CN113072087B - A kind of preparation method of high-purity alumina - Google Patents

Abstract

The invention belongs to the technical field of inorganic functional materials, and in particular relates to a preparation method of high-purity alumina. The preparation method of high-purity alumina provided by the present invention comprises the following steps of calcining pseudo-boehmite in a circulating oxidizing gas atmosphere; The cycle is obtained; the number of cycles repeated > 1. The preparation method provided by the present invention can fully contact the pseudo-boehmite with the oxidizing gas, and fully oxidize the alkoxy groups remaining in the pseudo-boehmite. The residual carbon content of high-purity alumina is <0.001wt.%, the purity is >99.99wt.%, and the whiteness value is >95%.

Description

A kind of preparation method of high-purity alumina

technical field

The invention belongs to the technical field of inorganic functional materials, and in particular relates to a preparation method of high-purity alumina.

Background technique

High-purity alumina is a very important fine chemical, which is used in sapphire single crystal, fine ceramics, high-pressure sodium lamp light-transmitting tubes and high-end abrasives.

The production methods of high-purity alumina include alkoxide hydrolysis method, metal aluminum hydration method, aluminum ammonium sulfate pyrolysis method and modified Bayer method. Among the above methods, aluminum alkoxide hydrolysis method has the advantages of stable product properties and environmentally friendly process. It is considered to be the most efficient method for preparing high-purity alumina.

The alkoxide hydrolysis method mainly uses aluminum alkoxide as raw material, mixes the aluminum alkoxide with water to obtain a hydrolyzed solution, and then is dried to obtain pseudo-boehmite, which is calcined to obtain alumina. However, since the alkoxy groups still remain after the aluminum alkoxide is hydrolyzed and dried, although the oxidizing atmosphere will oxidize and gasify the remaining alkoxy groups through the high-temperature calcination process, some alkoxy groups enclosed in the pseudo-boehmite particles will Carbonization occurs due to insufficient exposure to oxygen, and carbon remains in the alumina. The residual carbon content in the alumina prepared by the alkoxide hydrolysis method is 0.005-0.03wt.%, which has no adverse effect on fine ceramics, high-end abrasives, etc. , the resulting alumina polycrystalline or single crystal will appear pale yellow or even brown.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a preparation method of high-purity alumina. The high-purity alumina prepared by the preparation method provided by the present invention has a residual carbon content of <0.001wt.%, a purity of >99.99wt.%, and a white The degree value is more than 95%, and the alumina polycrystal or single crystal prepared from the high-purity alumina provided by the present invention is colorless by visual inspection.

The invention provides a preparation method of high-purity alumina, comprising the following steps:

calcining pseudo-boehmite in a circulating oxidizing gas atmosphere;

The circulating oxidizing gas atmosphere is obtained by the cycle of feeding the oxidizing gas to maintain pressure after vacuuming;

The number of repetitions of the cycle > 1.

Preferably, the temperature of the calcination is 500-1000°C, and the holding time of the calcination is 3-6h.

Preferably, the calcination temperature is obtained by heating, and the heating rate is 3-8°C/min.

Preferably, in each cycle, the vacuuming is performed to an absolute pressure <0.01Mpa; the first vacuuming is performed during the temperature rise;

In each cycle, the absolute pressure of the oxidizing gas is 0.08-0.12 MPa.

Preferably, in each cycle, the pressure holding time of the oxidizing gas is 5-15 min.

Preferably, the oxidizing gas contains oxygen, and the volume content of the oxygen in the oxidizing gas is ≥20%.

Preferably, the oxidizing gas is one or more of oxygen, ozone, nitrogen, carbon dioxide, chlorine, chlorine dioxide, sulfur dioxide, nitrogen monoxide and inert gases.

Preferably, the preparation method of the pseudo-boehmite comprises: mixing aluminum alkoxide and water to carry out a hydrolysis reaction to obtain pseudo-boehmite;

The temperature of the hydrolysis reaction is 60˜100° C., and the time of the hydrolysis reaction is 2.5˜8 h.

Preferably, the chemical formula of the aluminum alkoxide is Al(C _n H _2n+1 O) ₃ , and the 3≤n≤8;

Preferably, the mass ratio of the aluminum alkoxide to water is 4:(1-6).

