A high-strength, heat-resistant kaolin and its preparation method

Abstract

This invention provides a high-strength, heat-resistant porcelain clay and its preparation method, belonging to the field of ceramic technology. By mass percentage, it comprises 35-55 parts modified kaolin, 8-15 parts spodumene, 5-12 parts andalusite, 3-8 parts silane-modified nano-zirconia, 6-14 parts yttrium oxide-alumina composite powder, 2-5 parts surface-acidified silicon carbide whiskers, 3-6 parts pre-gelatinized starch binder, 2-4 parts water glass, and 1-3 parts rare earth oxide composite additives. This invention utilizes the combined action of modified kaolin, yttrium oxide-alumina composite powder, silane-modified nano-zirconia, and surface-acidified silicon carbide whiskers to construct a multi-scale reinforced structure. Combined with stepwise feeding and segmented heating processes, the fired porcelain clay exhibits high strength, a low coefficient of thermal expansion, and excellent thermal shock resistance.

Description

Technical Field

[0001] This invention belongs to the field of ceramic technology, specifically relating to a high-strength, heat-resistant porcelain clay and its preparation method. Background Technology

[0002] Porcelain clay, a type of clay mineral raw material used for firing porcelain, is mainly composed of minerals such as kaolinite, quartz, and feldspar. It is a fundamental material in the ceramics industry. After being mixed, shaped, dried, and sintered, porcelain clay is used to produce various ceramic products, widely applied in daily-use porcelain, building ceramics, electrical ceramics, and special industrial ceramics. With the development of the ceramics industry, the market's performance requirements for porcelain clay materials are increasingly stringent, especially in high-temperature applications such as kiln furniture, heat-resistant vessels, and electronic ceramic substrates. These applications demand that porcelain clay not only possess good plasticity and formability but also exhibit high mechanical strength and excellent heat resistance after firing.

[0003] A common practice in ceramics is to introduce low-expansion minerals such as spodumene and talc into the clay formula. These minerals' low expansion at high temperatures reduce the overall thermal expansion coefficient of the body, thereby improving heat resistance. Another approach is to add high-strength mineral powders such as alumina and zirconium oxide to the clay. The dispersion strengthening effect of these high-hardness particles enhances the mechanical strength after firing. Other technologies use nanoscale powders to modify traditional minerals; for example, utilizing the phase transformation toughening effect of nano-zirconia to improve the fracture toughness of the ceramic body. In terms of processing, some existing technologies attempt to improve the density and crystalline phase composition of the body by optimizing ball milling time, improving molding pressure, and adjusting sintering temperature profiles. Furthermore, some methods incorporate short-cut carbon fibers or natural fibers into the clay, using the bridging and pull-out effects of the fibers to prevent crack propagation and thus increase strength.

[0004] However, existing technologies still have many problems. First, simply mixing low-expansion minerals with basic kaolin often results in uneven mixing due to the large differences in surface properties and poor interfacial wettability between the two mineral particles. This leads to segregation and stress concentration after firing, which in turn reduces thermal stability. Second, nanoparticles such as nano-zirconia, due to their large specific surface area and high surface energy, are prone to agglomeration in kaolin slurry, resulting in poor dispersibility and hindering the full realization of their toughening and strengthening effects. Furthermore, the addition of nanomaterials often increases sintering temperature and energy consumption. Third, the bonding interface between natural fibers and the inorganic mineral matrix is ​​weak. Untreated fibers are prone to carbonization and shrinkage during high-temperature sintering, detaching from the matrix and failing to form an effective reinforcing structure. Fourth, the formulation ratios and process parameters rely heavily on empirical values, lacking reasonable range limits, leading to significant performance fluctuations and poor reproducibility between different batches of products. Therefore, it is necessary to design a high-strength, heat-resistant kaolin and its preparation method. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, a high-strength, heat-resistant kaolin and its preparation method are provided.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-strength, heat-resistant porcelain clay, by mass parts, comprises 35-55 parts modified kaolin, 8-15 parts spodumene, 5-12 parts andalusite, 3-8 parts silane-modified nano-zirconia, 6-14 parts yttrium oxide-alumina composite powder, 2-5 parts surface-acidified silicon carbide whiskers, 3-6 parts pregelatinized starch binder, 2-4 parts water glass, and 1-3 parts rare earth oxide composite additives.

[0008] Preferably, the preparation method of the modified kaolin includes the following steps: crushing the natural kaolin ore to a particle size of less than 5 mm, soaking it in hydrochloric acid with a mass concentration of 15%-25% for 12-24 hours at a soaking temperature of 40℃-60℃, washing it with deionized water until neutral after soaking, filtering it, and calcining it at 650℃-750℃ for 1-2 hours. The calcined product is then pulverized by air jet milling to a D50 of 3μm-8μm to obtain modified kaolin.

[0009] Preferably, the preparation method of the silane-modified nano-zirconia includes the following steps: dispersing nano-zirconia powder in anhydrous ethanol, ultrasonically dispersing for 20-40 minutes with an ultrasonic power of 200W-400W, then adding a silane coupling agent, refluxing and stirring at 65℃-85℃ for 2-4 hours, centrifuging after the reaction, washing three times with anhydrous ethanol, drying at 80℃-100℃ for 3-5 hours, and grinding to obtain silane-modified nano-zirconia.

[0010] Preferably, the preparation method of the surface-acidified silicon carbide whiskers includes the following steps: immersing silicon carbide whiskers in an inorganic acid solution with a mass concentration of 10%-20%, stirring and soaking at 40℃-60℃ for 1h-3h, filtering, washing with deionized water until neutral, and drying at 100℃-120℃ for 2h-4h to obtain surface-acidified silicon carbide whiskers.

