JP5334636B2 - Voltage non-linear resistor, lightning arrester equipped with voltage non-linear resistor, and method of manufacturing voltage non-linear resistor - Google Patents

Description

  The present invention relates to a voltage non-linear resistor suitably used for a lightning arrester, a surge absorber, and the like, a lightning arrester equipped with the voltage non-linear resistor, and a method for manufacturing the voltage non-linear resistor.

  Conventionally, voltage non-linear resistors used for lightning arresters, surge absorbers, etc. are effective additions to zinc oxide (ZnO), the main component, for improving electrical characteristics, including bismuth oxide, which is essential for the expression of voltage non-linearity. It is composed of a sintered body that has been subjected to pulverization, mixing, granulation, molding, firing, and post-heat treatment, and is provided with an electrode and a side high resistance layer on the sintered body. Yes.

The operation of the voltage non-linear resistor is broadly divided into a standby state where no surge energy is applied and an operation state where surge energy is applied. The flatness ratio is used as an index representing the quality of voltage nonlinearity in the operating state, and technological development for reducing this value has been intensively advanced. The flatness ratio is defined as the ratio of the voltages generated at both ends of the voltage nonlinear resistor when two currents having different sizes are passed through the voltage nonlinear resistor. It depends on the diameter of the linear resistor. For example, the ratio (V _10kA / V _2mA ) of the voltage value (V _10kA ) at the time of 10 kA energization and the voltage value (V _2mA ) at the time of 2 mA energization, which is a numerical value reflecting the large current region characteristics, is used as the flat rate. .

  The electrical characteristics such as the flatness of the voltage nonlinear resistor greatly depend on the microstructure of the sintered body. The sintered body is roughly composed of zinc oxide particles, spinel particles mainly composed of zinc and antimony, and a bismuth oxide phase existing in the vicinity of the triple point of the grain boundary. It is known that bismuth, which is an additive essential for the expression of voltage non-linearity, exists not only in a bismuth oxide phase but also in a grain boundary between zinc oxide particles in a small amount (for example, see Non-Patent Document 1) ). In addition, zinc silicate particles mainly composed of silicon are also observed depending on the additive.

It is known that the microstructure of the sintered body as described above largely depends on the type and amount of additive and the manufacturing conditions centering on firing, and so far, the electrical characteristics of the voltage nonlinear resistor are Various studies have been made to improve the situation.
For example, Patent Document 1 _discloses that a flattening ratio (V _{2.5 kA} / V _{1 mA} ) is 1. by baking a composition containing zinc oxide, antimony oxide and bismuth oxide in a specific ratio at a temperature of 1000 ° C. or lower. A method of obtaining a voltage non-linear resistor excellent in voltage non-linearity that is less than 80 at low cost is disclosed. In addition, Patent Document 2 discloses that the voltage change rate and moisture absorption characteristics after surge application are increased by adding sodium oxide as an additive to a voltage nonlinear resistor containing zinc oxide as a main component and containing bismuth oxide or the like. It is described that it is improved.

JP 2003-297612 A JP-A-4-253302

Kei-Iciro Kobayashi, Journal of American Ceramic Society, "Continuous Existence of Bismuth at Grain Boundaries of Zinc Oxide Varistor without Intergranular Phase", 81, [8], 2071-2076 (1998)

In order to manufacture a voltage nonlinear resistor at low cost, it is necessary to perform firing at 1000 ° C. or less as disclosed in Patent Document 1, but a conventional voltage nonlinear resistor obtained by firing at 1000 ° C. or less. There is a problem that variation in electrical characteristics such as a flat rate is large between voltage non-linear resistors as compared with a voltage non-linear resistor obtained by firing exceeding 1000 ° C. In particular, when the standard values for flatness ratio, operation start voltage (varistor voltage), etc. are severe, in the process of manufacturing voltage nonlinear resistors, a large number of defective electrical characteristics occur, and the defect rate cannot be reduced. There was a problem that the yield could not be increased.
Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a voltage non-linear resistor having excellent voltage non-linearity with a low defect rate.

