Preparation method of anti-corrosion high-temperature-resistant special ceramic

Abstract

The invention relates to the technical field of special ceramics, in particular to a preparation method of anti-corrosion and high-temperature-resistant special ceramics. The preparation method of the anti-corrosion high-temperature-resistant special ceramic comprises the following steps: weighing ceramic powder according to the weight ratio of 85-90% of alpha-alumina powder and 10-15% of talc, carrying out dry ball milling to obtain ball-milled powder, and mixing the ball-milled powder with lanthanum yttrium modified phenolic resin to obtain a ceramic mixture; the lanthanum-yttrium modified phenolic resin is obtained by mixing and modifying a phenolic resin prepolymer by using lanthanum-yttrium hydroxide prepared by a hydrothermal method and melamine. The prepared special ceramic has high strength, thermal shock resistance, thermal stability, corrosion resistance and toughness and is excellent in comprehensive performance, and a green body is prepared from the ceramic mixture through injection molding, and then the special ceramic is obtained through sintering.

Description

Technical Field

[0001] The present invention relates to the technical field of special ceramics, and particularly relates to a preparation method of an anti-corrosion and high-temperature-resistant special ceramic. Background Art

[0002] Traditional metal materials will soften under high-temperature conditions and generally have poor corrosion resistance, which limits the application of metal materials under high-temperature corrosive working conditions. Special ceramics are new ceramics formed by high-temperature sintering of selected raw materials. Special ceramics such as silicon nitride, silicon carbide, and alumina have better anti-corrosion and high-temperature resistance characteristics compared with metal materials and can be stably used in high-temperature and corrosive media for a long time. Compared with silicon nitride and silicon carbide, alumina raw materials are easy to prepare and have low prices, making alumina ceramics widely used in the fields of aerospace, energy, electric power, mechanical manufacturing, electronic devices, etc. Alumina special ceramics are special ceramic materials mainly composed of α-alumina, which have anti-corrosion, chemical thermal stability, and high strength. However, alumina ceramic materials have the problems of high brittleness and poor thermal shock resistance, and are prone to cracking and fracture during use and preparation. In addition, the sintering temperature of alumina ceramics exceeds 1600°C, making it difficult to process and form, which limits its application.

[0003] Adding sintering aids is an important measure to reduce the sintering temperature of alumina special ceramics and improve the insufficient thermal shock resistance of the materials. However, during the addition of some sintering aids, due to poor raw material selection and process control, defects such as poor mixing degree between ceramic raw materials, abnormal grain growth, and more sintering pores often occur, resulting in limited improvement effect of sintering aids on the thermal shock resistance of special ceramic materials and having an adverse impact on the material strength, thermal stability, and corrosion resistance.

[0004] Based on this, the present application aims to propose a preparation method of an anti-corrosion and high-temperature-resistant special ceramic. It is very necessary to use alumina as the ceramic base material, optimize the sintering aids and raw materials, and obtain high-performance special ceramics with high strength, thermal shock resistance, thermal stability, and anti-corrosion through preparation process control. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of an anti-corrosion and high-temperature-resistant special ceramic. The prepared special ceramic has high strength, thermal shock resistance, thermal stability, anti-corrosion property, and toughness, and has excellent comprehensive performance.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The present application provides a preparation method of an anti-corrosion and high-temperature-resistant special ceramic, including the following steps: S1. Weighing ceramic powder in a weight ratio of 85% to 90% α-alumina powder and 10% to 15% talc, dry-milling the obtained ball-milled powder, and mixing the ball-milled powder with lanthanum-yttrium-modified phenolic resin to obtain a ceramic mixture; The preparation method of lanthanum-yttrium modified phenolic resin comprises the following steps: (1) Preparation of lanthanum yttrium hydroxide: prepare lanthanum nitrate and yttrium nitrate solutions respectively, mix them in a molar ratio of lanthanum to yttrium of 4 to 5:1 to obtain a mixed salt solution, adjust the pH to alkaline, and then ultrasonicate the solution. Transfer the solution into a closed reactor for hydrothermal reaction, filter, and wash with water until neutral to obtain lanthanum yttrium hydroxide for later use. (2) Preparation of phenolic resin prepolymer: Phenol and formaldehyde solution are mixed and reacted under alkaline conditions to obtain phenolic resin prepolymer; (3) adding the lanthanum yttrium hydroxide prepared in step (1) to the phenolic resin prepolymer prepared in step (2), and then adding melamine, formaldehyde solution and triethanolamine, reacting under alkaline conditions, and removing unreacted raw materials under reduced pressure after the reaction is completed to obtain a lanthanum yttrium modified phenolic resin; S2. The ceramic mixture is prepared into a green body by injection molding, and then sintered.

