High-activity high-purity corundum micro powder as well as preparation method and application thereof
By generating a hydrated alumina shell structure on the surface of high-purity corundum micropowder and calcining it at high temperature, the problems of low sintering activity and impurity introduction in traditional methods are solved, and high-purity, high-activity corundum micropowder is prepared efficiently for the preparation of high-density, high-hardness alumina ceramics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2026-02-05
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies for preparing high-purity corundum micro powder suffer from problems such as low sintering activity, high energy consumption, high cost, easy introduction of impurities, and complex processes, making it difficult to effectively improve the performance of alumina-based materials.
The method for preparing highly active and high-purity corundum micro powder includes calcining aluminum hydroxide micro powder at high temperature to generate α-Al2O3, then forming a hydrated boehmite shell structure on its surface, and calcining at high temperature to form highly active and high-purity corundum micro powder, thereby controlling the impurity content and simplifying the process.
It improves the sintering activity and purity of corundum micro powder, reduces production costs, simplifies the process, avoids the introduction of impurities, and is suitable for preparing high-density and high-hardness alumina ceramics.
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Figure CN122010152A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of special alumina or fine alumina technology, and particularly to a highly active, high-purity corundum micro powder, its preparation method, and its application. Background Technology
[0002] Corundum micro powder, also known as α-Al₂O₃ micro powder, is widely used in ceramics, crucibles, refractories, and biomaterials. However, traditional corundum micro powder has low sintering activity, requiring high-temperature (>1600 ℃) and long-term sintering, deep grinding, the addition of additives, or the use of specific equipment for molding and sintering to obtain high-density alumina-based materials. This not only involves high energy consumption and investment, and may introduce impurities, but also makes post-processing difficult. Therefore, improving the sintering activity of corundum micro powder is of great significance for economically improving the performance of alumina-based materials.
[0003] The raw material for corundum micro powder mainly comes from aluminum hydroxide micro powder obtained by calcining aluminum oxide powder in sodium aluminate solution or subsequently roasting alumina powder, which is then calcined at high temperature (>1200℃) to obtain corundum micro powder. Generally, the micro powder is required to be in the α-Al₂O₃ phase, with an α-Al₂O₃ content greater than 90%. To improve the performance of alumina-based materials, current research mainly focuses on refining, purifying, surface modifying, and adding sintering aids to alumina powder. The main methods include: 1) Particle size refinement and purification, generally using nano-alumina powder or deeply ground alumina powder (CN200910040429.2); the powder can also be acid-washed (CN202411268378.X) or water-washed to remove impurities and purify corundum powder. These refinement and purification processes will significantly increase the cost of powder preparation or introduce impurities during grinding; 2) Surface modification, adding inorganic acids (CN202011555880.0) or organic substances to modify the surface and enhance particle dispersibility, such as adding alumina sol as a binder or adding organic substances to change particle agglomeration. These surface modification methods can enhance particle dispersibility. 3) Pyrometallurgical treatment of powders improves purity and α-Al2O3 content. Boric acid is often added for desodiuming, while the addition of mineralizers such as NH4Cl, NH4F, and AlF3 (CN200810029087.X, CN01803230.3) can lower the phase transformation temperature and increase the α-Al2O3 content. Although this improves sintering performance and increases the density of alumina ceramics, it introduces impurities, making it difficult to meet flue gas standards and affecting product performance; 4) Adding sintering additives, such as MgO, SiO2, TiO2, ZrO2, or other rare metal oxides (CN... Although the interface was improved, the particle size was suppressed, and the density and hardness of alumina-based materials were increased, the entry of impurities changed the physical properties of alumina-based materials; 5) New sintering equipment or new sintering processes were adopted (Xie Zhipeng et al., Research progress on new sintering technologies for advanced ceramic materials, China Materials Progress. 2019, 38(09): 821-830). These new technologies can improve the density and hardness of alumina-based materials, but they will also significantly increase the manufacturing cost.
[0004] The aforementioned powder post-processing or the use of new sintering technologies can all be referred to as "end-stage strengthening" processes in the preparation of alumina-based materials. These processes often lead to the introduction of impurities, increased process complexity, limited application areas, and higher costs. There is little focus on the impact of high-quality α-Al2O3 micropowder on the sintering performance of alumina-based materials from the source, and even less emphasis on proposing technologies to improve the sintering performance of alumina-based materials through the regulation of α-Al2O3 microstructure and reactivity. Summary of the Invention
[0005] This invention provides a highly active and high-purity corundum micro powder, its preparation method, and its application. The purpose is to provide a method to improve the quality and performance of α-Al2O3 micro powder without increasing the introduction of impurities and simplifying the process.
[0006] To achieve the above objectives, the present invention provides a method for preparing highly active, high-purity corundum micro powder, comprising the following steps: S1. Aluminum hydroxide micro powder was prepared by high-temperature seeding using sodium aluminate solution as raw material; S2. Calcining the aluminum hydroxide micro powder obtained in S1 at high temperature to prepare α-Al2O3 corundum micro powder; S3. The α-Al2O3 corundum micropowder obtained in S2 is wet-processed to generate boehmite on its surface, forming a corundum-boehmite mixed phase. The boehmite has a shell structure with a thickness of less than 200 nm and a mass of less than 10 wt% of the total mass of the corundum-boehmite mixed phase. S4. The corundum-diatomite mixture obtained in S4 is roasted or calcined at high temperature to generate highly active and high-purity corundum micro powder.