Until now, for example, as disclosed in Japanese Patent Laid-Open No. 8-138910, it has been recognized that when the amount of sodium or potassium in the voltage non-linear resistor increases, the electrical characteristics deteriorate, Attempts have been made to achieve excellent voltage non-linearity by minimizing. However, as a result of various studies on the composition and firing temperature of the composition containing zinc oxide as a main component and containing bismuth oxide, antimony oxide and chromium oxide as essential components, the inventors have conducted firing at 1000 ° C. or lower. It has been found that when an alkali metal such as sodium is added to the composition, there is a large difference in variation in flatness ratio between voltage nonlinear resistors. Further, as a result of examining the phenomenon in detail with an analytical instrument, when the variation in flatness is large, cubic Bi ₃₈ CrO ₆₀ is present in a certain ratio or more with respect to tetragonal Bi ₁₆ CrO ₂₇ , in other words, flatness. In the case where the variation in the rate is small, the abundance ratio of cubic Bi ₃₈ CrO ₆₀ to tetragonal Bi ₁₆ CrO ₂₇ is less than a certain value, and the abundance ratio is controlled by adjusting the addition amount of alkali metal. The inventors have found that this is possible and have completed the present invention.

That is, the present invention bakes a composition containing zinc oxide as a main component and containing at least one alkali metal selected from the group consisting of bismuth oxide, antimony oxide, chromium oxide, and potassium and sodium at 1000 ° C. or lower. A method for producing a voltage non-linear resistor, which is obtained by adjusting the amount of alkali metal added to the (123) plane X-ray diffraction peak intensity (A) of tetragonal Bi ₁₆ CrO ₂₇ in the obtained sintered body. A voltage nonlinearity characterized by adjusting the ratio (B / A) of the X-ray diffraction peak intensity (B) of the (321) plane of cubic Bi ₃₈ CrO ₆₀ to be in the range of 0 to 0.2. It is a manufacturing method of a resistor. The mechanism by which the formation of cubic Bi ₃₈ CrO ₆₀ is suppressed by the addition of alkali metal is unknown, but the abundance ratio of cubic Bi ₃₈ CrO ₆₀ and tetragonal Bi ₁₆ CrO ₂₇ affects the variation in flatness. It is clear.
In addition, the inventors analyzed the microstructure of the sintered body obtained by the above production method, and found that cubic Bi _{38 with} respect to the X-ray diffraction peak intensity (A) of the (123) plane of tetragonal Bi ₁₆ CrO _27. The voltage nonlinear resistor in which the ratio (B / A) of the X-ray diffraction peak intensity (B) of the (321) plane of CrO ₆₀ is in the range of 0 to 0.2 is the zinc oxide particles, zinc and antimony. It has also been found that at least one alkali metal selected mainly from the group consisting of potassium and sodium is present in the bismuth oxide phase mainly composed of spinel particles as main components and a bismuth oxide phase.

  According to the present invention, a voltage nonlinear resistor having excellent voltage nonlinearity can be provided with a low defect rate. Moreover, by using the voltage non-linear resistor according to the present invention, an overvoltage protection device such as a lightning arrester and a surge absorber having excellent protection performance can be realized at low cost.

3 is a schematic diagram of a fine structure of a voltage nonlinear resistor according to Embodiment 1. FIG. It is a schematic cross section of the sample for evaluation used by the Example and the comparative example.

