JP2012231091A - Current-voltage nonlinear resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current-voltage nonlinear resistor excellent in nonlinear resistance characteristics, energy resistance characteristics and temperature characteristics under high temperature.SOLUTION: A current-voltage nonlinear resistor 10 includes a sintered body 20 of a mixture including zinc oxide as main components and bismuth oxide, antimony oxide, manganese oxide, cobalt oxide and nickel oxide, as accessory components. Bismuth oxide particle and antimony oxide particles in the mixture have an average particle size of 1,000 nm or less, and a standard deviation based on particle size distribution of zinc oxide crystal particles in the sintered body is less than 25% of an average particle size of the zinc oxide crystal particles.

Description

  Embodiments described herein relate generally to a current-voltage nonlinear resistor and a method for manufacturing the same.

  In general, an overvoltage protection device such as a lightning arrester or a surge absorber is installed in a power system or electronic device circuit in order to protect the power system or electronic device from an abnormal voltage. In this overvoltage protection device, a current-voltage non-linear resistor that exhibits substantially insulation characteristics at a normal voltage and exhibits a low resistance value at an overvoltage is frequently used.

  This current-voltage non-linear resistor has a non-linear resistance characteristic in which the current value changes greatly due to a change in voltage, a life characteristic that does not easily deteriorate even if voltage is applied for a long period of time, and breakdown when a lightning surge or switching surge is applied In addition, an energy withstand characteristic that absorbs the energy of the surge is required.

The sintered body of the current-voltage non-linear resistor is composed mainly of zinc oxide (ZnO), and subcomponents thereof include bismuth oxide (Bi ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ), manganese oxide ( MnO), antimony oxide (Sb ₂ O ₃ ), and nickel oxide (NiO) are used as raw materials. The sintered body is produced by sufficiently mixing these raw materials together with water and a binder, granulating with a spray dryer or the like, molding and sintering. Then, an insulating material for preventing flashover is applied to the side surface of the sintered body, and heat treatment is performed to form an insulating layer. Moreover, the both ends of a sintered compact are grind | polished and an electrode is attached, and a current-voltage nonlinear resistor is obtained.

  In recent years, there has been a demand for miniaturization of transformers for the purpose of reducing manufacturing costs and environmental harmony. Current-voltage nonlinear resistors are used in lightning arresters because of their excellent nonlinear resistance characteristics. When the resistance value of the current-voltage non-linear resistor is improved, the number of current-voltage non-linear resistors stacked on the lightning arrester can be reduced, and the lightning arrester can be downsized.

  When the lightning arrester is downsized, the energy density at the time of surge energy absorption becomes high, so it is necessary to increase the amount of energy that can be absorbed. In addition, the current-voltage nonlinear resistor generates heat when absorbing the surge energy, and the leakage current increases as the temperature rises. Therefore, the lightning arrester may run away due to the commercial frequency current after absorbing the surge energy. Therefore, it is necessary to improve temperature characteristics at high temperatures and suppress leakage current.

  Conventionally, attempts have been made to improve the energy resistance by controlling the proportion of spinel particles in the sintered body of the current-voltage nonlinear resistor and the average particle size. Conventionally, attempts have been made to make the fine structure of the sintered body uniform and improve the energy resistance by finely pulverizing all the raw materials used for the current-voltage nonlinear resistor.

JP 2002-217006 A JP 2010-103440 A

  However, when all the raw materials used for the current-voltage nonlinear resistor are finely pulverized, the granulated powder is densified and hardened, and coarse pores are easily formed during molding. Therefore, there is a possibility that sufficient energy withstand capability cannot be obtained. Thus, it has been difficult for conventional current-voltage non-linear resistors to have excellent characteristics in all of non-linear resistance characteristics, energy withstand characteristics, and temperature characteristics at high temperatures.

  The problem to be solved by the present invention is to provide a current-voltage non-linear resistor excellent in non-linear resistance characteristics, energy tolerance characteristics, and temperature characteristics at high temperatures.

