Titanium dioxide filler for low-thermal-expansion ceramic and preparation method of titanium dioxide filler

Abstract

The invention relates to the field of titanium dioxide, and provides a preparation method of a titanium dioxide filler for low-thermal-expansion ceramic in order to solve the problem that the thermal expansion coefficient is synchronously increased after the titanium dioxide filler is promoted to increase the dielectric constant of the ceramic, and the preparation method comprises the following steps: S100, under a heating condition, adding a doped ion solution into a titanium dioxide precursor solution to obtain gel; the doped ion solution comprises Mo < 6 + > and Sn < 2 + >; the molar ratio of Mo < 6 + > to Ti < 4 + > is (10-30): (1-2), and the molar ratio of Sn < 2 + > to Ti < 4 + > is (10-20): (2-3); s200, the gel is prepared into a pre-product through a calcination process; s300, after the pre-product is coated with a film layer through a film coating process, the titanium dioxide filler is obtained; the film layer comprises a silicon dioxide layer. After the outer surface of the titanium dioxide is covered with the film layer through the coating process, the expansion of the titanium dioxide can be limited by utilizing the film layer at low temperature, and the possibility of structural defects caused by thermal expansion difference of raw materials is reduced; the silicon dioxide film layer is coated outside the titanium dioxide, so that the expansion of the titanium dioxide can be limited.

Description

Technical Field

[0001] The present invention relates to the field of titanium dioxide, and more specifically, to a titanium dioxide filler for low thermal expansion ceramics and a preparation method thereof. Background Art

[0002] Dielectric ceramics are an important type of electronic ceramics with excellent insulation and dielectric properties, and are widely used in the fields of electronics, communication, etc. Rutile titanium dioxide has a relatively high dielectric constant. When it is added to a ceramic system with a low dielectric constant, the dielectric constant of the ceramic can be increased to a certain extent. However, the difference in the thermal expansion coefficients between titanium dioxide and ceramic raw materials easily leads to structural defects during the ceramic sintering process, thereby affecting the overall dielectric properties of the ceramic. The dispersion and compatibility of titanium dioxide in the matrix also affect the dielectric properties of the final product.

[0003] During the improvement process of titanium dioxide by the applicant, although the increase in the dielectric constant of the ceramic is promoted, the final thermal expansion coefficient of the ceramic product also increases to a certain extent. Summary of the Invention

[0004] The purpose of the present invention is to provide a titanium dioxide filler for low thermal expansion ceramics and a preparation method thereof, so as to solve the problem that the thermal expansion coefficient increases synchronously after promoting the increase of the dielectric constant of the ceramic by the titanium dioxide filler.

[0005] The embodiments of the present invention are realized through the following technical solutions:

[0006] A preparation method of a titanium dioxide filler for low thermal expansion ceramics, comprising:

[0007] S100. Under heating conditions, a doping ion solution is added to the precursor solution of titanium dioxide to obtain a gel; the doping ion solution includes: Mo 6+ and Sn 2+ ; the molar ratio of Mo 6+ to Ti 4+ is (10 - 30):(1 - 2), and the molar ratio of Sn 2+ to Ti 4 + is (10 - 20):(2 - 3);

[0008] S200. The gel is prepared into a pre-product through a calcination process;

[0009] S300. After the pre-product is coated with a film layer through a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silicon dioxide layer.

[0010] The concentration of the precursor solution can be selected as 18wt% - 25wt%; the solvent of the precursor solution can be deionized water or alcohol, such as ethanol or n-octanol.

[0011] The precursor solution of titanium dioxide includes one or more of tetrabutyl titanate solution, titanyl sulfate solution, tetra-isopropyl titanate solution and titanium tetrachloride solution.

[0012] High-dielectric ceramics play an important role in electronic components such as capacitors and filters. Utilizing their high dielectric constant characteristics, the size of components can be reduced, the energy storage density and response speed can be improved, meeting the requirements of miniaturization and integration of modern electronic devices. High-dielectric ceramics can also be used as potential energy storage materials, with advantages such as high energy storage density and fast charge and discharge speed, and are expected to play an important role in future energy storage systems. The characteristic that high-dielectric ceramics are sensitive to electric field changes makes them an important material for sensors, capable of detecting and converting electric field changes into measurable signals. However, the production cost of high-dielectric ceramics is relatively high. When the usage scenario does not require an overly high dielectric constant, or even does not need to reach the dielectric constant of rutile ceramics, a certain amount of high-dielectric functional fillers can be added to relatively inexpensive raw materials to increase the dielectric constant of the ceramics to a certain extent on the premise of ensuring that the production cost will not increase significantly.

