Zinc alloy powder for alkaline cell and method for producing same

The present invention relates to a zinc alloy powder for alkaline batteries and a method for producing the same, and more particularly to a zinc alloy powder used as a negative electrode material for a battery such as an alkaline dry battery and a method for producing the same.

Conventionally, zinc powder having a high hydrogen overvoltage and being relatively inexpensive has been used as a negative electrode material for batteries such as alkaline batteries. However, when only zinc is used as the negative electrode material of the battery, a large amount of hydrogen gas is generated when the battery is used, so that there is a problem that the electrolytic solution in the battery leaks.

In order to solve this problem, zinc used as a negative electrode agent for batteries has been amalgamized with mercury having a high hydrogen overvoltage for many years. However, in this method, there is a problem of pollution caused by mercury when disposing of waste dry batteries, so that it has been required to develop a zinc powder that does not use mercury, that is, a zinc powder that is mercury-free.

Such anhydrous zinc powder is alloyed with elements such as bismuth, aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin, and lead, which have the highest hydrogen overvoltage next to mercury and have an inhibitory effect. Zinc alloy powder is used. Further, a method of stabilizing crystal grains in the zinc alloy powder by heat-treating the zinc alloy powder (see, for example, Patent Document 1 and Patent Document 2) and efficiency of bismuth and indium on the surface of the zinc alloy powder. A well-coated method (see, for example, Patent Document 3) has also been proposed.

However, in the methods described in Patent Documents 1 to 3 above, the amount of gas generated before discharging the battery can be suppressed by increasing the amount of bismuth or the like used as an inhibitor, but the amount of gas generated after discharging is increased. There was a problem of increasing. That is, in order to reduce the amount of gas generated before discharging the battery, it is effective to increase the amount of bismuth or the like added, while in order to reduce the amount of gas generated after discharging, bismuth or the like is used. Since it is effective to reduce the amount of gas added, there is a problem that it is not possible to reduce the amount of gas generated before and after the discharge at the same time.

In order to solve this problem, a method has been proposed in which a zinc alloy powder to which bismuth or the like is added as an inhibitor is heat-treated at a temperature of 150 to 250 ° C. for 2 hours or more in an inert gas atmosphere having an oxygen concentration of less than 100 ppm. (See, for example, Patent Document 4).

<patcit num="1"><text>Japanese Patent No. 2932285 (page 2)</text></patcit><patcit num="2"><text>Gazette 7-123043 (Paragraph No. 0005-0007)</text></patcit><patcit num="3"><text>Japanese Patent Application Laid-Open No. 2000-113883 (paragraph number 0007-0014)</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2001-273893 (paragraph number 0011-0013)</text></patcit>

<p> However, in the method described in Patent Document 4 above, since it is necessary to heat-treat the zinc alloy powder at a temperature of 150 to 250 ° C. for 2 hours or more, a long-time heat treatment is required, and hydrogen before discharging is required. It may not be possible to reduce the amount of gas generated sufficiently.</p><p> Therefore, in view of such conventional problems, the present invention provides a zinc alloy powder for alkaline batteries that can reduce the amount of hydrogen gas generated before and after discharge to prevent leakage of the electrolytic solution in the battery. An object of the present invention is to provide a zinc alloy powder for an alkaline battery and a method for producing the same, which can be produced by a short-time heat treatment.</p>

