JPS6055969B2 - Voltage nonlinear resistor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage nonlinear resistor made of a sintered body mainly composed of zinc oxide, which can be used for arresters, surge absorbers, etc., and a method for manufacturing the same.

As shown in FIG. 1, a conventional voltage nonlinear resistor has a structure in which electrodes 2 are formed on the upper and lower end surfaces of a sintered body 1 whose main component is zinc oxide. Such a zinc oxide-based voltage nonlinear resistor is manufactured using a generally well-known ceramic sintering technique.

The outline is that bismuth oxide, cobalt oxide, chromium oxide, manganese oxide, nickel oxide, etc. are added to zinc oxide powder, mixed thoroughly, water and a suitable binder such as polyvinyl alcohol are added, and the powder is granulated and molded. Firing is performed at a temperature of 900 to 1400°C using an electric furnace. Bi2O3 is added to the side of the molded body for the purpose of preventing bath surface discharge.
-Si), Os-SiO. Alternatively, a paste or the like may be applied and fired. Both end faces of the fired sintered body, which form electrodes, are polished to a predetermined thickness and then subjected to thermal spraying or baking.
An electrode is thus formed. In addition, when using the voltage nonlinear resistor obtained in this way in a lightning arrester for high voltage power transmission,
Furthermore, it is necessary to prevent smooth surface discharge, and a glass film may be formed on the side surface. The voltage nonlinear resistor obtained by this method has superior nonlinearity in working pressure-current characteristics compared to voltage nonlinear resistors made of silicon carbide, but it is difficult to apply a constant voltage for a long time. As a result, there was a problem that the characteristics deteriorated, the leakage current gradually increased, and eventually thermal runaway occurred. For example, as a voltage non-linear resistor element for a 1200 kV power transmission lightning arrester, the operating ambient temperature is 40
℃, and the applied voltage is 80% of the voltage that gives an initial current of 1 mA, and a life of more than 100 years is required. The causes of deterioration of voltage nonlinear resistors are: (1) When a voltage nonlinear resistor is heat treated in an N2 atmosphere, its characteristics deteriorate in the same way as when constant voltage is applied, and (2) When an element with deteriorated characteristics is exposed to air or an oxygen atmosphere, its characteristics deteriorate. Due to the fact that the characteristics of the heat treatment inside the sintered body return to their original state, oxygen in the grain boundary layer in the sintered body or adsorbed oxygen on the surface of the crystal grains is desorbed and escapes to the outside world when a constant voltage is applied, resulting in grain formation. It is thought that the electrostatic potential of the interface layer decreases and the leakage current increases. On the other hand, as a method to increase the stability of a zinc oxide-based voltage nonlinear resistor against constant voltage charging, Bl2O3
2. A method of increasing the proportion of γ-Bl2O3 phase in the Bl2O3 phase contained in the sintered body by controlling the firing temperature of the sintered body or the heat treatment temperature after firing, boron trioxide or oxidation A method using a sintered body to which glass containing boron is added has been proposed.

However, even these methods are still a step away from applying constant voltage over a long period of time. An object of the present invention is to provide a voltage nonlinear resistor that is particularly stable against long-term energization as described above, and a method for manufacturing the same.

The present invention provides a voltage non-linear resistor in which electrodes are attached to a sintered body mainly composed of zinc oxide, in which a conductive indium oxide film or tin oxide film is formed on the surface of the sintered body in contact with the electrode. It is characterized by This film forms an airtight film and prevents oxygen adsorbed on the surface of zinc oxide crystal particles in the sintered body and oxygen in the grain boundary layer from desorbing and escaping to the outside world when a constant voltage is applied. It is thought that this stabilizes the characteristics against electricity. Note that additives such as antimony oxide and tantalum oxide may be added to the film in order to further improve the conductivity. Although a sputtering method or a CVD method can be used as a method for forming the conductive film, it is most preferable to apply a solution of indium salt or tin salt to the surface of the sintered body, followed by heat treatment.