[0013] Due to the relatively high dielectric constant of titanium dioxide, it can be used as a functional filler in dielectric ceramics. Of course, the addition of titanium dioxide can also effectively improve the mechanical properties of ceramics. Ceramic raw materials generally mainly include silicon dioxide, alumina, zirconia, barium carbonate, magnesium oxide and organic matrix, etc. When adding inorganic fillers, the difference in thermal expansion coefficient between them and each component needs to be considered to avoid problems such as apparent quality defects in the product during the sintering process and large dielectric losses caused by low compatibility of inorganic fillers. Based on this, the usage amount of inorganic fillers will also be restricted. In addition, the firing process of ceramics is a densification process, which is not only accompanied by changes in the volume of raw material particles, but also accompanied by the filling of pores in the green body. During the firing process of ceramics, the volume usually shrinks. The sintering process of ceramics generally includes a preheating stage, an oxidation stage and a firing stage. The temperature in the oxidation stage is about 950°C, and the temperature in the firing stage of high-performance ceramics is generally above 1200°C, and can be as high as above 2000°C. The thermal expansion coefficient of silicon dioxide decreases with the increase of temperature during the firing process and is basically stable when the temperature exceeds 1200°C. Commonly used titanium dioxide is mainly in the anatase type and rutile type. Among them, the thermal expansion coefficient of the rutile type is less than that of the anatase type. However, regardless of whether titanium dioxide is in the anatase type or rutile type, its thermal expansion coefficient is higher than that of common raw materials such as silicon dioxide. Therefore, the applicant is thinking about how to reduce the thermal expansion difference between titanium dioxide and other raw materials during the ceramic firing process and reduce the internal stress in the green body.

[0014] Although rutile titanium dioxide has higher stability and dielectric constant than anatase titanium dioxide, and a smaller thermal expansion coefficient, it is reasonable to mix rutile titanium dioxide into the raw materials for firing to improve product performance and ensure appearance quality. However, the applicant hopes to use the shrinkage of anatase titanium dioxide when it is converted to rutile titanium dioxide to improve the sintering process of ceramics. In the early stage of sintering, especially during the heating period, the volume of the ceramic will expand to a certain extent. After the temperature is raised to a high enough level, the disappearance of pores and the filling of voids begin to cause the ceramic to shrink significantly in volume. The applicant expects that titanium dioxide can undergo crystal transformation in the early stage of sintering, and then the stress generated by spatial compression during expansion can be compensated to a certain extent by the shrinkage of titanium dioxide, which can reduce the possibility of fine lines in ceramics, and then the amount of titanium dioxide used can be increased to a certain extent, thereby improving the dielectric constant of ceramics. In addition, since titanium dioxide completes crystal transformation in the early stage of sintering, the overall shrinkage rate of the ceramic volume will not be accelerated due to the shrinkage of titanium dioxide in the later stage of sintering, and the possibility of cracks in the later stage of sintering will also be reduced, and the range of process parameters can be expanded. At present, the volume shrinkage of most ceramics during sintering occurs after 1000°C. The temperature at which anatase titanium dioxide begins to transform into rutile is around 800°C, but during the sintering process, the time from 800°C to 1000°C is relatively short, and it is difficult to completely transform the crystal form at a temperature between 800°C and 1000°C. Therefore, the applicant hopes to reduce the temperature at which anatase titanium dioxide transforms into rutile. The applicant promotes the transformation of anatase titanium dioxide to rutile through a doping process. At the same time, in order to regulate the transformation and avoid too fast transformation in the heating stage, resulting in too fast volume change and eventually microcracks, the applicant controls the doping amount through experiments. In addition, excessive doping may lead to uncontrolled grain growth and increased structural defects, which not only affects the dielectric constant, but also affects the mechanical properties and chemical stability of the product.

