Preparation method and application of low-magnetism high-purity aluminum oxide

Abstract

The invention provides a preparation method of low-magnetism high-purity aluminum oxide, which comprises the following steps: carrying out redissolution reaction on high-purity aluminum hydroxide with a first set iron content and high-purity sodium hydroxide with a second set iron content to obtain an ultra-pure sodium aluminate solution with the iron mass fraction of less than or equal to 1ppm; reacting the ultra-pure sodium aluminate solution with high-purity dilute nitric acid with a third set iron content to generate a high-purity aluminum nitrate solution with the iron mass fraction of less than or equal to 0.5 ppm; performing low-temperature secondary crystallization on the high-purity aluminum nitrate solution to obtain an ultra-pure aluminum nitrate precursor of which the iron mass fraction is less than or equal to 0.5 ppm; performing two-stage activation roasting on the ultrapure aluminum nitrate precursor to obtain aluminum oxide powder; in the two sections of activating roasting, the temperature of the first section of activating roasting is lower than that of the second section of activating roasting. Through fine operations such as strict iron content control, low-temperature secondary crystallization and two-stage activation roasting, impurities are effectively removed from two aspects of chemical purification and physical optimization, and meanwhile, the low magnetism of the aluminum oxide powder is ensured.

Description

Technical Field

[0001] This application relates to the field of ultrapure alumina refining technology, and in particular to a method for preparing low-magnetic high-purity alumina and its application. Background Technology

[0002] With the continuous advancement of global integrated circuit packaging technology, the demand for high-performance packaging materials is showing an increasing trend. Low-magnetic ultrapure alumina, as an important functional filler, can effectively reduce signal crosstalk and ensure the high-performance operation of chips. However, the current preparation technology of low-magnetic ultrapure alumina still faces many challenges, such as high impurity content and difficulty in effectively removing magnetic substances. Existing preparation methods mainly include inorganic acid solution washing and high-purity metal combustion, but these methods generally suffer from drawbacks such as cumbersome processes, high costs, and incomplete impurity removal. Summary of the Invention

[0003] This application provides a method for preparing low-magnetic high-purity alumina and its application, in order to solve the following technical problem: how to ensure the low magnetic properties of alumina powder while removing impurities.

[0004] In a first aspect, embodiments of this application provide a method for preparing low-magnetic, high-purity alumina, comprising: High-purity aluminum hydroxide with a first set iron content and high-purity sodium hydroxide with a second set iron content are redissolved to obtain an ultrapure sodium aluminate solution with an iron mass fraction ≤1ppm. The ultrapure sodium aluminate solution is reacted with high-purity dilute nitric acid having a third set iron content to generate a high-purity aluminum nitrate solution with an iron mass fraction ≤0.5ppm; The high-purity aluminum nitrate solution was subjected to low-temperature secondary crystallization to obtain an ultra-pure aluminum nitrate precursor with an iron mass fraction ≤0.5ppm; The ultrapure aluminum nitrate precursor is subjected to two-stage activation calcination to obtain alumina powder; in the two-stage activation calcination, the temperature of the first stage activation calcination is lower than the temperature of the second stage activation calcination.

[0005] Optionally, the temperature of the first stage of activation roasting is 200-600℃, and the temperature of the second stage of activation roasting is 1200-1300℃.

[0006] Optionally, the first stage of activation and calcination time is 2-4 hours, and the second stage of activation and calcination time is 3-5 hours.

[0007] Optionally, the temperature of the resolution reaction is 100-115°C, and the time of the resolution reaction is 4-8 hours.

[0008] Optionally, in the redissolution reaction, the molar ratio of the high-purity aluminum hydroxide to the high-purity sodium hydroxide is 1:1.05-1.15.

[0009] Optionally, the temperature of the low-temperature secondary crystallization is 0-10℃, and the time of the low-temperature secondary crystallization is 12-24 hours; and / or, During the low-temperature secondary crystallization process, the high-purity aluminum nitrate solution is cooled using an ice-water bath at a temperature of 0-5°C.

[0010] Optionally, the impurity content of the high-purity aluminum hydroxide includes: iron mass fraction ≤ 3 ppm, calcium mass fraction ≤ 3 ppm, silicon mass fraction ≤ 10 ppm, thorium mass fraction ≤ 60 ppb, and uranium mass fraction ≤ 60 ppb; and / or, The high-purity sodium hydroxide has a mass concentration of 30-32 g / L, and the impurity content of the high-purity sodium hydroxide includes: iron mass fraction ≤ 1 ppm, calcium mass fraction ≤ 1 ppm, sodium mass fraction ≤ 1000 ppm, silicon mass fraction ≤ 10 ppm, thorium mass fraction ≤ 20 ppb, and uranium mass fraction ≤ 20 ppb; and / or, The high-purity dilute nitric acid has a mass fraction of 5-35%, and the impurity content of the high-purity dilute nitric acid includes: iron mass fraction ≤0.5ppm, calcium mass fraction ≤1ppm, silicon mass fraction ≤5ppm, thorium mass fraction ≤5ppb and uranium mass fraction ≤5ppb.

[0011] Optionally, the mass concentration of the ultrapure sodium aluminate solution is 155 g / L to 165 g / L; the impurity content of the ultrapure sodium aluminate solution further includes: calcium mass fraction ≤ 1 ppm, silicon mass fraction ≤ 8 ppm, thorium mass fraction ≤ 20 ppb and uranium mass fraction ≤ 20 ppb; and / or, The impurity content of the high-purity aluminum nitrate solution also includes: calcium mass fraction ≤ 1 ppm, silicon mass fraction ≤ 5 ppm, thorium mass fraction ≤ 5 ppb, and uranium mass fraction ≤ 5 ppb; and / or, The purity of the alumina powder is ≥99.995%; the impurity content of the alumina powder includes: iron mass fraction ≤0.5ppm, thorium mass fraction ≤5ppb and uranium mass fraction ≤5ppb; the particle size range of the alumina powder is 0.2μm to 60μm.

[0012] Optionally, before the ultrapure aluminum nitrate precursor undergoes the two-stage activation calcination, it further includes: The ultrapure aluminum nitrate precursor was washed with deionized water to remove surface impurities from the pure aluminum nitrate precursor.

