Ceramic resistor containing continuous conductive layer and preparation method and application thereof

Abstract

The invention belongs to the technical field of production of special materials for electrical equipment, and particularly relates to a ceramic resistor containing a continuous conducting layer and a preparation method and application thereof. According to the preparation method provided by the invention, the conductive material is deposited in the fibrofelt supporting layer by adopting vacuum impregnation-air pressure sintering, then the ceramic material is deposited in the supporting layer containing the conductive layer by adopting vacuum impregnation-air pressure sintering, and all the structural layers are continuously communicated to form the novel ceramic resistor. According to the invention, the fibrofelt is used as the supporting layer, and the carbon nanotubes can be uniformly and continuously dispersed through in-situ generation of the carbon nanotubes in the supporting layer, so that a conductive channel is formed, and the resistivity is effectively reduced; meanwhile, the fiber felt is impregnated with ceramic mixed slurry and is subjected to air pressure sintering, so that the apparent porosity can be effectively reduced, and the volume density is increased. Therefore, the ceramic resistor prepared by the invention has good electrical properties, excellent mechanical properties and good use stability, and is suitable for industrial application as a closing resistor material.

Description

Technical Field

[0001] The present invention belongs to the technical field of special material production for electrical equipment, and in particular, relates to a ceramic resistor containing a continuous conductive layer, a preparation method and an application thereof. Background Art

[0002] With the rapid development of power grid construction and the electric power industry, the requirements for resistor materials used in high-voltage switchgear are increasing. In ultra-high voltage systems, closing resistors, as key electrical protection equipment, are indispensable key components in ultra-high voltage and UHV transmission and transformation equipment. Their safety and stability are directly related to the overall operation quality of the power grid, and are crucial to ensuring the safe and stable operation of the power grid.

[0003] In recent years, ceramic resistors have shown broad application prospects in the electrical field due to their excellent electrical and mechanical properties. Compared with traditional metal conductive materials, ceramic resistors have good oxidation resistance, wear resistance, corrosion resistance, high temperature resistance and adjustable resistivity. In recent years, they have been widely used in aviation, aerospace and military fields. Among them, carbon ceramics have shown great application potential in extreme environments such as ultra-high pressure, high temperature and high strength due to their more unique properties.

[0004] However, ceramic resistors still have problems such as excessive porosity, poor compressive strength, poor temperature stability or high cost. In addition, the carbon material in carbon ceramic resistors is prone to uneven distribution and agglomeration in the ceramic matrix, as well as possible segregation problems, which will significantly affect the performance of the material in the test environment or actual working conditions. Moreover, this non-uniformity will lead to a high concentration of energy absorption and release in the resistor area, causing local overheating, which in turn leads to safety risks. This also limits the further application of carbon ceramic resistors in electrical fields such as closing resistor materials.

[0005] Therefore, how to optimize the dispersion state of carbon materials in ceramics and reduce agglomeration and segregation is the key to improving the overall performance and reliability of composite materials. How to develop a new type of carbon ceramic resistor and its preparation process to comprehensively improve the conductivity, thermoelectric tolerance, structural stability and processing performance of carbon ceramic resistor materials to meet the high standards of ultra-high voltage circuit breakers for closing resistor materials has become a technical problem that needs to be solved in this field. Summary of the invention

[0006] To overcome the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a ceramic resistor with a continuous conductive layer. By using a vacuum impregnation combined with air pressure sintering method, a novel resistor with a continuous carbon nanotube conductive layer can be prepared, solving the problem of difficult dispersion of carbon materials, optimizing the dispersion state of carbon materials in ceramics, reducing agglomeration and segregation phenomena, and enhancing the stability and reliability of ceramic resistors. Moreover, the ceramic filling layer further prepared by the above method can effectively increase the volume density of the material, reduce the porosity, facilitate the sintering of dense ceramic resistors, and comprehensively improve the mechanical properties and use safety of the material.

[0007] In addition, the purpose of the present invention is also to provide a ceramic resistor with a continuous conductive layer prepared by the above preparation method.

[0008] In addition, the purpose of the present invention is also to provide the application of the above ceramic resistor with a continuous conductive layer.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a ceramic resistor with a continuous conductive layer, comprising the following steps:

[0011] (1) Place the fiber felt support layer material in a phenolic resin solution containing a catalyst for vacuum impregnation, then perform drying and air pressure sintering. Then, take the vacuum impregnation, drying, and air pressure sintering in this step as a treatment cycle, and repeat the treatment cycle 2 - 5 times to obtain a fiber felt support layer with a continuous carbon nanotube conductive layer.