[0011] Preferably, the preparation method of the pregelatinized starch binder includes the following steps: mixing corn starch and deionized water at a mass ratio of 1:3-1:5, stirring and heating to 80℃-95℃, maintaining the temperature and stirring for 20min-40min until complete gelatinization, then cooling to 50℃-60℃, drying under vacuum and pulverizing to obtain the pregelatinized starch binder.

[0012] Preferably, the preparation method of the yttrium oxide-alumina composite powder includes the following steps: mixing yttrium oxide powder and alumina powder at a mass ratio of 1:4-1:10, adding deionized water and ball milling for 2-4 hours, spray drying, calcining at 1400℃-1600℃ for 2-4 hours, cooling and pulverizing to a D50 of 3μm-8μm to obtain yttrium oxide-alumina composite powder.

[0013] Preferably, the rare earth oxide composite additive is composed of lanthanum oxide, cerium oxide and yttrium oxide in a mass ratio of 1:0.5:1.5-1:1:2.5; the mass ratio of spodumene to andalusite is 1.2:1-1.8:1.

[0014] This invention also provides a method for preparing high-strength, heat-resistant kaolin, comprising the following steps:

[0015] S1. Weigh each raw material according to the mass fraction, put the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder into a ball mill, add 35-50 parts of water for wet ball milling, and the ball milling time is 4h-8h to obtain the basic slurry;

[0016] S2. Add the silane-modified nano-zirconia to the base slurry, continue ball milling for 1-3 hours, then add the pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix evenly to obtain a mixed slurry;

[0017] S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 30-60 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 48-72 hours.

[0018] S4. The aged mud is dehydrated by pressure filtration to a moisture content of 22%-26%, and then sent to a mud-powdering machine for vacuum mud-powdering.

[0019] S5. Press the kneaded clay material under a molding pressure of 25MPa-40MPa to obtain a green body.

[0020] S6. Dry the green body in a drying kiln at 80℃-110℃ for 4h-6h;

[0021] S7. The dried green body is sent into the kiln and sintered according to the set heating curve. The maximum sintering temperature is 1280℃-1350℃, the holding time is 1.5h-3h, and the green body is cooled to room temperature with the kiln to obtain high-strength heat-resistant ceramics.

[0022] In step S1, the rotational speed of the ball mill is 350 r / min-500 r / min, the ball-to-material mass ratio is 3:1-5:1, and the solid content of the slurry is 55%-65%.

[0023] In step S3, the ambient temperature for the aging process is 20℃-30℃, and the mud is turned over every 12 hours during the aging period.

[0024] In step S7, the parameters of the heating curve are set as follows:

[0025] The first stage is at room temperature -600℃, with a heating rate of 3℃ / min - 5℃ / min;

[0026] The second stage is 600℃-1000℃, with a heating rate of 2℃ / min-4℃ / min;

[0027] The third stage involves heating from 1000℃ to the maximum sintering temperature at a rate of 1.5℃ / min to 3℃ / min.

[0028] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0029] 1. This invention constructs a multi-scale reinforcing structure in the fired ceramic green body through the interaction of modified kaolin, yttrium oxide-alumina composite powder, silane-modified nano-zirconia and surface-acidified silicon carbide whiskers, so that the green body can obtain a uniform and fine microstructure at a moderate temperature, and obtain high strength and heat resistance.

[0030] 2. This invention uses silane-modified nano-zirconia and surface-acidified silicon carbide whiskers to form a cross-scale composite reinforcement system between nano-zirconia particles and micron-sized whiskers within the green body. This system inhibits the formation and propagation of microcracks at different levels, thereby achieving a combined improvement in the strength and toughness of the porcelain clay material.

[0031] 3. This invention improves firing stability and yield by setting a segmented heating sintering curve, allowing the green body to undergo different physicochemical changes at different temperature stages. In the low-temperature stage from room temperature to 600℃, a faster heating rate promotes the rapid removal of moisture and organic matter such as pregelatinized starch binders, reducing energy waste caused by prolonged low-temperature residence. In the medium-temperature stage from 600℃ to 1000℃, a moderate heating rate allows minerals such as andalusite sufficient time to complete crystal transformation and preliminary reactions, avoiding phase transformation stress concentration. In the high-temperature stage from 1000℃ to the maximum sintering temperature, a slower heating rate allows for stable solid-phase reactions and liquid-phase sintering between the yttrium oxide-alumina composite powder and the surrounding matrix, preventing softening and deformation of the green body caused by rapid liquid phase formation due to sudden temperature increases. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the specific embodiments of this application, the sources of various main raw materials are briefly described as follows:

[0034] Natural kaolin ore: Longyan Kaolin Co., Ltd., whiteness not less than 90.

[0035] Spodumene: Xiamen Lushang Metal Materials Co., Ltd., with a Li2O content of not less than 5.0%.

[0036] Andalusite: A product of Xinjiang Xinrong Yilong Andalusite Co., Ltd., with an Al2O3 content of 55% to 58%, available in 200 mesh size.

[0037] Nano-zirconia powder: Wenzhou Jingcheng Chemical Co., Ltd., with a purity of not less than 99.0% and an average particle size of not more than 100 nanometers.

[0038] Silane coupling agent: Hubei Xinlantian New Material Co., Ltd., model KH-560, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, industrial grade, purity not less than 97%.

[0039] Anhydrous ethanol: Wuxi Xiangyue Chemical Co., Ltd., industrial grade, purity not less than 99.7%.

[0040] Silicon carbide whiskers: Xuzhou Jiechuang New Materials Technology Co., Ltd., model Hongwu Nano D500, diameter 0.1 micrometer to 2.5 micrometer, aspect ratio not less than 20, purity not less than 99%.

[0041] Hydrochloric acid: Zibo Shifukai Chemical Trading Co., Ltd., industrial grade synthetic hydrochloric acid, content 31%.

[0042] Sodium hydroxide: Luhu Chemical Co., Ltd., industrial grade caustic soda flakes, purity not less than 98.5%.

