JPS63296307A - Manufacture of zinc oxide type varistor - Google Patents

Abstract

PURPOSE:To obtain an element having large surge resistance and high varistor voltage per unit thickness by using silicon carbide as a starting material for the zinc oxide type varistor element. CONSTITUTION:Silicon carbide is employed as a starting material for a zinc oxide type varistor element in which zinc silicate is contained in a sintered body. When silicon carbide is used as the starting material, grinding progresses at rates quicker and more uniform than silicon carbide is employed, thus reducing the generation of voids in the sintered body while equalizing current distribution by the uniform distribution of zinc silicate. Accordingly, surge resistance is increased, and varistor voltage per unit thickness is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a zinc oxide type varistor whose main component is zinc oxide.

Conventional technology Zinc oxide type varistor elements have a large surge current withstand capacity and excellent voltage nonlinearity, and low-voltage type elements are widely used as surge absorbers, and high-voltage type elements as gapless arrester elements.

Conventionally, the main component of zinc oxide type varistor elements is zinc oxide (Z
Add bismuth oxide (Bi20s), antimony oxide (Sb20s), cobalt oxide (C'203), manganese monooxide (MnO2) + silicon oxide (Sin2), etc. to nO), add an appropriate binder, and wet process using a ball mill etc. After pulverization, it is manufactured through granulation, molding, and sintering processes. When manufacturing zinc oxide type varistors for arresters, the varistor voltage per unit thickness (v, 1□/mm
) is 200V or higher, which is necessary for downsizing and lowering the cost of devices. Among the above additives, silicon oxide (
Si02) is known as a substance that suppresses grain growth of zinc oxide and also improves temperature characteristics and electrification life characteristics.
It is an essential component of materials for high-voltage arrester elements. As a result of analysis using an X-ray microanalyzer and X-ray diffraction, silicon oxide is segregated near the triple point between zinc oxide grains in the sintered body, similar to antimony halide, and exists as zinc silicate (Zn25i04). This was confirmed.

Problems to be Solved by the Invention However, when silicon oxide (S-02) is used as the starting material for zinc oxide type varistors, its bulk specific gravity is significantly lighter than other additives, and even when sedimentary materials are used, As a result, voids are generated in the sintered body, and the surge resistance (2 m
s square wave current application test) was low. Silicon oxide (Si0) is still being used to increase the pressure of the material.
When 2) is added in an amount of 1 molar or more, the viscosity of the pulverized raw material slurry increases significantly, which also poses the problem of making granulation difficult.

The present invention solves these conventional problems,
The main purpose of this study is to improve the performance of zinc oxide varistors, especially to significantly improve surge resistance, and also to provide a method for manufacturing zinc oxide varistors that does not cause slurry gelation. Means to Solve the Problem In order to solve the above problems, the present invention is characterized in that at least silicon carbide (Sin) is used as an additive in zinc oxide, which is the main component.

Function: According to the method for producing a zinc oxide type varistor of the present invention, the bulk specific gravity of silicon carbide as an additive is high, and the pulverization proceeds quickly, making it difficult for voids to occur in the sintered body and achieving extremely high surge resistance. It is possible to manufacture a zinc oxide type varistor having the following properties.

EXAMPLES Hereinafter, the manufacturing method of the present invention and the zinc oxide type varistor obtained thereby will be explained in detail based on examples.

First, add 0 bismuth oxide to the total amount of zinc oxide powder.
．． 5 mol%, antimony oxide 1. Q mole ratio, 0.5 mol% of cobalt oxide, 0.5 mol% of manganese i-ide, and 0.5 to 20 mol of silicon carbide in SiC form are added to the raw material powder, and the solid content ratio is about 60. Add pure water to make the weight%, and use Pv (polyvinyl alcohol) as a binder.
was added in an amount of 0.5% by weight based on the solid content, and the whole was placed in a ball mill together with zirconia cobblestones and pulverized for 30 hours to obtain a slurry.

