JPS6011219A - Manufacture of zinc silicate - Google Patents

Abstract

PURPOSE:To obtain fine-grained zinc silicate of high purity suitable for use as an additive for a nonlinear zinc oxide voltage resistor with high reproducibility by converting zinc ions into a specified zinc complex and reacting the complex with an aqueous soln. contg. silicate ions. CONSTITUTION:A ligand consisting of atoms such as C, H and N, e.g., ammonia or ethylenediamine is added to an aqueous soln. contg. zinc ions such as an aqueous soln. of zinc nitrate to convert all of the zinc ions in the soln. at 8- 12pH into a zinc complex which is not decomposed and does not cause precipitation, e.g., a zinc ammine complex. To the resulting soln. is added an aqueous soln. contg. silicate ions such as an aqueous soln. of sodium metasilicate, and they are stirred under heating to cause a reaction. A white precipitate produced by the reaction is separated by filtration, washed, and dried to obtain desired zinc silicate powder. This zinc silicate powder contains a small amount of trace impurity elements and has a small average particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing zinc silicate by mixing an aqueous solution containing zinc ions and an aqueous solution containing silicate ions.

Zinc silicate is widely used as a material for phosphors and as an additive in zinc oxide voltage nonlinear resistors.

Particularly in the case of voltage nonlinear resistors, high purity zinc silicate with a stable composition is required as a zinc oxide additive since it is essential for improving voltage nonlinearity and service life. Zinc silicate is usually synthesized by mixing powders of zinc oxide and silicon dioxide and reacting at a high temperature of 1000 C or higher (powder synthesis method). In this method, the purity of the raw materials directly affects the purity of the product. , it is necessary to prepare high-purity zinc oxide and silicon dioxide. In addition, in this powder synthesis method, since the reaction is carried out at a high temperature of 1 ooor or higher, the zinc silicate particles grow and their particle size becomes thick. If this was not done, the distribution of zinc silicate within the resistor would become uneven, resulting in drawbacks such as thermal element destruction due to high energy surges.

Another method is to mix a zinc ion aqueous solution and a silicate ion aqueous solution to precipitate zinc silicate. However, in this conventional solution mixing method, when an alkaline silicate ion aqueous solution is added to a weakly acidic zinc ion aqueous solution (which becomes weakly acidic due to hydrolysis of the zinc compound) (or vice versa), ), zinc hydroxide precipitates simultaneously with zinc silicate. The formation of this zinc hydroxide precipitate changes depending on various synthesis conditions such as zinc ion concentration, silicate ion concentration, solution temperature, and stirring conditions, so the constituent element ratio of the final precipitate changes.
The drawback was that it was difficult to obtain zinc silicate of consistent quality. As a result, the characteristics (for example, life span) of the zinc oxide voltage nonlinear resistor were not stable.

This invention was made in order to eliminate the drawbacks of the conventional methods as described above. Ligands composed of C, H, N, etc., which can be removed by subsequent heat treatment, are added in advance to an aqueous zinc ion solution, and pg By converting all the zinc ions in the solution into stable zinc complexes in the state of f - / J and mixing them with an alkaline silicate ion aqueous solution, it is possible to prevent the formation of zinc hydroxide precipitates. (The purpose is to obtain chemically pure and fine zinc silicate. Ligands that satisfy the above conditions include ammonia,
Examples include ethylenediamine. For example, when aqueous ammonia is added to an aqueous zinc solution, a zinc ammine complex is formed. The above reaction can be expressed as a chemical reaction formula as follows.

Conventional solution method The method of this invention (when ammonia is used) will be explained based on the drawings.

1 and 1, the synthesis apparatus is a beaker/, a dropping funnel, a ring 3, a stander, a stirrer 51 with a hot plate, a stirring bar 6, and an aqueous solution of zinc ammine complex. ,
It consists of an aqueous solution of sodium metasilicate (g), water, etc.

The present invention will be explained below based on Examples.

Example! A diagram of the apparatus used in this example is shown in FIG.

Zinc nitrate (Zn(No,), ・AH,o) / #
t, 7 JF was dissolved in 3 ooml of water. While stirring this aqueous solution, 16θI of 30% ammonia water was gradually added. As ammonia water was added, a white precipitate was first formed, but as more ammonia water was added, the precipitate gradually dissolved and finally became a colorless and transparent solution.

This solution was placed in seven dropping funnels. On the other hand, sodium metasilicate (Na, 8i0. 9H, -0)?
/, /77 was dissolved in water Jθθd and placed in another dropping funnel. A beaker was filled with 1 t/CkθOwl of water, heated and stirred at SO to 6θC, and each aqueous solution was dropped into the water tank in the beaker from a rain dropping funnel. The dropping speed was set to O, S~ per second for both cases. Immediately after starting dropping, the aqueous solution in the beaker was clear and colorless and did not change at all, but as one drop of to-aom was added, it became cloudy and gradually turned white. Precipitate was now observed. Even after all the solution in the dropping funnel had been added, the solution in beaker 1 was continued to be heated and stirred for a while. After cooling the solution containing the precipitate in beaker I to room temperature, it was washed with water several times by decantation. Next, after performing suction P separation, the precipitate was washed several times with water and dried to obtain zinc silicate powder.