[0043] Yttrium oxide powder: Ganzhou Jiayuan New Materials Co., Ltd., with a purity of not less than 99.9% and an average particle size of not more than 5 micrometers.

[0044] Alumina powder: Yangzhou Zhongtianli New Material Co., Ltd., high-purity alumina powder, with a purity of not less than 99.9% and an average particle size of not more than 5 micrometers.

[0045] Corn starch: Shanghai Dinghe Biotechnology Co., Ltd., food grade, packaged in 25 kg bags.

[0046] Water glass: Foshan Zhongfa Water Glass Factory, industrial grade liquid sodium silicate, modulus 3.1 to 3.4, Baume degree not less than 40°Bé.

[0047] Lanthanum oxide: Ganzhou Gaosheng New Materials Co., Ltd., purity not less than 99.5%, industrial grade, average particle size not greater than 10 micrometers.

[0048] Cerium oxide: Ganzhou Gaosheng New Materials Co., Ltd., purity not less than 99.5%, industrial grade, average particle size not greater than 10 micrometers.

[0049] Yttrium oxide: Ganzhou Gaosheng New Materials Co., Ltd., purity not less than 99.5%, industrial grade, average particle size not greater than 10 micrometers.

[0050] The technical solution of this application is as follows:

[0051] A high-strength, heat-resistant porcelain clay, by mass parts, comprises 35-55 parts modified kaolin, 8-15 parts spodumene, 5-12 parts andalusite, 3-8 parts silane-modified nano-zirconia, 6-14 parts yttrium oxide-alumina composite powder, 2-5 parts surface-acidified silicon carbide whiskers, 3-6 parts pregelatinized starch binder, 2-4 parts water glass, and 1-3 parts rare earth oxide composite additives.

[0052] The method for preparing the modified kaolin includes the following steps: crushing natural kaolin ore to a particle size of less than 5 mm, soaking it in hydrochloric acid with a mass concentration of 15%-25% for 12-24 hours at a soaking temperature of 40℃-60℃, washing it with deionized water until neutral after soaking, filtering it, and calcining it at 650℃-750℃ for 1-2 hours. The calcined product is then pulverized by air jet milling to a D50 of 3μm-8μm to obtain modified kaolin.

[0053] The preparation method of the silane-modified nano-zirconia includes the following steps: dispersing nano-zirconia powder in anhydrous ethanol, ultrasonically dispersing for 20-40 minutes with an ultrasonic power of 200W-400W, then adding a silane coupling agent, refluxing and stirring at 65℃-85℃ for 2-4 hours, centrifuging after the reaction, washing three times with anhydrous ethanol, drying at 80℃-100℃ for 3-5 hours, and grinding to obtain silane-modified nano-zirconia.

[0054] The preparation method of the surface-acidified silicon carbide whiskers includes the following steps: immersing silicon carbide whiskers in an inorganic acid solution with a mass concentration of 10%-20%, stirring and soaking at 40℃-60℃ for 1h-3h, filtering, washing with deionized water until neutral, and drying at 100℃-120℃ for 2h-4h to obtain surface-acidified silicon carbide whiskers.

[0055] The preparation method of the pregelatinized starch binder includes the following steps: mixing corn starch and deionized water at a mass ratio of 1:3-1:5, stirring and heating to 80℃-95℃, maintaining the temperature and stirring for 20min-40min until complete gelatinization, then cooling to 50℃-60℃, drying under vacuum and pulverizing to obtain the pregelatinized starch binder.

[0056] The preparation method of the yttrium oxide-alumina composite powder includes the following steps: mixing yttrium oxide powder and alumina powder at a mass ratio of 1:4-1:10, adding deionized water and ball milling for 2-4 hours, spray drying, calcining at 1400℃-1600℃ for 2-4 hours, cooling and pulverizing to a D50 of 3μm-8μm to obtain yttrium oxide-alumina composite powder.

[0057] The rare earth oxide composite additive is composed of lanthanum oxide, cerium oxide and yttrium oxide in a mass ratio of 1:0.5:1.5-1:1:2.5; the mass ratio of spodumene to andalusite is 1.2:1-1.8:1.

[0058] This application also provides a method for preparing high-strength, heat-resistant kaolin, comprising the following steps:

[0059] S1. Weigh each raw material according to the mass fraction, put the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder into a ball mill, add 35-50 parts of water for wet ball milling, and the ball milling time is 4h-8h to obtain the basic slurry;

[0060] S2. Add the silane-modified nano-zirconia to the base slurry, continue ball milling for 1-3 hours, then add the pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix evenly to obtain a mixed slurry;

[0061] S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 30-60 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 48-72 hours.

[0062] S4. The aged mud is dehydrated by pressure filtration to a moisture content of 22%-26%, and then sent to a mud-powdering machine for vacuum mud-powdering.

[0063] S5. Press the kneaded clay material under a molding pressure of 25MPa-40MPa to obtain a green body.

[0064] S6. Dry the green body in a drying kiln at 80℃-110℃ for 4h-6h;

[0065] S7. The dried green body is sent into the kiln and sintered according to the set heating curve. The maximum sintering temperature is 1280℃-1350℃, the holding time is 1.5h-3h, and the green body is cooled to room temperature with the kiln to obtain high-strength heat-resistant ceramics.

[0066] In step S1, the rotational speed of the ball mill is 350 r / min-500 r / min, the ball-to-material mass ratio is 3:1-5:1, and the solid content of the slurry is 55%-65%.

[0067] In step S3, the ambient temperature for the aging process is 20℃-30℃, and the mud is turned over every 12 hours during the aging period.

[0068] In step S7, the parameters of the heating curve are set as follows:

[0069] The first stage is at room temperature -600℃, with a heating rate of 3℃ / min - 5℃ / min;

[0070] The second stage is 600℃-1000℃, with a heating rate of 2℃ / min-4℃ / min;

[0071] The third stage involves heating from 1000℃ to the maximum sintering temperature at a rate of 1.5℃ / min to 3℃ / min.