[0012] (2) Place the fiber felt support layer with a continuous carbon nanotube conductive layer obtained in step (1) in a ceramic mixed slurry for vacuum impregnation, then perform drying and air pressure sintering. Then, take the vacuum impregnation, drying, and air pressure sintering in this step as an operation cycle, and repeat the operation cycle 2 - 5 times to obtain a ceramic resistor with a continuous conductive layer.

[0013] Further preferably, in step (1), the fiber felt support layer material is one of polycrystalline mullite ceramic fiber felt, aluminosilicate fiber felt, and alumina fiber felt. More preferably, the fiber felt support layer material is polycrystalline mullite ceramic fiber felt. The single filament diameter of the fiber felt support layer material is 5 - 10 μm, and the density is 1 - 2 g / cm 3 . By using polycrystalline mullite fiber felt in the present invention, the mechanical strength of the ceramic resistor can be effectively improved, and the pulling out of the fibers will consume a large amount of energy, thereby improving the toughness and fracture resistance of the material.

[0014] Further preferably, in step (1), the catalyst is one of cobalt ferrite, iron chloride, and nickel nitrate, and more preferably cobalt ferrite. Further preferably, the phenolic resin solution is prepared by dissolving phenolic resin in an organic solvent; the organic solvent is ethanol or acetone. Further preferably, the mass ratio of the phenolic resin to the organic solvent is (2 - 4):1, and more preferably 3:1. Further preferably, the dosage of the catalyst is 0.5wt% - 2wt% of the mass of the phenolic resin, and more preferably 1wt%.

[0015] Further preferably, in step (1), the pressure of vacuum impregnation is -50 kPa to -98 kPa, and the time is 20 - 40 min; the temperature of air pressure sintering is 700 - 900 °C, and the time is 2 - 4 h.

[0016] Further preferably, in step (2), the ceramic mixed slurry is prepared by ball milling the ceramic composite in a solvent; the solvent is water or ethanol; the mass ratio of the ceramic composite to the solvent is 1:(0.8 - 1.2), and more preferably 1:1.

[0017] Further preferably, the ceramic composite includes the following components in parts by weight: 65 - 72 parts of bauxite, 15 - 20 parts of kaolin, 5 - 7 parts of magnesium oxide, 4 - 6 parts of clay, 1 - 3 parts of hexagonal boron nitride, 0.8 - 1.5 parts of polymethyl methacrylate, 0.8 - 1.5 parts of alkylphenol polyoxyethylene ether, and 0.4 - 1 part of acrylic acid; the particle size of the ceramic composite is 0.075 - 0.15 mm.

[0018] Further preferably, in step (2), the pressure of vacuum impregnation is -50 kPa to -98 kPa, and the time is 20 - 40 min; the temperature of air pressure sintering is 1200 - 1400 °C, and the time is 3 - 5 h.

[0019] A ceramic resistor with a continuous conductive layer prepared by the above preparation method mainly consists of a support layer, a conductive layer, and a filling layer; the support layer is a fiber felt support layer; the conductive layer is continuous carbon nanotubes in-situ generated by impregnation on the support layer; the filling layer is a composite ceramic layer further combined by impregnation on the support layer.

[0020] An application of the above ceramic resistor with a continuous conductive layer in the preparation of closing resistors.

[0021] Further preferably, the ceramic resistor with a continuous conductive layer is machined mechanically and then coated with electrodes to obtain the closing resistor.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (i) The preparation method of the ceramic resistor with a continuous conductive layer provided by the present invention uses vacuum impregnation to impregnate a phenolic resin solution containing a catalyst into a fiber felt support layer, and then through drying and air pressure sintering, a fiber felt with a continuous conductive layer is obtained; again through vacuum impregnation, a ceramic mixed slurry is impregnated into the fiber felt with a continuous conductive layer, and after drying and air pressure sintering, a ceramic resistor material is obtained. In the above preparation process of the present invention, using the fiber felt as the support layer, through the vacuum impregnation method, the organic precursor (phenolic resin) is evenly distributed in the fiber felt support layer. After air pressure sintering, carbon nanotubes with controllable thickness, evenly distributed and continuous are obtained, thus effectively improving the problem of easy agglomeration of nano-carbon and forming an effective conductive path. In addition, the present invention uses the fiber felt as the support layer, which is beneficial to improving the mechanical strength of the ceramic resistor. At the same time, the pulling out of the fibers will consume a large amount of energy, which is beneficial to improving the toughness and fracture resistance of the material. Further, the present invention uses vacuum impregnation and air pressure sintering to prepare the ceramic filling layer, which can further promote densification improvement, effectively reduce the apparent porosity, and increase the bulk density. Therefore, by using the above preparation process, the present invention can obtain a ceramic resistor with excellent mechanical properties, stable electrical properties and good durability.