<p> As a result of diligent research to solve the above problems, the present inventors have reduced the amount of bismuth added to the zinc powder and heat-treated the battery at a temperature higher than 250 ° C. In either case, they have found that a zinc alloy powder for an alkaline battery with a small amount of hydrogen gas generated can be produced by a short-time heat treatment, and have completed the present invention.</p><p> That is, in the method for producing a zinc alloy powder for an alkaline battery according to the present invention, 0.0001 at least one element selected from the group consisting of aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin and lead. Heat-treating a zinc alloy powder containing ~ 0.500% by weight, 0.001 to 0.050% by weight of bismuth, and the balance consisting of zinc and unavoidable impurities at a temperature higher than 250 ° C. in an inert gas or reducing gas atmosphere. It is characterized by.</p><p> In this method for producing zinc alloy powder for alkaline batteries, the amount of bismuth is preferably 0.004 to 0.050% by weight. When the heat treatment temperature is lower than 400 ° C, preferably 300 ° C or higher and lower than 400 ° C, the amount of bismuth is preferably 0.009 to 0.030% by weight, preferably 0.012 to 0.020% by weight. It is even more preferable to have it. When the heat treatment temperature is 400 ° C. or higher, the amount of bismuth is preferably 0.004 to 0.010% by weight.</p><p> The zinc alloy powder for alkaline batteries according to the present invention contains 0.0001 to 0.500% by weight of at least one element selected from the group consisting of aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin and lead. However, it contains 0.001 to 0.012% by weight of bismuth, the balance consists of zinc and unavoidable impurities, and the bulk density is 3.01 g / cm.³Above, preferably 3.03 g / cm³It is characterized by the above.</p><p> Further, the zinc alloy powder for an alkaline battery according to the present invention contains 0.0001 to 0.500 weight of at least one element selected from the group consisting of aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin and lead. %, Contains 0.027 ~ 0.050% by weight of bismuth, the balance consists of zinc and unavoidable impurities, and has a bulk density of 2.76 g / cm.³Above, preferably 2.78 g / cm³It is characterized by the above.</p><p> Further, the zinc alloy powder for an alkaline battery according to the present invention contains 0.0001 to 0.500 weight of at least one element selected from the group consisting of aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin and lead. %, Contains 0.012 ~ 0.027% by weight of bismuth, the balance consists of zinc and unavoidable impurities, the amount of Bi added is x (% by weight), and the bulk density is y (g / cm).³), It is characterized in that y 3.25-18x.</p><p> The zinc alloy powder for alkaline batteries is preferably heat-treated at a temperature higher than 250 ° C. in an inert gas or reducing gas atmosphere. Further, in the above zinc alloy powder for alkaline batteries, the ratio of the peak maximum value of the bismuth segregated product to the background average value (peak maximum value / background) is 4.0 or more at a sampling time of 300 ms in EPMA analysis. Is preferable, and 4.2 or more is more preferable.</p><p> Further, the alkaline primary battery according to the present invention is characterized in that the above-mentioned zinc alloy powder for alkaline batteries or the above-mentioned zinc alloy powder for alkaline batteries produced by the method for producing the zinc alloy powder for alkaline batteries is used as the negative electrode active material. To do.</p>

<p> According to the present invention, it is possible to produce a zinc alloy powder for an alkaline battery in which the amount of hydrogen gas generated before discharging the battery is very small and the amount of hydrogen gas generated after discharging is also small by a short-time heat treatment.</p>

In the embodiment of the method for producing zinc alloy powder for alkaline batteries according to the present invention, the molten zinc alloy obtained by adding bismuth or the like to zinc and mixing and melting it is atomized by a gas atomizing method, classified by a sieve, and then classified. It contains 0.0001 to 0.500% by weight of at least one element selected from the group consisting of aluminum, indium, gallium, tarium, magnesium, calcium, strontium, cadmium, tin and lead, and 0.001 to 0.050% by weight of bismuth, preferably. Produces a zinc alloy powder containing 0.004 to 0.050% by weight and the balance is zinc and unavoidable impurities, and heat-treats the obtained zinc alloy powder in an inert gas or reducing gas atmosphere at a temperature higher than 250 ° C. .. If the amount of bismuth added is less than 0.001% by weight, the effect of suppressing the amount of gas generated before discharge is not sufficient, while if the amount of bismuth added is more than 0.050% by weight, the amount of gas before discharge is due to excessive addition of bismuth. As the amount of gas generated increases, the amount of gas generated after over-discharging also increases.

