Potassium-containing insulating ceramic coating for piezoresistor and preparation method of potassium-containing insulating ceramic coating

Abstract

The invention discloses a preparation and application method of a potassium-containing insulating ceramic coating, and belongs to the technical field of electrical ceramics. The preparation method of the ceramic coating comprises the following steps: (1) preparing powder raw materials including kaolin powder, bismuth oxide powder, calcium oxide powder and zinc oxide powder; (2) mixing the powder raw material with a dispersing agent deionized water, and carrying out ball milling to obtain a powder dispersion liquid; (3) preparing a mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate; (4) further mixing the powder dispersion liquid with the mixed aqueous solution, and carrying out ball milling for 1-4 hours to obtain coating slurry; and applying the coating slurry to the side surface of the piezoresistor, and carrying out heating curing treatment to obtain the potassium-containing insulating ceramic coating. The inorganic ceramic coating prepared by the method can effectively inhibit large-current impact flashover, and can improve 2 ms square wave endurance capacity.

Description

Technical Field

[0001] The invention relates to the technical field of electrical ceramics, and in particular to a potassium-containing insulating ceramic coating for a varistor and a preparation method thereof. Background Art

[0002] A varistor is a resistor device with nonlinear volt-ampere characteristics. It is mainly used to clamp voltage when the circuit is subjected to overvoltage, absorbing excess current to protect sensitive devices. The varistor coated with side insulation coating can significantly improve its ability to withstand large current shocks. At present, the side coating materials of zinc oxide resistors include lead-containing side glazes, organic coatings mainly based on epoxy coatings and silicone coatings, and traditional inorganic coatings.

[0003] When the side of the zinc oxide resistor is glazed with lead, the lead is easily volatilized when the blank is sintered or processed at high temperature, which will cause harm to the human body and the environment.

[0004] When an organic coating is used on the side of a zinc oxide resistor, due to its poor bonding with the resistor blank, water is easily adsorbed or bubbles are generated on the surface, which makes its overvoltage tolerance worse. In addition, the thermal expansion coefficient of the coating is quite different from that of the resistor blank, and cracks may occur when impacted, resulting in side flashover.

[0005] When the side of the zinc oxide resistor is coated with a traditional inorganic coating, its insulation is poor, and a layer of lead-containing side glaze or organic coating needs to be applied to meet the insulation requirements of the product. Although the existing potassium-containing inorganic coating has strong insulation, the permeability of potassium is too strong, and the resistor body is prone to ring damage during the 2ms square wave test. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a potassium-containing insulating ceramic coating for a varistor and a preparation method thereof. The method for preparing an inorganic ceramic coating can effectively suppress large current impact flashover and improve the 2ms square wave tolerance.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a potassium-containing insulating ceramic coating for a varistor comprises the following steps:

[0009] (1) preparing powder raw materials: the powder raw materials are kaolin powder, bismuth oxide powder, calcium oxide powder, and zinc oxide powder;

[0010] (2) mixing the powder raw materials with deionized water as a dispersant, and ball milling for at least 1 hour to obtain a powder dispersion;

[0011] (3) preparing a mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate, wherein the mass ratio of potassium dihydrogen phosphate to aluminum dihydrogen phosphate in the solution is 1:(10-50);

[0012] (4) further mixing the powder dispersion described in step (1) with the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate described in step (3), and ball milling for 1-4 hours to obtain a coating slurry;

[0013] (5) The coating slurry in step (4) is uniformly applied to the side of the varistor, and subjected to a heating and curing treatment, so as to obtain the potassium-containing insulating ceramic coating on the side of the linear resistor.

[0014] In the above step (1), the weight percentage of each component in the powder raw material is as follows:

[0015] Kaolin powder 40-50%;

[0016] Bismuth oxide powder 20-35%;

[0017] Calcium oxide powder 5-15%;

[0018] Zinc oxide powder 10-25%.

[0019] In the above step (2), the ratio of the total weight of the powder raw material to the weight of the dispersant deionized water is 100:(0.5-1.2).

[0020] In the above step (3), the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate is prepared by dissolving potassium dihydrogen phosphate and aluminum dihydrogen phosphate in water, and the concentration of the solute (the total amount of potassium dihydrogen phosphate and aluminum dihydrogen phosphate) is 5-10wt.%.

