JP2896718B2 - Method for producing hydrogen storage alloy powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage alloy powder, and more particularly to a hydrogen storage alloy powder obtained by pulverizing an ingot having a columnar structure of 80% or more of a cast structure by controlling casting conditions. And a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, various alloy compositions of raw materials have been studied as a measure for improving the hydrogen storage ability of a hydrogen storage alloy. However, hydrogen storage capacity is not sufficient only in terms of alloy composition, and further improvement in performance is expected for practical use.

On the other hand, the following method has been proposed as a conventional method for producing a hydrogen storage alloy powder. That is,
A method of producing a molten metal of a hydrogen storage alloy using an arc melting furnace or a high-frequency melting furnace, pouring the molten metal into a mold, and allowing it to cool naturally.
Alternatively, a method of water-cooling in a copper mold to prepare a hydrogen storage alloy, coarsely pulverizing the alloy lump, and then finely pulverizing in a ball mill or the like to obtain a powder. However,
With such a method, a sufficiently satisfactory hydrogen storage capacity cannot be obtained.

[0004] As another method, a step of cooling a molten metal by a liquid quenching method to produce a flake or a ribbon, a step of heat-treating the same in an inert gas or in a vacuum, and pulverizing the flake or a ribbon There is a method of obtaining a hydrogen storage alloy powder by the step of performing. This method has a problem that not only is the process complicated, but also the flakes and ribbons are bulky, have poor handling properties, and are not suitable for mass production.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made to solve these problems. The present invention improves the hydrogen absorbing ability and the pulverizability, simplifies the manufacturing process, and particularly reduces the negative electrode of a nickel-hydrogen battery. An object of the present invention is to provide an ingot for a hydrogen-absorbing alloy powder which reduces the internal pressure rise when used in a steel sheet, and a method for producing the alloy powder.

[0006]

The above object of the present invention is attained by the following manufacturing method.

That is, in the method for producing a hydrogen storage alloy powder according to the present invention, the hydrogen storage alloy powder raw material is melted, the casting temperature is set to a temperature higher than its melting point by at least 250 ° C.
The casting is performed using a water-cooled mold under the conditions of 15 kg / sec / m ² (where the area is the total cooling area of the mold) and the space between the mold surfaces is 20 to 100 mm, and the obtained ingot is pulverized.

[0008] As the hydrogen storage alloy powder raw material used in the present invention, simple metals and alloys having hydrogen storage performance can be used and are not particularly limited. AB ₅ is a preferred alloy.
Alloy mainly composed of type crystals (however, A is a rare earth metal or misch metal (Mm), B is nickel, cobalt,
At least one selected from iron, manganese, aluminum, copper, silicon, titanium, molybdenum, and vanadium)
Is mentioned. In this alloy composition, A component is 30 to
It is desirable to contain 35% by weight, and it is more preferable that at least nickel is contained in the B component. As a specific alloy composition, for example, MmNi _{3.55
Co 0.75 Mn 0.4 Al 0.3, MmNi} 3.2 Co 1 .0 Mn 0.6
Al _{0.2 and the} like.

Next, the hydrogen storage alloy powder raw material is melted, and its casting temperature must be at least 250 ° C. higher than its melting point. Here, the melting point refers to a temperature at which the solid metal starts melting. Below this temperature, nucleation on the mold wall surface is intense, and the resulting ingot tends to have an equiaxed structure. The upper limit of the casting temperature is not particularly limited, but is preferably 2000 ° C. or lower. If the temperature exceeds 2000 ° C., the melting furnace and the mold require high heat resistance, which is inferior in economy.
The melting furnace used here includes a high-frequency melting furnace and the like, and the atmosphere is preferably an inert gas atmosphere such as an argon gas atmosphere.

The casting speed in this casting is 1 to 15 kg /
Seconds / m ² . However, the area here is the total cooling area of the mold. If the casting speed exceeds 15 kg / sec / m ² , the molten metal moves violently and tends to have an equiaxed structure. Also, 1K
If it is less than g / sec / m ² , the heat capacity is small, so that nucleation on the mold wall surface is intense, and the obtained ingot is likely to have an equiaxed structure.

[0011] Furthermore, the mold spacing, that is, the thickness of the obtained ingot needs to be 20 to 100 mm. If the mold spacing exceeds 100 mm, the heat transfer of the ingot obtained is limited, and the growth of the columnar structure cannot be maintained continuously. On the other hand, if the thickness is less than 20 mm, the operation is difficult to perform, and the cooling effect is strong, a chill structure is generated, and it is difficult to obtain a columnar structure.

The casting is performed in a water-cooled mold, preferably a copper-made water-cooled mold. When casting is performed using a cast iron spontaneous cooling mold or spontaneous cooling in a melting crucible, a columnar structure is hardly obtained. The preferred amount of water in the water-cooled mold is 100 to 3000 liter / min / m ² . FIGS. 1 and 2 show a plan view and a cross-sectional view of an example of such a metal mold. In the figure, 1 is a mold cooling surface, 2
Is a mold side surface, 3 is a mold bottom portion, 4 is a cooling water pipe, d is an interval between mold surfaces, and FIG. 2 is a cross-sectional view taken along a line ab in FIG.

