CN113292089A - Preparation method of high-purity alumina for sapphire - Google Patents

Preparation method of high-purity alumina for sapphire Download PDF

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CN113292089A
CN113292089A CN202110570234.XA CN202110570234A CN113292089A CN 113292089 A CN113292089 A CN 113292089A CN 202110570234 A CN202110570234 A CN 202110570234A CN 113292089 A CN113292089 A CN 113292089A
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ammonium
aluminum
drying
purity
carbon
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徐前进
刘坤吉
何香春
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Shandong Huiyuan Technology Development Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/30—Preparation of aluminium oxide or hydroxide by thermal decomposition or by hydrolysis or oxidation of aluminium compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

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Abstract

The invention provides a preparation method of high-purity alumina for sapphire, belonging to the technical field of preparation of inorganic functional materials. According to the invention, the carbon remover is used, and the strong oxidation effect or the auxiliary oxidation effect of the carbon remover is utilized to oxidize residual organic carbon into carbon dioxide at high temperature, so that the residual carbon content in alumina prepared by an aluminum alkoxide method is reduced, and the problem that sapphire produced by high-purity alumina prepared by the aluminum alkoxide method is yellowish or even brown and cannot be used as a photoelectric device is avoided. The results of the examples show that the carbon residue of the alumina prepared by the method is less than 0.001 wt%, the purity is higher than 99.99%, and the sapphire produced by the high-purity alumina prepared by the method has no variegation and meets the requirement of growing sapphire single crystals.

Description

Preparation method of high-purity alumina for sapphire
Technical Field
The invention relates to the technical field of preparation of inorganic functional materials, in particular to a preparation method of high-purity alumina for sapphire.
Background
Sapphire (alumina single crystal) is a window material for infrared military devices, satellite space technology and high-intensity laser because of the characteristics of chemical corrosion resistance, heat resistance, good heat conduction, high hardness, high transmittance and the like, and is also an ideal substrate material for semiconductor light-emitting diodes (LEDs), large-scale integrated circuits, superconducting nano-structure films and the like.
The growing sapphire single crystal mainly takes high-purity alumina as a raw material, and the production methods of the high-purity alumina include an aluminum alkoxide method, a metal aluminum hydration method, an aluminum ammonium sulfate pyrolysis method and an improved Bayer method. The aluminum alkoxide method uses easily purified aluminum alkoxide as a raw material, and alcohols generated by hydrolysis of the aluminum alkoxide can be recycled. The alcoaluminum method is the most important method for growing sapphire single crystals at present because of the advantages of high product purity, environment-friendly technological process and the like. However, the alkoxide is not sufficiently hydrolyzed during the hydrolysis process, and although the alkoxide remained in the high-temperature oxidation atmosphere is decomposed and gasified, some of the alkoxide wrapped inside the precursor particle is carbonized due to insufficient contact with oxygen, so that the sapphire produced from the high-purity alumina by the alkoxide method sometimes appears yellowish or even brown and cannot be used for photoelectric devices.
Disclosure of Invention
The invention aims to provide a preparation method of high-purity alumina for sapphire, the carbon residue of the prepared alumina is less than 0.001 wt%, the purity of the alumina is higher than 99.99%, and the sapphire produced by adopting the high-purity alumina prepared by the invention has no variegated color and meets the requirement of growing sapphire single crystals.
In order to achieve the above object, the present invention provides the following technical solutions:
a preparation method of high-purity alumina for sapphire comprises the following steps:
mixing aluminum alkoxide and water under the condition of stirring, and carrying out hydrolysis reaction to obtain pseudo-boehmite-alcohol-water slurry;
removing alcohol in the pseudo-boehmite-alcohol-water slurry, and then mixing the obtained material with a carbon removal agent and water to obtain a mixed material; the carbon removing agent is one or more of aqueous hydrogen peroxide solution, chlorine dioxide, ammonium chlorate, ammonium perchlorate, persulfuric acid, ammonium persulfate, nitric acid, ammonium nitrate, aluminum nitrate nonahydrate, concentrated sulfuric acid, ammonium sulfate, aluminum sulfate octadecahydrate, concentrated hydrochloric acid, ammonium chloride, aluminum chloride hexahydrate, ammonium fluoride, aluminum fluoride, ammonium iodate and ammonium bromide;
and drying and calcining the mixed material in sequence to obtain the high-purity alumina for the sapphire.