[0024] (ii) The ceramic resistor with a continuous conductive layer prepared by the present invention comprises a support layer, a conductive layer and a filling layer. Among them, the support layer of the present invention is a fiber felt material, which can maintain a stable form in various environments, withstand the stress and vibration that may occur during the operation of the ceramic resistor component, ensure the overall structural stability and reliability of the ceramic resistor, and extend the service life of the ceramic resistor. In addition, the pulling out of the fibers will consume a large amount of energy, which is beneficial to improving the toughness and fracture resistance of the ceramic material. Further, the present invention uses the continuous carbon nanotubes in-situ generated by the impregnation of organic matter on the support layer as the conductive layer. During its preparation, the organic precursor of the conductive layer is evenly deposited in the fiber felt support layer through vacuum impregnation, and continuous and uniform carbon nanotubes can be obtained after sintering, thus achieving the effect of evenly dispersing carbon nanotubes and obtaining a continuous conductive layer. The continuous conductive layer not only solves the problem of difficult dispersion of carbon nanotubes, optimizes the dispersion state of carbon nanotubes in the ceramic, but also reduces the phenomena of agglomeration and segregation, and improves the stability and reliability of the ceramic resistor. Further, the present invention uses the sintered composite ceramic as the filling layer, and its densification process is completed through impregnation-sintering, thereby effectively increasing the bulk density of the material (> 2.25 g / cm 3 ), reducing the porosity (≤ 25%), being beneficial to sintering to obtain a dense ceramic resistor, improving its mechanical properties, and being suitable for industrial applications as the closing resistor of an ultra-high voltage circuit breaker. Detailed implementation mode

[0025] The present invention is illustrated by way of example, but the present invention is not limited to the following embodiments. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as falling within the protection scope of the present invention. Under the preparation concept and raw material ratio given in the present invention, combined with the impregnation process and technical principles, a ceramic resistor with continuous and uniform carbon nanotubes can be prepared, and the prepared ceramic resistor has excellent performance when used industrially. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the raw materials used, etc., are all commonly used in the art, publicly available, or items that can be obtained through commercial channels unless otherwise specified.

[0026] Among them, in the following embodiments, the phenolic resin used has a purity ≥ 99.0% and is from Henan Borun Foundry Materials Co., Ltd. In the following embodiments, the kaolin (200 mesh), bauxite (200 mesh), magnesium oxide (purity ≥ 99.0%, 200 mesh), hexagonal boron nitride (purity ≥ 99.0%, 200 mesh), cobalt ferrite (purity ≥ 99.5%, 200 mesh), polymethacrylate (purity ≥ 99.0%, 200 mesh), alkylphenol polyoxyethylene ether (purity ≥ 99.0%, 200 mesh), and acrylic acid (purity ≥ 99.0%, 200 mesh) used are all commercially available raw materials.

[0027] The present invention provides a method for preparing a ceramic resistor with a continuous conductive layer, comprising the following steps:

[0028] (1) Placing the fiber felt support layer material in a phenolic resin solution containing a catalyst for vacuum impregnation, then drying and pressure sintering; taking the vacuum impregnation, drying, and pressure sintering in this step as one treatment cycle, repeating the treatment cycle 2 - 5 times to obtain a fiber felt support layer with a continuous carbon nanotube conductive layer;

[0029] (2) Placing the fiber felt support layer with a continuous carbon nanotube conductive layer obtained in step (1) in a ceramic mixed slurry for vacuum impregnation, then drying and pressure sintering; taking the vacuum impregnation, drying, and pressure sintering in this step as one operation cycle, repeating the operation cycle 2 - 5 times to obtain a ceramic resistor with a continuous conductive layer.

[0030] In the prior art, the common preparation method of ceramic resistors is mainly to mix ceramic powder with carbon materials and then perform atmospheric sintering after mechanical forming. When preparing ceramic resistors in this way, the process is complex, and the conductive filler is difficult to be uniformly dispersed, resulting in unstable resistivity and low safety in use.

