JP2001283842A - Zinc alloy powder for alkaline battery and method for producing the same - Google Patents

Abstract

(57) [Problem] To produce a zinc alloy powder for an alkaline battery with suppressed gas generation, which has been achieved by regulating impurities in the zinc alloy powder to a very small amount. The use of a very small amount increases the cost and fails to provide an inexpensive zinc alloy powder. SOLUTION: Even if specific impurities such as iron, nickel and chromium are mixed to some extent, it is possible to improve the zinc alloy composition and control the ratio of the supply amount of the molten zinc alloy and the supply amount of the atomized gas per unit time during atomization. It is possible to provide an alkaline battery alloy powder in which hydrogen gas generation is significantly suppressed. In other words, bismuth and indium as additive metals
On the basis of 0.1 to 1%, the same amount of aluminum, magnesium or group 13 (IIIB) element of the periodic table is specified to improve the alloy composition, and the metal / gas ratio is set to 1%.
５5 kg / Nm ³ .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc alloy powder for an alkaline battery in which hydrogen gas generation is suppressed and battery characteristics are improved, and a method for producing the same. Further, a zinc alloy powder containing Al, Mg or a group 13 (IIIB) element and having a small amount of hydrogen gas generated by defining the ratio of the supply amount of the molten zinc per unit time and the supply amount of the atomized gas during atomization. Is intended to be manufactured. Group 13 (IIIB) elements that can be used for this purpose include Sc, Y, and lanthanide series elements La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb and Lu and the actinide series Ac, Th, Pa, U, Np, Pu,
Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr are preferred, and Y and La are particularly preferred.

[0002]

2. Description of the Related Art Conventionally, zinc alloy powder for an alkaline battery used as a negative electrode of an alkaline battery in which an electrolytic solution is an aqueous alkaline solution such as caustic potash is produced by using industrially obtained zinc such as electric zinc as a raw material. It is manufactured by spraying molten metal alloyed with a small amount of additive metal by the atomizing method.

[0003] The zinc alloy powder thus obtained contains chromium, manganese, iron, cobalt, nickel, copper, silver, cadmium, antimony and the like as trace impurities detected in addition to the metal added as an alloying component. It is well known that all of these promote zinc corrosion and significantly increase hydrogen gas generation. Therefore, for example, Japanese Patent Publication No. 7-54705 sets the iron content of zinc powder to 1 ppm or less, and JP-A-3-56637 sets nickel, chromium and antimony to 1 ppm or less and iron to 20 ppm.
The following is described in JP-A-9-92278,
It is disclosed that the chromium content is 0.5 ppm or less.

However, in order to minimize impurities by these methods, it is necessary to use a high-purity raw material zinc, strictly control the atmosphere of the production line, or to remove the part in contact with zinc powder with Teflon. (Registered trademark) or the like. Therefore, the zinc powder to be produced is also expensive, and a method for producing zinc powder at low cost has been desired.

[0005]

As described above, in order to produce a zinc alloy powder for an alkaline battery in which gas generation is suppressed, it is effective to regulate impurities in the zinc alloy powder to a very small amount. However, regulating impurities to a very small amount leads to an increase in cost, and there is a disadvantage that zinc alloy powder for alkaline batteries cannot be provided at low cost.