According to this method, a portion of the solution is diffused into the grain boundaries and an indium oxide or tin oxide layer is formed also at the grain boundaries, so there is an advantage that desorption of oxygen from the grain boundaries becomes particularly difficult. FIG. 2 shows the structure of the voltage nonlinear resistor of the present invention. Specifically, the sintered body containing zinc oxide as a main component is produced by adding 0.01 to 10 mol% of bismuth oxide and manganese oxide to zinc oxide, and preferably 0.01 to 10 mol% of each.
Mol% cobalt oxide, antimony oxide, chromium oxide,
The conductive film 3 is provided on both end faces of the sintered body 1 which is made by adding boron oxide, silicon oxide, nickel oxide, etc. and firing at 900 to 1400°C, and the electrode 2 is provided thereon. In the present invention, it is important that the conductive film formed between the sintered body 1 and the electrode 2 has the following characteristics in addition to having the above-mentioned effects.

First, it is desirable that the resistivity be sufficiently low so that heat generation due to current passing between the sintered body and the electrodes will not be a problem. Since the resistivity of the zinc oxide particles of the sintered body is 1 to 10 Ω·Cm, the resistivity of the conductive film is preferably 1 Ω·Cm or less. Second, when the sintered body is heat-treated, 52
In the heat treatment temperature range of higher than 0°C and lower than 1000°C, the nonlinear coefficient of the resistor decreases. The reason for this is thought to be that bismuth oxide in the sintered body undergoes a phase change at this temperature. Furthermore, if the baking temperature of the conductive film exceeds 1000° C., the conductive film and the sintered body will react, impairing the characteristics of the nonlinear resistor. Therefore, it is necessary that the conductive film is baked into a sintered body at a temperature of 520° C. or lower, and that the baked conductive film has sufficient moisture resistance. Thirdly, in order to improve the adhesion between the sintered body and the conductive film, as well as to improve the airtightness and make it stable against long-term constant voltage application, the thickness of the conductive film must be 1 μm.
It is necessary to do more than that. Further, it is desirable that the thermal expansion coefficients of the sintered body and the conductive film are similar to each other. The conductive film in the present invention satisfies the above characteristics.

It is desirable to manufacture the voltage nonlinear resistor on which the conductive film is formed as follows. Both end faces of the sintered body containing zinc oxide as the main component were polished to a predetermined thickness, and a solution of indium nitrate dissolved in acetylacetone or metal tin dissolved in acetylacetone and nitric acid was applied to the face.
After baking at a temperature of 0 to 520°C, electrodes are formed on the formed film surface.

At this time, if the baking temperature of the conductive film is 520° C. or lower, the nonlinear coefficient of the resistor does not decrease from the original value of the resistor.

Furthermore, indium oxide and tin oxide films baked at temperatures lower than 350° C. have poor heat resistance and are undesirable for use. Furthermore, when the conductive film is thinner than 1 μm, it does not have the above effect;
If it is thicker than 0 pm, it will be difficult to form a uniform film due to the difference in thermal expansion coefficient from the sintered body. The present invention will be explained below with reference to Examples.

Example 1 Zinc oxide (ZnO) 2360V1 Bismuth oxide (Bl2
O3) 70g, cobalt oxide (CO2O3) 25V1 antimony oxide (Sb2O3) 87y1 manganese oxide (M
nO2)17y1 Chromium oxide (Cr2O3) 23y and silicon oxide (SiO2) 9V were wet mixed in a ball mill for 15 hours.

After drying the mixed powder, it is granulated into granules with a diameter of 20 mm and a thickness of 5 wrm.
was formed. Bi2O3-Sb2O3- on the side surface of the molded body
After applying the paste containing SiO2, 12
It was held at 50° C. for 2 hours and fired. During firing, the above paste reacts with ZnO, forming Zn2slO4 and Zn7 on the sides.
A high resistance layer mainly composed of sb2Ol2 was formed. Both end faces of the sintered body were polished to a thickness of 4wn. Separately, metal tin (Sn), acetylacetone (CH3COCH2C
OCH3) and nitric acid (I(NO3) in a weight ratio of 1:10
: 4 to dissolve tin, which was then polished to a predetermined thickness and applied to the polished surface of the sintered body using a dip method so that the tin oxide film had a thickness of 2 to 10 μm. .

This was heat treated at 450° C. for 2 hours in the air. The rate of temperature rise and fall at this time was 200°C/h. Coated with tin oxide film 1
An A1 sprayed electrode was formed on the tin oxide film forming surface of the sintered body. With this invention. A constant voltage accelerated charging test was conducted on a conventional product (one without a tin oxide film formed thereon), and the predicted life as a resistor for a 1200 kV lightning arrester and the value of the nonlinear coefficient were compared. The results are shown in Table 1. It can be seen that the formation of the conductive tin oxide film stabilizes the characteristics against constant voltage application, extends the life, and slightly improves the nonlinear coefficient of the resistor. Example 2 Thickness 37fn with both end faces polished in the same manner as Example 1
A sintered body was obtained.

