JPS62288115A - Production of zno crystal particle - Google Patents

Abstract

PURPOSE:To produce ZnO crystal particle having low anisotropy and useful for a varistor for low-voltage circuit, by mixing ZnO powder with a Ba compound and/or Sr compound and an Mg compound, forming and sintering the mixture and hydrolyzing the product. CONSTITUTION:ZnO powder is mixed with a Ba compound (e.g. BaCO3) and/or Sr compound (e.g. SrCO3) and 0.5-14mol% Mg compound (e.g. MgO) (in terms of MgO) and the powdery mixture is formed and sintered to obtain a sintered material, which is hydrolyzed by boiling in water to dissolve and remove the BaO layer and SrO layer. The product is washed with water and dried to obtain the objective particle.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Industrial Field of Application) The present invention is directed to the production of ZnO crystal particles for varistors for low voltage circuits containing zinc oxide (ZnO) as a main component. Regarding the method.

(Prior Art) Varistors containing ZnO as a main component have excellent nonlinearity and are therefore widely used for their surge absorption function.

However, the varistor voltage in this type of varistor is ZnO
It is determined by the number of grain boundary layers existing between the electrodes arranged on the surface of the sintered body. Therefore, in order to obtain a varistor for low voltage circuits, the thickness of the varistor element must be reduced, or Zn
It is necessary to increase the O particle size and reduce the number of grain boundary layers.

Considering a varistor with a rising voltage of 22V, the voltage per grain boundary layer is generally about 2.5V.

In other words, in the normal method, the ZnO particle size of the sintered body is 10~
Since the thickness of the sintered body is 20 μm, the thickness of the sintered body is only 0.2 mm TF 1 degree, which is not practical due to its low mechanical strength and the problem of cracking during the process. Therefore, Zno crystals (hereinafter referred to as crystalline particles) with a particle size larger than the particle size of the raw material are added to the ZnO powder raw material to promote grain growth and increase the Zn
Various methods have been devised to increase the O particle size, including adding a small amount of Ba compound or Sr compound to ZnO powder.
In the method of hydrolyzing the sintered body obtained by molding and firing the added and mixed powder, Ba compounds and 3R compounds used as grain growth promoters can be removed by hydrolysis, and the crystal nucleus particle size can be easily controlled. It is often used for this reason. However, as shown in Fig. 4, the crystal nucleus particle diameter obtained by this method varies greatly in the ratio X/Y of the longest part X and the uppermost part Y in the direction perpendicular to X, ranging from elongated to circular As shown in Figure 5, the ZnO crystal state of the varistor element obtained using these crystal nucleus particles is locally caused by anomalous grain growth.
The presence of crystal 1 creates a region with an extremely small number of grain boundary layers, and as a result, the electrical resistance of the region decreases, causing current concentration, resulting in a defect that may lead to destruction. 2 in the figure is an electrode. Therefore, as a method to eliminate these drawbacks, a sheet forming process is disclosed in JP-A No. 61-24201, in which a sintered body formed by adding Ba or Sr compound to ZnO, forming and firing is hydrolyzed. There is a method for producing ZnO crystal particles in which the thickness of the sintered body is 25 to 300 μm, and the crystal nucleus particle size is
By reducing the ratio of /Y, it can greatly contribute to the formation of particles that are close to circular shapes. However, such a method has a special design surface for forming a sheet, and Zn is
Not only is it impractical because it takes a lot of man-hours to make one O particle, but the molding pressure is low, so the particles themselves have the disadvantage of being uneven in size and coarse particles with uneven surfaces. However, it could not be said that it was an effective means.

(Problems to be Solved by the Invention) As described above, even with any of the above methods, it is difficult to obtain a grain boundary layer that is practical and desired as a varistor for a low voltage circuit.

The present invention solves the above problems and provides ZnO crystal particles that are effective as varistors for low voltage circuits. The purpose of this invention is to provide an IJ manufacturing method.

[Structure of the Invention] (Means for Solving the Problems) The method for producing ZnO crystal particles of the present invention is a method for producing ZnO crystal particles using zinc oxide (ZnO).
nO) powder and at least one of a barium (Ba) compound and a strontium (Br) compound and magnesium (
MQ) A product obtained by hydrolyzing a sintered body obtained by press-molding and firing a mixed powder to which a compound has been added, preferably adding 0.5 to 14 mol% of the magnesium compound in terms of MoO. It is characterized by:

(Function) According to the method for producing ZnO crystal particles having the above-described structure, by adding MgO, an anisotropic pattern in the grain growth of ZnO crystal nucleus particles, that is, the growth of X with respect to Y shown in FIG. It is possible to easily obtain uniform ZnO crystal particles by suppressing thickening of the ZnO crystal particles.

(Example) Examples of the present invention will be described below.

