Alumina ceramic low-temperature sintering preparation process doped with composite additive

Abstract

This invention relates to the field of alumina ceramics technology, specifically to a low-temperature sintering preparation process for alumina ceramics doped with composite additives. The process includes the following steps: alumina powder and modified composite additives are ball-milled with anhydrous ethanol; the ball-milled slurry is dried; the dried powder agglomerates are ground and screened to obtain a mixed powder; the mixed powder is placed in a mold to form a wet blank; the wet blank is naturally dried at room temperature to obtain a green blank; and the green blank is calcined to obtain alumina ceramics. This invention is prepared by compounding a modifying agent with a silane coupling agent and hydroxylating modification. After compounding with inorganic components such as magnesium oxide and calcium oxide, it can effectively reduce the interfacial tension between the additives and alumina powder. Subsequent modification of the calcined powder with γ-methacryloyloxypropyltrimethoxysilane further improves the dispersion uniformity of the composite additives in the alumina powder.

Description

Technical Field

[0001] This invention relates to the field of alumina ceramics technology, and in particular to a low-temperature sintering preparation process for alumina ceramics doped with composite additives. Background Technology

[0002] Alumina ceramics, as high-performance structural ceramics with α-Al2O3 as the main crystalline phase, occupy an irreplaceable position in many high-end fields such as electronic packaging, aerospace, machinery manufacturing, and semiconductor devices due to their excellent high hardness, high temperature resistance, corrosion resistance, high insulation, and good mechanical strength. However, the high melting point of alumina (2050℃) means that the sintering temperature in traditional preparation processes generally exceeds 1600℃, which not only causes huge energy consumption but also places stringent requirements on the high temperature resistance and temperature uniformity control of sintering equipment, significantly increasing production costs and industrialization difficulties. Against this backdrop, low-temperature sintering technology has become a research hotspot and core development direction in the field of alumina ceramics. Its core objective is to reduce the sintering temperature while ensuring or even improving the comprehensive performance of ceramic products, achieving the dual goals of energy saving and high performance.

[0003] Among the many implementation paths of low-temperature sintering technology, the sintering aid method has become the most promising technical solution in industrial applications due to its simple process, controllable cost, and significant modification effect. Compared with other paths such as powder refinement and special sintering processes, the thermodynamic and kinetic characteristics of the sintering process can be controlled by doping additives. This can effectively reduce the sintering activation energy of alumina, promote the densification process, and simultaneously optimize the microstructure of ceramics. It has become the preferred solution to balance cost and performance. Among them, composite additive systems can integrate the synergistic effects of multiple components and overcome the functional limitations of single additives. They have gradually replaced single additives as the mainstream research direction. For example, multiple objectives such as reducing sintering temperature, inhibiting abnormal grain growth, and strengthening grain boundary bonding can be achieved simultaneously through multi-component compounding.

[0004] In the low-temperature sintering preparation of alumina ceramics, the poor compatibility and uneven dispersion of composite additives with alumina powder, as well as the insufficient activity and poor flowability of the mixed powder, lead to difficulties in subsequent molding and poor low-temperature sintering performance. To address the problems mentioned above, this invention proposes a low-temperature sintering preparation process for alumina ceramics doped with composite additives. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature sintering preparation process for alumina ceramics doped with composite additives, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature sintering preparation process for alumina ceramics doped with composite additives, comprising the following steps:

[0007] S1. Add alumina powder and modified composite additives to anhydrous ethanol and ball mill for 20-24 hours. Dry the ball-milled slurry at 75-80℃ for 10-12 hours. Grind the dried powder agglomerates and pass them through a 200-230 mesh sieve to obtain mixed powder.

[0008] S2. Mix the powder with water and place it in a mold. Hold the mold under a pressure of 100-300MPa for 5-10 minutes to make a wet blank. Let the wet blank air dry at room temperature for 2-4 hours, and then dry it at 60-70℃ for 6.5-8 hours to obtain a green blank.

[0009] S3. The green body is heated to 600-650℃ at a rate of 3-5℃ / min, and then heated to 1270-1330℃ at a rate of 8-10℃ / min, and held for 4-6 hours to obtain alumina ceramic.

[0010] The modified composite additive is prepared through the following steps:

[0011] S11. Separate the doped mixture from the precipitate, wash the precipitate with deionized water to pH 6.4-7, vacuum dry at 75-80℃ for 10-12h, and calcine at 520-550℃ for 2.5-3h in a nitrogen-hydrogen mixed atmosphere.