  The current-voltage nonlinear resistor of the embodiment includes a sintered body of a mixture containing zinc oxide as a main component and bismuth oxide, antimony oxide, manganese oxide, cobalt oxide, and nickel oxide as subcomponents. The average particle size of bismuth oxide particles and antimony oxide particles in the mixture is 1000 nm or less, and the standard deviation based on the particle size distribution of the zinc oxide crystal particles in the sintered body is the average particle size of the zinc oxide crystal particles. Less than 25%.

It is a figure which shows the cross section of the current-voltage nonlinear resistor of embodiment which concerns on this invention. It is a figure which shows the measurement result of the limit absorption energy in the case where the average particle diameter of ZnO particle | grains in a mixture differs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a cross section of a current-voltage nonlinear resistor 10 according to an embodiment of the present invention.

  As shown in FIG. 1, a current-voltage nonlinear resistor 10 is a sintered body of a mixture containing zinc oxide as a main component and bismuth oxide, antimony oxide, manganese oxide, cobalt oxide and nickel oxide as subcomponents. 20 is provided. The current-voltage nonlinear resistor 10 includes an insulating layer 30 that covers the side surface of the sintered body 20 and electrodes 40 formed on the upper and lower surfaces of the sintered body 20.

  The average particle size of the bismuth oxide particles and antimony oxide particles in the mixture is 1000 nm or less, and the standard deviation based on the particle size distribution of the zinc oxide crystal particles in the sintered body 20 is 25% of the average particle size of the zinc oxide crystal particles. It is preferable that it is less than.

  By setting the average particle diameter of the bismuth oxide particles and antimony oxide particles to 1000 nm or less, the particles of bismuth oxide and antimony oxide are uniformly dispersed, so that the bismuth phase and spinel particles in the sintered body 20 are uniformly dispersed. The bismuth phase promotes the grain growth of zinc oxide crystal particles, and the spinel particles have the characteristic of suppressing the grain growth of zinc oxide crystal particles. For this reason, by uniformly dispersing each of them, the grain growth of the zinc oxide crystal particles becomes uniform and the current concentration is eliminated, so that the energy resistance is improved. Note that the lower limit of the average particle diameter of the bismuth oxide particles and antimony oxide particles is about 100 to 200 nm because the raw material particles easily aggregate in the slurry and the dispersibility deteriorates as the raw material becomes finer. .

  Here, the standard deviation based on the particle size distribution of the bismuth oxide particles is preferably 50% or less of the average particle diameter of the bismuth oxide particles in order to make the particle diameter of the bismuth oxide uniform. The standard deviation based on the particle size distribution of the antimony oxide particles is preferably 50% or less of the average particle size of the bismuth oxide particles in order to make the particle size of the antimony oxide uniform.

  By setting the standard deviation based on the particle size distribution of the zinc oxide crystal particles in the sintered body 20 to be less than 25% of the average particle size of the zinc oxide crystal particles, the particle size of the zinc oxide crystal particles is made uniform and localized. The bias of the conductive path is eliminated.

  The average particle diameter of the nickel oxide particles in the mixture is preferably 600 nm or less. By setting the average particle diameter of nickel oxide particles to 600 nm or less, the solid solution form of nickel oxide in zinc oxide particles, bismuth phase, and spinel particles changes, and the characteristics of grain boundaries existing between the zinc oxide particles are changed. to be influenced. Thereby, the nonlinear resistance characteristic can be improved. The lower limit of the average particle diameter of the nickel oxide particles is about 100 to 200 nm because the raw material particles easily aggregate in the slurry and the dispersibility deteriorates as the raw material is refined.