Preferably, the aluminum alkoxide has the formula Al (C)nH2n+1O)3Wherein n is more than or equal to 3 and less than or equal to 8, and n is an integer; the purity of the aluminum alkoxide is more than or equal to 99 percent.
Preferably, in the hydrolysis reaction, the molar ratio of water to aluminum alkoxide is (2.5-10): 1.
preferably, the temperature of the hydrolysis reaction is 25-120 ℃, and the time is 2-12 h.
Preferably, the stirring speed is 10-300 r/min.
Preferably, the mass of the carbon removing agent is 5% or less of the mass of the aluminum alkoxide.
Preferably, the calcining temperature is 500-1000 ℃, and the heat preservation time is 2-12 h.
Preferably, the calcination is carried out in an air atmosphere.
Preferably, the method for removing the alcohol from the pseudoboehmite-alcohol-water slurry comprises drying or centrifugal separation.
Preferably, the drying is spray drying, flash drying, vacuum drying, paddle drying or forced air drying.
The invention provides a preparation method of high-purity alumina for sapphire, which comprises the following steps: mixing aluminum alkoxide and water under the condition of stirring, and carrying out hydrolysis reaction to obtain pseudo-boehmite-alcohol-water slurry; removing alcohol in the pseudo-boehmite-alcohol-water slurry, and then mixing the obtained material with a carbon removal agent and water to obtain a mixed material; the carbon removing agent is one or more of aqueous hydrogen peroxide solution, chlorine dioxide, ammonium chlorate, ammonium perchlorate, persulfuric acid, ammonium persulfate, nitric acid, ammonium nitrate, aluminum nitrate nonahydrate, concentrated sulfuric acid, ammonium sulfate, aluminum sulfate octadecahydrate, concentrated hydrochloric acid, ammonium chloride, aluminum chloride hexahydrate, ammonium fluoride, aluminum fluoride, ammonium iodate and ammonium bromide; and drying and calcining the mixed material in sequence to obtain the high-purity alumina for the sapphire. According to the invention, the carbon remover is used, and the strong oxidation effect or the auxiliary oxidation effect of the carbon remover is utilized to oxidize residual organic carbon into carbon dioxide at high temperature, so that the residual carbon content in alumina prepared by an aluminum alkoxide method is reduced, and the problem that sapphire produced by high-purity alumina prepared by the aluminum alkoxide method is yellowish or even brown and cannot be used as a photoelectric device is avoided.
Furthermore, the preparation method has a particularly obvious carbon removal effect on alumina prepared by hydrolyzing long-chain aluminum alkoxide with more than 3C atoms in a carbon chain.
Drawings
Fig. 1 is an optical photograph of the aluminas prepared in example 2 and comparative example 2.
Detailed Description
The invention provides a preparation method of high-purity alumina for sapphire, which comprises the following steps:
mixing aluminum alkoxide and water under the condition of stirring, and carrying out hydrolysis reaction to obtain pseudo-boehmite-alcohol-water slurry;
removing alcohol in the pseudo-boehmite-alcohol-water slurry, and then mixing the obtained material with a carbon removal agent and water to obtain a mixed material; the carbon removing agent is one or more of aqueous hydrogen peroxide solution, chlorine dioxide, ammonium chlorate, ammonium perchlorate, persulfuric acid, ammonium persulfate, nitric acid, ammonium nitrate, aluminum nitrate nonahydrate, concentrated sulfuric acid, ammonium sulfate, aluminum sulfate octadecahydrate, concentrated hydrochloric acid, ammonium chloride, aluminum chloride hexahydrate, ammonium fluoride, aluminum fluoride, ammonium iodate and ammonium bromide;
and drying and calcining the mixed material in sequence to obtain the high-purity alumina for the sapphire.
In the present invention, the starting materials used are all commercially available products well known in the art, unless otherwise specified.
The invention mixes aluminum alkoxide and water under the condition of stirring, and carries out hydrolysis reaction to obtain pseudo-boehmite-alcohol-water slurry.