[0072] This invention utilizes the combined effects of modified kaolin, yttrium oxide-alumina composite powder, silane-modified nano-zirconia, and surface-acidified silicon carbide whiskers to construct a multi-scale reinforcing structure in the sintered ceramic green body. After acid washing and calcination activation, the modified kaolin exhibits reduced impurity content and increased reactivity, providing excellent forming properties and a solid foundation for sintering as a matrix material. The yttrium oxide-alumina composite powder, after pre-calcination, forms a structure containing a high-temperature stable phase, which can act as a skeletal reinforcing phase in the final sintered body, improving the material's strength retention and creep resistance at higher temperatures. The rare earth oxide composite additive, composed of lanthanum oxide, cerium oxide, and yttrium oxide in a specific ratio, promotes grain boundary migration, purifies grain boundaries, and regulates the microstructure during sintering, enabling the green body to achieve a uniform and fine microstructure at a suitable temperature, thus balancing high strength and heat resistance.

[0073] This invention utilizes silane-modified nano-zirconia and surface-acidified silicon carbide whiskers to create a cross-scale composite reinforcement system within the green body, thereby inhibiting the formation and propagation of microcracks at different levels and achieving a combined improvement in the strength and toughness of porcelain clay materials.

[0074] This invention, through step-by-step feeding and gentle mixing, avoids mechanical damage to silane-modified nano-zirconia and surface-acidified silicon carbide whiskers during high-intensity ball milling, thus ensuring the structural integrity of the functional components. Simultaneously, aging treatment makes the moisture distribution in the clay more uniform, promoting thorough wetting between the organic binder and inorganic particles, releasing mechanical stress introduced during the initial ball milling and clay preparation processes, and reducing the risk of deformation during subsequent firing. The vacuum clay preparation step effectively eliminates air bubbles trapped in the clay, reducing porosity after firing and preventing mechanical property degradation caused by stress concentration at the pore edges.

[0075] This invention improves firing stability and yield by setting a segmented heating sintering curve, allowing the green body to undergo different physicochemical changes at different temperature stages. In the low-temperature stage from room temperature to 600℃, a faster heating rate promotes the rapid removal of moisture and organic matter such as pregelatinized starch binders, reducing energy waste caused by prolonged low-temperature residence. In the medium-temperature stage from 600℃ to 1000℃, a moderate heating rate allows minerals such as andalusite sufficient time to complete crystal transformation and preliminary reactions, avoiding phase transformation stress concentration. In the high-temperature stage from 1000℃ to the maximum sintering temperature, a slower heating rate allows for smooth solid-phase reactions and liquid-phase sintering between the yttrium oxide-alumina composite powder and the surrounding matrix, preventing softening and deformation of the green body caused by rapid liquid phase formation due to sudden temperature increases. Meanwhile, in the yttrium oxide-alumina composite powder, yttrium oxide and alumina react at high temperature to form a high-melting-point compound. This compound can pin grain boundaries and inhibit abnormal grain growth, thereby broadening the sintering temperature range and enabling the green body to obtain a dense microstructure and stable dimensional accuracy in a wider range of sintering temperatures.

[0076] The present invention will be described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited to these examples. Unless otherwise specified, the chemical reagents and raw materials used in the following examples and comparative examples are all conventional commercially available products.

[0077] Example 1: Modified kaolin, silane-modified nano-zirconia, surface-acidified silicon carbide whiskers, pre-gelatinized starch binder, yttrium oxide-alumina composite powder, and rare earth oxide composite additives were prepared separately for later use.

[0078] Natural kaolin ore was crushed to a particle size of less than 5 mm, soaked in 25% hydrochloric acid for 18 h at a temperature of 40 °C, washed with deionized water until neutral after soaking, filtered, and calcined at 750 °C for 1.5 h. The calcined product was then pulverized by air jet milling to a D50 of 3 μm to obtain modified kaolin.

[0079] The nano-zirconia powder was dispersed in anhydrous ethanol and ultrasonically dispersed for 40 min at an ultrasonic power of 300 W. Then, a silane coupling agent was added, with the amount of silane coupling agent being 1.5% of the mass of the nano-zirconia. The mixture was refluxed and stirred at 85 °C for 3 h. After the reaction was completed, the mixture was centrifuged, washed three times with anhydrous ethanol, dried at 80 °C for 5 h, and ground to obtain silane-modified nano-zirconia.

[0080] Silicon carbide whiskers were immersed in a 15% inorganic acid solution and stirred at 60°C for 1 hour. After filtration, they were washed with deionized water until neutral and dried at 110°C for 2 hours to obtain surface-acidified silicon carbide whiskers.

[0081] Corn starch and deionized water were mixed at a mass ratio of 1:3, stirred and heated to 90°C, and stirred for 20 minutes until completely gelatinized. Then the mixture was cooled to 60°C, dried under vacuum and pulverized to obtain a pregelatinized starch binder.

[0082] Yttrium oxide powder and alumina powder were mixed at a mass ratio of 1:7, deionized water was added and the mixture was ball-milled for 2 hours. After spray drying, the mixture was calcined at 1600℃ for 3 hours, cooled and pulverized to a D50 of 3 μm to obtain yttrium oxide-alumina composite powder.

[0083] Lanthanum oxide, cerium oxide, and yttrium oxide were compounded in a mass ratio of 1:1:2.5 to obtain a rare earth oxide composite additive.

[0084] This embodiment describes a method for preparing high-strength, heat-resistant kaolin, comprising the following steps:

[0085] S1. Weigh the raw materials according to the following mass percentages: 55 parts modified kaolin, 11 parts spodumene, 5 parts andalusite, 8 parts silane-modified nano-zirconia, 10 parts yttrium oxide-alumina composite powder, 2 parts surface-acidified silicon carbide whiskers, 6 parts pregelatinized starch binder, 3 parts water glass, and 1 part rare earth oxide composite additive. The mass ratio of spodumene to andalusite is 1.5:1. Add the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder to a ball mill, add 35 parts water, and perform wet ball milling for 8 hours at a speed of 350 r / min. The ball-to-material mass ratio is 5:1, and the slurry solid content is 60%, yielding the basic slurry.

[0086] S2. Add silane-modified nano-zirconia to the base slurry, continue ball milling for 2 hours, then add pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix for 20 minutes to obtain mixed slurry.

[0087] S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 60 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 60 hours, the ambient temperature for aging treatment is 20℃, and the slurry is turned over once every 12 hours during the aging period.

[0088] S4. The aged mud is dehydrated by pressure filtration to a moisture content of 22%, and then sent to a mud-powdering machine for vacuum mud-powdering.

[0089] S5. Press the kneaded clay material into shape under a molding pressure of 40MPa to obtain a green body.

[0090] S6. Dry the green body in a drying kiln at 95°C for 4 hours.

[0091] S7. The dried green body is sent into the kiln and sintered according to the set heating curve. The heating rate from room temperature to 600℃ in the first stage is 5℃ / min, the heating rate from 600℃ to 1000℃ in the second stage is 3℃ / min, and the heating rate from 1000℃ to the maximum sintering temperature in the third stage is 1.5℃ / min. The maximum sintering temperature is 1350℃, the holding time is 2h, and the green body is cooled to room temperature in the furnace to obtain high-strength heat-resistant ceramic.

[0092] Example 2: In this example, the similarities with Example 1 will not be repeated, and the differences are as follows.

[0093] Natural kaolin ore was crushed to a particle size of less than 5 mm, soaked in 15% hydrochloric acid for 24 h at a temperature of 50 °C, washed with deionized water until neutral after soaking, filtered, and calcined at 650 °C for 2 h. The calcined product was then pulverized by air jet milling to a D50 of 5 μm to obtain modified kaolin.

[0094] The nano-zirconia powder was dispersed in anhydrous ethanol and ultrasonically dispersed for 20 min at an ultrasonic power of 400 W. Then, a silane coupling agent was added, with the amount of silane coupling agent being 2.5% of the mass of the nano-zirconia. The mixture was refluxed and stirred at 65 °C for 4 h. After the reaction was completed, the mixture was centrifuged, washed three times with anhydrous ethanol, dried at 90 °C for 3 h, and ground to obtain silane-modified nano-zirconia.

[0095] Silicon carbide whiskers were immersed in a 20% inorganic acid solution and stirred at 40°C for 2 hours. After filtration, they were washed with deionized water until neutral and dried at 120°C for 3 hours to obtain surface-acidified silicon carbide whiskers.

[0096] Corn starch and deionized water were mixed at a mass ratio of 1:5, stirred and heated to 95°C, and stirred for 30 minutes until completely gelatinized. Then the mixture was cooled to 50°C, dried under vacuum and pulverized to obtain a pregelatinized starch binder.

[0097] Yttrium oxide powder and alumina powder were mixed at a mass ratio of 1:4, deionized water was added and the mixture was ball-milled for 3 hours. After spray drying, the mixture was calcined at 1400℃ for 4 hours, cooled and pulverized to a D50 of 5 μm to obtain yttrium oxide-alumina composite powder.

[0098] Lanthanum oxide, cerium oxide, and yttrium oxide were compounded in a mass ratio of 1:0.75:2.0 to obtain a rare earth oxide composite additive.

[0099] This embodiment describes a method for preparing high-strength, heat-resistant kaolin, comprising the following steps:

[0100] S1. Weigh the raw materials according to the following mass percentages: 35 parts modified kaolin, 15 parts spodumene, 8 parts andalusite, 3 parts silane-modified nano-zirconia, 14 parts yttrium oxide-alumina composite powder, 3 parts surface-acidified silicon carbide whiskers, 3 parts pregelatinized starch binder, 4 parts water glass, and 2 parts rare earth oxide composite additives. The mass ratio of spodumene to andalusite is 1.8:1. Add the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder to a ball mill, add 42 parts water, and perform wet ball milling for 4 hours at a speed of 500 r / min. The ball-to-material mass ratio is 3:1, and the slurry solid content is 65%, yielding the basic slurry.

[0101] S2. Add silane-modified nano-zirconia to the base slurry, continue ball milling for 3 hours, then add pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix for 30 minutes to obtain mixed slurry.

[0102] S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 30 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 72 hours, the ambient temperature for aging treatment is 30℃, and the slurry is turned over once every 12 hours during the aging period.

[0103] S4. The aged mud is dehydrated by pressure filtration to a moisture content of 24%, and then sent to a mud-powdering machine for vacuum mud-powdering.

[0104] S5. Press the kneaded clay material into shape under a molding pressure of 25MPa to obtain a green body.

[0105] S6. Dry the green body in a drying kiln at 110℃ for 5 hours.

[0106] S7. The dried green body is sent into the kiln and sintered according to the set heating curve. The heating rate from room temperature to 600℃ in the first stage is 3℃ / min, the heating rate from 600℃ to 1000℃ in the second stage is 4℃ / min, and the heating rate from 1000℃ to the maximum sintering temperature in the third stage is 2℃ / min. The maximum sintering temperature is 1280℃, the holding time is 3h, and the green body is cooled to room temperature in the furnace to obtain high-strength heat-resistant ceramic.

[0107] Example 3: In this example, the similarities with Example 1 will not be repeated, and the differences are as follows.