[0012] S12. After the calcined product is cooled to room temperature, it is ball-milled for 1.5-2 hours and then passed through a 200-300 mesh sieve to obtain ball-milled powder.

[0013] S13. Add the ball-milled powder to a mixed solution of γ-methacryloxypropyltrimethoxysilane and ethanol, stir at room temperature for 25-30 min, and then vacuum dry at 50-60℃ for 2-3 h to obtain the modified composite additive.

[0014] As a preferred embodiment of the present invention, the doped and mixed system in step S11 is prepared through the following steps:

[0015] S111. A precursor solution is prepared by mixing lanthanum nitrate, yttrium nitrate, cerium nitrate, zirconium nitrate, and deionized water.

[0016] S112. Add the mixture of the modifying reagent, magnesium oxide, calcium oxide, zinc borate, and kaolin to an ethanol solution, stir at a constant temperature of 65-70℃ for 3.5-4 hours, and after the reaction is complete, centrifuge to separate the precipitate, wash the precipitate 3-4 times with a deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor.

[0017] S113. Add the modified precursor to the precursor solution, add citric acid as a complexing agent, and stir at 65-70℃ for 2.5-3h to obtain a doped mixed system.

[0018] As a preferred embodiment of the present invention, the modifying reagent in step S112 is prepared through the following steps:

[0019] S121. Dissolve γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in anhydrous ethanol to obtain a silane ethanol solution, add maleic anhydride and pyridine, and stir the reaction at 40-50℃ for 3-4 hours.

[0020] S122. After the reaction is complete, remove the unreacted maleic anhydride and pyridine to obtain the modified hydroxylating agent.

[0021] S123. Dissolve the modified hydroxylating agent in an ethanol-water mixture, and adjust the pH to 6.8-7.2 with sodium acetate-acetic acid buffer solution to obtain the modified agent.

[0022] As a preferred embodiment of the present invention, in step S1, the mass ratio of alumina powder, modified composite additive reagent, and anhydrous ethanol is 100:(2-8):(120-180), and in step S2, the mass ratio of the mixed powder to water is 100:(8-15).

[0023] As a preferred embodiment of the present invention, in step S13, the mass ratio of ball-milled powder, γ-methacryloyloxypropyltrimethoxysilane, and ethanol is 100:(1-5):(80-120).

[0024] As a preferred embodiment of the present invention, the mass ratio of lanthanum nitrate, yttrium nitrate, cerium nitrate, zirconium nitrate and deionized water in step S111 is (5-10):(5-10):(5-10):(70-85):(200-300).

[0025] As a preferred embodiment of the present invention, in step S112, the mass ratio of the modifying reagent, magnesium oxide, calcium oxide, zinc borate and kaolin is 100:(20-40):(10-20):(15-30):(25-45), and the mass ratio of the mixture to the ethanol solution is 100:(150-250).

[0026] As a preferred embodiment of the present invention, the mass ratio of the modified precursor, the precursor solution, and the citric acid in step S113 is 100:(300-500):(5-15).

[0027] As a preferred embodiment of the present invention, in step S121, the mass ratio of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and anhydrous ethanol is (40-60):(40-60):(200-300), and the mass ratio of the silane ethanol solution to maleic anhydride and pyridine is 100:(5-15):(1-3).

[0028] As a preferred embodiment of the present invention, the mass ratio of the modified hydroxylating agent and the ethanol-water mixed solution in step S123 is 100:(150-250).

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention is prepared by compounding a modifying reagent with a silane coupling agent and hydroxylating modification. After compounding with inorganic components such as magnesium oxide and calcium oxide, it can effectively reduce the interfacial tension between the additive and alumina powder. Subsequently, the powder is modified again by γ-methacryloyloxypropyltrimethoxysilane, which further improves the dispersion uniformity of the composite additive in alumina powder, avoids the problems of easy agglomeration and local segregation of traditional additives, and allows each component to participate in the reaction uniformly during sintering, ensuring the uniformity of the internal structure of the ceramic.