  The average particle diameter of the cobalt oxide particles in the mixture is preferably 750 nm or less. By setting the average particle size of the cobalt oxide particles to 750 nm or less, the solid solution form of cobalt oxide in the zinc oxide particles, bismuth phase, and spinel particles changes, and the characteristics of the grain boundaries existing between the zinc oxide particles are changed. to be influenced. Thereby, temperature characteristics can be improved. Note that the lower limit of the average particle diameter of the cobalt oxide particles is about 100 to 200 nm because the raw material particles easily aggregate in the slurry and the dispersibility deteriorates as the raw material is refined.

  The average particle size of the manganese oxide particles in the mixture is preferably 800 nm or less. By setting the average particle size of manganese oxide particles to 800 nm or less, the solid solution form of manganese oxide in each of zinc oxide particles, bismuth phase, and spinel particles changes, and the characteristics of grain boundaries existing between the zinc oxide particles are changed. to be influenced. Thereby, temperature characteristics can be improved. Note that the lower limit of the average particle size of the manganese oxide particles is about 100 to 200 nm because the raw material particles easily aggregate in the slurry and the dispersibility deteriorates as the raw material is refined.

  The average particle diameter of the zinc oxide particles in the mixture is preferably 500 nm or more. By pulverizing and refining zinc oxide, which is the main component, bismuth oxide, and antimony oxide, which are the subcomponents, the grain growth at the time of sintering becomes uniform and the fine structure tends to be uniform. As a result, energy tolerance may be improved. However, on the other hand, the granulated powder becomes denser as the particle size of the zinc oxide particles as the main component becomes finer. When the granulated powder is filled in a mold to obtain a predetermined molding density, the granulated powder becomes harder and more difficult to be crushed as the granulated powder becomes higher in density, so that the gap between the granulated particles tends to increase. As a result, the pores in the sintered body 20 that become the starting point of destruction increase, and the energy resistance decreases.

  Therefore, as described above, subcomponents such as bismuth oxide, antimony oxide, nickel oxide, cobalt oxide, and manganese oxide are refined to achieve a uniform microstructure, and the average particle diameter of zinc oxide particles is set to 500 nm or more. Thereby, densification of granulated powder and formation of coarse pores can be suppressed. Thereby, an excellent energy withstand characteristic can be obtained. The upper limit of the average particle diameter of the zinc oxide particles in the mixture is about 1500 to 2000 nm because the sintering reaction becomes nonuniform and the fine structure becomes nonuniform when the zinc oxide particles become large.

  The standard deviation based on the particle size distribution of each of the nickel oxide particles, the cobalt oxide particles, and the manganese oxide particles is also preferably 50% or less of the average particle size, as in the case of bismuth oxide and antimony oxide. Similarly, the standard deviation based on the particle size distribution of the zinc oxide particles is preferably 50% or less of the average particle size. By setting it as such a range, the spread of a particle size distribution is small and it can aim at equalization of the particle size in each raw material.

  Here, the mixing and grinding of the mixture, in particular, the mixing and grinding of the raw materials of the subcomponents are performed under the same conditions in the mixing and grinding apparatus. As described above, those having different average particle diameters are formed.

  The average particle diameter of each raw material particle in the above mixture is calculated as follows.

  First, a backscattered electron image is observed using a scanning electron microscope (SEM), and each raw material particle is identified by mapping of the observation photograph and energy dispersive X-ray analysis (EDX).

  Subsequently, for each raw material particle, SEM photographs of 10 different visual fields for one specimen to be observed are taken at a magnification of 10,000 times, and an area of 100 or more raw material component particles is obtained by image analysis with a visual field of 10,000 times. . It is converted into the diameter of a circle having the same area as that obtained by image analysis, and the particle diameter is obtained. For each raw material component particle, the calculated particle diameter is arithmetically averaged to obtain an average particle diameter.

  The average particle diameter of the zinc oxide crystal particles in the sintered body 20 is calculated as follows.

  First, a plurality of samples are cut out, the observation surface is mirror-polished, and the polished surface is etched with a 0.5% hydrochloric acid solution. By this etching treatment, a minute uneven surface is formed on the observation surface, and the zinc oxide crystal particles can be easily identified.