The amount of MCl0 added was 0.5 mol%, 3 mol%, and 8 mol% to the powder obtained by adding 0.5 mol% of BaC○ and SrCO3 in terms of Bad and SrO, respectively, to the ZnO raw powder.
, 12 mol %, 14 mol %, and 16 mol %, respectively, and 7 types of powder samples were prepared, including 6 types of mixed powders in which MQO was added instead of 12 mol %, 14 mol %, and 16 mol %, and 7 types of mixed powders in which MQO was not added. After mixing thoroughly, form into a disk shape, 11
The sintered body obtained by firing at 50°C for 4 hours was sufficiently boiled in pure water to dissolve the BaO layer and 5rOu. The ZnO crystal nucleus particles were thoroughly washed with water and dried, and the crystal nucleus particles for the addition of 1vloo were prepared. The shape, that is, the anisotropy (X/Y shown in FIG. 4) and the average grain size D5o of the crystal nucleus particles with respect to MGO addition m were investigated using micrographs, and the results were as shown in FIGS. 1 and 2. Next, MgO was added to the ZnO powder as the main component.
3.0 mol%.

B100.5 mol%, 5b203 0.05 mol%, COO 0.5 mol%.

Mn0.5 mol%, NiO0.5 mol%.

The above ZnO crystal grain nuclei were added to a slurry containing 00.5 mol % of Cr and thoroughly mixed.
't% added, thoroughly mixed, dried, granulated, and sintered at 1200°C for 4 hours to form a varistor element with a thickness of 1.0 shoes. Silver electrodes are provided on both sides of the varistor element. v1mA=2
MgO in the Zno crystal particle manufacturing method in the varistor of 2.
The results of examining the Δv1TrLA (%) after the surge test with respect to the amount added are shown in FIG. The test conditions in Figure 3 are current waveform 8/20 μsec, current density 50
0A/ci was applied 50 times. Note that the number of samples was 50 each. As is clear from FIG. 1, the crystal nucleus particle shape, that is, the anisotropy (X/Y shown in FIG. 4) without MqO added is 1.5 to 3. O (average value is 2.0) and has a large variation, whereas the shape of the crystal nucleus particle when MgO is added, that is, the anisotropy (X/Y shown in Fig. 4) is 1.0%, although there is a slight difference depending on the amount added. 1 to 1.8 (about 1 on average
．． 5) shows that the variation becomes smaller, and as is clear from Fig. 2, the average particle diameter D5o of the crystal nucleus particles becomes extremely small when the MaO addition m exceeds 14 mol%. As is clear, the surge resistance td of varistors using crystal grains to which MqO is not added has very large variations and is inferior in absolute terms (by 1 characteristic), whereas the surge resistance of varistors using crystal grains to which MqO is added is The variation is small, and the absolute value also shows inconsistent results.

From the above, tVIG can be used as a means of forming Zno crystal particles for varistors for low-voltage circuits whose main component is zinc oxide (ZnO).
It can be seen that the addition of 5 to 14 mol % of Ofo is superior. In the above example, barium (B) was used as an additive.
Although the example in which both the a) compound and the strontium (Br) compound are added at the same time has been described, the same effect can be obtained even if only one of them is added.

[Effect of the invention] As mentioned above, in producing Zno crystal particles, Z
By using 0.5 to 14 mol% of MQ compound in addition to Ba compounds and 3r compounds as additives added to nO powder, ZnO crystal nucleus particles with small anisotropy and uniform particle size can be obtained. It is possible to obtain excellent effects that are efficiently obtained and are optimal as ZnO crystal particles for low voltage circuits.

[Brief explanation of the drawing]

Figure 1 is a characteristic curve diagram showing the X/Y ratio of ZnO crystal nucleus particle shape with respect to the amount of MgO added, Figure 2 is a characteristic curve diagram showing the ZnO crystal nucleus particle size with respect to the amount of tVlo added, and Figure 3 is a characteristic curve diagram showing the amount of MgO added. △V1TrLA in the varistor for
FIG. 4 is an enlarged explanatory diagram of the ZnO crystal nucleus particle shape, and FIG. 5 is an enlarged diagram showing the ZnO crystal state of a varistor element according to a conventional reference example. Patent application Marcon Electronics Co., Ltd. 0 2 4 6 8 To 12
14 16 18 20 MGO addition amount (mol%) Fig. 1 0245 F3 To 12 +41618 MGIO addition 11 (mol%) Fig. 2 MgO addition II (mol%) Fig. 3 ZnO crystal crystallite powder bright diagram

Claims (1)

[Claims] Zinc oxide powder and at least one kind of barium (Ba) compound or strontium (Br) compound and 0.5~
A means for obtaining a mixed powder by adding 14 mol % of a magnesium (Mg) compound, a means for forming and sintering the mixed powder to obtain a sintered body, and a means for hydrolyzing the sintered body. A method for producing ZnO crystal particles, characterized by: