Low-gradient zinc oxide varistor disc and preparation method thereof

Abstract

The application relates to the field of electronic materials, and particularly discloses a low-gradient zinc oxide varistor disc and a preparation method thereof; the low-gradient zinc oxide varistor disc comprises the following raw materials in parts by weight: 88-96 parts of zinc oxide, 1.5-3 parts of diantimony trioxide, 2-5 parts of bismuth trioxide, 0.2-1.8 parts of nickel oxide, 0.1-0.9 parts of cobalt trioxide, 0.1-0.4 parts of manganese oxide, 0.02-0.07 parts of chromium trioxide, 0.15-0.18 parts of lithium acetate, 1.2-1.8 parts of a dispersing agent, 1.8-2.5 parts of a binding agent, 0.12-0.15 parts of aluminum nitrate and 0.001-0.003 parts of silver nitrate; under the synergistic action of the components, the use ratio of the components is adjusted, the potential gradient of the varistor disc is reduced, the large-current resistance of the varistor disc is improved, and the change of the electrical performance after impact is reduced.

Description

Technical Field

[0001] This application relates to the field of electronic materials, and in particular to a low-gradient zinc oxide varistor and its preparation method. Background Technology

[0002] Resistive elements for surge arrester monitors are crucial components. Classified by gradient, they can be categorized into high-gradient, medium-gradient, and low-gradient resistive elements. Low-gradient resistive elements generate relatively low voltage per unit thickness, effectively limiting overvoltages at lower voltage levels. They exhibit good nonlinear characteristics and high stability, and are widely used in power systems, industrial applications, and rail transportation.

[0003] However, in the existing technology, by adding a large amount of bismuth trioxide to make the potential gradient of the low-gradient resistor greater than 120, the grain size is too small, which increases the risk of local breakdown under high current impact and the electrical parameter change rate is high after multiple square wave withstand. Summary of the Invention

[0004] To reduce the potential gradient of existing resistors, this application provides a low-gradient zinc oxide varistor and its preparation method.

[0005] In a first aspect, this application provides a low-gradient zinc oxide varistor, employing the following technical solution:

[0006] A low-gradient zinc oxide varistor sheet comprises the following raw materials in parts by weight: 88-96 parts zinc oxide, 1.5-3 parts antimony trioxide, 2-5 parts bismuth trioxide, 0.2-1.8 parts nickel oxide, 0.1-0.9 parts cobalt trioxide, 0.1-0.4 parts manganese oxide, 0.02-0.07 parts chromium trioxide, 0.15-0.18 parts lithium acetate, 1.2-1.8 parts dispersant, 1.8-2.5 parts binder, 0.12-0.15 parts aluminum nitrate, and 0.001-0.003 parts silver nitrate; wherein the bismuth trioxide and antimony trioxide in the raw materials of the low-gradient zinc oxide varistor sheet are pre-coated with stearic acid.

[0007] By adopting the above technical solution, this application uses zinc oxide as the main crystalline phase raw material, combined with other components, to improve the nonlinear coefficient of the varistor and reduce the potential gradient. Bismuth trioxide can promote the growth of zinc oxide grains. During sintering, bismuth trioxide melts to form a liquid phase, which encapsulates the zinc oxide grains, optimizes the grain boundary barrier, and thus reduces the potential gradient.

[0008] Cobalt trioxide, manganese oxide, and nickel oxide can synergistically enhance the conductivity of the resistor, improve its stability, increase its high-current withstand capability, and reduce changes in electrical performance after impact. Antimony trioxide can inhibit excessive growth of zinc oxide grains, dissolving in the zinc oxide lattice, preventing grain boundary migration, stabilizing the grain structure, and improving the nonlinear coefficient of the varistor, thereby reducing the potential gradient. This improves the aging resistance of the resistor and avoids localized hot spots. In the composition of the raw materials, reducing the content of bismuth trioxide while increasing the content of cobalt trioxide, manganese oxide, and nickel oxide can lower the grain boundary barrier, thereby reducing the potential gradient of the resistor.