In the present invention, the chemical formula of the aluminum alkoxide is preferably Al (C)nH2n+1O)3Wherein n is more than or equal to 3 and less than or equal to 8, and n is an integer. In an embodiment of the invention, the aluminium alkoxide is in particular aluminium isopropoxide or aluminium hexanolate. In the present invention, the purity of the aluminum alkoxide is preferably equal to or greater than 99%, and the total content of Na, Fe, Si, K, Ca, Cu, Ti and Zn in the aluminum alkoxide is preferably less than 0.005 wt.%.
In the present invention, in the hydrolysis reaction, the molar ratio of water to aluminum alkoxide is preferably (2.5 to 10): 1, more preferably (3-8): 1, and still more preferably (5-6): 1; the water is preferably deionized water or high-purity water, and the deionized water or the high-purity water can be used for avoiding the influence of impurity ions in the water on the preparation of the high-purity aluminum oxide.
The mixing process is not particularly limited in the present invention, and a mixing process well known in the art may be used. In the invention, the rotation speed of the stirring is preferably 10-300 r/min, and more preferably 50-250 r/min. The invention utilizes stirring to promote mass transfer in the hydrolysis process.
In the invention, the temperature of the hydrolysis reaction is preferably 25-120 ℃, and more preferably 50-100 ℃; the time of the hydrolysis reaction is preferably 2-12 hours, more preferably 4-10 hours, and further preferably 6-8 hours. In the hydrolysis reaction process, aluminum alkoxide is hydrolyzed into pseudo-boehmite and alcohol under the action of water, and pseudo-boehmite-alcohol-water slurry is obtained. The hydrolysis reaction is preferably carried out in a reaction kettle with a reflux device.
After the pseudoboehmite-alcohol-water slurry is obtained, the alcohol in the pseudoboehmite-alcohol-water slurry is removed by the method.
In the present invention, the method for removing the alcohol in the pseudoboehmite-alcohol-water slurry preferably comprises drying or centrifugation. The invention has no special requirements on the drying conditions and the implementation mode, and the pseudoboehmite-alcohol-water slurry can be completely dried. In the embodiment of the invention, when the alcohol is removed by drying, the vacuum drying is carried out for 6h at 90 ℃, or the pseudoboehmite-alcohol-water slurry is treated in a closed cycle flash evaporation dryer, wherein the protective gas is nitrogen, the inlet temperature is 250 ℃, and the outlet temperature is 80 ℃. When the alcohol is removed by centrifugation, the present invention has no special requirement for the embodiment of the centrifugation, and the centrifugation method known in the art can be adopted, specifically, a horizontal screw centrifuge is adopted for centrifugation to obtain a paste for the subsequent steps.
After removing the alcohol in the pseudo-boehmite-alcohol-water slurry, mixing the obtained material with a carbon removing agent and water to obtain a mixed material; the carbon removing agent is one or more of aqueous hydrogen peroxide solution, chlorine dioxide, ammonium chlorate, ammonium perchlorate, persulfuric acid, ammonium persulfate, nitric acid, ammonium nitrate, aluminum nitrate nonahydrate, concentrated sulfuric acid, ammonium sulfate, aluminum sulfate octadecahydrate, concentrated hydrochloric acid, ammonium chloride, aluminum chloride hexahydrate, ammonium fluoride, aluminum fluoride, ammonium iodate and ammonium bromide.
In the present invention, the content of hydrogen peroxide in the aqueous hydrogen peroxide solution is preferably 30 wt.%; the mass fraction of the nitric acid is preferably 65%; the mass fraction of the concentrated sulfuric acid is preferably 98%; the mass fraction of the concentrated hydrochloric acid is preferably 37%.
In the invention, when the decarbonizer is a plurality of the above substances, the proportion of each decarbonizer is not particularly required.
In the present invention, the mass of the decarbonizer is preferably 5% or less, more preferably 0.1% to 2% of the mass of the aluminum alkoxide. The method utilizes the strong oxidation or auxiliary oxidation of the carbon remover to oxidize residual organic carbon which is not fully hydrolyzed by aluminum alkoxide into carbon dioxide at high temperature, thereby reducing the residual carbon content in aluminum oxide by an aluminum alkoxide method and avoiding the problem that sapphire produced by high-purity aluminum oxide by the aluminum alkoxide method is in faint yellow or even brown and cannot be used as a photoelectric device.
