JPH0323601A - Manufacture of nonlinear voltage resistor - Google Patents

Abstract

PURPOSE:To make elements highly dense and to enhance their nonlinearity and their voltage-impression life by a method wherein, in a manufacturing process in which a metal oxide is added to and mixed with a raw material composed mainly of zinc oxide and this mixture is baked, a temperature-raising process, a holding process of a highest temperature and a temperature-lowering process down to a specific temperature are executed in a reduced pressure state. CONSTITUTION:A metal oxide such as bismuth oxide, an antimony oxide or the like is added to and mixed with a raw material composed mainly of zinc oxide; this mixture is baked. In a heat-treatment schedule of this baking process, a temperature-raising process, a holding process of a highest temperature and a temperature-lowering process down to 1100 deg.C or lower are executed in a state that a pressure has been reduced to a prescribed value or lower. Thereby, it is possible to effectively remove that pores are produced inside an element by a vapor pressure of bismuth oxide or the like. The elements become highly dense and their nonlinearity and their voltage-impression life are enhanced.

Description

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

(Prior art) Voltage nonlinear resistors whose main component is zinc oxide are widely used in lightning arresters and surge absorbers for the purpose of voltage stabilization or surge absorption because of their excellent nonlinear voltage-current characteristics. This voltage nonlinear resistor is made by adding a small amount of metal oxide such as bismuth, antimony, cobalt, manganese, etc. that exhibits voltage nonlinearity to a certain amount of main zinc oxide.
Mixed, made. The grains are formed into shapes, fired, and preferably coated with an inorganic material on the side surfaces to form a high-resistance layer, then fired, and electrodes are attached to both end surfaces of the fired body.

When applying the voltage nonlinear resistor thus obtained to a lightning arrester intended for large surge absorption, it is desirable that the voltage nonlinear resistor has a large discharge withstand capacity. The discharge withstand capacity of a voltage non-linear resistor is determined by applying an impulse current with a waveform of 4/lOμs twice at 5-minute intervals, and increasing the current value in steps until the voltage non-linear resistor is destroyed or creeping flash occurs. It can be expressed as the maximum current value that does not cause destruction or creeping flash when It is thought that the discharge capacity of a voltage nonlinear resistor depends on the voids in the sintered body. In other words, the breakdown when an impulse current with a waveform of 4/10 μS is applied is thought to be due to thermal stress, so if voids are eliminated and the mechanical strength of the sintered body is increased, it is expected that the discharge withstand capacity will be improved. Ru. Further, since the dielectric constant of the void is about 1/iooo of that of the portion of the sintered body other than the void, a strong electric field is applied when an impulse current is applied, and discharge is likely to occur. When a discharge occurs from a void, the discharge triggers current concentration and generates large local thermal stress, which destroys the voltage nonlinear resistor. Therefore, it is desirable to remove voids in order to increase the mechanical strength of the sintered body and to prevent current concentration from occurring. Regarding the removal of voids from the sintered body, 800°C-1 during the heating process of the sintering process.
The method of heating up to 150℃ under reduced pressure below atmospheric pressure is
It is disclosed in Japanese Patent Application Laid-Open No. 58-28802.

(Problem to be Solved by the Invention) However, in the manufacturing method described in JP-A-58-28802, the actual firing temperature range around 1200°C is such that the vapor pressure of bismuth oxide contained in the element is low. This causes problems such as the formation of pores inside the device, and
During the temperature raising process, the pressure is reduced only in the range of 800 to 150°C, but the shrinkage of the element at this stage is due to the rearrangement of the particles, and there is a problem that small grain boundary pores are still left behind. Therefore, in either case, there was a problem in that high density of the element could not be achieved, and a voltage nonlinear resistor having good nonlinearity and a good energized life could not be obtained.

Furthermore, if the temperature is returned to atmospheric pressure during the heating process, gas is likely to be taken into the element surface, resulting in a bolus near the surface.

