JPH02134801A - Voltage non-linear resistor and manufacture of the same - Google Patents

Abstract

PURPOSE:To improve voltage non-linearity in large current range and obtain a voltage non-linear resistor having excellent applied voltage lifetime and surge resistance amount by containing metallic zinc phase in the center of zinc oxide particles in a sintered body. CONSTITUTION:In a sintered body with zinc oxide as its main components having voltage non-linearity, a metallic zinc phase is contained in the center of zinc oxide particles in a sintered body. When voltage non-linear resistors with zinc oxide manufactured by an indirect method of oxidizing zinc vapors as its main components, those obtained by oxidizing zinc vapors at an atmosphere of oxygen partial pressure 100Torr or less are used as zinc oxide feedstock. For example, the size (d) of metallic zinc phase in the center of ZnO particles having an average grain size D in a resistor should preferably be in the range of d/D=0.30 to 0.95. Such ZnO particles can be obtained by burning and oxidizing vapors of zinc in an oxidization room 3a in which they are maintained in an atmosphere of oxygen partial pressure inside a retort furnace 100Torr or less.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voltage nonlinear resistor containing zinc oxide as a main component and a method for manufacturing the same.

(Conventional technology) Conventionally, zinc oxide (ZnO) is the main component, and BxtOa+
5bz02+ 5sOz+ C0zOs+ FInOt
It is widely known that a resistor containing a small amount of additives such as .

Conventionally, in order to improve the nonlinearity in the large current region of this voltage nonlinear resistor whose main component is zinc oxide,
(1) A valence control method in which trace amounts of AI ions, Ga ions + In ions are diffused during sintering to lower the Zn0O resistivity, (2) ZnO and A120i + GatOi + disclosed in JP-A-58-122703. IntO+
A method is known in which A1*Ga+In ions are preliminarily calcined to diffuse into a sintered body, and then mixed with subcomponents and shaped.

(Problem to be Solved by the Invention) However, in the above-mentioned valence control method (1), since the main component ZnO and subcomponents are simply mixed and molded, ^l ions, etc. are mixed and sintered. AI+
Ga and In ions were not sufficiently uniformly dispersed in the ZnO crystal, and most of them were incorporated into the grain boundary layer and spinel phase. Therefore, the improvement of nonlinearity in the large current region is insufficient,
In addition to deteriorating the energizing life, the varistor voltage decreases significantly after a lightning surge is applied, so constant energization causes a problem of thermal runaway in the resistor.

Furthermore, method (2) disclosed in JP-A-58-122703 is more effective than the above-mentioned valence control method (1), but the surge resistance is reduced due to non-uniform grain growth of ZnO. There was a problem.

An object of the present invention is to solve the above-mentioned problems and provide a voltage nonlinear resistor that can improve voltage nonlinearity in a large current range and also has good charging life and surge resistance, and a method for manufacturing the same. It is.

(Means for Solving the Problems) The voltage nonlinear resistor of the present invention is a sintered body containing zinc oxide as a main component and having voltage nonlinearity. It is characterized by containing a phase.

In addition, the method for manufacturing a voltage nonlinear resistor of the present invention is a method for manufacturing a voltage nonlinear resistor whose main component is zinc oxide, which is manufactured by an indirect method of oxidizing zinc vapor. It is characterized in that it uses a material obtained by oxidation in an atmosphere with a partial pressure of 100 torr or less.

(Function) In the voltage nonlinear resistor of the present invention, in the above-described configuration, for example, as shown in FIG. 1, which shows a cross section of ZnO particles having an average grain size of about 10 μm, By forming ZnO particles with the metallic zinc phase of d and the surrounding zinc oxide phase, the resistance of each particle can be reduced and the potential barrier between each grain boundary can be made uniform, so that It is possible to improve voltage nonlinearity and obtain a resistor with good various characteristics. Note that the size of the metallic zinc phase is d/as is clear from the examples described later.
The range of D=0.30 to 0.95 is preferable. Here, it is preferable that the metallic zinc phase is contained in all the ZnO particles, but it is not necessarily limited to all the ZnO particles.

Further, in the method for manufacturing a voltage nonlinear resistor of the present invention, zinc vapor is heated to an oxygen partial pressure of IQQtorr or less, preferably 10 torr.
The above-mentioned Zn is oxidized in an atmosphere below rr.
If O particles can be obtained and a voltage nonlinear resistor is manufactured using these ZnO particles, voltage nonlinearity in a large current range can be improved as described above, and a resistor with good various characteristics can be produced. Obtainable.

At this time, either perform the main firing of the resistor with a low oxygen partial pressure and then perform an annealing treatment at 500 to 900°C, or perform the first half of the main firing with a low oxygen partial pressure and the second half in the atmosphere. This is preferable because the properties of the ZnO particles are less likely to change.

