An ultrahigh potential gradient zinc oxide varistor ceramic resistor material and a preparation method thereof

Abstract

This invention discloses an ultra-high potential gradient zinc oxide varistor ceramic material and its preparation method. The composition of the varistor material by weight is: ZnO 95-97%, and the total amount of other additives is 3-5%. The content ratio of other additives is (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3 = (0.2-0.4):(0.1-1.0):(0.0005-0.0015):1:(0.2-0.8):(0.5-1.0):(0.3-0.7):(0.2-0.6):(0.01-0.15):(0.01-0.05). The preparation method includes the preparation of ultrafine composite powder, controlling the median particle size of the powder to be 0.1-0.3 μm; the sintering adopts a two-step method, first sintering at 700-850℃ for 0.25-2.0 hours, and then sintering at 850-1000℃ for 2.0-6.0 hours, finally obtaining a rheostat material with a potential gradient as high as 10-55 kV / cm; it can meet the application requirements of ultra-high potential gradient and lightweight miniaturization, and is expected to broaden the application of commercial high-performance zinc oxide varistor ceramic rheostat materials in the equipment field.

Description

Technical Field

[0001] This invention belongs to the field of electrical materials preparation, specifically relating to an ultra-high potential gradient zinc oxide varistor ceramic material and its preparation method. Background Technology

[0002] Zinc oxide varistors are solid-state functional ceramic devices with grain boundary effects, sintered at specific temperatures using zinc oxide varistor ceramic material as their core. Their nonlinear characteristics originate from the avalanche effect of the Schottky barrier. During operation, zinc oxide varistors exhibit nanosecond-fast response and time repeatability, unmatched by any other material, making them widely used for overcurrent or overvoltage protection in power systems and electronic equipment. In recent years, they have also become key components in electromagnetic interference suppression equipment and have potential applications in specialized equipment. Simultaneously, the global development of transmission lines and substations is moving towards higher voltage and larger capacity, demanding high voltage gradients and large energy absorption capabilities from varistor ceramic materials. Fundamentally, the materials and components of these devices require ultra-high potential gradients, lightweight construction, and small size, with potential gradients reaching 20-40 kV / cm.

[0003] Although my country has been researching and producing zinc oxide ceramic rheostats for nearly 40 years, the highest potential gradient achieved in commercial applications is only 2-3 kV / cm. Furthermore, the high dielectric constant and capacitance of Chinese products result in longer charging and discharging times. Consequently, current zinc oxide ceramic devices are bulky and heavy, further limiting their potential application in specialized equipment. Therefore, the development of ultra-high potential gradient zinc oxide varistors is an urgent, pioneering task with significant strategic importance.

[0004] Previous studies have shown that simply lowering the sintering temperature and reducing the ZnO grain size has very limited effect on improving the potential gradient. As a promising semiconductor ceramic device, the improvement of the formulation and preparation method of zinc oxide varistors is crucial to meeting the demands of power systems and electronic devices for high potential gradients and miniaturization. Ultra-high potential gradient zinc oxide varistors are expected to broaden the application areas of commercial zinc oxide varistors and play a potential role in specialized equipment. Summary of the Invention

[0005] One of the objectives of this invention is to provide an ultra-high potential gradient zinc oxide varistor ceramic material with a potential gradient as high as 10-55kV / cm, which can meet the requirements of ultra-high potential gradient, lightweight and small size.

[0006] The second objective of this invention is to provide a method for preparing the ultra-high potential gradient zinc oxide varistor ceramic rheostat material. This method can be used to produce ultra-high potential gradient zinc oxide varistor ceramic rheostat material, overcoming the problems of complex processes, high sintering temperatures, and limited potential gradient improvement in existing technologies.

[0007] The third objective of this invention is to provide a method for preparing the ultra-high potential gradient zinc oxide varistor ceramic material that can be mass-produced, which not only improves the performance of the zinc oxide varistor ceramic material, but also promotes green manufacturing and reduces environmental pollution.

[0008] To achieve the above technical objectives, the technical solution adopted by this invention is as follows: The ultra-high potential gradient zinc oxide varistor ceramic rheostat material has the following composition by weight: ZnO 95-97%, and other additives totaling 3-5%. The content ratio of other additives is (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3 = (0.2-0.4):(0.1-1.0):(0.0005-0.0015):1:(0.2-0.8):(0.5-1.0):(0.3-0.7):(0.2-0.6):(0.01-0.15):(0.01-0.05).

