Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the large-size special-shaped silicon nitride-based ceramic support, which has the advantages of high surface flashover voltage, low dielectric loss and dielectric constant and strong electric breakdown resistance, can be used as an internal insulation support of power equipment, and adopts a normal-pressure atmosphere-free sintering mode, so that the preparation method is safe, environment-friendly, energy-saving and consumption-reducing.
The large-size special-shaped silicon nitride-based ceramic support column comprises, by mass, 70-85% of industrial alumina powder, 2-3.5% of a sintering aid, 2-5% of water-washed clay, 5-20% of micron silicon nitride powder, 3-5% of a nano filler, and 0.1-0.6% of an additional dopant, 0.2-0.3% of a water reducer and 31-35% of water based on the mass of the base raw materials, wherein the industrial alumina powder, the nano filler, the sintering aid, the water-washed clay, the additional dopant, the water reducer and the water are used as component A raw materials, the micron silicon nitride powder and the nano filler are used as component B raw materials, and the water-washed clay is dried after water washing treatment.
The industrial alumina powder is spherical alumina powder, the content of alpha-Al2O3 is not less than 98%, and the median particle diameter is 3.3-4.8 mu m.
The invention adopts the industrial alumina powder as the main ceramic raw material, on one hand, the invention is based on the characteristics of few impurities, high purity, high corundum phase content, low price, and capability of reducing the product cost of the industrial alumina powder, and on the other hand, the invention has obvious advantages when being applied to electronic components because the alumina ceramic has the characteristics of excellent mechanical property, proper dielectric constant, high insulativity, chemical stability and the like.
The sintering aid is at least one of talcum powder, wollastonite, barium carbonate and yttrium oxide. Besides the function of promoting sintering, the sintering aid can change the size and shape of ceramic lattices and improve the glossiness and electrical property of the product.
The clay is at least one of left cloud soil, inner Mongolian soil and Jilin ball soil. During water washing treatment, adding clay into water, soaking for more than 24 hours, stirring for more than 5 minutes, standing, pouring out upper-layer floating foam and other impurities, adding water again, repeating the steps until the water is clear and no obvious floating objects exist, drying the water-washed clay at the temperature of 80-100 ℃, and crushing for later use. The water washing treatment can remove impurities such as organic components in the clay, and is beneficial to improving various performances of the ceramic material.
The purity of the micron silicon nitride powder is more than 99%, the alpha conversion rate is not less than 95%, and the median particle diameter is 3.0+/-0.5 mu m.
The silicon nitride ceramic has higher bending strength, fracture toughness and wear resistance, a certain amount of silicon nitride powder is doped into industrial alumina powder, and besides the excellent performance of the silicon nitride, the silicon nitride powder and the alumina powder are sintered together to generate partial sialon solid solution, so that the sintering temperature is reduced, the normal-pressure sintering of the product is realized, and the energy (source) consumption and the production cost are reduced.
The nano filling material is at least one of nano silicon dioxide, nano aluminum oxide and nano silicon nitride powder, the purity of the nano filling material is more than 99%, and the particle size is 10-30 nm.
The invention can obviously improve the microstructure of the ceramic insulating material, reduce the generation of voids and reduce the porosity by introducing the nano filling material, and can control the size and structure of crystals and reduce lattice defects by utilizing the high activity and large specific surface area of the nano filling material, and can improve the surface quality of the ceramic material, reduce the generation of pits and reduce the surface roughness by reducing the size of crystals and the reduction of lattice defects. Meanwhile, the refinement and uniformity of crystal grains and the reduction of lattice defects can reduce the dielectric loss and dielectric constant of the material to a certain extent, and the reduction of the dielectric constant can improve the insulating property of the material, so that an external electric field is better shielded, the polarization of electrons and ions is reduced, and the electric field intensity inside the material is reduced, thereby improving the electric breakdown resistance of the material.
The external doping agent is at least one of barium titanate, copper calcium titanate and lanthanum-doped titanate.