[0031] 2. This invention introduces a precursor prepared from rare earth nitrates and zirconium salts into a doping and mixing system. After complexation with citric acid, a uniform sol system is formed. When combined with the modified precursor, a highly active nanoscale composite oxide phase is generated during calcination. This active phase can form a liquid phase in advance during low-temperature sintering, reducing the sintering activation energy of alumina and achieving low-temperature densification. At the same time, the modified composite additive can improve the interparticle forces of alumina powder, enhance the flowability and bulk density of the mixed powder, making it easier for the powder to fill the mold during molding, reducing porosity and defects inside the green body, and improving the density of the green body, thus laying the foundation for the subsequent sintering preparation of high-performance ceramics. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process for alumina ceramics in this invention;

[0033] Figure 2 This is a schematic diagram of the process for the modified composite additive in this invention;

[0034] Figure 3 This is a schematic diagram of the doping and mixing system in this invention;

[0035] Figure 4 This is a schematic diagram of the process for modifying the reagent in this invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0037] Please see Figures 1-4 This invention provides a technical solution for the low-temperature sintering preparation process of alumina ceramics doped with composite additives:

[0038] Example 1:

[0039] A low-temperature sintering process for preparing alumina ceramics doped with composite additives includes the following steps:

[0040] I. Preparation of Modifying Reagents:

[0041] S121: Take 40g of γ-aminopropyltriethoxysilane and 40g of γ-glycidoxypropyltrimethoxysilane, dissolve them in 200g of anhydrous ethanol to prepare a silane ethanol solution, add 5g of maleic anhydride and 1g of pyridine to the silane ethanol solution, and stir the reaction at 40℃ for 3h.

[0042] S122: Remove unreacted maleic anhydride and solvent to obtain the modified hydroxylating agent.

[0043] S123: Take 100g of the modified hydroxylation reagent, dissolve it in 150g of ethanol-water mixed solution, add sodium acetate-acetic acid buffer solution to adjust the pH to 6.8, and obtain the modified reagent.

[0044] II. Preparation of Doped Mixed Systems:

[0045] S111: Take 5g of lanthanum nitrate, 5g of yttrium nitrate, 5g of cerium nitrate, and 70g of zirconium nitrate, mix with 200g of deionized water to prepare a precursor solution.

[0046] S112: Take 100g of modifying reagent, 20g of magnesium oxide, 10g of calcium oxide, 15g of zinc borate and 25g of kaolin and mix them into a mixture (total 170g). Add the mixture to 255g of ethanol solution, stir at 65℃ for 3.5h, centrifuge to separate the precipitate, wash the precipitate 3 times with deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor.

[0047] S113: Take 100g of modified precursor, add it to 300g of precursor solution, add 5g of citric acid, stir at 65℃ for 2.5h to obtain a doped mixed system.

[0048] III. Preparation of Modified Composite Additives:

[0049] S11: Separate the doped mixture system and precipitate it. Wash the precipitate with deionized water until pH=6.4, dry it under vacuum at 75℃ for 10h, and calcine it at 520℃ for 2.5h in a nitrogen-hydrogen mixed atmosphere.

[0050] S12: After the calcined product is cooled to room temperature, it is ball-milled for 1.5 hours and passed through a 200-mesh sieve.

[0051] S13: Take 100g of ball-milled powder, add it to a mixed solution of 1g γ-methacryloxypropyltrimethoxysilane and 80g ethanol, stir at room temperature for 25min, and then vacuum dry at 50℃ for 2h to obtain the modified composite additive.

[0052] IV. Preparation of alumina ceramics:

[0053] S1: Take 100g of alumina powder and 2g of modified composite additive, add them to 120g of anhydrous ethanol and ball mill for 20h. After ball milling, dry the slurry at 75℃ for 10h. After drying, grind the powder agglomerates through a 200-mesh sieve to obtain mixed powder.

[0054] S2: Place 100g of mixed powder and 8g of water into a mold, press under 100MPa pressure for 5 minutes to make a wet blank, let the wet blank air dry at room temperature for 2 hours, and then dry at 60℃ for 6.5 hours to obtain a green blank.

[0055] S3: Heat the green body to 600℃ at a rate of 3℃ / min, then raise the temperature to 1270℃ at a rate of 8℃ / min, and hold at a constant temperature for 4 hours to obtain alumina ceramic.

[0056] Example 2:

[0057] A low-temperature sintering process for preparing alumina ceramics doped with composite additives includes the following steps:

[0058] I. Preparation of Modifying Reagents:

[0059] S121: Take 45g of γ-aminopropyltriethoxysilane and 45g of γ-glycidoxypropyltrimethoxysilane, dissolve them in 225g of anhydrous ethanol to prepare a silane ethanol solution, add 7.5g of maleic anhydride and 1.5g of pyridine to the silane ethanol solution, and stir the reaction at 42℃ for 3.2h.

[0060] S122: Remove unreacted maleic anhydride and solvent to obtain the modified hydroxylating agent.

[0061] S123: Take 100g of the modified hydroxylation reagent, dissolve it in 175g of ethanol-water mixed solution, add sodium acetate-acetic acid buffer solution to adjust the pH to 6.9, and obtain the modified reagent.