Note that the average particle size of the added silicon carbide is 3.0 μm. This slurry was dried with a spray dryer and granulated to prepare raw material powder. This raw material powder was compression molded to a size of 40 mm in diameter and 30 mm in thickness, and
It was sintered at 0'C. Both end faces of the sintered body thus obtained were polished to form sprayed aluminum electrodes.

Here, the viscosity of the slurry was measured using a rotational viscometer. For comparison, a system using silicon oxide as the starting material was also created using the same manufacturing process. The figure shows the change in slurry viscosity over time. When using 1 molar silicon oxide as the starting material, the viscosity exceeds so cps in about 5 hours, making it impossible to granulate with a spray dryer. Furthermore, when using silicon oxide with a 5 molar ratio, the initial viscosity is already s
It was confirmed that it exceeded o o cps. On the other hand, it can be seen that when 1 molar silicon carbide (SiC) is used as the starting material, almost no thickening phenomenon of the slurry is observed. Similarly, no thickening phenomenon was observed when using 1 mmol methylpolysiloxane. Therefore, the addition method of silicone resin allows granulation using a spray dryer for a long period of time. Table 1 below shows the initial characteristics of a sample in which electrodes were formed on a zero-order sintered body, which was found to be extremely convenient for processing a large amount of raw material. V,□,v,. 1□ was measured using a DC constant current power supply. Further, the limiting voltage characteristics were measured using an impulse with a current peak value of 500 μs and a waveform of 8/2 μs. It can be seen that there is almost no difference in initial characteristics between the silicon oxide addition method and the silicon carbide addition method, except for the thickening phenomenon of the slurry. Furthermore, by adopting the silicone resin addition method,
It becomes possible to add a large amount of 1 to 10 mol, and it is possible to easily realize miniaturization and cost reduction of the device. Also,
As a result of performing material analysis on the sintered body to which silicon carbide was added, it was confirmed that zinc silicate existed near the triple point between zinc oxides, just as in the case where silicon oxide was added.

(Left below) <Table 1> (1) This is a comparative study example and is different from the present invention.

(2) v5 K A /v1+1m Next, a surge resistance test was conducted on the above sample. The test conditions were to repeatedly apply a rectangular wave current of 2m1118,300m in the same direction at 6 minute intervals until the device was destroyed. The results are shown in Table 2 below. The values in the table are the average value of the number of square wave current applications that the device withstood without breaking, the number of samples (6 each), and the distribution range (highest value - lowest value)
It was shown in

<Table 2> (1) This is a comparative study example and is different from the present invention example.

From Table 2, it can be seen that by changing the starting material from silicon oxide to silicon carbide, the surge resistance is approximately doubled, and the performance is significantly improved. It can also be seen that the distribution range is narrower than the average value, and the reliability of the device is also improved. This is because when silicon carbide is used as a starting material, pulverization proceeds more quickly and uniformly than when silicon oxide is used, which reduces the generation of voids inside the sintered body, and also reduces the amount of zinc silicate. This is thought to be because the current distribution became uniform due to the uniform distribution. In addition, the reason why the surge resistance gradually decreases as the amount of silicon carbide added increases is that the varistor voltage per unit thickness (v4.n, 7 mm) increases due to the addition of silicon carbide.
increases, the energy applied per unit volume increases,
Although it is thought that heat stress makes it easier to break down,
Compared to conventional samples, this method has significant effects in terms of performance and reduction in device size and cost.

Effects of the Invention As described above, according to the present invention, by using silicon carbide as the starting material for a zinc oxide type varistor element, it is possible to easily manufacture an element with a large surge resistance and a high varistor voltage per unit thickness. can.

[Brief explanation of the drawing]

The figure is a diagram showing changes over time in the viscosity of raw material slurries obtained by the present invention and the conventional manufacturing method.

Claims (1)

[Claims] A method for producing a zinc oxide varistor, characterized in that silicon carbide is used as a starting material for a zinc oxide varistor element containing zinc silicate in a sintered body.