(Example) FIG. 2 is a diagram showing the configuration of an example of an apparatus for implementing the conventionally known method for manufacturing a voltage nonlinear resistor of the present invention. In Fig. 2, 1 is metal zinc as a raw material, 2 is a melting furnace for melting metal zinc 1, 3 is a retort furnace for carrying out an oxidation reaction, 4 is a cooling duct, 5 is a collection tank, and 6 is an exhaust gas. Wind fan 7 is a bang filter. In the apparatus configured as described above, the metal zinc 1 melted in the melting furnace 2 is transferred to the retort furnace 3.
When the zinc in the retort furnace 3 reaches its boiling point (approximately 900°C) and is ejected from the evaporation port, the oxygen partial pressure inside the retort furnace 3 decreases to 10
Combustion oxidation is performed in the oxidation chamber 3a maintained at an atmosphere of 0 torr or less. The high-temperature zinc oxide obtained in the oxidation chamber 3a through combustion oxidation is sucked by the suction force of the exhaust fan 6, passes through the cooling duct 4 and is cooled, and then most of the zinc oxide is transferred to the collection tank 5.
A part of the zinc oxide can be obtained in the bag filter 7 as zinc oxide, the center of which is substantially composed of a metallic zinc phase.

A method for obtaining a voltage nonlinear resistor from the zinc oxide raw material obtained as described above is as follows.

To obtain a voltage nonlinear resistor whose main component is zinc oxide,
First, zinc oxide raw material adjusted to a predetermined particle size of 0.1 to 3 μm, fine powder bismuth oxide, cobalt oxide, manganese oxide, antimony oxide adjusted to a predetermined particle size of 1 μm or less,
A predetermined amount of an additive consisting of chromium oxide, preferably amorphous silicon oxide, nickel oxide, boron oxide, silver oxide, etc. is mixed.

In this case, silver nitrate, silver oxide, and boron oxide are used instead of silver oxide and boron oxide.
Boric acid may also be used. Preferably, bismuth borosilicate glass containing silver is used. Here, as the additive raw material, it is preferable to use fine powder of 1 all or less, preferably 0.5 μm or less so that the material can be sintered at a low temperature. At this time, a predetermined amount of polyvinyl alcohol aqueous solution or the like is added to these raw material powders.

Next, deaeration is performed under reduced pressure, preferably at a vacuum level of 200 wHg or less, to obtain a mixed slurry. Here, the water content of the mixed slurry is 30
~35-t%, and the viscosity of the mixed slurry is 100%.
It is preferable to set it to ±50 cp. Next, the obtained mixed slurry is supplied to a spray drying device to obtain an average particle size of 50 to 150μ,
Preferably, the diameter is 80 to 120 μm and the water content is 0.5 to 2.
Granulated powder of Owt%, more preferably 0.9 to 1.5% is granulated. Next, the obtained granulated powder is subjected to a molding process and molded into a predetermined shape under a molding pressure of 800 to 7000 kg/cm" (7). Molding can be done by ordinary compression molding, isostatic pressing, or by hot pressing. Press molding, old P treatment, etc. may be used.

Then, an insulating coating layer is formed on the side surface of the molded body. In the present invention, BIJ*+5l)z(1+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 molded body to a thickness of 60 to 300 μm. Next, this temperature increase/decrease rate is 20-6
0°C/hr, 700~900°C preferably 700~
Main firing is performed at 800°C for 13 to 7 hours.

The conditions for the main firing are either firing with a low oxygen partial pressure and then annealing at 500 to 900°C.
Alternatively, it is more preferable to lower the oxygen partial pressure in the first half of the main firing and to carry out the second half in the atmosphere. In addition, before the main firing, the molded body was heated at a heating and cooling rate of 10 to 100°C/hr for 300 to 500°C.
It is preferable to scatter and remove the binder with a holding time of 1 to 10 hours at °C. In addition, a glass paste prepared by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to glass powder was applied to the insulating coating layer at a rate of 100%.
Coated to a thickness of ~300 μ- and heated at a heating/cooling rate of 50 μm in air.
~200° (: /hr400~800°C holding time 0
．． It is preferable to form the glass layer by heat treating for 5 to 2 hours.

After that, both end faces of the obtained voltage nonlinear resistor were bonded to SiC,
Al□03. Polishing is carried out using an abrasive agent equivalent to #400 to #2000, such as diamond, using water, preferably oil, as the polishing liquid. 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 nonlinear resistors within and outside the scope of the present invention will be described.