The invention provides a method for preparing high-purity alumina, which comprises the following steps: calcining pseudo-boehmite in a circulating oxidizing gas atmosphere; the circulating oxidizing gas atmosphere is evacuated and then introduced into oxidizing gas The cycle of holding pressure was obtained; the number of cycles repeated > 1. When the pseudo-boehmite is calcined by the preparation method provided by the present invention, with the cycle of vacuuming, feeding oxidizing gas and oxidizing gas maintaining pressure, the atmosphere environment during calcination (vacuuming and feeding oxidizing gas is continuously changed) Gas holding pressure), can make the pseudo-boehmite and the oxidizing gas more fully contact, fully oxidize the alkoxy group remaining in the pseudo-boehmite, thereby preparing high-purity alumina, the results of the examples show that, The high-purity alumina prepared by the preparation method provided by the present invention has a residual carbon content of <0.001wt.%, a purity of >99.99wt.%, and a whiteness value of >95%. The alumina prepared from the high-purity alumina provided by the present invention is more The crystal or single crystal is visually colorless.

Detailed ways

The invention provides a preparation method of high-purity alumina, comprising the following steps:

calcining pseudo-boehmite in a circulating oxidizing gas atmosphere;

The circulating oxidizing gas atmosphere is obtained by the cycle of feeding the oxidizing gas to maintain pressure after vacuuming;

The number of repetitions of the cycle > 1.

Unless otherwise specified, in the present invention, the raw materials used are all commercially available products well known to those skilled in the art.

In the present invention, the preparation method of described pseudo-boehmite preferably comprises:

Aluminium alkoxide and water are mixed to carry out hydrolysis reaction to obtain pseudo-boehmite;

The temperature of the hydrolysis reaction is 60˜100° C., and the time of the hydrolysis reaction is 2.5˜8 h.

In the present invention, the aluminum alkoxide is mixed with water to carry out the hydrolysis reaction, and the chemical formula of the aluminum alkoxide is preferably Al(C _n H _{2n+ 1} O) ₃ , and the 3≤n≤8; in the specific embodiment of the present invention , the aluminum alkoxide is preferably aluminum isopropoxide or aluminum n-hexaoxide. In the present invention, the purity of the aluminum alkoxide is preferably ≥99%, and the total content of Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element in the aluminum alkoxide is ≤ 0.001wt.%.

In the present invention, the water is preferably high-purity water.

In the present invention, the mass ratio of the aluminum alkoxide to water is preferably 4:(1-8), more preferably 4:(1.1-6).

In the present invention, the temperature of the hydrolysis reaction is 60-100°C, preferably 65-85°C; the time of the hydrolysis reaction is 2.5-8h, preferably 3-4h; in the present invention, the hydrolysis reaction It is preferably carried out under stirring conditions, and the present invention has no special requirements for the specific implementation process of the stirring. In the present invention, the hydrolysis reaction is preferably carried out in a reactor with a reflux device and a stirring device.

The hydrolysis reaction obtains a pseudo-boehmite slurry, and in the present invention, preferably, the pseudo-boehmite slurry is post-treated to obtain the pseudo-boehmite. In the present invention, the post-processing preferably includes: sequentially performing solid-liquid separation, drying and pulverization on the pseudo-boehmite slurry; in the present invention, the solid-liquid separation is preferably centrifugal separation, and the centrifugal The rotational speed of separation is preferably 4500-5500 r/min. The present invention has no special requirements for the specific implementation process of the centrifugal separation. In the specific implementation of the present invention, the centrifugal separation is preferably performed in a centrifuge.

The solid-liquid separation obtains a paste-like solid product. In the present invention, the paste-like solid product is preferably dried. In the present invention, the drying is preferably vacuum drying, flash drying, blast drying or spray drying; In the present invention, the temperature of the vacuum drying is preferably 80-95° C., and the time of vacuum drying is preferably 5-7 hours. The present invention has no special requirements for the vacuum degree of the vacuum drying; in the present invention, the flash evaporation Drying is preferably carried out in a closed-circuit flash dryer, the feed temperature of the closed-circuit flash dryer is preferably 200-250°C, and the discharge temperature is preferably 80-90°C, and the protective atmosphere for the flash-drying is preferably is nitrogen or inert gas, more preferably nitrogen; in the present invention, the temperature of the blast drying is preferably 100-110°C, and the blast drying time is 7-9 hours; in the present invention, the spraying Drying is preferably by mixing the paste-like solid product with water, and after obtaining the mixture, spray-drying it in a spray desiccant, the present invention has no special requirements on the amount of water, so that the obtained mixture can be spray-dried, The feed temperature of the spray drying is preferably 300-400°C, more preferably 350°C, and the discharge temperature of the spray-drying is preferably 95-105°C, more preferably 100°C.

The present invention preferably pulverizes the dried product. The present invention has no special requirements for the specific implementation process of the pulverization. In the present invention, the particle size of the pseudo-boehmite is preferably <150 μm. In the present invention , when the paste-like solid product is dried by spray drying, the pulverization is preferably omitted.

In the present invention, pseudo-boehmite is calcined in a circulating oxidizing gas atmosphere; in the present invention, the circulating oxidizing gas atmosphere is obtained by a cycle of vacuuming and then feeding an oxidizing gas to maintain pressure; the number of cycles repeated > 1.

In the present invention, in each cycle, the vacuuming is preferably to an absolute pressure <0.01Mpa, more preferably to an absolute pressure of 0.005-0.008MPa; it is preferable to increase the temperature during the first vacuuming, and more preferably to start the temperature increase. Vacuuming is carried out at the time of vacuuming; the present invention has no special requirements on the specific time of vacuuming, which is determined according to the specific working efficiency of the vacuuming device used in the actual production process.

In the present invention, the oxidizing gas is directly introduced after vacuuming, and the vacuuming time of the present invention is less than the heating time. When the first vacuuming of the present invention ends, the heating process does not end.

In the present invention, the absolute pressure of the oxidizing gas is preferably 0.08-0.12MPa, more preferably, the absolute pressure is 0.09-0.1MPa; the present invention has no special requirements for the specific time of the oxidizing gas, according to the actual It depends on the specific working efficiency of the device for oxidizing gas used in the production process.

In the present invention, the oxidizing gas contains oxygen, and the volume content of the oxygen in the oxidizing gas is preferably ≥20%, more preferably ≥21%; in the present invention, the oxidizing gas is preferably oxygen, One or more of ozone, nitrogen, carbon dioxide, chlorine, chlorine dioxide, sulfur dioxide, nitric oxide and inert gas, the inert gas is preferably helium and/or argon, in specific embodiments of the present invention The oxidizing gas is preferably a mixed gas of oxygen and nitrogen, a mixed gas of oxygen and ozone, a mixed gas of oxygen and chlorine dioxide, a mixed gas of oxygen and carbon monoxide, or a mixed gas of oxygen and chlorine.

In the present invention, in each cycle, the pressure holding time of the oxidizing gas is preferably 5-15 minutes, more preferably 6-12 minutes.

After the pressure keeping is over, the next cycle of vacuuming and feeding oxidizing gas is carried out to keep the pressure.

In the present invention, the temperature of the calcination is preferably 500-1000°C, more preferably 600-850°C; the holding time of the calcination is preferably 3-6h, more preferably 3.5-5h.

In the present invention, the calcination temperature is preferably obtained by heating up, and the heating rate is preferably 3-8°C/min, more preferably 3.5-4.5°C/min.

In the present invention, the calcination is preferably performed in a vacuum furnace. In a specific embodiment of the present invention, the pseudo-boehmite is preferably placed in the crucible of the vacuum furnace, and the pseudo-boehmite is preferably placed in a crucible of the vacuum furnace. The filling height in the crucible is preferably 145-155 mm, more preferably 150 mm. In the present invention, the material of the crucible is preferably corundum.

By controlling the filling height of the pseudo-boehmite in the crucible, the invention improves the calcination efficiency of the pseudo-boehmite in the calcination process, and further reduces the unit energy consumption of the preparation process to the maximum extent.

In the present invention, after the calcination is completed, the present invention preferably performs post-treatment on the obtained calcination system to obtain the high-purity alumina. In the present invention, the post-treatment preferably includes: vacuuming and oxygen supply in sequence and cooling. In the present invention, the specific implementation process of vacuuming and feeding oxygen is the same as the specific implementation process of vacuuming and feeding oxidizing gas in the calcination process described above, and will not be repeated here. In the present invention, the temperature after cooling is preferably room temperature.

When the pseudo-boehmite is calcined by the preparation method provided by the present invention, the pseudo-boehmite can be fully contacted with the oxidizing gas by circulating vacuum, oxidizing gas and pressure maintaining, and the pseudo-boehmite can be calcined. The residual alkoxy groups are fully oxidized, thereby preparing high-purity alumina with low residual carbon content.

In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to the examples, but they should not be construed as limiting the protection scope of the present invention.

Example 1

2kg of liquid aluminum isopropoxide (purity of 99.5%, Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element total content is 0.0008wt.%) into 4L with reflux In the reactor with stirring equipment, 550g of high-purity water was added into the reactor under the stirring condition of 80 °C, and after adding water, stirring was continued for 4 hours to hydrolyze aluminum isopropoxide into pseudo-boehmite-isopropanol-water slurry ; Use a centrifuge to separate the slurry (rotation speed is 5000r/min), and vacuum dry the obtained paste-like solid product at a drying temperature of 90°C and a drying time of 6h; the obtained dried product is pulverized into powder with a particle size of less than 150 μm body to obtain pseudo-boehmite;

Then, the pseudo-boehmite was placed in a corundum crucible with a filling height of 150 mm, and calcined in a vacuum furnace. During the heating calcination and heat preservation calcination, the vacuum system was first turned on to pump air, and the vacuum was stopped until the absolute pressure in the vacuum furnace was 0.005MPa, and oxygen and nitrogen (volume ratio of 21:79) were introduced into the vacuum furnace; After the gas reaches the absolute pressure of 0.1MPa in the vacuum furnace, the ventilation is stopped, and the pressure is maintained and oxidized for 10min. Then continue to repeat the cycle of vacuuming, feeding oxygen and nitrogen (volume ratio of 21:79) and maintaining pressure oxidation until the end of the heat preservation and calcination. At 0.1MPa), the high-purity alumina product was taken out after cooling in the vacuum furnace.

A carbon-sulfur analyzer, an inductively coupled plasma spectrometer and a whiteness meter were used to measure the residual carbon content, purity and whiteness of the high-purity alumina product prepared in Example 1, wherein the purity of the alumina product was measured as: The total amount of impurities of Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element in the middle, after deducting the total amount of impurities, is the purity of the alumina product; the product of Example 1 is that the whiteness is 96.5%, the residual carbon content is 0.0008wt.%, and the purity is 99.995%.

Comparative Example 1

Basically the same as the preparation method of Example 1, the difference is: the pseudo-boehmite is put into the corundum crucible, the filling height is 150mm, and calcined in the muffle furnace of the air atmosphere, and the heating rate is 5 ℃/min, Incubate at 600°C for 4h.

Measured by the same method as in Example 1, the alumina product prepared in Comparative Example 1 had a residual carbon content of 0.015 wt.%, a whiteness of 75.2%, a purity of 99.994%, and the product was gray to the naked eye.

Example 2

2000kg liquid aluminum isopropoxide (purity 99%, Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element total content is 0.0009wt.%) into 4000L with reflux device 550kg of high-purity water was added to the reaction kettle under stirring conditions at 80 °C, and after adding water, stirring was continued for 4 h to hydrolyze aluminum isopropoxide into pseudo-boehmite-isopropanol-water slurry; centrifugal The slurry is centrifugally separated by the machine (rotation speed is 5000r/min), and the obtained paste-like solid product is dried in a closed-circuit flash dryer, the protective gas is nitrogen, the feeding temperature is 250 °C, and the discharging temperature is 90 °C The obtained dried product is pulverized into powder with a particle size greater than 150 μm to obtain pseudo-boehmite;

Then, the pseudo-boehmite was placed in a corundum crucible with a filling height of 150 mm, and calcined in a vacuum furnace. During the heating and calcination to the heat preservation calcination beam, firstly open the vacuum system for pumping, until the absolute pressure in the vacuum furnace is 0.005MPa, stop vacuuming, and then introduce oxygen and nitrogen into the vacuum furnace (volume ratio is 21:79); After the oxidizing gas reaches the absolute pressure of 0.1MPa in the vacuum furnace, the ventilation is stopped, and the pressure is maintained and oxidized for 10min. Then continue to repeat the cycle of vacuuming, feeding oxygen and nitrogen (volume ratio of 21:79) and holding pressure oxidation for 10min until the end of heat preservation and calcination. maintained at 0.1MPa), and the high-purity alumina product was taken out after cooling in the vacuum furnace.

The product prepared in Example 2 was tested by the same method as in Example 1. The whiteness of the high-purity alumina prepared in Example 2 was greater than 96.0%, the residual carbon content was less than 0.0008wt.%, and the purity was higher than 99.995%.

Comparative Example 2

The preparation method is basically the same as that of Example 2, except that the pseudo-boehmite is put into the corundum crucible, and the filling height is 150 mm. Incubate at ℃ for 4h.

Measured by the same method as in Example 1, the alumina product prepared in Comparative Example 2 had a residual carbon content of 0.02 wt.%, a whiteness of 73.2%, and a purity of 99.993.

Example 3

The preparation method is basically the same as that of Example 1, except that the oxidizing gas is oxygen;

Measured by the same method as in Example 1, the alumina product prepared in Example 3 had a residual carbon content of 0.0009% wt, a whiteness of 96%, and a purity of 99.994%.

Example 4

Basically the same as the preparation method of Example 1, the difference is: the oxidizing gas is oxygen and argon (volume ratio is 80:20);

Measured by the same method as in Example 1, the alumina product prepared in Example 4 has a residual carbon content of 0.0009% wt, a whiteness of 95.7%, and a purity of 99.995.

Example 5

Basically the same as the preparation method of Example 1, the difference is: the oxidizing gas is oxygen and carbon dioxide (volume ratio is 50:50);

Measured by the same method as in Example 1, the alumina product prepared in Example 5 has a residual carbon content of 0.0008% wt, a whiteness of 95.5%, and a purity of 99.996%.

Example 6

1kg of liquid n-hexanoxide aluminum (purity of 99.5%, Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element total content of 0.0003wt.%) was introduced into 4L with reflux equipment. In the reaction kettle, 1.5kg of high-purity water was added to the hydrolysis kettle under the stirring condition of 100 °C. After adding water, stirring was continued for 8 hours to hydrolyze the aluminum n-hexaoxide into pseudo-boehmite-n-hexanol-water slurry; The slurry is centrifuged (rotation speed is 5000 r/min); the obtained paste-like solid product is dried in a blast drying oven at 105°C for 8 hours; the dried product is pulverized into powder with a particle size of less than 150 μm to obtain pseudo-boehmite;

Then, the pseudo-boehmite was placed in a corundum crucible with a filling height of 150 mm, and calcined in a vacuum furnace. During the heating calcination and heat preservation calcination, the vacuum system was first turned on to pump air, and the vacuum was stopped until the absolute pressure in the vacuum furnace was 0.005MPa, and oxygen and ozone (volume ratio of 50:50) were introduced into the vacuum furnace; When the absolute pressure of the gas in the vacuum furnace is 0.1MPa, the ventilation is stopped, and the pressure is maintained and oxidized for 5min. Then continue to repeat the operation of vacuuming, feeding oxygen and ozone (volume ratio is 50:50) and maintaining pressure oxidation until the end of heat preservation and calcination. MPa), and the high-purity alumina product is taken out after cooling in the vacuum furnace.

Measured by the same method as in Example 1, the whiteness of the high-purity alumina product prepared in Example 6 was 96.5%, the residual carbon content was 0.0007 wt.%, and the purity was 99.995%.

Comparative Example 3

Basically the same as the preparation method of Example 6, the difference is: the pseudo-boehmite is put into the corundum crucible, the filling height is 150mm, and calcined in the muffle furnace of the air atmosphere, and the heating rate is 5 ℃/min, Incubate at 600°C for 4h.

Measured by the same method as Example 1, the carbon residue of the alumina product prepared in Comparative Example 3 was 0.025wt.%, the whiteness was 70.4%, and the alumina purity was 99.993%. The bottom product of the crucible after calcination was Gray-black.

Example 7

1000kg of liquid n-hexanoxide aluminum (purity of 99%, Na element, Fe element, Si element, K element, Ca element, Cu element, Ti element and Zn element total content of 0.0003wt.%) was introduced into 4000L with reflux equipment In the reaction kettle, 1500kg of high-purity water was added to the hydrolysis kettle under the stirring condition of 100 ℃. After the water was added, the stirring was continued for 8 hours to hydrolyze the aluminum n-hexaoxide into pseudo-boehmite-n-hexanol-water slurry; use a horizontal screw centrifugal The slurry was centrifuged (4800 r/min) by the machine; the paste-like solid product obtained by separation and 200 kg of high-purity water were mixed uniformly; the obtained mixture was spray-dried, the feeding temperature was 350 ° C, and the discharging temperature was 100 ° C; after drying, a pseudo-thin diaspore;

Then, the pseudo-boehmite was placed in a corundum crucible with a filling height of 150 mm, and calcined in a vacuum furnace. During the heating and calcination to the heat preservation calcination beam, firstly open the vacuum system to pump air until the absolute pressure in the vacuum furnace is 0.005MPa and stop vacuuming, and then introduce oxygen and ozone into the vacuum furnace (volume ratio is 50:50); After the oxidizing gas reaches the absolute pressure of 0.1MPa in the vacuum furnace, the ventilation is stopped, and the pressure is maintained and oxidized for 5min. Then continue to repeat the operation of vacuuming, feeding oxygen and ozone (volume ratio is 50:50), and maintaining pressure for 5 minutes until the end of the thermal insulation calcination. maintained at 0.1MPa), and the high-purity alumina product was taken out after cooling in the vacuum furnace.

The product prepared in Example 7 was tested by the same method as in Example 1. The whiteness of the high-purity alumina prepared in Example 7 was 96.6%, the residual carbon content was 0.0006wt.%, and the purity was 99.995%. Alumina.

Comparative Example 4

Basically the same as the preparation method of Example 7, the difference is: put the pseudo-boehmite into the corundum crucible, the filling height is 150mm, and calcined in the kiln of air atmosphere, and the heating rate is 5 ℃/min, 800 Incubate at ℃ for 4h.

Measured by the same method as in Example 1, the alumina product prepared in Comparative Example 4 had a residual carbon content of 0.018% wt, a whiteness of 74%, and a purity of 99.994%.

Example 8

Basically the same as the preparation method of Example 6, the difference is: the oxidizing gas is oxygen and chlorine dioxide (volume ratio is 50:50);

Measured by the same method as in Example 1, the alumina product prepared in Example 8 had a residual carbon content of 0.00051% wt, a whiteness of 96.8%, and a purity of 99.993%.

Example 9

Basically the same as the preparation method of Example 6, the difference is: the oxidizing gas is oxygen and nitric oxide (volume ratio is 70:20);

Measured by the same method as in Example 1, the alumina product prepared in Example 9 has a residual carbon content of less than 0.0006% wt, a whiteness of 96.3%, and a purity of 99.996%.

Example 10

Basically the same as the preparation method of Example 6, the difference is: the oxidizing gas is oxygen and nitric oxide (volume ratio is 70:20);

Measured by the same method as in Example 1, the alumina product prepared in Example 10 has a residual carbon content of 0.0005% wt, a whiteness of 96.8%, and a purity of 99.994%.

Application example 1

The high-purity alumina powder (15 cm in thickness) and high-purity graphite sheet (0.5 cm in thickness) prepared in Example 2 were added to the cold crucible, and the water cooling system of the crucible and the high-frequency coil outside the crucible were started to generate a magnetic field. Heating until all the alumina powder in the crucible forms a molten liquid; start the crucible power system to move the crucible, and add high-purity alumina powder to the crucible during the movement until the crucible moves to the apex position, and at the same time make the crucible high. All the pure alumina powder forms a molten liquid, which is cooled to room temperature to obtain alumina polycrystals. Alumina polycrystals were visually colorless.

Comparative Example 5

The preparation method is basically the same as that of Application Example 1, except that: the alumina prepared in Comparative Example 2 is used as the raw material, and the product alumina polycrystals appear light yellow, yellow or brown and other variegated colors visually.

Application example 2

The preparation method is basically the same as that of Application Example 1, except that the high-purity alumina prepared in Example 7 is used as the raw material, and the product alumina polycrystal is colorless by visual inspection.

Comparative Example 6

The preparation method is basically the same as that of Application Example 1, except that the alumina prepared in Comparative Example 4 is used as the raw material, and the product alumina polycrystals appear light yellow, yellow or brown and other variegated colors visually.

The properties of the alumina products prepared in Examples 1 to 10 and Comparative Examples 1 to 4 are listed in Table 1. From Table 1, it can be concluded that compared with calcining in an air atmosphere, the preparation method provided by the present invention is adopted. : During the calcination process, vacuum pumping, oxidizing gas and pressure-holding oxidation are carried out in a cycle, which can make the pseudo-boehmite fully contact with the oxidizing gas, and fully oxidize the residual alkoxy groups in the pseudo-boehmite, thereby preparing the High-purity alumina with low residual carbon content is obtained, the residual carbon content is <0.001 wt.%, the purity is >99.99 wt.%, and the whiteness value is >95%.

Table 1 Performance test results of alumina prepared in Examples 1-10 and Comparative Examples 1-4

serial number Residual carbon/wt.% purity/% Whiteness value/% Example 1 0.0008 99.995 96.5 Example 2 0.0008 99.995 96.0 Example 3 0.0009 99.994 96.0 Example 4 0.0009 99.995 95.7 Example 5 0.0008 99.996 95.5 Example 6 0.0007 99.996 96.5 Example 7 0.0006 99.995 96.6 Example 8 0.0005 99.993 96.8 Example 9 0.0006 99.996 96.3 Example 10 0.0005 99.994 96.8 Comparative Example 1 0.015 99.994 75.2 Comparative Example 2 0.020 99.993 73.2 Comparative Example 3 0.025 99.993 70.4 Comparative Example 4 0.018 99.994 74.3

Although the above-mentioned embodiment has made a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments according to the present embodiment without creativity. These embodiments All belong to the protection scope of the present invention.

Claims (8)

1. A preparation method of high-purity alumina comprises the following steps:

calcining pseudo-boehmite in a circulating oxidizing gas atmosphere;

the circulating oxidizing gas atmosphere is obtained by the circulation of introducing oxidizing gas for pressure maintaining after vacuumizing; the oxidizing gas contains oxygen, and the volume content of the oxygen in the oxidizing gas is more than or equal to 20%;

the number of cycle repetitions is > 1.

2. The preparation method of claim 1, wherein the calcination temperature is 500-1000 ℃, and the calcination holding time is 3-6 h.

3. The preparation method according to claim 2, wherein the calcination temperature is obtained by raising the temperature, and the rate of raising the temperature is 3-8 ℃/min.

4. The method of claim 3, wherein the evacuation is to an absolute pressure <0.01Mpa per cycle; carrying out primary vacuum pumping during the temperature rise;

in each cycle, oxidizing gas is introduced to an absolute pressure of 0.08 to 0.12 MPa.

5. The production method according to claim 1 or 4, wherein the dwell time of the oxidizing gas in each cycle is 5 to 15 min.

6. The method of claim 1, wherein the pseudoboehmite is prepared by a method comprising: mixing aluminum alkoxide and water for hydrolysis reaction to obtain pseudo-boehmite;

the temperature of the hydrolysis reaction is 60-100 ℃, and the time of the hydrolysis reaction is 2.5-8 h.

7. The production method according to claim 6, wherein the aluminum alkoxide has a chemical formula of Al (C) _n H _2n+1 O) ₃ ，3≤n≤8。

8. The production method according to claim 6, wherein the mass ratio of the aluminum alkoxide to the water is 4: (1-6).