A method for preparing a high-gradient zinc oxide varistor

Abstract

The present invention discloses a method for preparing a high-gradient zinc oxide varistor sheet, and belongs to the technical field of electrical material preparation. The method comprises: (1) hydrothermally reacting Y2O3 with a surfactant aqueous solution at 160-180°C to obtain g-Y2O3; (2) preparing a first powder, including ZnO, Bi2O3, Sb2O3, Co2O3, MnCO3, NiO, Y2O3 and Ag-glass; (3) mixing the first powder with deionized water, an organic aqueous dispersion and a dispersant, and then ball milling the first powder, and then granulating the ball milled slurry through a 100-mesh screen to obtain a third powder; (4) pressing the third powder into a cylindrical sample; (5) calcining the cylindrical sample at high temperature. During high-temperature sintering, the rare earth oxide generates new spinel with Zn, Bi, etc., and the growth rate of ZnO grains is reduced due to the pinning effect of the spinel, resulting in a reduction in the grain size of the varistor, so that the potential gradient is improved.

Description

Technical Field

[0001] The invention relates to the technical field of electrical material preparation, and in particular to a method for preparing a high-gradient zinc oxide varistor sheet. Background Art

[0002] Nonlinear zinc oxide (ZnO) varistor (hereinafter referred to as resistor) is a highly nonlinear polycrystalline electronic ceramic electrical protection element with excellent nonlinear current-voltage characteristics. Its excellent nonlinear characteristics are widely used in the field of overvoltage protection. In the field of metal oxide arresters (hereinafter referred to as arresters), resistors are an indispensable core component. However, the resistor cylinders used in UHV power systems have a high height, which usually leads to uneven potential distribution and complex structure. Increasing the potential gradient of the resistor is an effective way to reduce the height of the arrester, but the increase in the potential gradient of the resistor is often accompanied by a decrease in the large current carrying capacity of the resistor. In addition, impurities and pores introduced during the manufacturing process of the resistor also seriously limit the improvement of the performance of the resistor.

[0003] At present, the gradient of ZnO varistor is improved by reducing the ZnO grain growth rate and reducing the grain growth time by lowering the sintering temperature of the varistor and shortening the holding time. However, this method makes the flow energy, nonlinearity and aging performance of the ZnO varistor worse. Another method is to add an appropriate amount of Al2O3, SiO2, etc. to inhibit the growth of ZnO grains to improve the potential gradient. Summary of the invention

[0004] In order to solve the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for preparing a high-gradient zinc oxide varistor sheet, in which rare earth oxides are added to the resistor sheet formula and the proportion of each component is optimized. During high-temperature sintering, the rare earth oxides react with Zn, Bi, Sb, etc. to generate new spinels. Due to the pinning effect of the spinels, the growth rate of the ZnO grains is reduced, resulting in a reduction in the grain size of the varistor, thereby improving the potential gradient.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a high-gradient zinc oxide varistor sheet, the method comprising the following steps:

[0007] (1) hydrothermally reacting Y2O3 with an aqueous solution of a surfactant at 160-180° C. for 10-12 h to obtain modified Y2O3 (g-Y2O3);

[0008] (2) preparing a first powder, wherein the first powder includes ZnO, Bi2O3, Sb2O3, Co2O3, MnCO3, NiO, Y2O3 and Ag-glass; the Ag-glass is silver glass powder;

[0009] (3) placing the first powder into a ball mill barrel, adding appropriate amounts of deionized water, organic aqueous dispersion and dispersant, and ball milling for a certain period of time, granulating the slurry obtained after ball milling in a spray granulation tower to obtain a second powder; passing the second powder through a 100-mesh sieve to obtain a third powder;

[0010] (4) Pressing the third powder into a cylindrical sample in a hydraulic press;

[0011] (5) calcining the cylindrical sample in a high-temperature calcining furnace at a certain temperature for a certain time to obtain the high-gradient zinc oxide varistor sheet.

[0012] In the above step (1), the aqueous solution of the surfactant is obtained by dispersing the surfactant in water, the surfactant is polyethylene glycol and / or glucose, and the weight ratio of Y2O3 to the surfactant is 100:(1-5).

[0013] In the above step (1), the solid content of the surfactant is 3-10wt%.

[0014] In the above step (2), the first powder has the following composition by weight percentage:

[0015]

[0016] In the above step (3), the mass ratio of the first powder, deionized water, organic aqueous dispersion and dispersant is (45-55): (45-50): (20-30): 1.