Implementation side design A diagram of the apparatus used in this example is shown in FIG. Zinc ammine complex aqueous solution 7 prepared in the same manner as in Example 1 was placed in a beaker/, and sodium metasilicate aqueous solution g prepared in the same manner as in Example 1 was placed in the dropping funnel. While heating and stirring the zinc ammine complex aqueous solution using a go-boc, the sodium metasilicate aqueous solution was added dropwise from a dropping funnel.

Other operations were performed in the same manner as in Example.

The table shows the elemental analysis results of the zinc silicates obtained in Examples 1 and - of the present invention, the conventional solution synthesis method, and the conventional powder synthesis method.

Bamboo Here, the powder produced by precipitation is amorphous according to X-ray diffraction, so it is decomposed. There is almost no change up to 0/300C.

As is clear from the table, the amount of trace elements contained in the zinc silicate obtained by the present invention is smaller than that by the conventional powder synthesis method. Furthermore, the reproducibility of the zinc silicate obtained by the present invention was also very good.

Also, regarding the relative average particle size of the powder, if the zinc silicate obtained by the conventional powder synthesis method is expressed as 800, then in Examples/and Co of the present invention, each is 0.1! ;.

o, go, and a finer powder than the conventional one can be obtained. Furthermore, the temperature required to produce zinc silicate is lower,
It is advantageous in terms of time and cost.

On the other hand, in the conventional powder synthesis method, the content of impurities is large, the particle size is large, and the temperature required to generate zinc silicate is high. In addition, although conventional solution synthesis methods have small particle sizes and low temperatures required to produce zinc silicate, reproducibility is poor, and the zinc ion concentration, silicate ion concentration, and solution temperature during synthesis are It is difficult to obtain highly pure zinc silicate with good stirrability.

Between Examples 1 and -, Example 1 had smaller amounts of trace elements and finer particle sizes, and the manufacturing method of Example I was preferable for use in adding zinc oxide voltage nonlinear resistors. . This is because the zinc ammine complex and sodium metasilicate were reacted under dilute concentration conditions using water as a medium in Example 1. Under these conditions, precipitation progressed gradually and impurities were adsorbed. , occlusion is extremely small (therefore, zinc silicate of high purity and extremely fine particle size is obtained.On the other hand, in Example--, when metasilicate ions are dropped into an aqueous solution of zinc ammine complex, metasilicate is temporarily weakly released). It is thought that because the acid ion concentration is high (and the zinc ammine complex concentration is also high), rapid precipitation occurs, leading to adsorption and occlusion of impurities.

In addition, in the above example, the case where a zinc ammine complex was synthesized by adding aqueous ammonia was explained, but when the pH is from g to
Other zinc complexes that do not decompose or do not cause precipitation in the saw state and that contain a ligand that can be removed by heat treatment may be used, and the same effects as in the above embodiments can be achieved. In addition, although the above example describes the case where sodium metasilicate and zinc nitrate are used, other metasilicates, silicates,
A zinc compound may also be used, and the same effect as in the above embodiment can be achieved. Further, in the above example, a case was explained in which the sodium metasilicate aqueous solution was dropped into the zinc ammine complex aqueous solution, but the reverse case may be used and the same effects as in the above example can be obtained.

As described above, according to the present invention, zinc ions are added to p
It is a zinc complex that does not decompose or form a precipitate when H is between t and l. It is converted into a zinc complex containing a ligand that can be removed by heat treatment and reacted with an aqueous silicate ion solution, resulting in high purity. Zinc silicate, which has a large and extremely fine particle size, has good reproducibility (effects obtained).

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a synthesis apparatus used in one embodiment of the method of the present invention, and FIG. 2 is a schematic diagram showing a synthesis apparatus used in another embodiment of the method of the invention. ! ... Beaker, C... Dripping funnel, 3... Ring, wide stand, S... Stirrer with hot plate, 6... Stirrer, 7... Zinc ammine complex aqueous solution, J. ... Sodium silicate aqueous solution? ···water. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa

Claims (1)

[Claims] When synthesizing zinc silicate by mixing a zinc ion aqueous solution and a silicate ion aqueous solution, zinc ions are added in advance to C, H, N
It is characterized by converting it into a zinc complex that does not decompose or precipitate at a pH of 1-/co, and reacting it with the resulting complex aqueous silicate ion solution. Method for manufacturing zinc silicate.