[0108] Natural kaolin ore was crushed to a particle size of less than 5 mm, soaked in 20% hydrochloric acid for 12 h at a temperature of 60 °C, washed with deionized water until neutral after soaking, filtered, and calcined at 700 °C for 1 h. The calcined product was then pulverized by air jet milling to a D50 of 8 μm to obtain modified kaolin.

[0109] The nano-zirconia powder was dispersed in anhydrous ethanol and ultrasonically dispersed for 30 min at an ultrasonic power of 200 W. Then, a silane coupling agent was added at an amount of 4% of the mass of the nano-zirconia. The mixture was refluxed and stirred at 75 °C for 2 h. After the reaction was completed, the mixture was centrifuged, washed three times with anhydrous ethanol, dried at 100 °C for 4 h, and ground to obtain silane-modified nano-zirconia.

[0110] Silicon carbide whiskers were immersed in a 10% inorganic acid solution and stirred at 50°C for 3 hours. After filtration, they were washed with deionized water until neutral and dried at 100°C for 4 hours to obtain surface-acidified silicon carbide whiskers.

[0111] Corn starch and deionized water were mixed at a mass ratio of 1:4, stirred and heated to 80°C, and stirred for 40 minutes until completely gelatinized. Then the mixture was cooled to 55°C, dried under vacuum and pulverized to obtain a pregelatinized starch binder.

[0112] Yttrium oxide powder and alumina powder were mixed at a mass ratio of 1:10, deionized water was added and the mixture was ball-milled for 4 hours. After spray drying, the mixture was calcined at 1500℃ for 2 hours, cooled and pulverized to a D50 of 8 μm to obtain yttrium oxide-alumina composite powder.

[0113] Lanthanum oxide, cerium oxide, and yttrium oxide were compounded in a mass ratio of 1:0.75:2.0 to obtain a rare earth oxide composite additive.

[0114] This embodiment describes a method for preparing high-strength, heat-resistant kaolin, comprising the following steps:

[0115] S1. Weigh the raw materials according to the following mass percentages: 45 parts modified kaolin, 8 parts spodumene, 12 parts andalusite, 5 parts silane-modified nano-zirconia, 6 parts yttrium oxide-alumina composite powder, 5 parts surface-acidified silicon carbide whiskers, 4 parts pregelatinized starch binder, 2 parts water glass, and 3 parts rare earth oxide composite additives. The mass ratio of spodumene to andalusite is 1.2:1. Add the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder to a ball mill, add 50 parts water, and perform wet ball milling for 6 hours at a speed of 500 r / min. The ball-to-material mass ratio is 4:1, and the slurry solid content is 55%, yielding the basic slurry.

[0116] S2. Add silane-modified nano-zirconia to the base slurry, continue ball milling for 1 hour, then add pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix for 40 minutes to obtain mixed slurry.

[0117] S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 45 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 48 hours, the ambient temperature for aging treatment is 30℃, and the slurry is turned over once every 12 hours during the aging period.

[0118] S4. The aged mud is dehydrated by pressure filtration to a moisture content of 26%, and then sent to a mud-powdering machine for vacuum mud-powdering.

[0119] S5. Press the kneaded clay material into shape under a molding pressure of 32MPa to obtain a green body.

[0120] S6. Dry the green body in a drying kiln at 80°C for 6 hours.

[0121] S7. The dried green body is fed into the kiln and sintered according to the set heating curve. The heating rate from room temperature to 600℃ in the first stage is 4℃ / min, the heating rate from 600℃ to 1000℃ in the second stage is 2℃ / min, and the heating rate from 1000℃ to the maximum sintering temperature in the third stage is 3℃ / min. The maximum sintering temperature is 1320℃, and the holding time is 1.5h. The green body is then cooled to room temperature in the furnace to obtain a high-strength heat-resistant ceramic.

[0122] Comparative Example 1:

[0123] In this comparative example, the similarities with Example 1 will not be repeated. The differences are as follows: no surface-acidified silicon carbide whiskers were added, nor were silane-modified nano-zirconia added. The remaining raw materials and preparation steps are the same as in Example 1.

[0124] Comparative Example 2:

[0125] In this comparative example, the similarities with Example 2 will not be repeated. The differences are as follows: the modified kaolin was not subjected to acid washing and calcination activation treatment, and the powder after crushing of natural kaolin ore was used directly. In addition, the yttrium oxide-alumina composite powder was not pre-calcined at 1400℃ to 1600℃, but was directly mixed with alumina powder at a mass ratio of 1:10 before use. The remaining raw materials and preparation steps are the same as in Example 2.

[0126] Comparative Example 3:

[0127] In this comparative example, the similarities with Example 3 will not be repeated. The differences are as follows: the mass ratio of spodumene to andalusite is changed to 0.8:1, which exceeds the range of 1.2:1 to 1.8:1 specified in this application. In addition, only lanthanum oxide is used as the rare earth oxide composite additive, and it is not compounded with cerium oxide or yttrium oxide. The remaining raw materials and preparation steps are the same as in Example 3.

[0128] Comparative Example 4:

[0129] In this comparative example, the similarities with Example 1 will not be repeated. The differences are as follows: in step one, all raw materials are put into the ball mill at once for wet ball milling. The stepwise feeding method of first preparing the basic slurry and then adding the functional components is not followed. In addition, the heating curve of the sintering process is a uniform heating from room temperature to the highest sintering temperature, and the heating rate is constant at 5℃ / min. The other raw materials and preparation steps are the same as in Example 1.

[0130] Comparative Example 5:

[0131] In this comparative example, the similarities with Example 1 will not be repeated. The differences are as follows: no pregelatinized starch binder and water glass were added, and the aging time was shortened to 12 hours. The remaining raw materials and preparation steps are the same as in Example 1.