A 5 weight percent solution of another indium nitrate [In(NOJ)3-9H20] dissolved in acetylacetone was polished to a predetermined thickness, and an indium oxide film was formed on the polished surface of the sintered body to a specified thickness.
It was coated using a dip method to a thickness of ~10 μm.

This was heat treated in the same manner as in Example 1 to form an N sprayed electrode. This was compared with one in which no indium oxide film was formed. The results are shown in Table 2. The results show that the formation of the conductive indium oxide film improves the lifetime and slightly increases the nonlinear coefficient.

Example 3 Zn02360y,. B1.0370y,. C0203
25y1Mn0217', Sb2O385f. ．． Cr2
O323f and SlO2lOg were wet mixed, dried, and granulated in the same manner as in Example 1, and formed into a diameter of 20wr1n1 and a thickness of 5cm.
A paste containing O2 was applied and fired at 1250° C. for 2 hours in the air.

The thickness of the sintered body is 4Tn! After polishing to n, a solution of tin and antimony (3% by weight) obtained in the same manner as in Example 1 was applied to both end faces to a thickness of 15 to 20 μm, and heated at 250'C and 300°C in the atmosphere. , 350℃, 450℃, 520℃
The sample was then heat treated at six temperatures of 600'C for a holding time of 30 minutes. The rate of temperature rise and fall at this time was 100'C/h.
The moisture resistance and resistivity of each of the tin oxide films obtained in this way were investigated, and a constant voltage accelerated electrification test was conducted on the resistor obtained by spraying an Al electrode on the surface on which the tin oxide film was formed. The nonlinear coefficients were compared. The results are shown in Table 3. The humidity resistance of the tin oxide film was checked by checking whether the tin oxide film changed color or came off after being immersed in boiling water. According to Table 3, tin oxide films baked at temperatures of 250°C and 300°C desorb and change color after being immersed in boiling water.
Moreover, the resistivity is also greater than 1ΩG. Furthermore, a resistor whose tin film is baked at a temperature of 600° C. has a significantly reduced nonlinear coefficient. Therefore, the baking temperature for forming the tin oxide film on the sintered body is preferably in the range of 350 to 520°C. Example 4 Zn02360y,. B120370y. ．． C0203
25y,. Mn017y. ．． Sb,0385y. ．． Cr
20323y and SiO2lOy were mixed in a ball mill for 1 hour.

Dry and granulate the mixed powder, diameter 20Tn1 thickness 6? It was molded into a mold and fired at 1250° C. for 2 hours in the air. The fired sintered body is 4W thick! 77! The indium solution of Example 2 was applied to the polished surface to a thickness of 15 to 20 pm, and heated at 2505C, 300℃, 350℃ in the atmosphere.
Heat treatment was performed at six temperatures: 4500°C, 520°C, and 600°C for a holding time of 30 minutes. The rate of temperature rise and fall at this time was 100°C/h. The moisture resistance and resistivity of the indium oxide film thus obtained were investigated, and an N electrode was thermally sprayed on the surface of the indium oxide film to perform a constant voltage accelerated charging test.
The measurement method and the like are the same as in Example 3. The results are shown in Table 4. According to Table 4, indium oxide films heat-treated at temperatures of 250°C and 300°C undergo desorption and discoloration after being immersed in boiling water, and their resistivity is also greater than 1Ω·d.

Furthermore, the nonlinear coefficient of the nonlinear resistor formed with the indium oxide film at 600° C. is significantly reduced. Therefore, the baking temperature for forming an indium oxide film on the sintered body is 350~
A range of 520°C is preferable. Example 5 Zn02340f. ．． B1203140y. ．． C020
325y1Mn0217q. ．． Sb20388y. ．． N
1023y,. Cr2035q and SiO25q were wet mixed in the same manner as in Example 1, dried, and granulated.