[0007] Preferably, in the high-temperature fraction described in S1, the sodium aluminate solution contains sodium oxide (Na₂O). k Concentration of 80~160 g / L, caustic ratio α k The concentration is 1.35~1.60; the high-temperature seeding specifically includes: adding active seed crystals at 0.5~20 g / L, and seeding at an initial temperature of 75~80℃ and a final temperature of 60~65℃ to prepare aluminum hydroxide micropowder with a gibbsite phase. The particle size of the aluminum hydroxide micropowder is d50<4μm, d90≤11.7μm, and more preferably d90<10μm; the purity of aluminum hydroxide is >99.6%, wherein, by mass percentage, Na2O≤0.11%, Fe2O3<0.02%, SiO2<0.02%, CaO<0.002%, MgO<0.002%. More preferably, Na2O≤0.10%.
[0008] Preferably, the high-temperature calcination temperature in step S2 is 1150~1350 ℃, and the time is 1~6 h. The prepared α-Al2O3 corundum micro powder contains ≥90% α-Al2O3 by mass, of which AlO6 structural unit content is >90% by atomic percentage, and the density of the α-Al2O3 corundum micro powder is >3.90 g / cm³. 3 Specific surface area S BET <4 m 2 / g; by mass percentage, Na2O≤0.16%, Fe2O3<0.02%, SiO2<0.02%, CaO<0.002%, MgO<0.002%. More preferably, Na2O≤0.12%.
[0009] Preferably, the wet processing of corundum micro powder described in S3 includes at least one of the following methods: Option 1: In Na2O k <20 g / L, caustic ratio α k In a supersaturated sodium aluminate solution with a concentration of 1.35–2.0, the temperature was controlled at 80–130 °C, and the seeding time was 60 min–10 h. Option 2: Add pseudoboehmite sol to α-Al2O3 corundum micro powder at a concentration of 0.5~5 g / L and treat at a temperature of 90~130℃ for 1~6 h; Option 3: Disperse α-Al2O3 corundum micro powder with water by wet ball milling at a ratio of 100~400 g / L, and treat at a temperature of 90~130℃ for 2~6 h.
[0010] Preferably, in the wet processing step S3, a surfactant is added. The surfactant includes one or more of glucose, stearic acid, oleic acid, Tween 80, or polyethylene glycol 6000-20000, and the amount added is 0-30 ppm. The resulting aluminum hydroxide micropowder has a particle size of less than 1 μm and a uniformly encapsulated core-shell structure. The addition of the surfactant can promote the uniform encapsulation of boehmite monohydrate, forming more uniform corundum-boehmite microparticles.
[0011] Preferably, after the wet processing described in S3, the resulting wet filter cake is hydrothermally treated at 150~220 °C for no more than 2 hours. Hydrothermal treatment promotes the formation of pure monohydrate diaspore and reduces interference from impurities.
[0012] Preferably, the high-temperature roasting or calcination temperature in S4 is 900~1200 ℃, and the time is 1~5 h.
[0013] Under the same technical concept, the present invention also provides a high-activity, high-purity corundum micro powder, wherein all phases of the high-activity, high-purity corundum micro powder are α-Al₂O₃, wherein, by atomic percentage, the content of AlO₆ structural units is >89%, the content of AlO₄ structural units is not less than 4.5%, and the density of the high-activity, high-purity corundum micro powder is >3.89 g / cm³. 3 Specific surface area S BET <7 m 2 / g; The high-activity, high-purity corundum micro powder has a d50 < 4 μm and a d90 < 10 μm. By mass, the micro powder contains Na2O ≤ 0.12%, Fe2O3 < 0.02%, SiO2 < 0.02%, CaO < 0.002%, MgO < 0.002%, and α-Al2O3 ≥ 91.7%.
[0014] Under the same technical concept, the present invention also provides an application of highly active and high-purity corundum micro powder, which is used to prepare high-density and high-hardness alumina ceramics.
[0015] Preferably, the method for preparing high-hardness alumina ceramics includes: molding and degreasing high-activity, high-purity corundum micro powder, and then sintering it at 1350~1500℃ for 2~5 hours to obtain high-density and high-hardness alumina ceramics.
[0016] This invention addresses the problems of low activity and high sintering temperature of α-Al2O3 powder during sintering. Based on the inventors' research on alumina phase transformation, α-Al2O3 structure, and the sintering mechanism of alumina ceramics, the following specific findings are made: (1) In the thermal decomposition of gibbsite to generate α-Al2O3, fine particle size, few impurities, and thin-layer calcination can be converted into α-Al2O3 through a single path; while coarse particle size, many impurities, thick-layer calcination, and saturated steam can be converted into α-Al2O3 through multiple paths.
[0017] (2) When gibbsite and boehmite are converted into α-Al2O3 under similar particle size (d50 ~ 5 μm) and the same calcination conditions (e.g., 1500℃, 4h), the α-Al2O3 converted from gibbsite has a higher density (>3.85 g / cm³). 3 It has a small specific surface area and low reactivity (AlO6 structural unit content >92%, AlO4 structural unit content <8%); while the density of α-Al2O3 converted from boehmite is low (<3.75 g / cm³). 3 It has a small specific surface area and high reactivity (AlO6 structural unit content <89%, AlO4 structural unit content >11%).
[0018] (3) During the roasting process, the α-Al2O3 inside the core and shell can be used as seed crystals to promote the transformation of gibbsite or boehmite into α-Al2O3 during low-temperature roasting. Compared with the usual roasting scheme, the phase transformation temperature is reduced by more than 100 °C. At the same time, the α-Al2O3 generated at low temperature has good sintering activity.
[0019] (4) During the sintering of alumina ceramics, the process is mainly controlled by the interfacial diffusion mechanism. Compared with corundum powder with a perfect structure and approximately 100% AlO6 structural units, if the content of AlO4 units in corundum is high, the aluminum-oxygen interface will diffuse more easily during sintering, resulting in slower particle growth, which is beneficial for preparing high-density, high-hardness alumina ceramics.
[0020] (5) Based on FTIR, XPS and 27AlNMR analysis of the content of structural units such as AlO6, AlO4, or AlO5 in alumina revealed a linear relationship between the density of α-Al2O3 and the content of AlO6 structural units. Furthermore, during the sintering of alumina-based materials, the higher the AlO4 content in the α-Al2O3 powder, the lower the sintering temperature.
[0021] (6) In the conversion of aluminum hydroxide (gibbsite or Bayerite) into boehmite, the finer the particle size, the higher the temperature and the greater the alkali concentration, the easier the conversion of boehmite.
[0022] The above-described solution of the present invention has the following beneficial effects: (1) The corundum micro powder prepared by the present invention has high sintering activity. The present invention modifies the surface of high-density α-Al2O3 with a layer of highly active α-Al2O3 to form "isomorphic" α-Al2O3 micro powder, and sintersects at <1500℃ to produce alumina ceramic with a relative density greater than 98% and a Vickers hardness greater than 25 GPa.
[0023] (2) No impurities are introduced, resulting in high purity. Both gibbsite and boehmite are precursors of α-Al2O3, thus corundum powder has few impurities and high purity, reaching 99.96%; the alkali content is low, reaching 0.008%. At the same time, compared with the addition of inorganic additives such as H3BO3, MgO, TiO2, ZrO2 and La2O3 in traditional sintering, this invention does not require the introduction of additives, does not introduce impurities, will not generate other impurity phases, and will not affect the physical properties of the product.
[0024] (3) High quality of alumina-based materials. The high-activity α-Al2O3 prepared by this invention has high purity, fine particle size, pure phase and high sintering activity, and high added value; the core is high-density α-Al2O3 and the surface is a thin layer of high-activity α-Al2O3. The linear shrinkage rate during sintering is low, the product deformation is small, and the amount of post-processing is small. Therefore, the ceramic performance is good and the production cost is low.
[0025] (4) Green process. The mother liquor, dilute alkali solution, and washing liquid in the production process are all returned to the Bayer process, and there is no waste liquid or waste residue; there are no mineralizers or sintering aids in the sintering process, the flue gas indicators are qualified, and the production process is a green process.
[0026] (5) Easy to industrialize. The high-activity α-Al2O3 micro powder of the present invention has a simple process and low investment; it does not contain concentrated alkali and concentrated acid, has low operating costs, and is easy to industrialize. Attached Figure Description
[0027] Figure 1 This is a schematic flowchart of a method for preparing highly active and high-purity corundum micro powder according to the present invention; wherein, the dotted part (hydrothermal treatment) is selected to be performed depending on the aluminum hydroxide phase encapsulated; Figure 2 This is a schematic diagram of highly active, high-purity corundum micro powder with isomorphism. Figure 3 This is a SEM image of highly active, high-purity corundum micro powder; the product particle size d50 is 1.89 μm. Figure 4 In Comparative Example 1, the high-density perfect α-Al2O3 powder and Example 1, the high-activity α-Al2O3 powder 27 Al-NMR spectrum; the top is α-Al2O3 obtained by high-temperature calcination, which has all characteristic peaks of AlO6, and the bottom is corundum powder, which shows characteristic peaks of AlO4. Figure 5 This is a high-resolution transmission electron microscope (HRTEM) image of α-Al₂O₃ surface modified with a layer of diaspore monohydrate. The spherical particles are α-Al₂O₃, and the surface is covered with diaspore monohydrate. Detailed Implementation
[0028] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0031] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0032] Example 1 This embodiment provides a method for preparing highly active, high-purity corundum micro powder. A schematic flowchart is shown below. Figure 1 As shown, the dashed section (hydrothermal treatment) is performed according to the aluminum hydroxide phase being encapsulated.