[0007] Furthermore, the particle size D of the α-alumina powder in S1 50 1 μm; the particle size of talc D 50 3μm.

[0008] Furthermore, S1 further includes adding 0.5% to 0.8% of a ball milling aid by weight of the ceramic powder to the ceramic powder before dry ball milling, wherein the ball milling aid is selected from at least one of stearic acid, polyvinyl pyrrolidone and polyacrylamide; In the dry ball milling method, the ball-to-material ratio is 2 to 3:1, the ball milling speed is 60 rpm to 100 rpm, and the ball milling time is 6 hours to 8 hours.

[0009] Furthermore, the preparation method of the lanthanum-yttrium modified phenolic resin in S1 is: (1) Preparation of lanthanum yttrium hydroxide: prepare 0.2 mol / L lanthanum nitrate and 0.2 mol / L yttrium nitrate solution respectively, mix them in a molar ratio of lanthanum to yttrium of 4 to 5:1 to obtain a mixed salt solution, add 1% polyacrylic acid as a dispersant to the mixed salt solution, add ammonia water dropwise to adjust the pH to 9.5, and then ultrasonically treat for 30 minutes, carry out hydrothermal reaction at 100°C to 120°C in a closed reactor for 12 hours, filter and wash with water until neutral, to obtain lanthanum yttrium hydroxide, which is set aside; (2) Preparation of phenolic resin prepolymer: Mix phenol and formaldehyde solution with a concentration of 35% - 40%, add ammonia water dropwise to adjust the pH to 9, and react at 60°C - 70°C for 0.5 h - 1 h to obtain the phenolic resin prepolymer; (3) Add the lanthanum-yttrium hydroxide prepared in step (1) to the phenolic resin prepolymer prepared in step (2), then add melamine, formaldehyde solution with a concentration of 37%, and triethanolamine, adjust the pH to 9 with ammonia water, stir and react at 80°C for 15 min, and remove the unreacted raw materials under reduced pressure after the reaction to obtain lanthanum-yttrium modified phenolic resin.

[0010] Further, in step (2), the molar ratio of phenol to formaldehyde in the phenol and formaldehyde solution is added according to 1:1.4; In step (3), the molar ratio of melamine, triethanolamine to phenol in step (2) is 0.1 - 0.2:0.001 - 0.002:1; the molar ratio of melamine to formaldehyde in the melamine and formaldehyde solution in step (3) is 1:1.2 - 1.3.

[0011] Further, in step (3), the lanthanum-yttrium hydroxide is 12% - 18% of the weight of the lanthanum-yttrium modified phenolic resin.

[0012] Further, in S1, the lanthanum-yttrium modified phenolic resin is 5% - 10% of the weight of the ceramic powder in S1.

[0013] Further, in S2, the injection molding method is to inject the ceramic mixture into the mold by an injection machine at 100 MPa - 110 MPa, and mold at a temperature of 170°C - 180°C and a pressure of 80 MPa - 85 MPa.

[0014] Further, in S2, the sintering method is to place the green body into the sintering furnace cavity, evacuate, heat up to 650°C at a rate of 3°C / min, hold for 4.5 h, heat up to 1350°C - 1380°C at a rate of 7°C / min, hold for 5 h - 6 h, then heat up to 1500°C - 1550°C at a rate of 7°C / min, fill nitrogen to a pressure of 15 MPa - 17 MPa at this temperature, hold for 1.5 h, and cool down to room temperature at a rate of 3°C / min.

[0015] Further, S2 also includes polishing the sintered special ceramic. The polishing method is to polish the sintered ceramic with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The present invention uses α-aluminum oxide powder as the main raw material of special ceramics, compounded with talc and lanthanum yttrium hydroxide as a sintering aid. Talc as a sintering aid can effectively reduce the sintering temperature of special ceramics, refine the grains, improve the density and flexural strength of the ceramic structure, and improve the fluidity and dispersibility of the ball-milled powder, facilitating subsequent shaping and sintering. Lanthanum yttrium hydroxide prepared by the hydrothermal method and melamine are used to mix and modify the phenolic resin prepolymer to make lanthanum yttrium modified phenolic resin. Soluble nitrates are used as raw materials to prepare lanthanum yttrium hydroxide colloidal particles with fine particle size by the hydrothermal method. Through the hydrogen bond combination between the active amino group in the melamine structure and the hydroxyl group in the lanthanum yttrium hydroxide, the lanthanum yttrium hydroxide can be combined and dispersed in the resin. Then, with the help of the mixing of phenolic resin and ball-milled powder, the lanthanum yttrium hydroxide forms good dispersion in the ball-milled powder. Lanthanum hydroxide and yttrium hydroxide are used as sintering aids. During the sintering process, they can be in-situ decomposed into lanthanum oxide and yttrium oxide. With good dispersion uniformity and fine particle size, they play a role in filling the sintering holes and cracks. Combining the sintering process and parameters, the densification of the sintered body can be increased, and the toughness and strength can be improved. Lanthanum oxide can also react with talc to further reduce the sintering temperature, inhibit the abnormal growth of alumina grains, and improve the strength and toughness of the ceramic. Yttrium oxide particles can synergistically improve the fracture toughness and crack resistance of the material.

[0017] In the preparation method of special ceramics in the present invention, after α-aluminum oxide powder and talc are fully mixed by dry grinding method, lanthanum yttrium modified phenolic resin is added and fully mixed, then injection molding is carried out and sintered, and the specific sintering process parameters are optimized and controlled, so that high-performance special ceramics with high strength, thermal shock resistance, thermal stability, corrosion resistance and toughness can be prepared. Detailed implementation mode

[0018] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention.

[0019] Unless otherwise specified, the methods described are all conventional methods, and the raw materials described can all be obtained from public commercial channels unless otherwise specified.

[0020] Example 1 This example provides a preparation method of anti-corrosion and high-temperature resistant special ceramics, including the following steps: 1. According to 85% of α-aluminum oxide powder (D 50 is 1μm), talc (D 50Ceramic powder (15% of 3μm) was weighed and added into a planetary ball mill, and then 0.5% stearic acid was added to the ceramic powder. Ball-milled powder was obtained after dry ball milling. The ball-to-material ratio used in the ball milling was 3:1, the ball milling speed was 100 rpm, and the ball milling time was 6 h. 2. Take 8% of the weight of the ceramic powder of lanthanum yttrium hydroxide modified phenolic resin, stir and mix the ball mill powder and lanthanum yttrium modified phenolic resin in a high-speed mixer to obtain a ceramic mixture, and stir at a speed of 500 rpm for 30 minutes. The preparation method of lanthanum yttrium modified phenolic resin is as follows: (1) Preparation of lanthanum yttrium hydroxide: 0.2 mol / L lanthanum nitrate and 0.2 mol / L yttrium nitrate solution were prepared respectively, and mixed in a molar ratio of lanthanum to yttrium of 5:1 to obtain a mixed salt solution, and then 1% by weight of polyacrylic acid of the mixed salt solution was added as a dispersant, 28% ammonia water was added dropwise to adjust the pH to 9.5, and then ultrasonically treated for 30 minutes, and transferred to a closed reactor for hydrothermal reaction at 100°C for 12 hours to obtain lanthanum yttrium hydroxide, which was filtered and washed with water until neutral, and set aside; (2) Preparation of phenolic resin prepolymer: Phenol and 37% formaldehyde solution were mixed according to the molar ratio of phenol to formaldehyde of 1:1.4, 28% ammonia water was added dropwise to adjust the pH to 9, and the mixture was reacted at 60°C for 1 hour to obtain a phenolic resin prepolymer; (3) Adding lanthanum yttrium hydroxide to the obtained phenolic resin prepolymer, and then adding melamine, 37% formaldehyde solution and triethanolamine (the molar ratio of melamine, triethanolamine and phenol in step (2) is 0.1:0.001:1; the molar ratio of melamine in step (3) and melamine to formaldehyde in the formaldehyde solution in step (3) is 1:1.3), adjusting the pH to 9 with 28% ammonia water, stirring and reacting at 80°C for 15 minutes, and removing unreacted raw materials under reduced pressure after the reaction is completed to obtain a lanthanum yttrium modified phenolic resin, wherein the lanthanum yttrium hydroxide (dry basis) is 15% of the weight of the lanthanum yttrium modified phenolic resin.

