JPS61136915A - Production of granular silver oxide - Google Patents

Abstract

PURPOSE:To obtain granular silver oxide excellent in fluidity without necessitating a granulating process in a period of cell production by adding silver nitrate and an aq. alkali hydroxide soln. to an aq. alkali soln. so that the specified acidity is maintained. CONSTITUTION:Silver nitrate and an aq. alkali hydroxide soln. are added within the range of 9.0-11.0pH to an aq. soln. which is regulated to the prescribed pH within the range of 9.0-11.0pH by adding alkali to water while stirring this aq. soln. so that the above-mentioned pH is maintained and the retention time of the product is regulated to >=6hr. While the reaction is continued, the pH is within 9.0-11.0 and it is preferable that the pH is not fluctuated remarkably from the prescribed value decided at first. When this fluctuation is remarkably large, the roundness of produced granular silver oxide particles is marred and the cause wherein the fine particles are mixed thereinto is generated. Therefore it is preferable that the pH value of the liquid is maintained within the range of + or -0.3 of the pH value preset at first while the reaction is continued.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for producing granular silver oxide with good weighing accuracy, which is used as an anode material for silver oxide batteries.

[Problem that the invention seeks to solve]

Silver oxide is widely used as an anode material for small batteries because of its high energy density and good discharge characteristics. Silver oxide conventionally used as anode material has a particle size of 1
Fine powder of ~10 μm is used, and the weighing method in the battery manufacturing process is to fill a square with a predetermined volume with silver oxide, and move a partition rod along the upper edge of the square to separate the top surface of the filled silver oxide. However, when silver oxide remains in the form of fine powder, it has poor fluidity, making it difficult to weigh as described above, and the amount of glue in the hopper is 9.
Generally, silver oxide powder is passed between compression rolls to form a sheet, which is then crushed and sieved to a powder size of, for example, 60 to
It was used after being sized to 200 mesh.

However, those that have gone through the granulation method have large particle sizes and large variations, and do not have sufficient fluidity. In addition, the granulation process has many problems such as dust generation, silver loss, and an increase in the number of steps. Ta.

[Prior art]

The conventional method for producing silver oxide is to add alkali hydroxide (generally hydroxide) to an aqueous solution of silver nitrate.
17um) aqueous solution or add a silver nitrate aqueous solution to an aqueous alkali hydroxide solution to form 2A yNO3 + 2NaOH= At20 + 2Na N
ArtOt- is generated using the reaction formula of O3+HtO. In this case, the pH is not particularly controlled, and the reaction time is usually within 1 hour. The silver oxide obtained by this method has a small particle size, with a particle diameter of 5 μm measured using a scanning electron microscope.
m or less, and even if post-reaction aging treatment is performed, it is at most 5 to 1
It is 0 μm. Since these particles have poor fluidity, they require a granulation process as described above.

[Means for Solving the Problems] The present invention improves the conditions of the conventional silver oxide production process and grows the obtained particle size to 10 μm or more, thereby obtaining granular silver oxide with good fluidity. The object of the present invention is to provide a method for manufacturing a product with good weighing accuracy in the molding process of battery manufacturing without using a granulation process.

In order to achieve this purpose, the inventors conducted various research and found that
The present invention was achieved by discovering that the particle size can be increased by appropriately combining pH and reaction time.

That is, the method of the present invention adds an alkali to water and adjusts the pH to 9.
An aqueous solution of silver nitrate and alkali hydroxide is added to an aqueous solution adjusted to a predetermined pH in the range of 0 to 11.0 while stirring the aqueous solution of f P ! The product was added so as to maintain the pH within the range of 9.0 to 11.0, and the residence time of the product was 6.
It takes more than an hour and nine degrees.

P1 in reaction! The reason for limiting the range of variation in pH to within the range of 9.0 to 11.0 is that if the pH is below 9.0 or above 11.0, the particle size produced will be small even if other conditions are met, and the fluidity will be poor. Because it's not good. The pH during the reaction is 9
．． It is preferably set within the range of 0 to 11.0 and then not allowed to vary greatly from the predetermined value; if the value is varied too much, the roundness of the granular silver oxide particles produced will be impaired and fine particles may be mixed in. Therefore, it is preferable to keep the pH value of the liquid during the reaction within a range of ±0.3 from the initially set value, and more preferably within a range of ±0.2.

The reaction temperature is not particularly limited and may be room temperature, but a temperature of 40° C. or higher, preferably 50° C. or higher is convenient for producing particles with smooth surfaces and increasing fluidity.

The concentration of the silver nitrate aqueous solution used is not particularly limited, and the concentration may be high. Furthermore, instead of an aqueous solution, a fine powder can also be used.

To react silver nitrate aqueous solution and alkali hydroxide, first prepare an alkaline aqueous solution with a predetermined pH value in the reaction tank.
This is because the reaction between a relatively high concentration silver nitrate aqueous solution and a high concentration alkali hydroxide proceeds directly, making it difficult to control the PH of the mixed aqueous solution in the early stages of the reaction, which adversely affects the properties of the product.