[0017] The organic aqueous dispersion is obtained by dispersing organic matter in water. The organic matter is one of polyvinyl alcohol, ethylene copolymer and sodium carboxymethyl cellulose. The mass concentration of the organic matter in the organic aqueous dispersion is 5-10%. The dispersant is methyl amyl alcohol or polyacrylamide.

[0018] In the above step (3), the ball milling method is drum ball milling or stirring ball milling, the ball milling speed is 300-500rpm, and the ball milling time is 5-10h; the particle size of the second powder is 50-80μm.

[0019] In the above step (4), the height of the cylindrical sample is 10-50 mm and the diameter is 30-80 mm.

[0020] In the above step (5), the calcination temperature is 1100-1250° C. and the calcination time is 2-4 hours.

[0021] The advantages and beneficial effects of the present invention are as follows:

[0022] 1. The more grains and grain boundaries per unit thickness of a ZnO varistor, the higher its potential gradient. Therefore, the miniaturization of resistor grains is an important way to increase the potential gradient. The present invention improves the formula by adding rare earth oxides to the formula. During high-temperature sintering, the rare earth oxides react with Zn, Bi, Sb, etc. to generate new spinels. Due to the pinning effect of the spinels, the growth rate of the ZnO grains is reduced, resulting in a reduction in the grain size of the varistor and an increase in the potential gradient. The method does not destroy the original process, has strong adaptability, and is conducive to industrial application.

[0023] 2. The rare earth oxide Y2O3 in the resistor formula of the present invention uses a surface grafting modification process to coat a layer of hydrophilic organic matter on the surface of Y2O3, so that Y2O3 is more evenly distributed in the system, and the spinel generated by Y2O3 and Zn, Bi, Sb, etc. is more evenly distributed. In addition, this process can reduce the pores introduced in the resistor manufacturing process to ensure the stable and controllable quality of the product.

[0024] 3. Benxu introduced surface-grafted rare earth oxide g-Y2O3 into the system. During high-temperature sintering, the g-Y2O3 and Zn, Bi, Sb, etc. generated new spinel. The pinning effect of the spinel reduced the growth rate of the ZnO grains, resulting in a decrease in the grain size of the varistor, an increase in the number of grains and grain boundaries per unit thickness of the ZnO varistor, and an improvement in the potential gradient. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with the embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] Embodiment 1:

[0029] The preparation method of the high gradient zinc oxide varistor sheet in this embodiment is as follows:

[0030] S1: hydrothermally react Y2O3 with a 3 wt% solid content polyethylene glycol aqueous solution at 170° C. for 12 h to obtain modified Y2O3 (g-Y2O3). The weight ratio of Y2O3 to polyethylene glycol is 100:2.

[0031] S2: Prepare the first powder, which is ZnO, Bi2O3, Sb2O3, Co2O3, MnCO3, NiO, Y2O3 and Ag-glass (silver glass powder); the first powder components are as follows by mass content: ZnO is 90%, Bi2O3 is 2%, Sb2O3 is 3%, Co2O3 is 1%, MnCO3 is 1.5%, g-Y2O3 is 0.5%, and Ag-glass is 1%.

[0032] S3: Put the first powder into a ball mill barrel, add appropriate amount of deionized water, organic aqueous dispersion and dispersant, and ball mill for 6 hours, wherein: the mass ratio of the first powder, deionized water, organic aqueous dispersion and dispersant is 50:50:20:1. The slurry after ball milling is granulated in a spray granulation tower to obtain a second powder with a particle size of 50-80μm, and the second powder is passed through a 100-mesh sieve to obtain a third powder. Among them: the organic aqueous dispersion is obtained by dispersing polyvinyl alcohol in water, with a concentration of 8%; the dispersant is polyacrylamide. The ball milling method is stirred ball milling, and the ball milling speed is 450rpm.

[0033] S4: The third powder was pressed into a cylindrical sample with a diameter of 50 mm and a height of 15 mm using a hydraulic press.

[0034] S5: Calcine the cylindrical sample in a high temperature calcination furnace at 1200℃ for 2h. After high temperature calcination, the size of the ceramic sample will shrink in the radial and axial directions. The actual sintered sample is a cylindrical zinc oxide varistor with a diameter of 40.12mm and a height of 12.32mm.