[0062] II. Preparation of Doped Mixed Systems:

[0063] S111: Take 6.25g of lanthanum nitrate, 6.25g of yttrium nitrate, 6.25g of cerium nitrate, and 73.75g of zirconium nitrate, mix them with 225g of deionized water to prepare a precursor solution.

[0064] S112: Take 100g of modifying reagent, 25g of magnesium oxide, 12.5g of calcium oxide, 18.75g of zinc borate, and 31.25g of kaolin and mix them into a mixture (total 187.5g). Add the mixture to 375g of ethanol solution, stir at 66℃ for 3.6h, centrifuge to separate the precipitate, wash the precipitate three times with a deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor.

[0065] S113: Take 100g of modified precursor, add it to 350g of precursor solution, add 7.5g of citric acid, stir at 66℃ for 2.6h to obtain a doped mixed system.

[0066] III. Preparation of Modified Composite Additives:

[0067] S11: Separate the doped mixture system and precipitate it. Wash the precipitate with deionized water until pH=6.6, dry it under vacuum at 76℃ for 10.5h, and calcine it at 530℃ for 2.6h in a nitrogen-hydrogen mixed atmosphere.

[0068] S12: After the calcined product is cooled to room temperature, it is ball-milled for 1.6 hours and passed through a 225-mesh sieve.

[0069] S13: Take 100g of ball-milled powder, add it to a mixed solution of 2g γ-methacryloxypropyltrimethoxysilane and 90g ethanol, stir at room temperature for 26min, and then vacuum dry at 52.5℃ for 2.2h to obtain the modified composite additive.

[0070] IV. Preparation of alumina ceramics:

[0071] S1: Take 100g of alumina powder and 4g of modified composite additive, add them to 135g of anhydrous ethanol and ball mill for 21h. After ball milling, dry the slurry at 76℃ for 10.5h. After drying, grind the powder agglomerates through a 210-mesh sieve to obtain mixed powder.

[0072] S2: Place 100g of mixed powder and 10g of water into a mold, press under 150MPa pressure for 6min to make a wet blank, let the wet blank air dry at room temperature for 2.5h, and then dry at 62.5℃ for 7h to obtain a green blank.

[0073] S3: The green body is heated to 612℃ at a rate of 3.5℃ / min, and then heated to 1290℃ at a rate of 8.5℃ / min. The temperature is held constant for 4.5h to obtain alumina ceramic.

[0074] Example 3:

[0075] A low-temperature sintering process for preparing alumina ceramics doped with composite additives includes the following steps:

[0076] I. Preparation of Modifying Reagents:

[0077] S121: Take 55g of γ-aminopropyltriethoxysilane and 55g of γ-glycidoxypropyltrimethoxysilane, dissolve them in 275g of anhydrous ethanol to prepare a silane ethanol solution, add 12.5g of maleic anhydride and 2.5g of pyridine to the silane ethanol solution, and stir the reaction at 47.5℃ for 3.7h.

[0078] S122: Remove unreacted maleic anhydride and solvent to obtain the modified hydroxylating agent.

[0079] S123: Take 100g of the modified hydroxylation reagent, dissolve it in 225g of ethanol-water mixed solution, add sodium acetate-acetic acid buffer solution to adjust the pH to 7.1, and obtain the modified reagent.

[0080] II. Preparation of Doped Mixed Systems:

[0081] S111: Take 8.75g of lanthanum nitrate, 8.75g of yttrium nitrate, 8.75g of cerium nitrate, and 81.25g of zirconium nitrate, mix them with 275g of deionized water to prepare a precursor solution.

[0082] S112: Take 100g of modifying reagent, 35g of magnesium oxide, 17.5g of calcium oxide, 26.25g of zinc borate, and 41.25g of kaolin and mix them into a mixture (total 220g). Add the mixture to 440g of ethanol solution, stir at 68℃ for 3.8h, centrifuge to separate the precipitate, wash the precipitate 4 times with deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor.

[0083] S113: Take 100g of modified precursor, add it to 450g of precursor solution, add 12.5g of citric acid, stir at 68℃ for 2.8h to obtain a doped mixed system.

[0084] III. Preparation of Modified Composite Additives:

[0085] S11: Separate the precipitate from the doped mixture system, wash the precipitate with deionized water until pH=6.8, vacuum dry at 78℃ for 11.5h, and calcine at 540℃ for 2.8h in a nitrogen-hydrogen mixed atmosphere.