In the embodiment of the method for producing zinc alloy powder for alkaline batteries, the amount of bismuth is when the heat treatment temperature is lower than 400 ° C, preferably 300 ° C or higher and lower than 400 ° C. Is preferably 0.009 to 0.030% by weight, more preferably 0.012 to 0.020% by weight. When the heat treatment temperature is in the above range, the amount of gas generated before and after discharge can be significantly reduced when the amount of bismuth is 0.009 to 0.030% by weight, and the amount of bismuth is 0.012. In the case of ~ 0.020% by weight, the amount of gas generated before and after discharge can be further significantly reduced.

When the heat treatment temperature is 400 ° C. or higher, the amount of bismuth is preferably 0.004 to 0.010% by weight. When the amount of bismuth is in this range, the amount of gas generated before discharge and the amount of gas generated after over-discharge can be significantly reduced.

Further, at least one selected from the group consisting of aluminum, indium, gallium, thallium, magnesium, calcium, strontium, cadmium, tin and lead according to the embodiment of the above-mentioned method for producing a zinc alloy powder for an alkaline battery according to the present invention. A zinc alloy powder for alkaline batteries containing 0.0001 to 0.500% by weight of elements above the species, 0.001 to 0.050% by weight of bismuth, and the balance consisting of zinc and unavoidable impurities, and the content of bismuth is 0.001 to 0.012% by weight. In the case of%, the bulk density is 3.01 g / cm³Above, preferably 3.03 g / cm³As mentioned above, when the content of bismuth is 0.027 to 0.050% by weight, the bulk density is 2.76 g / cm.³Above, preferably 2.78 g / cm³As described above, when the content of bismuth is 0.012 to 0.027% by weight, the amount of Bi added is x (% by weight) and the bulk density is y (g / cm).³), A zinc alloy powder for alkaline batteries with y 3.25-18x can be produced.

The higher the filling rate, the larger the battery capacity of the same volume. Therefore, the higher the bulk density is, the more preferable. However, as described above, according to the embodiment of the method for producing a zinc alloy powder for an alkaline battery according to the present invention. Since the bulk density can be increased even if the amount of bismuth added is the same, the filling rate can be improved and the battery capacity of the same volume can be increased. It is considered that the reason why the bulk density can be increased by the embodiment of the method for producing the zinc alloy powder for alkaline batteries is that the surface of the zinc alloy powder becomes smooth. It is considered that when the surface of the zinc alloy powder becomes smooth, the surface activity of the zinc alloy powder decreases and the amount of hydrogen gas generated decreases. Therefore, the amount of hydrogen gas generated can be reduced by increasing the bulk density.

Hereinafter, examples of the zinc alloy powder for alkaline batteries and the method for producing the same according to the present invention will be described in detail.

[Examples 1 to 7] First, a zinc alloy molten metal obtained by mixing and melting Al, Bi and In metals with zinc is sprayed in the air by a gas atomization method to atomize it, and then classified by a sieve to have a particle size of about 35 to 200 mesh. Zinc alloy powder was produced. The composition of each zinc alloy powder was analyzed by atomic absorption spectroscopy and found to be the composition shown in Table 1.

<tables num="1"><img file="JP5114763B2_D0001.tif" /></tables>

Next, each of the obtained zinc alloy powders was heat-treated in a nitrogen gas atmosphere at 300 ° C. for 30 minutes in a heat treatment furnace, and then slowly cooled to room temperature in a nitrogen gas atmosphere. The bulk density of each zinc alloy powder heat-treated in this manner was measured according to JIS Z 2504. In addition, the crystal grain size was determined from the particle cross-section photograph by the Zeferi-planimeter method (a method of dividing the area of the particle cross-section by the number of crystal grains contained therein to obtain a square root). These results are shown in Table 2 and Figure 1.

