High specific surface area α-Al2O3 and its low-temperature preparation method

Abstract

A large specific surface area α-Al2O3 and its low-temperature preparation method belong to the technical field of α-Al2O3. The specific low-temperature preparation method of the large specific surface area α-Al2O3 is as follows: A hydroxylated precursor is prepared by using low-carbon alcohol and aluminum chloride as raw materials. After grinding the precursor, ball milling treatment is carried out, and the product after ball milling is calcined to obtain the α-Al2O3. The preparation method provided by the present invention greatly reduces the calcination temperature of α-Al2O3, and the energy consumption is significantly reduced. At the same time, the α-Al2O3 prepared by the above method is all flaky, has good dispersibility, and has a large specific surface area. This method is suitable for industrial large-scale production applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of α-Al2O3, and particularly relates to a large specific surface area α-Al2O3 and a low-temperature preparation method thereof. Background Art

[0002] As a common and important inorganic material, alumina is a white powder particle, having good thermal stability and chemical properties, insoluble in water and organic substances, and the highest melting point of the high-temperature phase can reach about 2000 °C. It is one of the most commonly used materials in various fields such as chemical engineering, electronics, aerospace, and medical devices.

[0003] The molecular formula of alumina is Al2O3. As an amphoteric metal oxide, its crystal structure is relatively complex and different transition phases will be formed at different temperatures. There are nine known structures of alumina, including α, θ, γ, η, δ, κ, χ, β, ρ. Among all the phases of alumina, α-Al2O3 is the most stable phase. α-Al2O3 belongs to the hexagonal crystal system, and its crystal structure determines its stable properties. It has a hardness second only to diamond and has excellent optical, mechanical, and chemical properties. It is often used in various fields such as catalysis and electronic ceramics.

[0004] In the actual industrial preparation process of α-Al2O3, aluminum hydroxide or boehmite is used as the raw material, and it is necessary to carry out calcination at a relatively high temperature (not less than 1200 °C) to obtain α-Al2O3. However, this preparation temperature is high, resulting in high energy consumption, and the specific surface area of the obtained α-Al2O3 is small, which is not suitable for large-scale industrial production. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a low-temperature preparation method of large specific surface area α-Al2O3 that can reduce energy consumption and is conducive to large-scale industrial production.

[0006] Another purpose of the present invention is to provide a large specific surface area α-Al2O3 prepared by using the low-temperature preparation method of the large specific surface area α-Al2O3.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0008] A low-temperature preparation method of large specific surface area α-Al2O3 includes the following steps:

[0009] (1) Add aluminum chloride to low-carbon alcohol and heat and stir to completely alcoholize aluminum chloride in the low-carbon alcohol to obtain an alcoholate solution. Place the alcoholate solution in an oven to dry to obtain a hydroxylated precursor;

[0010] (2) Grind the hydroxylated precursor and then perform ball milling to make the particle size of the powder reach the nanometer level through ball milling. Sieve the product after ball milling to obtain sample A;

[0011] (3) Place sample A in a muffle furnace and calcine it at 650 - 800 °C for 2 h to obtain flaky α-Al2O3.

[0012] Preferably, the lower alcohol is any one of methanol, ethanol, propanol, and butanol.

[0013] Preferably, in step (1), a dispersant is further added to the alcohol aluminum salt solution. By utilizing the interaction between the dispersant and the hydroxyl groups in the alcohol aluminum salt solution, the specific surface area of the α-Al2O3 obtained by calcination is increased; the mass of the dispersant accounts for 10% of the mass of aluminum chloride.

[0014] Preferably, the dispersant is polyether P123.

[0015] Preferably, in step (2), a salt additive is further added during the ball milling process; the mass of the salt additive accounts for 1% of the mass of the precursor.

[0016] Preferably, the salt additive is sodium chloride.

[0017] Preferably, in step (1), the heating temperature during stirring is 40 - 50 °C, the oven temperature is 80 - 110 °C, and the drying time is 32 - 48 h.

[0018] Preferably, in step (2), the ball milling time is 4 h and the rotation speed is 400 rpm.

[0019] A large specific surface area α-Al2O3 is prepared by the above-mentioned low-temperature preparation method of large specific surface area α-Al2O3.

[0020] Preferably, the specific surface area of the α-Al2O3 is 5 - 56 m 2 / g.