Embodiments of the present invention will be described below.
Embodiment 1 FIG.
The voltage non-linear resistor according to the embodiment of the present invention is composed of zinc oxide (ZnO) as a main component and at least one alkali metal selected from the group consisting of bismuth oxide, antimony oxide, chromium oxide, and potassium and sodium. It is obtained by calcining a composition containing no more than 1000 ° C. The sintered body thus obtained is mainly composed of zinc oxide particles 1, spinel particles 2 mainly composed of zinc and antimony, and bismuth oxide phase 3, as shown in FIG. There are twin boundaries 4 in the grains. Further, the presence of added alkali metal in the bismuth oxide phase has been confirmed by microstructural analysis. Moreover, since the generation of the cubic Bi ₃₈ CrO ₆₀ by the alkali metal present in the bismuth oxide phase is suppressed, absent cubic Bi ₃₈ CrO ₆₀ is in the sintered body, or tetragonal Bi ₁₆ CrO ₂₇ More specifically, the cubic Bi _{38 with} respect to the X-ray diffraction peak intensity (A) of the (123) plane of tetragonal Bi ₁₆ CrO ₂₇ is analyzed by the X-ray diffraction method. The amount is such that the ratio (B / A) of the X-ray diffraction peak intensity (B) of the (321) plane of CrO ₆₀ is in the range of 0 or more and less than 0.24. The reason for defining the abundance of cubic Bi ₃₈ CrO ₆₀ in this numerical range, cubic Bi ₃₈ variation in electrical characteristics of the abundance of CrO ₆₀ becomes 0.24 or higher than the voltage nonlinear resistor becomes extremely large This is because the defect rate cannot be reduced.

  In the present embodiment, the composition to be fired contains zinc oxide as a main component and contains at least one alkali metal selected from the group consisting of bismuth oxide, antimony oxide, chromium oxide, and potassium and sodium. It is.

  Zinc oxide (ZnO) is preferably contained in the composition in a range of 90 mol% or more and 98 mol% or less from the comprehensive viewpoint of improvement in voltage nonlinearity, improvement in energy resistance and life extension. More preferably, it is contained in the range of 95 mol% or more and 98 mol% or less. As zinc oxide, it is usually preferable to use a powder having an average particle diameter of 1 μm or less.

Bismuth oxide (Bi ₂ O ₃ ) is preferably contained in the composition in the range of 0.5 mol% or more and 2 mol% or less in order to further improve the voltage non-linearity and the charging life. More preferably, it is contained in the range of 7 mol% or more and 1.5 mol% or less.
Antimony oxide (Sb ₂ O ₃ ) is preferably contained in the composition in the range of 0.1 mol% or more and 2 mol% or less in order to further improve the voltage non-linearity and the charging life. More preferably, it is contained in the range of 2 mol% or more and 0.8 mol% or less.
Further, in order to further improve the voltage nonlinearity and the charging life, bismuth oxide (Bi ₂ O ₃ ) and antimony oxide (Sb ₂ O ₃ ) are added in a total amount of 0.5 mol% or more and 2 mol. %, Preferably in the range of 1.0 mol% or more and 1.5 mol% or less.

Chromium oxide (Cr ₂ O ₃ ) is preferably contained in the composition in a range of 0.05 mol% or more and 0.5 mol% or less in order to further improve the voltage nonlinearity and the charging life. More preferably, it is contained in the range of 0.1 mol% or more and 0.3 mol% or less.

At least one alkali metal selected from the group consisting of potassium and sodium is cubic Bi ₃₈ CrO ₆₀ with respect to the X-ray diffraction peak intensity (A) of the (123) plane of tetragonal Bi ₁₆ CrO ₂₇ in the sintered body. A voltage non-linearity with a small flatness ratio may be added by appropriately adjusting the ratio (B / A) of the X-ray diffraction peak intensity (B) of the (321) plane to be in the range of 0 to less than 0.24. In order to obtain a resistor with a low defect rate, it is preferable to add it in the range of 0.02 mol% or more and 0.06 mol% or less in the composition. If the amount of alkali metal added exceeds 0.06 mol%, the defective rate is reduced, but the flatness tends to deteriorate, which is not preferable. This alkali metal is usually preferably blended as Na ₂ CO ₃ powder and K ₂ CO ₃ powder having an average particle size of 1 μm or less, or as an aqueous solution in which these are dissolved.