  Subsequently, the backscattered electron image is observed using SEM, and the zinc oxide crystal particles are identified by the shade of the observation photograph. SEM photographs of 10 different visual fields for one specimen to be observed are taken at a magnification of 10,000 times, and areas of 100 or more zinc oxide crystal particles are obtained by image analysis with a visual field of 10,000 times. It is converted into the diameter of a circle having the same area as that obtained by image analysis, and the particle diameter is obtained. The average particle diameter can be obtained from the calculated particle diameter. In addition, as described above, the standard deviation is calculated based on the particle size distribution of the zinc oxide crystal particles in the sintered body 20 obtained from the measured average particle diameter.

  Next, each raw material component composition which comprises the mixture for comprising the sintered compact 20 is demonstrated.

The mixture for constituting the sintered body 20 is bismuth oxide in terms of Bi ₂ O ₃ , 0.1 to ₂ mol%, antimony oxide in terms of Sb ₂ O ₃ , 0.1 to 5 mol%, cobalt oxide Is converted to Co ₂ O _{3 and} contains 0.1 to 5 mol%, manganese oxide converts to MnO and contains 0.1 to 5 mol%, and nickel oxide converts to NiO and contains 0.1 to 5 mol%. In addition, it is preferable that 75 mol% or more of zinc oxide which is a main component is converted into ZnO in a mixture.

The content of bismuth oxide in terms of Bi ₂ O ₃ is 0.1 to ₂ mol% because bismuth oxide is present at the grain boundaries of zinc oxide, which is the main component, and exhibits nonlinear resistance characteristics. Therefore, when the content is less than 0.1 mol%, the effect of developing this non-linear resistance characteristic cannot be obtained sufficiently. Further, when the content exceeds 2 mol%, the growth of zinc oxide crystal particles during sintering proceeds excessively, and a current-voltage nonlinear resistor having a high resistance value cannot be obtained.

The content of antimony oxide was converted to Sb ₂ O ₃ to 0.1 to 5 mol% because antimony oxide formed spinel particles with zinc oxide and caused the growth of zinc oxide crystal particles during sintering. Since it is a component that has the effect of suppressing and equalizing, and the effect of improving the non-linear resistance characteristic, when the content is less than 0.1 mol%, the effect of improving this non-linear resistance characteristic It is because it cannot get enough. Moreover, when content exceeds 5 mol%, it is because the insulation component in the inside of the sintered compact 20 increases, and energy tolerance falls.

The reason why the content of cobalt oxide is 0.1 to 5 mol% in terms of Co ₂ O ₃ is that cobalt oxide is mainly dissolved in spinel particles to effectively improve the non-linear resistance characteristics. This is because if the content is less than 0.1 mol%, the effect of improving the non-linear resistance characteristics cannot be sufficiently obtained. Moreover, when content exceeds 5 mol%, it is because the insulation component in the inside of the sintered compact 20 increases, and energy tolerance falls.

  The content of manganese oxide in terms of MnO is 0.1 to 5 mol%. Manganese oxide is an effective component for greatly improving the non-linear resistance characteristics by mainly dissolving in spinel particles. For this reason, when the content is less than 0.1 mol%, the effect of improving the non-linear resistance characteristic cannot be sufficiently obtained. Moreover, when content exceeds 5 mol%, it is because the insulation component in the inside of the sintered compact 20 increases, and energy tolerance falls.

  The content of nickel oxide is 0.1 to 5 mol% in terms of NiO. Nickel oxide is an effective component for greatly improving the non-linear resistance characteristic by mainly dissolving in spinel particles. For this reason, when the content is less than 0.1 mol%, the effect of improving the non-linear resistance characteristic cannot be sufficiently obtained. Moreover, when content exceeds 5 mol%, it is because the insulation component in the inside of the sintered compact 20 increases, and energy tolerance falls.