[0033] The method in this embodiment specifically includes the following steps: Preparation of gibbsite-phase aluminum hydroxide micron powder: 2.5 g of aluminum hydroxide seed crystals (d50 1.7 μm) were added to 500 mL of purified sodium aluminate solution (caustic ratio α). k : 1.45; Na2O k In a solution containing 160 g / L of aluminum hydroxide and 182.10 g / L of Al₂O₃, the initial temperature was 75℃, the final temperature was 60℃, and the solution was uniformly cooled for 35 hours. After separation, washing, and drying, aluminum hydroxide micropowder with a trihydrate phase was obtained (median diameter d50 1.5μm, d90 6.3μm; by mass percentage, Na₂O 0.11%, SiO₂ 0.009%, Fe₂O₃ 0.008%, CaO 0.0014%, MgO 0.0012%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1200 ℃ for 4 h. After furnace cooling, corundum micro-powder was obtained. (d50 1.5 μm, by mass percentage: Na₂O 0.16%, SiO₂ 0.009%, Fe₂O₃ 0.008%, CaO 0.0014%, MgO 0.0013%; α-Al₂O₃ 93.2%, by atomic percentage: AlO₆ structural unit content 94.9%, true density 3.95 g / cm³) 3 Specific surface area S BET 3.2 m 2 / g) Wet processing of activated α-Al₂O₃ powder: High-density α-Al₂O₃ powder is transferred into a reaction tank, and dilute sodium aluminate solution (Na₂O) is added at a ratio of α-Al₂O₃ powder to solution volume of 1:2. k 10 g / L, α k 1.4) After pretreatment at 130℃ for 3 h, and filtration and washing, α-Al2O3 powder containing 5 wt% boehmite was obtained.
[0034] Powder calcination: The powder was calcined at 1200℃ for 2 h to obtain highly active α-Al2O3 micro powder. (d50 1.3μm, by mass percentage: Na2O 0.12%, SiO2 0.009%, Fe2O3 0.009%, CaO 0.001%, MgO 0.0012%; α-Al2O3 94.2%, by atomic percentage: AlO4 structural unit content 5.9%, AlO6 structural unit content 94.1%, true density 3.94 g / cm³) 3 Specific surface area S BET 3.3m 2 / g).
[0035] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.53 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1500 °C to prepare pure alumina ceramic with a density of 3.95 g / cm³. 3 Hardness 25 GPa.
[0036] Figure 2 This is a schematic diagram of isomorphic high-activity, high-purity corundum micro powder. Based on the preparation process of the high-activity, high-purity corundum micro powder and the structural unit characteristics of the final powder, it can be roughly estimated that the inner layer of the powder is high-density α-Al2O3 with an AlO6 structural unit content greater than 92%; the outer layer is high-activity α-Al2O3 with a thickness of less than 50 nm and an AlO4 structural unit content greater than 11%. Figure 2 The right side shows schematic diagrams of aluminum-oxygen tetracoordination and hexacoordination.
[0037] Figure 3 This is a SEM image of highly active, high-purity corundum micro powder; the product particle size d50 is 1.89 μm. Figure 5 This is a high-resolution transmission electron microscope (HRTEM) image of an α-Al₂O₃ surface modified with a layer of diaspore, the thickness of which is approximately 100 nm.
[0038] Example 2 Preparation of gibbsite-phase aluminum hydroxide micron powder: 0.25 g of aluminum hydroxide seed crystals (d50 0.9 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.53; Na2O kIn a solution containing 130 g / L Al₂O₃ and 140 g / L Al₂O₃, the initial seeding temperature was 80 ℃, the final temperature was 65 ℃, and the temperature was uniformly lowered for 35 h. After separation, washing, and drying, aluminum hydroxide micropowder with a gibbsite phase was obtained (d50 1.2 μm, d90 5.8 μm, and by mass percentage, Na₂O 0.09%, SiO₂ 0.007%, Fe₂O₃ 0.005%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1150 ℃ for 6 h. After furnace cooling, corundum micro-powder was obtained. (d50 1.1 μm, by mass percentage: Na₂O 0.13%, SiO₂ 0.009%, Fe₂O₃ 0.008%, CaO 0.0009%, MgO 0.0010%; α-Al₂O₃ 94.7%, AlO₆ structural unit content 96.1% by atomic percentage, true density 3.96 g / cm³) 3 Specific surface area S BET 2.6 m 2 / g) Wet processing of activated α-Al₂O₃ powder: High-density α-Al₂O₃ powder is transferred into a reaction tank, and dilute sodium aluminate solution (Na₂O) is added at a ratio of α-Al₂O₃ powder to solution volume of 1:2. k 2 g / L, caustic ratio α k 1.35) After pretreatment at 120℃ for 10 h, and after filtration and washing, α-Al2O3 powder containing 3 wt% boehmite was obtained.
[0039] Powder calcination: The powder was calcined at 1200℃ for 1 h to obtain highly active α-Al2O3 micro powder. (d50 1.2μm, by mass percentage, Na2O 0.04%, SiO2 0.006%, Fe2O3 0.007%, CaO 0.0009%, MgO 0.0009%; α-Al2O3 94.2%), by atomic percentage, AlO4 structural unit content 5.6%, AlO6 structural unit content 94.4%, true density 3.95 g / cm³. 3 Specific surface area S BET 3.8 m 2 / g).