[0021] 3. The ceramic mixture is injected into the mold using an injection molding machine at 100 MPa and formed at a temperature of 180°C and a pressure of 80 MPa to prepare a green body; 4. Place the green body in the sintering furnace chamber, evacuate to a vacuum degree of less than 0.01Pa, heat up to 650℃ at a rate of 3℃ / min, hold for 4.5h, heat up to 1350℃ at a rate of 7℃ / min, hold for 6h, then heat up to 1500℃ at a rate of 7℃ / min, fill with nitrogen to a pressure of 17MPa at this temperature, hold for 1h, and cool down to room temperature at a rate of 3℃ / min; 5. Polish the sintered special ceramics with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface.

[0022] Example 2 This example provides a preparation method of an anti-corrosion and high-temperature resistant special ceramic, which includes the following steps: 1. Weigh ceramic powder materials according to the ratio of 90% α-aluminum oxide powder (D 50 is 1 μm) and 10% talc (D 50 is 3 μm), add them into a planetary ball mill, and then add 0.8% stearic acid of the ceramic powder materials. After dry ball milling, ball-milled powder materials are obtained. The ball-to-material ratio used for ball milling is 3:1, the ball milling speed is 100 rpm, and the ball milling time is 6 h; 2. Take 10% of lanthanum-yttrium hydroxide modified phenolic resin by the weight of the ceramic powder materials. Stir and mix the ball-milled powder materials and the lanthanum-yttrium modified phenolic resin in a high-speed mixer to obtain ceramic mixture materials. The mixing is carried out at a stirring speed of 500 rpm for 30 min. The preparation method of the lanthanum-yttrium modified phenolic resin is as follows: (1) Preparation of lanthanum-yttrium hydroxide: Prepare 0.2 mol / L lanthanum nitrate solution and 0.2 mol / L yttrium nitrate solution respectively. After mixing them according to the molar ratio of lanthanum to yttrium of 5:1 to obtain a mixed salt solution, add 1% by weight of polyacrylic acid as a dispersant to it, adjust the pH to 9.5 by dropping 28% ammonia water, and then carry out ultrasonic treatment for 30 minutes. Transfer it into a sealed reaction kettle and carry out hydrothermal reaction at 100 °C for 12 h to obtain lanthanum-yttrium hydroxide. After filtration, wash it with water until it is neutral and reserve it; (2) Preparation of phenolic resin prepolymer: Mix phenol and 37% formaldehyde solution according to the molar ratio of phenol to formaldehyde of 1:1.4, drop 28% ammonia water to adjust the pH to 9, and react at 60 °C for 1 h to obtain a phenolic resin prepolymer; (3) Add lanthanum-yttrium hydroxide to the obtained phenolic resin prepolymer, and then add melamine, 37% formaldehyde solution and triethanolamine (the molar ratio of melamine, triethanolamine and phenol in step (2) is 0.1:0.001:1; the molar ratio of melamine and formaldehyde in step (3) melamine and step (3) formaldehyde solution is 1:1.3). After adding, adjust the pH to 9 by using 28% ammonia water, stir and react at 80 °C for 15 min. After the reaction is completed, remove the unreacted raw materials under reduced pressure to obtain lanthanum-yttrium modified phenolic resin. The lanthanum-yttrium hydroxide (dry basis) is 18% of the weight of the lanthanum-yttrium modified phenolic resin.

[0023] 3. Inject the ceramic mixture materials into a mold by an injection machine at 100 MPa, and form a green body at a temperature of 180 °C and a pressure of 80 MPa; 4. Place the green body into the sintering furnace chamber, evacuate to a vacuum degree less than 0.01 Pa, heat it up to 650 °C at a rate of 3 °C / min, hold for 4.5 h, heat it up to 1380 °C at a rate of 7 °C / min, hold for 5 h, then heat it up to 1550 °C at a rate of 7 °C / min, fill nitrogen into it at this temperature until the pressure reaches 15 MPa, hold for 1.5 h, and cool it down to room temperature at a rate of 3 °C / min; 5. Polish the sintered special ceramic with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface, thus obtaining the product.