In addition, 5 g of zinc alloy powder heat-treated as described above was mixed in 10 g of a 40% KOH solution saturated with zinc oxide and held at 60 ° C for 3 days, and the average rate of the generated gas amount was measured as the initial gas amount. Calculated as (gas amount before discharge). The results are shown in Table 2 and Fig. 2.

Further, the zinc alloy powder heat-treated as described above is mixed with a 40% KOH solution saturated with zinc oxide and polyacrylic acid to prepare a gel, and this gel is used as a negative electrode agent and manganese dioxide is used as a positive electrode agent. An LR6 battery (AA alkaline battery) was manufactured. After discharging this battery with a resistance of 10Ω for 48 hours, the battery was held at 60 ° C for 8 hours, and the amount of gas generated in the battery (the amount of gas after over-discharging) was measured. The results are shown in Table 2 and Fig. 3.

<tables num="2"><img file="JP5114763B2_D0002.tif" /></tables>

[Examples 8 to 14] Zinc alloy powder having the composition shown in Table 1 was produced by the same method as in Examples 1 to 7, and then heat-treated by the same method as in Examples 1 to 7 except that the heat treatment temperature was set to 400 ° C. For the alloy powder, the bulk density, the initial gas amount and the gas amount after over-discharge were measured by the same method as in Examples 1 to 7 (only the bulk density was measured in Examples 10 to 14). These results are shown in Table 2 and Figures 1 to 3.

[Comparative Examples 1 to 8] After producing the zinc alloy powder having the composition shown in Table 1 by the same method as in Examples 1 to 7, the zinc alloy powder not subjected to heat treatment is subjected to the bulk density and initial gas by the same method as in Examples 1 to 7. The amount and the amount of gas after over-discharging were measured. These results are shown in Table 2 and Figures 1 to 3.

[Comparative Examples 9 to 13] Zinc alloy powder having the composition shown in Table 1 was produced by the same method as in Examples 1 to 7, and then heat-treated by the same method as in Examples 1 to 7 except that the heat treatment temperature was set to 200 ° C. The bulk density of the alloy powder was measured by the same method as in Examples 1 to 7. These results are shown in Table 2 and Figure 1.

As can be seen from Table 1, Table 2 and FIG. 1, when the heat treatment as in Examples 1 to 14 is performed, it is low as in the case where the heat treatment is not performed as in Comparative Examples 1 to 8 or as in Comparative Examples 9 to 13. Compared to heat treatment at a temperature (200 ° C), the bulk density is higher even with the same amount of Bi added, and even if the amount of Bi added is reduced, the high bulk density can be maintained and the filling rate can be increased. Can be improved. In particular, when the amount of Bi added is 122 ppm or less as in Examples 1 to 3 and 8 to 10, the bulk density is 3.03 g / cm.³When the amount of Bi added is 272 ppm or more as in Examples 5 to 7 and 12 to 14, the bulk density is 2.78 g / cm.³It can be more than that. Further, when the amount of Bi added is 151 ppm as in Examples 4 and 11, the bulk density can be 2.99 or more, and when the amount of Bi added is 122 to 272 ppm, the amount of Bi added can be increased. x (ppm), bulk density y (g / cm)³), Y 3.25-0.0018x (ppm). That is, the amount of Bi added is x (% by weight), and the bulk density is y (g / cm).³), Y 3.25-18x (% by weight).