[0009] Chemical substances containing Zn as the main ingredient and additive elements Bi, Sb, Cr, Mn, Co, Ni, Sn, Si, Y, and Al are selected as raw materials for formulation. These chemical substances are at least one of the following: oxides, nitrates, acetates, citrates, and alkoxides containing the main ingredient and additive elements. Among these, nitrates, acetates, citrates, and alkoxides undergo a series of ceramic preparation processes, ultimately decomposing into corresponding oxides during the plasticizing and sintering stages. These oxides then undergo further physical and chemical processes to obtain zinc oxide varistor ceramic materials, which function in the same way as the oxide raw materials.

[0010] For ZnO-Bi2O3-based zinc oxide varistor ceramic materials, Bi 3+ Most importantly, during the sintering process, Bi 3+ Bi cannot dissolve in ZnO grains; it can only segregate at grain boundaries to form Bi-rich thin layers, generating surface states. The nonlinearity of varistor ceramics arises from the segregation of elements such as Bi, Cr, Mn, Co, and Ni at ZnO grain boundaries, forming deep-level acceptors that capture free carriers from ZnO grains, creating depletion layers and forming grain boundary barriers. 3+ During the firing process, the antimony-zinc spinel phase Zn7Sb2O is mainly formed. 12SiO2, distributed along grain boundaries, acts as a pinning agent, inhibiting ZnO grain growth. SnO2 primarily functions as a sintering aid, lowering the sintering temperature of ceramic materials to reduce ZnO grain size. During sintering, some SiO2 reacts with ZnO to form Zn2SiO4, which, like spinel, inhibits grain growth; another portion of SiO2 reacts with Bi2O3 and ZnO to form a liquid phase, increasing the wettability of the liquid phase on ZnO grains and affecting the segregation concentration of Bi, Cr, Mn, Co, Ni, etc., on the ZnO grain surface, thus improving nonlinearity. The addition of Y2O3 can effectively prevent grain growth, improve microstructure uniformity, and significantly increase the potential gradient. Al 3+ Solid solution in ZnO grains increases donor concentration, decreases grain resistance, and improves nonlinearity. Simultaneously, it reduces the Zn concentration. 2+ The reduced mass transfer rate slows down ZnO grain growth, makes the reaction smoother, and reduces stress accumulation at high temperatures, which is beneficial for improving performance.

[0011] Meanwhile, in the preparation method, refining the raw materials can improve the sintering activity of the powder, which is beneficial for lowering the sintering temperature. It also helps to improve the uniform distribution of additive elements around the ZnO grains, thus improving the uniformity of the ceramic microstructure. The above formulation and preparation method together achieve the purpose of this invention in preparing zinc oxide varistor ceramic materials with ultra-high potential gradients.

[0012] Specifically, this invention also discloses a method for preparing the ultra-high potential gradient zinc oxide varistor ceramic material, comprising the following steps: (a) Preparation of ultrafine composite powder: A chemical substance containing Zn as the main ingredient and additive elements Bi, Sb, Cr, Mn, Co, Ni, Sn, Si, Y, and Al is selected as raw material for formulation. The main ingredient accounts for 95-97% by weight, with the remainder being additives. The molar ratio of the additive elements is Bi : Sb : Cr : Mn : Co : Ni : Sn : Si : Y : Al = (0.4~0.8):(0.2~2.0):(0.0010~0.0030):1:(0.4~1.6):(0.5~1.0):(0.3~0.7):(0.2~0.6):(0.02~0.30):(0.02~0.10); After the materials are thoroughly mixed, the above raw materials are prepared into ultrafine composite powder by at least one of chemical coprecipitation, sol-gel method, high-energy ball milling, etc., and the median particle size of the obtained powder is 0.1-0.3μm; (b) Add an appropriate amount of binder to the above ultrafine composite powder for granulation, press into tablets, and obtain green body. After isostatic pressing, the green body is de-plasticized at 400-600℃. (c) The above-mentioned green blank after plastic removal is sintered: firstly, it is sintered at 700-850℃ for 0.25-2.0 hours, and then sintered at 850-1000℃ for 2.0-6.0 hours to obtain ultra-high potential gradient zinc oxide varistor ceramic rheostat material.