[0024] Example 3 This example provides a preparation method of an anti-corrosion and high-temperature resistant special ceramic, which includes the following steps: 1. Weigh ceramic powder materials according to the ratio of 85% of α-aluminum oxide powder (D 50 is 1 μm) and 15% of talc (D 50 is 3 μm), add them into a planetary ball mill, and then add 0.5% of stearic acid based on the weight of the ceramic powder materials. After dry ball milling, ball-milled powder materials are obtained. The ball-to-material ratio used for ball milling is 2:1, the ball milling speed is 60 rpm, and the ball milling time is 8 h; 2. Take 5% of lanthanum-yttrium hydroxide modified phenolic resin based on the weight of the ceramic powder materials. Stir and mix the ball-milled powder materials and the lanthanum-yttrium modified phenolic resin in a high-speed mixer to obtain ceramic mixture materials. Stir at a speed of 500 rpm for 30 min. The preparation method of the lanthanum-yttrium modified phenolic resin is as follows: (1) Preparation of lanthanum-yttrium hydroxide: Prepare 0.2 mol / L lanthanum nitrate solution and 0.2 mol / L yttrium nitrate solution respectively. After mixing them according to the molar ratio of lanthanum and yttrium being 4:1, a mixed salt solution is obtained. Then add 1% by weight of polyacrylic acid as a dispersant to it, adjust the pH to 9.5 by dropping 28% ammonia water, and then perform ultrasonic treatment for 30 minutes. Transfer it into a sealed reaction kettle and carry out hydrothermal reaction at 100 °C for 12 h to obtain lanthanum-yttrium hydroxide. After filtration, wash it with water until it is neutral and reserve it for use; (2) Preparation of phenolic resin prepolymer: Mix phenol and 37% formaldehyde solution according to the molar ratio of phenol and formaldehyde being 1:1.4, adjust the pH to 9 by dropping 28% ammonia water, and react at 60 °C for 1 h to obtain the phenolic resin prepolymer; (3) Add lanthanum-yttrium hydroxide to the obtained phenolic resin prepolymer, then add melamine, 37% formaldehyde solution and triethanolamine (the molar ratio of melamine, triethanolamine to phenol in step (2) is 0.1:0.001:1; the molar ratio of melamine to formaldehyde in step (3) melamine and formaldehyde solution in step (3) is 1:1.3). After adding, adjust the pH to 9 with 28% ammonia water, stir and react at 80 °C for 15 min. After the reaction, unreacted raw materials are removed under reduced pressure to obtain lanthanum-yttrium modified phenolic resin. Lanthanum-yttrium hydroxide (dry basis) is 12% of the weight of lanthanum-yttrium modified phenolic resin.

[0025] 3. Inject the ceramic mixture into the mold with an injection machine at 100 MPa, and form a green body at a temperature of 180 °C and a pressure of 80 MPa; 4. Place the green body into the sintering furnace cavity, evacuate to a vacuum degree less than 0.01 Pa, heat up to 65 °C at a rate of 3 °C / min, hold for 4.5 h, heat up to 1350 °C at a rate of 7 °C / min, hold for 6 h, then heat up to 1500 °C at a rate of 7 °C / min. At this temperature, fill nitrogen until the pressure is 17 MPa, hold for 1 h, and cool down to room temperature at a rate of 3 °C / min; 5. Polish the sintered special ceramic with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface, and then it is obtained.

[0026] Example 4 This example provides a preparation method of an anti-corrosion and high-temperature resistant special ceramic, including the following steps: 1. Weigh ceramic powder according to the ratio of 85% α-aluminum oxide powder (D 50 is 1 μm) and 15% talc (D 50 is 3 μm), add it to a planetary ball mill, and then add 0.5% stearic acid of the ceramic powder. After dry ball milling, ball milled powder is obtained. The ball-to-powder ratio used for ball milling is 3:1, the ball milling speed is 100 rpm, and the ball milling time is 6 h; 2. Take 7% of the lanthanum-yttrium hydroxide modified phenolic resin by weight of the ceramic powder. Stir and mix the ball milled powder and the lanthanum-yttrium modified phenolic resin in a high-speed mixer to obtain a ceramic mixture. The mixing speed is 500 rpm and the mixing time is 30 min. The preparation method of the lanthanum-yttrium modified phenolic resin is: (1)Preparation of lanthanum yttrium hydroxide: Prepare 0.2 mol / L lanthanum nitrate and 0.2 mol / L yttrium nitrate solutions respectively. Mix them according to the molar ratio of lanthanum to yttrium of 5:1 to obtain a mixed salt solution. Then add 1% by weight of polyacrylic acid as a dispersant to the mixed salt solution. Dropwise add 28% ammonia water to adjust the pH to 9.5, and then perform ultrasonic treatment for 30 minutes. Transfer it to a sealed reaction kettle and carry out hydrothermal reaction at 120 °C for 12 h to obtain lanthanum yttrium hydroxide. After filtration, wash it with water until neutral and set aside; (2)Preparation of phenolic resin prepolymer: Mix phenol and 37% formaldehyde solution according to the molar ratio of phenol to formaldehyde of 1:1.4. Dropwise add 28% ammonia water to adjust the pH to 9, and react at 70 °C for 0.5 h to obtain a phenolic resin prepolymer; (3)Add lanthanum yttrium hydroxide to the obtained phenolic resin prepolymer, and then add melamine, 37% formaldehyde solution and triethanolamine (the molar ratio of melamine, triethanolamine to phenol in step (2) is 0.2:0.002:1; the molar ratio of melamine to formaldehyde in melamine and formaldehyde solution in step (3) is 1:1.2). After adding, adjust the pH to 9 with 28% ammonia water, stir and react at 80 °C for 15 min. After the reaction is completed, remove the unreacted raw materials under reduced pressure to obtain a lanthanum yttrium modified phenolic resin. The lanthanum yttrium hydroxide (dry basis) is 16% of the weight of the lanthanum yttrium modified phenolic resin.