Further, as can be seen from Table 1, Table 2 and FIG. 2, when the heat treatment as in Examples 1 to 9 is performed, the same Bi is added as compared with the case where the heat treatment is not performed as in Comparative Examples 1 to 8. As for the amount, the initial gas amount (gas amount before discharge) is significantly reduced. Further, when the heat treatment as in Examples 1 to 9 is performed, the initial gas amount (gas amount before discharge) decreases as the Bi addition amount increases until the Bi addition amount is 151 ppm (Example 4), and then the Bi addition amount decreases. Is increasing as the amount of Bi added increases. On the other hand, as can be seen from Table 1, Table 2 and FIG. 3, the amount of gas after over-discharge increases as the amount of Bi added increases. Therefore, if the heat treatment as in Examples 1 to 9 is performed, the initial gas amount (gas amount before discharge) can be significantly reduced even if the Bi addition amount is small, so that the Bi addition amount is reduced. It can be seen that the amount of gas can also be reduced after over-discharging. That is, it is possible to reduce the amount of gas before discharge and the amount of gas after overdischarge at the same time.

Further, in Examples 1 to 9 and Comparative Examples 1 to 8, the relationship between the crystal particle size and the amount of gas before discharge is shown in FIG. 4, and the relationship between the crystal particle size and the amount of gas after overdischarge is shown in FIG. As can be seen from these figures and Table 2, when the heat treatment as in Examples 1 to 9 is performed, the crystal grains are crystallized even if the amount of Bi added is the same as in the case where the heat treatment is not performed as in Comparative Examples 1 to 8. The diameter becomes large, and the initial gas amount and the gas amount after over-discharging can be reduced even if the crystal grain size is the same.

[Examples 15 to 19, Comparative Examples 14 to 17] Zinc alloy powders containing 30 ppm Al, 90 ppm Bi, and 500 ppm In were prepared and heat-treated as shown in Table 3 (the heat treatment was not performed in Comparative Example 9), and the same method as in Examples 1 to 7 was used. The initial gas amount (gas amount before discharge) was measured. The results are shown in Table 3 and FIG. As can be seen from Table 3 and FIG. 6, the initial gas amount can be significantly reduced by performing the heat treatment at the heat treatment temperature of 300 to 400 ° C as in Examples 15 to 19.

<tables num="3"><img file="JP5114763B2_D0003.tif" /></tables>

[Examples 20 to 24, Comparative Examples 18 to 21] Zinc alloy powders containing 200 ppm Al, 40 ppm Bi and 200 ppm In were prepared and heat-treated as shown in Table 4 (the heat treatment was not performed in Comparative Example 18), respectively, by the same method as in Examples 1 to 7. The initial gas amount (gas amount before discharge) was measured. The results are shown in Table 4 and FIG. As can be seen from Table 4 and FIG. 7, the initial gas amount can be significantly reduced by performing the heat treatment at the heat treatment temperature of 300 to 400 ° C as in Examples 20 to 24.

<tables num="4"><img file="JP5114763B2_D0004.tif" /></tables>

[Example 25] First, a molten zinc alloy containing 40 ppm of bismuth, 200 ppm of aluminum, and 200 ppm of indium was sprayed in the air by the gas atomization method to atomize, and then a zinc alloy powder whose particle size was adjusted by a sieve of 35 to 200 mesh was prepared. .. Next, this zinc alloy powder was heat-treated in a nitrogen gas atmosphere at 400 ° C. for 30 minutes in a heat treatment furnace, and then slowly cooled to room temperature in a nitrogen gas atmosphere.

After embedding the obtained zinc alloy powder in a resin and polishing the surface, an EPMA device (Electron Probe Micro Analysis device) (JXA-8200 manufactured by JEOL Ltd.) was used to accelerate the voltage to 20 kV. Irradiation current 2 × 10^-8A, When surface analysis was performed under the measurement conditions of 300 ms sampling time, 30 × 30 pixels, and pixel size 0.5 μm, the maximum peak value of the Bi segregated product was 37 counts, and the average background value was 8.9 counts. The ratio of the peak maximum value to the background (peak maximum value / background) was 4.2.

In addition, 5 g of zinc alloy powder heat-treated as described above was mixed in 10 g of a 40% KOH solution saturated with zinc oxide and held at 60 ° C for 3 days, and the average rate of the generated gas amount was measured as the initial gas amount. When calculated as (gas amount before discharge), the initial gas amount was 6.1 μl / g · day.