[0015] Although the transformation of anatase titanium dioxide to rutile can be promoted by doping with specific ions, the applicant found through product testing that the thermal expansion coefficient of the product increased overall at different temperatures. The applicant speculates that the reason is that the structural defects that appear after crystal doping also increase the nonlinear degree of thermal expansion coefficient of titanium dioxide with temperature changes. The behavior of materials at different temperatures is difficult to predict. For example, the thermal expansion coefficient of the matrix material increases almost linearly, but the thermal expansion coefficient of the filler increases nonlinearly, and the thermal matching of ceramic products becomes worse when the temperature changes. The applicant hopes to reduce the thermal expansion coefficient of the product when it is applied to ceramic products without affecting the improvement of the dielectric properties of ceramics by titanium dioxide fillers as much as possible. Therefore, the applicant uses a coating technology to coat the titanium dioxide with a layer of high temperature resistant, low thermal expansion and excellent mechanical properties.

[0016] Preferably, the film coating process includes: after configuring the pre-product into a slurry, adding a dispersant, a silicon source, and PMMA microspheres to the slurry to obtain a first slurry; after filtering, washing, drying, and grinding the first slurry, titanium dioxide filler is obtained; the dosage of the dispersant is 0.1wt%-0.2wt% of the pre-product; the dosage of the silicon source is 3wt%-5wt% of the pre-product in terms of silicon dioxide; the dosage of the PMMA microspheres is 0.1wt%-0.3wt% of the pre-product, and the particle size of the PMMA microspheres is 1μm-20μm.

[0017] The present invention can limit the expansion of titanium dioxide and the ceramic matrix material through the silicon dioxide film, and to a certain extent reduce the thermal expansion coefficient of the whole ceramic. The PMMA microspheres make the silicon dioxide film have a porous structure. When the silicon dioxide film is under pressure, the stress is more easily dispersed, and the stability of the film structure is better, so the limiting effect is better. The silicon dioxide film has a certain pore space that can also compensate for the space required for expansion.

[0018] Preferably, the film coating process specifically further includes: adding a dispersant, 60wt%-70wt% of PMMA microspheres, and all of the silicon source to the slurry at 80°C-90°C, stirring for 30min-60min, then cooling the slurry to 50°C-70°C, adding the remaining PMMA microspheres, stirring for 45min-60min, and then standing for 10min-15min to obtain a first slurry.

[0019] Preferably, the film coating process further includes: by weight, putting 3 parts-5 parts of triethanolamine and 2 parts-6 parts of coupling agent into the first slurry for a mixing reaction to obtain a second slurry; drying the second slurry to obtain titanium dioxide filler; based on the weight of the pre-product in the first slurry, the first slurry is 100 parts-120 parts.

[0020] Since anatase titanium dioxide will also have a certain degree of expansion before transforming into rutile type and its expansion coefficient is greater than that of conventional ceramic raw materials, it may cause product structure defects and finally affect the dielectric properties of the product. Therefore, the present invention coats multiple layers of film on the titanium dioxide, limits the expansion of titanium dioxide through the film layer, and can also provide expansion space for the ceramic matrix through the film layer space decomposed or volatilized by the triethanolamine film layer. Therefore, the temperature at which the triethanolamine layer is damaged in the present invention is lower than the crystal form transformation temperature of anatase titanium dioxide.

[0021] In the early stage of the ceramic forming process, in order to ensure the stability of the shape, the dispersibility of titanium dioxide can be improved by selecting the film layer material, and the bonding degree between titanium dioxide and the organic binder during the forming process can also be improved. The stability of the film layer can be improved by a coupling agent, thereby increasing the decomposition temperature, and the decomposition temperature can be adjusted to 400°C - 600°C. The selection of PMMA microspheres in the present invention can not only improve the bonding degree between the triethanolamine film and the silica film layer, but also increase the decomposition temperature of the triethanolamine film.

[0022] The coupling agent can be one or more of isostearoyl titanate isopropyl ester, GR-501, and KH570.

[0023] Through experiments, it is found that the products prepared with isostearoyl titanate isopropyl ester have good performance.