[0031] In the present invention, the conductive layer is first deposited in the fiber felt support layer by vacuum impregnation - gas pressure sintering method, and then the ceramic filling layer is deposited in the support layer containing the conductive layer by vacuum impregnation - gas pressure sintering method. Each structural layer is continuously penetrated, and finally a new type of ceramic resistor containing a continuous carbon nanotube conductive layer is formed. In the above process of the present invention, on the one hand, using the fiber felt as the support layer, by impregnating the organic precursor into the support layer and then performing catalytic carbonization, the thickness of the carbon layer can be increased, and the uniform and continuous dispersion of carbon nanotubes can be achieved, thereby forming a conductive channel and effectively reducing the resistivity. On the other hand, using phenolic resin, catalyst, bauxite, kaolin, magnesium oxide, hexagonal boron nitride, acrylic acid, alkylphenol polyoxyethylene ether and polymethacrylate as raw materials, by impregnating in the fiber felt and adopting gas pressure sintering, the densification improvement can be further promoted, the apparent porosity can be effectively reduced, and the bulk density can be increased. Therefore, the ceramic resistor prepared by the present invention has uniform and continuous distribution of carbon nanotubes, good electrical properties, excellent mechanical properties and good durability.

[0032] Further, in step (1), the fiber felt support layer material is one of polycrystalline mullite ceramic fiber felt, aluminosilicate fiber felt, and alumina fiber felt, and more preferably polycrystalline mullite ceramic fiber felt; the single - filament diameter of the fiber felt support layer material is 5 - 10 μm, and the density is 1 - 2 g / cm 3 . Specifically, in the following examples, the polycrystalline mullite ceramic fiber felt used has a single - filament diameter of 7 μm and a density of 1.28 g / cm 3 . The present invention uses polycrystalline mullite fiber felt, which can effectively improve the mechanical strength of the ceramic resistor, and the pulling out of the fibers will consume a large amount of energy, thereby improving the toughness and fracture resistance of the material. Further optionally, before use, the fiber felt support layer material can be pre - cut into the required fixed size.

[0033] In step (1), the phenolic resin solution containing the catalyst is deposited in the fiber felt by the impregnation method, and after drying and gas pressure sintering, a fiber felt support layer containing a continuous carbon nanotube conductive layer is obtained. Preferably, the catalyst is one of cobalt ferrite, ferric chloride, and nickel nitrate; more preferably cobalt ferrite. Preferably, the phenolic resin solution is prepared by dissolving phenolic resin in an organic solvent. Among them, the organic solvent can be conventionally selected as long as it can dissolve phenolic resin. For example, the organic solvent can be ethanol or acetone, and more preferably ethanol. Further, the mass ratio of phenolic resin to organic solvent is (2 - 4)∶1, and more preferably 3∶1. Further preferably, the dosage of the catalyst is 0.5 wt% - 2 wt% of the mass of phenolic resin, and more preferably 1 wt%.

[0034] In the present invention, vacuum impregnation has the conventional meaning understood in the art, that is, a process of pouring an impregnating liquid into an object to be impregnated or injecting the impregnating liquid into a special impregnating container containing the object to be impregnated under vacuum conditions. During the impregnation process, the liquid level of the impregnating liquid needs to cover the object to be impregnated to maintain the impregnation effect. Further, in step (1), the pressure of the vacuum impregnation is -50 kPa to -98 kPa, and the time is 20 to 40 min; the temperature of the gas pressure sintering is 700 to 900 °C, and the time is 2 to 4 h. Further preferably, the gas pressure sintering is carried out in a reducing atmosphere.

[0035] Further, in step (1), the present invention does not specifically limit the drying process, and those skilled in the art can perform conventional control according to the drying effect. Preferably, a multi-stage drying method can be adopted. For example, the drying process adopted can be: first drying at 40 to 60 °C for 3 to 5 h, then heating to 70 to 90 °C and drying for 8 to 12 h, and then heating to 100 to 120 °C and drying for 6 to 10 h.

[0036] Further, in step (2), the ceramic mixed slurry is prepared by ball milling a ceramic composite material in a solvent. The solvent is water or ethanol, and those skilled in the art can conventionally select it. Further, the mass ratio of the ceramic composite material to the solvent is 1:(0.8 to 1.2). Further preferably, the solvent used in the preparation of the ceramic mixed slurry is water, specifically deionized water; the mass ratio of the ceramic composite material to water is 1:1.

[0037] Further, the present invention does not specifically limit the ball milling process, and those skilled in the art can conventionally adjust the ball milling parameters as long as the mixing effect is achieved. For example, the preparation of the ceramic mixed slurry can be carried out by ball milling and mixing in an all-round planetary ball mill. Specifically, the ball milling process can be, for example: placing the ceramic composite material in a solvent, and in an all-round planetary ball mill, wet ball milling and mixing at 300 to 500 r / min for 3 to 6 h, thereby preparing the ceramic mixed slurry.