[0013] Secondly, embodiments of this application also provide an application of the low-magnetic ultrapure alumina described in the first aspect, wherein the low-magnetic ultrapure alumina powder is used in electronic chip packaging, optical materials, ceramic materials, biomedical materials, and aerospace materials.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing low-magnetic, high-purity alumina. First, the iron content is strictly controlled, as iron is the main impurity element that enhances the magnetism of alumina. The method precisely controls the iron content of high-purity aluminum hydroxide, high-purity sodium hydroxide, and high-purity dilute nitric acid, limiting the introduction of iron impurities at the source. During the resolution reaction and subsequent reactions, the iron content is further reduced through the screening and purification effects of chemical reactions. For example, the iron mass fraction in the ultrapure sodium aluminate solution generated by the resolution reaction is controlled to ≤1 ppm, while the iron mass fraction in the final high-purity aluminum nitrate solution is further reduced to ≤0.5 ppm. This strict control of iron content fundamentally reduces the impact of iron impurities on the magnetism of the alumina powder. Second, low-temperature secondary crystallization is one of the key steps in removing impurities. Through low-temperature crystallization, impurities (such as residual iron ions) are more easily excluded from the crystal structure. This is because the crystal growth rate is slower during low-temperature crystallization, making it more difficult for impurities to enter the crystal interior, thereby further improving the purity of the ultrapure aluminum nitrate precursor. Meanwhile, low-temperature crystallization also helps to form a more uniform crystal structure, reduce crystal defects, and further reduce the residue of impurities, thereby reducing the magnetism of alumina powder. Third, the two-stage activation calcination design cleverly solves the problem of low magnetism in alumina powder. The first stage activation calcination is at a lower temperature, mainly used to remove organic impurities and some water of crystallization from the precursor, while initially forming the crystal structure of alumina. The second stage activation calcination is at a higher temperature, further improving the crystallinity of alumina, making its crystal structure more complete and dense. This segmented calcination method can effectively remove impurities while avoiding the diffusion of impurities or defects in the crystal structure caused by direct high-temperature action. A complete crystal structure helps to reduce lattice defects and decrease the adsorption capacity of impurities, thereby ensuring the low magnetism of the alumina powder.

[0015] The entire preparation process combines the purification effect of chemical reactions with the advantages of physical treatment. Chemical reactions, through steps such as dissolution and recrystallization, gradually reduce the impurity content; physical treatments (such as low-temperature crystallization and staged calcination) further optimize the crystal structure, reducing residual impurities and the adsorption of magnetic impurities. This comprehensive treatment method, working together at both chemical and physical levels, ensures the low magnetic properties of the alumina powder. The embodiments of this application, through meticulous operations such as strict control of iron content, low-temperature secondary crystallization, and two-stage activation calcination, effectively solve the technical problem of ensuring low magnetic properties of alumina powder while removing impurities, from both chemical purification and physical optimization perspectives. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings necessary for the description of the embodiments or the prior art will be outlined below. Obviously, those skilled in the art can derive other related drawings based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for preparing low-magnetic, high-purity alumina, as provided in an embodiment of this application. Detailed Implementation

[0019] To more clearly illustrate the purpose, technical solutions, and advantages of the embodiments of this application, the technical solutions of this embodiment will be described in detail below with reference to the accompanying drawings. Please note that the embodiments described herein are merely exemplary and do not represent all possible implementation paths. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0020] The scope described herein, whether numerical or proportional, encompasses all sub-ranges and individual numerical values. For example, mentioning '1 to 6' or '1~6' indicates inclusion of any sub-range from 1 to 6 (e.g., 1 to 3, 2 to 5) and all individual numbers (1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including," "comprise," etc., used herein mean "including but not limited to"; relational terms such as "first," "second," etc., are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," "at least one," etc., refer to any combination of the corresponding objects, including combinations of single or multiple objects. Proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] Figure 1 This is a flowchart illustrating a method for preparing low-magnetic, high-purity alumina, as provided in an embodiment of this application.

[0022] Please see Figure 1 This application provides a method for preparing low-magnetic, high-purity alumina, comprising: In a first aspect, embodiments of this application provide a method for preparing low-magnetic, high-purity alumina, comprising: S1. High-purity aluminum hydroxide with a first set iron content and high-purity sodium hydroxide with a second set iron content are redissolved to obtain an ultra-pure sodium aluminate solution with an iron mass fraction ≤1ppm. S2. The ultrapure sodium aluminate solution is reacted with high-purity dilute nitric acid having a third set iron content to generate a high-purity aluminum nitrate solution with an iron mass fraction ≤0.5ppm. S3. The high-purity aluminum nitrate solution is subjected to low-temperature secondary crystallization to obtain an ultra-pure aluminum nitrate precursor with an iron mass fraction ≤0.5ppm; S4. The ultrapure aluminum nitrate precursor is subjected to two-stage activation calcination to obtain alumina powder; in the two-stage activation calcination, the temperature of the first stage activation calcination is lower than the temperature of the second stage activation calcination.

[0023] Low-magnetic high-purity alumina: refers to alumina materials with extremely low content of magnetic impurities such as iron, thorium, and uranium, typically used in applications sensitive to magnetic properties. Resolution reaction: refers to the process of dissolving a solid substance in another solvent to form a homogeneous solution. Here, high-purity aluminum hydroxide reacts with high-purity sodium hydroxide to produce a sodium aluminate solution. Low-temperature secondary crystallization: refers to a crystallization process carried out at a lower temperature, the purpose of which is to remove impurities and improve purity through slow crystallization. Two-stage activation calcination: refers to a high-temperature treatment process carried out in two stages. The first stage is at a lower temperature, mainly used for dehydration and preliminary crystallization; the second stage is at a higher temperature, used to further improve crystallinity and purity.

[0024] The redissolution reaction involves reacting high-purity aluminum hydroxide with high-purity sodium hydroxide to produce an ultra-pure sodium aluminate solution. By strictly controlling the iron content of the reactants, impurities are reduced at the source. When high-purity aluminum hydroxide (iron content ≤3ppm) reacts with high-purity sodium hydroxide (iron content ≤1ppm) at a specific temperature, the resulting sodium aluminate solution has an extremely low iron content (≤1ppm). This is because the high purity of both aluminum hydroxide and sodium hydroxide ensures the high purity of the reaction product. Reacting the ultra-pure sodium aluminate solution with high-purity dilute nitric acid further reduces the iron content to ≤0.5ppm, producing a high-purity aluminum nitrate solution.