[0013] Preferably, the chemical substances of the main ingredient and additives are at least one of oxides, nitrates, acetates, citrates, and alkoxides containing the main ingredient and additive elements.

[0014] Preferably, the binder is a 5 wt.% PVA aqueous solution, and the amount added is 8-15% of the powder weight.

[0015] Preferably, the descaling process after isostatic pressing involves heating the temperature to 430–540°C at a rate of 0.5–2.0°C / min and holding it at that temperature for 2.0–6.0 hours.

[0016] Preferably, the sintering in step (c) is based on a two-step heating method, first heating to 740-830°C at a heating rate of 3.0-15.0°C / min and holding at that temperature for 0.5-1.0 hours, and then heating to a sintering temperature of 860-970°C at a heating rate of 1.0-3.0°C / min and sintering for 3.0-6.0 hours. Attached Figure Description

[0017] Figure 1 The image shows the morphology of the ultrafine composite powder obtained in Example 1. Figure 2 for Figure 1 Energy dispersive spectroscopy (EDS) analysis at any point in the powder; Figure 3 The microstructure of the ceramic material obtained in Example 11; Figure 4 The microstructure of the ceramic material obtained in Example 22; Figure 5 The current density-electric field intensity curves of the ceramic materials obtained in Examples 9, 28, 29 and 38 are shown. Detailed Implementation

[0018] The technical solution of the present invention is further illustrated below through embodiments, but the present invention is not limited thereto. Unless otherwise specified, the preparation methods and usage conditions used in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials used in the following embodiments are commercially available. Example 1

[0019] The rheostat material composition by weight is: ZnO: 97%, and the total amount of other additives is 3%. The content ratio of other additives is as follows (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=0.3:0.5:0.0015:1:0.5:0.8:0.3:0.2:0.01:0.01.

[0020] The main materials and additive oxides were weighed according to stoichiometric ratio, and then ball-milled in a high-energy ball mill for 6 hours to achieve a median particle size of 0.26 μm. A 12% (5 wt.%) PVA aqueous solution was added to the obtained ultrafine composite powder, followed by granulation, tableting, isostatic pressing, and then heating to 500℃ at a rate of 1.0℃ / min and holding for 6.0 hours for desizing. The sample was then heated to 800℃ at a rate of 3.0℃ / min and held for 0.5 hours, followed by sintering at 900℃ at a rate of 1℃ / min for 4.0 hours.

[0021] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 35kV / cm, nonlinear coefficient α The value is 25, leakage current I L It is 2μA.

[0022] The morphology of the ultrafine composite powder prepared in Example 1 is as follows: Figure 1 As shown, the powder particles are uniform in size, ranging from 50 to 500 nm, and are spherically shaped. Energy dispersive spectroscopy (EDS) analysis was performed on any part of the powder sample, yielding... Figure 2 It can be seen that Zn, Bi, Sb, Mn, Co, Ni and other elements were detected, but Si, Sn, Y, Al and other elements were not detected, possibly because the content of these elements was too low. Example 2

[0023] The rheostat material composition by weight is: ZnO: 96%, and the total amount of other additives is 4%. The content ratio of other additives is as follows (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:SiO2:NiO:SnO2:Y2O3:Al2O3=0.2:0.2:0.001:1:0.2:0.6:0.4:0.5:0.01:0.01.

[0024] The raw materials selected were the nitrates of the main ingredients and additives mentioned above, weighed according to stoichiometric ratios, and then a composite powder with a median particle size of 0.1 μm was prepared by chemical co-precipitation. A 10% (5 wt.%) PVA aqueous solution was added to the obtained powder, followed by granulation, tableting, isostatic pressing, and then heating to 450℃ at a rate of 2.0℃ / min and holding for 6.0 hours for desizing. The sample was then heated to 800℃ at a rate of 3.0℃ / min and held for 0.5 hours, followed by sintering at 900℃ at a rate of 1℃ / min for 3.0 hours.

[0025] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 40kV / cm, nonlinear coefficient α The value is 21, leakage current I L It is 2.5 μA. Example 3

[0026] The rheostat material composition by weight is: ZnO: 95%, and other oxides: 5%. Other oxides and their content ratios are as follows (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=0.3:0.6:0.001:1:0.2:0.6:0.5:0.5:0.05:0.02.