[0086] S12: After the calcined product is cooled to room temperature, it is ball-milled for 1.8 hours and passed through a 275-mesh sieve.

[0087] S13: Take 100g of ball-milled powder, add it to a mixed solution of 4g γ-methacryloxypropyltrimethoxysilane and 110g ethanol, stir at room temperature for 28min, and then vacuum dry at 57.5℃ for 2.7h to obtain the modified composite additive.

[0088] IV. Preparation of alumina ceramics:

[0089] S1: Take 100g of alumina powder and 6g of modified composite additive, add them to 165g of anhydrous ethanol and ball mill for 23h. After ball milling, dry the slurry at 78℃ for 11.5h. After drying, grind the powder agglomerates through a 220-mesh sieve to obtain mixed powder.

[0090] S2: Place 100g of mixed powder and 12g of water into a mold, hold it under 250MPa pressure for 8.7min to make a wet blank, let the wet blank air dry at room temperature for 3.5h, and then dry it at 67.5℃ for 7.5h to obtain a green blank.

[0091] S3: The green body is heated to 637℃ at a rate of 4.5℃ / min, and then heated to 1310℃ at a rate of 9.5℃ / min. The temperature is held constant for 5.5h to obtain alumina ceramic.

[0092] Example 4:

[0093] A low-temperature sintering process for preparing alumina ceramics doped with composite additives includes the following steps:

[0094] I. Preparation of Modifying Reagents:

[0095] S121: Take 60g of γ-aminopropyltriethoxysilane and 60g of γ-glycidoxypropyltrimethoxysilane, dissolve them in 300g of anhydrous ethanol to prepare a silane ethanol solution, add 15g of maleic anhydride and 3g of pyridine to the silane ethanol solution, and stir the reaction at 50℃ for 4h.

[0096] S122: Remove unreacted maleic anhydride and solvent to obtain the modified hydroxylating agent.

[0097] S123: Take 100g of the modified hydroxylation reagent, dissolve it in 250g of ethanol-water mixed solution, add sodium acetate-acetic acid buffer solution to adjust the pH to 7.2, and obtain the modified reagent.

[0098] II. Preparation of Doped Mixed Systems:

[0099] S111: Take 10g of lanthanum nitrate, 10g of yttrium nitrate, 10g of cerium nitrate, and 85g of zirconium nitrate, mix with 300g of deionized water to prepare a precursor solution.

[0100] S112: Take 100g of modifying reagent, 40g of magnesium oxide, 20g of calcium oxide, 30g of zinc borate and 45g of kaolin and mix them into a mixture (total 235g). Add the mixture to 587.5g of ethanol solution, stir at 70℃ for 4h, centrifuge to separate the precipitate, wash the precipitate 4 times with deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor.

[0101] S113: Take 100g of modified precursor, add it to 500g of precursor solution, add 15g of citric acid, stir at 70℃ for 3h to obtain a doped mixed system.

[0102] III. Preparation of Modified Composite Additives:

[0103] S11: Separate the doped mixture system and precipitate it. Wash the precipitate with deionized water until pH=7, dry it under vacuum at 80℃ for 15h, and calcine it at 550℃ for 3h in a nitrogen-hydrogen mixed atmosphere.

[0104] S12: After the calcined product is cooled to room temperature, it is ball-milled for 2 hours and passed through a 300-mesh sieve.

[0105] S13: Take 100g of ball-milled powder, add it to a mixed solution of 5g γ-methacryloxypropyltrimethoxysilane and 120g ethanol, stir at room temperature for 30min, and then vacuum dry at 60℃ for 3h to obtain the modified composite additive.

[0106] IV. Preparation of alumina ceramics:

[0107] S1: Take 100g of alumina powder and 8g of modified composite additive, add them to 180g of anhydrous ethanol and ball mill for 24h. After ball milling, dry the slurry at 80℃ for 12h. After drying, grind the powder agglomerates through a 230-mesh sieve to obtain mixed powder.

[0108] S2: Place 100g of mixed powder and 15g of water into a mold, press under 300MPa pressure for 10min to make a wet blank, let the wet blank air dry at room temperature for 4h, and then dry at 70℃ for 8h to obtain a green blank.

[0109] S3: Heat the green body to 650℃ at a rate of 5℃ / min, then raise the temperature to 1330℃ at a rate of 10℃ / min, and hold at a constant temperature for 6 hours to obtain alumina ceramic.

[0110] Comparative Example 1:

[0111] Compared to Example 1, Comparative Example 1 replaces the modified composite additive with a silicate additive, while the remaining steps are exactly the same as in Example 1.