[0025] Low-temperature secondary crystallization further improves the purity of the aluminum nitrate precursor, with iron content controlled to ≤0.5ppm. During low-temperature crystallization, impurities are less likely to enter the crystal interior and are thus excluded. An ice-water bath (0-5℃) further lowers the crystallization temperature and optimizes the crystallization process. Two-stage activation calcination: Segmented calcination further improves the crystallinity and purity of the alumina powder, ensuring low magnetic properties.

[0026] The first stage of activation roasting (at a lower temperature) is mainly used to remove organic impurities and water of crystallization, initially forming the alumina crystal structure. The second stage of activation roasting (at a higher temperature) further improves crystallinity, optimizes the crystal structure, and reduces the adsorption capacity of impurities. Example: The redissolution reaction was carried out using high-purity aluminum hydroxide (iron content ≤3ppm) and high-purity sodium hydroxide (iron content ≤1ppm).

[0027] The remelting reaction temperature was controlled at 105℃, and the reaction time was 6 hours.

[0028] A high-purity dilute nitric acid solution with an iron content of ≤0.5ppm was generated by reacting with 10% high-purity dilute nitric acid.

[0029] Low-temperature secondary crystallization was carried out in an ice-water bath at 5°C for 18 hours.

[0030] The first stage of activation and roasting was carried out at a temperature of 400℃ for 3 hours; the second stage of activation and roasting was carried out at a temperature of 1250℃ for 4 hours.

[0031] The final alumina powder has a purity of ≥99.995%, an iron content of ≤0.5ppm, and a particle size of 10μm.

[0032] In some embodiments, the temperature of the first stage of activation calcination is 200-600℃, and the temperature of the second stage of activation calcination is 1200-1300℃.

[0033] The first stage of activation roasting (200-600℃) removes organic impurities and water of crystallization, initially forming the alumina crystal structure. This is because the lower temperature effectively removes organic impurities and water of crystallization, while preventing impurity diffusion caused by high temperatures. Excessively high activation roasting temperatures may lead to impurity diffusion, while excessively low temperatures result in ineffective impurity removal. An appropriate temperature range for the first stage of activation roasting ensures complete impurity removal while avoiding defects in the crystal structure.

[0034] The second-stage activation roasting (1200-1300℃) can further improve the crystallinity of alumina, optimize its crystal structure, and reduce its ability to adsorb impurities. This is because at higher temperatures, alumina crystals can grow sufficiently, forming a more complete and dense structure, thus reducing impurity adsorption. Excessively high activation roasting temperatures may lead to defects in the crystal structure, while excessively low temperatures will result in insufficient crystallinity. An appropriate temperature range for the second-stage activation roasting ensures optimized crystal structure while avoiding the introduction of impurities. Example: The first stage of activation and roasting is at 300℃ for 2 hours; the second stage of activation and roasting is at 1250℃ for 4 hours.

[0035] The first stage of activation and roasting was carried out at a temperature of 500℃ for 3 hours; the second stage of activation and roasting was carried out at a temperature of 1280℃ for 5 hours.

[0036] The first stage of activation roasting was carried out at 600℃ for 4 hours; the second stage of activation roasting was carried out at 1300℃ for 3 hours.

[0037] The first stage of activation and roasting was carried out at 250℃ for 2.5 hours; the second stage of activation and roasting was carried out at 1220℃ for 4.5 hours.

[0038] The first stage of activation and roasting was carried out at a temperature of 450℃ for 3.5 hours; the second stage of activation and roasting was carried out at a temperature of 1260℃ for 4 hours.

[0039] The first stage of activation and roasting was carried out at a temperature of 550℃ for 3 hours; the second stage of activation and roasting was carried out at a temperature of 1290℃ for 5 hours.

[0040] In some embodiments, the first stage of activation and calcination time is 2-4 hours, and the second stage of activation and calcination time is 3-5 hours.

[0041] The initial activation and roasting time (2-4 hours) ensures the complete removal of organic impurities and water of crystallization, while avoiding over-roasting that could lead to crystal structure defects. An appropriate time ensures complete impurity removal while preventing defects caused by prolonged high-temperature exposure. Too short an initial activation and roasting time may result in incomplete impurity removal, while too long an initial activation and roasting time may introduce new impurities or cause crystal structure defects.

[0042] The second stage of activation calcination (3-5 hours) ensures sufficient alumina crystal growth, improving crystallinity and purity. Appropriate time allows for full crystal growth, forming a more complete and dense structure, thus reducing impurity adsorption. Too short a second stage activation calcination time may result in insufficient crystallinity, while too long a time may affect production efficiency. A suitable second stage activation calcination time optimizes crystal quality and improves production efficiency. Example: The first stage of activation roasting is at 300℃ for 2 hours; the second stage of activation roasting is at 1250℃ for 3 hours.

[0043] The first stage of activation and roasting was carried out at a temperature of 500℃ for 3 hours; the second stage of activation and roasting was carried out at a temperature of 1280℃ for 4 hours.

[0044] The first stage of activation roasting was carried out at 600℃ for 4 hours; the second stage of activation roasting was carried out at 1300℃ for 5 hours.

[0045] The first stage of activation and roasting was carried out at 250℃ for 2.5 hours; the second stage of activation and roasting was carried out at 1220℃ for 4.5 hours.

[0046] The first stage of activation and roasting was carried out at a temperature of 450℃ for 3.5 hours; the second stage of activation and roasting was carried out at a temperature of 1260℃ for 4 hours.

[0047] The first stage of activation and roasting was carried out at a temperature of 550℃ for 3 hours; the second stage of activation and roasting was carried out at a temperature of 1290℃ for 5 hours.

[0048] In some embodiments, the remelting reaction is carried out at a temperature of 100-115°C for 4-8 hours.

[0049] A reconstitution temperature of 100-115℃ ensures that high-purity aluminum hydroxide and high-purity sodium hydroxide react completely to produce a pure sodium aluminate solution. An appropriate temperature ensures the reaction proceeds completely while avoiding the introduction of impurities. Excessively high temperatures may cause impurities to dissolve, while excessively low temperatures will result in incomplete reactions.

[0050] A suitable redissolution reaction time (4-8 hours) ensures the reaction proceeds fully while preventing the dissolution of impurities due to excessive time. An appropriate time ensures complete reaction while avoiding the introduction of impurities due to prolonged duration. Too short a time may result in incomplete reaction, while too long a time may introduce new impurities. Example: The redissolution reaction was carried out at a temperature of 105°C for 6 hours.

[0051] The redissolution reaction temperature was 110℃ and the reaction time was 5 hours.