[0040] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.56 g / cm³. 3The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1450 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0041] Example 3 Preparation of gibbsite-phase aluminum hydroxide micron powder: 1.0 g of aluminum hydroxide seed crystals (d50 5 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.37; Na2O k In a solution containing 80 g / L Al₂O₃ and 95 g / L Al₂O₃, the initial temperature was 80 ℃, the final temperature was 60 ℃, and the temperature was uniformly lowered for 30 h. After separation, washing, and drying, aluminum hydroxide micropowder with trihydrate phase was obtained (d50 3.7 μm, d90 10.1 μm, and by mass percentage of Na₂O 0.06%, SiO₂ 0.007%, Fe₂O₃ 0.005%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1350 ℃ for 1 h. After furnace cooling, corundum micro-powder was obtained. (d50 3.4 μm, by mass percentage: Na₂O 0.09%, SiO₂ 0.009%, Fe₂O₃ 0.009%, CaO 0.0008%, MgO 0.0007%; α-Al₂O₃ 91.7%, by atomic percentage: AlO₆ structural unit content 94.4%, true density 3.92 g / cm³) 3 Specific surface area S BET 2.2m 2 / g) Wet treatment of active α-Al2O3 powder: High-density α-Al2O3 powder was transferred into a ball mill, and boehmite sol was added at 1 g / L to 100 g / L α-Al2O3. A mixture of stearic acid and polyethylene glycol (mass ratio 1:1) was added at 10 ppm. The mixture was pretreated at 100℃ for 3 h. After filtration and washing, α-Al2O3 powder containing 4 wt% boehmite was obtained.
[0042] Powder calcination: The powder was calcined at 1200℃ for 2 h to obtain highly active α-Al2O3 micro powder. (d50 3.2μm, by mass percentage: Na2O 0.08%, SiO2 0.009%, Fe2O3 0.009%, CaO 0.0008%, MgO 0.0006%, α-Al2O3 92.2%, true density 3.92 g / cm³) 3On an atomic percentage basis, the AlO4 structural unit content is 5.1%, and the AlO6 structural unit content is 94.9%. Specific surface area S BET 3.4m 2 / g).
[0043] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.48 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1500 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0044] Example 4 Preparation of gibbsite-phase aluminum hydroxide micron powder: 2.0 g of aluminum hydroxide seed crystals (d50 0.9 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.60; Na2O k In a solution containing 130 g / L of aluminum hydroxide and 133.67 g / L of Al₂O₃, the initial temperature was 70 ℃, the final temperature was 65 ℃, and the temperature was uniformly lowered for 30 h. After separation, washing, and drying, aluminum hydroxide micropowder with a gibbsite phase was obtained (d50 1.1 μm, by mass percentage: Na₂O 0.09%, SiO₂ 0.007%, Fe₂O₃ 0.005%, CaO 0.0011%, MgO 0.0008%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1150 ℃ for 5 h. After furnace cooling, corundum micro-powder was obtained. (D50 1.1 μm, d90 6.8 μm, by mass percentage: Na₂O 0.07%, SiO₂ 0.008%, Fe₂O₃ 0.007%, CaO 0.0011%, MgO 0.0009%; α-Al₂O₃ 95.7%, by atomic percentage: AlO₆ structural unit content 95.8%, true density 3.96 g / cm³) 3 ) Wet processing of activated α-Al₂O₃ powder: High-density α-Al₂O₃ powder is transferred into a ball mill, and dilute sodium aluminate solution (Na₂O) is added at a ratio of 200 g / L α-Al₂O₃ powder to solution volume of 1:2. k 5 g / L, caustic ratio α k 1.6) After pretreatment at 80℃ for 10 h, followed by filtration and washing, wet-processed α-Al2O3 powder is obtained.
[0045] Hydrothermal treatment: The wet-processed α-Al2O3 powder was treated at 150 ℃ for 2 h, and after filtration and washing, α-Al2O3 powder containing 2 wt% boehmite monohydrate was obtained.
[0046] Powder calcination: The powder was calcined at 950℃ for 4 h to obtain highly active α-Al₂O₃ micro powder. (d50 1.0 μm, by mass percentage: Na₂O 0.02%, SiO₂ 0.006%, Fe₂O₃ 0.007%, CaO 0.0008%, MgO 0.0007%; α-Al₂O₃ 93.2%, by atomic percentage: AlO₄ structural unit content 6.4%, AlO₆ structural unit content 93.6%, true density 3.93 g / cm³) 3 Specific surface area S BET 4.0 m 2 / g).
[0047] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.58 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1450 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0048] Example 5 Preparation of gibbsite-phase aluminum hydroxide micron powder: 0.25 g of aluminum hydroxide seed crystals (d50 0.9 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.40; Na2O k In a solution containing 110 g / L Al2O3 (129.1 g / L), the initial seeding temperature was 80 ℃, the final temperature was 65 ℃, and the temperature was uniformly lowered for 30 h. After separation, washing, and drying, aluminum hydroxide micron powder with a gibbsite phase was obtained (d50 3.1 μm, d90 11.5 μm, and by mass percentage: Na2O 0.08%, SiO2 0.007%, Fe2O3 0.005%, CaO 0.0004%, MgO 0.0004%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1150 ℃ for 5 h. After furnace cooling, corundum micro-powder was obtained. (d50 3.2 μm, by mass percentage: Na₂O 0.07%, SiO₂ 0.008%, Fe₂O₃ 0.007%, CaO 0.0006%, MgO 0.0005%; α-Al₂O₃ 95.7%, true density 3.96 g / cm³)3 By atomic percentage, AlO6 contains 97.1% structural units and has a specific surface area S. BET 2.9 m 2 / g) Wet processing of active α-Al2O3 powder: High-density α-Al2O3 powder was transferred into a ball mill, and pseudoboehmite sol was added at 2 g / L to 200 g / L α-Al2O3 powder. A mixture of glucose and Tween 80 (mass ratio 1:1) was added at 30 ppm. The mixture was pretreated at 130℃ for 6 h. After filtration and washing, α-Al2O3 powder containing 3 wt% boehmite was obtained.