The thus obtained ingot for a hydrogen storage alloy powder according to the present invention has a columnar structure in which at least 80% of the cast structure is a columnar structure. FIG. 3 is a schematic sectional view of this ingot. In the figure, A indicates a chill structure, and B indicates a columnar structure. An ingot having such a structure is obtained by facing two ingots as shown in FIGS.
By casting in a metal water-cooled mold whose surface is cooled, solidification proceeds from each surface to the inside and in a direction perpendicular to the mold surface, and columnar tissue bands grown from each cooled surface collide. By the completion of coagulation,
The generation of the equiaxed structure is suppressed, and an alloy ingot having a columnar structure hydrogen storage capacity of 80% or more can be obtained. In addition, the ratio of the columnar structure in the ingot is obtained by vertically dividing the center of the cast ingot, and calculating the ratio of the columnar structure to the cross-sectional area by using trace graph paper.

On the other hand, in the prior art, only an ingot having a structure as shown in FIG. 4 can be obtained. In the drawing, reference numerals indicate the same components as those in FIG. 3, and C is an equiaxed structure. The reason for this is that when a molten metal is cast into a mold as in the past, generally, the metal in contact with the mold surface is quenched, first forming a chill layer, and then conducting heat to the mold. A columnar structure is formed toward the inside in a direction perpendicular to the mold surface.However, when the solidification is directed inward and the heat conduction gradually becomes less directional, the solidified structure becomes an equiaxial structure having no direction. As a result, solidification is completed, and a chill structure, a columnar structure, and an equiaxial structure are formed as shown in FIG.

The thus obtained alloy ingot having a columnar structure of 80% or more is either crushed as it is or heat-treated in a vacuum or argon gas atmosphere at a temperature of 900 to 1100 ° C. for 4 to 8 hours. Smash. The pulverization is desirably performed in three stages. In the first stage, the powder is coarsely pulverized using a single-tickle crusher into a powder having a particle size of 1 to 10 mm. In the second stage, this powder is formed into a powder having a particle size of about 30 mesh below a sieve using a stamp mill. A powder having this particle size range is used as a hydrogen storage measurement sample. Further, as a third step, this powder is finely ground to an average of about 20 μm using a ball mill or the like. The powder thus pulverized is suitably used as a negative electrode of a nickel-hydrogen battery.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

Example 1 The composition of the alloy ingot was MmNi _3.55 Co _0.75 Mn _0.4
The hydrogen storage alloy powder raw material prepared to be Al _0.3 was melted in a high-frequency melting furnace in an argon gas atmosphere,
FIG. 1 described above at 500 ° C. (temperature higher than the melting point by 400 ° C.)
Into a copper water-cooled mold shown in Table 2
m, and an ingot was cast at a casting speed of 3 kg / sec / m ² . The ingot structure obtained in this way is 95%
Was a columnar structure. In addition, the ratio of the columnar structure in the ingot casting structure, the center of the casting ingot is divided vertically,
The ratio of the columnar structure to the cross-sectional area was determined using trace graph paper.

Next, the obtained ingot is subjected to a heat treatment at 1050 ° C. for 6 hours in an argon gas atmosphere, and then 100 g is collected from roughly crushed to about 1 to 10 mm with a crusher, and is collected using a stamp mill. The mixture was pulverized for 10 minutes and sieved with a 32 mesh sieve to obtain a hydrogen storage ability measurement sample, and the hydrogen storage ability was measured by the following method. Table 1 shows the results. As a result, as shown in Table 1, the equilibrium pressure was 5 ° C., 0 ° C., 1 atm conversion, and the hydrogen storage amount was 132 cc / g.

At this time, the ratio under the sieve, which is the pulverization yield, was 86.3% as shown in Table 1, which was used as a measure of the pulverizability.

On the other hand, the powder under the 32 mesh sieve was pulverized into an average powder of 20 μm using a ball mill to obtain a sample for a nickel-hydrogen battery negative electrode. A test cell was prepared by the method shown below, and the internal pressure of the battery was indicated by an index with the internal pressure of Comparative Example 6 being a conventional method being 100, and the results are shown in Table 1.

<Hydrogen storage capacity> Using a sample under a 32 mesh sieve, about 20 g of this measurement sample was accurately weighed,
Using a Siebeltz apparatus under the conditions of 3 ° C and measurement temperature of 45 ° C,
The hydrogen storage / release characteristics of the alloy powder as the measurement sample were measured according to a conventional method, and a PCT curve was created. H / M at an equilibrium pressure of 5 atm was determined from the PCT curve, and the hydrogen storage amount was calculated by the following equation.