According to the method described above, Bit03. CO:+04.
Mn0z+5bzOs+ CrzO=, Nip,
0.1 to 2.0 mol% of Sing, 0.01 to 0.3 wt% of bismuth borosilicate glass containing silver, and the balance of ZnO produced from an atmosphere with an oxygen partial pressure shown in Table 1. Diameter 47mm, thickness 22.5m from the raw material
m shape with varistor voltage (Vl, A) of 250 to 280
Voltage nonlinear resistors of the present invention samples kl~5 and comparative samples Nα1~2 shown in Table 1 of V/mn+ were prepared. The resistor was fired at 400°C for 5 hours at an oxygen partial pressure of 1 torr after degreasing. The temperature was raised to 800° C. in an h+ox atmosphere, and the temperature was further maintained at 800° C. for 5 hours in the air, and then the temperature was lowered.

In addition, the resistor was observed by SEM after polishing, and the average particle size of the ZnO particles and the average particle size d of the metallic zinc phase at the center of the ZnO particles were determined.
As a result, d/D=0.3 to 0.95.

Conventional method 1 of Comparative example 1 uses zinc oxide powder obtained by oxidizing with zinc vapor in air according to the conventional method, adds 1 mol% of Ni (NO3), z 98zOO, 0.01% to the raw material mixture, and fires. The method based on the valence control method in which AI ions are diffused by
As disclosed in Japanese Patent No. 122703, using zinc oxide powder obtained by a conventional method, this and A1. O.

The figure shows the mixture which was calcined at 900°C after mixing.

For the prepared resistors of the present invention and comparative examples, the limiting voltage ratio, VIIIA reduction rate, lightning surge withstand capacity, and switching surge withstand capacity were measured, and the leakage current ratio was determined.

The results are shown in Table 1. Here, the limiting voltage ratio is the varistor voltage V,. It was determined from the ratio of □ and VImA. The V1mA reduction rate is 10% with a current of 30KA and a current waveform of 8720μs.
It was determined from Vl and A before and after the voltage was applied. The lightning surge resistance is indicated by "×" for those that were destroyed after applying currents of 100 KA, 110 KA, and 120 KA twice with a current waveform of 4/10 gs, and as "O" for those that were not destroyed. Opening/closing surge resistance is 800A, 900A, 100A
After repeatedly applying the OA current with a current waveform of 2 ms 20 times, the samples that were destroyed were marked with "×", and those that were not broken were marked with "○". Furthermore, the ratio of leakage current is
“Charging at C1 charging rate of 95%, charging 1 immediately after charging
Current ratio after 00 hours! 10° hours/■. I asked for it from time.

From the results in Table 1, it can be seen that the resistor of the present invention, which uses a zinc oxide raw material having a metallic zinc phase in the center obtained by oxidation in an atmosphere with a predetermined atmospheric partial pressure, has better characteristics than the comparative example. It can be seen that the results are good.

2. In accordance with Example 1 described above, using zinc oxide produced in an N2+0□ atmosphere with an oxygen partial pressure of 100 torr or less,
In order to investigate the effect of changes in the diameter of the metal zinc phase on a resistor that has a metal zinc phase in the center of the Zoo particles after firing, resistors were fabricated with the d/D value changed in Figure 1. Then, various characteristics were measured in the same manner as in Example 1.

Note that the resistor was fired in the same manner as in Example 1. The results are shown in Table 2.

=4- From the results in Table 2, it is clear that any voltage nonlinear resistor with good characteristics can be obtained by following the method of the present invention, but among them, those with d/D = 0.30 to 0.95 can be obtained. was found to be good. Further, it has been found that when the value of d/D exceeds 0.95, the voltage nonlinearity of the voltage nonlinear resistor becomes so small as to be impractical.

(Effects of the Invention) As is clear from the above description, according to the voltage nonlinear resistor and the manufacturing method thereof of the present invention, metal zinc is formed in the center by oxidizing zinc vapor in an atmosphere with an oxygen partial pressure of 100 torr or less. By manufacturing a voltage nonlinear resistor using ZnO particles in which a phase exists, voltage nonlinearity in a large current range can be improved, and a voltage nonlinear resistor with good charging life and surge resistance can be obtained. be able to.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of ZnO particles of a voltage non-linear resistor of the present invention, and FIG. 2 is a diagram showing the configuration of an example of an apparatus for carrying out the method of manufacturing a voltage non-linear resistor of the present invention. . 1...Metal zinc 2...Melting furnace 3...Retorts 3a...Oxidation chamber 4...Cooling duct
5... Collection tank 6... Ventilator 7...
・Bag filter patent applicant Nippon Insulator Co., Ltd.

Claims (2)

[Claims] 1. A voltage nonlinear resistor characterized in that the sintered body contains zinc oxide as a main component and has voltage nonlinearity, and contains a metallic zinc phase in the center of zinc oxide particles in the sintered body. 2. In a method for manufacturing a voltage nonlinear resistor whose main component is zinc oxide, which is manufactured by an indirect method of oxidizing zinc vapor,
Zinc vapor is used as a zinc oxide raw material at an oxygen partial pressure of 100 torr.
A method for manufacturing a voltage nonlinear resistor, characterized by using a resistor obtained by oxidation in the following atmosphere.