[0049] Powder calcination: The powder was calcined at 800℃ for 5 h to obtain highly active α-Al2O3 micro powder. (d50 1.0 μm, by mass percentage: Na2O 0.05%, SiO2 0.006%, Fe2O3 0.007%, CaO 0.0005%, MgO 0.0005%; α-Al2O3 91.7%, by atomic percentage: AlO4 structural unit content 8.2%, AlO6 structural unit content 91.8%, true density 3.90 g / cm³) 3 Specific surface area S BET 4.6 m 2 / g).
[0050] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.58 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1450 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0051] Example 6 Preparation of gibbsite-phase aluminum hydroxide micron powder: 5 g of aluminum hydroxide seed crystals (d50 0.9 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.40; Na2O k In a solution containing 130 g / L Al2O3 (152.80 g / L), the initial temperature was 80 ℃, the final temperature was 65 ℃, and the temperature was uniformly lowered for 30 h. After separation, washing, and drying, aluminum hydroxide micro powder with trihydrate phase was obtained (d50 1.1 μm, d90 6.5 μm, and by mass percentage: Na2O 0.07%, SiO2 0.007%, Fe2O3 0.005%, CaO 0.0012%, MgO 0.0008%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1200 ℃ for 5 h. After furnace cooling, corundum micro-powder was obtained. (d50 1.0 μm, by mass percentage: Na₂O 0.07%, SiO₂ 0.008%, Fe₂O₃ 0.007%, CaO 0.0012%, MgO 0.0009%; α-Al₂O₃ 95.7%, by atomic percentage: AlO₆ structural unit content 96.4%, true density 3.96 g / cm³) 3 ) Wet treatment of active α-Al2O3 powder: High-density α-Al2O3 powder was transferred into a ball mill. Boehmite sol was added at a ratio of 2 g / L to 300 g / L α-Al2O3 powder, and a mixture of oleic acid and polyethylene glycol 20000 (mass ratio 2:1) was added at 10 ppm. The mixture was pretreated at 90℃ for 6 h. After filtration and washing, α-Al2O3 powder containing boehmite was obtained.
[0052] Hydrothermal treatment: The wet-processed α-Al2O3 powder was treated at 140 ℃ for 3 h, and after filtration and washing, α-Al2O3 powder containing 3.2 wt% boehmite monohydrate was obtained.
[0053] Powder calcination: The powder was calcined at 900℃ for 5 hours to obtain highly active α-Al₂O₃ micro powder. (d50 1.0 μm, by mass percentage: Na₂O 0.008%, SiO₂ 0.006%, Fe₂O₃ 0.007%, CaO 0.0005%, MgO 0.0006%; α-Al₂O₃ 94.2%, by atomic percentage: AlO₄ structural unit content 6.2%, AlO₆ structural unit content 93.8%, true density 3.94 g / cm³) 3 Specific surface area S BET 4.1 m 2 / g).
[0054] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.58 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1450 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0055] Example 7 Preparation of gibbsite-phase aluminum hydroxide micron powder: 0.5 g of aluminum hydroxide seed crystals (d50 0.9 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.42; Na2O k In a solution containing 145 g / L Al₂O₃ and 168.10 g / L Al₂O₃, the initial temperature was 80 ℃, the final temperature was 60 ℃, and the temperature was uniformly lowered for 48 h. After separation, washing, and drying, aluminum hydroxide micron powder with a gibbsite phase was obtained (d50 3.8 μm, d90 11.7 μm, and by mass percentage: Na₂O 0.11%, SiO₂ 0.007%, Fe₂O₃ 0.005%, CaO 0.0010%, MgO 0.0008%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1150 ℃ for 5 h. After furnace cooling, corundum micro-powder was obtained. (d50 3.7 μm, by mass percentage: Na₂O 0.07%, SiO₂ 0.008%, Fe₂O₃ 0.007%, CaO 0.0012%, MgO 0.0009%; α-Al₂O₃ 91.7%, by atomic percentage: AlO₆ structural unit content 93.9%, true density 3.91 g / cm³) 3 Specific surface area S BET 2.7 m 2 / g) Wet treatment of active α-Al2O3 powder: High-density α-Al2O3 powder was transferred into a ball mill, and α-Al2O3 powder was added at 100 g / L. The powder was pretreated at 130℃ for 2 h. After filtration and washing, wet-treated α-Al2O3 powder was obtained.
[0056] Hydrothermal treatment: The wet-processed α-Al2O3 powder was treated at 150 °C for 1 h, and after filtration and washing, α-Al2O3 powder containing 5 wt% boehmite monohydrate was obtained.