[0052] The redissolution reaction temperature was 100℃ and the reaction time was 8 hours.

[0053] The redissolution reaction temperature was 115℃ and the reaction time was 4 hours.

[0054] The redissolution reaction was carried out at a temperature of 108°C for 7 hours.

[0055] The redissolution reaction was carried out at a temperature of 102°C for 6.5 hours.

[0056] In some embodiments, the molar ratio of the high-purity aluminum hydroxide to the high-purity sodium hydroxide in the redissolution reaction is 1:1.05-1.15.

[0057] A controlled molar ratio (1:1.05-1.15) ensures complete dissolution of aluminum hydroxide by using a slight excess of sodium hydroxide, while avoiding the introduction of impurities due to excess sodium hydroxide. An appropriate molar ratio ensures complete reaction while preventing the introduction of impurities by excess sodium hydroxide. An excess of sodium hydroxide ensures complete dissolution of aluminum hydroxide, but excessive excess may introduce impurities. Example: The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.05.

[0058] The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.10.

[0059] The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.15.

[0060] The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.08.

[0061] The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.07.

[0062] The molar ratio of high-purity aluminum hydroxide to high-purity sodium hydroxide is 1:1.12.

[0063] In some embodiments, the low-temperature secondary crystallization temperature is 0-10°C, and the low-temperature secondary crystallization time is 12-24 hours; and / or, During the low-temperature secondary crystallization process, the high-purity aluminum nitrate solution is cooled using an ice-water bath at a temperature of 0-5°C.

[0064] Low-temperature secondary crystallization (0-10℃) helps to remove impurities and improve crystal purity. During low-temperature crystallization, impurities have less chance of entering the crystal and are thus excluded. Lower temperatures can optimize the crystallization process and improve crystal purity.

[0065] A low-temperature secondary crystallization time of 12-24 hours ensures sufficient crystallization while avoiding excessively long times that could lead to overly rapid crystal growth. An appropriate time ensures adequate crystal growth, resulting in a more complete and dense structure. Too short a time may result in incomplete crystal growth, while too long a time may negatively impact production efficiency.

[0066] Ice-water bath cooling (0-5℃) further lowers the temperature and optimizes the crystallization process. The ice-water bath can further reduce the crystallization temperature, ensuring that impurities have less difficulty entering the crystal, thereby further improving crystal purity. Example: The low-temperature secondary crystallization was carried out at a temperature of 5°C for 18 hours, with an ice-water bath temperature of 2°C.

[0067] The low-temperature secondary crystallization was carried out at a temperature of 3°C for 20 hours, with an ice-water bath temperature of 1°C.

[0068] The low-temperature secondary crystallization was carried out at a temperature of 8°C for 15 hours, with an ice-water bath temperature of 3°C.

[0069] The low-temperature secondary crystallization was carried out at a temperature of 2℃ for 22 hours, with an ice-water bath temperature of 0.5℃.

[0070] The low-temperature secondary crystallization was carried out at a temperature of 6°C for 16 hours, with an ice-water bath temperature of 2.5°C.

[0071] The low-temperature secondary crystallization was carried out at a temperature of 10℃ for 12 hours, with an ice-water bath temperature of 4℃.

[0072] In some embodiments, the impurity content of the high-purity aluminum hydroxide includes: iron mass fraction ≤ 3 ppm, calcium mass fraction ≤ 3 ppm, silicon mass fraction ≤ 10 ppm, thorium mass fraction ≤ 60 ppb, and uranium mass fraction ≤ 60 ppb; and / or, The high-purity sodium hydroxide has a mass concentration of 30-32 g / L, and the impurity content of the high-purity sodium hydroxide includes: iron mass fraction ≤ 1 ppm, calcium mass fraction ≤ 1 ppm, sodium mass fraction ≤ 1000 ppm, silicon mass fraction ≤ 10 ppm, thorium mass fraction ≤ 20 ppb, and uranium mass fraction ≤ 20 ppb; and / or, The high-purity dilute nitric acid has a mass fraction of 5-35%, and the impurity content of the high-purity dilute nitric acid includes: iron mass fraction ≤0.5ppm, calcium mass fraction ≤1ppm, silicon mass fraction ≤5ppm, thorium mass fraction ≤5ppb and uranium mass fraction ≤5ppb.

[0073] Strict control of impurity levels is crucial to the purity of the final product. An appropriate range of impurity levels ensures efficient reaction while preventing the introduction of impurities. Example It was prepared using high-purity aluminum hydroxide with an iron mass fraction of 2 ppm, a calcium mass fraction of 2 ppm, a silicon mass fraction of 8 ppm, a thorium mass fraction of 40 ppb, and a uranium mass fraction of 40 ppb.

[0074] High-purity sodium hydroxide with a mass concentration of 31 g / L was used, with iron mass fraction of 0.8 ppm, calcium mass fraction of 0.8 ppm, sodium mass fraction of 800 ppm, silicon mass fraction of 8 ppm, thorium mass fraction of 15 ppb, and uranium mass fraction of 15 ppb.

[0075] High-purity dilute nitric acid with a mass fraction of 15% was used, with iron mass fraction of 0.3 ppm, calcium mass fraction of 0.8 ppm, silicon mass fraction of 3 ppm, thorium mass fraction of 3 ppb, and uranium mass fraction of 3 ppb.

[0076] High-purity aluminum hydroxide with an iron content of 2.5 ppm was mixed with high-purity sodium hydroxide with an iron content of 0.9 ppm and a mass concentration of 32 g / L and reacted.

[0077] High-purity sodium hydroxide with a mass concentration of 30 g / L and an iron content of 0.5 ppm was reacted with high-purity dilute nitric acid with a mass fraction of 20% and an iron content of 0.4 ppm.

[0078] The reaction was carried out using high-purity aluminum hydroxide with an iron content of 1.5 ppm and high-purity dilute nitric acid with an iron content of 0.2 ppm and a mass fraction of 35%.

[0079] In some embodiments, the mass concentration of the ultrapure sodium aluminate solution is 155 g / L to 165 g / L; the impurity content of the ultrapure sodium aluminate solution further includes: calcium mass fraction ≤ 1 ppm, silicon mass fraction ≤ 8 ppm, thorium mass fraction ≤ 20 ppb and uranium mass fraction ≤ 20 ppb; and / or, The impurity content of the high-purity aluminum nitrate solution also includes: calcium mass fraction ≤ 1 ppm, silicon mass fraction ≤ 5 ppm, thorium mass fraction ≤ 5 ppb, and uranium mass fraction ≤ 5 ppb; and / or, The purity of the alumina powder is ≥99.995%; the impurity content of the alumina powder includes: iron mass fraction ≤0.5ppm, thorium mass fraction ≤5ppb and uranium mass fraction ≤5ppb; the particle size D50 of the alumina powder ranges from 0.2μm to 60μm.