[0112] Comparative Example 2:

[0113] Compared to Example 1, Comparative Example 2 replaces the doping and mixing system with a composite system of magnesium oxide, calcium oxide, and zinc borate; the remaining steps are exactly the same as in Example 1.

[0114] Comparative Example 3:

[0115] Comparative Example 3 differs from Example 1 in that the modifying agent is replaced with γ-aminopropyltriethoxysilane, while the remaining steps are exactly the same as in Example 1.

[0116] Comprehensive performance testing was conducted on the alumina ceramic products prepared in Examples 1-4 and Comparative Examples 1-3. The test items covered density, flexural strength, Vickers hardness, fracture toughness, volume resistivity (room temperature), and coefficient of thermal expansion (20-800℃). All tests were conducted in accordance with the alumina ceramic industry standards (GB / T1964-2006, GB / T3851-2015, etc.). All test samples were coarsely ground with diamond abrasive, finely ground with 400#, 800#, 1200#, and 2000# metallographic sandpaper in sequence, and then polished with diamond polishing agent until the surface was free of scratches. After polishing, the samples were ultrasonically cleaned with anhydrous ethanol for 10 minutes, dried in an 80℃ oven for 2 hours, and cooled to room temperature before use. Different test items were processed into standard sample sizes as required.

[0117] I. Physical and Mechanical Properties Testing of Alumina Ceramics

[0118] The density of alumina ceramics was tested according to GB / T25995-2010: The dry weight of the pretreated sample was weighed using an electronic analytical balance and recorded as follows: Place the sample in a vacuum impregnation apparatus, evacuate to 0.1 MPa, maintain this pressure for 15 minutes, then inject deionized water and continue vacuum impregnation for 30 minutes to allow the sample to fully absorb water. Suspend the water-absorbed sample on the balance hook, completely immersing it in deionized water (the sample should not touch the container walls or bottom), and weigh the buoyant weight, recording it as _____. Remove the sample, blot the surface moisture with filter paper (without squeezing the internal pores of the sample), weigh the wet weight, and record it as follows. Calculate the density using the formula:

[0119]

[0120] The density of water is that of deionized water at room temperature.

[0121] According to GB / T16534-2009, the Vickers hardness of alumina ceramics was tested as follows: The pretreated sample was placed on the Vickers hardness tester's worktable. The worktable was adjusted so that the sample surface was perpendicular to the indenter axis. The test parameters were set as follows: test force 9.8 N, holding time 15 s, and a diamond square pyramid indenter. The hardness tester was started, and the indenter pressed into the sample surface. After the holding time was completed, the indenter automatically retracted. The lengths of the two diagonals of the indentation were measured using the built-in microscope of the hardness tester and recorded as follows: , Calculate Vickers hardness using the formula:

[0122] in, The specific test results are shown in Table 1 below:

[0123] Table 1

[0124] Implementation Density (%) Vickers hardness (GPa) Example 1 98.2 18.5 Example 2 98.8 19.2 Example 3 98.9 19.3 Example 4 98.3 18.6 Comparative Example 1 92.5 15.1 Comparative Example 2 94.3 16.4 Comparative Example 3 95.7 17.2

[0125] As can be seen from the data in Table 1, the alumina ceramics prepared by the process of this invention have significantly better density and Vickers hardness than the comparative examples. Examples 2 and 3 exhibit the best performance, while the density of Examples 1-4 is all 98.2% or higher, and the Vickers hardness is not lower than 18.5 GPa. Example 3, with a density of 98.9% and a Vickers hardness of 19.3 GPa, is the best among all samples. In contrast, the density of Comparative Examples 1-3 is only 95.7%, and the Vickers hardness is only 17.2 GPa, showing a significant difference from the examples. This indicates that the modified composite additive system of this invention can effectively improve the sintering densification of alumina powder, reduce internal porosity in the ceramic, and significantly increase the ceramic hardness. Compared with traditional silicate additives, simple composite systems, and single silane modifying agents, the composite modification scheme of this invention allows for better compatibility between the additive and alumina powder, resulting in a more uniform ceramic crystal phase after sintering and a fundamental improvement in the basic physical and mechanical properties.

[0126] II. Electrical and Thermal Properties Testing of Alumina Ceramics

[0127] According to GB / T3851-2015, the flexural strength of alumina ceramics was tested as follows: The specimen was processed into a standard strip shape of 3mm × 4mm × 36mm. The support span of the three-point bending tester was adjusted to 30mm. The load sensor of the tester was calibrated, and the loading rate was set to 0.5mm / min. The specimen was placed on the support with the tension surface facing down, and the central axis of the specimen coincided with the central axis of the support and the indenter. The tester was started, and the indenter applied downward pressure at a uniform speed until the specimen fractured. The maximum load at fracture was recorded. Calculate the flexural strength according to the formula. :

[0128] in, For span, The width of the sample. This represents the height of the sample.

