Silicon-doped zinc oxide varistor composite powder and preparation method thereof

Abstract

The invention discloses silicon-doped zinc oxide varistor composite powder and a preparation method thereof, and belongs to the technical field of preparation of electronic ceramic materials. The method adopts a silane hydrolysate as a dispersing agent of a zinc oxide varistor formula material, and comprises the following specific steps: hydrolyzing silane in an acidic alcohol-water mixed system to obtain a stable silane hydrolysate, then adding the zinc oxide varistor formula material into the silane hydrolysate, dispersing and grinding, and finally carrying out spray granulation. The silicon-doped zinc oxide varistor composite powder prepared by the method can be pressed and molded without adding an organic adhesive, and a zinc oxide varistor with good comprehensive performance can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of electronic ceramic material preparation, and in particular to a silicon-doped zinc oxide varistor composite powder and a preparation method thereof. Background Art

[0002] ZnO varistors rely on their excellent nonlinear volt-ampere characteristics to clamp voltage when the circuit is subjected to overvoltage, absorbing excess current to protect sensitive devices. This nonlinear volt-ampere characteristic for overvoltage protection comes from the unique microstructure of its grains and grain boundaries, and its microstructural characteristics depend on the formula materials and preparation process. Among them, pores and residual carbon are major factors affecting the electrical properties of zinc oxide varistors. The resulting uneven microstructure will lead to uneven current distribution, seriously reducing its undervoltage protection capability.

[0003] The main source of pores and residual carbon is organic binder. In order to ensure the molding of zinc oxide varistor powder, a certain amount of organic binder must be added to increase the strength of the green embryo, and then high-temperature debinding is carried out. The long debinding process not only produces porosity but also leaves residual carbon impurities, which have an adverse effect on the electrical properties of zinc oxide varistor. The function of organic binder is mainly to make zinc oxide varistor powder bonded under pressure through its interaction with the surface of the powder; if some particles in the powder have the property of mutual bonding, there is no need to introduce polymer compounds as binders.

[0004] In view of this, a silicon-doped zinc oxide varistor composite powder and a preparation method thereof are provided, which increase the bonding function of the particle surface to avoid the introduction of polymer compounds in the production of zinc oxide varistor, thereby ensuring minimum porosity and maximum microstructure uniformity. Summary of the invention

[0005] The object of the present invention is to provide a silicon-doped zinc oxide varistor composite powder and a preparation method thereof, which increases the bonding function of the particle surface to avoid the introduction of polymer compounds in the production of zinc oxide varistor, thereby ensuring minimum porosity and maximum microstructure uniformity.

[0006] The object of the present invention is achieved in that: A silicon-doped zinc oxide varistor composite powder comprises the following components: 99.8% to 99.99% of a zinc oxide formula material and 0.01% to 0.2% of a silicon element are prepared by molar percentage, wherein the silicon element is mixed with the zinc oxide formula material in the state of a silane hydrolyzate.

[0007] The weight ratio of the silane hydrolyzate to the zinc oxide formula material is 0.8-1.5.

[0008] The silane hydrolyzate comprises silane, water, monohydric alcohol and polyhydric alcohol, wherein the weight ratio of the monohydric alcohol to water is 0-15, and the weight ratio of the polyhydric alcohol to water is 0.01-0.5.

[0009] The silane includes one or more elements selected from the group consisting of silicon, oxygen, hydrogen and carbon.

[0010] The silane includes silicon, oxygen and hydrogen.

[0011] The monohydric alcohol is a monohydric alcohol having less than 3 carbon atoms, and the average molecular weight of the polyhydric alcohol is 62-1000.

[0012] The silane hydrolyzate is an acidic hydrolyzate, and an organic weak acid is used to adjust the pH value of the acidic hydrolyzate to 4.0-6.5; the organic acid is an organic acid with a dissociation constant (pKa) greater than 1 and a molecular weight less than 300.

[0013] The zinc oxide formula material includes Bi2O3 3.12%, Sb2O3 3.33%, Co2O3 1.95%, Mn3O4 0.55%, Cr2O3 0.42%, NiO 0.38%, MgO 0.06%, Al(NO3)3·9H2O 0.03%, boron glass powder 0.15% and ZnO 89.99%.

[0014] A method for preparing a silicon-doped zinc oxide varistor composite powder, characterized in that it comprises the following steps: Step 1: Evenly mix silane, monohydric alcohol, polyhydric alcohol and water, and use organic acid to adjust the pH of the solution to 4-6.5 to obtain a stable silane hydrolyzate; Step 2: Then add the silane hydrolyzate and the zinc oxide formula material into the grinding equipment according to a weight ratio of 0.8 to 1.5, so that the particle size (D97) of the dispersed system is fully ground to less than 5 μm to obtain a zinc oxide varistor composite slurry; Step 3: The zinc oxide varistor composite slurry in step 2 is granulated to obtain silicon-doped zinc oxide varistor composite powder.

[0015] The hydrolyzed silane is mixed with the zinc oxide formulation material before spray granulation, or the hydrolyzed silane is mixed with the zinc oxide formulation material after granulation when the material contains water.

