A sodium-containing ZnO varistor and a method of making the same

Abstract

The application discloses a kind of sodium-containing ZnO varistors and preparation method thereof, belong to electrical material technical field.The raw material formula of the varistor:ZnO, Bi2O3, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, SiO2, NaBiO3.Preparation, Bi2O3, NaBiO3 First mixed and kept at 500-600 ℃ for 0.5-2h, make Bi2O3 powder and NaBiO3 Powder partially melt together, after cooling, crush and add other raw materials and Al (NO3) 3·9H2O, dispersing agent, binder and deionized water to obtain total slurry;After granulation, compression molding, sintering, form stable resistor piece blank;The application is introduced NaBiO3 in ZnO varistor, and NaBiO3 Can be decomposed and release sodium ion in sintering process, these sodium ions help to improve the electrical properties and stability of resistor piece.

Description

Technical Field

[0001] This invention relates to the field of electrical materials technology, specifically to a sodium-containing ZnO varistor and its preparation method. Background Technology

[0002] ZnO varistors are semiconductor ceramic components with nonlinear voltage-current characteristics, widely used in power and electronic equipment. To improve the performance of ZnO varistors, researchers have been exploring new additives and fabrication processes. Sodium, as an amphoteric dopant, can occupy both lattice and interstitial sites, offering potential advantages in ZnO varistor fabrication. However, the amount of sodium salt added is extremely critical; too little or too much will drastically degrade the performance of the ZnO varistor. Therefore, expanding the appropriate range for sodium salt addition is crucial for its successful application. Summary of the Invention

[0003] In view of the above-mentioned shortcomings in the existing technology, the purpose of this invention is to provide a sodium-containing ZnO varistor and its preparation method. By introducing NaBiO3 as a sodium source into the ZnO varistor formulation and optimizing the resistor preparation process, NaBiO3 can decompose and release sodium ions during sintering. These sodium ions help to improve the electrical performance and stability of the resistor.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A sodium-containing ZnO varistor, the raw material formula for preparing the sodium-containing ZnO varistor, by weight percentage, is as follows: ZnO 82-92 wt.%, Bi2O3 2-6 wt.%, Sb2O3 1-4 wt.%, NiO 0-3 wt.%, Cr2O3 0-2 wt.%, Mn3O4 0.5-3 wt.%, Co3O4 0.5-3 wt.%, SiO2 0.5-3 wt.%, NaBiO3 0.1-1 wt.%.

[0006] The method for preparing the sodium-containing ZnO varistor includes the following steps:

[0007] (1) Prepare the raw material powders according to the raw material formula for the preparation of resistor sheets;

[0008] (2) Preparation of total slurry, including the following steps (a)-(d):

[0009] (a) After mixing Bi2O3, NaBiO3 and deionized water in the raw material powder, the mixture is ball-milled, dried and pulverized to obtain mixed powder I;

[0010] (b) The mixed powder I obtained in step (a) is kept at 500-600℃ for 0.5-2h to partially melt Bi2O3 powder and NaBiO3 powder together. After cooling, it is pulverized to obtain mixed powder II.

[0011] (c) The raw material powders ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, SiO2, mixed powder II prepared in step (b), Al(NO3)3·9H2O, dispersant, binder and deionized water are mixed and added to a ball mill for mixing and grinding. The resulting slurry is passed through a 120-mesh sieve to obtain the total slurry.

[0012] (3) Preparation of the blank:

[0013] The total slurry prepared in step (2) is sprayed to obtain granules. The granules, deionized water and release agent are mixed evenly and then passed through a 30-mesh sieve. The powder obtained after sieving is aged to obtain blanking powder. The blanking powder is pressed to obtain a blank.

[0014] (4) Sintering of the green body:

[0015] After the blank is pre-calcined, it is placed in a high-temperature environment of 1000-1300℃ and calcined for at least 2 hours to form a stable resistor blank; after metal electrodes are prepared on the surface of the resistor blank, the finished sodium ZnO varistor is obtained.

[0016] Further, in step (a), the ball milling is carried out in a ball mill. After ball milling for 3-6 hours, the resulting mixture is dried at 100-200°C and then pulverized.