Water is prepared in a reaction vessel, and only the alkali hydroxide used in the reaction of the present invention is added prior to the reaction to reach a predetermined pH value, and then a silver nitrate aqueous solution and an alkali hydroxide aqueous solution are added to the predetermined pH value. It should be added to maintain the .

Next, the reason why the silver oxide produced in the reaction vessel is allowed to stay for more than 6 hours is that the reaction rate of silver oxide production is fast, so the residence time is usually not a problem, but if the residence time is extended, the silver oxide particles will gradually grow. This is because the particle size becomes larger and therefore the angle of repose becomes smaller when dried, making it possible to obtain granules with good weighing accuracy. Therefore, it is necessary to continue adding silver nitrate and aqueous alkali hydroxide to the reaction vessel for at least 6 hours from the start of the reaction.Industrially, it is desirable that the liquids do not overflow from the vessel while the reaction continues, but if the liquid overflows, It is necessary to collect the product by decanting it into a separate vessel and return it to the original reaction vessel to increase the residence time.

Normally, the concentration of the silver nitrate aqueous solution and alkali hydroxide aqueous solution added during the reaction is constant, but in order to prevent overflow of the solution when the reaction time is long, it is possible to increase the concentration of the aqueous solution in the latter half of the reaction. Operations can also be performed as needed.

〔Example〕

Example 1 1 t of pure water was placed in a beaker with a capacity of 36 cm and heated to 60°C.
Add a small amount of 120'/z sodium hydroxide aqueous solution to this to make P)flO,0, and while stirring with a stirrer, Af
A 150 f/l silver nitrate aqueous solution is added continuously using a roller pump at a constant rate of 1.2 mm. On the other hand, the above sodium hydroxide aqueous solution was set in a beaker and
The mixture was added continuously or semi-continuously using a roller pump in conjunction with the nail so that the pH was maintained at 10.1:0.2, and the reaction was continued for 3 to 96 hours. The overflow from the beaker was collected in a separate container, from which the product was collected by decanting and returned to the original beaker, so that the residence time of the product was approximately equal to the duration of the reaction. The reaction beaker was maintained at 60°C in a water bath. Table 1 shows the physical properties of the silver oxide produced when the reaction time was changed.

As a comparative example, test Na8 was prepared using a conventional method to show the physical properties of silver fertilized oxide. That is, it was produced by putting 1,000 ml of an 85 f/l aqueous sodium hydroxide solution in a 3 t beaker, adding 600 ml of a 360 Vt silver nitrate aqueous solution over about 5 minutes without stirring, and aging for 1 hour.

(Page 8 and below margins) Table 1 In Table 1, the particle diameters are measured using a scanning electron microscope.
Angle of repose is 515M-1902 (for measuring physical properties of alumina)
It was measured by Fluidity was determined qualitatively by placing a sample in a plastic bag and tilting the bag to qualitatively determine the flow of silver oxide.

×: Not possible, Δ: Some flow but not so good, ○: Good The sample was thoroughly washed with pure water after the reaction was completed, thoroughly dried at 105° C., and used for evaluation. From the results in Table 1, if the reaction time, that is, the residence time is too short, for example, for 3 or 5 hours, the particle size is less than 10 μm and the angle of repose is large, but if the residence time is 6 hours or more, It can be seen that as the time increases, the particle size becomes relatively large9 and the fluidity improves.

Example 2 The same silver nitrate and sodium hydroxide aqueous solutions as in Example 1 were prepared, the pH of the initially prepared solutions was set to 8.5 to 11.5, and the pH during the reaction was adjusted to a predetermined value ± the same as in Example 1. 0
．． 2 and the residence time of the product was set to 12 hours. The results are shown in Table 2.

(Margins below page 10) From the results in Table 2, it can be seen that when pg is set to 9.0 or less or 110 or more, the particle size of the silver oxide obtained is small and the fluidity is poor.

〔effect〕

As explained above in detail, according to the method of the present invention, the reaction between silver nitrate and an aqueous alkali hydroxide solution is
By controlling the addition amount of both so that it is in the range of ~11.0 and making the residence time of the product t-6 hours or more, granular silver oxide with good fluidity can be obtained, and it can be used for batteries. Satisfactory weighing accuracy can be obtained as an anode material without going through a granulation process.

Claims (3)

[Claims] (1) In a method for producing silver oxide from silver nitrate and alkali hydroxide, an alkali is added to water to reach a pH of 9.0 to 11.
0 is prepared, and the silver nitrate and alkali hydroxide aqueous solution are added to the aqueous solution while stirring to maintain the pH, and the residence time of the product is 6 hours or more. Method for producing silver oxide. (2) When adding silver nitrate and aqueous alkali hydroxide solution, the addition is performed so as to maintain the pH of the liquid being stirred within ±0.3 of the initially adjusted pH value of the liquid. A method for producing granular silver oxide according to item 1. (3) The method for producing granular silver oxide according to claim 1, wherein the silver nitrate added to the liquid being stirred is an aqueous solution.