[0009] Bismuth trioxide and antimony trioxide are high surface energy powders. Coating their surfaces with stearic acid reduces the surface energy of the powder particles. The long-chain molecules of stearic acid form a physical barrier between the powder particles, reducing contact agglomeration and improving the uniformity of resistor sheet sintering. The coated bismuth trioxide and antimony trioxide particles are more evenly dispersed, spreading uniformly at the zinc oxide grain boundaries during sintering. This enhances the interfacial bonding strength between bismuth trioxide / antimony trioxide and zinc oxide, alleviates sintering stress, and reduces grain boundary cracks.

[0010] Preferably, the raw material of the low-gradient zinc oxide varistor sheet is pre-coated with bismuth trioxide and antimony trioxide using stearic acid, including the following specific steps: drying bismuth trioxide and antimony trioxide, grinding and sieving to obtain dispersed powder, then mixing stearic acid with a solvent to obtain a stearic acid solution, adding the dispersed powder to the stearic acid solution, ultrasonically dispersing, heating and stirring simultaneously, drying and sieving to obtain stearic acid-coated bismuth trioxide-antimony trioxide.

[0011] Preferably, the total mass ratio of bismuth trioxide and antimony trioxide to stearic acid and solvent is 10:(0.5-0.8):(1-3).

[0012] Preferably, the heating temperature is 80-90℃.

[0013] Preferably, the binder is ethyl cellulose.

[0014] By adopting the above technical solution, ethyl cellulose can provide sufficient green strength after powder mixing, ensuring that the resistor sheet does not break during pressing and reducing the risk of cracking during drying and sintering. Simultaneously, in subsequent preparation processes, it can act as a binder phase to promote the formation of uniform spherical granules from all components.

[0015] Preferably, the dispersant is one of polyvinyl alcohol and ethanol.

[0016] By adopting the above technical solutions, polyvinyl alcohol and ethanol as dispersants can reduce the phenomenon of powder agglomeration and promote a more uniform grain size distribution after sintering.

[0017] Secondly, this application provides a method for preparing a low-gradient zinc oxide varistor, which adopts the following technical solution:

[0018] A method for preparing a low-gradient zinc oxide varistor includes the following specific steps:

[0019] The coated bismuth trioxide, antimony trioxide, zinc oxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binder, aluminum nitrate, and silver nitrate are mixed, and then water and dispersant are added. The mixture is then wet-milled and dried to obtain granulated powder.

[0020] The granulated powder is dry-pressed into shape, then subjected to debinding and pre-firing, main firing, and side insulation treatment in sequence, and finally ground into a low-gradient zinc oxide varistor sheet.

[0021] By adopting the above technical solution, pre-firing with binder removal followed by main firing avoids excessive grain growth. The combination of these process steps reduces the potential gradient of the prepared resistor, significantly improving its high-current withstand capability and reducing the rate of change in its electrical parameters.

[0022] Preferably, the pressure in the dry pressing process is 80-150 MPa, and the holding time is 10-15 seconds.

[0023] By adopting the above technical solution, controlling the pressure during the molding process within a low range can reduce excessive density increase, reduce the occurrence of cracks, ensure uniform density of the blank, and improve the stability of the electrical performance of the resistor sheet.

[0024] Preferably, the pre-firing temperature for removing glue is 400-600℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h; the main firing temperature is 950-1100℃, the holding time is 2-4h, and the cooling rate is 5-10℃ / min.

[0025] By adopting the above technical solution, pre-firing with binder debinding can initially form a grain boundary structure, preparing for the main firing. Simultaneously, it removes binders and dispersants, improving the nonlinear coefficient and electrical properties of the resistor sheet. Controlling the pre-firing time within a suitable range avoids oxidation or reduction of the raw materials. Main firing temperature is controlled at 950-1100℃. Using a lower firing temperature reduces the grain growth rate, while controlling the cooling rate avoids thermal stress cracking, improving the stability of the resistor sheet.