[0006] The impurities are mixed into the zinc alloy powder by the following route in addition to the mixing from the raw materials to be used. First, zinc alloy powder is usually produced by the atomization method. This is to dissolve zinc as a raw material, add a predetermined alloying metal, flow down the molten metal in a fine stream, and inject high-pressure gas into it. This is a method of processing into a powder. The zinc alloy powder for an alkaline battery is a product obtained by classifying the atomized zinc alloy powder to a desired particle size and then removing iron mixed from a production line by a magnetic separator. In this manufacturing method, in the step of dissolving the raw materials,
Pollution due to contamination of iron remaining in the melting furnace and contamination of iron, nickel and chromium from the material of the dross processing machine occur during dross treatment accompanying the dissolution of raw material zinc. Further, the fine molten droplets generated in the atomizing step collide with the cooling chamber. However, since the material of the cooling chamber is usually stainless steel, iron, nickel, chromium and the like are mixed in the zinc powder. Therefore, zinc powder produced by the usual method contains 1-3 ppm of iron, nickel,
Since about 1 ppm of chromium is contained, it has been difficult to stably and inexpensively produce a zinc alloy powder having sufficiently reduced gas generation, which can be used in an alkaline battery without the use of calomel.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks. The object of the present invention is to improve the alloy composition and to supply the molten zinc per unit time at the time of atomization, even if specific impurities are mixed to some extent. Another object of the present invention is to provide a zinc alloy powder for an alkaline battery in which the generation of hydrogen gas is significantly suppressed by controlling the ratio of the amount of supplied hydrogen and the amount of atomized gas.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies for this purpose, and have found that a specific additive metal is added to a molten zinc and a ratio of a molten metal supply amount to an atomized gas supply amount per unit time. Is set to 1 to 5 kg / Nm ³ , it has been found that the added metal has an effect of effectively reducing gas generation, and even when the content of impurities in the zinc alloy powder is high, the amount of generated hydrogen gas is large. And reached the present invention. That is, by using a zinc alloy melt having a specific composition and atomizing while controlling the ratio of the supply amount of the zinc melt per unit time and the supply amount of the gas used for spraying to a value within an appropriate range, the conventional method is used. It was confirmed that a zinc alloy powder with a reduced amount of hydrogen gas generated can be produced even when a zinc alloy containing many impurities, which are considered to be impossible, is used as a raw material. As a result, iron as an impurity
ppm or more of zinc alloys, for example, 2 to 5 which were conventionally considered to be unusable as zinc alloys for alkaline batteries
The use of a zinc alloy containing 1 ppm of iron or a zinc alloy containing at least one of nickel and chromium in an amount exceeding 1 ppm in addition to the above as a raw material for spraying can also reduce the amount of hydrogen gas generated, for example, to 25 μL / g · d.
It is possible to produce a zinc alloy powder sufficiently suppressed to ay or less and suitable for an alkaline battery without any problem.

That is, the present invention firstly provides 0.001 to 0.1% by weight of bismuth and 0.001% to indium.
A zinc alloy powder for an alkaline battery, comprising 0.1% by weight, with the balance being zinc and unavoidable impurities;
Second, the zinc alloy powder for an alkaline battery according to the first aspect, wherein the zinc alloy powder contains 0.001 to 0.1% by weight of aluminum;
1% by weight or 1% by weight.
4. The zinc alloy powder for an alkaline battery according to any one of the first to third aspects, wherein the zinc alloy powder further comprises 0.001 to 0.1% by weight of a Group 13 (IIIB) element of the periodic table. Fifth, the zinc alloy powder for an alkaline battery according to the fourth aspect, wherein the group 13 (IIIB) element is yttrium or lanthanum;
7. The zinc alloy powder for an alkaline battery according to any one of the first to fifth aspects, wherein the zinc alloy powder contains at least one of iron or nickel or chromium in an amount exceeding 1 ppm, or both iron and nickel or chromium; Is 25μ
The zinc alloy powder for an alkaline battery according to any one of the first to sixth aspects, wherein L / (g · day) or less; eighthly, 0.001 to 0.1% by weight of bismuth and 0.00% of indium.
When atomizing a molten zinc alloy containing 1 to 0.1% by weight, with the balance being zinc and unavoidable impurities, by atomizing into a zinc alloy powder, the ratio between the supply amount of the molten zinc alloy and the supplied amount of the atomized gas. There, 1-5 kg / Nm ³ manufacturing method of the zinc alloy powder for alkaline batteries, which is a; ninth, the zinc alloy is of bismuth, in addition to 0.001 wt% aluminum indium Tenth, the tenth aspect is that the zinc alloy contains 0.001 to 0. 0 of magnesium in addition to bismuth and indium.
The method for producing a zinc alloy powder for an alkaline battery according to the eighth or ninth aspect containing 1% by weight; eleventh, the zinc alloy contains 0.001 to 13 (IIIB) group elements of the periodic table in addition to bismuth and indium. 11. A method for producing a zinc alloy powder for an alkaline battery according to any one of the eighth to tenth aspects, wherein the zinc alloy powder contains 0.1% by weight.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the addition of each alloy element in the production of a zinc alloy powder for an alkaline battery according to the present invention are as follows. Hydrogen gas generation by the reaction between zinc and an alkaline electrolyte represented by a KOH aqueous solution is caused by electrolysis of water in the electrolyte on a local battery existing on the surface of zinc particles as in the following reaction. It is assumed. ^{_{2H 2 O + 2e - → 2OH}} - + H 2 ↑

This local battery is generated by a potential difference between zinc and impurities in zinc. When a local battery is formed with an element having a low hydrogen overvoltage such as iron, nickel, and chromium, gas is generated on the impurity element, The greater the content of these impurities, the greater the amount of gas generated. Therefore, if an element having a higher potential than the impurities and having a higher hydrogen overvoltage is added to zinc, gas generation due to the impurities can be suppressed. Bismuth and indium are added to suppress this gas generation, but since these elements have a relatively noble potential and a high hydrogen overpotential of themselves, zinc is added to zinc as described above. It is presumed that the hydrogen overvoltage is increased and the effect of suppressing gas generation is exhibited.