[0038] Further, the ceramic composite material includes the following components in parts by weight: 65 to 72 parts of bauxite, 15 to 20 parts of kaolin, 5 to 7 parts of magnesium oxide, 4 to 6 parts of clay, 1 to 3 parts of hexagonal boron nitride, 0.8 to 1.5 parts of polymethyl methacrylate, 0.8 to 1.5 parts of alkylphenol polyoxyethylene ether, and 0.4 to 1 part of acrylic acid. In the ceramic composite material of the present invention, magnesium oxide and hexagonal boron nitride (h-BN) are particularly introduced. On the one hand, it can effectively reduce the sintering temperature of the ceramic resistance, and on the other hand, it helps to reduce the open porosity and prevent oxygen from entering, effectively improving the mechanical properties and electrical properties of the material.

[0039] Further, in step (2), the present invention does not specifically limit the drying process, and those skilled in the art can perform conventional control according to the drying effect. Preferably, a multi-stage drying method can be adopted. For example, the drying process adopted can be: first drying at 70-90°C for 5-8 hours, then raising the temperature to 90-110°C and drying for 2-4 hours, then raising the temperature to 180-220°C and drying for 2-4 hours, and finally raising the temperature to 280-320°C and drying for 2-4 hours to perform complete drying and debinding treatment.

[0040] In step (2), the ceramic mixed slurry is deposited into the fiber felt support layer containing the continuous carbon nanotube conductive layer by the impregnation method, and a ceramic resistor is obtained through drying and air pressure sintering treatment. Further, in step (2), the pressure of vacuum impregnation is -50 kPa to -98 kPa, and the time is 20-40 minutes.

[0041] Preferably, in step (2), the temperature of air pressure sintering is 1200-1400°C, and the time is 3-5 hours. Further preferably, air pressure sintering is carried out in a reducing atmosphere.

[0042] Further, the ceramic resistor prepared by the above process of the present invention can be processed mechanically and sprayed with electrodes to obtain a closing resistor, which can be used as the closing resistor of an ultra-high voltage circuit breaker for industrial applications.

[0043] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0044] Example 1

[0045] This example provides a ceramic resistor with a continuous conductive layer, which mainly consists of a support layer, a conductive layer, and a filling layer; the support layer is a fiber felt support layer; the conductive layer is continuous carbon nanotubes in-situ generated by impregnation on the support layer; the filling layer is a composite ceramic layer further combined by impregnation on the support layer.

[0046] The preparation method of the above ceramic resistor with a continuous conductive layer includes the following steps:

[0047] (1) Weigh and mix phenolic resin, ethanol, and a catalyst (cobalt ferrite) in proportion; among them, the mass ratio of phenolic resin to ethanol is 3:1, and the mass of cobalt ferrite is 1 wt% of the phenolic resin; put the mixed material on a magnetic stirrer until the phenolic resin is completely dissolved and evenly mixed with the catalyst to obtain a phenolic resin solution containing the catalyst.

[0048] Place the polycrystalline mullite ceramic fiber felt in a vacuum barrel, turn on the vacuum pump to evacuate the gas in the barrel. When the pressure gauge reading stabilizes at -0.098 MPa, slowly open the side valve switch connected to the phenolic resin solution containing the catalyst, and completely inject the phenolic resin solution containing the catalyst into the vacuum barrel. Then close the valve switch; ensure that the fiber felt is fully and completely wetted, maintain vacuum impregnation for 30 min. After the impregnation process is completed, turn off the vacuum pump and take out the fiber felt impregnated with phenolic resin;

[0049] Put the fiber felt impregnated with phenolic resin in the above step into an oven for complete drying treatment. The drying procedure is: dry at 50 °C for 4 h, dry at 80 °C for 10 h, dry at 110 °C for 8 h to obtain the dried fiber felt containing the carbon precursor;

[0050] Place the dried fiber felt containing the carbon precursor under Ar atmosphere for sintering. The sintering method is gas pressure sintering, the sintering temperature is 800 °C, and the holding time is 3 h. After the holding is completed, cool down to room temperature with the furnace and take out the green body; then repeat the above vacuum impregnation-drying-gas pressure sintering steps 2 times (that is, the vacuum impregnation-drying-gas pressure sintering steps are carried out 3 times in total). After cooling, obtain the fiber felt with a continuous carbon nanotube conductive layer.