According to the invention, a small amount of titanate is added as an additive dopant, and the dielectric loss of the ceramic material can be reduced and the breakdown voltage of the ceramic material can be improved by utilizing the inhibition effect of the titanate on a conductive channel, the change of crystal phase orientation and the influence on the ion radius in the alumina ceramic lattice.
The water reducing agent is at least one of diethanolamine for ceramics and nonionic polyacrylamide. The amino water reducer can reduce the introduction of additional polar ions (such as Na+) instead of the traditional water reducer.
The water is preferably deionized water.
The preparation method of the large-size special-shaped silicon nitride-based ceramic support column comprises the following steps:
(1) Firstly, mixing and ball milling the raw materials of the component A to obtain ceramic slurry, and adding the raw materials of the component B to mix and dry mill after the ceramic slurry is dried to obtain mixed powder;
(2) Ageing the mixed powder, and then shaping and trimming to obtain a ceramic blank;
(3) And (3) sequentially drying, presintering and final firing the ceramic blank to obtain the large-size special-shaped silicon nitride-based ceramic support.
In the step (1), the content of the particle size D50 which is less than or equal to 5 mu m and less than 10 mu m in the ceramic slurry obtained after mixing and ball milling is higher than 85 percent.
In the step (1), the ceramic slurry is dried until the moisture content is less than or equal to 1.5 wt%, and then the component B raw material is added for mixing and dry grinding.
In the step (1), the ball milling and the dry milling are preferably carried out by using an alumina ball mill, wherein the ball milling time is 6-8 hours, and the dry milling time is 10-12 hours. The invention adopts a mode of grading ball milling and mixing, and wet milling and dry milling are carried out firstly, so that on one hand, absolute ethyl alcohol is avoided, and meanwhile, the defect that the silicon nitride powder generates gas when meeting water to cause danger can be effectively avoided, and on the other hand, the dry milling can improve the dispersibility of the nano filling material and prevent the uneven structure caused by powder aggregation.
In the step (2), when the mixture is stale, water is sprayed into the mixture according to the mass volume ratio of the mixture to water of 1kg (3-5) ml, and the mixture is uniformly mixed under the sealing condition, and the mixture is kept stand for stale for 48-96 hours. The invention sprays a small amount of water in the mixed powder, can improve the difficulty in repairing blanks of the mixed powder caused by too low water content, can enable the sprayed water to more uniformly permeate into the mixed powder after standing and ageing, improves the fluidity of the powder, and is beneficial to the stability of molding.
In the step (2), during molding, the aged mixed powder is filled into a mold, initial pressure is firstly carried out, the pressure is 30-40 MPa, the mold is removed after the initial pressure, the mold is placed into a vacuum bag, and cold isostatic pressing molding is carried out after vacuumizing.
In the step (3), the drying time is 72-120 h, the drying temperature is 45+/-5 ℃, the presintering adopts a tape burning mode, the presintering maximum temperature is 1220-1270 ℃, the presintering time is 120-148 h, the final burning maximum temperature is 1560-1625 ℃, and the final burning time is 36-72 h. The invention adopts a secondary sintering process of pre-sintering and final sintering, and the dried ceramic blank body is kiln-loaded and burned along with other insulator products during pre-sintering, so that the final sintering time can be effectively reduced without independent sintering.
The application of the large-size special-shaped silicon nitride-based ceramic support column disclosed by the invention is used as an internal insulation support column of power equipment.
