Alpha-alumina powder and preparation method thereof

Abstract

The invention discloses alpha-aluminum oxide powder and a preparation method thereof.The preparation method of the alpha-aluminum oxide powder comprises the following steps that an aluminum source is subjected to segmented pretreatment through deionized water and organic acid, and the pretreated aluminum source is obtained; preparing aluminum hydroxide sol from the pretreated aluminum source; preparing a TiO2-ZrO2 precursor solution; the preparation method comprises the following steps: preparing core-shell intermediate powder from a TiO2-ZrO2 precursor solution and aluminum hydroxide sol; carrying out shell layer mechanical shell breaking on the core-shell intermediate powder to obtain pre-sintered powder; carrying out segmented sintering on the powder to be sintered, and then grinding to obtain alpha-aluminum oxide powder; the prepared alpha-alumina powder is low in sodium content, large in grain size and uniform in grain size.

Description

Technical Field

[0001] The present invention relates to the field of α-aluminum oxide powder, and in particular to the technical field of an α-aluminum oxide powder and a preparation method thereof. Background Art

[0002] α-aluminum oxide powder has the characteristics of high melting point, good thermal stability, good chemical stability, good insulation performance, high acid and alkali resistance, high mechanical strength, wear and impact resistance, etc., and is widely used in shaped and unshaped refractory materials, refractory castable binders, wear-resistant abrasives, high-purity refractory fibers, special ceramics, electronic ceramics, etc.; among them, the current application of electronic ceramics has strict requirements for α-aluminum oxide powder, which requires high strength and high thermal conductivity at the same time. Therefore, it is necessary to increase the grain size of α-aluminum oxide powder and make the grain size distribution uniform. Specifically, the sodium ion content (Na + <100 ppm), the grain size D50≥6.5μm, and the particle size distribution is uniform (D90 / D10<3).

[0003] Traditional preparation processes (such as Bayer method calcination or high-temperature solid-phase method) have limitations: the residual sodium impurities in the raw materials are easy to form a β-Al2O3 (Na2O·11Al2O3) solid solution, resulting in a high sodium content in the final product (usually Na + >200 ppm); at the same time, high-temperature sintering (>1500°C) is easy to cause abnormal grain growth, resulting in a too wide grain size distribution (D90 / D10>5).

[0004] Therefore, how to reduce the sodium impurity content while achieving large α-aluminum oxide grain size, uniform grain size, and improving the dielectric properties and reliability of electronic ceramic devices is a difficult problem that urgently needs to be solved in the field. Summary of the Invention

[0005] In order to solve the above technical problems, an α-aluminum oxide powder and a preparation method thereof are provided to achieve a low sodium content, large grain size, and uniform grain size in the prepared α-aluminum oxide powder.

[0006] According to one aspect of the present invention, a method for preparing an α-aluminum oxide powder is provided, including the following steps: Segmented pretreatment of an aluminum source with deionized water and an organic acid to obtain a pretreated aluminum source; Preparing aluminum hydroxide sol from the pretreated aluminum source; Preparing a TiO2-ZrO2 precursor solution; Preparing a core-shell intermediate powder from the TiO2-ZrO2 precursor solution and the aluminum hydroxide sol; Mechanically breaking the shell of the core-shell intermediate powder to obtain a powder for preliminary sintering; The preliminary sintered powder is subjected to segmented sintering and then ground to obtain α-aluminum oxide powder.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: By subjecting the aluminum source to segmented pretreatment with deionized water and organic acids, the sodium content in the α-aluminum oxide powder is low; By using a TiO2-ZrO2 precursor solution and aluminum hydroxide sol to prepare a core-shell intermediate powder, it is realized that the prepared core-shell intermediate powder includes an Al2O3 shell layer and a TiO2-ZrO2 nanocore coated with the Al2O3 shell layer, so that the distribution of Al2O3 and TiO2-ZrO2 in the preliminary sintered powder is uniform, thus avoiding the problem of abnormal growth of some particle sizes caused by the uneven distribution of Al2O3 and TiO2-ZrO2 during the sintering process, realizing uniform grain size in the prepared α-aluminum oxide powder, and at the same time, TiO2-ZrO2 reduces the grain boundary energy, which is beneficial to achieving a large grain size in the prepared α-aluminum oxide powder; By mechanically breaking the shell of the core-shell intermediate powder, it is realized that part of the alumina shell of the core-shell intermediate powder is broken, and part of the TiO2-ZrO2 crystal nucleus is exposed, avoiding the problem of slow heating rate of TiO2-ZrO2 during the sintering process caused by TiO2-ZrO2 being coated inside the core-shell structure, thus avoiding the problem of too high sintering temperature caused by the relatively high temperature at which TiO2-ZrO2 forms a liquid phase; avoiding the problem that the grain boundary energy of the outer-coated alumina decreases rapidly and too much due to TiO2-ZrO2 forming a liquid phase at a relatively high temperature, thus avoiding the phenomenon that some alumina grains fuse with each other to produce some abnormally grown grains, and realizing uniform grain size in the α-aluminum oxide powder; By subjecting the preliminary sintered powder to segmented sintering, it is realized that during the sintering process, the alumina shell of the core-shell intermediate powder first continues to break, then the alumina shell is completely dehydrated and crystal nuclei are generated, and subsequently the grains gradually grow, obtaining large grains with a grain D50≥6.5μm and uniform particle size.

[0008] Furthermore, the process of subjecting the aluminum source to segmented pretreatment includes a water washing section, an acid washing section, and a hot washing section; The process of the water washing section is to mix the aluminum source with deionized water in a double-helix staggered-layer water washing tank, add polyethylene glycol-400 for water washing, the water washing temperature is 60±2°C, and the water washing time is 15-25 min; The process of the acid washing section is to mix the water-washed aluminum source with the organic acid for cleaning, the acid washing temperature is 45±2°C, and the acid washing time is 8-12 min; The process of the hot washing section is to mix the acid-washed aluminum source with deionized water again for heating and cleaning, and the temperature is 80±2°C; Preferably, during the water washing stage, polyethylene glycol - 400 accounts for (0.018 - 0.022) wt% of the total mass of the aluminum source and deionized water; During the pickling stage, the organic acids used for cleaning include two or more of acetic acid, lactic acid, oxalic acid, malic acid, tartaric acid, and citric acid.

[0009] The beneficial effect of the previous step is that it is conducive to achieving a low sodium content in the α - alumina powder. The sodium removal from the surface of the aluminum source reaches more than 92% through the water washing stage; the lattice sodium removal rate within the aluminum source reaches more than 98% through the two - stage pickling; after the hot washing stage, the acid radical residue is < 5 ppm.

[0010] Furthermore, the double - helix staggered - layer water washing tank includes a main screw rod and a secondary screw rod; the rotation direction of the main screw rod is opposite to that of the secondary screw rod; The pitch ratio of the main screw rod to the secondary screw rod is (1.6 - 2.0):1; The difference between the inclination angle of the main screw rod with the horizontal direction and the inclination angle of the secondary screw rod with the horizontal direction is 11 - 20°; During the segmented pretreatment of the aluminum source, a turbulent flow area is formed in the double - helix staggered - layer water washing tank, and the Reynolds number of the turbulent flow area > 2200; During the hot washing stage, when the conductivity of the mixed solution of the aluminum source and water < 50 μS / cm and the redox potential > 200 mV, the segmented pretreatment of the aluminum source ends; Preferably, the pitch of the main screw rod is 145 - 155 mm, and the inclination angle of the main screw rod with the horizontal direction is 43 - 48°; the pitch of the secondary screw rod is 75 - 85 mm, and the inclination angle of the secondary screw rod with the horizontal direction is 28 - 32°.

[0011] The beneficial effect of the previous step is that by having the rotation direction of the main screw rod opposite to that of the secondary screw rod, a turbulent flow area is formed in the solution, strengthening the penetration of the acid radical into the aluminum source and increasing the sodium removal rate; By ending the segmented pretreatment of the aluminum source when the conductivity of the mixed solution of the aluminum source and water < 50 μS / cm and the redox potential > 200 mV, a high sodium removal rate is achieved while effectively avoiding a high aluminum loss rate, and the aluminum loss rate < 0.8% is realized.

[0012] Furthermore, the preparation process of the aluminum hydroxide sol includes the following steps: Add the pretreated aluminum source into deionized water, then add the organic acid for reaction, and react at 100 - 120 °C for 5 - 10 h to obtain the aluminum hydroxide sol; The molar ratio of aluminum element in the pretreated aluminum source to the carboxylate group of the organic acid for reaction is 1:(3.5 - 4); The organic acids for reaction include two or more of formic acid, acetic acid, lactic acid, and oxalic acid.

[0013] Further, the preparation process of the TiO2-ZrO2 precursor solution includes the following steps: Add tetrabutyl titanate and zirconium oxychloride into deionized water to obtain a first mixed solution; Then adjust the pH of the first mixed solution to 3.0 - 4.0; Then age at 55 - 65 °C for 0.8 - 1.2 h to obtain the TiO2-ZrO2 precursor solution; The molar ratio of tetrabutyl titanate to zirconium oxychloride is (2.5 - 6.5):1.

[0014] Further, the preparation process of the core-shell intermediate powder includes the following steps: Add Al(OH)3 sol into the TiO2-ZrO2 precursor to obtain a second mixed solution; Adjust the pH of the second mixed solution to 2.2 - 2.8, and then stir at 75 - 85 °C for 2 - 4 h to obtain a third mixed solution; Adjust the pH of the third mixed solution to 4.0 - 5.0, and then perform spray drying to obtain the core-shell intermediate powder.

[0015] The beneficial effect of the previous step is that by adding Al(OH)3 sol into the TiO2-ZrO2 precursor and adjusting the pH of the second mixed solution to 2.2 - 2.8, TiO2-ZrO2 nanocrystals are formed in the second mixed solution, and at the same time, silicon impurities in the Al(OH)3 sol and the TiO2-ZrO2 precursor jointly form TiO2-ZrO2-SiO2 nanocrystals; By adjusting the pH of the third mixed solution to 4.0 - 5.0, an aluminum hydroxide shell layer is coated outside the nanocrystals; By performing spray drying, dehydration is achieved to obtain the core-shell intermediate powder.

[0016] Further, the third mixed solution includes TiO2-ZrO2 nanocrystals and TiO2-ZrO2-SiO2 nanocrystals; the diameter of the TiO2-ZrO2 nanocrystals is 5 - 8 nm, and the diameter of the TiO2-ZrO2-SiO2 nanocrystals is 5 - 8 nm; The core-shell intermediate powder includes an Al2O3 shell layer, and TiO2-ZrO2 nanocrystals and TiO2-ZrO2-SiO2 nanocrystals coated with the Al2O3 shell layer; The thickness of the Al2O3 shell layer is 10 - 100 nm; The mass ratio of the Al2O3 shell layer to the TiO2-ZrO2 nanocrystals is (0.5 - 0.7):(99.3 - 99.5).

[0017] The beneficial effect of the previous step is that by including TiO2-ZrO2 nano-nuclei and TiO2-ZrO2-SiO2 nano-nuclei in the third mixed solution, the silicon content in the lattice of the α-alumina powder is reduced.

[0018] Further, the preparation process of the preliminary sintered powder includes the following steps: adding the core-shell intermediate powder into a differential stirring device and stirring at room temperature, with the rotation speed of the device being 80-120 rpm and the stirring time being 12-18 min to obtain the preliminary sintered powder; preferably, the differential stirring device is a kneader.

[0019] The beneficial effect of the previous step is that partial fragmentation of the alumina shell of the core-shell intermediate powder is achieved.

[0020] Further, the process of segmental sintering the preliminary sintered powder includes: Performing the first-stage sintering on the preliminary sintered powder, heating from room temperature to 600-800 °C at a heating rate of 8-10 °C / min, with the sintering atmosphere being air and the heating time at 600-800 °C being 12-18 min; Then performing the second-stage sintering, heating from 600-800 °C to 1000-1200 °C at a heating rate of 4-6 °C / min, with the sintering atmosphere being air and the heating time at 1000-1200 °C being 18-22 min; Then performing the third-stage sintering, heating from 1000-1200 °C to 1650 ± 10 °C at a heating rate of 1-3 °C / min, with the sintering atmosphere being an oxygen-rich atmosphere and the heating time at 1650 ± 10 °C being 40-50 min; In the rapid cooling stage, cooling from 750-850 °C to 180-220 °C at a cooling rate of 8-15 °C / min, with the cooling atmosphere being air; Preferably, the oxygen-rich atmosphere has a mass fraction of O2 of 28%.

[0021] The beneficial effect of the previous step is that rapid dehydration is achieved through the first-stage sintering, which is beneficial for further fragmentation of the alumina shell of the core-shell intermediate powder; Dehydration of the alumina shell and formation of crystal nuclei are achieved through the second-stage sintering; Orientation growth of grains is achieved through the third-stage sintering, resulting in large and uniformly sized grains; Through the rapid cooling stage, it is beneficial to avoid secondary agglomeration of the generated α-alumina powder.

[0022] Another aspect of the present invention provides an α-alumina powder, which is prepared by the α-alumina powder preparation method; The D50 of the α-aluminum oxide powder grains is ≥6.5 μm, and D90 / D10 < 3; the sodium residue in the α-aluminum oxide powder is < 100 ppm, and the silicon residue is < 100 ppm; the dielectric constant (1 MHz) of the α-aluminum oxide powder is 9.0 - 10.0.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: achieving large grain sizes of the α-aluminum oxide powder, achieving uniform grain sizes of the α-aluminum oxide powder, and having low sodium residue and low silicon residue in the α-aluminum oxide powder. Specific Embodiments

[0024] To better understand the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0025] Example 1: This example provides a method for preparing α-aluminum oxide powder, including the following steps: The aluminum source is pretreated in sections with deionized water and organic acids to obtain a pretreated aluminum source; The process of pretreating the aluminum source in sections includes a water washing section, an acid washing section, and a hot washing section; The process of the water washing section is to mix the aluminum source with deionized water in a double-helix staggered water washing tank, add polyethylene glycol-400 for water washing, the water washing temperature is 60 °C, and the water washing time is 20 min; The process of the acid washing section is to mix the water-washed aluminum source with the organic acid for cleaning, the acid washing temperature is 45 °C, and the acid washing time is 10 min; the organic acid for cleaning includes acetic acid and lactic acid; The process of the hot washing section is to mix the acid-washed aluminum source with deionized water again for heating and cleaning, the temperature is 80 °C, and when the conductivity in the mixed solution of the aluminum source and water < 50 μS / cm and the redox potential > 200 mV, the sectional pretreatment of the aluminum source ends; In the process of the water washing section, polyethylene glycol-400 accounts for 0.02 wt% of the total mass of the aluminum source and deionized water; The double-helix staggered water washing tank includes a main screw rod and a secondary screw rod; the rotation direction of the main screw rod is opposite to that of the secondary screw rod; The pitch of the main screw rod is 150 mm, and the inclination angle of the main screw rod with the horizontal direction is 45°; The pitch of the secondary screw rod is 80 mm, and the inclination angle of the secondary screw rod with the horizontal direction is 30°; During the sectional pretreatment of the aluminum source, a turbulent flow area is formed in the double-helix staggered water washing tank, and the Reynolds number of the turbulent flow area > 2200.

[0026] Prepare aluminum hydroxide sol from the pretreated aluminum source; the process of preparing the aluminum hydroxide sol includes the following steps: Add the pretreated aluminum source to deionized water, then add the organic acid for the reaction, and react at 119 °C for 7.5 h to obtain an aluminum hydroxide sol; The molar ratio of aluminum element in the pretreated aluminum source to the carboxylate group of the organic acid for the reaction is 1:3.8; the organic acid for the reaction includes formic acid and acetic acid.