  The reason why the content of zinc oxide as the main component is 75 mol% or more in terms of ZnO is that when the content of zinc oxide is less than 75 mol%, the insulating component inside the sintered body 20 increases. This is because the energy resistance is reduced.

  The insulating layer 30 covering the side surface of the sintered body 20 is made of, for example, an inorganic insulating material such as a glass frit that is an electrically insulating material. The insulating layer 30 is formed by, for example, applying or spraying the above-described electrical insulating material to the side surface of the sintered body 20 and performing heat treatment. The insulating layer 30 is preferably formed to have a thickness of about 0.05 to 0.2 mm from the viewpoint of insulating performance and mechanical strength.

  The electrodes 40 formed on the upper and lower surfaces of the sintered body 20 are made of, for example, a material such as aluminum or silver having electrical conductivity. The electrode 40 is formed on the upper and lower surfaces of the sintered body 20 by, for example, spraying the above-described conductive material. The thickness of the electrode 40 is preferably about 0.05 to 0.15 mm from the viewpoint of adhesion to the sintered body.

  Here, the current-voltage nonlinear resistor 10 has, for example, a cylindrical shape having a diameter of 20 to 150 mm and a thickness of 1 to 50 mm. The shape of the current-voltage nonlinear resistor 10 is not limited to this.

  Next, a method for manufacturing the current-voltage nonlinear resistor 10 according to the present invention will be described.

First, 0.1 to 2 mol% in terms of bismuth oxide _Bi 2 _{O 3,} in terms 0.1 to 5 mol% in terms of antimony oxide _Sb 2 _{O 3,} cobalt oxide to _Co 2 _{O 3} 0 0.1 to 5 mol%, manganese oxide is converted to MnO, 0.1 to 5 mol%, nickel oxide is converted to NiO and 0.1 to 5 mol% is contained, and the remainder is weighed so as to be zinc oxide. At this time, zinc oxide as a main component is adjusted to contain 75 mol% or more in terms of ZnO.

  Subsequently, other raw materials (bismuth oxide, antimony oxide, cobalt oxide, manganese oxide, nickel oxide) excluding the weighed zinc oxide and water for adjusting the solid content concentration of this raw material to 10 to 30% by mass are mixed. Put into the crusher. Then, mixing and grinding are performed for a predetermined time.

  After a predetermined time has passed, weighed zinc oxide and an organic solvent are added to a mixing and pulverizing apparatus, water is further added so that the solid content concentration is 30 to 60% by mass, and mixing and pulverization are performed for a predetermined time. For example, polyvinyl alcohol is used as the organic solvent.

  Here, the average particle diameter of the initial raw material charged into the mixing and grinding apparatus is 1000 to 3000 nm for zinc oxide particles, 6000 to 8000 nm for bismuth oxide particles, 2000 to 4000 nm for antimony oxide particles, and for manganese oxide particles. It is 4000 to 6000 nm, 2000 to 4000 nm for cobalt oxide particles, and 1000 to 3000 nm for nickel oxide particles.

  Here, as the mixing and grinding device, for example, a circulation type device using zirconia beads having a diameter of 0.05 to 3 mm is used. Further, the bead filling rate in the vessel in the mixing and pulverizing apparatus is set to 35 to 95%, for example, the peripheral speed of the stirring rotor is set to 500 to 1500 rpm, and the circulating flow rate is set to 5 to 50 L / min, for example. Can do.

  The average particle diameter of each raw material in the mixed and pulverized mixture after a predetermined time is within the range of the average particle diameter of each raw material particle in the mixture described above. In addition, the predetermined time after throwing in zinc oxide is set to the time until the average particle diameter of each raw material in a mixture becomes the range mentioned above. The mixture after a predetermined time becomes a slurry.

  Here, the other raw materials excluding zinc oxide are mixed and pulverized under the same conditions. However, as described above, depending on the difference in the average particle diameter of the initial raw materials and the hardness of each raw material that are put into the mixing and pulverizing apparatus. Those having different average particle diameters are formed.

