JPH03265559A - Zinc oxide as starting material for voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To reduce internal defects and to improve the uniformity and electric discharge resistance of an element by specifying average particle size, particle size distribution, acicular crystal content and SiC content. CONSTITUTION:Metallic zinc 1 is melted in a melting furnace 2 made of SiC and fitted with a weir 8. Sludge 9 is removed and molten zinc is fed into a retort furnace 3 and boiled by heating to 1,1001,400 deg.C. Generated zinc vapor is introduced into the oxidation chamber 3a of the furnace 3 through an evaporation hole and hot ZnO is obtd. by burning the vapor. This ZnO is slowly cooled to about 400 deg.C in a cooling duct 4, most of it is captured in capturing tanks 5 and part of it is captured with bag filters 7. ZnO as starting material for a voltage nonlinear resistor is obtd. This ZnO contains <=0.001wt.% SiO as an impurity and has <=20wt.% acicular crystal content, 0.1-2.0mum average particle size and particle size distribution in which >=70wt.% of the particles are present within the range of 1/2-2 times the average particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zinc oxide raw material that can be suitably used for voltage nonlinear resistors containing zinc oxide as a main component.

(Prior art) B12031 has traditionally been made with zinc oxide (ZnO) as its main component.
Resistors containing small amounts of additives such as SbzO3+ 5iOi and CozOz+ MnO2 as subcomponents are widely known to exhibit excellent voltage nonlinearity, and are used in lightning arresters etc. by taking advantage of this property. .

It is known that in order to improve the discharge withstand capacity of this voltage nonlinear resistor whose main component is zinc oxide, it is good to reduce internal defects in the fired body. As described in JP-A-56-115503, the slurry is passed through a sieve to remove foreign substances before granulation.

(Problems to be Solved by the Invention) However, with the conventional methods for reducing internal defects described above, the internal defects cannot be sufficiently reduced, and therefore sufficient effects cannot be obtained. There was a problem that the discharge withstand capacity could not be sufficiently improved. In particular, depending on the properties of the zinc oxide raw material that occupies about 90 wt% of the device width, the occurrence of internal defects may increase.

An object of the present invention is to solve the above-mentioned problems and provide a zinc oxide raw material that can reduce internal defects, improve device uniformity, and obtain a voltage nonlinear resistor with good discharge withstand capacity. It is something.

(Means for Solving the Problems) The zinc oxide raw material for voltage nonlinear resistors of the present invention has a particle size of 0.1 to 2.0 μm and 1/2 to 2 of the average particle size.
It has a particle size distribution of 70-t% or more between times, needle-like crystals are 20-t% or less, and SiC as an impurity
It is characterized in that the content is 0.0O1ivt% or less.

(Function) In the above-mentioned configuration, if a voltage nonlinear resistor is manufactured using zinc oxide particles with a predetermined particle size and particle size distribution, a predetermined crystal form, and a predetermined impurity, particularly SiCl, reduced, internal defects can be sufficiently eliminated. It has been found that it is possible to obtain a voltage non-linear resistor having a good discharge withstand capacity, which can reduce the amount of discharge and improve the uniformity of the element.

Zinc oxide is generally produced by oxidizing zinc, and its crystal system is mainly hexagonal, and its form is block-like or plate-like. However, depending on the manufacturing conditions, needle-shaped crystals may also be formed and mixed into the zinc oxide raw material.

In the present invention, the average particle size of zinc oxide is limited to 0.1 to 2.0 μm, preferably 0.3 to 0.8μ sheath, and the particle size distribution is determined such that 172 to 2 times the average particle size is 70-t% or more. More preferably, it is limited to 80-t% or more, but this is because zinc oxide particles grow uniformly during the firing process of the zinc oxide element.
This is because inherent defects such as voids are reduced. In addition, the reason why the acicular crystals are limited to 20iIlt% or less, preferably 10-t% or less, is to prevent abnormal particle growth of zinc oxide during the firing process, which causes deterioration of the characteristics of the voltage nonlinear resistor. This is because it is advantageous. When this zinc oxide particles grow abnormally, the uniformity of the device is greatly reduced and the discharge withstand capacity is also reduced.

On the other hand, the SiC content as an impurity in zinc oxide is 0.0
01wt% or less, preferably O,OOOO1imt%
The reason why it is limited to the following is that internal defects such as voids in the element can be sufficiently reduced and good discharge withstand capacity can be obtained. The reason for this is thought to be that if SiC is mixed in zinc oxide, the SiC decomposed gas forms closed pores at temperatures above about 1000° C. during the firing process, causing internal defects. In addition, bismuth oxide is added as an additive to zinc oxide elements.
．． 5 wt% or less (noticeable at wt% or more), antimony oxide at least 0.3-t% (noticeable at 1,5 wt% or more), praseodymium oxide at least 0.01 wt% (0,0
5wt% or less), the decomposition reaction of SiC is promoted and the decomposed gas tends to form closed pores, which has a negative effect on the characteristics of the zinc oxide element. Further, the additives include bismuth oxide of 2 wt% or more, antimony oxide of 1.5 wt% or less, and praseodymium of 0.5 wt% or less.
If the amount is less than 0.05 wt%, the above-mentioned decomposition reaction of SiC is further promoted, and the characteristics of the zinc oxide element are significantly adversely affected. For this reason, SiC in the zinc oxide raw material
It is extremely important to keep the content below a predetermined amount in order to produce a zinc oxide element with excellent and uniform properties.