[0016] The beneficial effects of the present invention are: 1. The silicon-doped zinc oxide varistor composite powder proposed by the present invention has silicon uniformly distributed in the zinc oxide varistor formula system in the form of silane solution. Compared with the traditional method of doping silicon in the form of solid particles such as silicon dioxide and silicic acid, the present invention optimizes the distribution efficiency and microstructure uniformity of silicon, and improves the electrical performance of zinc oxide varistor.

[0017] 2. The silicon-doped zinc oxide varistor composite powder proposed in the present invention contains abundant Si-O-Si bonds and hydrogen bonds, and the forces of Si-O-Si bonds and hydrogen bonds are relatively strong. Therefore, the zinc oxide varistor green body after pressing has relatively high strength, and will not crack during the subsequent sintering process, thereby avoiding the increase in porosity and carbon residue due to the use of organic binders. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the embodiments.

[0019] Embodiment 1: The raw materials of this embodiment are prepared according to the following molar percentages, and the specific formula is as follows: Bi2O3: 3.12%; Sb2O3: 3.33%; Co2O3: 1.95%; Mn3O4: 0.55%; Cr2O3: 0.42%; NiO: 0.38%; MgO: 0.06%; Al(NO3)3·9H2O: 0.03%; boron glass powder: 0.15%; ZnO: 89.99%; Silicon: 0.04%.

[0020] The silicon element is added in the form of silane hydrolyzate. The specific implementation method is as follows: First, dissolve tetraethyl orthosilicate in a mixed solution of ethanol, water, and propylene glycol, wherein the weight ratio of ethanol / water is 10, and the weight ratio of propylene glycol / water is 0.1. Use acetic acid to adjust the pH to 6. According to the above formula, the zinc oxide formula material is added to the hydrolyzate of tetraethyl orthosilicate at a weight ratio of 1, and appropriate dispersants and defoamers are added for grinding; the conventional production process of zinc oxide varistor such as granulation, water, dry pressing, sintering, heat treatment, aluminum spraying, glazing, and testing is used to produce zinc oxide varistor. The prepared zinc oxide varistor has a diameter of 42 mm and a height of 20 mm.

[0021] Example 2 The raw materials of this embodiment are prepared according to the following molar percentages, and the specific formula is as follows: Bi2O3: 3.12%; Sb2O3: 3.33%; Co2O3: 1.95%; Mn3O4: 0.55%; Cr2O3: 0.42%; NiO: 0.38%; MgO: 0.06%; Al(NO3)3·9H2O: 0.03%; boron glass powder: 0.15%; ZnO: 89.99%; Silicon: 0.02%.

[0022] The silicon element is added in the form of a silane aqueous solution. The specific implementation method is as follows: First, 1,2-bis(triethoxysilyl)ethane is dissolved in a mixed solution of ethanol, water, and propylene glycol, wherein the weight ratio of ethanol / water is 0.25, and the weight ratio of propylene glycol / water is 0.2. Use acetic acid to adjust the pH to 6. According to the above formula, the zinc oxide formula material is added to the hydrolyzed solution of ethyl orthosilicate at a weight ratio of 1, and appropriate dispersants and defoamers are added for grinding; the conventional production process of zinc oxide varistors such as granulation, water, dry pressing, sintering, heat treatment, aluminum spraying, glazing, and testing is used to produce zinc oxide varistors. The prepared zinc oxide varistor has a diameter of 42 mm and a height of 20 mm.

[0023] Example 3 The raw materials of this embodiment are prepared according to the following molar percentages, and the specific formula is as follows: Bi2O3: 3.12%; Sb2O3: 3.33%; Co2O3: 1.95%; Mn3O4: 0.55%; Cr2O3: 0.42%; NiO: 0.38%; MgO: 0.06%; Al(NO3)3·9H2O: 0.03%; boron glass powder: 0.15%; ZnO: 89.99%; Silicon: 0.02%.

[0024] The silicon element is added in the form of a silane aqueous solution. The specific implementation method is as follows: First, 1,2-bis(triethoxysilyl)ethane is dissolved in a mixed solution of ethanol, water, and propylene glycol, wherein the weight ratio of ethanol / water is 0.25 and the weight ratio of propylene glycol / water is 0.2. Use acetic acid to adjust the pH to 6. According to the above formula, the zinc oxide formula material is added to pure water at a weight ratio of 1, and appropriate dispersants and defoamers are added for grinding, and zinc oxide composite powder is obtained after spray granulation; the zinc oxide composite powder is treated with water using the above silane hydrolyzate, and then produced through conventional production processes of zinc oxide varistors such as dry pressing, sintering, heat treatment, aluminum spraying, glazing, and testing to prepare zinc oxide varistor. The prepared zinc oxide varistor has a diameter of 42 mm and a height of 20 mm.