[0027] Prepare a TiO2-ZrO2 precursor solution; the preparation process of the TiO2-ZrO2 precursor solution includes the following steps: Add tetrabutyl titanate and zirconium oxychloride to deionized water to obtain a first mixed solution; then adjust the pH of the first mixed solution to 3.5; then age at 60 °C for 1 h to obtain a TiO2-ZrO2 precursor solution; the molar ratio of tetrabutyl titanate to zirconium oxychloride is 4.5:1.

[0028] Prepare a core-shell intermediate powder from the TiO2-ZrO2 precursor solution and the aluminum hydroxide sol; the preparation process of the core-shell intermediate powder includes the following steps: Add the Al(OH)3 sol to the TiO2-ZrO2 precursor to obtain a second mixed solution; Adjust the pH of the second mixed solution to 2.5, then stir at 80 °C for 3 h to obtain a third mixed solution; the third mixed solution includes TiO2-ZrO2 nanocores and TiO2-ZrO2-SiO2 nanocores; the diameter of the TiO2-ZrO2 nanocores is 6.2 - 6.8 nm, and the diameter of the TiO2-ZrO2-SiO2 nanocores is 6.2 - 6.8 nm; Adjust the pH of the third mixed solution to 4.5, then perform spray drying to obtain a core-shell intermediate powder; The core-shell intermediate powder includes an Al2O3 shell layer, and TiO2-ZrO2 nanocores and TiO2-ZrO2-SiO2 nanocores coated with the Al2O3 shell layer; the thickness of the Al2O3 shell layer is 53 - 58 nm; The mass ratio of the Al2O3 shell layer to the TiO2-ZrO2 nanocores is 0.6:99.38.

[0029] Mechanically break the shell of the core-shell intermediate powder to obtain a pre-sintered powder; the preparation process of the pre-sintered powder includes the following steps: add the core-shell intermediate powder to a kneader and stir at room temperature, the rotation speed of the equipment is 100 rpm, and the stirring time is 10 min to obtain a pre-sintered powder.

[0030] Perform segmented sintering on the pre-sintered powder, and then grind to obtain α-aluminum oxide powder.

[0031] The process of performing segmented sintering on the pre-sintered powder includes: The preliminary sintered powder is subjected to the first-stage sintering, heated from room temperature to 700 °C at a heating rate of 9 °C / min, the sintering atmosphere is air, and the heating time at 700 °C is 10 min; Then, the second-stage sintering is carried out, heated from 700 °C to 1100 °C at a heating rate of 5 °C / min, the sintering atmosphere is air, and the heating time at 1100 °C is 20 min; Then, the third-stage sintering is carried out, heated from 1100 °C to 1650 °C at a heating rate of 2 °C / min, the sintering atmosphere is an oxygen-rich atmosphere, and the heating time at 1650 °C is 45 min; the oxygen-rich atmosphere has a mass fraction of O2 of 28%; In the rapid cooling stage, it is cooled from 800 °C to 200 °C at a cooling rate of 12 °C / min, and the cooling atmosphere is air.

[0032] Another aspect of this embodiment provides an α-aluminum oxide powder, which is prepared by the α-aluminum oxide powder preparation method; The grain size D50 of the α-aluminum oxide powder is 7 μm, D90 / D10 = 2.7; the sodium residue in the α-aluminum oxide powder is 85 ppm, and the silicon residue is 75 ppm; the dielectric constant (1 MHz) of the α-aluminum oxide powder is 9.2.

[0033] Example 2: The same content as in Example 1 will not be elaborated here; the different solutions from Example 1 are as follows: One aspect of this embodiment provides an α-aluminum oxide powder preparation method, The pretreated aluminum source is added to deionized water, and then the organic acid for reaction is added, and the reaction is carried out at 118 °C for 5.5 h to obtain an aluminum hydroxide sol; The molar ratio of aluminum element in the pretreated aluminum source to the carboxylate group of the organic acid for reaction is 1:3.9; the organic acid for reaction includes lactic acid and oxalic acid.