[0057] Powder calcination: The powder was calcined at 1100℃ for 3.5 h to obtain highly active α-Al2O3 micro powder. (d50 1.0 μm, by mass percentage: Na2O 0.009%, SiO2 0.006%, Fe2O3 0.007%, CaO 0.0008%, MgO 0.0005%; α-Al2O3 95.2%, by atomic percentage: AlO4 structural unit content 6.4%, AlO6 structural unit content 93.6%, true density 3.95 g / cm³) 3 Specific surface area S BET 3.5 m 2 / g).
[0058] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa. The green embryo density was 2.47 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1450 °C to prepare pure alumina ceramic with a density of 3.96 g / cm³. 3 Hardness 28 GPa.
[0059] Example 8 Preparation of gibbsite-phase aluminum hydroxide micron powder: 10 g of aluminum hydroxide seed crystals (d50 1.2 μm) were added to 500 mL of purified sodium aluminate solution (α-coated aluminum hydroxide). k : 1.35; Na2O k In a solution containing 90 g / L Al2O3 (109.68 g / L), the initial temperature was 85 ℃, the final temperature was 65 ℃, and the temperature was uniformly lowered for 25 h. After separation, washing, and drying, aluminum hydroxide micro powder with trihydrate phase was obtained (d50 1.5 μm, d90 7.0 μm, and by mass percentage: Na2O 0.05%, SiO2 0.007%, Fe2O3 0.006%, CaO 0.0008%, MgO 0.0008%). Preparation of high-density α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1350 ℃ for 1 h. After furnace cooling, corundum micro-powder was obtained. (d50 1.4 μm, by mass percentage: Na₂O 0.08%, SiO₂ 0.008%, Fe₂O₃ 0.007%, CaO 0.0009%, MgO 0.0009%; α-Al₂O₃ 94.7%, by atomic percentage: AlO₆ structural unit content 95.4%, true density 3.94 g / cm³) 3 ) Wet treatment of active α-Al2O3 powder: High-density α-Al2O3 powder was transferred into a ball mill, and α-Al2O3 powder was added to distilled water at a concentration of 400 g / L. The powder was pretreated at 90°C for 6 h. After filtration and washing, wet-treated α-Al2O3 powder was obtained.
[0060] Hydrothermal treatment: The wet-processed α-Al2O3 powder was treated at 130 ℃ for 2 h, and after filtration and washing, α-Al2O3 powder containing 5.7 wt% boehmite monohydrate was obtained.
[0061] Powder calcination: The powder was calcined at 900℃ for 4 h to obtain highly active α-Al2O3 micro powder. (d50 1.1μm, by mass percentage: Na2O 0.02%, SiO2 0.006%, Fe2O3 0.006%, CaO 0.0007%, MgO 0.0008%; α-Al2O3 95.2%, by atomic percentage: AlO4 structural unit content 5.7%, true density 3.92 g / cm³) 3 Specific surface area S BET 4.1 m 2 / g).
[0062] Polyvinyl alcohol and highly active α-Al₂O₃ powder were thoroughly mixed, and a green embryo was prepared under a pressure of 300 MPa with a density of 2.55 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1400 °C to prepare pure alumina ceramic with a density of 3.95 g / cm³. 3 Hardness 25.3 GPa.
[0063] Comparative Example 1 Preparation of gibbsite-phase aluminum hydroxide micron powder: 2.5 g of aluminum hydroxide seed crystals (d50 1.7 μm) were added to 500 mL of purified sodium aluminate solution (caustic ratio α). k : 1.45; Na2O k In a solution containing 160 g / L of aluminum hydroxide and 182.10 g / L of Al₂O₃, the initial temperature was 65℃, the final temperature was 55℃, and the temperature was uniformly lowered for 35 hours. After separation, washing, and drying, aluminum hydroxide powder with a trihydrate phase was obtained (median diameter d50 20.3 μm, d90 46.2 μm; by mass percentage, Na₂O 0.25%, SiO₂ 0.02%, Fe₂O₃ 0.014%, CaO 0.009%, MgO 0.005%). Preparation of α-Al₂O₃ powder: Gibbsite micro-powder was transferred to a muffle furnace and calcined at 1250 ℃ for 6 h. After furnace cooling, corundum micro-powder was obtained. (d50 21.3 μm; by mass percentage: Na₂O 0.32%, SiO₂ 0.02%, Fe₂O₃ 0.016%, CaO 0.010%, MgO 0.007%; α-Al₂O₃ 87.1%, true density 3.82 g / cm³) 3 Specific surface area S BET 4.8 m 2 / g) After grinding the powder into fine powder (d50 3.7 μm), polyvinyl alcohol and α-Al2O3 micro powder were added and thoroughly mixed. A green embryo was prepared under a pressure of 300 MPa, with a green embryo density of 2.53 g / cm³. 3 The green blank was degreased by heating to 550 °C at a rate of 2 °C / min and holding for 2 h; after cooling, the degreased blank was sintered at 1650 °C to prepare pure alumina ceramic with a density of 3.89 g / cm³. 3 Hardness 19.9 GPa.