[0027] The main materials and additive oxides were weighed according to stoichiometric ratio, and then ball-milled in a high-energy ball mill for 6 hours to achieve a median particle size of 0.24 μm. A 15% PVA aqueous solution (concentration 5 wt.%) was added to the obtained ultrafine composite powder, followed by granulation, tableting, isostatic pressing, and then heating to 480℃ at a heating rate of 1.0℃ / min and holding for 5.0 hours for desizing. The sample was then heated to 810℃ at a heating rate of 8.0℃ / min and held for 0.5 hours, followed by heating to a sintering temperature of 980℃ at a heating rate of 3.0℃ / min and holding for 4.0 hours for sintering.

[0028] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 32kV / cm, nonlinear coefficient α The value is 19, leakage current I L It is 5μA. Example 4

[0029] The rheostat material composition by weight is: ZnO: 97%, and other oxides: 3%. Other oxides and their content ratios are as follows (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=0.4:0.8:0.0012:1:0.4:0.9:0.6:0.6:0.05:0.03.

[0030] The raw materials selected were the nitrates of the main ingredients and additives mentioned above, which were weighed and mixed according to stoichiometric ratios. A composite powder with a median particle size of 0.3 μm was then prepared using the sol-gel method. An 8% (5 wt.%) PVA aqueous solution was added to the obtained powder, followed by granulation, tableting, isostatic pressing, and then heating to 440℃ at a rate of 1.0℃ / min and holding for 2.0 hours for desizing. The sample was then heated to 800℃ at a rate of 15.0℃ / min and held for 2.0 hours, followed by sintering at 920℃ at a rate of 3.0℃ / min for 2.0 hours.

[0031] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 24kV / cm, nonlinear coefficient α The value is 20, leakage current I L It is 6μA. Example 5

[0032] Zinc oxide varistor ceramic materials were prepared using the same method as in Example 1, except that the content ratios of other additives were as follows (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=0.3:1.0:0.0015:1:0.8:1.0:0.7:0.5:0.01:0.05.

[0033] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 20kV / cm, nonlinear coefficient α The value is 21, leakage current I L It is 7μA. Example 6

[0034] Zinc oxide varistor ceramic material was prepared using the same method as in Example 2, except that the raw materials selected were acetates of the main materials and additive elements mentioned above.

[0035] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA 38kV / cm, nonlinear coefficient α The value is 19, leakage current I L It is 5μA. Example 7

[0036] Zinc oxide varistor ceramic material was prepared using the same method as in Example 2, except that the raw material selected was citrate of the main material and additive elements mentioned above.

[0037] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA The value is 39 kV / cm, and the nonlinear coefficient is... α The value is 22, leakage current I L It is 8μA. Example 8

[0038] Zinc oxide varistor ceramic material was prepared using the same method as in Example 2, except that the main raw material selected was ZnO and the additives were bismuth nitrate, antimony nitrate, chromium nitrate, manganese nitrate, cobalt nitrate, nickel acetate, tin ethoxide, ethyl silicate, yttrium nitrate, and aluminum ethoxide.

[0039] The potential gradient of the obtained zinc oxide varistor material was measured. E 1mA The value is 39 kV / cm, and the nonlinear coefficient is... α The value is 22, leakage current I L It is 8μA. Examples 9-38

[0040] Zinc oxide varistor ceramic material was prepared using the same method as in Example 1. The composition of the rheostat material and the parameter adjustments during the preparation process are shown in Tables 1 and 2 below.

[0041] The rheostat material composition by weight is: ZnO: 95%, and the total amount of other additives (expressed as oxides) is 5%. The molar ratios of Bi, Sb, Cr, Mn, Co, Ni, Sn, and Si oxides are kept constant, while the contents of Y₂O₃ and Al₂O₃ are varied. Details are shown in Table 1 below. Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=0.2:0.1:0.0005:1:0.2:0.5:0.3:0.2: (0.01~0.15): (0.01~0.02).

[0042] Table 1. Molar ratio of other additive oxides in Examples 9-38

[0043] In Table 2, preparation method A is high-energy ball milling, method B is chemical coprecipitation, and method C is sol-gel method.