The purpose of the present invention is to provide a method for manufacturing a voltage nonlinear resistor that can obtain good nonlinearity and a good life when charged by eliminating the above-mentioned 5iJ and increasing the density of the element. This is what we are trying to provide. (Means for Solving the Problems) The method for manufacturing a voltage nonlinear resistor of the present invention involves adding metal oxides such as bismuth oxide and antimony oxide to a raw material containing zinc oxide as a main component, mixing it, and firing it. The method for manufacturing the voltage nonlinear resistor obtained is characterized in that among the firing steps, the temperature raising step, the maximum temperature holding step, and the temperature lowering step to at least 1100° C. are performed under reduced pressure.

(Function) In the above structure, the vapor pressure of bismuth oxide decreases during the temperature raising step, the maximum temperature holding step, and the temperature lowering step to at least 1100° C., preferably 950° C., in the heat treatment schedule of the sintering step. The process up to this point is preferably carried out under reduced pressure below 1QQ torr.
It is possible to effectively eliminate the generation of pores inside the device due to the high vapor pressure of bismuth oxide, and it is possible to achieve higher density of the device. Here, the reason why the temperature is returned to atmospheric pressure below 1100°C, preferably below 950°C during the cooling process is because when the pressure is reduced below 950°C, bismuth oxide transitions from the liquid phase to the solid phase and fills the micropores. This is because densification cannot be achieved because many people are left behind. In addition, the atmosphere at temperatures below 1100°C, preferably below 950°C during the cooling step may be air, but it is preferable to use an oxidizing atmosphere, that is, an oxygen concentration of 20 vol% or more, as the properties will be more stable. It is suitable. (Example) To obtain a voltage nonlinear resistor whose main component is zinc oxide,
First, zinc oxide raw material adjusted to a specified particle size, bismuth oxide, cobalt oxide, manganese oxide, adjusted to a specified consistency,
A predetermined amount of additives such as antimony oxide, chromium oxide, preferably amorphous silicon oxide, nickel oxide, 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. Alternatively, the additive may be calcined at goo-iooo°C and then pulverized and adjusted to a predetermined particle size and mixed with the zinc oxide raw material. At this time, a predetermined amount of polyvinyl alcohol aqueous solution or the like is added to these raw material powders.

Next, vacuum degassing is preferably performed at a vacuum level of 200 MHJI or less, and the water content of the mixed slurry is preferably about 30-35-L%, and the viscosity of the mixed slurry is preferably 100±50 cp. Next, the obtained mixed slurry is fed to a spray dryer to obtain an average particle size of 50 to 150 uII1, preferably 80 uII1.
-120μ and a moisture content of 0.5 to 2.0 wt%, more preferably 0.9 to 1.5 wt%. Next, the obtained granulated powder is shaped into a predetermined shape in a shaping process under a shaping pressure of 800 to 1000 kg/cya''.

Next, the precept-shaped body is heated and cooled at a rate of 10 to 50°C/hr.
The organic components are removed by scattering at a temperature of 400 to 700°C to obtain a degreased body.

Next, a high resistance layer is formed on the side surface of the degreased body. In this example, B
iz03+ Sb=0=, ZnO. An insulating coating mixture paste prepared by adding ethyl cellulose, butyl carbitol, n-butyl acetate, etc. as an organic binder to a predetermined amount of Sing et al. is applied to the side surface of the degreased body to a thickness of 60 to 300 μm. Next, this is heated at a temperature raising/lowering rate of 20-100°C/hr) a maximum holding temperature of 1000-1300°C, preferably 1050-12
Final firing was performed at 50°C for 13 to 7 hours. In the present invention, the temperature raising step, the maximum temperature holding step, and the temperature lowering step to at least 1100° C., preferably 950° C., are preferably performed in a reduced pressure atmosphere of 100 torr or less, and at 1100° C. ℃ or less, preferably 950℃ or less at atmospheric pressure, preferably oxygen concentration 20V
Calcinate in an oxidizing atmosphere of ol% or more.

