of 45 A.

In the fourth step, when the power is turned on to generate an induced current in the raw material and heat it, gas is generated from the raw material, so at this time, inert gas such as A or N2 is used to was replaced. In this case, the gas pressure of the inert gas is 0
．． The negative pressure was adjusted to 5 atmospheres. If necessary depending on the gas generation situation, it is desirable to evacuate the gas in the furnace vessel and refill it with inert gas.

In the fifth step, the melting of the raw materials started and the melting progressed, but at this time, the melting state, the supplied power, and the temperature of the molten metal were monitored while making sure not to boil. The molten metal was stirred so that the molten ferrozirconium, chromium, and zirconium were uniformly mixed. If stirring at this time is not sufficient, an alloy having a predetermined composition cannot be obtained.

The maximum power supplied during the above melting is a high frequency voltage of 300μ,
The induced current was 13OA.

In the sixth step, the molten metal was slowly cooled to room temperature while the inside of the furnace tank was maintained in an inert gas atmosphere.

In the second step, several layers of ferrozirconium, chromium, and iron were alternately laminated in the magnesia crucible, and by laminating them alternately in this way, subsequent dissolution can be promoted. That is, the 8 points of iron (1536℃) and the melting point of ferrozirconium (about 1600-1700℃)
is lower than the melting point of chromium (1875° C.), so when melting, iron first dissolves, then the surrounding ferrozirconium melts, followed by the surrounding chromium. During this melting, C, is heated locally by the induced current and at the same time is heated and melted by the surrounding molten metal, so the molten metal as a whole melts at a relatively low temperature of about 1700 to 1750°C. become.

In the above embodiment, the raw material in the crucible was heated and melted using a high-frequency induction melting furnace, but a melting furnace such as a plasma arc furnace or an electron beam furnace may also be used.

Next, the characteristics of the hydrogen storage alloy manufactured by the above manufacturing method will be explained.

Tl) Analysis, basic physical properties, etc. 1) The prototype alloy Z, (C, XF, I-X)2 is 0.
In the range of 2<X≦0.8, it exhibited an orthogonal crystal structure, and the basic structure was an MgZfi□ type of Laves phase. Its lattice constants are a=4.98~5.04, c
=8.14 to 8624 people, and the lattice constant increases as the chromium composition X increases. These are pure metal Z,,
Almost the same results as those produced using C,,F, as raw materials were obtained.

2) S, , M, , T contained in ferrozirconium
, etc. and the crucible material M9 were present in very small amounts in the alloy, and no influence on the hydrogen absorption/release properties was observed.

3) The hydrogen storage alloy itself produced as described above,
A comparison was made between the alloys that had been heat treated (annealed) at 1100°C for 15 hours and the hydrogen storage and release properties were almost the same, so there is no need to heat treat the hydrogen storage alloys produced using this manufacturing method. It turned out that.

4) Ferrozirconium contains approximately 1% Hf, and the above alloy contains Hf0.0 in atomic ratio in the indicated formula.
04 exists. It is thought that due to this influence, the hydrogen equilibrium pressure temperature for occlusion and desorption decreased compared to those manufactured using pure metal, and the flatness shape of the equilibrium pressure changed.

(2) Initial activation In order for the alloy to acquire the function of storing hydrogen, an initial activation process is necessary. This involves putting an appropriate amount of the hydrogen-absorbing association material pulverized into several pieces into a pressure-resistant container, evacuation of the container (~IQ-3 torr), and then leaving the container sealed with hydrogen gas at a pressure of about 30 atm. Hydrogen storage capacity was obtained by repeating this operation at room temperature. When the Cr composition ratio X is 0.4 or more, hydrogen is occluded by repeating several times, but when X is less than 0.4, this number of times increases and activation becomes somewhat difficult. Further, in the case of X≦0.2, hydrogen storage capacity cannot be easily obtained, and high pressure and temperature control are required.

