Preparation method of anti-corrosion and high-temperature resistant special ceramics

Abstract

The present invention relates to the technical field of special ceramics, and in particular to a method for preparing corrosion-resistant and high-temperature resistant special ceramics. The method for preparing corrosion-resistant and high-temperature resistant special ceramics is as follows: ceramic powder is weighed according to a weight ratio of 85% to 90% of α-alumina powder and 10% to 15% of talc, and dry-milled to obtain ball-milled powder, and the ball-milled powder is mixed 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 with lanthanum-yttrium hydroxide prepared by a hydrothermal method and melamine. The ceramic mixture is prepared into a green body by injection molding, and then sintered to obtain a green body. The prepared special ceramics have high strength, thermal shock resistance, thermal stability, corrosion resistance and toughness, and excellent comprehensive performance.

Description

Technical Field

[0001] The present invention relates to the technical field of special ceramics, and in particular to a method for preparing corrosion-resistant and high-temperature-resistant special ceramics. Background Art

[0002] Traditional metal materials soften under high temperature conditions and generally have poor corrosion resistance, which limits their application in high-temperature corrosive working conditions. Special ceramics are new ceramics formed by high-temperature sintering of carefully selected raw materials. Special ceramics such as silicon nitride, silicon carbide, and alumina have better corrosion resistance and high-temperature resistance than metal materials, and can be used stably for a long time in high-temperature, corrosive media. Compared with silicon nitride and silicon carbide, alumina raw materials are easy to prepare and inexpensive, making alumina ceramics widely used in aerospace, energy, electricity, machinery manufacturing, electronic devices and other fields. Alumina special ceramics are special ceramic materials with α-alumina as the main component. They have corrosion resistance, chemical thermal stability and high strength. However, alumina ceramics are brittle and have poor thermal shock resistance. They are prone to cracking and fracture during use and preparation. In addition, the sintering temperature of alumina ceramics exceeds 1600°C, making them difficult to process and shape, which limits their 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 material. However, during the addition process of some sintering aids, due to poor raw material selection and process control, it often leads to defects such as poor mixing between ceramic raw materials, abnormal grain growth, and a large number of sintering holes. As a result, the sintering aids have limited effect on improving the thermal shock resistance of special ceramic materials, and have adverse effects on the material strength, thermal stability and corrosion resistance.

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

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing corrosion-resistant and high-temperature resistant special ceramics. The prepared special ceramics have high strength, thermal shock resistance, thermal stability, corrosion resistance and toughness, and have excellent comprehensive performance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present application provides a method for preparing corrosion-resistant and high-temperature resistant special ceramics, comprising the following steps:

[0008] 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;

[0009] The preparation method of lanthanum-yttrium modified phenolic resin comprises the following steps:

[0010] (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.

[0011] (2) Preparation of phenolic resin prepolymer: Phenol and formaldehyde solution are mixed and reacted under alkaline conditions to obtain phenolic resin prepolymer;

[0012] (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;

[0013] S2. The ceramic mixture is prepared into a green body by injection molding, and then sintered.

[0014] Furthermore, the particle size D of the α-alumina powder in S1 50 1 μm; the particle size of talc D 50 3μm.

[0015] 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;

[0016] 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.

[0017] Furthermore, the preparation method of the lanthanum-yttrium modified phenolic resin in S1 is:

[0018] (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;

[0019] (2) Preparation of phenolic resin prepolymer: Phenol and 35% to 40% formaldehyde solution were mixed, ammonia was added dropwise to adjust the pH to 9, and the mixture was reacted at 60°C to 70°C for 0.5h to 1h to obtain a phenolic resin prepolymer;

[0020] (3) Adding the lanthanum yttrium hydroxide prepared in step (1) to the phenolic resin prepolymer prepared in step (2), and then adding melamine, 37% formaldehyde solution and triethanolamine, adjusting the pH to 9 with ammonia water, stirring and reacting at 80°C for 15 minutes, and removing the unreacted raw materials under reduced pressure after the reaction is completed to obtain a lanthanum yttrium modified phenolic resin.

[0021] Furthermore, the phenol in step (2) and the formaldehyde solution in step (2) are added at a molar ratio of phenol to formaldehyde of 1:1.4;

[0022] The molar ratio of melamine and triethanolamine in step (3) and phenol in step (2) is 0.1-0.2:0.001-0.002:1; the molar ratio of melamine in step (3) and melamine to formaldehyde in the formaldehyde solution in step (3) is 1:1.2-1.3.