[0026] Preferably, the side insulation treatment involves spraying a glass glaze layer onto the side.

[0027] In summary, this application has the following beneficial effects:

[0028] 1. Since this application uses zinc oxide as the main crystalline phase, the addition of cobalt trioxide, manganese oxide, nickel oxide, and antimony trioxide components to the raw materials stabilizes the grain structure, improves the nonlinear coefficient of the varistor, and reduces the potential gradient. Simultaneously, reducing the bismuth trioxide content while increasing the content of cobalt trioxide, manganese oxide, and nickel oxide in the raw material formulation lowers the grain boundary barrier, thereby reducing the potential gradient of the resistor.

[0029] 2. In this application, bismuth trioxide and antimony trioxide are pre-coated with stearic acid. The long-chain molecules of stearic acid can form a physical barrier between powder particles, reducing the agglomeration of powder particles and promoting more uniform dispersion of coated bismuth trioxide and antimony trioxide particles. During sintering, they can be evenly spread at the zinc oxide grain boundaries, relieving sintering stress and reducing grain boundary cracks. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments.

[0031] All raw materials used in the examples are commercially available.

[0032] Example

[0033] Example 1

[0034] This embodiment provides a low-gradient zinc oxide varistor, comprising the following raw materials in parts by weight: 92g zinc oxide, 2.2g antimony trioxide, 3.5g bismuth trioxide, 1g nickel oxide, 0.5g cobalt trioxide, 0.3g manganese oxide, 0.045g chromium trioxide, 0.17g lithium acetate, 1.5g dispersant, 2.1g binder, 0.14g aluminum nitrate, and 0.002g silver nitrate. The dispersant is polyvinyl alcohol (PVA-205), and the binder is ethyl cellulose.

[0035] The preparation method of low-gradient zinc oxide varistor includes the following specific steps:

[0036] S1: Bismuth trioxide and antimony trioxide are dried, ground, and sieved to obtain dispersed powder. Then, stearic acid and solvent (ethanol) are mixed. The total mass ratio of bismuth trioxide and antimony trioxide to stearic acid and solvent is 10:0.8:3 to obtain a stearic acid solution. The dispersed powder is added to the stearic acid solution and ultrasonically dispersed for 3 hours. Then, it is heated and stirred until it reaches 85°C. After drying, it is sieved to obtain stearic acid-coated bismuth trioxide-antimony trioxide.

[0037] S2: Zinc oxide, fatty acid-coated bismuth trioxide-antimony trioxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binder, aluminum nitrate, and silver nitrate are mixed, and then water and dispersant are added and wet ball milled for 40 hours. The mass ratio of water to total powder is 1:1. After drying, granulated powder is obtained.

[0038] S3: The granulated powder is dry-pressed at 80MPa for 15s, then heated to 600℃ at a heating rate of 3℃ / min and held for 2h. The temperature is then increased to 1100℃ for main firing and held for 2h. Finally, the temperature is reduced to room temperature at a cooling rate of 10℃ / min to obtain a semi-finished resistor sheet. A glass glaze layer is then sprayed onto the side of the semi-finished resistor sheet at 530℃ and held for 10h. Finally, the sheet is ground and dried to obtain a low-gradient zinc oxide varistor sheet.

[0039] Example 2

[0040] The difference between Example 2 and Example 1 is that the amount of zinc oxide used in the low-gradient zinc oxide varistor sheet raw material is 88g, antimony trioxide is 3g, bismuth trioxide is 2g, nickel oxide is 1.8g, cobalt trioxide is 0.1g, manganese oxide is 0.4g, chromium trioxide is 0.02g, lithium acetate is 0.18g, dispersant is 1.2g, binder is 1.8g, aluminum nitrate is 0.15g, and silver nitrate is 0.001g.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that the amount of zinc oxide used in the low-gradient zinc oxide varistor sheet raw material is 96g, antimony trioxide is 1.5g, bismuth trioxide is 5g, nickel oxide is 0.2g, cobalt trioxide is 0.9g, manganese oxide is 0.1g, chromium trioxide is 0.07g, lithium acetate is 0.15g, dispersant is 1.8g, binder is 2.5g, aluminum nitrate is 0.12g, and silver nitrate is 0.003g.

