JPH05258914A - Manufacture of voltage non-linear resistor - Google Patents

Abstract

PURPOSE:To lessen the irregularity in particle diameter and the like of the zinc oxide particles in the calcined body of the title voltage non-linear resistor which is mainly composed of zinc oxide and containing an additive for development of non-linearity of voltage. CONSTITUTION:The title voltage non-linear resistor is mainly composed of zinc oxide powder, and it contains one or more kinds of additive powders. The powder grains, having the configuration of the ratio of length of major axis and minor axis of 2 or less, occupies 90wt.% or more, and average grain diameter is 0.1 to 2.0mum. This mixed powder is molded, and the molded body is calcined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a voltage non-linear resistor containing zinc oxide as a main component and containing an additive for exhibiting voltage non-linearity.

[0002]

2. Description of the Related Art Since a voltage non-linear resistor containing zinc oxide as a main component has excellent non-linear voltage-current characteristics, it is widely used in surge arresters and surge absorbers for the purpose of voltage stabilization or surge absorption. ing. Such a voltage non-linear resistor is obtained by adding and mixing bismuth oxide, antimony oxide, cobalt oxide, silicon oxide, etc. to zinc oxide powder, if necessary, and further adding an organic binder such as polyvinyl alcohol, and mixing. A slurry is obtained by drying the slurry, granulating the granulated powder, molding the granulated powder, and firing the molded body.

Of these, in the mixing and pulverizing steps,
The technology for homogenizing the structure of the fired body by defining the average particle size and the particle size distribution of the powdered material after crushing
It is disclosed in the Japanese Patent Publication No. -35803. A technique for defining the particle size distribution of zinc oxide raw material powder is disclosed in JP-A-57-188803, and a technique for defining the particle size of additive raw material particles is disclosed in JP-B-60-927. There is.

[0004]

However, within the framework of such a conventional technique, it is difficult to actually control the microstructure of the fired body microscopically, and it is difficult to form a homogeneous structure. Such structural nonuniformity causes problems such as reduction in discharge withstand capability of the fired body and nonuniformity of voltage in-plane distribution. An object of the present invention is to make the microstructure of the fired body uniform and improve the discharge withstand capability and the like of the fired body.

[0005]

The present invention is a mixed powder containing zinc oxide powder as a main component and one or more kinds of additive powders, wherein the ratio of the major axis length to the minor axis length ( 90% by weight or more of powder particles having a shape of (major axis / minor axis) of less than 2 are formed, and a mixed powder having an average particle size of 0.1 to 2.0 μm is formed, and the formed body is fired. The present invention relates to a method for manufacturing a voltage non-linear resistor.

[0006]

The present inventor has completed the present invention by finding that the shape of the powder particles in the mixed powder is important in homogenizing the fine structure of the fired body. That is, the particle shape of the mixed powder greatly influences the moldability and the reactivity during firing. According to the present invention, powder particles having a shape in which the length ratio of the long axis and the short axis (long axis / short axis) is less than 2 are
90% by weight or more, and the average particle size of the mixed powder is 0.1-
By selecting so as to be in the range of 2.0 μm, needle-like crystals, distorted particles, too fine particles, and large particles can be removed, and the moldability of the mixed powder can be improved. In addition, the reactivity can be made uniform, abnormal grain growth due to needle-like crystals, etc. can be prevented, and the structure of the sintered body can be made uniform.

There are two methods for obtaining the mixed powder as described above. First, each raw material of a zinc oxide powder and an additive powder is selected, then mixed, and at the stage of mixing them, a powder having a shape in which the length ratio of the major axis to the minor axis is less than 2. The particles may account for 90% by weight or more of the mixed powder. Further, even if the above requirements are not met at the stage of mixing the zinc oxide powder and the additive powder, by performing pulverization or the like after this, the ratio of the length of the major axis to the minor axis is less than 2. Powder particles having a certain shape can occupy 90% by weight or more of the mixed powder.

The major axis and the minor axis will be described. It is assumed that the longest straight line passing through the center O of the powder particles 1A having a relatively spherical shape as shown in FIG. 1 is L and the shortest straight line is S. In this powder particle 1A, the length ratio L / S of the major axis and the minor axis is close to 1. FIG. 2 shows elongated needle-shaped powder particles 1B. The longest straight line passing through the center O is L, and the shortest straight line is S. In powder particle 1B, L / S is 2 or more.