[0023] Furthermore, in step (3), the lanthanum yttrium hydroxide is 12% to 18% by weight of the lanthanum yttrium modified phenolic resin.

[0024] Furthermore, the lanthanum-yttrium modified phenolic resin in S1 is 5% to 10% by weight of the ceramic powder in S1.

[0025] Furthermore, the injection molding method in S2 is to inject the ceramic mixture into the mold at 100MPa to 110MPa using an injection molding machine, and mold it at a temperature of 170°C to 180°C and a pressure of 80MPa to 85MPa.

[0026] Furthermore, the sintering method in S2 is to place the green body into the sintering furnace chamber, evacuate the chamber, heat it to 650°C at a rate of 3°C / min, keep it warm for 4.5 hours, heat it to 1350°C~1380°C at a rate of 7°C / min, keep it warm for 5 hours to 6 hours, and then heat it to 1500°C~1550°C at a rate of 7°C / min. At this temperature, nitrogen is filled in to a pressure of 15MPa~17MPa, keep it warm for 1.5 hours, and then cool it to room temperature at a rate of 3°C / min.

[0027] Furthermore, S2 also includes polishing the sintered special ceramics. The polishing method is to polish the sintered ceramics using a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the sintered surface oxide layer and microcracks.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention uses α-alumina powder as the main raw material for special ceramics, compounded with talc and lanthanum yttrium hydroxide to aid sintering. Talc as a sintering aid can effectively reduce the sintering temperature of special ceramics, refine grains, increase the density and flexural strength of the ceramic structure, improve the fluidity and dispersibility of the ball-milled powder, and facilitate subsequent molding and sintering. Lanthanum yttrium hydroxide prepared by a hydrothermal method and melamine are mixed and modified to form a lanthanum yttrium-modified phenolic resin. Lanthanum yttrium hydroxide colloidal particles are prepared by a hydrothermal method using soluble nitrate as a raw material, and the particle size is fine. The lanthanum yttrium hydroxide is combined and dispersed in the resin through hydrogen bonding between the active amino groups in the melamine structure and the hydroxyl groups in the lanthanum yttrium hydroxide. Then, by mixing the phenolic resin with the ball-milled powder, the lanthanum yttrium hydroxide is well dispersed in the ball-milled powder. Lanthanum hydroxide and yttrium hydroxide serve as sintering aids. During the sintering process, they can be decomposed into lanthanum oxide and yttrium oxide in situ. With good dispersion uniformity and fine particle size, they can fill sintering holes and cracks. Combined with the sintering process and parameters, they can increase the density of the sintered body and improve the toughness and strength. 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.

[0030] The preparation method of the special ceramics in the present invention comprises the following steps: firstly, α-alumina powder and talc are fully mixed by dry grinding, then lanthanum-yttrium-modified phenolic resin is added and fully mixed, and then injection molding is performed and then sintered. 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 DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] Unless otherwise specified, the methods are conventional methods, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0033] Example 1

[0034] This embodiment provides a method for preparing corrosion-resistant and high-temperature resistant special ceramics, comprising the following steps:

[0035] 1. According to α-alumina powder (D 50 1μm) 85%, talc (D 50 Ceramic 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.

[0036] 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:

[0037] (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;

[0038] (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;

[0039] (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.

[0040] 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;

[0041] 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;

[0042] 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.

[0043] Example 2

[0044] This embodiment provides a method for preparing corrosion-resistant and high-temperature resistant special ceramics, comprising the following steps:

[0045] 1. According to α-alumina powder (D 50 1μm) 90%, talc (D 50 Ceramic powder (10% of 3μm) was weighed and added into a planetary ball mill, and then 0.8% 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.

[0046] 2. Take 10% 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:

[0047] (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;

[0048] (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;

[0049] (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 and 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 18% of the weight of the lanthanum yttrium modified phenolic resin.

[0050] 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;

[0051] 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 1380℃ at a rate of 7℃ / min, hold for 5h, then heat up to 1550℃ at a rate of 7℃ / min. At this temperature, fill with nitrogen to a pressure of 15MPa, hold for 1.5h, and cool to room temperature at a rate of 3℃ / min.

[0052] 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.

[0053] Example 3

[0054] This embodiment provides a method for preparing corrosion-resistant and high-temperature resistant special ceramics, comprising the following steps:

[0055] 1. According to α-alumina powder (D 50 1μm) 85%, talc (D 50Ceramic powder (15% by weight, 3 μm) was weighed and added into a planetary ball mill. Stearic acid (0.5% by weight) was added to the ceramic powder and dry-milled to obtain ball-milled powder. The ball-to-material ratio used in the ball milling was 2:1, the ball milling speed was 60 rpm, and the ball milling time was 8 h.