Further, since aluminum, magnesium and group 13 (IIIB) elements themselves have a low hydrogen overpotential, it is presumed that suppression of gas generation is caused by a different effect from bismuth and indium described above. Here, the local battery that causes hydrogen gas generation is also formed of zinc oxide in addition to the above-described impurities, which is said to generate gas. By suppressing generation, gas generation can be reduced.

The zinc oxide is mainly generated by the reaction between the molten zinc and the atomizing gas. Therefore, a method of suppressing the formation of oxides by using an atomizing gas as an inert gas is conceivable. However, when the atomizing gas is used as an inert gas, the generation of hydrogen gas can be reduced, but the discharge performance deteriorates. This is because when atomized with an inert gas, the zinc particle shape becomes spherical due to surface tension in the process of solidification of the fine droplets. It is believed that when the is processed into a gel, the number of contacts between zinc particles and between the zinc particles and the current collecting rod is reduced, and the internal resistance of the battery is increased, so that the discharge performance is deteriorated. Therefore, as an atomizing gas, a gas containing oxygen is used, and the surface of the zinc melt is oxidized at the same time as the molten zinc is dispersed in the fine molten droplets, and while maintaining the shape by forming an oxide film, the molten droplets are solidified. A method of forming an irregular shape such as a needle shape or a teardrop shape is generally used. Therefore, an oxide is present in the zinc particles. Therefore, by adding an element that is more easily bonded to oxygen than zinc in order to suppress the formation of zinc oxide, the formation of zinc oxide is suppressed by bonding oxygen in the zinc particles to these added elements. As a result, it is expected that the hydrogen overvoltage of zinc is increased and the generation of hydrogen gas is reduced. Aluminum, magnesium and 13 (IIIB)
It is presumed that the group-group element is more likely to bond with oxygen than zinc, and thus effectively suppresses the formation of zinc oxide generated during atomization, thereby suppressing the generation of hydrogen gas.

However, it has been found that even if an element having the above-mentioned action is added to zinc, the effect may not be sufficiently exhibited. Then, the present inventors examined the control conditions in the atomizing process in detail, and found that the ratio of the molten metal supply amount and the atomized gas supply amount was set to a predetermined value, so that the effect of the added metal was more effectively exerted. I knew it could be done. The reason for this has not been clarified yet, but is presumed to be roughly as follows. When the ratio between the supply amount of the molten metal and the supply amount of the atomizing gas is small, the cooling rate of the droplet is high,
Because of the rapid cooling, the element added for suppressing gas generation is cooled while being uniformly dispersed throughout the particles. On the other hand, when the ratio between the supply amount of the molten metal and the supply amount of the atomizing gas is large, the cooling rate is relatively low. Is concentrated. Al, 13 (III
When the cooling rate is low and the temperature of the molten droplet is high, elements that easily bond to oxygen in the atomizing gas such as group B) elements are concentrated near the particle surface due to the progress of the oxidation reaction. In addition,
These trivalent elements increase the conductivity of zinc oxide by forming a solid solution in zinc oxide particles formed on the surface of zinc particles, thereby increasing the hydrogen overvoltage of zinc oxide generated on the surface of zinc particles. Can be. Due to these facts, each added metal is concentrated on the surface of the zinc particles to increase the hydrogen overvoltage on the surface of the zinc particles.Even with the same amount of addition, compared to the case where the value of the ratio is not within an appropriate range, iron, It is considered possible to reduce the adverse effects of impurities such as nickel and chromium. In addition, the reason why the ratio of the supply amount of the molten zinc to the supply amount of the atomizing gas is set to 1 to 5 kg / Nm ³ is that if the amount is less than 1 kg / Nm ³ , the surface concentration of the above-described additional element is not sufficiently performed.
5 kg / N
Beyond m ^3, although the additive element is concentrated to near the surface, the dispersion of the fine Torushizuku is not sufficiently, can not be obtained a predetermined particle size as used in the zinc alloy powder for alkaline batteries Because. Hereinafter, the present invention will be described in detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[0015]