(Example) FIG. 1 is a diagram showing an example of a conventionally known apparatus for manufacturing a zinc oxide raw material. In FIG. 1, 1 is metallic zinc as a raw material, 2 is a melting furnace having a SiC melting tank for melting the metallic zinc 1, 3 is a retort furnace for carrying out an oxidation reaction, 4 is a cooling duct, and 5 is a collection tank, 6 is a ventilator,
7 is a bag filter. In the apparatus configured as described above, when the metal zinc 1 melted in the melting furnace 2 is put into the retort furnace 3 and heated from the outside to about 1100 to 1400°C,
Zinc in the retort furnace 3 reaches its boiling point (approximately 900°C),
It is ejected from the evaporation port and combusted and oxidized in the oxidation chamber 3a inside the retort furnace 3. The high-temperature zinc oxide obtained in the oxidation chamber 3a through combustion oxidation is sucked in by the suction force of the exhaust fan 6, passes through the cooling duct 4, and is cooled, and then most of it is stored in the collection tank 5. Also, a portion can be obtained as zinc oxide in the bag filter 7.

In the apparatus shown in Fig. 1, in order to make the resulting zinc oxide raw material have a predetermined particle size, particle size distribution, and crystal form, the amount of evaporation of metallic zinc, the air volume by the exhaust fan, the temperature of the oxidation chamber, and the high temperature are required. It is necessary to control the cooling rate of zinc oxide. In particular, cooling of high temperature zinc oxide is necessary to reduce needle crystals.
It is necessary to cool slowly to 00°C. In addition, in order to reduce the SiC content in the zinc oxide raw material, (1) the material of the melting furnace 2 should be changed from the current SiC material to another material such as Aha, A weir 8 is installed on the molten metal surface to prevent sludge 9 from entering the retort furnace 3. (3) The most downstream tank of the collection tank 5, which is usually composed of several stages of tanks arranged in series. ZnO obtained in
It is important to use raw materials, etc.

In order to obtain a voltage nonlinear resistor whose main component is a zinc oxide raw material having a predetermined average particle size, particle size distribution, crystal morphology, and SiC content obtained by the method described above, first,
Zinc oxide raw material adjusted to a predetermined particle size of 1 μm, finely divided bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, chromium oxide, preferably amorphous silicon oxide, nickel oxide, adjusted to a predetermined particle size of 1 μm or less, A predetermined amount of additives such as boron oxide, silver oxide, etc. are mixed. In this case, silver nitrate or boric acid may be used instead of silver oxide or boron oxide. Preferably, bismuth borosilicate glass containing silver is used. Here, the additive raw material is preferably 2 μm or less, preferably 0.0 μm or less so that it can be sintered at a low temperature.
It is preferable to use a fine powder of 5μ or less. At this time, a predetermined amount of polyvinyl alcohol aqueous solution and a predetermined amount of aluminum nitrate solution as an aluminum oxide source are added to these raw material powders to obtain a mixture.

Next, deaeration is performed under reduced pressure, preferably at a vacuum level of 200 mmHg or less, to obtain a mixed slurry. Here, the water content of the mixed slurry is 3
0 to 35-t%, and the viscosity of the mixed slurry is 10
It is preferable to set it to 0±50 cp. Next, the obtained mixed slurry was fed to a spray dryer to have an average particle size of 50 to 150 μm.
, preferably 80 to 120 μm and moisture content of 0.5 to 2
．． Granulated powder with OwL%, more preferably 0.9 to 1.5 wt%, is granulated. Next, the obtained granulated powder is molded into a predetermined shape under a molding pressure of 800 to 7000 kg/+m'' in a molding process.Molding can be done by ordinary compression molding,
It may be performed by isostatic pressing or the like.

Then, the molded body is pre-fired under conditions of a temperature increase/decrease rate of 100°C/hr or less and a holding time of 800 to 1000°C2 for 1 to 5 hours. Note that, before calcining, it is preferable to remove the binder and the like by scattering the molded body at a heating/cooling rate of 100'' C/hr or less and holding time at 400 to 600° C. for 1 to 10 hours.

Next, an insulating coating layer is formed on the side surface of the calcined body.

In the present invention, Bi2O3,5bz03. ZnO, 5
An insulating coating mixture paste prepared by adding organic binders such as ethyl cellulose, butyl calpitol, n-butyl acetate, etc. to a predetermined amount of i02, etc. is applied to the side surface of the calcined body to a thickness of 60 to 300 μm. Next, this temperature increase/decrease rate is 20~
Main firing is performed at 60°C/hr, 1000 to 1300°C, preferably 1050 to 1250°C, for 13 to 7 hours.