[0129] According to GB / T1672-2008, the room temperature volume resistivity of alumina ceramics is tested as follows: The sample is processed into a circular sheet with a diameter of 20 mm × 5 mm. Both ends are polished to a mirror finish. A high resistance meter is used with circular electrodes. The test environment is room temperature of 25℃ and relative humidity ≤60%. Conductive silver paste is evenly applied to both ends of the sample. The electrodes are then attached, ensuring good contact between the electrodes and the sample without air bubbles. The sample is left to stand for 10 minutes to allow the silver paste to cure. The sample and electrodes are then connected to the high resistance meter. The test parameters are set as follows: DC test voltage 500V, voltage holding time 60s. The test is started, and the resistivity value is recorded after the reading stabilizes.

[0130] According to GB / T16535-2008, the coefficient of thermal expansion of alumina ceramics in the range of 20-800℃ was tested as follows: The sample was machined into a cylindrical shape of Φ5mm×20mm, ensuring that the upper and lower end faces of the sample were parallel, the axis was straight, and there were no bends or cracks. The sample was placed in the sample holder of the thermal dilatometer, and the holder was adjusted to ensure that the sample was firmly fixed and in coaxial contact with the dilatometer probe without additional stress. The temperature and displacement sensors of the thermal dilatometer were calibrated, and the test parameters were set as follows: heating rate 5℃ / min, test temperature range 20-800℃, holding at 800℃ and then allowing to cool naturally. The test was started, and the thermal dilatometer automatically recorded the change in sample length at different temperatures. The sample length at an initial temperature of 20℃ was recorded. Calculate the coefficient of linear expansion using the formula:

[0131] in, The average coefficient of thermal expansion in the temperature range of 20-800℃ was used as the test result. The specific test results are shown in Table 2 below:

[0132] Table 2

[0133] Implementation Maximum load (N) Flexural strength (MPa) Resistivity (Ω·m) <![CDATA[Coefficient of thermal expansion (×10 -6 / °C)]]> Example 1 286 358 <![CDATA[1.2×10 14 ]]> 7.8 Example 2 302 378 <![CDATA[1.5×10 14 ]]> 7.6 Example 3 305 382 <![CDATA[1.6×10 14 ]]> 7.5 Example 4 289 362 <![CDATA[1.3×10 14 ]]> 7.7 Comparative Example 1 215 269 <![CDATA[0.4×10 14 ]]> 8.9 Comparative Example 2 238 298 <![CDATA[0.7×10 14 ]]> 8.5 Comparative Example 3 256 320 <![CDATA[0.9×10 14 ]]> 8.2

[0134] As can be seen from the data in Table 2, the alumina ceramics prepared by the process of this invention have significant advantages in comprehensive performance. Examples 2 and 3 represent the optimal performance range. The flexural strength of Examples 1-4 all exceed 350 MPa, with Example 3 reaching 382 MPa, while the highest of the comparative examples is only 320 MPa. This indicates that the modified composite additive can enhance the grain boundary bonding force of the ceramic and improve its resistance to flexural fracture. In terms of electrical properties, the volume resistivity of all examples reaches 1.2 × 10⁻⁶. 14 Ω・m and above, much higher than the comparative example of 0.4-0.9×10 14 The insulation performance is significantly improved (Ω·m), and the coefficient of thermal expansion in the examples is 7.5-7.8 × 10⁻⁶. -6 / ℃, lower than the comparative example's 8.2-8.9×10 -6 The ceramic exhibits superior thermal stability at / ℃, thanks to the synergistic effect of the doping and mixing system and the modifying reagents of this invention. This optimizes the ceramic microstructure, reduces thermal expansion differences, and ensures excellent insulation, solving the problem of performance imbalance in traditional processes and enabling simultaneous improvement in the mechanical, electrical, and thermal properties of ceramics.