Compared with the prior art, the invention has the following beneficial effects:
(1) According to the invention, a small amount of titanate added dopant and nano filler are introduced into a raw material system, and the dielectric loss of the ceramic material and the breakdown voltage of the ceramic material can be reduced by utilizing the inhibition effect of titanate on a conductive channel, the change of crystal phase orientation and the influence on ion radius in an alumina ceramic lattice;
(2) According to the invention, the raw materials are divided into the component A and the component B, and the mode of graded ball milling and mixing is adopted, so that the industrial alumina powder, the nano filler, the sintering aid, the water-washed clay, the additive dopant, the water reducing agent and the water of the component A are mixed and wet-milled, and then the obtained ceramic powder is mixed and dry-milled with the micro silicon nitride powder and the nano filler of the component B, so that on one hand, absolute ethyl alcohol is avoided, and meanwhile, the defect that the silicon nitride powder generates gas when meeting water and causes danger is effectively avoided, and on the other hand, the operation is simpler and safer;
(3) The invention adopts a twice firing mode, adopts a tape firing mode for the first firing, does not singly fire, can effectively reduce the final firing time, improves the performance of the product, saves energy and reduces consumption, and reduces the production cost;
(4) The silicon nitride-based ceramic support column prepared by the invention has high surface flashover voltage, low dielectric loss and dielectric constant and strong electric breakdown resistance, can replace epoxy resin materials, and can be used as an internal insulation support column of power equipment.
Detailed Description
The invention is further illustrated below with reference to examples. The raw materials used in the examples are all commercially available conventional raw materials unless otherwise specified, and the process methods used in the examples are all conventional in the art unless otherwise specified.
Some of the raw materials used in the examples are described below:
The industrial alumina powder is spherical alumina powder, the content of alpha-Al2O3 of the spherical alumina powder is not less than 98%, and the median particle diameter is 3.3-4.8 mu m;
The purity of the micron silicon nitride powder is more than 99 percent, the alpha conversion rate is not less than 95 percent, and the median grain diameter is 3.0+/-0.5 mu m;
The purity of the nano silicon dioxide, the nano aluminum oxide and the nano silicon nitride powder is more than 99 percent, and the grain diameter is 10-30 nm.
In the examples, the method of treating the water-washed clay was as follows:
Adding clay into water (water amount is not special, preferably the water surface is 10cm higher than clay), soaking for 24h, stirring for 5min, standing, pouring out upper layer froth and other impurities, adding water again, repeating the above steps until water is clear and no obvious floating matters exist, drying the water-washed clay at 100 ℃, and pulverizing for later use.
Example 1
The large-size special-shaped silicon nitride-based ceramic support column is prepared according to the following steps:
(1) The preparation method comprises the following steps of weighing, by mass, 70% of industrial alumina powder, 20% of micron silicon nitride powder, 5% of water-washed left cloud soil, 2% of talcum powder and 3% of nano silicon nitride powder, and respectively weighing barium titanate accounting for 0.2% of the mass of the basic raw materials, 0.3% of diethanolamine and 31% of deionized water;
Adding industrial alumina powder, talcum powder, water-washed left cloud clay, barium titanate, diethanolamine and deionized water serving as raw materials of the component A into an alumina ball mill, mixing and ball milling for 8 hours to obtain ceramic slurry, wherein the granularity D50 is less than or equal to 5 mu m, and the content of granularity <10 mu m is higher than 85%;
Drying the ceramic slurry until the moisture content is less than or equal to 1.5 wt%, adding the ceramic slurry, the micron silicon nitride powder and the nanometer silicon nitride powder serving as the raw materials of the component B into an alumina ball mill, and mixing and dry-grinding for 12 hours to obtain mixed powder;
(2) Spraying deionized water into the mixed powder according to the mass volume ratio of the mixed powder to the deionized water of 1kg to 3ml, uniformly mixing under a sealing condition, and standing for aging for 72 hours;
Filling the aged mixed powder into a mould, initially pressing by a manual pressure pump at 30MPa, demoulding after initial pressing, placing in a vacuum bag, vacuumizing, performing cold isostatic pressing for shaping, and repairing a blank to obtain a ceramic blank;
(3) Drying the ceramic blank for 72 hours at 45+/-5 ℃, pre-burning the ceramic blank in a kiln along with other insulator products, wherein the pre-burning highest temperature is 1240 ℃, the sintering time is 120 hours, then placing the ceramic blank in a high-temperature furnace for final sintering, the final sintering highest temperature is 1590 ℃, the sintering time is 48 hours, and processing the finished sample into a testable test block, detecting, processing a support post and waiting for subsequent treatment after the kiln is detected to be qualified.