A glass paste prepared by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to glass powder is applied to a thickness of 100 to 300 μm on the above-mentioned insulating coating layer, and the temperature is raised and cooled in air at a rate of 50 to 300 μm. 200″C/
It is preferable to form the glass layer by heat treatment under the following conditions: hr, 400 to 800°C, holding time 0.5 to 2 hours.

After that, both end faces of the obtained voltage nonlinear resistor were bonded to SiC,
to 1203. Polishing is performed using water, preferably oil, as the polishing liquid with a polishing agent of #400 to #2000 such as diamond. Next, after cleaning the polished surfaces, electrodes made of aluminum or the like are provided on both polished end surfaces by, for example, thermal spraying to obtain a voltage nonlinear resistor.

Hereinafter, the results of actually measuring various characteristics of voltage linear resistors within and outside the scope of the present invention will be described.

According to the method described above, CO3041MnO2,Crz
0.1 to 2.0 mol% each of O3Nip and SiO□,
A l (NO3) 3.91 (200,005 mol%
, 0.1 wt% bismuth borosilicate glass containing silver,
4.5wt% Bi2O3, 3.0wt% 5bzOz
, and the average particle size, particle size distribution, percentage of needle-like crystals, and SiC content shown in Table 1. A varistor voltage (V
Voltage nonlinear resistors of present invention test Nos. 1 to 9 and comparative example test Nos. 1 to 5 shown in Table 1 with l, A) of 200 V/mm were prepared.

For the prepared resistors of the present invention example and comparative example, the fired body defect occurrence rate (%) and the switching surge discharge withstand breakdown rate (%)
, the lightning surge discharge withstand breakdown rate (%) and the variation in varistor voltage were measured. The results are shown in Table 1. Here, the defect occurrence rate of the fired product is determined by ultrasonic flaw detection test with a diameter of 0.5 m.
It was determined as the percentage of resistors that had the above defects. The breakdown rate of switching surge discharge capacity was determined as the percentage of breakdowns after 20 repeated applications of currents of 1200 A and 1300 A with a current waveform of 2 ms. The lightning surge discharge withstand breakdown rate is 4/10 t with a current of 120 KA and 140 KA.
It was determined as the percentage of the breakdown after repeated application of the current waveform of ts twice. The variation in the varistor voltage was determined by cutting and polishing the central part of the element 11 to prepare a sample with a thickness of a=2 mm, as shown in FIG. 2(b), as shown in FIG. 2(a).
At all of the measurement points 12 shown in FIG. 2(c), an electrode 13 is provided on the bottom surface, and the varistor voltage (VIAA/+a+a) is measured on the surface with a probe 14 with a diameter of 1 inch, and its variation is sought and evaluated.

The SiC content was determined by dissolving the raw material with an acid, alkali, etc., and quantifying the undissolved residue after filtration and washing using fluorescent X-rays, X-ray diffraction, etc.

From the results in Table 1, it can be seen that tests of the present invention using zinc oxide raw materials with a predetermined average particle size and particle size distribution, a predetermined proportion of acicular crystals, and a SiC content reduced to a predetermined value or less, Comparative example test Nα that does not meet the requirements of the present invention in terms of
It can be seen that the characteristics are better than those of Nos. 1 to 5.

Although the above embodiment describes a bismuth oxide varistor, the same applies to a praseodymium oxide varistor in which bismuth oxide is replaced with praseodymium oxide. Furthermore, as for the method for manufacturing zinc oxide, a method using oxidation of metal zinc has been described, but the same method as described above is also applied to a zinc oxide raw material obtained by a method using thermal decomposition of basic zinc carbonate.

(Effects of the Invention) As is clear from the above explanation, according to the zinc oxide raw material of the present invention, which has a predetermined average particle size and particle size distribution, and satisfies a predetermined acicular crystal and a predetermined SiC content, By manufacturing a voltage nonlinear resistor using the method, it is possible to reduce inherent defects, improve device uniformity, and obtain a voltage nonlinear resistor with good electrical characteristics.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus for manufacturing the zinc oxide raw material of the present invention, and FIGS. 2(a) to 2(c) are diagrams for explaining a method for measuring variations in varistor voltage, respectively. 1... Metallic zinc 2... Melting furnace 3... Retort furnace 3a... Oxidation chamber 4... Cooling duct 5... Collection tank 6... Exhaust fan
7... Hasog filter Figure 2 + a) (b) Procedural amendment document February 26, 1991

Claims (1)

[Claims] 1. It has an average particle size of 0.1 to 2.0 μm and a particle size distribution of 70 wt% or more between 1/2 and 2 times the average particle size, and has acicular crystals of 20 wt% or less and contains no impurities. A zinc oxide raw material for a voltage nonlinear resistor, characterized in that the SiC content is 0.001 wt% or less.