[0056] 2. Take 5% 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:

[0057] (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 4:1 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;

[0058] (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;

[0059] (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 and formaldehyde in the formaldehyde solution in step (3) is 1:1.3), adjusting the pH to 9 with 28% ammonia water after the addition, 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 12% of the weight of the lanthanum yttrium modified phenolic resin.

[0060] 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;

[0061] 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;

[0062] 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.

[0063] Example 4

[0064] This embodiment provides a method for preparing corrosion-resistant and high-temperature resistant special ceramics, comprising the following steps:

[0065] 1. According to α-alumina powder (D 50 1μm) 85%, talc (D 50 Ceramic 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.

[0066] 2. Take 7% 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:

[0067] (1) Preparation of lanthanum yttrium hydroxide: 0.2 mol / L lanthanum nitrate and 0.2 mol / L yttrium nitrate solution were prepared respectively, and the mixture was mixed in a molar ratio of lanthanum to yttrium of 5:1 to obtain a mixed salt solution, and polyacrylic acid (1% by weight 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. The mixture was transferred to a closed reactor and hydrothermally reacted at 120°C for 12 hours to obtain lanthanum yttrium hydroxide, which was filtered and washed with water until neutral and set aside.

[0068] (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 70°C for 0.5 h to obtain a phenolic resin prepolymer;

[0069] (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 0.2:0.002:1; the molar ratio of melamine in step (3) and melamine to formaldehyde in step (3) formaldehyde solution is 1:1.2), adjusting the pH to 9 with 28% ammonia water after the addition, 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 16% of the weight of the lanthanum yttrium modified phenolic resin.

[0070] 3. The ceramic mixture is injected into the mold using an injection molding machine at 110 MPa and formed at a temperature of 170°C and a pressure of 85 MPa to prepare a green body;

[0071] 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;

[0072] 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.

[0073] Comparative Example 1

[0074] The method of Example 1 is followed, except that the lanthanum-yttrium-modified phenolic resin is prepared as follows:

[0075] (1) Preparation of phenolic resin prepolymer: Phenol and 37% formaldehyde solution were mixed at a 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 h to obtain a phenolic resin prepolymer;

[0076] (2) adding melamine, 37% formaldehyde solution and triethanolamine to the obtained phenolic resin prepolymer (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 after the addition, 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 melamine-modified phenolic resin;

[0077] (3) Lanthanum hydroxide and yttrium hydroxide (the molar ratio of lanthanum to yttrium is 5:1) were added to the melamine-modified phenolic resin, and the mixture was stirred at 300 rpm for 20 minutes to obtain a lanthanum-yttrium-modified phenolic resin. The lanthanum hydroxide and yttrium hydroxide accounted for 15% of the weight of the lanthanum-yttrium-modified phenolic resin.

[0078] Comparative Example 2

[0079] This comparative example provides a method for preparing a special ceramic, comprising the following steps:

[0080] 1. According to α-alumina powder (D 50 1μm) 85%, talc (D 50Ceramic powder (15% by weight, 3 μm) was weighed and added to a planetary ball mill. A mixture of lanthanum hydroxide and yttrium hydroxide (1.2% by weight, wherein the molar ratio of lanthanum to yttrium was 5:1) was added. Stearic acid (0.5% by weight, wherein the molar ratio of lanthanum to yttrium was 5:1) was then added to the ceramic powder. The mixture was dry-milled to obtain a ball-milled powder. 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.

[0081] 2. Take 6.8% of the weight of the ceramic powder as phenolic resin, stir and mix the ball mill powder and phenolic resin in a high-speed mixer to obtain a ceramic mixture, and mix at a stirring speed of 500 rpm for 30 minutes. The preparation method of the phenolic resin is as follows: phenol and 37% formaldehyde solution are mixed according to the molar ratio of phenol to formaldehyde of 1:1.4, 28% ammonia water is added dropwise to adjust the pH to 9, and the phenolic resin is obtained after reacting at 60°C for 3 hours. After the reaction is completed, the unreacted raw materials are removed under reduced pressure to obtain the phenolic resin.

[0082] 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;

[0083] 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;

[0084] 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.