[0021] The beneficial effects of the present invention compared with the prior art are as follows: The present invention for the first time uses low-carbon alcohol and aluminum chloride as raw materials to prepare a precursor of α-Al2O3. During the calcination process of this precursor, the surface energy of α-Al2O3 can be reduced, thereby lowering the nucleation barrier of α-Al2O3, further reducing the calcination temperature of α-Al2O3. Through ball milling treatment, while the particle size of the precursor powder reaches the nanometer level, the crystal lattice is activated, further reducing the calcination temperature of α-Al2O3. The preparation method provided by the present invention significantly reduces the calcination temperature of α-Al2O3, and the energy consumption is significantly reduced. At the same time, the α-Al2O3 prepared by the above method is all flaky, with good dispersion and a large specific surface area. This method is suitable for industrial large-scale production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is an infrared spectrogram of the product obtained by the reaction of aluminum chloride with different low-carbon alcohols.

[0023] Figure 2 It is an XRD schematic diagram of the products obtained by calcining the precursors prepared with different low-carbon alcohols at different temperatures.

[0024] Figure 3 It is an SEM schematic diagram of α-Al2O3 provided in Example 1.

[0025] Figure 4 It is an N2 adsorption-desorption curve of α-Al2O3 prepared with different low-carbon alcohols.

[0026] Figure 5 It is an SEM schematic diagram of α-Al2O3 provided in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0027] The following further elaborates in detail on the technical solutions and technical effects of the embodiments of the present invention in conjunction with the drawings of the present invention.

[0028] The present invention provides a low-temperature preparation method for α-Al2O3 with a large specific surface area, including the following steps:

[0029] (1) Add aluminum chloride to low-carbon alcohol and heat and stir to completely alcoholize aluminum chloride in the low-carbon alcohol to obtain an alcohol aluminum salt solution. Place the alcohol aluminum salt solution in an oven to dry to obtain a hydroxylated precursor;

[0030] The present invention uses aluminum chloride and lower alcohols as precursor raw materials. Since anhydrous aluminum chloride (AlCl3) is a salt of strong acid and weak base and has relatively low alcoholysis ability, external heating and the exotherm during the dissolution of AlCl3 are used to increase the reaction rate, enabling AlCl3 to completely dissolve in the lower alcohol to obtain an alcohol aluminum salt. Taking ethanol as an example, aluminum chloride is dissolved in excessive ethanol to undergo an alcoholysis reaction to generate an alcohol aluminum salt. The specific reaction formula is:

[0031] AlCl3 + 6EtOH → AlCl2(OEt)·5EtOH + HCl

[0032] The alcohol aluminum salt further undergoes a non-hydrolytic polycondensation reaction to remove halogenated hydrocarbons, generating a large number of =Al-O-Al= bonds and forming a sol. The sol further undergoes polycondensation during the drying process, and the formed xerogel is the precursor. In the reaction between aluminum chloride and lower alcohols, on the one hand, the gel can be directly obtained through polycondensation without going through a hydrolysis step, which is conducive to the precursor achieving a nano-level uniform mixture, improving the uniformity of the sample, and thus reducing the calcination temperature; on the other hand, during the reaction process, the large number of =Al-O-Al= bonds formed reduces the energy required for the breaking of old bonds, the formation of new bonds, and the diffusion of reaction substances during the crystallization process of α-Al2O3, thereby reducing the nucleation barrier of α-Al2O3 and thus reducing the necessary temperature for the formation of α-Al2O3. This is the key reason why aluminum chloride and lower alcohols can synthesize α-Al2O3 at 800 °C.

[0033] (2) The hydroxylated precursor is ground and then put into a ball mill for ball milling treatment. Through ball milling, the particle size of the powder reaches the nano level. The product after ball milling is sieved to obtain sample A;

[0034] When the precursor is sufficiently ball milled for more than 2 h, the particle size of the powder reaches the nano level. As the particle size of the precursor powder decreases, its specific surface area increases, so the contact area of the powder increases, and thus the calcination activity during calcination is correspondingly improved, the driving force for calcination is stronger, and finally it is manifested as a decrease in the calcination temperature, thereby effectively promoting the calcination and reducing the calcination temperature; while the powder is refined, the crystal lattice is activated, and the internal energy of the powder continuously accumulates, thereby effectively reducing the subsequent calcination temperature.

[0035] (3) Sample A is placed in a muffle furnace and calcined at 650 - 800 °C for 2 h to obtain flaky α-Al2O3.

[0036] Furthermore, the lower alcohol is any one of methanol, ethanol, propanol, and butanol.

[0037] Further, in order to prepare α-Al2O3 with a large specific surface area, in step (1), a dispersant is further added to the aluminum alkoxide solution. By utilizing the interaction between the dispersant and the hydroxyl groups in the aluminum alkoxide solution, the specific surface area of the calcined α-Al2O3 is increased; the mass of the dispersant accounts for 10% of the mass of aluminum chloride. Specifically, the dispersant is polyether P123.