[0043] Example 4

[0044] The difference between Example 4 and Example 1 lies in the preparation method of the low-gradient zinc oxide varistor, which includes the following specific steps:

[0045] S1: Bismuth trioxide and antimony trioxide are dried, ground, and sieved to obtain dispersed powder. Then, stearic acid and solvent (ethanol) are mixed. The total mass ratio of bismuth trioxide and antimony trioxide to stearic acid and solvent is 10:0.8:3 to obtain a stearic acid solution. The dispersed powder is added to the stearic acid solution and ultrasonically dispersed for 3 hours. Then, it is heated and stirred until it reaches 85°C. After drying, it is sieved to obtain stearic acid-coated bismuth trioxide-antimony trioxide.

[0046] S2: Zinc oxide, fatty acid-coated bismuth trioxide-antimony trioxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binder, aluminum nitrate, and silver nitrate are mixed, and then water and dispersant are added and wet ball milled for 40 hours. The mass ratio of water to total powder is 1:1. After drying, granulated powder is obtained.

[0047] S3: The granulated powder is dry-pressed at 150MPa for 10s, then heated to 600℃ at a heating rate of 3℃ / min and held for 2h. The temperature is then increased to 1100℃ for main firing and held for 2h. Finally, the temperature is reduced to room temperature at a cooling rate of 10℃ / min to obtain a semi-finished resistor sheet. A glass glaze layer is then sprayed onto the side of the semi-finished resistor sheet at 530℃ and held for 10h. Finally, the sheet is ground and dried to obtain a low-gradient zinc oxide varistor sheet.

[0048] Example 5

[0049] The difference between Example 5 and Example 1 lies in the preparation method of the low-gradient zinc oxide varistor, which includes the following specific steps:

[0050] S1: Bismuth trioxide and antimony trioxide are dried, ground, and sieved to obtain dispersed powder. Then, stearic acid and solvent (ethanol) are mixed. The total mass ratio of bismuth trioxide and antimony trioxide to stearic acid and solvent is 10:0.8:3 to obtain a stearic acid solution. The dispersed powder is added to the stearic acid solution and ultrasonically dispersed for 3 hours. Then, it is heated and stirred until it reaches 85°C. After drying, it is sieved to obtain stearic acid-coated bismuth trioxide-antimony trioxide.

[0051] S2: Zinc oxide, fatty acid-coated bismuth trioxide-antimony trioxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binder, aluminum nitrate, and silver nitrate are mixed, and then water and dispersant are added and wet ball milled for 40 hours. The mass ratio of water to total powder is 1:1. After drying, granulated powder is obtained.

[0052] S3: The granulated powder is dry-pressed at 80MPa for 15s, then heated to 400℃ at a heating rate of 1℃ / min and held for 4h. The temperature is then increased to 950℃ for main firing and held for 4h. Finally, the temperature is reduced to room temperature at a cooling rate of 5℃ / min to obtain a semi-finished resistor sheet. A glass glaze layer is then sprayed onto the side of the semi-finished resistor sheet at 530℃ and held for 10h. Finally, the sheet is ground and dried to obtain a low-gradient zinc oxide varistor sheet.