[0085] Comparative Example 3

[0086] The method of Example 1 is followed, except that the sintering method of step 4 is different. The sintering method adopted in this comparative example is: placing the green body into the sintering furnace chamber, heating it to 650°C at a rate of 3°C / min, keeping it warm for 4.5 hours, heating it to 1350°C at a rate of 7°C / min, keeping it warm for 6 hours, then heating it to 1500°C at a rate of 7°C / min and keeping it warm for 1 hour, and then cooling it to room temperature at a rate of 3°C / min.

[0087] The special ceramics prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to performance tests. The fracture toughness test method was carried out in accordance with the provisions of GB / T 23806-2009, and the remaining test items were carried out in accordance with the provisions of GB / T 5593-2015. The performance test results of the samples of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Tables 1 and 2 below:

[0088] Table 1: Performance test results of samples from Examples 1 to 4

[0089]

[0090] Table 2: Performance test results of samples of Comparative Examples 1 to 3

[0091]

[0092] It can be seen from Table 1 and Table 2 above that the special ceramic samples prepared in Examples 1 to 4 of the present application have high density, and have high strength, thermal shock resistance, thermal stability, corrosion resistance and fracture toughness, and have excellent comprehensive performance.

[0093] In combination with Example 1 and Comparative Example 1, in the preparation of the lanthanum-yttrium-modified phenolic resin in Comparative Example 1, lanthanum hydroxide and yttrium hydroxide were directly added to the melamine-modified phenolic resin, and the performance of the prepared special ceramic sample was reduced, especially the linear expansion coefficient was significantly increased, and the flexural strength and fracture toughness were significantly reduced.

[0094] In combination with 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-alumina powder and talc. The performance of the prepared special ceramic sample is reduced, especially the linear expansion coefficient is significantly increased, and the flexural strength, acid resistance, alkali resistance and fracture toughness are significantly reduced.

[0095] In combination with 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 significantly reduced, and the seismic resistance is insufficient.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them. Although the present application has been described in detail with reference to preferred embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present application can still be modified or some technical features can be replaced by equivalents, which should all be included in the scope of the technical solutions requested for protection in this application.

Claims

1. A method for preparing anti-corrosion and high-temperature resistant special ceramics, characterized in that: The following steps are involved: 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, preparing a green body by injection molding the ceramic mixture, and then sintering it; The sintering method in S2 is to place the green body into the sintering furnace chamber, evacuate the chamber, heat it to 650℃ at a rate of 3℃ / min, keep it warm for 4.5h, heat it to 1350℃~1380℃ at a rate of 7℃ / min, keep it warm for 5h~6h, then heat it to 1500℃~1550℃ at a rate of 7℃ / min, fill it with nitrogen to a pressure of 15MPa~17MPa at 1500℃~1550℃, keep it warm for 1h~1.5h, and cool it to room temperature at a rate of 3℃ / min.

2. The method for preparing a corrosion-resistant and high-temperature-resistant special ceramic according to claim 1, characterized in that: Particle size D of α-alumina powder in S1 50 1 μm; the particle size of talc D 50 3μm.

3. The method for preparing a corrosion-resistant and high-temperature-resistant special ceramic according to claim 1, characterized in that: S1 further includes adding a ball milling aid in an amount of 0.5% to 0.8% 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.

4. The method for preparing a corrosion-resistant and high-temperature-resistant special ceramic according to claim 1, characterized in that: The preparation method of 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, transfer to a closed reactor and carry out hydrothermal reaction at 100°C to 120°C 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: Phenol and 35% to 40% formaldehyde solution were mixed, ammonia was added dropwise to adjust the pH to 9, and the mixture was reacted at 60°C to 70°C for 0.5h to 1h to obtain a 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, 37% formaldehyde solution and triethanolamine, adjusting the pH to 9 with ammonia water, stirring and reacting at 80°C for 15 minutes, and removing the unreacted raw materials under reduced pressure after the reaction is completed to obtain a lanthanum yttrium modified phenolic resin.

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

3.

6. The method for preparing a corrosion-resistant and high-temperature-resistant special ceramic according to claim 4, characterized in that: In step (3), the lanthanum yttrium hydroxide is 12% to 18% by weight of the lanthanum yttrium modified phenolic resin.

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

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

9. The method for preparing a corrosion-resistant and high-temperature-resistant special ceramic according to claim 1, characterized in that: S2 also includes polishing the sintered special ceramics. The polishing method is to polish the sintered ceramics using a polishing wheel at 1000 rpm and a linear speed of 2 m / s to remove the sintered surface oxide layer and microcracks.

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