[0051] (2) Prepare the ceramic composite material by mixing the raw materials according to the following mass parts: Take 18 parts of kaolin, 69 parts of bauxite, 5 parts of clay, 5.5 parts of magnesium oxide, 2.5 parts of hexagonal boron nitride, and additionally mix 1 part of polymethacrylate, 1 part of alkylphenol polyoxyethylene ether and 0.5 part of acrylic acid to obtain the ceramic composite material (particle size 0.075 - 0.15 mm); place the ceramic composite material in a ball mill tank, add deionized water with the same mass as the ceramic composite material (mass ratio 1:1) as the solvent, and carry out wet ball milling and mixing at 360 r / min for 4 h to prepare a ceramic mixed slurry;

[0052] Place the fiber felt with a continuous carbon nanotube conductive layer prepared in step (1) in a vacuum barrel, turn on the vacuum pump to evacuate the gas in the barrel. When the pressure gauge reading stabilizes at -0.098 MPa, slowly open the side valve switch connected to the ceramic mixed slurry, and completely inject the ceramic mixed slurry into the vacuum barrel. Then close the valve switch; ensure that the fiber felt with a continuous carbon nanotube conductive layer is fully and completely wetted, maintain vacuum impregnation for 30 min. After the impregnation process is completed, turn off the vacuum pump and take out the fiber felt impregnated with the ceramic slurry;

[0053] Put the fiber felt impregnated with the ceramic slurry into an oven for complete drying and debinding treatment; the drying procedure adopted is: dry at 80 °C for 6 h, dry at 100 °C for 3 h, dry at 200 °C for 3 h, dry at 300 °C for 3 h to obtain the dried fiber felt containing carbon nanotubes and ceramic materials;

[0054] The fiber felt containing carbon nanotubes and ceramic materials after drying is sintered in an Ar gas atmosphere. The sintering method is gas pressure sintering, the sintering temperature is 1300 °C, and the heat preservation time is 4 h. After the heat preservation is completed, it is cooled in the furnace to room temperature, and the green body is taken out; the above vacuum impregnation-drying-gas pressure sintering steps are repeated 2 times (that is, the vacuum impregnation-drying-gas pressure sintering steps are carried out 3 times in total). After cooling, the ceramic resistor of Example 1 is obtained. Further, the ceramic resistor of Example 1 is machined and electrode-sprayed to obtain a closing resistor.

[0055] Example 2

[0056] This example provides a ceramic resistor with a continuous conductive layer. Its preparation method is basically the same as that of Example 1, but different from Example 1: in steps (1) and (2), the total number of vacuum impregnation-drying-sintering steps is adjusted from 3 times to 4 times. And in step (2), the sintering temperature is adjusted to 1320 °C. Thus, the ceramic resistor of Example 2 is prepared. Further, the ceramic resistor of Example 2 is machined and electrode-sprayed to obtain a closing resistor.

[0057] Example 3

[0058] This example provides a ceramic resistor with a continuous conductive layer. Its preparation method is basically the same as that of Example 1, but different from Example 1: in steps (1) and (2), the total number of vacuum impregnation-drying-sintering steps is adjusted from 3 times to 5 times. And in step (2), the sintering temperature is adjusted to 1320 °C. Thus, the ceramic resistor of Example 3 is prepared. Further, the ceramic resistor of Example 3 is machined and electrode-sprayed to obtain a closing resistor.

[0059] Example 4

[0060] This example provides a ceramic resistor with a continuous conductive layer. Its preparation method is basically the same as that of Example 1, but different from Example 1: in steps (1) and (2), the total number of vacuum impregnation-drying-sintering steps is adjusted from 3 times to 5 times. And in step (2), the sintering temperature is adjusted to 1350 °C. Thus, the ceramic resistor of Example 4 is prepared. Further, the ceramic resistor of Example 4 is machined and electrode-sprayed to obtain a closing resistor.

[0061] Comparative Example 1

[0062] This comparative example provides a ceramic resistor, whose preparation method is basically the same as that of Example 1, but different from Example 1 in that: in steps (1) and (2), the repeated operations of the vacuum impregnation-drying-sintering steps are no longer carried out (that is, the vacuum impregnation-drying-sintering steps are all ended after being carried out once). And, in step (2), the sintering temperature is adjusted to 1350 °C. Thus, the ceramic resistor of Comparative Example 1 is prepared. Further, after the ceramic resistor of Comparative Example 1 is machined and electrode-sprayed, a closing resistor is obtained.

[0063] Comparative Example 2

[0064] This comparative example provides a ceramic resistor, whose preparation method is basically the same as that of Example 4, but different from Example 4 in that: in steps (1) and (2), the vacuum impregnation is adjusted to impregnation in an atmospheric environment, and other process parameters remain unchanged, obtaining the ceramic resistor of Comparative Example 2. Further, after the ceramic resistor of Comparative Example 2 is machined and electrode-sprayed, a closing resistor is obtained.