[0027] 3. Inject the ceramic mixture into the mold by an injection machine at 110 MPa, and form a green body at a temperature of 170 °C and a pressure of 85 MPa; 4. Place the green body into the sintering furnace cavity, evacuate to a vacuum degree less than 0.01 Pa, heat up to 650 °C at a rate of 3 °C / min, hold for 4.5 h, heat up to 1350 °C at a rate of 7 °C / min, hold for 6 h, then heat up to 1500 °C at a rate of 7 °C / min. At this temperature, fill nitrogen until the pressure is 17 MPa, hold for 1 h, and cool down to room temperature at a rate of 3 °C / min; 5. Polish the sintered special ceramic with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface, thus obtaining the product.

[0028] Comparative Example 1 According to the method of Example 1, the difference is that the lanthanum yttrium modified phenolic resin is prepared as follows: (1)Preparation of phenolic resin prepolymer: Mix phenol and 37% formaldehyde solution according to the molar ratio of phenol to formaldehyde of 1:1.4. Dropwise add 28% ammonia water to adjust the pH to 9, and react at 60 °C for 1 h to obtain a phenolic resin prepolymer; (2) Melamine, 37% formaldehyde solution and triethanolamine were added to the obtained phenolic resin prepolymer (the molar ratio of melamine, triethanolamine to phenol in step (2) was 0.1:0.001:1; the molar ratio of melamine to formaldehyde in melamine and formaldehyde solution in step (3) was 1:1.3). After addition, 28% ammonia water was used to adjust the pH to 9, and the mixture was stirred at 80 °C for 15 min. After the reaction, the unreacted raw materials were removed under reduced pressure to obtain melamine-modified phenolic resin; (3) Lanthanum hydroxide and yttrium hydroxide (the molar ratio of lanthanum to yttrium was 5:1) were added to the melamine-modified phenolic resin, and the mixture was stirred and mixed at 300 rpm for 20 min to obtain lanthanum-yttrium-modified phenolic resin. Lanthanum hydroxide and yttrium hydroxide accounted for 15% of the weight of the lanthanum-yttrium-modified phenolic resin.

[0029] Comparative Example 2 This comparative example provides a method for preparing special ceramics, including the following steps: 1. Weigh ceramic powder in the ratio of 85% α-aluminum oxide powder (D 50 is 1 μm), 15% talc (D 50 is 3 μm) and add it to a planetary ball mill. Then, a mixture of lanthanum hydroxide and yttrium hydroxide accounting for 1.2% of the ceramic powder was added, in which the molar ratio of lanthanum to yttrium was 5:1. Then, 0.5% stearic acid of the ceramic powder was added, and dry ball milling was carried out to obtain ball-milled powder. The ball-to-powder ratio used for ball milling was 3:1, the ball milling speed was 100 rpm, and the ball milling time was 6 h; 2. Take 6.8% of the phenolic resin by weight of the ceramic powder. The ball-milled powder and the phenolic resin were stirred and mixed in a high-speed mixer to obtain a ceramic mixture. The stirring speed was 500 rpm and the mixing time was 30 min. The preparation method of the phenolic resin was: phenol and 37% formaldehyde solution were mixed according to the molar ratio of phenol to formaldehyde of 1:1.4, 28% ammonia water was added dropwise to adjust the pH to 9, and after reacting at 60 °C for 3 h, the phenolic resin was obtained. After the reaction, the unreacted raw materials were removed under reduced pressure.