[0034] The preparation process of the TiO2-ZrO2 precursor solution includes the following steps: Tetrabutyl titanate and zirconium oxychloride are added to deionized water to obtain a first mixed solution; then the pH of the first mixed solution is adjusted to 3.8; then it is aged at 63 °C for 0.9 h to obtain a TiO2-ZrO2 precursor solution; the molar ratio of tetrabutyl titanate to zirconium oxychloride is 6.3:1.

[0035] The preparation process of the core-shell intermediate powder includes the following steps: The Al(OH)3 sol is added to the TiO2-ZrO2 precursor to obtain a second mixed solution; Adjust the pH of the second mixed solution to 2.7, and then stir at 83 °C for 2.5 h to obtain a third mixed solution; the diameter of the TiO2-ZrO2 nanocore is 5.3 - 5.5 nm, and the diameter of the TiO2-ZrO2-SiO2 nanocore is 5.3 - 5.5 nm; Adjust the pH of the third mixed solution to 4.8, and then perform spray drying to obtain a core-shell intermediate powder; The core-shell intermediate powder includes an Al2O3 shell layer, and a TiO2-ZrO2 nanocore and a TiO2-ZrO2-SiO2 nanocore coated with the Al2O3 shell layer; the thickness of the Al2O3 shell layer is 88 - 92 nm; The mass ratio of the Al2O3 shell layer to the TiO2-ZrO2 nanocore is 0.68:99.3.

[0036] Perform the first-stage sintering on the preliminary sintering powder, heat from room temperature to 780 °C at a heating rate of 9.8 °C / min, the sintering atmosphere is air, and the heating time at 780 °C is 13 min; Then perform the second-stage sintering, heat from 780 °C to 1180 °C at a heating rate of 5.8 °C / min, the sintering atmosphere is air, and the heating time at 1180 °C is 19 min; Then perform the third-stage sintering, heat from 1180 °C to 1656 °C at a heating rate of 2.8 °C / min, the sintering atmosphere is an oxygen-rich atmosphere, and the heating time at 1656 °C is 43 min; In the rapid cooling stage, cool from 800 °C to 200 °C at a cooling rate of 9 = 11 °C / min, and the cooling atmosphere is air.

[0037] Another aspect of this embodiment provides an α-aluminum oxide powder, which is prepared by the α-aluminum oxide powder preparation method; The grain size D50 of the α-aluminum oxide powder is 8.8 μm, D90 / D10 = 2.5; the sodium residue in the α-aluminum oxide powder is 80 ppm, and the silicon residue is 65 ppm; the dielectric constant (1 MHz) of the α-aluminum oxide powder is 9.4.

[0038] Example 3: The same content as in Example 1 will not be repeated; the different solutions in this example from Example 1 are as follows: One aspect of this example provides an α-aluminum oxide powder preparation method, Add the pretreated aluminum source to deionized water, and then add the organic acid for reaction. React at 106 °C for 9.8 h to obtain an aluminum hydroxide sol; The molar ratio of aluminum element in the pretreated aluminum source to the carboxylate group of the organic acid for reaction is 1:3.6; The organic acid for reaction includes formic acid and oxalic acid.

[0039] The preparation process of the TiO2-ZrO2 precursor solution includes the following steps: Add tetrabutyl titanate and zirconium oxychloride into deionized water to obtain a first mixed solution; then adjust the pH of the first mixed solution to 3.2; then age at 56°C for 1.1 h to obtain the TiO2-ZrO2 precursor solution; the molar ratio of tetrabutyl titanate to zirconium oxychloride is 3:1.