[0132] Performance test results and analysis:

[0133] The ceramic products obtained according to the parameters of the examples and comparative examples were subjected to performance tests. The test methods are as follows: the three-point bending method was used to determine the flexural strength; the top rod method was used to determine the average coefficient of thermal expansion in the range of room temperature to 1000℃; the air-cooling method was used to determine the thermal shock resistance, that is, the fired ceramic products were heated to 800℃ and held at that temperature for 15 minutes, then removed and allowed to cool naturally to room temperature in air, and the number of cycles at which visible cracks or fractures appeared was recorded; the Archimedes displacement method was used to determine the bulk density and water absorption rate; and the linear dimensions before and after firing were measured with vernier calipers to calculate the firing shrinkage rate. The specific test results are shown in Table 1.

[0134] Table 1 Analysis of test results:

[0135]

[0136] Test results show that the flexural strength of all three embodiments reached over 82 MPa, and the coefficient of thermal expansion was controlled within 2.0 × 10⁻⁶. -6 / ℃-2.3×10 -6 Within a temperature range of / ℃, the thermal shock resistance exceeds 42 cycles, the bulk density is higher than 2.42 g / cm³, the water absorption rate is lower than 0.18%, and the firing shrinkage rate is lower than 8.8%. This invention utilizes the interaction of modified kaolin, yttrium oxide-alumina composite powder, silane-modified nano-zirconia, and surface-acidified silicon carbide whiskers, combined with a stepwise feeding and segmented heating process, to prepare ceramic products with high strength and low thermal expansion.

[0137] Compared to Example 1, Comparative Example 1, without the addition of surface-acidified silicon carbide whiskers and silane-modified nano-zirconia, exhibited a flexural strength reduced to 55 MPa, approximately 35% lower than that of Example 1, while its coefficient of thermal expansion increased to 2.8 × 10⁻⁶. -6 The temperature was similar to that of Example 1, and the thermal shock resistance cycle was only 25 cycles. After treatment with inorganic acid solution, the number of surface active hydroxyl groups of silicon carbide whiskers increased, and the interfacial bonding with the ceramic matrix was enhanced. Under stress, the fracture energy was consumed through whisker pull-out and bridging. Silane-modified nano-zirconia, through treatment with silane coupling agent, improved its dispersibility in the slurry and exerted dispersion strengthening and phase transformation toughening effects in the sintered body. Without these two components, there was a lack of effective crack propagation inhibition mechanisms inside the green body, and the mechanical properties and thermal stability were significantly reduced, while the coefficient of thermal expansion remained at a low level due to the lack of a high-expansion reinforcing phase.

[0138] Compared to Example 2, Comparative Example 2, which did not undergo acid washing and calcination activation, and whose yttrium oxide-alumina composite powder was not pre-calcined, exhibited a flexural strength of 60 MPa, a bulk density of only 2.28 g / cm³, a water absorption rate as high as 0.92%, and a firing shrinkage rate of 10.2%. When natural kaolin ore is untreated, impurities such as quartz and mica it contains can form low-melting-point liquid or gas phases during firing, interfering with the densification process. Simultaneously, unactivated flaky kaolinite particles have low reactivity and insufficient sintering driving force. Since the yttrium oxide-alumina composite powder was not pre-calcined at 1400°C to 1600°C, the yttrium oxide and alumina did not fully react to form the yttrium aluminum garnet phase. During final sintering, the in-situ reaction generated a large volume effect and localized stress, leading to microcracks and pores inside the green body. Therefore, the density and strength of Comparative Example 2 are lower than those of Example 2, illustrating the necessity of modified kaolin and pre-fired composite powder for forming a uniform and fine microstructure.

[0139] Compared with Example 3, Comparative Example 3 changed the mass ratio of spodumene to andalusite to 0.8:1, and used only lanthanum oxide as the rare earth oxide composite additive, which has a high coefficient of thermal expansion of 3.0 × 10⁻⁶.-6 The temperature was / ℃, and the thermal shock resistance cycle was only 22 times, with a firing shrinkage rate of 10.5%. When the spodumene content was too low relative to andalusite, the offsetting effect of the low-expansion spodumene mineral on the thermal expansion of the matrix was weakened. At the same time, the micro-volume expansion of andalusite during the mullite-forming process did not receive sufficient liquid-phase buffering, resulting in expansion stress inside the green body. A single lanthanum oxide additive could not synergistically regulate grain boundary migration and liquid phase viscosity during sintering as it could with a combination of lanthanum oxide, cerium oxide, and yttrium oxide. This resulted in uneven grain growth and insufficient removal of pores, thus deteriorating thermal stability and dimensional accuracy.

[0140] Compared to Example 1, Comparative Example 4 involved wet ball milling of all raw materials in a single batch, with a constant heating rate of 5°C / min from room temperature to the maximum temperature during sintering. The resulting material exhibited a flexural strength of 62 MPa, a water absorption rate of 0.78%, and a thermal shock resistance of 30 cycles. This single-batch ball milling subjected the silane-modified nano-zirconia and surface-acidified silicon carbide whiskers to prolonged and intense mechanical shearing and impact. The silane coupling agent coating peeled off the nano-zirconia surface, and the silicon carbide whiskers were ground and broken, losing their original reinforcing morphology and interfacial activity. Uniform heating failed to remove moisture and organic matter in time at the low-temperature stage, and did not provide sufficient time for the crystal transformation of andalusite at the medium-temperature stage. Furthermore, the rapid formation of the liquid phase at the high-temperature stage led to deformation and cracking of the green body. Therefore, the performance degradation of Comparative Example 4 demonstrates that step-by-step feeding and segmented heating are not simply adjustments to the process sequence, but crucial measures to ensure the structural integrity of functional components and the stability of sintering.