  Subsequently, the produced slurry is sprayed and granulated by, for example, a rotating disk method or a pressurized nozzle method to produce a granulated powder. Here, the particle size of the granulated powder is preferably 70 to 130 μm. The particle size of the granulated powder is measured using a laser diffraction / scattering particle size distribution measuring device or the like. Here, the reason why the particle size of the granulated powder is preferably 70 to 130 μm is that moldability is good and a dense molded body can be obtained.

  The obtained granulated powder is molded into a columnar shape by using, for example, a hydraulic press molding machine to produce a molded body.

  Subsequently, the molded body is heated to a temperature of 350 to 500 ° C., and maintained at this temperature for 1 to 3 hours, for example, to degrease the organic solvent.

  Subsequently, the molded body is heated to a temperature of 1000 to 1200 ° C., and is fired at this temperature, for example, for 2 hours or more. The firing is performed, for example, by using a tunnel-type continuous furnace and placing the compact in a refractory container such as alumina or mullite. Moreover, it is preferable that the heating rate from the degreasing temperature to the firing temperature is 50 to 200 ° C./hour from the viewpoint of temperature uniformity in the firing object and firing process lead time.

  After firing, the fired molded body is cooled to room temperature. In this cooling step, in order to obtain excellent non-linear characteristics, thermal stability, etc., it is preferable that the cooling rate of the molded body is 100 to 200 ° C./hour. Through this cooling step, the sintered body 20 is obtained.

  The insulating layer 30 is formed by applying or spraying the above-described inorganic insulator onto the side surface of the sintered body 20 cooled to room temperature.

  Further, the upper and lower end surfaces of the sintered body 20 are polished, and the electrode 40 is formed on the polished surface by, for example, spraying the above-described conductive material.

  In addition, the order which performs the process of forming the insulating layer 30, and the process of forming the electrode 40 is not specifically limited, Any may be performed first.

  Thus, the current-voltage nonlinear resistor 10 is produced through the above-described steps.

  As described above, according to the current-voltage nonlinear resistor 10 of the embodiment, the subcomponents (bismuth oxide, antimony oxide, cobalt oxide, manganese oxide, oxidation) constituting the mixture for forming the sintered body 20 are described. By making the nickel fine, the microstructure becomes uniform, and the average particle diameter of zinc oxide is set to a predetermined value or more, thereby suppressing the densification of the granulated powder and the formation of coarse pores in the sintered body 20. can do. As a result, it is possible to obtain the current-voltage nonlinear resistor 10 having excellent nonlinear resistance characteristics, energy withstand characteristics, and temperature characteristics at high temperatures.

(Evaluation of non-linear resistance characteristics, energy tolerance characteristics, and temperature characteristics at high temperatures)
Next, it will be specifically described below that the current-voltage nonlinear resistor 10 of the embodiment is excellent in nonlinear resistance characteristics, energy withstand characteristics, and temperature characteristics at high temperatures.

First, ZnO was used as a main component. As subcomponents, Bi ₂ O ₃ is weighed so that it contains 0.6 mol%, MnO and Co ₂ O ₃ each contain 1.5 mol%, NiO and Sb ₂ O ₃ each contain 2.5 mol%, and the balance is ZnO. did. At this time, the main component ZnO was adjusted to contain 75 mol% or more.

Subsequently, other raw materials excluding the weighed ZnO and water for setting the solid content concentration of the raw materials to 10 to 30% by mass were charged into the mixing and pulverizing apparatus. Furthermore, aluminum was made into an aluminum hydroxide (Al ₂ O ₃ ) aqueous solution, and 0.005 mol% of the aqueous solution was charged into a mixing and grinding apparatus. Then, mixing and pulverization were performed for a predetermined time.