[0024] Preferably, the temperature of the second slurry reaction system is 50°C - 70°C, and the reaction time is 1.5 h - 3 h.

[0025] By adjusting the raw material dosage, reaction temperature, and reaction time, the film layer thickness can be controlled so that the film layer is not too large, avoiding excessive increase in the voids of the formed embryo, too high volume shrinkage rate of the product after high-temperature sintering, and extension of the time for the densification process. If the film layer thickness is too small, it is difficult to adapt to the expansion process before the transformation of anatase titanium dioxide. Through the experiments of the applicant, it is found that the products with the parameters of the present invention have excellent performance.

[0026] Preferably, the S100 includes:

[0027] Dissolve phosphomolybdic acid in ethanol to obtain solution A;

[0028] Dissolve tin tetrachloride in ethanol to obtain solution B;

[0029] Under heating conditions, add solution A and solution B to the precursor solution of titanium dioxide, and mix them in an ultrasonic environment for 10 min - 30 min, then let it stand at room temperature for 8 h - 12 h to obtain a gel; the ultrasonic frequency is 20 KHz - 30 KHz.

[0030] Preferably, after adding solution B to the precursor solution of titanium dioxide at one time, gradually add solution A.

[0031] During the doping experiment, the applicant found that when both solution A and solution B are added to the precursor solution at one time or gradually, the doping amount of Sn 4+ is limited. The applicant conjectures that the reason is that there is a competitive relationship between the two ions during the doping process.

[0032] Preferably, the temperature of the reaction system in S100 is 60°C - 80°C, and the pH value is 7.5 - 9.

[0033] The pH value can be adjusted using ammonia water. Appropriate system temperature and pH value are beneficial for metal ions to enter the titanium dioxide lattice, the completion of hydrolysis of the precursor solution, and the stability of the hydrolysis products.

[0034] Preferably, the silicon source includes one or more of sodium silicate, potassium silicate, and tetraethyl orthosilicate.

[0035] A titanium dioxide filler prepared by the described preparation method.

[0036] The present invention has at least the following beneficial effects:

[0037] The present invention utilizes the crystal form change of anatase titanium dioxide in the early stage of sintering to reduce the possibility of ceramic microcracks; anatase titanium dioxide can complete the transformation to rutile type before high-temperature sintering, avoiding exacerbating shrinkage in the case of a high volume shrinkage rate during high-temperature sintering, which increases the possibility of ceramic structural defects under the same process conditions; the titanium dioxide prepared by the doping process of titanium dioxide can promote its transformation to rutile titanium dioxide; after covering a film layer on the outer surface of titanium dioxide through a coating process, the film layer can limit the expansion of titanium dioxide at low temperature, reducing the possibility of structural defects caused by the difference in thermal expansion of raw materials; the triethanolamine film layer volatilizes or decomposes before the crystal form transformation of titanium dioxide, so that the released film layer space can be used for the expansion of the surrounding matrix, reducing internal stress; the presence of the film layer can also increase the dispersibility of titanium dioxide and its compatibility with the matrix, thereby increasing the dielectric properties of the product; by coating a silicon dioxide film layer on the outside of titanium dioxide, the thermal expansion of titanium dioxide during the use of ceramic products can be restricted; using a porous silicon dioxide film can provide a certain lateral expansion space for the film layer when it is under pressure, reducing stress concentration; using PMMA microspheres can not only provide a pore-forming function but also improve the bonding degree between the silicon dioxide film and the triethanolamine film. Specific embodiments

[0038] To make the objectives, method solutions, and advantages of the embodiments of the present invention clearer, the method solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0039] Example 1: A preparation method of a titanium dioxide filler for low thermal expansion ceramics, including:

[0040] S100. Dissolve phosphomolybdic acid in ethanol to obtain solution A; dissolve tin tetrachloride in ethanol to obtain solution B;

[0041] Under heating conditions, add solution A and solution B to the precursor solution of titanium dioxide, and mix them in an ultrasonic environment for 10 min, then let it stand at room temperature for 8 h to obtain a gel; the ultrasonic frequency is 20 KHz. The doping ion solution includes: Mo 6+and Sn 4 + ; The Mo 6+ and Ti 4+ has a molar ratio of 10:2, and the Sn 2+ and Ti 4+ has a molar ratio of 10:3;

[0042] S200. The gel is calcined to obtain a pre-product;

[0043] S300. After the pre-product is coated with a film layer by a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silica layer.