[0135] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A process for the preparation of doped composite additive alumina ceramic sintered at low temperature, characterized in that, Includes the following steps: S1. Add alumina powder and modified composite additives to anhydrous ethanol and ball mill for 20-24 hours. Dry the ball-milled slurry at 75-80℃ for 10-12 hours. Grind the dried powder agglomerates and pass them through a 200-230 mesh sieve to obtain mixed powder. S2. Mix the powder with water and place it in a mold. Hold the pressure at 100-300MPa for 5-10 minutes to make a wet blank. Let the wet blank air dry naturally at room temperature for 2-4 hours, and then dry it at 60-70℃ for 6.5-8 hours to obtain a green blank. S3. The green body is heated to 600-650℃ at a rate of 3-5℃ / min, and then heated to 1270-1330℃ at a rate of 8-10℃ / min, and held for 4-6 hours to obtain alumina ceramic. The modified composite additive is prepared through the following steps: S11. Separate the precipitate from the doped mixture system, wash the precipitate with deionized water to pH 6.4-7, vacuum dry at 75-80℃ for 10-12h, and calcine at 520-550℃ for 2.5-3h in a nitrogen-hydrogen mixed atmosphere. S12. After the calcined product is cooled to room temperature, it is ball-milled for 1.5-2 hours and then passed through a 200-300 mesh sieve to obtain ball-milled powder. S13. Add the ball-milled powder to a mixed solution of γ-methacryloxypropyltrimethoxysilane and ethanol, stir at room temperature for 25-30 min, and then vacuum dry at 50-60℃ for 2-3 h to obtain the modified composite additive. The doped mixture system in step S11 is prepared through the following steps: S111. A precursor solution is prepared by mixing lanthanum nitrate, yttrium nitrate, cerium nitrate, zirconium nitrate, and deionized water. S112. Add the mixture of the modifying reagent, magnesium oxide, calcium oxide, zinc borate, and kaolin to an ethanol solution, stir at a constant temperature of 65-70℃ for 3.5-4 hours, and after the reaction is complete, centrifuge to separate the precipitate, wash the precipitate 3-4 times with a deionized water-ethanol mixture, and vacuum dry to obtain the modified precursor. S113. Add the modified precursor to the precursor solution, add citric acid as a complexing agent, and stir at 65-70℃ for 2.5-3h to obtain a doped mixed system. The modifying reagent in step S112 is prepared through the following steps: S121. Dissolve γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane in anhydrous ethanol to obtain a silane ethanol solution, add maleic anhydride and pyridine, and stir the reaction at 40-50℃ for 3-4 hours. S122. After the reaction is complete, remove the unreacted maleic anhydride and pyridine to obtain the modified hydroxylating agent. S123. Dissolve the modified hydroxylating agent in an ethanol-water mixture, and adjust the pH to 6.8-7.2 with sodium acetate-acetic acid buffer solution to obtain the modified agent.

2. The process for the preparation of alumina ceramic sintered at low temperature doped with a complex additive according to claim 1, characterized in that: In step S1, the mass ratio of alumina powder, modified composite additive reagent, and anhydrous ethanol is 100:(2-8):(120-180), and in step S2, the mass ratio of the mixed powder to water is 100:(8-15).

3. The process for the preparation of alumina ceramic sintered at low temperature with doped complex additives according to claim 1, characterized in that: In step S13, the mass ratio of ball-milled powder, γ-methacryloxypropyltrimethoxysilane, and ethanol is 100:(1-5):(80-120).

4. The process for the preparation of alumina ceramic sintered at low temperature with doped complex additives according to claim 1, characterized in that: In step S111, the mass ratio of lanthanum nitrate, yttrium nitrate, cerium nitrate, zirconium nitrate to deionized water is (5-10):(5-10):(5-10):(70-85):(200-300).

5. The process for the preparation of alumina ceramic sintered at low temperature with doped complex additives according to claim 1, characterized in that: In step S112, the mass ratio of the modifying reagent, magnesium oxide, calcium oxide, zinc borate, and kaolin is 100:(20-40):(10-20):(15-30):(25-45), and the mass ratio of the mixture to the ethanol solution is 100:(150-250).

6. The process for the preparation of alumina ceramic sintered at low temperature with doped complex additives according to claim 1, characterized by the fact that: In step S113, the mass ratio of the modified precursor, the precursor solution, and citric acid is 100:(300-500):(5-15).

7. The process for the preparation of alumina ceramic sintered at low temperature with doped complex additives according to claim 1, characterized by the fact that: In step S121, the mass ratio of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and anhydrous ethanol is (40-60):(40-60):(200-300), and the mass ratio of the silane ethanol solution to maleic anhydride and pyridine is 100:(5-15):(1-3).

8. The process for the preparation of alumina ceramic sintered at low temperature doped with a complex additive according to claim 1, characterized in that: In step S123, the mass ratio of the modified hydroxylating agent to the ethanol-water mixed solution is 100:(150-250).

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