[0080] Strict control of impurity content is crucial for the purity of intermediate products. An appropriate range of impurity content ensures efficient reaction while preventing the introduction of impurities. A suitable particle size range ensures efficient product application while meeting the needs of different application scenarios. Example: An ultrapure sodium aluminate solution with a mass concentration of 160 g / L was prepared, containing 0.8 ppm calcium, 6 ppm silicon, 15 ppb thorium, and 10 ppb uranium.

[0081] A high-purity aluminum nitrate solution with a calcium mass fraction of 0.5 ppm, a silicon mass fraction of 3 ppm, a thorium mass fraction of 3 ppb, and a uranium mass fraction of 2 ppb was generated.

[0082] The final product was alumina powder with a purity of 99.998%, an iron mass fraction of 0.3 ppm, a thorium mass fraction of 3 ppb, a uranium mass fraction of 2 ppb, and a particle size range of 10 μm.

[0083] Starting from an ultrapure sodium aluminate solution with a mass concentration of 162 g / L and a calcium content of 0.7 ppm, alumina powder with a particle size of 20 μm and an iron content of 0.4 ppm was finally obtained after a series of treatments.

[0084] Through a specific process, a high-purity aluminum nitrate solution with a calcium content of 0.6 ppm is converted into alumina powder with a purity of 99.997% and a particle size of 30 μm.

[0085] Starting with an ultrapure sodium aluminate solution with a mass concentration of 158 g / L and a silicon content of 7 ppm, the process involves reaction, crystallization, and calcination to finally obtain alumina powder with a purity of 99.996%, a thorium content of 4 ppb, and a particle size of 50 μm.

[0086] In some embodiments, the ultrapure aluminum nitrate precursor further includes, prior to the two-stage activation calcination, the following: The ultrapure aluminum nitrate precursor was washed with deionized water to remove surface impurities from the pure aluminum nitrate precursor.

[0087] Washing with deionized water removes impurities from the surface of the ultrapure aluminum nitrate precursor, further improving its purity. Deionized water effectively removes impurities from the precursor surface, especially organic and soluble impurities. This washing step further enhances the purity of the precursor.

[0088] Secondly, embodiments of this application also provide an application of the low-magnetic ultrapure alumina described in the first aspect, wherein the low-magnetic ultrapure alumina powder is used in electronic chip packaging, optical materials, ceramic materials, biomedical materials, and aerospace materials.

[0089] Low magnetic properties prevent magnetic impurities from affecting chip performance. Low-magnetic, high-purity alumina powder (iron content ≤0.5ppm, thorium content ≤5ppb, uranium content ≤5ppb) effectively avoids the impact of magnetic impurities on chip performance. Magnetic impurities can cause electromagnetic interference in chips, affecting their performance and reliability.

[0090] High purity ensures the chemical stability and physical properties of materials. High-purity alumina powder (purity ≥ 99.995%) ensures the chemical stability and physical properties of materials. High-purity materials avoid the influence of impurities on material properties, thereby improving their application performance in chip packaging. Example: Electronic chip packaging: Low-magnetic, high-purity alumina powder can be used for electronic chip packaging to avoid the impact of magnetic impurities on chip performance.

[0091] High-end optical materials: High-purity alumina powder can be used to manufacture high-end optical materials, ensuring the optical performance of the materials.

[0092] High-precision ceramic materials: High-purity alumina powder can be used to manufacture high-precision ceramic materials, ensuring the mechanical properties and chemical stability of the materials.

[0093] Biomedical materials: High-purity alumina powder can be used to manufacture biomedical materials, ensuring the biocompatibility and chemical stability of the materials.

[0094] Aerospace materials: High-purity alumina powder can be used to manufacture aerospace materials, ensuring high performance and reliability.

[0095] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0096] Example 1 Objective: To prepare low-magnetic, high-purity alumina powder, ensuring that its purity and particle size meet the requirements.

[0097] Redissolution reaction: High-purity aluminum hydroxide (Fe≤3ppm, Ca≤3ppm, Si≤10ppm, Th≤60ppb, U≤60ppb) is used. High-purity sodium hydroxide (concentration 30-32g / L, Fe≤1ppm, Ca≤1ppm, Na≤1000ppm, Si≤10ppm, Th≤20ppb, U≤20ppb) is used. The reaction is carried out at 108℃ for 6 hours to produce an ultra-pure sodium aluminate solution (concentration 160g / L, Fe≤1ppm, Ca≤1ppm, Si≤8ppm, Th≤20ppb, U≤20ppb).

[0098] Reaction with high-purity dilute nitric acid: Use high-purity dilute nitric acid (mass fraction 15%, Fe≤0.5ppm, Ca≤1ppm, Si≤5ppm, Th≤5ppb, U≤5ppb). The reaction produces a high-purity aluminum nitrate solution (Fe≤0.5ppm, Ca≤1ppm, Si≤5ppm, Th≤5ppb, U≤5ppb).

[0099] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 1°C for 18 hours to obtain ultrapure aluminum nitrate precursor (Fe≤0.5ppm, Ca≤1ppm, Si≤5ppm, Th≤5ppb, U≤5ppb).

[0100] Two-stage activation roasting: First stage activation roasting: temperature 550℃, duration 3 hours. Second stage activation roasting: temperature 1280℃, duration 4 hours.

[0101] The final product is alumina powder (purity ≥99.995%, Fe≤0.5ppm, Th≤5ppb, U≤5ppb, particle size 35.209μm).

[0102] Example 2 Objective: To optimize reaction conditions and further improve the purity of alumina powder.

[0103] Redissolution reaction: High-purity aluminum hydroxide (Fe=1.5ppm, Ca=2ppm, Si=8ppm, Th=40ppb, U=40ppb) was used. High-purity sodium hydroxide (concentration 31g / L, Fe=0.8ppm, Ca=0.8ppm, Na=800ppm, Si=8ppm, Th=15ppb, U=15ppb) was used. The reaction was carried out at 110℃ for 5 hours to produce an ultra-pure sodium aluminate solution (concentration 162g / L, Fe=0.5ppm, Ca=0.5ppm, Si=5ppm, Th=10ppb, U=8ppb).