[0017] Further, in step (c), the dispersant is an anionic polyacrylate dispersant, and the binder is polyvinyl alcohol.

[0018] Further, in step (c), the added Al(NO3)3·9H2O is 0.01-0.03 wt% of the total weight of the raw material powder, the added dispersant is 0.3-0.8 wt% of the total weight of the raw material powder, and the added binder is 0.5-1.0 wt% of the total weight of the raw material powder.

[0019] Further, in step (3), a spray dryer is used for spray granulation; the mixing ratio of the granulated material, deionized water and release agent is 1:1:(0.005~0.01), and the release agent is zinc stearate lubricant; when the sieved powder is aged, the aging time is not less than 20 hours to ensure that the mass percentage moisture content of the powder reaches 1.0-1.5%.

[0020] Furthermore, in step (3), during the pressing and molding of the blank powder, the pressure is controlled to ensure that the density of the formed blank is 3.2-3.3 g / cm³. 3 .

[0021] Further, in step (4), the green body is placed in a sintering equipment for pre-calcination treatment. The pre-calcination temperature is 400-500℃ and the pre-calcination time is 2-6h. During the pre-calcination stage, the organic matter in the green body will be discharged, and the debinding treatment is completed.

[0022] Further, in step (4), after the calcined resistor sheet is ground and cleaned, a metal electrode is prepared on its surface to obtain the finished ZnO varistor.

[0023] The design principle and beneficial effects of this invention are as follows:

[0024] 1. Introduction and optimization of sodium salt:

[0025] This invention innovatively introduces NaBiO3 as a sodium source into the formulation of ZnO varistors, and optimizes the resistive performance by precisely controlling its addition amount (0.1-1 wt.%). NaBiO3 decomposes and releases sodium ions during sintering, which help improve the electrical performance and stability of the resistor.

[0026] 2. Pretreatment of powder materials:

[0027] This invention employs a unique powder pretreatment process, which includes mixing Bi₂O₃ and NaBiO₃, followed by ball milling, drying, and pulverizing, and then holding at a specific temperature (500-600℃) to partially melt both. This process promotes the uniform mixing of Bi₂O₃ and NaBiO₃ and improves the diffusion efficiency of sodium ions during subsequent sintering.

[0028] 3. In the resistor formulation designed in this invention, the proportion of each component, especially the amount of NaBiO3 added and its ratio with other components, is the key to optimizing the resistance performance.

[0029] 4. In the powder pretreatment process of this invention, there are ball milling, drying, pulverizing and heat preservation treatment at a specific temperature after mixing Bi2O3 and NaBiO3. These steps are crucial for improving the diffusion efficiency of sodium ions and the performance stability of the resistor sheet.

[0030] 5. Through optimization of the resistor sheet formulation and preparation process, this invention can produce ZnO varistors with excellent electrical properties, especially those that can balance good nonlinearity and excellent pulse current impact stability. Detailed Implementation

[0031] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0032] This invention innovatively introduces NaBiO3 as a sodium source into the ZnO varistor formulation. NaBiO3 is insoluble in water, and by precisely controlling its addition amount (0.1-1 wt.%) and pre-mixing and pre-calcining it with Bi2O3, the aim is to allow Na... + The ions are released more uniformly and slowly during the sintering process and penetrate into the ZnO grains, thereby expanding the appropriate range of sodium salt addition and optimizing the resistivity.

[0033] Example 1:

[0034] This embodiment involves adding sodium to the ZnO varistor formulation. The specific preparation process is as follows:

[0035] a. Preparation of raw materials for preparing resistor sheets:

[0036] Prepare the raw material powder according to the following raw material formula, based on the component mass percentage:

[0037] ZnO: 88.1wt.%, Bi2O3: 3.5wt.%, Sb2O3: 1.2wt.%, NiO: 1.2wt.%, Cr2O3: 0.5wt.%, Mn3O4: 2.3wt.%, Co3O4: 1.4wt.%, SiO2: 1.3wt.%, NaBiO3: 0.5wt.%.