In the composition of the present embodiment, in order to further improve the voltage non-linearity and the charging life, in addition to the above components, nickel oxide (NiO), manganese dioxide (MnO ₂ ), cobalt oxide (Co ₃ O _4). ), Aluminum nitrate (Al (NO ₃ ) ₃ ), boric acid (H ₃ BO ₃ ), silicon dioxide or the like may be blended. These oxides are usually in the range of 1 mol% to 2 mol% in the total amount in the composition. Moreover, as these oxides, it is usually preferable to use a powder having an average particle diameter of 1 μm or less.

In order to further improve the voltage non-linearity and the service life, nickel oxide may be blended in the composition in the range of 0.1 mol% to 2 mol%.
In order to further improve the voltage nonlinearity and the charging life, manganese dioxide may be blended in the composition in the range of 0.1 mol% to 2 mol%.
In order to further improve the voltage non-linearity and the service life, cobalt oxide may be blended in the composition in the range of 0.1 mol% to 2 mol%.
In order to further improve the voltage nonlinearity, aluminum nitrate may be blended in the composition in the range of 0.001 mol% to 0.01 mol%.
In order to further improve the voltage non-linearity, reduce pores in the sintered body and further improve the energy resistance, boron is added in the range of 0.01 mol% to 0.2 mol% in the composition. An acid may be blended.

Next, a method for manufacturing the voltage nonlinear resistor according to the embodiment of the present invention will be specifically described. After preparing the composition composed of the above-mentioned raw materials, water, a dispersant, and a binder (binder) such as polyvinyl alcohol are added thereto, and the mixture is sufficiently pulverized and mixed to prepare a slurry having a uniform composition. . This slurry is dried and granulated with a spray dryer to obtain a granulated product. The obtained granules to obtain a molded body having a predetermined shape by molding, for example, 200 kgf / cm ² or more 500 kgf / cm ² or less of the molding pressure. Next, the molded body is heated to about 450 ° C. in air or an oxygen atmosphere to remove the binder, and then fired at 1000 ° C. or lower to obtain a sintered body. If necessary, an electrode may be formed on the sintered body by, for example, aluminum spraying, or a side high resistance layer may be formed by baking a glass or introducing a diffusion layer having a high resistance value.
According to the method for manufacturing a voltage non-linear resistor according to the present embodiment, the firing temperature is as low as 1000 ° C. or lower despite the fact that a voltage non-linear resistor having excellent voltage non-linearity can be obtained with a low defect rate. Therefore, the power consumption during firing can be greatly reduced. Thus, the method for manufacturing a voltage non-linear resistor according to the present embodiment can be said to be an environmentally friendly method because CO ₂ emission during manufacturing can be greatly reduced as compared with the conventional manufacturing method.

  Furthermore, if the voltage non-linear resistor obtained by the present embodiment is singly or stacked and mounted on a lightning arrester, an overvoltage protection device such as a lightning arrester and surge absorber having excellent protection performance can be provided at low cost. .

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these.
<Examples 1-10 and Comparative Examples 1-6>
Bismuth oxide (Bi ₂ O ₃ ) powder 0.9 mol%, antimony oxide (Sb ₂ O ₃ ) powder 0.4 mol%, nickel oxide (NiO) powder 0.5 mol%, manganese dioxide (MnO ₂ ) powder 0 0.5 mol%, chromium oxide (Cr ₂ O ₃ ) powder 0.1 mol%, cobalt oxide (Co ₃ O ₄ ) powder 0.4 mol%, aluminum nitrate (Al (NO ₃ ) ₃ .9H ₂ O) 0 0.004 mol% and boric acid (H ₃ BO ₃ ) 0.16 mol% are used as the basic composition, and Na ₂ CO ₃ or K ₂ CO ₃ ranges from 0 mol% to 0.08 mol%. 16 compositions shown in Table 1 were prepared. The balance is zinc oxide (ZnO). In addition, an industrial raw material or a reagent was used for each raw material, and all powder raw materials having an average particle diameter of 1 μm or less were used.
Pure water, a dispersant, and a binder were added to each of the compositions shown in Table 1, and pulverization and mixing were sufficiently performed to prepare a slurry having a uniform composition.
The produced slurry was granulated with a spray dryer, and the resulting granulated powder was molded at a molding pressure of 500 kgf / cm ² to obtain a disk-shaped molded body having a diameter of about 40 mm and a thickness of about 10 mm.