[0009]

Example A mixed powder containing zinc oxide powder as a main component and additive powder having the following mixing ratio was prepared. This blending ratio is
Bi ₂ O ₃ 1.0 mol%, Sb ₂ O ₃ 1.0 mol%, Cr ₂ O ₃ 0.5 mol%, Mn
O ₂ 0.5 mol%, Co ₂ O ₃ 0.5 mol%, SiO ₂ 0.5 mol%, NiO
It consists of 0.5 mol%, Al ₂ O ₃ 0.002 mol% and the balance ZnO. In this mixed powder, the content rate of powder particles having a shape in which the length ratio of the major axis to the minor axis is less than 2 was changed as shown in Table 1.

Next, the mixed powders are wet mixed in a ball mill for 40 hours, dried and granulated, and then a constant pressure, for example, 200 kg.
Molded under / cm ² . The molded body obtained is degreased and pre-baked at a predetermined schedule, for example 900 ° C x 2 hours, and after applying an inorganic substance paste for forming a high resistance layer, it is heated to 1300 ° C x
Firing was performed for 5 hours to obtain a fired body. After polishing both end faces of this fired body, aluminum electrodes were provided on both end faces by a method such as thermal spraying to obtain a voltage non-linear resistor having a diameter of 35 mm, an electrode diameter of 34 mm and a thickness of 17 mm.

Under the same manufacturing conditions, the voltage nonlinear resistors of the examples in the table were manufactured. For each voltage nonlinear resistor,
The microstructure was observed by a scanning electron microscope (SEM) and the electrical characteristics were measured. Then, the relationship between the content ratio of the powder particles having the major axis / the minor axis <2 in the mixed powder and the voltage nonlinear resistor produced by using each mixed powder was investigated. The results are shown in the table.

The measuring method for each item in the table is shown below. The content ratio of powder particles with long axis / short axis <2 in the mixed powder is 300 particles arbitrarily extracted from the electron micrograph of the mixed powder, and the long axis and short axis of each powder particle And the length were measured, and the ratio of the two was investigated. The average particle size of the mixed powder was measured by the laser scattering method. The compact density was calculated from the weight and dimension measurement results of the compact. The particle size of zinc oxide particles in the fired body is measured by taking a microstructure SEM photograph of the polished surface, extracting 100 particles arbitrarily from the photograph, measuring each particle size with a ruler, and measuring the average particle size and the standard. The method of calculating the deviation was used. Regarding the 2 mS limit discharge withstand capability, 10 resistors were manufactured using the mixed powder of each example, and a 2 mS square wave with a predetermined current value was applied to each of these resistors at an interval of 1 minute.
It was applied once and evaluated by the average value of the maximum processing energies of 10 resistors.

[0013]

[Table 1]

As can be seen from the results in Table 1, the proportion of powder particles having a shape in which the length ratio of the major axis to the minor axis is less than 2 is
90% by weight or more, and the average particle size of the mixed powder is 0.1 to 2.
When it is 0 μm, the compact density is high, the variation in the particle size of the zinc oxide particles in the fired body is small, and the 2 mS limit discharge withstand capability is also good. On the other hand, if the proportion of powder particles having a shape in which the length ratio of the major axis to the minor axis is less than 2 is less than 90% by weight, or if the average particle size is less than 0.1 μm or greater than 2.0 μm, the molded article The density is reduced, the variation in particle size of zinc oxide particles is large, and the 2 mS limit discharge withstand capability is also low. Therefore, the present invention improves the moldability of the mixed powder,
The microstructure of the fired body becomes uniform, and the 2 mS limit discharge withstand capability becomes good.

[0015]

As described above, according to the present invention, the moldability of the mixed powder is improved, the variation in the particle size of the zinc oxide particles in the fired body is reduced, and a uniform microstructure is obtained. Obtainable. As a result, electrical characteristics such as discharge withstand capability of the voltage non-linear resistor are improved.

[Brief description of drawings]

FIG. 1 is a front view schematically showing a powder particle 1A having a relatively spherical shape.

FIG. 2 is a front view schematically showing a needle-shaped powder particle 1B.

[Explanation of symbols]

 1A, 1B Powder particle L Long axis S Short axis O Center

Claims (1)

[Claims] 1. A mixed powder containing zinc oxide powder as a main component and one or more kinds of additive powders, wherein the ratio of the major axis to the minor axis (long axis / short axis) is 2. 90% by weight or more of powder particles having a shape of less than 0.1 and an average particle diameter of 0.1 to 2.0 μ
A method for producing a voltage non-linear resistor, which comprises molding a mixed powder in the range of m 2 and firing the molded body.