[0044] The film coating process includes: mixing the pre-product with deionized water to form a slurry, adding a dispersant, 60 wt% PMMA microspheres and all the silicon source to the slurry at 80°C, stirring for 30 min, then cooling the slurry to 50°C, adding the remaining PMMA microspheres, stirring for 45 min, and then standing for 10 min to obtain a first slurry; by weight, 3 parts of triethanolamine and 2 parts of triisostearoyl titanate are added to the first slurry and mixed and reacted to obtain a second slurry; the second slurry is filtered, washed, dried, and ground to obtain a titanium dioxide filler; based on the weight of the pre-product in the first slurry, the first slurry is 100 parts.

[0045] The mass ratio of deionized water to the pre-product is 100:90;

[0046] The dosage of the dispersant is 0.1 wt% of the pre-product; the dispersant is polyethylene glycol;

[0047] The dosage of the silicon source is 3 wt% of the pre-product calculated as silica; the silicon source is sodium silicate.

[0048] The dosage of the PMMA microspheres is 0.1 wt% of the pre-product, and the particle size of the PMMA microspheres is 1 μm.

[0049] The temperature of the reaction system of the second slurry is 50°C, and the reaction time is 1.5 h.

[0050] The temperature of the reaction system in S100 is 60°C, and the pH value is 7.5.

[0051] Example 2: A method for preparing a titanium dioxide filler for a low thermal expansion ceramic, including:

[0052] S100. Dissolve phosphomolybdic acid in ethanol to obtain solution A; dissolve tin tetrachloride in ethanol to obtain solution B;

[0053] Under heating conditions, solution A and solution B are added to the precursor solution of titanium dioxide, and after mixing for 30 min under an ultrasonic environment, it is left standing at room temperature for 12 h to obtain a gel; the ultrasonic frequency is 30 KHz. The doped ion solution includes: Mo 6+ and Sn 4+ ; the molar ratio of the Mo 6+ to Ti 4+ is 30:1, and the molar ratio of the Sn 2+ to Ti 4+ is 20:2;

[0054] S200. The gel is obtained as a pre-product through a calcination process;

[0055] S300. After the pre-product is coated with a film layer through a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silica layer.

[0056] The film coating process includes: mixing the pre-product with deionized water to form a slurry, adding a dispersant, 70 wt% PMMA microspheres, and all the silicon source to the slurry at 90°C, stirring for 60 min, then cooling the slurry to 70°C, adding the remaining PMMA microspheres, stirring for 60 min, and then leaving it standing for 15 min to obtain a first slurry; by weight, 5 parts of triethanolamine and 6 parts of triisooctanoyl titanate are added to the first slurry and mixed and reacted to obtain a second slurry; the second slurry is filtered, washed, dried, and ground to obtain a titanium dioxide filler;

[0057] The mass ratio of deionized water to the pre-product is 120:90;

[0058] The dosage of the dispersant is 0.2 wt% of the pre-product; the dispersant is polyethylene glycol;

[0059] The dosage of the silicon source is 5 wt% of the pre-product calculated as silica; the silicon source is sodium silicate.

[0060] The dosage of the PMMA microspheres is 0.3 wt% of the pre-product, and the particle size of the PMMA microspheres is 20 μm.

[0061] The temperature of the reaction system of the second slurry is 70°C, and the reaction time is 3 h.

[0062] The temperature of the reaction system in S100 is 80°C, and the pH value is 9.

[0063] Example 3: A method for preparing a titanium dioxide filler for a low thermal expansion ceramic, including:

[0064] S100. Dissolve phosphomolybdic acid in ethanol to obtain solution A; dissolve tin tetrachloride in ethanol to obtain solution B;

[0065] Under heating conditions, solution A and solution B are added to the precursor solution of titanium dioxide, and after mixing for 20 min under an ultrasonic environment, it is left standing at room temperature for 10 h to obtain a gel; the ultrasonic frequency is 25 KHz. The doped ion solution includes: Mo 6+ and Sn 4+ ; the molar ratio of the Mo 6+ to Ti 4+ is 20:1.5, and the molar ratio of the Sn 2+ to Ti 4+ is 1.5:2.5;

[0066] S200. The gel is prepared into a pre-product through a calcination process;

[0067] S300. After the pre-product is coated with a film layer through a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silica layer.