Further, the zinc alloy powder heat-treated as described above is mixed with a 40% KOH solution saturated with zinc oxide and polyacrylic acid to prepare a gel, and this gel is used as a negative electrode agent and manganese dioxide is used as a positive electrode agent. An LR6 battery (AA alkaline battery) was manufactured. After discharging this battery with a resistance of 10Ω for 48 hours, it was held at 60 ° C for 8 hours, and the amount of gas generated in the battery (gas amount after overdischarge) was measured. The amount of gas after overdischarge was 2.8 ml / It was a cell.

[Example 26] When the zinc alloy powder obtained by the same method as in Example 25 was subjected to surface analysis by the same method as in Example 25 except that the amount of bismuth added was 100 ppm, the peak maximum value of the Bi segregated product was found. The average value of 41 counts and background was 8.8 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 4.6. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 3.1 μl / g · day and the gas amount after over-discharge was 4.0 ml / cell. ..

[Example 27] The surface of the zinc alloy powder obtained by the same method as in Example 25 except that the amount of bismuth added was 150 ppm, the amount of aluminum added was 30 ppm, and the amount of indium added was 500 ppm. As a result of the analysis, the peak maximum value of the Bi segregated product was 123 counts, the background mean value was 8.2 counts, and the ratio of the peak maximum value to the background (peak maximum value / background) was 15.1. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 1.6 μl / g · day and the gas amount after over-discharge was 4.7 ml / cell. ..

[Comparative example 22] When the surface analysis of the zinc alloy powder obtained by the same method as in Example 25 except that the heat treatment was not performed was performed by the same method as in Example 25, the peak maximum value of the Bi segregated product was 21 counts. The mean value of the background was 9.9 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 2.1. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 26.9 μl / g · day and the gas amount after over-discharge was 2.9 ml / cell. ..

[Comparative example 23] When the surface analysis of the zinc alloy powder obtained by the same method as in Example 26 except that the heat treatment was not performed was performed by the same method as in Example 25, the peak maximum value of the Bi segregated product was 22 counts. The mean value of the background was 9.4 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 2.3. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 5.3 μl / g · day and the gas amount after over-discharge was 3.6 ml / cell. ..

[Comparative Example 24] When the surface analysis of the zinc alloy powder obtained by the same method as in Example 27 except that the heat treatment was not performed was performed by the same method as in Example 25, the peak maximum value of the Bi segregated product was 22 counts. The mean value of the background was 9.3 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 2.4. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 5.0 μl / g · day and the gas amount after over-discharge was 4.5 ml / cell. ..

[Comparative example 25] The zinc alloy powder obtained by the same method as in Example 25 except that the heat treatment temperature was 150 ° C. and the heat treatment time was 120 minutes was subjected to surface analysis by the same method as in Example 25. The maximum peak value of the object was 30 counts, the average value of the background was 8.7 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 3.4. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 25.0 μl / g · day and the gas amount after over-discharge was 3.0 ml / cell. ..

[Comparative example 26] The zinc alloy powder obtained by the same method as in Example 26 except that the heat treatment temperature was 150 ° C. and the heat treatment time was 120 minutes was surface-analyzed by the same method as in Example 25. The maximum peak value of the object was 32 counts, the average value of the background was 8.8 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 3.6. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 6.1 μl / g · day and the gas amount after over-discharge was 4.1 ml / cell. ..

[Comparative example 27] The zinc alloy powder obtained by the same method as in Example 27 except that the heat treatment temperature was 150 ° C. and the heat treatment time was 120 minutes was subjected to surface analysis by the same method as in Example 25. As a result, Bi segregation was performed. The maximum peak value of the object was 35 counts, the average value of the background was 8.9 counts, and the ratio of the maximum peak value to the background (maximum peak value / background) was 3.9. Further, when the initial gas amount and the gas amount after over-discharge were determined by the same method as in Example 25, the initial gas amount was 5.9 μl / g · day and the gas amount after over-discharge was 4.8 ml / cell. ..