A glass paste prepared by adding ethyl cellulose, butyl carbitol, n-butyl acetate, etc. as an organic binder to glass powder was applied to a thickness of 100 to 300 μm on the high-resistance layer on the side surface, and the temperature was raised and lowered in air. 50~200'C
/hr, 400 to 900°C for a holding time of 0.5 to 4 hours to form the glass layer. After that, both end faces of the obtained voltage nonlinear resistor were bonded to SiC,
Polishing is performed with an abrasive equivalent to 1400 to 2000, such as ^hO, diamond, using water, preferably oil, as the polishing liquid. Next, after cleaning the polished surfaces, electrodes are provided on both polished end surfaces using, for example, aluminum ξium, etc., by 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, 1.0 mol % of BizOi was added. C
O: lOJ 0.5 mol%, MnOt o. smol%
, SbgOs 1-0 mol%, CrzOs 0.5
mol%, Ni0 0.5 mol%, A1tOs O. 0
05 mol%, SiOz 1-2 mol% and the balance ZnO
The raw material consists of borosilicate bismuth glass and
．． 1 wt% was added, the heating rate was 44°C/hr, the maximum temperature holding step was 12lO°C x 5br, and the cooling rate was 60"C/hr.
hr condition to the temperature during the cooling step shown in Table 1.
Fired under reduced pressure of XIO” torr, diameter 47 mm,
l't sa 22.5+ma (7) Shape: Voltage nonlinear resistors of the present invention examples and comparative examples shown in Table 1 having voltages (L-a) of 169 to 206 V/mm were prepared.

Then, for the voltage nonlinear resistor obtained, the voltage nonlinearity index α, porosity, and lightning surge limit discharge withstand capacity were measured,
After taking a photograph, the pore area occupancy rate (pore area/element area) was measured from the photograph using an image analysis device, and this was determined as the porosity. Furthermore, the lightning surge discharge withstand breakdown rate is IOOK^
．． IIOKA, 120KA. It was determined as the percentage of breakdown after repeatedly applying a current of 130 K^ twice with a current waveform of 4/10/73.

It was determined from the measured values of currents of 0.1 mA and 1 mA.

Here, ■ is a current, ■ is a voltage, and C is a constant.

In addition, the porosity was measured using Sr! after polishing the sample. From the results in Table 1 observed at M, test kl~4 of the present invention, in which the reduced pressure during temperature cooling was up to 1100'C, was 1150°C and 950°C.
Compared to comparative test Nαl~5 in which the pressure was reduced to less than °C and comparative test NllL6 in which normal pressure burning was performed without reducing the pressure, both the voltage nonlinearity index α and the lightning surge limit discharge withstand breakdown rate were better. We were able to obtain the following characteristics. In addition, in the present invention test Nα1, in which the pressure was reduced only to 1100°C during the temperature drop, the porosity was higher than other examples of the present invention, and the lightning surge limit discharge capacity was slightly deteriorated. I know that there is. In order to investigate the influence of the degree of vacuum during depressurization, the temperature was lowered to 1000°C under the same conditions as in Example 1 at various degrees of vacuum shown in Table 2.
For the voltage nonlinear resistor obtained under reduced pressure up to
In the same manner as in Example 1, the porosity and lightning surge limit discharge withstand breakdown rate were determined, and the pass rate in the ultrasonic flaw detection test was determined. The results are shown in Table 2. From the results in Table 2, it can be seen that the present invention test Nal~6 in which the predetermined range was in a reduced pressure state had lower porosity, ultrasonic deep damage pass rate, and lightning surge limit discharge capacity than the comparative example in which the pressure was not reduced and the pressure was normal. All of them were good, confirming the effectiveness of decompression, and
Test NI12-6 with vacuum degree below 100 torr is 5
It can be seen that various characteristics are better than the test Na 1 at 00 torr.

(Effects of the Invention) As is clear from the above description, according to the method of manufacturing a voltage nonlinear resistor of the present invention, the lifting step, the maximum temperature holding step, and at least
Since the process up to 100°C is under reduced pressure, it is possible to effectively eliminate the generation of pores inside the device due to the high vapor pressure of bismuth oxide, and it is possible to achieve high density of the device, resulting in good results. It is possible to obtain a voltage nonlinear resistor having good nonlinearity, discharge withstand capacity, and good energized life.

Claims (1)

[Claims] 1. In the method for manufacturing a voltage nonlinear resistor obtained by adding, mixing, and firing a metal oxide such as bismuth oxide or antimony oxide to a raw material containing zinc oxide as a main component, the firing step includes a heating step, A method for manufacturing a voltage nonlinear resistor, characterized in that the step of holding the maximum temperature and the step of lowering the temperature to at least 1100° C. are performed in a reduced pressure state.