[0038] Since the aluminum alkoxide solution obtained by the reaction of aluminum chloride and lower alcohols has a large number of hydroxyl groups, and polyether P123 has hydrophilic and lipophilic groups. After introducing it into the precursor, during the calcination process, the hydrophilic and lipophilic groups of polyether P123 interact with the hydroxyl groups, thereby affecting the growth of particles, making the particles more inclined to grow along the {0001} crystal plane. Therefore, the lamellae are thinner, and holes are generated due to the excessive thinness in some places during the growth process of the lamellae, resulting in a significant increase in the specific surface area.

[0039] Further, in step (3), a salt additive is added during the ball milling process, and the mass of the salt additive accounts for 1% of the mass of the precursor. Specifically, the salt additive is sodium chloride.

[0040] The inventors found that only adding a dispersant during the preparation of the precursor can increase the specific surface area of α-Al2O3, but the calcination temperature does not change further and remains at 800 °C. Therefore, in order to further reduce the calcination temperature, a trace amount of salt additive is introduced during the ball milling of the precursor. Through the ball milling process, the salt is evenly dispersed in the precursor. When reaching a certain temperature, anions in the salt such as Cl - 、F - form Al-Cl-Al bridge bonds or Al-F-Al bridge bonds with Al 3+ in the intermediate phase. Due to the existence of these two bridge bonds, they have a certain weakening effect on the chemical bonds, thereby reducing the nucleation barrier of α-Al2O3, accelerating the nucleation rate, and further reducing the calcination temperature of α-Al2O3.

[0041] Further, in step (1), the heating temperature during stirring is 40 - 50 °C, the oven temperature is 80 - 110 °C, and the drying time is 32 - 48 h.

[0042] Further, in step (2), the ball milling time is 4 h and the rotation speed is 400 rpm.

[0043] The following details the present application with reference to embodiments, but the present application is not limited to these embodiments.

[0044] Example 1

[0045] The present invention provides a low-temperature preparation method for α-Al2O3 with a large specific surface area, comprising the following steps:

[0046] (1) Slowly add 4 g of anhydrous aluminum chloride to 100 mL of lower alcohol, and stir while heating on a heating and stirring table. Keep the temperature at 40 °C to completely alcoholize aluminum chloride in the lower alcohol to obtain an alcohol aluminum salt solution. Place the alcohol aluminum salt solution in an oven for drying. The oven temperature is 80 °C and the drying time is 48 h to obtain a hydroxylated precursor; wherein, the lower alcohol is selected from any one of methanol, ethanol, propanol, and butanol;

[0047] (2) After grinding the hydroxylated precursor, weigh 4 g of the sample, put it into a ball milling tank, then put 60 g of ball milling beads, and then place it in a planetary ball mill for ball milling. The rotation speed is 400 rpm and the ball milling time is 4 h. The product after ball milling is sieved to obtain sample A;

[0048] (3) Place sample A in a muffle furnace, heat it to 800 °C at a heating rate of 5 °C / min, and calcine for 2 h to obtain flaky α-Al2O3.

[0049] Example 2

[0050] The present invention provides a low-temperature preparation method of α-Al2O3 with a large specific surface area, including the following steps:

[0051] (1) Slowly add 4 g of anhydrous aluminum chloride to 100 mL of lower alcohol, and stir while heating on a heating and stirring table. Keep the temperature at 40 °C to completely alcoholize aluminum chloride in the lower alcohol to obtain an alcohol aluminum salt solution. Place the alcohol aluminum salt solution in an oven for drying. The oven temperature is 80 °C and the drying time is 48 h to obtain a hydroxylated precursor; wherein, the lower alcohol is selected from any one of methanol, ethanol, propanol, and butanol; Before drying the alcohol aluminum salt solution, add 0.4 g of polyether P123 to the solution and stir on the stirring table for 10 min;

[0052] (2) After grinding the hydroxylated precursor, weigh 4 g of the sample, put it into a ball milling tank, then put 60 g of ball milling beads, and then place it in a planetary ball mill for ball milling. The rotation speed is 400 rpm and the ball milling time is 4 h. The product after ball milling is sieved to obtain sample A; wherein, 0.04 g of sodium chloride is added during the ball milling process;

[0053] (3) Place sample A in a muffle furnace, heat it to 650 °C at a heating rate of 5 °C / min, and calcine for 2 h to obtain flaky α-Al2O3.

[0054] Figure 1 It is the infrared spectrum diagram of the products obtained by the reaction of aluminum chloride with different lower alcohols. It can be seen that the infrared spectra of the four products are almost the same, and at a wavelength of 3750 - 3000 cm -1There is a broad hydroxyl peak in the range of, which proves the existence of hydroxyl groups in the precursor. Among them, the hydroxyl peaks are between 3750-3000 cm -1 and at 1637 cm -1 . The peaks at 1070 cm -1 and around 885 cm -1 are related to the stretching vibration of the Al-O-Al bond, and the peaks around 620 cm -1 are related to the stretching vibration of the Al-O bond, and the peaks around 1460 cm -1 are related to the stretching vibration of -CH2.