[0104] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (mass fraction 20%, Fe=0.2ppm, Ca=0.5ppm, Si=2ppm, Th=2ppb, U=2ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.3ppm, Ca=0.4ppm, Si=2ppm, Th=2ppb, U=1ppb).

[0105] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 3°C ​​for 20 hours to obtain ultrapure aluminum nitrate precursor (Fe=0.3ppm, Ca=0.4ppm, Si=2ppm, Th=2ppb, U=1ppb).

[0106] Two-stage activation roasting: First stage activation roasting: temperature 500℃, duration 3.5 hours. Second stage activation roasting: temperature 1280℃, duration 4.5 hours.

[0107] The final product was alumina powder (purity ≥99.998%, Fe=0.2ppm, Th=2ppb, U=1ppb, particle size 35.209μm).

[0108] Example 3 Objective: To verify the effect of different remelting reaction temperatures on product purity.

[0109] Redissolution reaction: High-purity aluminum hydroxide (Fe=2ppm, Ca=2.5ppm, Si=7ppm, Th=50ppb, U=50ppb) was used. High-purity sodium hydroxide (concentration 30g / L, Fe=0.9ppm, Ca=0.9ppm, Na=1000ppm, Si=7ppm, Th=20ppb, U=20ppb) was used. The reaction was carried out at 100℃ for 8 hours to produce an ultra-pure sodium aluminate solution (concentration 158g / L, Fe=0.9ppm, Ca=0.9ppm, Si=7ppm, Th=20ppb, U=15ppb).

[0110] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (mass fraction 10%, Fe=0.4ppm, Ca=0.9ppm, Si=4ppm, Th=4ppb, U=4ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.5ppm, Ca=0.8ppm, Si=4ppm, Th=4ppb, U=3ppb).

[0111] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 8°C for 15 hours to obtain ultrapure aluminum nitrate precursor (Fe=0.5ppm, Ca=0.8ppm, Si=4ppm, Th=4ppb, U=3ppb).

[0112] Two-stage activation roasting: First stage activation roasting: temperature 300℃, duration 2 hours. Second stage activation roasting: temperature 1220℃, duration 4 hours.

[0113] The final product is alumina powder (purity ≥99.997%, Fe=0.4ppm, Th=4ppb, U=3ppb, particle size 30μm).

[0114] Example 4 Objective: To verify the effect of different low-temperature secondary crystallization times on product purity.

[0115] Redissolution reaction: High-purity aluminum hydroxide (Fe=1.8ppm, Ca=2.2ppm, Si=6ppm, Th=45ppb, U=45ppb) was used. High-purity sodium hydroxide (concentration 31.5g / L, Fe=0.7ppm, Ca=0.7ppm, Na=700ppm, Si=6ppm, Th=18ppb, U=18ppb) was used. The reaction was carried out at 108℃ for 7 hours to produce an ultra-pure sodium aluminate solution (concentration 163g / L, Fe=0.7ppm, Ca=0.7ppm, Si=6ppm, Th=18ppb, U=12ppb).

[0116] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (mass fraction 12%, Fe=0.35ppm, Ca=0.7ppm, Si=3.5ppm, Th=3.5ppb, U=3.5ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.35ppm, Ca=0.6ppm, Si=3.5ppm, Th=3.5ppb, U=2.5ppb).

[0117] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 2°C for 22 hours to obtain ultrapure aluminum nitrate precursor (Fe=0.35ppm, Ca=0.6ppm, Si=3.5ppm, Th=3.5ppb, U=2.5ppb).

[0118] Two-stage activation roasting: First stage activation roasting: temperature 450℃, duration 3 hours. Second stage activation roasting: temperature 1260℃, duration 4 hours.

[0119] The final product is alumina powder (purity ≥99.998%, Fe=0.3ppm, Th=3ppb, U=2ppb, particle size 15μm).

[0120] Example 5 Objective: To verify the effect of different two-stage activation and calcination temperatures on product purity.

[0121] Redissolution reaction: High-purity aluminum hydroxide (Fe=2.5ppm, Ca=2.8ppm, Si=9ppm, Th=55ppb, U=55ppb) was used. High-purity sodium hydroxide (concentration 32.5g / L, Fe=1ppm, Ca=1ppm, Na=900ppm, Si=9ppm, Th=20ppb, U=20ppb) was used. The reaction was carried out at 115℃ for 4 hours to produce an ultra-pure sodium aluminate solution (concentration 165g / L, Fe=1ppm, Ca=1ppm, Si=9ppm, Th=20ppb, U=18ppb).

[0122] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (35% by mass, Fe=0.5ppm, Ca=1ppm, Si=5ppm, Th=5ppb, U=5ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.5ppm, Ca=0.9ppm, Si=5ppm, Th=5ppb, U=4ppb).

[0123] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 10°C for 12 hours to obtain ultrapure aluminum nitrate precursor (Fe=0.5ppm, Ca=0.9ppm, Si=5ppm, Th=5ppb, U=4ppb).

[0124] Two-stage activation roasting: First stage activation roasting: temperature 600℃, duration 4 hours. Second stage activation roasting: temperature 1300℃, duration 5 hours.

[0125] The final product is alumina powder (purity ≥99.996%, Fe=0.5ppm, Th=5ppb, U=4ppb, particle size 50μm).

[0126] Example 6 Objective: To verify the effect of different washing conditions on product purity.

[0127] Redissolution reaction: High-purity aluminum hydroxide (Fe=1.2ppm, Ca=1.8ppm, Si=7ppm, Th=35ppb, U=35ppb) was used. High-purity sodium hydroxide (concentration 30.5g / L, Fe=0.6ppm, Ca=0.6ppm, Na=500ppm, Si=7ppm, Th=12ppb, U=12ppb) was used. The reaction was carried out at 102℃ for 6.5 hours to produce an ultra-pure sodium aluminate solution (concentration 155g / L, Fe=0.6ppm, Ca=0.6ppm, Si=7ppm, Th=12ppb, U=8ppb).

[0128] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (5% by mass, Fe=0.2ppm, Ca=0.5ppm, Si=2ppm, Th=2ppb, U=2ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.25ppm, Ca=0.45ppm, Si=2ppm, Th=2ppb, U=1.5ppb).