(3) Hydrogen storage capacity Table 1 shows the hydrogen storage capacity of typical compositions in the practical temperature and pressure range. In the table, H/M represents the atomic ratio, which is given as the number of hydrogen atoms per mole of atoms of the alloy, and H2wt% represents the weight percent of hydrogen in the hydride of the alloy. From this table, it can be seen that it has excellent hydrogen storage capacity. With respect to this hydrogen storage capacity, the absolute amount of hydrogen storage decreases as the temperature rises for alloys with the same composition. Moreover, this performance was almost equivalent to that of an alloy made from pure metal.

(4) Hydrogen absorption/desorption equilibrium pressure Kerr composition - isothermal characteristics x
Isothermal occlusion for = 0.3.0.4.0.6
The release characteristic curves are shown in FIGS. 1, 2, and 3.

The horizontal axis is the atomic ratio (the number of hydrogen atoms per mole of alloy atoms)
The vertical axis gives the equilibrium pressure (atmospheric pressure) on a logarithmic scale. As shown in these figures, by appropriately changing the value of It is possible to control and adjust.

For x > 0.7, the width of the plateau decreases or disappears.

The above-mentioned plateau is a region where the pressure does not change much even when the atomic ratio increases, and has flatness in terms of pressure, and for practical purposes, it is necessary to have a certain width of the plateau.

In the figure, the upper curve shows occlusion and the lower curve shows release at each temperature.

(5) Hysteresis characteristics As shown in Figures 1 to 3, the larger the ratio of Cr to F8, that is, the larger have For x = 0.4~0.6, use temperature range 100~
At 200°C, hysteresis is small and suitable for heat pump system applications.

(6) Storage/desorption reaction rate The reaction rate of hydrogen storage/desorption changes depending on the equilibrium pressure and temperature, but this hydrogen storage alloy has an effective reaction rate in the practical pressure and temperature range. Occlusion at X=0.6
The release rates are shown in Figures 4 and 5, respectively. The horizontal axis represents the time (seconds) from the start of the reaction, and the vertical axis represents the pressure change corresponding to f: pressure change). In Figure 4, regarding the occlusion reaction, the sample container part Okg/cnl
(Occluded amount 0), dead volume part 10 kg/cni The release reaction shown in Figure 5 shows the reaction from the initial state of sample container part 1.
0kg/ci (storage amount H/M=1.8, weight%=0.9
%), dead volume Okg/co! represents the change from the initial state. As shown in the figure, for 80% and 90% of hydrogen absorption/release amount (reaction amount when equilibrium is reached), absorption takes 27 seconds and 68 seconds, and release takes 53 seconds.
A value of 125 seconds was obtained.

(7) Thermodynamic data Calculating the standard enthalpy change ΔHO1 standard entropy change ΔS0 from Vupunt-Hopf's constant pressure equilibrium equation % formula % (0) x = o, 2: ΔH0 = -25KJ/mole, ΔS'
= −94J/deg-molex=o, 7:ΔH0=
-40KJ/mole, ΔS' = -110J/de
The g-mole value was obtained, and it was shown that the hydrogen storage alloy has performance equivalent to that of other hydrogen storage alloys and is suitable for utilizing waste heat.

[Brief Description of the Drawings] The drawings show the characteristics of the hydrogen storage alloy manufactured by the manufacturing method of the present invention, and Figures 1 to 3 are occlusion and desorption characteristic curves at constant temperature, respectively. is a characteristic diagram of the hydrogen absorption rate, and FIG. 5 is a characteristic diagram of the hydrogen release rate. Figure 4 (kq/d) time

Claims (1)

[Claims] (1) In producing a hydrogen storage alloy expressed by the formula Zr(C_r_xF_e_1_-_x)_2, ferrozirconium, iron, and chromium are weighed so that the weight ratio corresponds to the value of x above, The above weighed ferrozirconium, iron and chromium are heated and melted in a melting furnace,
A method for producing a hydrogen storage alloy, which comprises cooling to room temperature after melting.