[0141] Compared to Example 1, Comparative Example 5, which lacked pregelatinized starch binder and water glass, and had a shortened aging time of 12 hours, exhibited a flexural strength of only 52 MPa, a bulk density of 2.25 g / cm³, a water absorption rate as high as 1.05%, and a firing shrinkage rate of 11.0%. Pregelatinized starch binder and water glass provide temporary bonding during the green body stage. Without these two components, the green body is prone to defects such as edge chipping and corner breakage during handling and drying, and the interparticle bonding is loose, leading to increased porosity after firing. Insufficient aging time prevents sufficient homogenization of moisture in the clay, resulting in inadequate wetting of the organic binder and inorganic particles. The mechanical stress introduced during the initial ball milling and clay refining processes is not released, leading to increased deformation and cracking tendencies during firing. Comparative Example 5, from the opposite perspective, verifies the crucial role of pregelatinized starch binder, water glass, and sufficient aging time in ensuring the quality of the green body and the density of the final product.

[0142] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-strength, heat-resistant kaolin, characterized in that: By mass, it includes 35-55 parts modified kaolin, 8-15 parts spodumene, 5-12 parts andalusite, 3-8 parts silane-modified nano-zirconia, 6-14 parts yttrium oxide-alumina composite powder, 2-5 parts surface-acidified silicon carbide whiskers, 3-6 parts pregelatinized starch binder, 2-4 parts water glass, and 1-3 parts rare earth oxide composite additives.

2. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The preparation method of the modified kaolin includes the following steps: crushing the natural kaolin ore to a particle size of less than 5 mm, soaking it in hydrochloric acid with a mass concentration of 15%-25% for 12-24 hours at a soaking temperature of 40℃-60℃, washing it with deionized water until neutral after soaking, filtering it, and calcining it at 650℃-750℃ for 1-2 hours. The calcined product is then pulverized by air jet milling to a D50 of 3μm-8μm to obtain modified kaolin.

3. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The preparation method of the silane-modified nano-zirconia includes the following steps: dispersing nano-zirconia powder in anhydrous ethanol, ultrasonically dispersing for 20-40 minutes with an ultrasonic power of 200W-400W, then adding silane coupling agent, refluxing and stirring at 65℃-85℃ for 2-4 hours, centrifuging after the reaction, washing three times with anhydrous ethanol, drying at 80℃-100℃ for 3-5 hours, and grinding to obtain silane-modified nano-zirconia.

4. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The preparation method of the surface-acidified silicon carbide whiskers includes the following steps: immersing silicon carbide whiskers in an inorganic acid solution with a mass concentration of 10%-20%, stirring and soaking at 40℃-60℃ for 1h-3h, filtering, washing with deionized water until neutral, and drying at 100℃-120℃ for 2h-4h to obtain surface-acidified silicon carbide whiskers.

5. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The preparation method of the pregelatinized starch binder includes the following steps: mixing corn starch and deionized water at a mass ratio of 1:3-1:5, stirring and heating to 80℃-95℃, maintaining the temperature and stirring for 20min-40min until complete gelatinization, then cooling to 50℃-60℃, drying under vacuum and pulverizing to obtain the pregelatinized starch binder.

6. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The preparation method of the yttrium oxide-alumina composite powder includes the following steps: mixing yttrium oxide powder and alumina powder at a mass ratio of 1:4-1:10, adding deionized water and ball milling for 2-4 hours, spray drying, calcining at 1400℃-1600℃ for 2-4 hours, cooling and pulverizing to a D50 of 3μm-8μm to obtain yttrium oxide-alumina composite powder.

7. The high-strength, heat-resistant kaolin according to claim 1, characterized in that, The rare earth oxide composite additive is composed of lanthanum oxide, cerium oxide and yttrium oxide in a mass ratio of 1:0.5:1.5-1:1:2.5; the mass ratio of spodumene to andalusite is 1.2:1-1.8:

1.

8. A method for preparing a high-strength, heat-resistant kaolin, used to prepare the high-strength, heat-resistant kaolin as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Weigh each raw material according to the mass fraction, put the modified kaolin, spodumene, andalusite, and yttrium oxide-alumina composite powder into a ball mill, add 35-50 parts of water for wet ball milling, and the ball milling time is 4h-8h to obtain the basic slurry; S2. Add the silane-modified nano-zirconia to the base slurry, continue ball milling for 1-3 hours, then add the pregelatinized starch binder, water glass and rare earth oxide composite additive, stir and mix evenly to obtain a mixed slurry; S3. Add surface-acidified silicon carbide whiskers to the mixed slurry, stir and mix for 30-60 minutes, then pass through a 180-mesh sieve and transfer to an aging tank for aging treatment. The aging time is 48-72 hours. S4. The aged mud is dehydrated by pressure filtration to a moisture content of 22%-26%, and then sent to a mud-powdering machine for vacuum mud-powdering. S5. Press the kneaded clay material under a molding pressure of 25MPa-40MPa to obtain a green body. S6. Dry the green body in a drying kiln at 80℃-110℃ for 4h-6h; S7. The dried green body is sent into the kiln and sintered according to the set heating curve. The maximum sintering temperature is 1280℃-1350℃, the holding time is 1.5h-3h, and the green body is cooled to room temperature with the kiln to obtain high-strength heat-resistant ceramics.

9. The method for preparing a high-strength, heat-resistant kaolin according to claim 8, characterized in that: In step S1, the rotational speed of the ball mill is 350 r / min-500 r / min, the ball-to-material mass ratio is 3:1-5:1, and the solid content of the slurry is 55%-65%. In step S3, the ambient temperature for the aging process is 20℃-30℃, and the mud is turned over every 12 hours during the aging period.

10. The method for preparing a high-strength, heat-resistant kaolin according to claim 8, characterized in that: In step S7, the parameters of the heating curve are set as follows: The first stage is at room temperature -600℃, with a heating rate of 3℃ / min - 5℃ / min; The second stage is 600℃-1000℃, with a heating rate of 2℃ / min-4℃ / min; The third stage involves heating from 1000℃ to the maximum sintering temperature at a rate of 1.5℃ / min to 3℃ / min.

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