  After a lapse of a certain time, weighed ZnO and an appropriate amount of polyvinyl alcohol were added to a mixing and pulverizing apparatus, and water was further added so that the solid concentration was 30 to 60% by mass, followed by mixing and pulverizing for a predetermined time.

  Here, the average particle diameter of the initial raw material charged into the mixing and grinding apparatus is 2000 nm for zinc oxide particles, 6500 nm for bismuth oxide particles, 3000 nm for antimony oxide particles, 5000 nm for manganese oxide particles, and 5000 nm for cobalt oxide particles. Was set to 3000 nm, and nickel oxide particles were set to 1500 nm.

  Here, as a mixing and pulverizing apparatus, a circulating apparatus using zirconia beads having a diameter of 0.05 to 3 mm was used, and the mixture was made into a slurry. Further, eight kinds of slurries with different average particle diameters of subcomponents were prepared by changing the bead filling rate in the vessel, the peripheral speed of the stirring rotor, the circulation flow rate, and the mixing time in the mixing and grinding apparatus.

  The average particle diameter of each raw material in 8 types of slurries was measured. In addition, the measuring method of an average particle diameter is as having mentioned above. In addition, the average particle diameter of the ZnO particle | grains after slurry preparation was 600 nm in any slurry.

  Subsequently, the produced slurry was sprayed and granulated to produce a granulated powder having a particle size of about 100 μm.

  The obtained granulated powder of each slurry was formed into a cylindrical shape having a diameter of 40 mm and a thickness of 18 mm by a hydraulic press molding machine, thereby preparing 8 types of molded bodies.

  Subsequently, the compact was heated to a temperature of 400 ° C. and maintained at this temperature for 1 hour to degrease an organic binder as an organic solvent.

  Subsequently, the compact was heated at a temperature of 1100 ° C. for 2 hours or more and fired. After firing, the fired molded body was cooled at a cooling rate of 100 ° C./hour until it reached room temperature to obtain a sintered body 20.

  An insulating layer 30 was formed by applying an inorganic insulator to the side surface of the sintered body 20 cooled to room temperature. Furthermore, the upper and lower end surfaces of the sintered body 20 were polished, and the conductive material described above was sprayed on the polished surface to form the electrode 40. In this way, eight types of samples (Sample 1 to Sample 8) were produced.

  Each sample was evaluated for non-linear resistance characteristics, energy tolerance characteristics, and temperature characteristics at high temperatures.

The non-linear resistance characteristic was measured for each sample by measuring the varistor voltage (V _{1 mA} ) and the voltage (V _{2.5 kA} ) when an 8 × 20 μs impulse current passed through _{2.5 kA,} and the ratio (V _{2. 5 kA} / V _{1 mA} ) was evaluated as a nonlinear coefficient. It shows that the nonlinear resistance characteristic is excellent, so that the value of this nonlinear coefficient is small. The varistor voltage (V _{1 mA} ) is a voltage when a current of 1 mA commercial frequency is applied, and the varistor voltage (V _{1 mA} ) in each sample was measured according to JEC0202-1994.

  The energy resistance characteristic was evaluated based on the limit absorption energy resistance test result. In the limit absorbed energy tolerance test, lightning impulse energy with a waveform of 4 × 10 μs is applied to each sample at intervals of 10 minutes until it is electrically destroyed while increasing the discharge energy amount by 20 J / cc from 400 J / cc. did. Then, the absorbed energy immediately before the destruction is defined as the limit absorption energy. It shows that it is excellent in energy tolerance, so that this limit absorption energy is large.

As for the temperature characteristics under high temperature, the sample was heated to 200 ° C., a voltage of 95% of the varistor voltage (V _{1 mA} ) was applied, and the leakage current was measured. The smaller the leakage current, the better the temperature characteristics at high temperatures.

  In each of the above-described evaluation tests, 10 pieces of each sample were produced, tested for 10 pieces, and evaluated using the average value.