[0025] Comparative Example 1 The raw materials of comparative example 1 are prepared according to the following molar percentages, and the specific formula is as follows: Bi2O3: 3.12%; Sb2O3: 3.33%; Co2O3: 1.95%; Mn3O4: 0.55%; Cr2O3: 0.42%; NiO: 0.38%; SiO2: 0.71%; MgO: 0.06%; Al(NO3)3·9H2O: 0.03%; silver glass powder: 0.15%; ZnO: 89.30%. The zinc oxide varistor is produced according to the conventional production process of the zinc oxide varistor. The prepared zinc oxide varistor has a diameter of 42 mm and a height of 20 mm.

[0026] The physical properties and electrical properties of the zinc oxide-based varistors of Example 1, Example 2, Example 3 and Comparative Example 1 obtained by testing are shown in Table 1 and Table 2, respectively.

[0027] In summary, it can be seen from Examples 1 to 3, Comparative Example 1 and Table 1 that the strength and density of the zinc oxide varistor green embryos prepared by Examples 1 to 3 using the silicon-doped zinc oxide varistor composite powder proposed by the present invention are greater than the strength and density of the zinc oxide varistor green embryos prepared in Comparative Example 1, and the debinding time of the zinc oxide varistor green embryos prepared by Examples 1 to 3 is shorter than the debinding time of the zinc oxide varistor green embryos prepared in Comparative Example 1, indicating that the green embryos still have good strength without adding an organic binder, which not only reduces the organic matter content, but also shortens the debinding time by 43%, thereby greatly reducing energy consumption.

[0028] It can be seen from Examples 1 to 3, Comparative Example 1 and Table 2 that the nonlinear coefficient of the zinc oxide varistors prepared in Examples 1 to 3 is larger than the nonlinear coefficient of the zinc oxide varistors prepared in Comparative Example 1, and the residual voltage ratio of the zinc oxide varistors prepared in Examples 1 to 3 is higher than the residual voltage ratio of the zinc oxide varistors prepared in Comparative Example 1, so both the volt-ampere characteristics and the residual voltage ratio are significantly improved, which fully verifies the beneficial technical effects described in the present invention.

Claims

1. A silicon-doped zinc oxide varistor composite powder, characterized in that: The invention comprises the following components: the zinc oxide formula comprises 99.8% to 99.99% of each element and 0.01% to 0.2% of silicon element, and the silicon element is mixed with the zinc oxide formula material in the state of silane hydrolyzate.

2. The silicon-doped zinc oxide varistor composite powder according to claim 1, characterized in that: The weight ratio of the silane hydrolyzate to the zinc oxide formula material is 0.8-1.

5.

3. The silicon-doped zinc oxide varistor composite powder according to claim 1, characterized in that: The silane hydrolyzate comprises silane, water, monohydric alcohol and polyhydric alcohol, wherein the weight ratio of the monohydric alcohol to water is 0-15, and the weight ratio of the polyhydric alcohol to water is 0.01-0.

5.

4. The silicon-doped zinc oxide varistor composite powder according to claim 3, characterized in that: The silane includes one or more elements selected from the group consisting of silicon, oxygen, hydrogen and carbon.

5. The silicon-doped zinc oxide varistor composite powder according to claim 3, characterized in that: The silane includes silicon, oxygen and hydrogen.

6. The silicon-doped zinc oxide varistor composite powder according to claim 3, characterized in that: The monohydric alcohol is a monohydric alcohol having less than 3 carbon atoms, and the average molecular weight of the polyhydric alcohol is 62-1000.

7. The silicon-doped zinc oxide varistor composite powder according to claim 1 or 3, characterized in that: The silane hydrolyzate is an acidic hydrolyzate, and an organic weak acid is used to adjust the pH value of the acidic hydrolyzate to 4.0-6.5; the organic acid is an organic acid with a dissociation constant greater than 1 and a molecular weight less than 300.

8. The silicon-doped zinc oxide varistor composite powder according to claim 1, characterized in that: The zinc oxide formula material includes Bi2O3 3.12%, Sb2O3 3.33%, Co2O3 1.95%, Mn3O4 0.55%, Cr2O3 0.42%, NiO 0.38%, MgO 0.06%, Al(NO3)3·9H2O 0.03%, boron glass powder 0.15% and ZnO 89.99%.

9. A method for preparing a silicon-doped zinc oxide varistor composite powder according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: Evenly mix silane, monohydric alcohol, polyhydric alcohol and water, and use organic acid to adjust the pH of the solution to 4-6.5 to obtain a stable silane hydrolyzate; Step 2: Then add the silane hydrolyzate and the zinc oxide formula material into the grinding equipment according to a weight ratio of 0.8 to 1.5, so that the particle size of the dispersed system is fully ground to less than 5 μm, and the zinc oxide varistor composite slurry is obtained; Step 3: The zinc oxide varistor composite slurry in step 2 is granulated to obtain silicon-doped zinc oxide varistor composite powder.

10. The method for preparing the silicon-doped zinc oxide varistor composite powder according to claim 9, characterized in that: The hydrolyzed silane is mixed with the zinc oxide formulation material before spray granulation, or the hydrolyzed silane is mixed with the zinc oxide formulation material after granulation when the material contains water.

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