Examples 1 to 15 Zinc having a purity of 99.995% or more was melted at about 500 ° C., and a predetermined amount of aluminum, bismuth, indium, magnesium and a 13 (IIIB) group element shown in Table 1 were added thereto. Yttrium and lanthanum were added to prepare a molten zinc alloy. Using a ceramic nozzle, the molten metal is dropped in a rivulet form, and compressed air or nitrogen gas to which oxygen has been added is jetted onto the molten metal.
A zinc alloy powder was obtained. The obtained zinc alloy powder was # 35-
After classifying to a particle size of 200 mesh, the iron content and gas generation were determined. Measurement of gas generation amount is as follows: After a predetermined amount of zinc alloy powder is added, a 40% KOH solution is added, a test tube filled with liquid paraffin and sealed with a silicone rubber stopper is kept in a thermostat at 60 ° C. for a predetermined time. The gas generation rate was determined by reading the scale of the massage after the passage. As shown in Table 1, even when the iron content is about 2 to 5 ppm, it has a specific composition and a specific molten metal-gas supply rate ratio (the amount of molten metal supplied per unit time per unit time). In all of Examples 1 to 15 in which the ratio of the amount of atomized gas supplied was 25 μL / (g · da) where the amount of generated gas was an allowable limit.
less than y).

[0016]

[Table 1]

[0017]

Comparative Examples 1 to 8 In Comparative Examples 1 to 3, in which only the molten metal-gas supply speed ratio was changed, the gas generation amount exceeded the allowable limit. In Comparative Examples 4 to 8, the molten metal-gas supply rate ratio was within the range, but the added components were all outside the range, and the gas generation amount exceeded the allowable limit in all cases.

[0018]

As described above, according to the method of the present invention, the content of iron, which is a typical impurity of zinc powder, is reduced to a specific alloy composition range without being reduced to an extremely small amount. By setting the molten metal-gas supply rate ratio at the time of atomization to a specific range, a zinc alloy powder for an alkaline battery which can suppress generation of hydrogen gas and improve battery characteristics can be easily obtained.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hikoichi Harikai 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Yasuyuki Koyama 1-8-2 Marunouchi, Chiyoda-ku, Tokyo No. Dowa Mining Co., Ltd. (72) Inventor Fumihiro Sato 1-8-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4K017 AA04 BA01 BB01 BB03 BB04 BB06 BB12 BB18 DA09 EB07 FA09 4K018 BA10 BD10 KA38 5H050 AA15 BA04 CA05 CB13 DA09 EA02 EA03 EA07 FA17 HA00 HA01

Claims (11)

[Claims] 1. Bismuth in an amount of 0.001 to 0.1% by weight,
A zinc alloy powder for an alkaline battery, comprising 0.001 to 0.1% by weight of indium, with the balance being zinc and unavoidable impurities. 2. The zinc alloy powder for an alkaline battery according to claim 1, comprising 0.001 to 0.1% by weight of aluminum. 3. The zinc alloy powder for an alkaline battery according to claim 1, comprising 0.001 to 0.1% by weight of magnesium. 4. An element of group 13 (IIIB) of the periodic table having a content of 0.001
4 to 0.1% by weight.
The zinc alloy powder for an alkaline battery according to any one of the above. 5. The zinc alloy powder for an alkaline battery according to claim 4, wherein the group 13 (IIIB) element is yttrium or lanthanum. 6. The method according to claim 1, which comprises from 2 to 5 ppm of iron or at least one of nickel and chromium in an amount exceeding 1 ppm or both said iron and nickel or chromium.
6. The zinc alloy powder for an alkaline battery according to any one of items 1 to 5. 7. The gas generation amount is 25 μL / (g · day).
The zinc alloy powder for an alkaline battery according to any one of claims 1 to 6, which is: 8. Bismuth in an amount of 0.001 to 0.1% by weight,
When the molten zinc alloy containing 0.001 to 0.1% by weight of indium and the remainder consisting of zinc and unavoidable impurities is atomized by an atomizing method into a zinc alloy powder, the supply amount of the molten zinc alloy and the supply of the atomized gas The ratio with the amount is 1-5
kg / Nm ^{3. A} method for producing a zinc alloy powder for an alkaline battery. 9. The method according to claim 8, wherein the zinc alloy contains 0.001 to 0.1% by weight of aluminum in addition to bismuth and indium. 10. The method for producing a zinc alloy powder for an alkaline battery according to claim 8, wherein the zinc alloy contains 0.001 to 0.1% by weight of magnesium in addition to bismuth and indium. 11. The zinc alloy contains 0.001 to 0.1 of a Group 13 (IIIB) element of the periodic table in addition to bismuth and indium.
The method for producing a zinc alloy powder for an alkaline battery according to any one of claims 8 to 10, wherein the method further comprises a percentage by weight.