[0055] Figure 2 is the XRD schematic diagram of the products obtained by calcining the precursors prepared with different lower-carbon alcohols at different temperatures. Among them, (a) is aluminum chloride-methanol; (b) is aluminum chloride-ethanol; (c) is aluminum chloride-propanol; (d) is aluminum chloride-butanol. It can be seen that the alumina calcined at 800 °C from different lower-carbon alcohols is all α-Al2O3.

[0056] Figure 3 is the SEM schematic diagram of the α-Al2O3 provided in Example 1. Among them, (a) is aluminum chloride-methanol; (b) is aluminum chloride-ethanol; (c) is aluminum chloride-propanol; (d) is aluminum chloride-butanol. It can be seen that the alumina calcined at 800 °C is flaky α-Al2O3 without any impurity phases, indicating that no other impurities are introduced during the preparation process, and the purity of the prepared powder is high.

[0057] Figure 4 is the N2 adsorption-desorption curve of α-Al2O3 prepared with different lower-carbon alcohols. Among them, (a) is methanol and ethanol; (b) is propanol and butanol. The specific surface area of α-Al2O3 is obtained from the adsorption isotherm curve through the BET theory. The specific surface area of α-Al2O3 prepared by the traditional high-temperature method in the prior art is only 2-3 m 2 / g, while the specific surface area of α-Al2O3 prepared by the present invention using aluminum chloride and lower-carbon alcohols as raw materials has a very obvious increase. For example, when using aluminum chloride-methanol as the precursor, the specific surface area of the finally obtained α-Al2O3 is 5 m 2 / g, and when using aluminum chloride-ethanol and aluminum chloride-butanol as the precursors, the finally obtained α-Al2O3 sheets are thinner, and the specific surface areas are 13 m 2 / g and 10 m 2 / g respectively; while when using aluminum chloride-propanol as the precursor, the grain size of the obtained α-Al2O3 is smaller, only 200-300 nm, and it has good dispersibility, and the specific surface area can reach 25 m 2 / g, which is about 8 times higher than the specific surface area of α-Al2O3 prepared by the traditional high-temperature method in the prior art.

[0058] Figure 5 SEM schematic diagram of α-Al2O3 provided for Example 2, where the α-Al2O3 is prepared from aluminum chloride-ethanol as raw materials. It can be seen that after adding polyether P123, the prepared α-Al2O3 is in the form of relatively thin flakes. After measurement, the specific surface area reaches 56 m 2 / g, which is more than 28 times higher than that of α-Al2O3 prepared by the traditional high-temperature method.

[0059] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand the whole or part of the processes of the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A low-temperature preparation method of α-Al2O3 with a large specific surface area, characterized in that: It includes the following steps: (1) Add aluminum chloride to a lower alcohol, heat and stir to completely alcoholize the aluminum chloride in the lower alcohol to obtain an alcohol aluminum salt solution, and place the alcohol aluminum salt solution in an oven for drying to obtain a hydroxylated precursor; (2) Grind the hydroxylated precursor and then perform ball milling treatment. Through ball milling, the particle size of the powder reaches the nanometer level. The product after ball milling is sieved to obtain sample A; (3) Place sample A in a muffle furnace and calcine it at 650 - 800 °C for 2 h to obtain flaky α-Al2O 3； The lower alcohol is any one of methanol, ethanol, propanol, and butanol; In step (1), a dispersant is further added to the alcohol aluminum salt solution. By utilizing the interaction between the dispersant and the hydroxyl groups in the alcohol aluminum salt solution, the specific surface area of the calcined α-Al2O3 is increased; the mass of the dispersant accounts for 10% of the mass of aluminum chloride; The dispersant is polyether P123; In step (2), a salt additive is further added during the ball milling process; the mass of the salt additive accounts for 1% of the mass of the precursor; The salt additive is sodium chloride; 2. The low-temperature preparation method of α-Al2O3 with a large specific surface area according to claim 1, characterized in that: In step (1), the heating temperature during stirring is 40 - 50 °C, the oven temperature is 80 - 110 °C, and the drying time is 32 - 48 h; 3. The low-temperature preparation method of α-Al2O3 with a large specific surface area according to claim 1, characterized in that: In step (2), the ball milling time is 4 h and the rotation speed is 400 rpm; 4. A large specific surface area α-Al2O3, characterized in that: It is prepared by using the low-temperature preparation method of α-Al2O3 with a large specific surface area according to any one of claims 1 to 3.

5. The large specific surface area α-Al2O3 according to claim 4, characterized in that: The specific surface area of the α-Al2O3 is 5-56 m 2 / g.

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