  The molded body was heat-treated in the atmosphere at 450 ° C. for 5 hours (debinding step), and then fired at a firing temperature of 950 ° C. for 5 hours (firing step). The temperature raising and lowering rate was 50 ° C./hour.

[Evaluation of flatness and calculation of defect rate]
A side high resistance layer 6 (resin) for preventing side flashing when an impulse voltage is applied is applied to the side surface of the sintered body 5, and an aluminum electrode 7 is formed on both sides of the disk by aluminum spraying. It was. A schematic cross-sectional view of the sample is shown in FIG.

The flatness was evaluated based on V _{2.35 kA} / V _{0.46 mA} . For V _{2.35 kA,} an impulse voltage of 8 × 20 μs was applied to the sample, and the peak value was read as V _{2.35 kA} . V _{0.46 mA} was measured using an AC voltage (sine wave) of 60 Hz. When alternating current is applied, the current flowing through the sample is divided into a resistive component (Ir) and a capacitive component (Ic). Ir was extracted using a resistance leakage current extraction device. Specifically, the applied voltage at which Ir becomes 0.46 mA was read and set to V _{0.46 mA} .
In the samples of Examples 1 to 10 and Comparative Examples 1 to 6, the defect rate after firing was evaluated. Compared with non-defective electrical characteristics (the value of V _{0.46 mA} is the largest among the examples and comparative examples), V _{0.46 mA} is reduced by ₂₀ to 30 V / mm and the flatness is increased by about 0.1. The defective rate was calculated according to the following formula. Those having a non-defective rate of 0% showed a flat rate as a non-defective product having no decrease in the value of V _{0.46 mA} . Table 1 shows the evaluation results of the flatness and defect rate of the good products.
Defect rate = number of defective electrical characteristics / total number x 100 (%)

  As shown in Table 1, in Examples 1 to 10, the variation in the flat rate between samples was extremely small, and the defect rate was 0%. Among these, Examples 1 to 3 and 6 to 8 in which sodium or potassium is added in the range of 0.02 mol% or more and 0.06 mol% or less have a small flatness and particularly excellent non-linearity. I understand that On the other hand, in Comparative Examples 1-6, the variation of the flat rate was large between samples, and the defect rate was 35% to 100%.

[Analysis of microstructure]
After cutting the fired body, it was pulverized with agate milk beak for about 30 minutes, and the crystal structure of the product of bismuth contained in the fired body was analyzed using a powder X-ray diffraction method. The presence of Bi ₂ O ₃ and Bi ₁₆ CrO ₂₇ was confirmed, and the presence of Bi ₃₈ CrO ₆₀ was also confirmed from some samples. Furthermore, when the analysis of the defective electrical property product in which the variation occurred was advanced, in these samples, the intensity of the X-ray diffraction peak (A) of the (123) plane of Bi ₁₆ CrO ₂₇ was set as Bi ₃₈ CrO ₆₀ . It was confirmed that B / A was 0.24 or more when the intensity (B) of the X-ray diffraction peak of the (321) plane was used. In Examples 5 and 10, the presence of Bi ₃₈ CrO ₆₀ was confirmed, and B / A was 0.15 to 0.20. However, the variation in the flatness ratio between samples was extremely small, and the defect rate was 0. %Met. The results are shown in Table 1.
Furthermore, when a sample to which sodium or potassium was added was analyzed using a high performance electron probe microanalyzer (EPMA), it was confirmed that sodium or potassium added was present in the bismuth oxide phase.