The results of Examples 25 to 27 and Comparative Examples 22 to 27 are shown in Tables 5, 6, 8 and 9.

<tables num="5"><img file="JP5114763B2_D0005.tif" /></tables>

<tables num="6"><img file="JP5114763B2_D0006.tif" /></tables>

As can be seen from Tables 5 and 6, in Comparative Examples 22 to 27, the ratio of the peak maximum value to the background (peak maximum value / background) is less than 4.0, but in Examples 25 to 27, this ratio is It is 4.0 or more, and when the same amount of bismuth is added, the initial gas amount can be reduced without increasing the gas amount after over-discharging. In particular, in Example 25 in which the amount of bismuth added was 40 ppm, the initial gas amount could be significantly reduced as shown in FIG. 8 as compared with Comparative Examples 22 and 25 in which the same amount of bismuth was added, which is shown in FIG. As described above, the amount of gas after over-discharge is not increased, and the smaller the amount of bismuth added, the smaller the amount of gas after over-discharge, which is particularly preferable. That is, in Examples 25 to 27, the amount of bismuth added can be reduced to prevent the amount of gas added after overdischarge from increasing, and the amount of initial gas can be reduced even with a small amount of bismuth added. In particular, Example 25 The effect becomes remarkable when the amount of bismuth added is small as in.

Further, from the reflected electron images of the cross sections of the zinc alloy powders for alkaline batteries of Examples 25 to 27, more bismuth was segregated in the grain boundary phase than in the matrix, and bismuth and indium alone, a solid solution or an intermetallic phase was segregated in the grain boundary phase. It was found that the compound was present. Since hydrogen gas before discharge of a battery is mainly generated by corrosion of zinc grain boundaries, zinc crystals are selectively segregated at these grain boundaries in the form of a single substance, a solid solution, or an intermetallic compound. It is considered that the portion where the grain boundaries are corroded can be reduced, and the gas generation of zinc powder can be effectively suppressed even if the amount of bismuth or indium added is small. Further, since this effect can be obtained even if the amount of bismuth added is reduced as in Example 25, the amount of gas generated after discharge can be suppressed.

<figref num="1">3 is a graph showing the relationship between the amount of Bi added and the bulk density in Examples 1 to 14 and Comparative Examples 1 to 13.</figref><figref num="2">It is a graph which shows the relationship between the amount of Bi addition and the amount of gas before discharge in Examples 1-9 and Comparative Examples 1-8.</figref><figref num="3">3 is a graph showing the relationship between the amount of Bi added and the amount of gas after overdischarge in Examples 1 to 9 and Comparative Examples 1 to 8.</figref><figref num="4">It is a graph which shows the relationship between the crystal particle diameter and the amount of gas before discharge in Examples 1-9 and Comparative Examples 1-8.</figref><figref num="5">3 is a graph showing the relationship between the crystal grain size and the amount of gas after over-discharge in Examples 1 to 9 and Comparative Examples 1 to 8.</figref><figref num="6">3 is a graph showing the relationship between the heat treatment time and the amount of gas before discharge in Examples 15 to 19 and Comparative Examples 14 to 17.</figref><figref num="7">3 is a graph showing the relationship between the heat treatment time and the amount of gas before discharge in Examples 20 to 24 and Comparative Examples 18 to 21.</figref><figref num="8">It is a graph which shows the relationship between the ratio of the peak maximum value (peak maximum value / background), and the initial gas amount with respect to the background in Examples 25 to 27 and Comparative Examples 22 to 27.</figref><figref num="9">It is a graph which shows the relationship between the ratio of the peak maximum value (peak maximum value / background) with respect to the background, and the amount of gas after over-discharge in Examples 25-27 and Comparative Examples 22-27.</figref>