[0040] The preparation process of the core-shell intermediate powder includes the following steps: Add Al(OH)3 sol into the TiO2-ZrO2 precursor to obtain a second mixed solution; Adjust the pH of the second mixed solution to 2.3, and then stir at 78°C for 3.6 h to obtain a third mixed solution; the diameter of the TiO2-ZrO2 nanocore is 7.3 - 7.8 nm, and the diameter of the TiO2-ZrO2-SiO2 nanocore is 7.3 - 7.8 nm; Adjust the pH of the third mixed solution to 4.3, and then perform spray drying to obtain the core-shell intermediate powder; The thickness of the Al2O3 shell layer is 33 nm; The mass ratio of the Al2O3 shell layer to the TiO2-ZrO2 nanocore is 0.5:99.45.

[0041] Perform the first-stage sintering on the pre-sintered powder, heat from room temperature to 630°C at a heating rate of 8.8°C / min, the sintering atmosphere is air, and the heating time at 630°C is 13.5 min; Then perform the second-stage sintering, heat from 630°C to 1020°C at a heating rate of 4.3°C / min, the sintering atmosphere is air, and the heating time at 1020°C is 18 - 22 min; Then perform the third-stage sintering, heat from 1020°C to 1650°C at a heating rate of 1.5°C / min, the sintering atmosphere is an oxygen-rich atmosphere, and the heating time at 1650°C is 43 min; In the rapid cooling stage, cool from 750 - 850°C to 180 - 220°C at a cooling rate of 8 - 15°C / min, and the cooling atmosphere is air.

[0042] Another aspect of this embodiment provides an α-aluminum oxide powder, which is prepared by the α-aluminum oxide powder preparation method; The grain size D50 of the α-aluminum oxide powder is 7.8 μm, D90 / D10 = 2.9; the sodium residue in the α-aluminum oxide powder is 70 ppm, and the silicon residue is 63 ppm; the dielectric constant (1 MHz) of the α-aluminum oxide powder is 9.7.

[0043] The above description is only a preferred embodiment of the present application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solution formed by mutually replacing the above features with the technical features (but not limited to) disclosed in the present application that have similar functions.

Claims

1. A method for preparing α-aluminum oxide powder, characterized in that, It includes the following steps: Segmentally pre-treat the aluminum source with deionized water and organic acid to obtain the pre-treated aluminum source; Prepare aluminum hydroxide sol from the pre-treated aluminum source; Prepare TiO2-ZrO2 precursor solution; Prepare core-shell intermediate powder from TiO2-ZrO2 precursor solution and aluminum hydroxide sol; Mechanically break the shell of the core-shell intermediate powder to obtain the pre-sintering powder; Segmentally sinter the pre-sintering powder and then grind it to obtain α-aluminum oxide powder.

2. The preparation method of α-aluminum oxide powder according to claim 1, characterized in that, The process of segmentally pre-treating the aluminum source includes a water washing section, an acid washing section, and a hot washing section; The process of the water washing section is to mix the aluminum source with deionized water in a double-helix staggered-layer water washing tank, add polyethylene glycol-400 for water washing, the water washing temperature is 60±2°C, and the water washing time is 15-25 min; The process of the acid washing section is to mix the water-washed aluminum source with the organic acid for cleaning, the acid washing temperature is 45±2°C, and the acid washing time is 8-12 min; The process of the hot washing section is to mix the acid-washed aluminum source with deionized water again for heating and cleaning, and the temperature is 80±2°C.

3. The method for preparing α-aluminum oxide powder according to claim 2, wherein, The double-helix staggered-layer water washing tank includes a main screw rod and a secondary screw rod; the rotation direction of the main screw rod is opposite to that of the secondary screw rod; The pitch ratio of the main screw rod to the secondary screw rod is (1.6-2.0):1; The difference between the inclination angle of the main screw rod with the horizontal direction and the inclination angle of the secondary screw rod with the horizontal direction is 11-20°; During the process of segmentally pre-treating the aluminum source, a turbulent zone is formed in the liquid in the double-helix staggered-layer water washing tank, and the Reynolds number of the turbulent zone > 2200; During the process of the hot washing section, when the conductivity of the mixed solution of the aluminum source and water < 50 μS / cm and the redox potential > 200 mV, the segmental pre-treatment of the aluminum source ends.