[0129] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 4°C for 16 hours to obtain an ultrapure aluminum nitrate precursor (Fe=0.25ppm, Ca=0.45ppm, Si=2ppm, Th=2ppb, U=1.5ppb).

[0130] Washing: Wash the ultrapure aluminum nitrate precursor with deionized water to further remove surface impurities.

[0131] Two-stage activation roasting: First stage activation roasting: temperature 250℃, duration 2.5 hours. Second stage activation roasting: temperature 1220℃, duration 4.5 hours.

[0132] The final product is alumina powder (purity ≥99.997%, Fe=0.2ppm, Th=2ppb, U=1ppb, particle size 25μm).

[0133] Comparative Example 1 Objective: To verify the effect of not performing low-temperature secondary crystallization on product purity.

[0134] Redissolution reaction: High-purity aluminum hydroxide (Fe=1.5ppm, Ca=2ppm, Si=8ppm, Th=40ppb, U=40ppb) was used. High-purity sodium hydroxide (concentration 31g / L, Fe=0.8ppm, Ca=0.8ppm, Na=800ppm, Si=8ppm, Th=15ppb, U=15ppb) was used. The reaction was carried out at 105℃ for 6 hours to produce an ultra-pure sodium aluminate solution (concentration 160g / L, Fe=0.8ppm, Ca=0.8ppm, Si=6ppm, Th=15ppb, U=10ppb).

[0135] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (mass fraction 15%, Fe=0.3ppm, Ca=0.8ppm, Si=3ppm, Th=3ppb, U=3ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.4ppm, Ca=0.5ppm, Si=3ppm, Th=3ppb, U=2ppb).

[0136] Two-stage activation roasting: First stage activation roasting: temperature 400℃, duration 3 hours. Second stage activation roasting: temperature 1250℃, duration 4 hours.

[0137] The final product is alumina powder (purity ≥99.995%, Fe=0.6ppm, Th=4ppb, U=3ppb, particle size 10μm).

[0138] Comparative Example 2 Objective: To verify the effect of pre-decomposition rate on product purity.

[0139] Redissolution reaction: High-purity aluminum hydroxide (Fe=1ppm, Ca=1.5ppm, Si=5ppm, Th=30ppb, U=30ppb) was used. High-purity sodium hydroxide (concentration 32g / L, Fe=0.5ppm, Ca=0.5ppm, Na=600ppm, Si=5ppm, Th=10ppb, U=10ppb) was used. The reaction was carried out at 110℃ for 5 hours to produce an ultra-pure sodium aluminate solution (concentration 162g / L, Fe=0.5ppm, Ca=0.5ppm, Si=5ppm, Th=10ppb, U=8ppb).

[0140] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (mass fraction 20%, Fe=0.2ppm, Ca=0.5ppm, Si=2ppm, Th=2ppb, U=2ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.3ppm, Ca=0.4ppm, Si=2ppm, Th=2ppb, U=1ppb).

[0141] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 3°C ​​for 20 hours to obtain ultrapure aluminum nitrate precursor (Fe=0.3ppm, Ca=0.4ppm, Si=2ppm, Th=2ppb, U=1ppb).

[0142] Two-stage activation roasting: First stage activation roasting: temperature 500℃, duration 3.5 hours. Second stage activation roasting: temperature 1280℃, duration 4.5 hours.

[0143] The final product was alumina powder (purity ≥99.99%, Fe=0.5ppm, Th=3ppb, U=2ppb, particle size 35.209μm).

[0144] Comparative Example 3 Objective: To verify the effect of not performing two-stage activation calcination on product purity.

[0145] Redissolution reaction: High-purity aluminum hydroxide (Fe=1.2ppm, Ca=1.8ppm, Si=7ppm, Th=35ppb, U=35ppb) was used. High-purity sodium hydroxide (concentration 30.5g / L, Fe=0.6ppm, Ca=0.6ppm, Na=500ppm, Si=7ppm, Th=12ppb, U=12ppb) was used. The reaction was carried out at 102℃ for 6.5 hours to produce an ultra-pure sodium aluminate solution (concentration 155g / L, Fe=0.6ppm, Ca=0.6ppm, Si=7ppm, Th=12ppb, U=8ppb).

[0146] Reaction with high-purity dilute nitric acid: High-purity dilute nitric acid (5% by mass, Fe=0.2ppm, Ca=0.5ppm, Si=2ppm, Th=2ppb, U=2ppb) is used. The reaction produces a high-purity aluminum nitrate solution (Fe=0.25ppm, Ca=0.45ppm, Si=2ppm, Th=2ppb, U=1.5ppb).

[0147] Low-temperature secondary crystallization: Crystallization was carried out in an ice-water bath at 4°C for 16 hours to obtain an ultrapure aluminum nitrate precursor (Fe=0.25ppm, Ca=0.45ppm, Si=2ppm, Th=2ppb, U=1.5ppb).

[0148] Single-stage activation roasting: Temperature 1250℃, duration 4 hours.

[0149] The final product is alumina powder (purity ≥99.996%, Fe=0.5ppm, Th=3ppb, U=2ppb, particle size 20μm).

[0150] Effect data: The effect data of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

[0151] Experimental methods for obtaining effect data: 1. Qualitative analysis: X-ray diffraction (XRD) was used to determine the crystal structure of alumina.

[0152] Instrument: X-ray diffractometer (such as Bruker D8 Advance).

[0153] Conditions: Cu Kα radiation, tube voltage 40 kV, tube current 40 mA, scan range 10°-80°, step size 0.02°, scan speed 2° / min.

[0154] 2. Specific surface area: Nitrogen adsorption-desorption isotherm tests were performed using a specific surface area analyzer (such as Micromeritics Tristar 3000), and the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method.

[0155] Instrument: Surface area analyzer.

[0156] Conditions: The sample was degassed under vacuum at 100℃ for 2 hours, and the nitrogen adsorption temperature was 77 K.

[0157] 3. Particle size D50: The particle size distribution of the sample is measured using a laser particle size analyzer (such as Malvern Mastersizer 3000). D50 represents the median of the particle size distribution.

[0158] Instrument: Laser particle size analyzer.

[0159] Conditions: The sample was dispersed in deionized water and sonicated for 1 minute. The measurement range was 0.01-3000 μm.

[0160] 4. Purity: The purity of alumina was calculated by gravimetric and chemical analysis methods, by dissolving the sample and titrating it with a standard solution.

[0161] Instruments: Electronic balance (accuracy 0.0001 g), titrator.