[0053] Example 6

[0054] The difference between Example 6 and Example 1 is that the total mass ratio of bismuth trioxide and antimony trioxide in the raw material of the low-gradient zinc oxide varistor is 10:0.5:1.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 1 is that cobalt trioxide is not used in the raw materials of the low-gradient zinc oxide varistor.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 1 is that cobalt trioxide and manganese oxide are not used in the raw materials of the low-gradient zinc oxide varistor.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 1 is that cobalt trioxide, nickel oxide, and manganese oxide are not used in the raw materials of the low-gradient zinc oxide varistor.

[0061] Comparative Example 4

[0062] The difference between Comparative Example 4 and Example 1 is that the amount of bismuth trioxide used in the raw material of the low-gradient zinc oxide varistor is 10g.

[0063] Comparative Example 5

[0064] The difference between Comparative Example 5 and Example 1 is that the raw material of the low-gradient zinc oxide varistor does not pre-coat bismuth trioxide and antimony trioxide with stearic acid.

[0065] The preparation method of low-gradient zinc oxide varistor includes the following specific steps:

[0066] S1: Zinc oxide, fatty acid-coated bismuth trioxide-antimony trioxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binder, aluminum nitrate, and silver nitrate are mixed, and then water and dispersant are added and wet ball milled for 40 hours. The mass ratio of water to total powder is 1:1. After drying, granulated powder is obtained.

[0067] S2: The granulated powder is dry-pressed at 80MPa for 15s, then heated to 600℃ at a heating rate of 3℃ / min and held for 2h. The temperature is then increased to 1100℃ for main firing and held for 2h. Finally, the temperature is reduced to room temperature at a cooling rate of 10℃ / min to obtain a semi-finished resistor sheet. A glass glaze layer is then sprayed onto the side of the semi-finished resistor sheet at 530℃ and held for 10h. Finally, the sheet is ground and dried to obtain a low-gradient zinc oxide varistor sheet.

[0068] According to the low-gradient zinc oxide varistors provided in Examples 1-6 and Comparative Examples 1-5 of this application, varistor samples with a diameter of 99 mm and a height of 12 mm were fired and subjected to the following performance tests. The specific test results are shown in Table 1.

[0069] I. Electrical Performance

[0070] The voltage gradient and varistor voltage (V1mA) of the varistor sample prepared in this application were detected at a current density of 1mA / cm², and the leakage current was detected when a voltage of 75%V1mA was applied. The voltage of the varistor sample prepared in this application at 1mA / cm² and 10mA / cm² was detected, and the nonlinear coefficient β was measured, β= lg(U10 / U1) / lg(10).

[0071] II. Appearance Performance Testing

[0072] Appearance: After fabricating electrodes on the varistor sample prepared in this application, the surface was examined under a microscope for cracks and electrode detachment. The thickness and diameter of the sample's center and perimeter were measured using vernier calipers to test dimensional deviations. The flexural strength of the varistor sample prepared in this application was tested using the three-point bending method.

[0073] Table 1: Performance Test Results Data Table

[0074]

[0075] Continued from Table 1: Performance Test Results Data Table

[0076]

[0077] The performance test results show that the varistor prepared in this application can effectively reduce the potential gradient, significantly improve the high current withstand capability, and reduce the rate of change of electrical parameters after multiple square wave withstand.

[0078] A comparison of Comparative Examples 1-4 with Example 1 shows that Comparative Example 1 does not use cobalt trioxide, Comparative Example 2 does not use cobalt trioxide and manganese oxide, Comparative Example 3 does not use cobalt trioxide, nickel oxide, and manganese oxide, and Comparative Example 4 increases the amount of bismuth trioxide. Performance testing results show that adjusting the proportions of bismuth trioxide, cobalt trioxide, manganese oxide, and nickel oxide in the varistor material significantly reduces the potential gradient of the varistor. Comparative Example 1, by omitting cobalt trioxide, results in uneven current distribution, making it prone to localized breakdown under surge impact, leading to varistor failure and reducing its current withstand capability. Comparative Example 2, by removing cobalt trioxide and manganese oxide, weakens the grain-refining effect of cobalt trioxide and manganese oxide, leading to an increase in breakdown voltage per unit thickness, failing to meet the low gradient requirement. Comparative Example 3, by removing cobalt trioxide, nickel oxide, and manganese oxide, significantly increases leakage current, causing severe heating of the varistor under normal operating voltage, rapid performance degradation under long-term operation or high-temperature environments, and a significantly shortened lifespan.