[0065] Comparative Example 3

[0066] This comparative example provides a ceramic resistor, and its preparation method is as follows: Take 18 parts of kaolin, 69 parts of bauxite, 5 parts of clay, 5.5 parts of magnesium oxide, 2.5 parts of hexagonal boron nitride, and additionally add 3 parts of conductive carbon black for direct mixing, then add 1 part of polymethyl methacrylate, 1 part of alkylphenol polyoxyethylene ether and 0.5 part of acrylic acid for mixing, add the same mass of deionized water, ball-mill to prepare a mixed slurry, then dry, and then directly granulate and mold, and carry out gas-pressure sintering in an Ar gas atmosphere (the sintering temperature is 1320 °C, and the heat preservation time is 4 h), and after cooling, the ceramic resistor of Comparative Example 3 is prepared (the ball-milling and drying processes are the same as those of Example 1). Further, after the ceramic resistor of Comparative Example 3 is machined and electrode-sprayed, a closing resistor is obtained.

[0067] Comparative Example 4

[0068] This comparative example provides a ceramic resistor, whose preparation method is basically the same as that of Example 1, but different from Example 1 in that: in step (1), ultrasonic impregnation is used instead of vacuum impregnation, and in step (2), the gas-pressure sintering temperature is 1350 °C and the heat preservation time is 4 h, and the rest of the process steps and process parameters remain unchanged, preparing the ceramic resistor of Comparative Example 4. Further, after the ceramic resistor of Comparative Example 4 is machined and electrode-sprayed, a closing resistor is obtained.

[0069] Test Example

[0070] In this test example, the properties (bulk density, compressive strength, resistance value, temperature coefficient of resistance, voltage coefficient) of the closing resistors prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were tested. Among them, the bulk density was tested by the weighing method in accordance with GB / T 25995-2010, the water absorption rate was tested by the weighing method in accordance with GB / T 25995-2010, and the compressive strength was tested by a pressure testing machine in accordance with GB / T 8489-2006. The temperature coefficient of resistance and the voltage coefficient were tested by corresponding instruments. Among them, the temperature coefficient of resistance reflects the change of the resistance value with temperature, and studying the change trend of the resistance value with temperature is beneficial to judging the influence of the temperature on the resistance value when the ceramic resistor is working. The voltage coefficient is the relative change of the resistance value when the voltage changes by one volt within the specified voltage range, which reflects the stability of the ceramic resistor under working conditions. Therefore, the temperature coefficient of resistance and the voltage coefficient are indicators for evaluating the resistance stability. When they change little, they can ensure the safe operation of the ultra-high voltage power transmission and transformation system. The performance test results of the closing resistors in each example and comparative example are shown in Table 1.

[0071] Table 1

[0072]

[0073] From the test results in Table 1, it can be seen that for the closing resistors prepared in Examples 1 to 4 of the present invention, after sampling tests, their bulk density, compressive strength, and resistance value all meet the performance requirements of the industry standard for ceramic closing resistors (bulk density ≥ 2.25 g / cm 3 , compressive strength ≥ 120 MPa, resistance value is 5 ± 0.25 Ω). Moreover, the fluctuation ranges of the temperature coefficient of resistance and the voltage coefficient of the closing resistors in Examples 1 to 4 are both small, indicating good working stability of the ceramic resistors.

[0074] Furthermore, for the closing resistors prepared in Comparative Example 1 and Comparative Example 2, the resistance value far exceeds the industry standard, and the compressive strength is relatively low. Both the mechanical properties and the electrical properties are much lower than those of the closing resistors prepared in the examples of the present invention. At the same time, it is found through testing that the resistivity deviation is large and cannot meet the requirements of the industry standard. For the closing resistor prepared in Comparative Example 3, although its mechanical properties and electrical properties meet the requirements, at the same sintering temperature, its compressive strength is inferior to that of the ceramic resistors prepared in Examples 2 and 3 of the present invention. In particular, the fluctuation values of the temperature coefficient of resistance and the voltage coefficient of the resistor in Comparative Example 3 are both greater than those in the examples of the present invention, indicating poor working stability; it can be seen that compared with directly adding carbon materials using the traditional preparation process in Comparative Example 3, the in-situ generation of carbon nanotubes in the present invention can make the carbon materials more evenly dispersed and effectively ensure the safety and stability of the resistor. For the closing resistor prepared by ultrasonic impregnation in Comparative Example 4, the resistivity deviation is large, and due to the large aspect ratio / large specific surface area between carbon nanotubes, it is easy to exist in the form of entanglement and agglomeration, resulting in a large resistance value and unable to meet the use requirements.