Hydrogen storage amount (cc / g) = [(H / M)
× 22.4 × 10 ³ × 6] / (2 × alloy molecular weight) [where, H is the number of moles of occluded hydrogen atoms, M is the number of moles of alloy] <Battery internal pressure> Average obtained by grinding with a ball mill Using a 20 μm powder, 100 parts by weight of this alloy powder and 10 parts by weight of polytetrafluoroethylene were kneaded, and pressed together with a nickel mesh current collector into a pellet having a diameter of 20 mm and a thickness of 0.8 mm to form an electrode. And This electrode was placed in the test cell shown in FIG. 5, and charged and discharged at 0.1 C for 16 hours using a nickel electrode as a counter electrode using a 30% by weight aqueous solution of KOH as an electrolyte, and discharged at 0.2 C for 100 cycles. Thereafter, the internal pressure of the battery was checked, and the internal pressure of Comparative Example 6, which is a conventional method, was set to 100 and indicated by an index. In FIG. 5, 5 indicates an alloy electrode, 6 indicates a nickel electrode, 7 indicates a pressure gauge, and 8 indicates a gas release valve.

Examples 2 to 10 and Comparative Examples 1 to 5 An ingot was obtained in the same manner as in Example 1 except that the alloy composition, the casting temperature, the distance between the mold surfaces, and the casting speed were changed as shown in Table 1. Of the cast structure was measured, and the results are shown in Table 1.

Further, this ingot was pulverized in the same manner as in Example 1, and the pulverizability, hydrogen storage capacity and internal pressure of the battery were measured.
The results are shown in Table 1.

Comparative Example 6 An ingot was obtained in the same manner as in Example 1 except that a natural cooling mold made of cast iron was used instead of the water-cooled mold made of copper, and the ratio of the columnar structure in the cast structure of the ingot was measured. The results are shown in Table 1.

Further, this ingot was pulverized in the same manner as in Example 1, and the pulverizability, hydrogen storage capacity and battery internal pressure were measured.
The results are shown in Table 1.

Comparative Example 7 The molten metal of Example 1 was directly cooled in a crucible to obtain an ingot. The ratio of the columnar structure in the ingot structure was measured, and the results are shown in Table 1.

Further, this ingot was pulverized in the same manner as in Example 1, and the pulverizability, hydrogen storage capacity and battery internal pressure were measured.
The results are shown in Table 1.

[0029]

[Table 1] As shown in the results in Table 1, Examples 1 to 10 had a columnar structure of 80% or more, were excellent in pulverizability and hydrogen absorbing ability, and were excellent in nickel-hydrogen as compared with Comparative Examples 1 to 7. When used for the negative electrode of a battery, the internal pressure was small.

[0030]

By using the hydrogen storage alloy powder ingot of the present invention, the hydrogen storage capacity of the alloy of 10 cm square is superior to that of the alloy containing a large amount of equiaxed structure by about 25 liters compared to the alloy containing a large amount of equiaxed structure. In addition, when converted into electrochemical energy per unit weight, a capacity difference of about 10 mAh / g is obtained. Further, by using the negative electrode of a nickel-hydrogen battery, the internal pressure can be reduced by 30% or more as compared with the conventional case.

Further, the production method of the present invention improves the pulverizability and makes it possible to obtain a hydrogen storage alloy powder by a simple production process.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a metallic water-cooled mold used in the present invention.

FIG. 2 is a sectional view taken along the line ab of FIG. 1;

FIG. 3 is a schematic sectional view of an ingot of the hydrogen storage alloy powder obtained according to the present invention.

FIG. 4 is a schematic sectional view of an ingot obtained by conventional casting.

FIG. 5 is a cross-sectional view of a test cell used for a charge / discharge test and internal pressure measurement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold cooling surface 2 Mold side surface 3 Mold bottom 4 Cooling water pipe d Mold surface spacing 5 Alloy electrode 6 Nickel electrode 7 Pressure gauge 8 Gas release valve A chill organization B columnar organization C equiaxed organization

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification symbol FI B22D 27/20 B22D 27/20 Z C22C 1/00 C22C 1/00 N H01M 4/24 H01M 4/24 J (58) Field (Int.Cl. ⁶ , DB name) B22F 9/04 B22D 7/00 B22D 7/06 B22D 27/20 C22C 1/00 H01M 4/24

Claims (3)

(57) [Claims] 1. A method for dissolving a hydrogen storage alloy powder raw material, setting the casting temperature at 400 ° C. or more higher than its melting point, at a casting speed of 1 to 15 kg / sec / m ² (where the area is the total cooling area of the mold), A method for producing a hydrogen storage alloy powder, comprising: casting an ingot having a columnar structure of 80% or more of a cast structure using a water-cooled mold under the condition of a surface spacing of 20 to 100 mm, and pulverizing the ingot. 2. The method according to claim 1, wherein the casting temperature is 400 ° C. or higher and lower than 800 ° C. higher than the melting point.
3. The method for producing a hydrogen storage alloy powder according to item 1. 3. The method for producing a hydrogen storage alloy powder according to claim 1, which is used for a negative electrode of a nickel-hydrogen battery.