[0038] b. Preparation of total slurry:

[0039] b1. After mixing Bi2O3, NaBiO3 and deionized water prepared in step a, add them to a ball mill and ball mill for 5 hours. Collect the resulting mixture, then dry the mixture at 150°C and pulverize it into powder to obtain mixed powder I.

[0040] b2. The mixed powder I obtained in step b1 is kept at 550°C for 1 hour to partially melt the Bi2O3 powder and NaBiO3 powder together. After cooling, it is pulverized to obtain mixed powder II.

[0041] b3. The ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, SiO2, mixed powder II prepared in step a, Al(NO3)3·9H2O, dispersant, binder, and deionized water prepared in step b2 are mixed and ground in a ball mill. The resulting slurry is passed through a 120-mesh sieve to obtain the total slurry. The dispersant is ammonium polyacrylate, and the binder is polyvinyl alcohol. The added Al(NO3)3·9H2O is 0.02 wt% of the total mass of the raw material powder prepared in step a; the added dispersant is 0.5 wt% of the total mass of the raw material powder prepared in step a; and the added binder is 0.7 wt% of the total mass of the raw material powder prepared in step a.

[0042] c. Preparation of the green body:

[0043] c1. The total slurry prepared in step b is spray-dried using a spray dryer to obtain granulated material;

[0044] c2. Mix the granulated material obtained in step c1, deionized water, and zinc stearate lubricant in a weight ratio of 1:1:0.009 until homogeneous, and then screen the mixture through a 30-mesh sieve. The screened powder is then aged for 24 hours to ensure that the moisture content reaches 1.2% by weight, ultimately yielding powder suitable for blank preparation.

[0045] c3. The preform powder obtained in step c2 is pressed into a shape, and the pressure is controlled so that the density of the resulting preform is 3.25 g / cm³. 3 The diameter of the blank is 40mm and the thickness is 3.5mm.

[0046] d. Sintering process:

[0047] d1. Place the green body prepared in step c into the sintering equipment and perform pre-calcination treatment at 480℃ for 2.5 hours. During this stage, the organic matter in the green body will be removed, completing the debinding process.

[0048] d2. After pre-calcination, the billet is placed in a high-temperature environment of 1160℃ and then calcined for 2.5 hours. This step ensures that the billet is completely sintered, forming a stable resistor sheet billet;

[0049] d3. The resistor blank obtained in step d2 is ground and cleaned, and then a metal Al electrode is sputtered onto the surface of the treated resistor blank to obtain the finished ZnO varistor.

[0050] Experimental test analysis:

[0051] The ZnO varistor prepared in this embodiment was used as a test sample for experimental verification.

[0052] The ZnO varistor prepared by the method in this embodiment has a diameter of 33.5 mm and a thickness of 3.0 mm. The varistor has a varistor potential gradient of 220 V / mm, a nonlinear coefficient of 53, and a residual voltage ratio of 1.78 under a 10 kA 8 / 20 μs lightning surge. After 20 20 kA 8 / 20 μs lightning surges, the forward varistor voltage differs by 3% from the value before the surge, and the reverse varistor voltage differs by -1%.

[0053] Comparative Example 1:

[0054] The difference between this example and Example 1 is that Comparative Example 1 uses the same molar amount of soluble salt NaNO3 to replace the insoluble salt NaBiO3 in Example 1; the other processes are the same as in Example 1.

[0055] Experimental test analysis:

[0056] The ZnO varistor prepared in Comparative Example 1 was used as the test sample for experimental verification.

[0057] The ZnO varistor prepared by the method in Comparative Example 1 has a diameter of 33.5 mm and a thickness of 3.0 mm. The varistor has a varistor potential gradient of 197 V / mm, a nonlinear coefficient of 18, and a residual voltage ratio of 1.88 after 20 20 kA 8 / 20 μs lightning surges. After 20 lightning surges, the forward varistor voltage differs by 4% from the value before the surge, and the reverse varistor voltage differs by 1%.

[0058] Comparative Example 2:

[0059] The difference between this example and Example 1 is that no Na salt or other Na-containing additives were added to the resistor in Comparative Example 2.