[0075] It can be seen from this that in the preparation method of the ceramic resistor with a continuous conductive layer provided by the present invention, through the vacuum impregnation - air pressure sintering process, a carbon nanotube conductive layer is in-situ generated within the polycrystalline mullite fiber felt, which helps the carbon nanotubes to come into contact with each other within the ceramic matrix, facilitates the formation of a continuous carbon nanotube conductive layer network, and improves the conductivity of the ceramic resistor; meanwhile, the introduction of the fiber felt improves the mechanical strength of the ceramic resistor in a fiber toughening manner; further, by preparing the ceramic filler layer through air pressure sintering, the porosity is effectively reduced and the bulk density is increased. Therefore, the ceramic resistor prepared by using the preparation process of the present invention and the closing resistor obtained by further processing not only have excellent mechanical properties, but also have a lower and more stable resistivity and high mechanical strength, can effectively ensure the safe operation of the product, provide an effective safety guarantee for the stable operation of the power system, and are very suitable for industrial application as the closing resistor of an ultra-high voltage circuit breaker.

[0076] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a ceramic resistor containing a continuous conductive layer, characterized in that: The following steps are involved: (1) placing the fiber felt support layer material in a phenolic resin solution containing a catalyst for vacuum impregnation, and then drying and gas pressure sintering; the vacuum impregnation, drying and gas pressure sintering in this step is repeated 2 to 5 times to obtain a fiber felt support layer containing a continuous carbon nanotube conductive layer; (2) placing the fiber felt support layer containing the continuous carbon nanotube conductive layer obtained in step (1) in a ceramic mixed slurry for vacuum impregnation, followed by drying and gas pressure sintering; repeating the vacuum impregnation, drying and gas pressure sintering in this step as one operation cycle 2 to 5 times to obtain a ceramic resistor containing a continuous conductive layer.

2. The method for preparing a ceramic resistor containing a continuous conductive layer according to claim 1, characterized in that: In step (1), the fiber felt support layer material is one of polycrystalline mullite ceramic fiber felt, aluminum silicate fiber felt, and alumina fiber felt; the single fiber diameter of the fiber felt support layer material is 5 to 10 μm, and the density is 1 to 2 g / cm 3 .

3. The method for preparing a ceramic resistor containing a continuous conductive layer according to claim 1, characterized in that: In step (1), the catalyst is one of cobalt ferrite, ferric chloride and nickel nitrate; the phenolic resin solution is prepared by dissolving phenolic resin in an organic solvent; the organic solvent is ethanol or acetone; the amount of the catalyst is 0.5wt% to 2wt% of the mass of the phenolic resin.

4. The method for preparing a ceramic resistor containing a continuous conductive layer according to claim 1, characterized in that: In step (1), the pressure of vacuum impregnation is -50 kPa to -98 kPa, and the time is 20 to 40 minutes; the temperature of gas pressure sintering is 700 to 900°C, and the time is 2 to 4 hours.

5. The method for preparing a ceramic resistor containing a continuous conductive layer according to any one of claims 1 to 4, characterized in that: In step (2), the ceramic mixed slurry is prepared by ball milling a ceramic composite material in a solvent; the solvent is water or ethanol; and the mass ratio of the ceramic composite material to the solvent is 1:(0.8-1.2).

6. The method for preparing a ceramic resistor containing a continuous conductive layer according to claim 5, characterized in that: The ceramic composite material comprises the following components in parts by weight: 65 to 72 parts of bauxite, 15 to 20 parts of kaolin, 5 to 7 parts of magnesium oxide, 4 to 6 parts of clay, 1 to 3 parts of hexagonal boron nitride, 0.8 to 1.5 parts of polymethacrylate, 0.8 to 1.5 parts of alkylphenol polyoxyethylene ether, and 0.4 to 1 part of acrylic acid; the particle size of the ceramic composite material is 0.075 to 0.15 mm.

7. The method for preparing a ceramic resistor containing a continuous conductive layer according to any one of claims 1 to 4, characterized in that: In step (2), the pressure of vacuum impregnation is -50 kPa to -98 kPa, and the time is 20 to 40 minutes; the temperature of gas pressure sintering is 1200 to 1400°C, and the time is 3 to 5 hours.

8. A ceramic resistor containing a continuous conductive layer prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The ceramic resistor containing a continuous conductive layer is mainly composed of a support layer, a conductive layer and a filling layer; the support layer is a fiber felt support layer; the conductive layer is continuous carbon nanotubes generated in situ by impregnation on the support layer; the filling layer is a composite ceramic layer further combined by impregnation on the support layer.

9. Use of a ceramic resistor containing a continuous conductive layer as claimed in claim 8, characterized in that: Application in the preparation of closing resistors.

10. Use of the ceramic resistor containing a continuous conductive layer according to claim 9, characterized in that: The ceramic resistor containing the continuous conductive layer is mechanically processed, and then the electrodes are painted to obtain the closing resistor.

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