JPS6325219A - Production of zno crystal particle - Google Patents

Abstract

PURPOSE:To obtain the titled crystal particles having low anisotropy and uniform particle size and suitable for low-voltage circuit, in high efficiency, by adding a Ba or Sr compound and an Mg compound to specific ZnO powder, sintering the powdery mixture and hydrolyzing the sintered material. CONSTITUTION:A powdery mixture is produced by mixing (A) ZnO powder containing Al, In and/or Ga with (B) a barium compound (e.g. BaCO3) and/or a strontium compound (e.g. SrCO3) and (C) 0.5-14mol% Mg compound (e.g. MgO). The powder is compression molded and sintered e.g. at about 1,150 deg.C for about 4hr. The sintered product is hydrolyzed by boiling in pure water to dissolve the BaO layer and SrO layer. The obtained ZnO crystal particles are washed with water and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing ZnO crystal particles for a varistor for a low voltage circuit, the main component of which is zinc oxide (ZnO).

(Prior Art) Varistors containing ZnO as a main component are often used as having a surge absorbing function due to their cloudy co-linearity.

However, the varistor voltage in this scale varistor is ZnO
It is determined by the number of grain boundary layers existing between the electrodes provided on both the front and back surfaces of the sintered body. Therefore, in order to obtain a varistor for a low voltage circuit, it is necessary to reduce the thickness of the varistor element or to increase the ZnO 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 7-no particle size of the sintered body is 10 to 20μ.
m, so the fA viscosity is only about 0.2 mm,
This is not practical due to its low mechanical strength and the problem of cracking during the process. Therefore, a method has been devised to increase the ZnO particle size by adding a small amount of ZnO crystals (hereinafter referred to as crystal nucleus particles) with a particle size larger than the raw material particle size to the ZnO powder raw material to promote grain growth and increase the ZnO particle size. Among them, a method in which a sintered body obtained by molding and firing a powder obtained by adding and mixing a small amount of a 3a compound or a 3r compound to ZnO powder is hydrolyzed is a Ba compound used as a grain growth promoter.

It is widely used because Sr compounds can be removed by hydrolysis and the crystal nucleus particle size can be easily controlled. However, the crystal nucleus particle size obtained by such a method is determined by the size of the longest part X and the uppermost part Y in the direction perpendicular to X, as shown in Figure 4.
The ratio X/Y varies greatly, and varies from elongated to nearly circular, so the varistor element obtained using this crystal nucleus particle has an extremely small number of grain boundary layers. As a result, the electric resistance of the parts decreases, and current concentrates, 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, which involves hydrolyzing a sintered body obtained by adding Ba or 3r compound to ZnO, forming it, and firing it. There is a method for producing ZnO crystal particles in which the sintered body has a thickness of 25 to 300 μm, which greatly contributes to the formation of particles with a circular shape by reducing the ratio of X/Y, which is exemplified as the crystal nucleus particle size. can. However, such a method requires special equipment for sheet formation and requires a large number of man-hours to obtain ZnO particles from a sheet-shaped compact, which is not only impractical, but also because the molding pressure is low. The size of the grains is not uniform, and at the same time, the grains are coarse and have an uneven surface, which cannot be said to be an effective means.

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

An object of the present invention is to solve the above problems and provide a manufacturing method for obtaining ZnO crystal particles that are effective as varistors for low voltage circuits.

[Structure of the Invention] (Means for Solving the Problems) The method for producing ZnO crystal particles of the present invention includes aluminum (1
), indium (In), and gallium (Ga) at least 1g! A sintered body obtained by press-molding and firing a mixed powder obtained by adding at least one of a barium (Ba) compound, a strontium (Sr) compound, and a magnesium (MO) compound to suboxide tD (ZnO) powder containing Preferably, the magnesium compound is converted into MCl0 and added in an amount of 0.5 to 14 mol %.

(Function) According to the method for manufacturing ZnO crystal particles having the above-described structure, by adding MQO, anisotropy in grain growth of ZnO crystal nucleus particles, that is, growth of X with respect to Y shown in FIG. It is possible to easily obtain 1 q of uniform ZnO crystal particles by suppressing the increase in size of ZnO crystal particles.

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

Ba is added to the ZnO raw powder containing 20 ppm as AfJ atoms.
Bad for C0 and SrCO3.