[0068] The film coating process includes: mixing the pre-product with deionized water to form a slurry, adding a dispersant, 65 wt% PMMA microspheres, and all the silicon source to the slurry at 85°C, stirring for 45 min, then cooling the slurry to 60°C, adding the remaining PMMA microspheres, stirring for 50 min, and then leaving it standing for 12 min to obtain a first slurry; by weight, 4 parts of triethanolamine and 4 parts of isopropyl triisostearoyl titanate are added to the first slurry and mixed and reacted to obtain a second slurry; the second slurry is filtered, washed, dried, and ground to obtain a titanium dioxide filler;

[0069] The mass ratio of deionized water to the pre-product is 110:90;

[0070] The dosage of the dispersant is 0.15 wt% of the pre-product; the dispersant is polyethylene glycol;

[0071] The dosage of the silicon source is 4 wt% of the pre-product calculated as silica; the silicon source is sodium silicate.

[0072] The dosage of the PMMA microspheres is 0.2 wt% of the pre-product, and the particle size of the PMMA microspheres is 8 μm.

[0073] The temperature of the reaction system of the second slurry is 60°C, and the reaction time is 2 h.

[0074] The temperature of the reaction system in S100 is 70°C, and the pH value is 8.

[0075] Example 4: A method for preparing a titanium dioxide filler for a low thermal expansion ceramic, including:

[0076] S100. Dissolve phosphomolybdic acid in ethanol to obtain solution A; dissolve tin tetrachloride in ethanol to obtain solution B;

[0077] Under heating conditions, after adding solution B to the precursor solution of titanium dioxide at one time, solution A with a concentration of 25 vt% is added every 5 minutes. During this period, the system is in an ultrasonic environment. After 20 minutes, it is left standing at room temperature for 10 h to obtain a gel; the ultrasonic frequency is 25 KHz. The doped ion solution includes: Mo 6+ and Sn 4+ ; the molar ratio of the Mo 6+ to Ti 4+ is 20:1.5, and the molar ratio of the Sn 2+ to Ti 4+ is 1.5:2.5;

[0078] S200. The gel is prepared into a pre-product through a calcination process;

[0079] S300. After the pre-product is coated with a film layer through a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silica layer.

[0080] The film coating process includes: mixing the pre-product with deionized water to form a slurry, adding a dispersant, 65 wt% PMMA microspheres, and all the silicon source to the slurry at 85°C, stirring for 45 minutes, then cooling the slurry to 60°C, adding the remaining PMMA microspheres, stirring for 50 minutes, and then leaving it standing for 12 minutes to obtain a first slurry; by weight, 4 parts of triethanolamine and 4 parts of isopropyl triisostearoyl titanate are added to the first slurry and mixed and reacted to obtain a second slurry; the second slurry is filtered, washed, dried, and ground to obtain a titanium dioxide filler;

[0081] The mass ratio of deionized water to the pre-product is 110:90;

[0082] The dosage of the dispersant is 0.15 wt% of the pre-product; the dispersant is polyethylene glycol;

[0083] The dosage of the silicon source, calculated as silica, is 4 wt% of the pre-product; the silicon source is sodium silicate.

[0084] The dosage of the PMMA microspheres is 0.2 wt% of the pre-product, and the particle size of the PMMA microspheres is 8 μm.

[0085] The temperature of the reaction system of the second slurry is 60°C, and the reaction time is 2 h.

[0086] The temperature of the reaction system in S100 is 70°C, and the pH value is 8.