This has a diameter of 20T1r! After applying a paste containing Bl2O3-Sb2O3-SlO2 to the side surface of the molded product, it was held at 1270'C in the air for 2 hours and fired. After polishing the sintered body to a thickness of 4 mm, the tin solution of Example 1 was applied to both end faces with a brush so that the thickness of the tin oxide film was 0.5 μM, 1 μM, 10 μM, 20 μM, 30 μm, and 40 μm. After coating, it was baked at 500° C. in the atmosphere for 30 minutes. It was examined whether cracks had occurred in the tin oxide film after baking, and N sprayed electrodes were formed on those without cracks, and a constant voltage accelerated electrification test was performed on the obtained voltage nonlinear resistor. The results are shown in Table 5. As seen in Table 5, it can be seen that cracks occur when the conductive tin oxide film is made as thick as 40 pm.

This is thought to be due to the difference in thermal expansion coefficient between the sintered body and the tin oxide film. Also, the thickness of the conductive tin oxide film is 0.5
It can be seen that when the film is as thin as μm, the constant voltage accelerated charging test results are the same as when no tin oxide film is formed. This is because the tin oxide film is thin and produces pinholes, and is not effective in preventing oxygen adsorbed by zinc oxide crystal particles and oxygen in the grain boundary layer from desorbing and escaping to the outside world when a constant voltage is applied. Conceivable. Therefore, it can be seen that the thickness of the conductive tin oxide film formed on the sintered body is preferably in the range of 1 to 30 μm. Example 6 A mixed powder having the same composition as in Example 5 was granulated, and the diameter was 20 mm and the thickness was 6 mm. It was molded into.

After coating the molded body with a paste containing SiO2-Bi2O3-Sb2O3, it was held at 1270 DEG C. for 2 hours and fired. The fired sintered body was polished to a thickness of 4 m, and the indium solution of Example 2 was applied with a brush to the polished surface to give an indium oxide film thickness of 0.5 μM, 1 μM, 10 μM, 20 μM,
500℃ after coating to 30μm and 45μm
It was baked in a 3-minute atmosphere. The indium oxide film after baking was examined to see if any cracks had occurred, and those without cracks were formed into AI sprayed electrodes, and the obtained voltage nonlinear resistor was subjected to a constant voltage accelerated charging test. The result is the 6th
Shown in the table. As shown in Table 6, it can be seen that cracks occur when the indium oxide film is made as thick as 45 μm.

Furthermore, it can be seen that when the indium oxide film is formed as thin as 0.5 μm, the constant voltage accelerated charging test results are the same as when no indium oxide film is formed. Example 5 Tin oxide films were formed by sputtering on both main surfaces of a zinc oxide-based sintered body obtained in the same manner as in Example 1, and then A
1 electrode was formed.

In this case as well, it was found that when the thickness of the tin oxide film was 1 μm or more, the constant voltage application life was improved.

Example 8 An indium oxide film was formed by sputtering on both main surfaces of a zinc oxide-based sintered body obtained in the same manner as in Example 2, and an N electrode was further formed thereon.

In this case as well, it was found that when the thickness of the indium oxide film was 1 μm or more, the constant voltage application life was improved.

As is clear from the above examples, according to the present invention, a voltage nonlinear resistor can be obtained that has a long energized lifetime without impairing nonlinearity.

[Brief explanation of drawings]

Figure 1 shows the structure of a conventional voltage non-linear resistor, Figure 2 shows the structure of the voltage non-linear resistor of the present invention, and Figure 3 shows the heat treatment temperature and non-linear resistance of a sintered body mainly composed of zinc oxide. It is a figure showing the relationship with a coefficient. 1... Sintered body, 2... Electrode, 3...
...Conductive film.

Claims (1)

[Claims] 1. A voltage nonlinear resistor in which electrodes are formed on the upper and lower end surfaces of a sintered body mainly composed of zinc oxide, in which a conductive indium oxide film or A voltage nonlinear resistor characterized by having a tin oxide film interposed therein. 2. The voltage nonlinear resistor according to claim 1, wherein the conductive indium oxide film or tin oxide film has a thickness in the range of 1 to 30 μm. 3. Applying a solution containing an indium salt or a tin salt to the surface of a sintered body containing zinc oxide as a main component, 350-5
A voltage non-linear method characterized by comprising the steps of heat treatment in a temperature range of 20°C to decompose the solution to form a conductive indium oxide or tin oxide film, and a step of forming an electrode on the conductive film. Manufacturing method of resistor. 4. A method for producing a voltage nonlinear resistor according to claim 3, characterized in that the solution containing an indium salt or tin salt is a solution in which indium nitrate is dissolved in acetylacetone or tin is dissolved in nitric acid and acetylacetone.