[0030] 3. The ceramic mixture was injected into a mold by an injection machine at 100 MPa, and a green body was formed at a temperature of 180 °C and a pressure of 80 MPa; 4. The green body was placed in a sintering furnace cavity, the vacuum was pumped to a vacuum degree less than 0.01 Pa, and the temperature was raised to 650 °C at a rate of 3 °C / min, held for 4.5 h, then raised to 1350 °C at a rate of 7 °C / min, held for 6 h, and then raised to 1500 °C at a rate of 7 °C / min. At this temperature, nitrogen was filled until the pressure reached 17 MPa, held for 1 h, and then cooled to room temperature at a rate of 3 °C / min; 5. The sintered special ceramics are polished by a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface, thus obtaining the product.

[0031] Comparative Example 3 According to the method of Example 1, the difference lies in that the sintering method in Step 4 is different. The sintering method adopted in this comparative example is as follows: The green body is placed in the sintering furnace cavity, heated to 650 °C at a rate of 3 °C / min, held for 4.5 h, heated to 1350 °C at a rate of 7 °C / min, held for 6 h, then heated to 1500 °C at a rate of 7 °C / min and held for 1 h, and cooled to room temperature at a rate of 3 °C / min.

[0032] Perform performance tests on the special ceramics prepared in Examples 1 to 4 and Comparative Examples 1 to 3. Among them, the test method for fracture toughness is carried out according to the regulations in GB / T 23806-2009, and the remaining test items are carried out according to the regulations in GB / T5593-2015. The sample performance test results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 and Table 2 below: Table 1: Sample performance test results of Examples 1 to 4

[0033] Table 2: Sample performance test results of Comparative Examples 1 to 3

[0034] As can be seen from Table 1 and Table 2 above, the special ceramic samples prepared in Examples 1 to 4 of this application have high density, and also have high strength, thermal shock resistance, thermal stability, corrosion resistance and fracture toughness, and the comprehensive performance is excellent.

[0035] Combining Example 1 and Comparative Example 1, in the preparation of lanthanum-yttrium modified phenolic resin in Comparative Example 1, lanthanum hydroxide and yttrium hydroxide are directly added to the melamine modified phenolic resin, and the performance of the prepared special ceramic samples is reduced, especially the linear expansion coefficient is significantly increased, and the flexural strength and fracture toughness are significantly reduced.

[0036] Combining Example 1 and Comparative Example 2, Comparative Example 2 does not involve the preparation of lanthanum-yttrium modified phenolic resin. Lanthanum hydroxide and yttrium hydroxide are directly added to the ball mill and ball milled together with α-aluminum oxide powder and talc, and the performance of the prepared special ceramic samples is reduced, especially the linear expansion coefficient is significantly increased, and the flexural strength, acid resistance, alkali resistance and fracture toughness are significantly reduced.

[0037] Combining Example 1 and Comparative Example 3, the special ceramics prepared in Comparative Example 3 adopt the conventional atmospheric pressure sintering method, and the performance of the prepared special ceramic samples is reduced, and the bulk density, flexural strength, acid resistance, alkali resistance and fracture toughness are all significantly decreased, and the seismic resistance is insufficient.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that it is still possible to modify the specific implementation manners of the present application or perform equivalent replacements on some technical features, and all of them should be covered within the scope of the technical solutions claimed in the present application.

Claims

1. A preparation method of an anti-corrosion and high-temperature resistant special ceramic, characterized in that, It includes the following steps: S1. Weigh ceramic powder materials according to the weight ratio of 85% - 90% of α-aluminum oxide powder and 10% - 15% of talc, perform dry ball milling to obtain ball-milled powder, and mix the ball-milled powder with lanthanum-yttrium modified phenolic resin to obtain a ceramic mixture; Among them, the preparation method of the lanthanum-yttrium modified phenolic resin includes the following steps: (1) Preparation of lanthanum-yttrium hydroxide: Prepare lanthanum nitrate and yttrium nitrate solutions respectively, mix them according to the molar ratio of lanthanum to yttrium of 4 - 5:1 to obtain a mixed salt solution, adjust the pH to alkaline and then perform ultrasonic treatment, transfer it to a sealed reaction kettle for hydrothermal reaction, filter and wash with water until neutral to obtain lanthanum-yttrium hydroxide for standby; (2) Preparation of phenolic resin prepolymer: Mix phenol and formaldehyde solution, and react under alkaline conditions to obtain a phenolic resin prepolymer; (3) Add the lanthanum-yttrium hydroxide prepared in step (1) to the phenolic resin prepolymer prepared in step (2), then add melamine, formaldehyde solution and triethanolamine, and react under alkaline conditions. After the reaction is completed, unreacted raw materials are removed under reduced pressure to obtain lanthanum-yttrium modified phenolic resin; S2. Prepare a green body by injection molding the ceramic mixture, and then obtain the product through sintering.

2. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, characterized in that, The particle size D of α-aluminum oxide powder in S1 50 is 1 μm; the particle size D of talc 50 is 3 μm.

3. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, wherein, S1 also includes adding a ball milling aid of 0.5% - 0.8% of the weight of the ceramic powder materials to the ceramic powder materials before dry ball milling. The ball milling aid is selected from at least one of stearic acid, polyvinylpyrrolidone and polyacrylamide; In the method of the dry ball milling, the ball-to-material ratio is 2 - 3:1, the ball milling speed is 60 rpm - 100 rpm, and the ball milling time is 6 h - 8 h.

4. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, wherein, The preparation method of the lanthanum-yttrium modified phenolic resin in S1 is: (1) Preparation of lanthanum-yttrium hydroxide: Prepare 0.2 mol / L lanthanum nitrate and 0.2 mol / L yttrium nitrate solutions respectively, mix them according to the molar ratio of lanthanum to yttrium of 4 - 5:1 to obtain a mixed salt solution, add 1% of polyacrylic acid by weight of the mixed salt solution as a dispersant to the mixed salt solution, dropwise add ammonia water to adjust the pH to 9.5 and then perform ultrasonic treatment for 30 min, transfer it to a sealed reaction kettle and carry out hydrothermal reaction at 100°C - 120°C for 12 h, filter and wash with water until neutral to obtain lanthanum-yttrium hydroxide for standby; (2) Preparation of phenolic resin prepolymer: Mix phenol and formaldehyde solution with a concentration of 35% - 40%, dropwise add ammonia water to adjust the pH to 9, and react at 60°C - 70°C for 0.5 h - 1 h to obtain a phenolic resin prepolymer; (3) Add the lanthanum-yttrium hydroxide prepared in step (1) to the phenolic resin prepolymer prepared in step (2), then add melamine, 37% formaldehyde solution and triethanolamine, adjust the pH to 9 with ammonia water, stir and react at 80°C for 15 min. After the reaction is completed, unreacted raw materials are removed under reduced pressure to obtain lanthanum-yttrium modified phenolic resin.

5. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 4, wherein, In step (2), the molar ratio of phenol to formaldehyde in the phenol and formaldehyde solution in step (2) is added according to 1:1.4; In step (3), the molar ratio of melamine, triethanolamine and phenol in step (2) is 0.1 - 0.2:0.001 - 0.002:1; the molar ratio of melamine in step (3) and formaldehyde in the formaldehyde solution in step (3) is 1:1.2 - 1.

3.

6. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 4, wherein, In step (3), the lanthanum-yttrium hydroxide is 12% - 18% of the weight of the lanthanum-yttrium modified phenolic resin.

7. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, characterized in that, In S1, the lanthanum-yttrium modified phenolic resin is 5% - 10% of the weight of the ceramic powder in S1.

8. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, characterized in that, The injection molding method in S2 is to inject the ceramic mixture into the mold by an injection machine at 100 MPa - 110 MPa, and mold it at a temperature of 170 °C - 180 °C and a pressure of 80 MPa - 85 MPa.

9. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, wherein, The sintering method in S2 is to put the green body into the sintering furnace cavity, evacuate the air, heat it up to 650 °C at a rate of 3 °C / min, hold for 4.5 h, heat it up to 1350 °C - 1380 °C at a rate of 7 °C / min, hold for 5 h - 6 h, then heat it up to 1500 °C - 1550 °C at a rate of 7 °C / min. At this temperature, nitrogen is filled until the pressure reaches 15 MPa - 17 MPa, hold for 1 h - 1.5 h, and then cool it down to room temperature at a rate of 3 °C / min.

10. The preparation method of a special anti-corrosion and high-temperature resistant ceramic according to claim 1, wherein, S2 also includes polishing the sintered special ceramic. The polishing method is to polish the sintered ceramic with a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the oxide layer and microcracks on the sintered surface.

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