  Further, for the sintered body 20 constituting each sample, the average particle diameter of the zinc oxide crystal particles in the sintered body 20 is calculated by the method described above, and based on the average particle diameter, the zinc oxide crystal particles in the sintered body 20 are calculated. The ratio of the standard deviation based on the particle size distribution to the average particle size of the zinc oxide crystal particles was determined.

  Table 1 shows the measurement results of the average particle diameter of the subcomponent raw materials in the mixture and the results of the respective evaluation tests in each sample. As described above, also in each sample, the average particle diameter of ZnO particles in the mixture was 600 nm. In Table 1, * marks are comparative examples showing samples that are outside the scope of the present invention.

  As shown in Table 1, Sample 1 to Sample 5 were found to have a smaller nonlinearity coefficient, a higher limit absorption energy, and a smaller leakage current than Samples 6 to 8. Furthermore, in Sample 1 to Sample 5, the ratio of the standard deviation based on the particle size distribution of the zinc oxide crystal particles in the sintered body 20 to the average particle size of the zinc oxide crystal particles is smaller than in Samples 6 to 8. Both were found to be below 25%.

  From the above results, it was found that Sample 1 to Sample 5 were excellent in non-linear resistance characteristics, energy withstand characteristics, and temperature characteristics at high temperatures.

(Influence of average particle size of zinc oxide particles in the mixture)
Here, when preparing the sample 3 of Table 1, the timing at which the weighed ZnO was charged into the mixing and pulverizing apparatus was changed to prepare six types of slurries having different average particle diameters of ZnO particles in the mixture. The average particle size of each subcomponent material (bismuth oxide, antimony oxide, cobalt oxide, manganese oxide, nickel oxide) in the mixture is the same as the value shown in Sample 3.

  Using the six types of slurry, the sintered body 20, the insulating layer 30, and the electrode 40 were formed by the same method as described above, and Samples 9 to 14 were produced. Sample 12 corresponds to sample 3 described above.

  FIG. 2 is a diagram showing the measurement results of the limit absorption energy when the average particle diameters of ZnO particles in the mixture are different. The method for measuring the limit absorption energy is the same as the method described above. Moreover, 10 pieces of samples were produced and tested for 10 pieces.

  As shown in FIG. 2, when the average particle diameter of ZnO particles in the mixture is 500 nm or more (samples 11 to 14), the limit absorption energy exceeds 500 J / cc, and the energy withstand characteristics are excellent. all right. When the average particle diameter of ZnO particles in the mixture was 500 nm or more (samples 11 to 14), although not shown, the non-linear resistance characteristics and the temperature characteristics at high temperatures were excellent.

  According to the embodiment described above, it is possible to obtain excellent non-linear resistance characteristics, energy withstand characteristics, and temperature characteristics at high temperatures.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  DESCRIPTION OF SYMBOLS 10 ... Current-voltage nonlinear resistor, 20 ... Sintered body, 30 ... Insulating layer, 40 ... Electrode.

Claims (4)

In a current-voltage nonlinear resistor comprising a sintered body of a mixture containing zinc oxide as a main component and subcomponents including bismuth oxide, antimony oxide, manganese oxide, cobalt oxide and nickel oxide,
The average particle size of bismuth oxide particles and antimony oxide particles in the mixture is 1000 nm or less,
The current-voltage nonlinear resistor, wherein a standard deviation based on a particle size distribution of the zinc oxide crystal particles in the sintered body is less than 25% of an average particle size of the zinc oxide crystal particles.   2. The current-voltage nonlinear resistor according to claim 1, wherein an average particle diameter of nickel oxide particles in the mixture is 600 nm or less.   The current-voltage nonlinear resistor according to claim 1 or 2, wherein the average particle diameter of the cobalt oxide particles in the mixture is 750 nm or less.   The current-voltage nonlinear resistor according to any one of claims 1 to 3, wherein an average particle diameter of the manganese oxide particles in the mixture is 800 nm or less.

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