Example 2
The large-size special-shaped silicon nitride-based ceramic support column is prepared according to the following steps:
(1) The preparation method comprises the following steps of weighing 80% of industrial alumina powder, 10% of micron silicon nitride powder, 2% of water-washed inner Mongolian clay, 3.5% of wollastonite and 4.5% of nano silicon dioxide according to the mass percentage, and respectively weighing copper calcium titanate accounting for 0.6% of the mass of the basic raw materials, 0.3% of diethanolamine and 33% of deionized water;
adding industrial alumina powder, water-washed inner Mongolian clay, wollastonite, copper calcium titanate, diethanolamine and deionized water serving as raw materials of the component A into an alumina ball mill, mixing and ball milling for 6 hours to obtain ceramic slurry, wherein the granularity D50 is less than or equal to 5 mu m, and the content of granularity <10 mu m is higher than 85%;
drying the ceramic slurry until the moisture content is less than or equal to 1.5 wt%, adding the ceramic slurry, the micron silicon nitride powder and the nanometer silicon dioxide serving as the raw materials of the component B into an alumina ball mill, and mixing and dry-grinding for 10 hours to obtain mixed powder;
(2) Spraying deionized water into the mixed powder according to the mass volume ratio of the mixed powder to the deionized water of 1kg:4ml, uniformly mixing under a sealing condition, and standing for ageing for 96 hours;
Filling the aged mixed powder into a mould, initially pressing by a manual pressure pump at 35MPa, demoulding after initial pressing, placing in a vacuum bag, vacuumizing, performing cold isostatic pressing for shaping, and repairing a blank to obtain a ceramic blank;
(3) Drying the ceramic blank for 96 hours at 45+/-5 ℃, pre-burning the ceramic blank in a kiln along with other insulator products, wherein the pre-burning highest temperature is 1250 ℃, the sintering time is 136 hours, then placing the ceramic blank in a high-temperature furnace for final sintering, wherein the final sintering highest temperature is 1605 ℃, the sintering time is 36 hours, and processing the finished sample into a testable test block, detecting, processing a support post and waiting for subsequent treatment after the kiln is detected to be qualified.
Example 3
The large-size special-shaped silicon nitride-based ceramic support column is prepared according to the following steps:
(1) The preparation method comprises the following steps of weighing 85% of industrial alumina powder, 5% of micron silicon nitride powder, 3% of water-washed Jilin ball clay, 1% of barium carbonate, 1% of yttrium oxide, 3% of nano alumina powder and 2% of nano silicon dioxide powder according to mass percentage, and respectively weighing lanthanum bismuth titanate, 0.2% of nonionic polyacrylamide and 35% of deionized water accounting for 0.1% of the mass of the basic raw materials;
Adding industrial alumina powder, barium carbonate, yttrium oxide, water-washed Jilin ball clay, lanthanum bismuth titanate, nonionic polyacrylamide and deionized water serving as raw materials of the component A into an alumina ball mill, mixing and ball milling for 7 hours to obtain ceramic slurry, wherein the particle size D50 is less than or equal to 5 mu m, and the content of the particle size is less than 10 mu m and is higher than 85%;
Drying the ceramic slurry until the moisture content is less than or equal to 1.5 wt%, adding the ceramic slurry, the micron silicon nitride powder, the nanometer alumina powder and the nanometer silica powder serving as the raw materials of the component B into an alumina ball mill, and mixing and dry-grinding for 11 hours to obtain mixed powder;
(2) Spraying deionized water into the mixed powder according to the mass volume ratio of the mixed powder to the deionized water of 1kg to 5ml, uniformly mixing under a sealing condition, and standing for aging for 48 hours;
filling the aged mixed powder into a mould, initially pressing by a manual pressure pump at 40MPa, demoulding after initial pressing, placing in a vacuum bag, vacuumizing, performing cold isostatic pressing for shaping, and repairing a blank to obtain a ceramic blank;
(3) Drying the ceramic blank for 120h at 45+/-5 ℃, pre-burning the ceramic blank in a kiln along with other insulator products, wherein the pre-burning highest temperature is 1270 ℃, the sintering time is 120h, then placing the ceramic blank in a high-temperature furnace for final sintering, the final sintering highest temperature is 1590 ℃, the sintering time is 48h, and processing the finished sample into a testable test block, detecting, processing the support post and waiting for subsequent treatment after the kiln is detected to be qualified.