4. The method for preparing α-aluminum oxide powder according to claim 1, wherein The process of preparing the aluminum hydroxide sol includes the following steps: Add the pre-treated aluminum source into deionized water, then add the organic acid for reaction, and react at 100-120°C for 5-10 h to obtain aluminum hydroxide sol; The molar ratio of aluminum element in the pre-treated aluminum source to the carboxylate group of the organic acid for reaction is 1:(3.5-4); The organic acid for reaction includes two or more of formic acid, acetic acid, lactic acid, and oxalic acid.

5. The method for preparing α-aluminum oxide powder according to claim 1, wherein The process of preparing the TiO2-ZrO2 precursor solution includes the following steps: Add tetrabutyl titanate and zirconium oxychloride into deionized water to obtain a first mixed solution; Then adjust the pH of the first mixed solution to 3.0-4.0; Then age at 55-65°C for 0.8-1.2 h to obtain TiO2-ZrO2 precursor solution; The molar ratio of tetrabutyl titanate to zirconium oxychloride is (2.5-6.5):

1.

6. The method for preparing α-aluminum oxide powder according to claim 1, characterized in that, The process of preparing the core-shell intermediate powder includes the following steps: Add the Al(OH)3 sol into the TiO2-ZrO2 precursor to obtain a second mixed solution; Adjust the pH of the second mixed solution to 2.2-2.8, then stir at 75-85°C for 2-4 h to obtain a third mixed solution; Adjust the pH of the third mixed solution to 4.0-5.0, and then perform spray drying to obtain the core-shell intermediate powder.

7. The method for preparing α-aluminum oxide powder according to claim 6, characterized in that, The third mixed solution includes TiO2-ZrO2 nanocores and TiO2-ZrO2-SiO2 nanocores; the diameter of the TiO2-ZrO2 nanocores is 5-8 nm, and the diameter of the TiO2-ZrO2-SiO2 nanocores is 5-8 nm; The core-shell intermediate powder includes an Al2O3 shell layer, and TiO2-ZrO2 nanocores and TiO2-ZrO2-SiO2 nanocores coated with the Al2O3 shell layer; The thickness of the Al2O3 shell layer is 10-100 nm; The mass ratio of the Al2O3 shell layer to the TiO2-ZrO2 nanocores is (0.5-0.7):(99.3-99.5).

8. The method for preparing α-aluminum oxide powder according to claim 1, characterized in that, The preparation process of the preliminary sintered powder includes the following steps: adding the core-shell intermediate powder into a differential stirring device and stirring at room temperature, the rotation speed of the device is 80-120 rpm, and the stirring time is 12-18 min to obtain the preliminary sintered powder.

9. The method for preparing α-aluminum oxide powder according to claim 1, wherein, The process of subjecting the preliminary sintered powder to staged sintering includes: Performing the first-stage sintering on the preliminary sintered powder, heating from room temperature to 600-800 °C, the heating rate is 8-10 °C / min, the sintering atmosphere is air, and the heating time at 600-800 °C is 12-18 min; Then performing the second-stage sintering, heating from 600-800 °C to 1000-1200 °C, the heating rate is 4-6 °C / min, the sintering atmosphere is air, and the heating time at 1000-1200 °C is 18-22 min; Then performing the third-stage sintering, heating from 1000-1200 °C to 1650±10 °C, the heating rate is 1-3 °C / min, the sintering atmosphere is an oxygen-rich atmosphere, and the heating time at 1650±10 °C is 40-50 min; In the rapid cooling stage, cooling from 750-850 °C to 180-220 °C, the cooling rate is 8-15 °C / min, and the cooling atmosphere is air.

10. An α-aluminum oxide powder, characterized in that, Prepared by the method for preparing α-aluminum oxide powder according to any one of claims 1-9; The α-aluminum oxide powder has a grain size D50≥6.5 μm and D90 / D10<3; the sodium residue in the α-aluminum oxide powder is<100 ppm, and the silicon residue is<100 ppm.