From these, the sodium and potassium, found that there is a direct effect of inhibiting the formation of Bi ₃₈ CrO ₆₀ believed to be responsible for the electrical characteristic failure, also, by adding sodium or potassium Bi ₃₈ CrO ₆₀ It was revealed that the defect rate can be remarkably reduced by adjusting the generation amount to less than a specific amount. However, as can be seen from the results of Examples 4 and 9, when sodium or potassium is added excessively, the defective rate remains 0%, but the flat rate deteriorates. The reason why the flatness is increased in this way is considered to be that the added sodium or potassium starts to dissolve in not only the bismuth oxide phase but also the zinc oxide particles, and the resistance of the zinc oxide particles is greatly increased.

  In addition, an experiment of adding lithium was conducted in the same manner as sodium and potassium, but the sample was in a state close to an insulator, and the electrical characteristics could not be evaluated. That is, it was also confirmed that lithium, which is an alkali metal, greatly increases the resistance of zinc oxide and makes the sintered body almost in the state of an insulator. As suggested in Japanese Patent Application Laid-Open No. 8-138910, the alkali metal contained in the voltage nonlinear resistor has been recognized so far as deteriorating the electrical characteristics. It can be said that the effect that a voltage nonlinear resistor having excellent voltage nonlinearity can be obtained with a low defect rate by positively adding an alkali metal to is a peculiar effect completely different from the conventional one.

From the above, a composition containing zinc oxide as a main component and containing at least one alkali metal selected from the group consisting of bismuth oxide, antimony oxide, chromium oxide, and potassium and sodium is fired at 1000 ° C. or lower. When manufacturing a voltage nonlinear resistor, X-ray diffraction of (321) plane of cubic Bi ₃₈ CrO ₆₀ with respect to (123) plane X-ray diffraction peak intensity (A) of tetragonal Bi ₁₆ CrO ₂₇ in the sintered body By adjusting the addition amount of the alkali metal so that the ratio (B / A) of the peak intensity (B) is in the range of 0 or more and less than 0.24, variation in electrical characteristics between the voltage nonlinear resistors is reduced, It was confirmed that the defect rate can be greatly reduced. In particular, by adding an alkali metal in the range of 0.02 mol% or more and 0.06 mol% or less, a voltage nonlinear resistor having excellent electrical characteristics can be obtained with a low defect rate.

Claims (4)

A sintered body mainly composed of zinc oxide particles, spinel particles mainly composed of zinc and antimony, and a bismuth oxide phase, and at least one selected from the group consisting of potassium and sodium in the bismuth oxide phase X-ray diffraction peak intensity of (321) plane of cubic Bi ₃₈ CrO ₆₀ with respect to (123) plane X-ray diffraction peak intensity (A) of tetragonal Bi ₁₆ CrO _{27 in} the sintered body ( A voltage non-linear resistor, wherein the ratio (B / A) of B) is in the range of 0 to 0.2 .   2. The voltage nonlinear resistor according to claim 1, comprising at least one alkali metal selected from the group consisting of potassium and sodium in a range of 0.02 mol% to 0.06 mol%.   A lightning arrester comprising the voltage nonlinear resistor according to claim 1. A voltage non-linear resistor for firing a composition containing zinc oxide as a main component and containing at least one alkali metal selected from the group consisting of bismuth oxide, antimony oxide, chromium oxide, and potassium and sodium at 1000 ° C. or lower. Cubic Bi ₃₈ CrO _{60 with} respect to the X-ray diffraction peak intensity (A) of the (123) plane of tetragonal Bi ₁₆ CrO ₂₇ in the sintered body obtained by adjusting the amount of alkali metal added. (321) The X-ray diffraction peak intensity (B) ratio (B / A) of the (321) plane is adjusted so as to be in the range of 0 or more and 0.2 or less .

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