In the invention, when the obtained material is mixed with the carbon removing agent and water, the mass of the water is preferably less than 1 time of that of the aluminum alkoxide; the water is preferably deionized water or high purity water. The invention utilizes water to uniformly mix the decarbonizer and the pseudo-boehmite.
After the mixed material is obtained, the mixed material is sequentially dried and calcined to obtain the high-purity alumina for sapphire.
In the present invention, the drying means is preferably spray drying, flash drying, vacuum drying, paddle drying or forced air drying. In the invention, the drying temperature is preferably 90-350 ℃, more preferably 120-300 ℃, and further preferably 150-250 ℃. The invention has no special requirement on the drying time and can completely dry. In the invention, the main component of the dried material is pseudo-boehmite, and the AlOOH content is more than 80 wt.%.
In the present invention, when drying is performed by means of forced air drying or vacuum drying, after the drying is completed, it is preferable that the material obtained by drying is pulverized to obtain a powder, and then calcined. In the present invention, the particle size of the powder is preferably less than 150. mu.m. The invention facilitates the contact of oxygen with particles and the release of generated gas by crushing.
In the invention, the calcination temperature is preferably 500-1000 ℃, more preferably 600-900 ℃, and further preferably 700-800 ℃; the heat preservation time is preferably 2-12 h, more preferably 4-10 h, and further preferably 6-8 h. The temperature rise rate of the temperature rise to the calcination temperature is not particularly required, and the temperature rise rate known in the art can be adopted, and is specifically 5 ℃/min in the embodiment of the invention. In the present invention, the calcination is preferably performed in an air atmosphere. In the calcining process, the pseudo-boehmite is decomposed at high temperature to obtain alumina; the method utilizes the strong oxidation or auxiliary oxidation of the carbon remover to oxidize residual organic carbon which is not fully hydrolyzed by aluminum alkoxide into carbon dioxide at high temperature, thereby reducing the residual carbon content in aluminum oxide by an aluminum alkoxide method and avoiding the problem that sapphire produced by high-purity aluminum oxide by the aluminum alkoxide method is in faint yellow or even brown and cannot be used as a photoelectric device.
In the invention, the carbon content of the product is analyzed by a carbon-sulfur tester; the whiteness of the product is analyzed by a whiteness meter; impurity elements of Na, Fe, Si, K, Ca, Cu, Ti and Zn in the product are analyzed by an inductively coupled plasma spectrometer, and the purity of the product is 100% -impurity content. The evaluation standard that the high-purity alumina prepared by the aluminum alkoxide method meets the requirements of growing the colorless transparent sapphire is as follows: the high-purity alumina powder is heated by adopting electromagnetic induction of a cold crucible, the alumina is cooled into alumina polycrystal after being melted, and the alumina polycrystal is colorless or white and does not present faint yellow, yellow or brown and other miscellaneous colors when observed by naked eyes.
The following will describe the preparation method of high purity alumina for sapphire provided by the present invention in detail with reference to the examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Introducing 2kg of liquid aluminum isopropoxide (the purity is not lower than 99%, and the total content of metallic element impurities such as Na, Fe, Si, K, Ca, Cu, Ti, Zn and the like is lower than 0.005 wt.%) into a 4L reaction kettle with reflux equipment, adding 550g of high-purity water into the reaction kettle under the stirring condition of 80 ℃ (the rotating speed is 120r/min), and continuing stirring for 4 hours after water is added, so that the aluminum isopropoxide is hydrolyzed into pseudo-boehmite-isopropanol-water slurry; carrying out vacuum drying on the slurry, wherein the drying temperature is 90 ℃, and the drying time is 6 h; adding dried pseudoboehmite (AlOOH content is 88.2 wt.%) and 10g of aluminum chloride hexahydrate into 700g of high-purity water in sequence, and mixing the three uniformly; drying the obtained mixed material in a forced air drying oven at 105 ℃ for 8 h; the obtained dry product is crushed into powder with the particle size of less than 150 microns, then the powder is put into a breathable corundum crucible with a cover, the filling rate is 70 percent, the filling height is 150mm, the powder is calcined in a muffle furnace in an air atmosphere, the heating rate is 5 ℃/min, the temperature is kept for 4h at 600 ℃, and the product obtained after cooling is high-purity alumina with the residual carbon content of 0.0004wt percent, the whiteness of 95.2 percent and the purity of 99.993 percent.
Comparative example 1
Alumina was prepared in the same manner as in example 1 except that no aluminum chloride hexahydrate was added, and the obtained alumina had a carbon residue of 0.01 wt.%, a whiteness of 73%, and a product was gray with the naked eye.
Example 2
Introducing 2000kg of liquid aluminum isopropoxide (the purity is not lower than 99%, and the total content of Na, Fe, Si, K, Ca, Cu, Ti and Zn is lower than 0.005 wt.%) into a 4000L reaction kettle, adding 550kg of high-purity water into the reaction kettle under the stirring condition of 80 ℃ (the rotating speed is 40r/min), and continuing stirring for 4 hours after the water is added, so that the aluminum isopropoxide is hydrolyzed into pseudo-boehmite-isopropanol-water slurry; treating the slurry in a closed-cycle flash dryer with nitrogen as protective gas, the inlet temperature of 250 ℃ and the discharge temperature of 80 ℃; adding dried pseudoboehmite (AlOOH content is 84 wt.%) and 10kg of aluminum chloride hexahydrate into 2000kg of high-purity water in sequence, and simultaneously uniformly mixing the three by using a mixer; spray drying the obtained mixture, wherein the inlet temperature is 350 ℃, and the outlet temperature is 100 ℃; and putting the powder obtained by spray drying into a breathable corundum crucible with a cover, wherein the filling rate is 70%, the filling height is 150mm, calcining in a kiln in an air atmosphere, the heating rate is 5 ℃/min, keeping the temperature at 800 ℃ for 4h, and cooling to obtain the high-purity alumina with the residual carbon content of 0.0009 wt%, the whiteness of 96% and the purity of 99.995%.
Specifically, the high-purity alumina powder and the high-purity graphite obtained in example 2 are added into a cold crucible, a water cooling system of the crucible and a high-frequency coil outside the crucible are started to generate a magnetic field, and the crucible is heated by the magnetic field until all the alumina powder in the crucible forms molten liquid; and starting a crucible power system to move the crucible, adding high-purity alumina powder into the crucible in the moving process until the crucible moves to the top point position, simultaneously enabling the high-purity alumina powder in the crucible to completely form molten liquid, and cooling to room temperature to obtain the alumina polycrystal. The alumina polycrystal was visually observed to be colorless.
Comparative example 2
High purity alumina was prepared in the same method steps as in example 2, except that no aluminum trichloride was added, and the obtained product had a carbon residue of 0.005 wt.% and a whiteness of 85%. The alumina polycrystalline body melted by the cold crucible has a faint yellow, yellow or brown color. In addition, the whiteness is measured and compared by a cold crucible method, and the whiteness is proved to be related to the growth of the polycrystalline without variegated colors.
FIG. 1 is an optical photograph of alumina polycrystals prepared in example 2 and comparative example 2, wherein the alumina polycrystals prepared in comparative example 2 are on the left side and the alumina polycrystals prepared in example 2 are on the right side, it can be seen from FIG. 1 that the alumina polycrystals prepared in comparative example 2 exhibit a distinct mottle, while the alumina polycrystals prepared in example 2 are colorless, which shows that the alumina prepared in the present invention has a higher purity, and sapphire produced therefrom does not exhibit mottle, satisfying the requirement for growing a sapphire single crystal.
Example 3
The decarbonizer of example 1 was changed from 10g of aluminum chloride hexahydrate to 10g of ammonium chloride under otherwise unchanged conditions, resulting in an alumina residue of 0.0009 wt% and a whiteness of 95.6%.
Example 4
The carbon remover in example 1 was changed from 10g of aluminum chloride hexahydrate to 10g of concentrated hydrochloric acid (37 wt.%), and the resulting alumina had a carbon residue of 0.0008 wt.% and a whiteness of 96% without changing other conditions.
Example 5
The decarbonizer of example 1 was changed from 10g of aluminum chloride hexahydrate to 10g of concentrated sulfuric acid (98 wt.%), the calcination temperature was changed to 900 deg.C, and other conditions were unchanged, resulting in an alumina carbon residue of 0.0009 wt.% and a whiteness of 95.3%.
Example 6
The carbon remover in example 5 was changed from 10g of concentrated sulfuric acid (98 wt.%) to 5g of persulfuric acid, and the conditions were unchanged, so that the alumina had a carbon residue of 0.0008 wt.% and a whiteness of 95.8%.
Example 7
The decarbonizer of example 1 was changed from 10g of aluminum chloride hexahydrate to 5g of concentrated nitric acid (65 wt.%), with the remaining conditions unchanged, resulting in an alumina carbon residue of 0.0009 wt.% t and a whiteness of 95.3%.
Example 8
Introducing 1kg of liquid aluminum hexanol (the total content of Na, Fe, Si, K, Ca, Cu, Ti and Zn is lower than 0.005 wt.%) into a 4L reaction kettle, adding 1.5kg of high-purity water into a hydrolysis kettle under the condition of stirring at 100 ℃, and continuing stirring for 8 hours after the water is added to hydrolyze the aluminum hexanol into pseudo-boehmite-n-hexanol-water slurry; centrifuging the slurry by using a centrifuge; uniformly mixing the paste obtained by separation with 200g of high-purity water and 5g of concentrated nitric acid (65 wt.%); drying the obtained mixture in a forced air drying oven at 105 ℃ for 8 h; the dried product (AlOOH content 87.6 wt.%) was crushed to powder with a particle size of less than 150 microns, then the powder was put into a vented corundum crucible with a cover, the filling rate was 70%, the filling height was 150mm, the powder was calcined in a muffle furnace in an air atmosphere, the temperature rise rate was 5 ℃/min, the temperature was maintained at 600 ℃ for 4h, and the product obtained after cooling was high purity alumina with a residual carbon content of less than 0.0008 wt.%, a whiteness of 95.2%, and a purity of 99.995%.
Comparative example 3
Alumina was prepared in the same manner as in example 8, except that concentrated nitric acid was not added, and the obtained alumina had a carbon residue of 0.04 wt.%, a whiteness of 68%, and a product at the bottom of the corundum crucible was gray-black as seen with naked eyes.
Example 9
Introducing 1000kg of liquid aluminum hexanol (the total content of Na, Fe, Si, K, Ca, Cu, Ti and Zn is lower than 0.005 wt.%) into a 4000L reaction kettle, adding 1500kg of high-purity water into a hydrolysis kettle under the condition of stirring at 100 ℃, and continuing stirring for 8 hours after the water is added to hydrolyze the aluminum hexanol into pseudo-boehmite-hexanol-water slurry; centrifuging the slurry by using a horizontal screw centrifuge; uniformly mixing the paste obtained by separation with 200kg of high-purity water and 5kg of concentrated nitric acid (65 wt.%); spray drying the obtained mixture at the inlet temperature of 350 ℃ and the outlet temperature of 100 ℃; then putting the dried powder (the AlOOH content is 88.2 wt.%) into a breathable corundum crucible with a cover, wherein the filling rate is 70%, the filling height is 150mm, calcining the powder in a muffle furnace in an air atmosphere, the heating rate is 5 ℃/min, keeping the temperature at 800 ℃ for 4h, and obtaining a product which is high-purity alumina with the residual carbon content of less than 0.001 wt.%, the whiteness of 95.2% and the purity of 99.995% after cooling.
Adding the obtained high-purity alumina powder and high-purity graphite into a cold crucible, starting a water cooling system of the crucible and a high-frequency coil outside the crucible to generate a magnetic field, and heating the magnetic field until all the alumina powder in the crucible forms molten liquid; and starting a crucible power system to move the crucible, adding high-purity alumina powder into the crucible in the moving process until the crucible moves to the top point position, simultaneously enabling the high-purity alumina powder in the crucible to completely form molten liquid, and cooling to room temperature to obtain the alumina polycrystal. The alumina polycrystal was visually observed to be colorless.
Comparative example 4
Alumina was prepared in the same manner as in example 9, except that concentrated nitric acid was not added, and the obtained product had a residual carbon content of 0.01 wt.%, a whiteness of 74%, and a product was gray with the naked eye. The alumina polycrystalline body melted by the cold crucible has a faint yellow, yellow or brown color.