[0079] A comparison of Examples 1-4 and Example 1 shows that removing these three components one by one significantly reduces the stability and nonlinear coefficient of the resistor, and also reduces the current withstand capability. However, excessively increasing the bismuth trioxide content can cause significant changes in the electrical properties of the resistor after impact, thus reducing its stability.

[0080] A comparison of Comparative Example 5 and Example 1 shows that pre-coating bismuth trioxide and antimony trioxide with stearic acid can effectively improve the stability of the resistor sheet, enhance the dispersion of bismuth trioxide and antimony trioxide particles in the resistor sheet system, alleviate sintering stress, reduce grain boundary cracks, and improve the dimensional stability of the resistor sheet.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-grad zinc oxide varistor chip, characterized by, The raw materials include the following weight parts: zinc oxide 88-96 parts, antimony trioxide 1.5-3 parts, bismuth trioxide 2-5 parts, nickel oxide 0.2-1.8 parts, cobalt trioxide 0.1-0.9 parts, manganese oxide 0.1-0.4 parts, chromium trioxide 0.02-0.07 parts, lithium acetate 0.15-0.18 parts, dispersant 1.2-1.8 parts, binding agent 1.8-2.5 parts, aluminum nitrate 0.12-0.15 parts, silver nitrate 0.001-0.003 parts; the low-gradient zinc oxide varistor disc raw material uses stearic acid to coat bismuth trioxide and antimony trioxide in advance, and includes the following specific steps: drying, grinding and sieving bismuth trioxide and antimony trioxide to obtain dispersed powder, then mixing stearic acid with a solvent to obtain a stearic acid solution, adding the dispersed powder into the stearic acid solution, ultrasonic dispersion, heating and stirring, sieving after drying to obtain stearic acid-coated bismuth trioxide-antimony trioxide; the mass ratio of the total mass of bismuth trioxide and antimony trioxide to the mass of stearic acid and the solvent is 10: (0.5-0.8): (1-3).

2. The low-gradient zinc oxide varistor disc of claim 1, wherein, The heating temperature is 80-90℃.

3. The low gradient zinc oxide varistor disc of claim 1, wherein, The binding agent is ethyl cellulose.

4. The low gradient zinc oxide varistor disc of claim 1, wherein, The dispersant is one of polyvinyl alcohol and ethanol.

5. A method of producing a low-grad zinc oxide varistor disc according to any one of claims 1 to 4, characterized by, The method includes the following specific steps: Mixing the coated bismuth trioxide, antimony trioxide and zinc oxide, nickel oxide, cobalt trioxide, manganese oxide, chromium trioxide, lithium acetate, binding agent, aluminum nitrate and silver nitrate, then adding water and dispersant for wet ball milling, and drying to obtain granulated powder; Dry pressing the granulated powder, then sequentially performing glue removal pre-burning, main burning, side insulation treatment, and finally grinding to obtain the low-gradient zinc oxide varistor disc.

6. The method of producing a low-gradient zinc oxide varistor sheet according to claim 5, wherein The pressure in the dry pressing is 80-150Mpa, and the pressure maintaining time is 10-15s.

7. The method of producing a low-gradient zinc oxide varistor disc according to claim 5, wherein The glue removal pre-burning temperature is 400-600℃, the heating rate is 1-3℃ / min, and the holding time is 2-4h; the main burning temperature is 950-1100℃, the holding time is 2-4h, and the cooling rate is 5-10℃ / min.

8. The method of producing a low-gradient zinc oxide varistor disc according to claim 5, wherein The side insulation treatment is to spray a glass glaze layer on the side.

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