[0064] Figure 4 The figures below show the 27Al-NMR spectra of the highly dense and perfect α-Al2O3 in Comparative Example 1 and the highly active α-Al2O3 powder in Example 1. The top figure shows the α-Al2O3 obtained by high-temperature calcination in Comparative Example 1, which is full of AlO6 characteristic peaks. The bottom figure shows the highly active and high-purity corundum micro powder in Example 1, which shows AlO4 characteristic peaks.
[0065] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing highly active, high-purity corundum micro powder, characterized in that, Includes the following steps: S1. Aluminum hydroxide micro powder was prepared by high-temperature seeding using sodium aluminate solution as raw material; S2. Calcining the aluminum hydroxide micro powder obtained in S1 at high temperature to prepare α-Al2O3 corundum micro powder; S3. The α-Al2O3 corundum micropowder obtained in S2 is wet-processed to generate boehmite on its surface, forming a core-shell structured corundum-boehmite mixed phase. The boehmite is a shell structure with a thickness of less than 200 nm and a mass less than 10 wt% of the total mass of the corundum-boehmite mixed phase. S4. The corundum-diatomite mixture obtained in S4 is roasted or calcined at high temperature to generate highly active and high-purity corundum micro powder.
2. The preparation method according to claim 1, characterized in that, In the high-temperature fraction described in S1, sodium aluminate solution contains sodium oxide (Na2O). k Concentration of 80~160 g / L, caustic ratio α k The value is 1.35~1.60; the high-temperature seeding specifically includes: adding active seed crystals at 0.5~20 g / L, and preparing aluminum hydroxide micro powder with gibbsite phase at an initial temperature of 75~80℃ and a final temperature of 60~65℃. The particle size of the aluminum hydroxide micro powder is d50<4μm, d90≤11.7μm; the purity of aluminum hydroxide is >99.6%, of which, by mass percentage, Na2O≤0.11%, Fe2O3<0.02%, SiO2<0.02%, CaO<0.002%, MgO<0.002%.
3. The preparation method according to claim 1, characterized in that, The high-temperature calcination temperature described in S2 is 1150~1350℃, and the time is 1~6 h. The α-Al2O3 corundum micro powder prepared contains ≥90% α-Al2O3 by mass, of which AlO6 structural unit content is >90% by atomic percentage, and the density of α-Al2O3 corundum micro powder is >3.90 g / cm³. 3 Specific surface area S BET <4 m 2 / g; by mass percentage, Na2O≤0.16%, Fe2O3<0.02%, SiO2<0.02%, CaO<0.002%, MgO<0.002%.
4. The preparation method according to claim 1, characterized in that, The wet processing of corundum micro powder described in S3 includes at least one of the following methods: Option 1: In Na2O k <20 g / L, caustic ratio α k In a supersaturated sodium aluminate solution with a concentration of 1.35–2.0, the temperature was controlled at 80–130 °C, and the seeding time was 60 min–10 h. Option 2: Add pseudoboehmite sol at a concentration of 0.5~5 g / L to α-Al2O3 corundum micro powder and treat at a temperature of 90~130 ℃ for 1~6 h; Option 3: Disperse α-Al2O3 corundum micro powder with water by wet ball milling at a ratio of 100~400 g / L, and treat at a temperature of 90~130 ℃ for 2~6 h.
5. The preparation method according to claim 4, characterized in that, In the wet processing described in S3, a surfactant is added, including one or more of glucose, stearic acid, oleic acid, Tween 80 or polyethylene glycol 6000~20000, in an amount of 0~30 ppm; the resulting aluminum hydroxide micropowder has a particle size of less than 1 μm and a uniformly encapsulated core-shell structure.
6. The preparation method according to claim 4, characterized in that, After the wet processing described in S3, the resulting wet filter cake is subjected to hydrothermal treatment at 150~220 ℃ for no more than 2 h.
7. The preparation method according to claim 1, characterized in that, The high-temperature roasting or calcination temperature described in S4 is 900~1200 ℃, and the time is 1~5 h.
8. A highly active, high-purity corundum micro powder, characterized in that, The high-activity, high-purity corundum micro powder has α-Al₂O₃ as its entire phase, with AlO₆ structural units accounting for >89% and AlO₄ structural units accounting for not less than 4.5% by atomic percentage. The density of the high-activity, high-purity corundum micro powder is >3.89 g / cm³. 3 Specific surface area S BET <7 m 2 / g; The high-activity, high-purity corundum micro powder has a d50 < 4 μm and a d90 < 10 μm. By mass, the micro powder contains Na2O ≤ 0.12%, Fe2O3 < 0.02%, SiO2 < 0.02%, CaO < 0.002%, MgO < 0.002%, and α-Al2O3 ≥ 91.7%.
9. An application of a highly active, high-purity corundum micro powder prepared according to any one of claims 1-7 or as described in claim 8, characterized in that, The highly active and high-purity corundum micro powder is used to prepare high-density and high-hardness alumina ceramics.
10. The application as described in claim 9, characterized in that, The method for preparing high-hardness alumina ceramics includes: shaping and degreasing high-activity, high-purity corundum micro powder, and then sintering it at 1350~1500℃ for 2~5 hours to obtain high-density and high-hardness alumina ceramics.