[0021] When preparing the coating slurry in the above step (4), the ratio of the weight of the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate to the total weight of the powder raw materials is 1:(1-2).

[0022] The coating slurry prepared in the above step (4) is passed through a 30-120 mesh sieve to obtain a coating slurry with uniform particle size, and the sieved coating slurry is then evenly applied to the varistor element.

[0023] During the coating in step (5), the coating mass is not less than 0.06 g / cm 2 .

[0024] In the above step (6), the temperature for heating and curing the coating slurry is 400-600°C (preferably 450-550°C), and the heating and curing holding time is 1-3h.

[0025] During the heating and curing process of the above step (6), potassium dihydrogen phosphate in the coating slurry partially penetrates into the varistor body under the set short-time heating and curing conditions (400-600° C., 1-3 h), thereby controlling the amount of potassium ions penetrated.

[0026] The varistor with ceramic coating prepared by the above method in the present invention has a 4 / 10 large current impact capability and a 2ms current carrying capacity greatly improved compared with the varistor without coating.

[0027] The design principle and beneficial effects of the present invention are as follows:

[0028] 1. The inorganic ceramic coating prepared on the side of the varistor of the present invention contains potassium dihydrogen phosphate. Under the condition of short-term heating and curing at 400-600°C, potassium ions partially penetrate into the varistor body, and the amount of potassium ions penetrated is controlled. The voltage gradient at the edge of the varistor body can be increased, the current density near the edge can be reduced, the current distribution during large current impact can be improved, and the insulation pressure can be reduced; at the same time, the flow area of ​​the resistor is only slightly affected.

[0029] 2. After applying a potassium-containing inorganic ceramic coating on the side of the varistor, the present invention effectively suppresses large current impact flashover and improves the 4 / 10 large current impact capability and 2ms square wave tolerance capability of the varistor.

[0030] 3. The inorganic ceramic coating prepared on the side of the varistor of the present invention does not contain lead elements and has no environmental pollution problem.

[0031] 4. The insulating coating prepared by the present invention is easy to apply and has good insulation properties, and the insulating coating has little effect on the voltage gradient and nonlinear coefficient of the varistor.

[0032] 5. The process of the present invention is simple, easy to control and low in cost. DETAILED DESCRIPTION

[0033] In order to further understand the present invention, the present invention is described below in conjunction with examples, but the examples are only for further elaboration of the features and advantages of the present invention, rather than for limiting the claims of the present invention.

[0034] Example 1

[0035] This embodiment is a potassium-containing insulating ceramic coating for a varistor and a preparation method thereof, and the preparation process is as follows:

[0036] 1. Mix the powder raw materials (kaolin powder, bismuth oxide powder, calcium oxide powder and zinc oxide powder) with dispersant deionized water and ball mill for 2 hours to obtain a powder dispersion; the proportion of each component in the powder raw materials is: kaolin powder is 45wt.%, bismuth oxide powder is 32wt.%, calcium oxide powder is 10wt.%, and zinc oxide powder is 13wt.%.

[0037] The mixing ratio of powder raw material and dispersant deionized water is 100:0.9.

[0038] 2. Dissolve potassium dihydrogen phosphate and aluminum dihydrogen phosphate in deionized water to obtain a mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate; the mass ratio of potassium dihydrogen phosphate to aluminum dihydrogen phosphate in the mixed aqueous solution is 1:25, and the concentration of the solute (potassium dihydrogen phosphate and aluminum dihydrogen phosphate) is 8wt.%.

[0039] 3. The powder dispersion prepared in step 1 is further mixed with the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate prepared in step 2, and ball milled for 2 hours to prepare a coating slurry; during mixing, the ratio of the mass of the aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate to the mass of the powder raw material is 1:1.5.

[0040] 4. Pass the coating slurry prepared in step 3 through a 120-mesh sieve to obtain a coating slurry with uniform particle size, and then evenly apply the sieved coating slurry on the side of the varistor; the coating mass is 0.1 g / cm 2 .

[0041] 5. The linear resistor element coated with the coating slurry is subjected to a heat curing treatment at a curing temperature of 500° C. and a curing time of 1.5 h to obtain a linear resistor insulating coating after curing.