MCl0 was added to the powder to which 0.5 mol% was added in exchange for SrO.
6 types of mixed powders in which the amount of MQO added is changed to 0.5 mol%, 3 mol%, 8 mol%, 12 mol%, 14 mol%, and 16 mol%, and mixed powder without MQO added. Seven types of powder samples were prepared, each powder sample was thoroughly mixed, formed into a disk shape, and fired at 1150°C for 41111 m. The obtained sintered body was thoroughly boiled in pure water. The ZnO crystal nucleus particles that were able to dissolve the BaO layer and the sro layer were thoroughly washed with water and dried, and the shape and size of the crystal nucleus particles, that is, the anisotropy (X/Y shown in Fig. 4) and M
The average particle diameter D5o of the crystal nucleus particles with respect to the addition of QO was examined using micrographs, and the results were as shown in FIGS. 1 and 2. Next, MqO3 is added to ZnO powder as the main component.
,0 mol%, 3i203 0.5 mol%, 3b
○ 0.05 mol%, CO ○ 0.5 mol%, MnOO
,5 mol%, Ni00.5 mol%, CrOO,5-
5 wt% of the solid content of the slurry was added to the slurry which had been thoroughly mixed with Ele%.
We investigated ΔV1rrLA (%) after a surge test for MqO addition using the ZnO crystal particle production method in a v1mA = 22V varistor with silver electrodes on both sides of a varistor element with a thickness of 1°0m formed by sintering for 4 hours. The result was as shown in Figure 3. The test conditions in FIG. 3 are a current waveform of 8/20 μsec, a current density of 500 A/i, and 50 applications. Note that the number of samples was 50 each. 1st
As is clear from the figure, the shape of the crystal nucleus particle without adding MoO, that is, the anisotropy (X/Y shown in Figure 4)G, tl,
While there is a large variation of 2 to 3°2 (average value is 2.3), the shape of the crystal nucleus particle with MgO added, that is, the anisotropy (X/Y shown in Figure 4), varies slightly depending on the amount added. Although there is a difference between 1.0 and 2.0 (approximately 1.5 on average), the results show that the variation is small, and as is clear from FIG. d is 14
When Tnyl% is exceeded, the result becomes extremely small, and the third
As is clear from the figure, the surge resistance of the varistor using crystal grains to which MqO is not added is very variable and the absolute value characteristics are inferior, whereas the surge resistance of the varistor using crystal grains to which MQO is added is The variation is small and the absolute values also show excellent results.

In addition, in the above example, Zn as a raw material for ZnO crystal particles
The explanation has been given using aluminum (Aρ) as an additive to O, but aluminum (All )
The same effect can be obtained by adding indium (r, n) or gallium (Ga) alone, or by adding two or more of aluminum (Al), indium (In), and gallium (Ga). Can be done.

From the above, formation of ZnO crystal particles for varistors for low-voltage circuits whose main component is zinc oxide (ZnO) containing at least one of All, In, and Ga ・MgO as a means
It can be seen that the addition of 0.5 to 14 mol % is advantageous. In the above example, barium (Ba
) compound and a strontium (Sr) compound are added at the same time, but the same effect can be obtained even if only one of the species is added.

[Efficacy of invention! $! ] As mentioned above, in the production of ZnO crystal particles, in addition to Ba compounds and Sr compounds, additives are added to ZnO powder containing at least one of aluminum (All), indium (In), and gallium (Ga). By using 0.5 to 14 mol% of the MO compound, it is possible to efficiently obtain ZnO crystal nucleus particles with small anisotropy and uniform particle diameter, which can be used as ZnO crystal particles for low voltage circuits. You can get the best and best effect.

[Brief explanation of the drawing]

Figure 1 is a characteristic curve diagram showing the X/Y ratio of ZnO crystal nucleus particle shape for MgO addition, Figure 2 is a characteristic curve diagram showing the ZnO crystal nucleus particle size for MQOWi suspension, and Figure 3 is MgO addition. 4 is an enlarged explanatory diagram of the ZnO crystal nucleus particle shape, and FIG. 5 is a characteristic curve diagram showing 8 V mA in a varistor according to a conventional reference example.
FIG. 3 is an enlarged view showing the n30 crystal state. Patent application Hito Marukon Electronics Co., Ltd. ~ +00 addition l (mol%) Figure 1 0246810124446 +a MQO addition 1! &(mol%) Mao addition addition top %)

Claims (1)

[Claims] Barium (Ba) compound or strontium (Sr) is added to zinc oxide powder containing at least one of aluminum (Al), indium (In), and gallium (Ga).
A means for obtaining a mixed powder by adding at least one type of compound and 0.5 to 14 mol% of a magnesium (Mg) compound; a means for obtaining a sintered body by molding and sintering the mixed powder; and a means for obtaining a sintered body by molding and sintering the mixed powder. 1. A method for producing ZnO crystal particles, comprising: means for hydrolyzing ZnO crystal particles.