[0060] Experimental test analysis:

[0061] The ZnO varistor prepared in Comparative Example 2 was used as the test sample for experimental verification.

[0062] The ZnO varistor prepared by method 2 has a diameter of 33.5 mm and a thickness of 3.0 mm. The varistor has a varistor potential gradient of 224 V / mm, a nonlinear coefficient of 74, and a residual voltage ratio of 1.77 after 20 20 kA 8 / 20 μs lightning surges. After 20 lightning surges, the forward varistor voltage differs by 4% from the value before the surge, while the reverse varistor voltage differs by -11%.

Claims

1. A method for preparing a sodium-containing ZnO varistor, characterized in that: The raw material formula for preparing the sodium-containing ZnO varistor is as follows, by weight percentage: ZnO 82-92wt.%, Bi2O3 2-6wt.%, Sb2O3 1-4wt.%, NiO 0-3wt.%, Cr2O3 0-2wt.%, Mn3O40.5-3wt.%, Co3O4 0.5-3wt.%, SiO2 0.5-3wt.%, NaBiO3 0.1-1wt.%; The method for preparing the sodium-containing ZnO varistor includes the following steps: (1) Prepare the raw material powders according to the raw material formula for the preparation of resistor sheets; (2) Preparation of total slurry, including the following steps (a)-(d): (a) After mixing Bi2O3, NaBiO3 and deionized water in the raw material powder, the mixture is ball-milled, dried and pulverized to obtain mixed powder I; (b) The mixed powder I obtained in step (a) is kept at 500-600℃ for 0.5-2h to partially melt Bi2O3 powder and NaBiO3 powder together. After cooling, it is pulverized to obtain mixed powder II. (c) The raw material powders ZnO, Sb2O3, NiO, Cr2O3, Mn3O4, Co3O4, SiO2, mixed powder II prepared in step (b), Al(NO3)3·9H2O, dispersant, binder and deionized water are mixed and added to a ball mill for mixing and grinding. The resulting slurry is passed through a 120-mesh sieve to obtain the total slurry. (3) Preparation of the green body: The total slurry prepared in step (2) is sprayed to obtain granules. The granules, deionized water and release agent are mixed evenly and then passed through a 30-mesh sieve. The powder obtained after sieving is aged to obtain blanking powder. The blanking powder is pressed to obtain blanks. (4) Sintering of the green body: After the blank is pre-calcined, it is placed in a high-temperature environment of 1000-1300℃ and calcined for at least 2 hours to form a stable resistor blank; after metal electrodes are prepared on the surface of the resistor blank, the finished sodium ZnO varistor is obtained.

2. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (a), the ball milling is carried out in a ball mill. After ball milling for 3-6 hours, the resulting mixture is dried at 100-200℃ and then pulverized.

3. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (c), the dispersant is an anionic polyacrylate dispersant, and the binder is polyvinyl alcohol.

4. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (c), the added Al(NO3)3·9H2O is 0.01-0.03 wt% of the total weight of the raw material powder, the added dispersant is 0.3-0.8 wt% of the total weight of the raw material powder, and the added binder is 0.5-1.0 wt% of the total weight of the raw material powder.

5. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (3), a spray dryer is used for spray granulation. The mixing ratio of the granulated material, deionized water and release agent is 1:1:(0.005~0.01). The release agent is zinc stearate lubricant. When the sieved powder is aged, the aging time shall not be less than 20 hours to ensure that the mass percentage moisture content of the powder reaches 1.0-1.5%.

6. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (3), when the blank powder is pressed into shape, the density of the formed blank is 3.2-3.3 g / cm³ by controlling the pressure.

7. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (4), the green body is placed in a sintering equipment for pre-calcination treatment. The pre-calcination temperature is 400-500℃ and the pre-calcination time is 2-6h. During the pre-calcination stage, the organic matter in the green body will be discharged, and the debinding treatment is completed.

8. The method for preparing a sodium-containing ZnO varistor according to claim 1, characterized in that: In step (4), after the calcined resistor sheet is ground and cleaned, a metal electrode is prepared on its surface to obtain the finished ZnO varistor.