[0042] Test and analysis of the insulating coating on the side of the prepared varistor:

[0043] The finished ZnO varistor prepared by the method of this embodiment has a diameter of 48 mm and a thickness of 12 mm. The varistor coated with the potassium-containing insulating ceramic coating has a varistor voltage gradient of 223 V / mm and a nonlinear coefficient of 53. It can withstand 100 kA 4 / 10 high current impact twice and 450 A 2 ms square wave current impact 16 times.

[0044] Comparative Example 1:

[0045] The difference from Example 1 is that the varistor is not coated with a potassium-containing insulating ceramic coating.

[0046] After testing, its varistor voltage gradient is 225V / mm, the nonlinear coefficient is 59, it can withstand 70kA 4 / 10 large current impact twice, but cannot pass 80kA 4 / 10 large current impact test, it can withstand 400A 2ms square wave current impact 16 times, but cannot pass 450A 2ms square wave current impact test 16 times.

[0047] In summary, the preparation method of the potassium-containing insulating ceramic coating provided by the present invention is simple and easy to operate, and the raw materials are non-toxic, pollution-free and easy to obtain. The prepared insulating coating is easy to apply, has good insulation, and has little effect on the voltage gradient and nonlinear coefficient of the varistor. The 4 / 10 large current impact capability and 2ms flow capacity of the varistor are greatly improved. The insulating coating successfully achieves the protection of the varistor element.

Claims

1. A method for preparing a potassium-containing insulating ceramic coating for a varistor, characterized in that: The method comprises the following steps: (1) preparing powder raw materials: the powder raw materials are kaolin powder, bismuth oxide powder, calcium oxide powder, and zinc oxide powder; (2) mixing the powder raw materials with deionized water as a dispersant, and ball milling for at least 1 hour to obtain a powder dispersion; (3) preparing a mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate, wherein the mass ratio of potassium dihydrogen phosphate to aluminum dihydrogen phosphate in the solution is 1:(10-50); (4) further mixing the powder dispersion described in step (1) with the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate described in step (3), and ball milling for 1-4 hours to obtain a coating slurry; (5) The coating slurry in step (4) is uniformly applied to the side of the varistor, and subjected to a heating and curing treatment, so as to obtain the potassium-containing insulating ceramic coating on the side of the linear resistor.

2. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: In step (1), the weight percentage of each component in the powder raw material is as follows: Kaolin powder 40-50%; Bismuth oxide powder 20-35%; Calcium oxide powder 5-15%; Zinc oxide powder 10-25%.

3. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: In step (2), the ratio of the total weight of the powder raw material to the weight of the dispersant deionized water is 100:(0.5-1.2).

4. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: In step (3), the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate is prepared by dissolving potassium dihydrogen phosphate and aluminum dihydrogen phosphate in water, and the concentration of the solute (the total amount of potassium dihydrogen phosphate and aluminum dihydrogen phosphate) is 5-10wt.%.

5. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: When preparing the coating slurry in step (4), the ratio of the weight of the mixed aqueous solution of potassium dihydrogen phosphate and aluminum dihydrogen phosphate to the total weight of the powder raw materials is 1:(1-2).

6. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: The coating slurry prepared in step (4) is passed through a 30-120 mesh sieve to obtain a coating slurry with uniform particle size, and the sieved coating slurry is then evenly applied to the varistor element.

7. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: During the coating step (5), the coating mass is not less than 0.06 g / cm 2 .

8. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 1, characterized in that: In step (6), the coating slurry is heated and cured at a temperature of 400-600°C (preferably 450-550°C), and the heating and curing holding time is 1-3h.

9. The method for preparing a potassium-containing insulating ceramic coating for a varistor according to claim 8, characterized in that: During the heating and curing process of step (6), potassium dihydrogen phosphate in the coating slurry partially penetrates into the varistor body under the set short-time heating and curing conditions (400-600° C., 1-3 h), thereby controlling the amount of potassium ions penetrated.

10. A potassium-containing insulating ceramic coating for a varistor prepared by the method of claim 1, characterized in that: The 4 / 10 high current impact capability and 2ms current carrying capacity of the varistor prepared with the ceramic coating are greatly improved compared with the varistor without coating.