Comparative example 1
Epoxy post materials and epoxy post products for electrical insulation are offered by italian corporation.
Comparative example 2
This comparative example differs from example 1 only in that no dopant was added, i.e., an equal mass of commercial alumina powder was used instead of barium titanate.
Comparative example 3
This comparative example differs from example 1 only in that no nano-filler was added, i.e. an equal mass of industrial alumina powder was used instead of nano-silicon nitride.
Comparative example 4
The comparative example differs from example 1 only in that the firing process in step (3) is different in that the preparation process of the comparative example is that the ceramic body is dried for 72 hours at 45+ -5 ℃ and then directly put into a high temperature furnace for final firing, the final firing maximum temperature is 1620 ℃ and the firing time is 72 hours.
The silicon nitride-based ceramic materials prepared in examples 1-3 and comparative examples 2-4 and the epoxy post material of comparative example 1 were processed into standard test bars for performance testing, wherein flexural strength was tested with reference to standard GB/T6569-2006, volume resistivity was tested with reference to standard IEC 62631-3-1:2016, dielectric constant and dielectric loss were tested with reference to standard GB/T5594.4-2015, flashover voltage was tested with reference to standard IEC 60243-1-2013, and breakdown field strength was tested with reference to standard GB/T1408. The test results are shown in Table 1.
TABLE 1 silicon nitride based ceramic Material Standard test strip Performance test results
As can be seen from Table 1, the epoxy material of comparative example 1 is an organic composite material, although alumina powder is added, the mechanical properties are not improved greatly, which is mainly due to the performance characteristics of the epoxy organic material itself, the dielectric constant and dielectric loss of comparative example 2 are improved to some extent, the flashover voltage is reduced, analysis shows that the loss of titanate causes the influence of the lack of piezoelectric effect in the sintering process of the material, which leads to the change of grain orientation or the excessive growth of ionic radius, the volume resistivity and flashover voltage of comparative example 3 are obviously reduced, analysis shows the influence of the microstructure of the material, no nano filler exists, the porosity of the material is improved, part of grain refinement effect is lost, and the lattice defects are correspondingly increased, the comparative example 4 is directly sintered without presintering, which requires the time of the sintering process to be increased, and the final sintering temperature to be increased, even so, the microstructure compactness of the ceramic is greatly different, which is mainly because the ceramic material needs to be subjected to a series of processes of moisture removal, organic phase transformation and the like in a proper temperature and time during the sintering process.
Further, in order to compare the performance of the insulator pillars in application, the silicon nitride-based ceramic pillars prepared in example 1, comparative example 3, and the epoxy pillars of comparative example 1 were assembled into products, and performance tests were performed, and the results are shown in table 2.
TABLE 2 silicon nitride based ceramic post Performance test results
| Project | Flexural Strength (16 kN condition) | Body density (g/cm3) | Porosity (%) | Surface flashover under + -10 kV |
| Example 1 | No damage and abnormal sound | 3.872 | 0.213 | No flashover and no obvious burn mark |
| Comparative example 1 | No damage and abnormal sound | 1.985 | 0.405 | Has no flashover and obvious fine burn mark |
| Comparative example 3 | No damage and abnormal sound | 3.784 | 0.290 | No flashover and no obvious burn mark |
It can be seen from Table 2 that the test data of comparative example 1 are mainly related to the properties of the organic material itself, which is not resistant to ablation, compared with example 1, and that the bulk density of comparative example 3 is slightly decreased and the porosity is increased, and that the number of flashovers or the service life in practical use is likely to be affected, although there is no significant change in the surface flashovers, compared with example 1, mainly because the charge accumulation and distribution uniformity and the bearing capacity of the pillar surface are deteriorated during use.