[0162] Conditions: Weigh an appropriate amount of sample, dissolve it in an appropriate amount of dilute acid, titrate with a standard solution to the endpoint, and calculate the purity.

[0163] Table 1

[0164] The above effect data table provides a clear comparison of the differences between various embodiments and comparative examples. The following conclusions can be drawn: 1. Process optimization: Low-temperature secondary crystallization: Low-temperature secondary crystallization can effectively remove impurities and improve the purity of the sample. The purity of Examples 1-6 all reached or exceeded 99.995%, while Comparative Example 1 did not undergo low-temperature secondary crystallization and its purity was only 99.99%.

[0165] Two-stage activation calcination: Two-stage activation calcination can further optimize the purity and particle size distribution of the samples. The particle size D50 of Examples 1-6 is between 15 μm and 50 μm, while Comparative Example 3, which did not undergo two-stage activation calcination, has a particle size D50 of 33.803 μm and a purity of 99.99%.

[0166] Pre-decomposition rate control: In Examples 1-6, controlling the pre-decomposition rate between 5% and 8% effectively improved the purity of the samples. Comparative Example 2 had a pre-decomposition rate of only 3% and a purity of 99.99%, indicating that the pre-decomposition rate has a significant impact on impurity removal.

[0167] 2. Particle size control: Examples 1-6 demonstrate that adjusting process conditions (such as sand mills, air jet mills, etc.) can effectively control particle size distribution to meet the needs of different application scenarios. Particle size D50 ranges from 15 μm to 50 μm, indicating high process flexibility and controllability.

[0168] 3. Significantly improved purity: The purity of Examples 1-6 all reached or exceeded 99.995%, significantly higher than the 99.99% of the comparative example. This indicates that by optimizing process conditions, such as low-temperature secondary crystallization and two-stage activation calcination, impurities can be effectively removed and the purity of the product can be improved.

[0169] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing low-magnetic high-purity alumina, comprising: reacting high-purity aluminum hydroxide with a first set iron content with high-purity sodium hydroxide with a second set iron content to obtain an ultra-pure sodium aluminate solution with an iron mass fraction of ≤1ppm; reacting the ultra-pure sodium aluminate solution with high-purity dilute nitric acid with a third set iron content to obtain a high-purity aluminum nitrate solution with an iron mass fraction of ≤0.5ppm; performing low-temperature secondary crystallization on the high-purity aluminum nitrate solution to obtain an ultra-pure aluminum nitrate precursor with an iron mass fraction of ≤0.5ppm; performing two-stage activation roasting on the ultra-pure aluminum nitrate precursor to obtain an alumina powder; and the temperature of the first-stage activation roasting is lower than the temperature of the second-stage activation roasting. The temperature of the first-stage activation roasting is 200-600℃, and the temperature of the second-stage activation roasting is 1200-1300℃. The time of the first-stage activation roasting is 2-4 hours, and the time of the second-stage activation roasting is 3-5 hours. The temperature of the re-dissolution reaction is 100-115℃, and the time of the re-dissolution reaction is 4-8 hours. In the re-dissolution reaction, the molar ratio of the high-purity aluminum hydroxide to the high-purity sodium hydroxide is 1:1.05-1.

15. The temperature of the low-temperature secondary crystallization is 0-10℃, and the time of the low-temperature secondary crystallization is 12-24 hours; and / or, the high-purity aluminum nitrate solution is cooled using an ice-water bath during the low-temperature secondary crystallization, and the temperature of the ice-water bath is 0-5℃.

2. The method of claim 1, wherein, The impurity content of the high-purity aluminum hydroxide includes: an iron mass fraction of ≤3ppm, a calcium mass fraction of ≤3ppm, a silicon mass fraction of ≤10ppm, a thorium mass fraction of ≤60ppb, and a uranium mass fraction of ≤60ppb; and / or, the mass concentration of the high-purity sodium hydroxide is 30-32g / L, and the impurity content of the high-purity sodium hydroxide includes: an iron mass fraction of ≤1ppm, a calcium mass fraction of ≤1ppm, a sodium mass fraction of ≤1000ppm, a silicon mass fraction of ≤10ppm, a thorium mass fraction of ≤20ppb, and a uranium mass fraction of ≤20ppb; and / or, the mass fraction of the high-purity dilute nitric acid is 5-35%, and the impurity content of the high-purity dilute nitric acid includes: an iron mass fraction of ≤0.5ppm, a calcium mass fraction of ≤1ppm, a silicon mass fraction of ≤5ppm, a thorium mass fraction of ≤5ppb, and a uranium mass fraction of ≤5ppb.

3. The method of claim 2, wherein, The mass concentration of the ultra-pure sodium aluminate solution is 155g / L to 165g / L, and the impurity content of the ultra-pure sodium aluminate solution further includes: a calcium mass fraction of ≤1ppm, a silicon mass fraction of ≤8ppm, a thorium mass fraction of ≤20ppb, and a uranium mass fraction of ≤20ppb; and / or, the impurity content of the high-purity aluminum nitrate solution further includes: a calcium mass fraction of ≤1ppm, a silicon mass fraction of ≤5ppm, a thorium mass fraction of ≤5ppb, and a uranium mass fraction of ≤5ppb; and / or, 4. The method of claim 1, wherein, ​ 5. The method of claim 1 or 4, wherein the low-magnetic ultra-pure alumina is prepared by the steps of: ​ ​ 6. The method of claim 1, wherein the low-magnetic, ultra-pure aluminum oxide is prepared by the steps of: ​ ​ ​ 7. The method of claim 1, wherein, ​ ​ ​ 8. The method of claim 1, wherein, ​ ​ The purity of the alumina powder is ≥99.995%; the impurity content of the alumina powder includes: iron mass fraction ≤0.5ppm, thorium mass fraction ≤5ppb and uranium mass fraction ≤5ppb; the particle size D50 of the alumina powder ranges from 0.2μm to 60μm.

9. The method for preparing low-magnetic ultrapure alumina according to claim 1, characterized in that, Before the two-stage activation roasting of the ultra-pure aluminum nitrate precursor, further comprising: using deionized water to wash the ultra-pure aluminum nitrate precursor to remove the surface impurities of the pure aluminum nitrate precursor.

10. Application of the low-magnetic ultra-pure alumina powder of any one of claims 1 to 9, wherein the low-magnetic ultra-pure alumina powder is applied to electronic chip packaging, optical materials, ceramic materials, biomedical materials and aerospace materials.

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