[0087] Comparative Example 1: A method for preparing a titanium dioxide filler for a low thermal expansion ceramic, including:

[0088] S100. Dissolve phosphomolybdic acid in ethanol to obtain solution A; dissolve tin tetrachloride in ethanol to obtain solution B;

[0089] Under heating conditions, add solution B to the precursor solution of titanium dioxide at one time, and then add 25 vt% of solution A every 5 minutes. During this period, the system is in an ultrasonic environment. After 20 minutes, let it stand at room temperature for 10 h to obtain a gel; the ultrasonic frequency is 25 KHz. The doped ion solution includes: Mo 6+ and Sn 4+ ; the molar ratio of the Mo 6+ to Ti 4+ is 20:1.5, and the molar ratio of the Sn 2+ to Ti 4+ is 1.5:2.5;

[0090] S200. The gel is prepared into a pre-product through a calcination process;

[0091] S300. After the pre-product is coated with an outer coating layer through a coating process, a titanium dioxide filler is obtained;

[0092] The coating process includes: mixing the pre-product with deionized water to prepare a first slurry, and then, by weight, adding 4 parts of triethanolamine and 4 parts of isostearoyl titanate isopropyl ester to the first slurry and mixing them for reaction to obtain a second slurry; the second slurry is filtered, washed, dried, and ground to obtain a titanium dioxide filler;

[0093] The mass ratio of deionized water to the pre-product is 110:90;

[0094] The temperature of the second slurry reaction system is 60 °C, and the reaction time is 2 h.

[0095] The temperature of the reaction system in S100 is 70 °C, and the pH value is 8.

[0096] Comparative Example 2: The difference from Example 4 is that PMMA microspheres are not added.

[0097] Comparative Example 3: The difference from Example 4 is that after mixing and preparing the pre-product with deionized water into a slurry, a dispersant, all PMMA microspheres, and all silicon sources are added to the slurry at 85 °C, stirred for 45 min, then cooled to 60 °C, stirred for 50 min, and then allowed to stand for 12 min to obtain a first slurry.

[0098] Experiment:

[0099] Preparation method of experimental samples: Ceramic powder and binder PVA are mixed by wet ball milling for 30 hours to obtain a slurry, and the dosage of the binder is 4% of the powder. After the slurry is pressed into a blank, sintering begins. Sintering process: First, preheat at 300°C for 1 h, then increase the temperature to 1000°C at a rate of 80°C / h, hold for 1 h, and then increase the temperature to 1300°C at a rate of 60°C / h and hold for 5 h. The ceramic powder includes 70 wt% alumina powder, 10 wt% magnesia powder, 1 wt% silica, and the balance titanium dioxide filler.

[0100] Experiment 1: The titanium dioxide fillers prepared by the preparation methods provided in Examples 1-4 and Comparative Examples 1-3 were used for the preparation of experimental samples, and then the dielectric constant of the prepared samples was tested with reference to the standard of GB / T5594.4-2015. Test conditions: 1 MHz, 25°C, thickness 5 mm. The average value was taken after 5 tests for each group, and the test results are shown in Table 1.

[0101] Table 1

[0102] Example 1 Example 2 Example 3 Example 4 Dielectric constant 31.6 28.3 32.8 33.5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Dielectric constant 33.7 29.1 31.9

[0103] It can be seen from the test results of Examples 1-4 that the titanium dioxide filler prepared by the preparation method provided by the present invention still has a significant effect on improving the ceramic dielectric constant.

[0104] It can be seen from the comparison of the test results of Comparative Example 1 and Example 4 that, compared with only coating with a triethanolamine layer, the titanium dioxide filler obtained by coating a silica layer and a triethanolamine layer on titanium dioxide in the present invention has almost no decrease in improving the ceramic dielectric constant.

[0105] It can be seen from the comparison of the test results of Comparative Examples 2-3 and Example 4 that the addition of PMMA microspheres and their addition methods both affect the promoting effect of the titanium dioxide filler on the ceramic dielectric constant. The applicant conjectures that the reason is that the stability and uniformity of the silica film structure, etc., all affect the compatibility between the titanium dioxide and the ceramic matrix and the limiting effect of the film on the expansion of titanium dioxide.

[0106] Experiment 2: The titanium dioxide fillers prepared by the preparation methods provided in Examples 1-4 and Comparative Examples 1-3 were used for the preparation of experimental samples, and then the coefficient of thermal expansion (×10 -6 / °C) of the prepared samples was measured by the linear expansion method. Test conditions: 25°C, thickness 5 mm. The average value was taken after 5 tests for each group, and the test results are shown in Table 2.