[0035] Embodiment 2:

[0036] The preparation method of the high gradient zinc oxide varistor sheet in this embodiment is as follows:

[0037] S1: hydrothermally react Y2O3 with a 5 wt% solid content glucose aqueous solution at 175° C. for 10 h to obtain modified Y2O3 (g-Y2O3). The weight ratio of Y2O3 to glucose is 100:2.

[0038] S2: Prepare a first powder, which is ZnO, Bi2O3, Sb2O3, Co2O3, MnCO3, NiO, Y2O3 and Ag-glass (silver glass powder); the first powder components are as follows by mass content: ZnO is 90%, Bi2O3 is 2%, Sb2O3 is 3%, Co2O3 is 1%, MnCO3 is 1%, NiO is 1%, g-Y2O3 is 1%, and Ag-glass is 1%.

[0039] S3: Put the first powder into a ball mill barrel, add appropriate amount of deionized water, organic aqueous dispersion and dispersant, and ball mill for 6 hours; wherein: the mass ratio of the first powder, deionized water, organic aqueous dispersion and dispersant is 50:50:20:1. The slurry after ball milling is granulated in a spray granulation tower to obtain a second powder with a particle size of 50-80μm, and the second powder is passed through a 100-mesh sieve to obtain a third powder. wherein: the organic aqueous dispersion is obtained by dispersing sodium carboxymethyl cellulose in water, with a concentration of 8%; the dispersant is polyacrylamide. The ball milling method is drum ball milling, and the ball milling speed is 400rpm.

[0040] S4: The third powder was pressed into a cylindrical sample with a diameter of 50 mm and a height of 15 mm using a hydraulic press.

[0041] S5: Calcine the cylindrical sample in a high temperature calcination furnace at 1220℃ for 2h. After high temperature calcination, the size of the ceramic sample will shrink in the radial and axial directions. The actual sintered sample is a cylindrical zinc oxide varistor with a diameter of 40.15mm and a height of 12.30mm.

[0042] Performance test: The U of the ZnO varistor sheet of the embodiment is tested using a metal oxide DC parameter tester. 1mA The test results are shown in Table 1.

[0043] Table 1: Electrical performance test results of the embodiments:

[0044]

[0045] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0046] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a high-gradient zinc oxide varistor sheet, characterized in that: The method comprises the following steps: (1) hydrothermally reacting Y2O3 and an aqueous solution of a surfactant at 160-180° C. for 10-12 h to obtain modified g-Y2O3; the aqueous solution of the surfactant is obtained by dispersing the surfactant in water, the surfactant is polyethylene glycol and / or glucose, and the weight ratio of Y2O3 to the surfactant is 100:(1-5); (2) preparing a first powder, wherein the first powder includes ZnO, Bi2O3, Sb2O3, Co2O3, MnCO3, NiO, Y2O3 and Ag-glass; the Ag-glass is silver glass powder; the first powder has the following composition by weight percentage: (3) placing the first powder into a ball mill, adding appropriate amounts of deionized water, organic aqueous dispersion and dispersant, and ball milling for a certain period of time, granulating the slurry obtained after ball milling in a spray granulation tower to obtain a second powder; passing the second powder through a 100-mesh sieve to obtain a third powder; the mass ratio of the first powder, deionized water, organic aqueous dispersion and dispersant is (45-55): (45-50): (20-30): 1; the organic aqueous dispersion is obtained by dispersing organic matter in water, and the organic matter is one of polyvinyl alcohol, ethylene copolymer and sodium carboxymethyl cellulose; the mass concentration of organic matter in the organic aqueous dispersion is 5-10%; the dispersant is methyl amyl alcohol or polyacrylamide; the ball milling method is drum ball milling or stirring ball milling, the ball milling speed is 300-500rpm, and the ball milling time is 5-10h; the particle size of the second powder is 50-80μm; (4) Pressing the third powder into a cylindrical sample in a hydraulic press; (5) The cylindrical sample is calcined in a high temperature calcination furnace at 1200-1220° C. for 2-4 hours to obtain the high gradient zinc oxide varistor sheet.

2. The method for preparing a high gradient zinc oxide varistor sheet according to claim 1, characterized in that: In step (1), the solid content of the surfactant is 3-10wt%.

3. The method for preparing a high gradient zinc oxide varistor sheet according to claim 1, characterized in that: In step (4), the height of the cylindrical sample is 10-50 mm and the diameter is 30-80 mm.

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