Example 10
The decarbonizer of example 8 was changed from 5g of concentrated nitric acid to 5g of ammonium nitrate, with the other conditions unchanged, and the resulting alumina had a carbon residue of 0.0005 wt.%, a whiteness of 96.5% and a purity of 99.993%.
Example 11
The decarbonizer of example 8 was changed from 5g of concentrated nitric acid to 2g of hydrogen peroxide (H)2O2Content 30 wt.%) and 5g of ammonium chloride, with the other conditions being unchanged, the resulting alumina has a carbon residue of 0.0009 wt.%, a whiteness of 95.1% and a purity of 99.993%.
Example 12
The decarbonizer of example 8 was changed from 5g of concentrated nitric acid to 5g of ammonium perchlorate without changing other conditions, resulting in an alumina residue of 0.0004 wt.%, a whiteness of 96.7% and a purity of 99.991%.
Example 13
The decarbonizer of example 8 was changed from 5g of concentrated nitric acid to 2g of chlorine dioxide and 3g of ammonium chloride, with the remaining conditions unchanged, resulting in an alumina residue of 0.0007 wt.%, a whiteness of 96.2% and a purity of 99.993%.
Example 14
The decarbonizer in example 8 was changed from 5g of concentrated nitric acid to 10g of ammonium persulfate, the calcination temperature was changed from 600 ℃ to 900 ℃, and the other conditions were unchanged, the carbon residue of the obtained alumina was 0.0003 wt.% t, the whiteness was 96.2%, and the purity was higher than 99.992%.
It can be seen from the above examples and comparative examples that the present invention provides a method for preparing high purity alumina for sapphire, which reduces the amount of carbon residue in alumina prepared by an aluminum alkoxide method by using a carbon scavenger and oxidizing the residual organic carbon into carbon dioxide at a high temperature by utilizing the strong oxidation or auxiliary oxidation of the carbon scavenger, thereby avoiding the problem that sapphire prepared from high purity alumina prepared by an aluminum alkoxide method is yellowish or even brown and cannot be used as a photovoltaic device.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (10)

1. A preparation method of high-purity alumina for sapphire is characterized by comprising the following steps:
mixing aluminum alkoxide and water under the condition of stirring, and carrying out hydrolysis reaction to obtain pseudo-boehmite-alcohol-water slurry;
removing alcohol in the pseudo-boehmite-alcohol-water slurry, and then mixing the obtained material with a carbon removal agent and water to obtain a mixed material; the carbon removing agent is one or more of aqueous hydrogen peroxide solution, chlorine dioxide, ammonium chlorate, ammonium perchlorate, persulfuric acid, ammonium persulfate, nitric acid, ammonium nitrate, aluminum nitrate nonahydrate, concentrated sulfuric acid, ammonium sulfate, aluminum sulfate octadecahydrate, concentrated hydrochloric acid, ammonium chloride, aluminum chloride hexahydrate, ammonium fluoride, aluminum fluoride, ammonium iodate and ammonium bromide;
and drying and calcining the mixed material in sequence to obtain the high-purity alumina for the sapphire.
2. The method according to claim 1, wherein the aluminum alkoxide has a chemical formula of Al (C)nH2n+1O)3Wherein n is more than or equal to 3 and less than or equal to 8, and n is an integer; the purity of the aluminum alkoxide is more than or equal to 99 percent.
3. The preparation method according to claim 1, wherein in the hydrolysis reaction, the molar ratio of water to aluminum alkoxide is (2.5-10): 1.
4. the preparation method according to claim 1, wherein the hydrolysis reaction is carried out at a temperature of 25-120 ℃ for 2-12 hours.
5. The method according to claim 1, wherein the stirring rate is 10 to 300 r/min.
6. The method according to claim 1, wherein the mass of the carbon removing agent is 5% or less of the mass of the aluminum alkoxide.
7. The preparation method of claim 1, wherein the calcining temperature is 500-1000 ℃ and the holding time is 2-12 h.
8. The method according to claim 1 or 7, wherein the calcination is performed in an air atmosphere.
9. The method of claim 1, wherein the alcohol is removed from the pseudoboehmite-alcohol-water slurry by a method comprising drying or centrifugation.
10. The method according to claim 1, wherein the drying is performed by spray drying, flash drying, vacuum drying, paddle drying or forced air drying.
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