[0107] Table 2

[0108] Example 1 Example 2 Example 3 Example 4 Coefficient of thermal expansion 6.72 7.03 6.58 6.42 Comparative Example 1 Comparative Example 2 Comparative Example 3 Coefficient of thermal expansion 8.40 7.11 6.78

[0109] From the test results of Examples 1-4, it can be seen that after the ceramic uses the titanium dioxide filler provided by the present invention, while improving the dielectric constant, it also has the advantage of low thermal expansion.

[0110] From the comparison between Comparative Example 1 and Example 4, it can be seen that after adding the silica film layer provided by the present invention on the basis of the triethanolamine layer, the thermal expansion coefficient of titanium dioxide can be reduced.

[0111] From the comparison between Comparative Examples 2-3 and Example 4, it can be seen that the addition of PMMA microspheres and their addition methods both affect the reduction effect of the titanium dioxide filler on the thermal expansion coefficient of the ceramic.

[0112] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of titanium dioxide filler for low thermal expansion ceramics, characterized in that, Including: S100. Under heating conditions, a doping ion solution is added to a precursor solution of titanium dioxide to obtain a gel. The doped ion solution includes: Mo 6+ and Sn 4+ ; The molar ratio of the Mo 6+ to Ti 4+ is (10 - 30):(1 - 2), and the molar ratio of the Sn 2+ to Ti 4+ is (10 - 20):(2 - 3); S200. The gel is prepared into a pre-product through a calcination process. S300. After the pre-product is coated with a film layer through a film coating process, a titanium dioxide filler is obtained; the film layer includes: a silica layer.

2. The preparation method according to claim 1, wherein The film coating process includes: configuring the pre-product into a slurry, adding a dispersant, a silicon source, and PMMA microspheres to the slurry to obtain a first slurry; after the first slurry is filtered, washed, dried, and ground, a titanium dioxide filler is obtained. The dosage of the dispersant is 0.1wt%-0.2wt% of the pre-product. The dosage of the silicon source, calculated as silica, is 3wt%-5wt% of the pre-product. The dosage of the PMMA microspheres is 0.1wt%-0.3wt% of the pre-product, and the particle size of the PMMA microspheres is 1μm-20μm.

3. The preparation method according to claim 2, characterized in that, The film coating process specifically further includes: adding a dispersant, 60wt%-70wt% of PMMA microspheres, and all of the silicon source to the slurry at 80°C-90°C, stirring for 30min-60min, then cooling the slurry to 50°C-70°C, adding the remaining PMMA microspheres, stirring for 45min-60min, and then standing for 10min-15min to obtain a first slurry.

4. The preparation method according to claim 2, characterized in that, The film coating process further includes: by weight, adding 3 parts-5 parts of triethanolamine and 2 parts-6 parts of a coupling agent to the first slurry for a mixed reaction to obtain a second slurry; the second slurry is dried to obtain a titanium dioxide filler; based on the weight of the pre-product in the first slurry, the first slurry is 100 parts-120 parts.

5. The preparation method according to claim 4, wherein, The temperature of the reaction system of the second slurry is 50°C-70°C, and the reaction time is 1.5h-3h.

6. The preparation method according to any one of claims 1-5, characterized in that, The S100 includes: Dissolving phosphomolybdic acid in ethanol to obtain solution A. Dissolving stannic chloride in ethanol to obtain solution B. Under heating conditions, adding solution A and solution B to the precursor solution of titanium dioxide, and mixing in an ultrasonic environment for 10min-30min, then standing at room temperature for 8h-12h to obtain a gel; the ultrasonic frequency is 20KHz-30KHz.

7. The preparation method according to claim 6, characterized in that, Adding solution B to the precursor solution of titanium dioxide at one time, and then gradually adding solution A.

8. The preparation method according to claim 6, characterized in that, The temperature of the reaction system in S100 is 60°C-80°C, and the pH value is 7.5-9.

9. The preparation method according to claim 6, characterized in that, The silicon source includes one or more of sodium silicate, potassium silicate, and tetraethyl orthosilicate.

10. A titanium dioxide filler prepared by the preparation method according to any one of claims 1-9.