[0044] Table 2. Adjustments to preparation parameters in Examples 9-38

[0045] The potential gradient of the zinc oxide varistor material prepared in Examples 9-38 was tested. E 1mA Nonlinear coefficients α and leakage current I L The results are shown in Table 3 below: Table 3 Performance test results of the products in Examples 9-38

[0046] Figure 5 The current density-electric field intensity curves of the ceramic materials obtained in Examples 9, 28, 29, and 38 correspond to the potential gradient of the zinc oxide varistor material. E 1mA The values ​​are 10.0 kV / cm, 27 kV / cm, 25 kV / cm, and 55 kV / cm, respectively. This demonstrates that the formulation and preparation method of this invention can yield zinc oxide varistor materials with potential gradients as high as 10–55 kV / cm, meeting the requirements for ultra-high potential gradients and lightweight miniaturization, and is expected to broaden the application of commercial high-performance zinc oxide varistor materials in the equipment field.

[0047] The above description merely illustrates preferred embodiments of the present invention, and while the description is specific and detailed, it should not be construed as limiting the scope of protection of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A high potential gradient zinc oxide varistor ceramic material, characterized in that: The rheostat material composition by weight is: ZnO 95-97%, and other additives totaling 3-5%; wherein, the content ratio of other additives is (with MnO2 content as 1, molar ratio): Bi2O3:Sb2O3:Cr2O3:MnO2:Co2O3:NiO:SnO2:SiO2:Y2O3:Al2O3=(0.2~0.4):(0.1~1.0):(0.0 005~0.0015):1:(0.2~0.8):(0.5~1.0):(0.3~0.7):(0.2~0.6):(0.01~0.15):(0.01~0.05).

2. The ultra-high potential gradient zinc oxide varistor material according to claim 1, characterized in that: The potential gradient of the zinc oxide varistor material E 1mA The voltage is 10–55 kV / cm, the nonlinear coefficient α > 18, and the leakage current I L <10μA.

3. A method for preparing an ultra-high potential gradient zinc oxide varistor ceramic material, characterized in that, Includes the following steps: (a) Preparation of ultrafine composite powder: A chemical substance containing Zn as the main ingredient and additive elements Bi, Sb, Cr, Mn, Co, Ni, Sn, Si, Y, and Al is selected as raw material for formulation. The main ingredient accounts for 95-97% by weight, with the remainder being additives. The molar ratio of the additive elements is Bi : Sb : Cr : Mn : Co : Ni : Sn : Si : Y : Al = (0.4~0.8):(0.2~2.0):(0.0010~0.0030):1:(0.4~1.6):(0.5~1.0):(0.3~0.7):(0.2~0.6):(0.02~0.30):(0.02~0.10); After the materials are thoroughly mixed, the above raw materials are prepared into ultrafine composite powder by at least one of chemical coprecipitation, sol-gel method, and high-energy ball milling. The median particle size of the powder is 0.1-0.3μm. (b) Add a binder to the above ultrafine composite powder, granulate, compress into tablets to obtain a green body, and then perform plastic removal at 400-600°C after isostatic pressing treatment. (c) The above-mentioned green blank after plastic removal is sintered: firstly, it is sintered at 700-850℃ for 0.25-2.0 hours, and then sintered at 850-1000℃ for 2.0-6.0 hours to obtain the zinc oxide varistor ceramic rheostat material.

4. The method for preparing an ultra-high potential gradient zinc oxide varistor material according to claim 3, characterized in that, The chemical substances of the main ingredients and additives are at least one of the following: oxides, nitrates, acetates, citrates, and alkoxides containing the main ingredients and additive elements.

5. The method for preparing an ultra-high potential gradient zinc oxide varistor material according to claim 3, characterized in that, The binder is a 5 wt.% PVA aqueous solution, and the amount added is 8-15% of the powder weight.

6. The method for preparing an ultra-high potential gradient zinc oxide varistor material according to claim 3, characterized in that, The descaling process after isostatic pressing involves heating the temperature to 430–540°C at a rate of 0.5–2.0°C / min and holding it at that temperature for 2.0–6.0 hours.

7. The method for preparing an ultra-high potential gradient zinc oxide varistor material according to claim 3, characterized in that, The sintering described in step (c) is based on a two-step heating method. First, the temperature is raised to 740-830℃ at a heating rate of 3.0-15.0℃ / min and held for a short time for 0.5-1.0 hours. Then, the temperature is raised to the sintering temperature of 860-970℃ at a heating rate of 1.0-3.0℃ / min and sintered for 3.0-6.0 hours.

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