Preparation method of flaky alumina
Technical Field
The invention relates to the field of material preparation, in particular to a preparation method of aluminum oxide with a hexagonal flaky structure.
Background
The alumina has the excellent performances of high hardness, high melting point, oxidation resistance, high temperature resistance, corrosion resistance, high thermal conductivity, high resistivity and the like, and is rich in reserves and low in price. As a special alumina and an important powder material, the flaky alumina not only has the excellent performance of common alumina, but also has been researched and developed in a large amount due to a special two-dimensional flaky structure, moderate surface activity, good adhesion, light reflection capability, obvious shielding effect and the like. In addition, in practical application, the designability of the structure and the function of the material can be realized by changing experimental conditions to control the crystal morphology (such as thickness, particle size, diameter-thickness ratio, distribution and the like) of the flaky alumina. Therefore, the flaky alumina has become a new growth point in the alumina industry and has been widely used in various fields such as pigments, chemical industry, catalysis, cosmetics, automobile paint, refractory materials, toughened ceramics, etc.
CN104724741a discloses a preparation method of flaky alumina, which mainly comprises the following steps: preparing a solution by taking an aluminum source, amine organic matters and an auxiliary agent as raw materials according to a certain proportion, heating and stirring, volatilizing the solution, concentrating and then pyrolyzing to obtain precursor powder; then reacting the precursor powder for 2-4 hours at 800-1700 ℃ in flowing air atmosphere; finally obtaining the flaky alumina with the granularity of 3-8 mu m and the diameter-thickness ratio of 25-80. The reaction raw materials of the method contain auxiliary agents and amine organic matters, and the method has the defect of environmental pollution during thermal decomposition.
CN106276992a discloses a preparation method of leaf-shaped nano gamma-alumina, the preparation process of the method is as follows: (1) Dissolving inorganic aluminum salt and urea in water to obtain transparent solution, and transferring the solution into a high-pressure reaction kettle; (2) Introducing hydrogen into the high-pressure reaction kettle, and maintaining certain pressure and temperature for reaction; (3) After the reaction is finished, the reaction materials are filtered, washed and dried to obtain a boehmite precursor, and then the vane-shaped nano gamma-alumina is obtained after roasting. The method needs to introduce hydrogen into the high-pressure reaction kettle, and has the defects of complex operation process and potential safety hazard.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of flaky alumina. The alumina prepared by the method has a hexagonal flaky structure, smooth surface, uniform particle size, simple preparation process and wide application prospect.
The preparation method of the flaky alumina comprises the following steps: gamma-Al 2 O 3 Mixing the powder, lauric acid and ammonium bicarbonate water solution uniformly, sealing, heat treating, separating solid from liquid after heat treating, drying and roasting the solid material to obtain the flaky alumina.
In the method of the invention, the gamma-Al 2 O 3 The powder may be commercially available or prepared according to methods known in the art, such as precipitation, aluminum alkoxide hydrolysis, inorganic salt sol-gel, hydrothermal, vapor deposition, and the like.
In the method of the invention, lauric acid and gamma-Al are used 2 O 3 The mass ratio of (2) is 0.5:100-2:100, preferably 0.5:100-1:100.
In the method, the mass percentage concentration of the ammonium bicarbonate aqueous solution is generally 10-20%, and the dosage of the ammonium bicarbonate aqueous solution is at least immersedγ-Al 2 O 3 And (5) powder.
In the method of the invention, the sealing heat treatment is generally carried out in a closed container, preferably a high-pressure reaction kettle, and the heat treatment conditions are as follows: the temperature is 100-160deg.C, preferably 100-140deg.C, and the time is 4-8 hr, preferably 4-6 hr.
In the method of the invention, the solid-liquid separation process generally comprises a filtration and washing process, and the process is well known to those skilled in the art; the drying temperature is 100-160 ℃, the drying time is 6-10 hours, the roasting temperature is 450-750 ℃, and the roasting time is 4-8 hours.
The flaky alumina prepared by the method has a hexagonal structure, the side length is 50-600nm, the thickness is 30-50nm, and the specific surface area is 160-230m 2 Per g, pore volume of 0.65-0.9mL/g, and average pore diameter of 10-25nm.
Compared with the prior art, the preparation method has the advantages of low-cost and easily-obtained raw materials, simple preparation process, regular shape of the prepared hexahedral flaky alumina, smooth surface and uniform particle size, and can be used in the fields of catalytic materials, adsorption materials, aerospace materials, environment-friendly materials and the like.
Drawings
FIG. 1 is a high-magnification SEM image of the alumina prepared in example 1.
FIG. 2 is a low-magnification SEM image of the alumina prepared in example 1.
Detailed Description
The technical scheme and effect of the present invention will be further described with reference to the following examples, but is not limited thereto.
Application N 2 Physical adsorption-desorption method is used for characterizing pore structures of samples of the examples and the comparative examples, and the specific operation is as follows: using ASAP-2420 type N 2 The physical adsorption-desorption instrument characterizes the structure of the sample hole. And (3) taking a small amount of samples, carrying out vacuum treatment at 300 ℃ for 3-4 hours, and finally placing the products under the condition of low temperature (-200 ℃) of liquid nitrogen for nitrogen adsorption-desorption test. Wherein the specific surface area is obtained according to a BET equation, and the pore size distribution and pore volume are obtained according to a BJH model.
The microstructure of the sample is characterized by applying a scanning electron microscope, and the specific operation is as follows: the JSM-7500F scanning electron microscope is adopted to characterize the microstructure of the carrier, the accelerating voltage is 5KV, the accelerating current is 20 mu A, and the working distance is 8mm.
Example 1
500 g of pseudo-boehmite A1 (produced by Winzhou fine grain alumina Co., ltd., dry basis weight content: 70%) was weighed and calcined at 500℃for 6 hours to obtain alumina powder.
Weighing 100 g of the alumina powder, adding 500 g of ammonium bicarbonate aqueous solution with the mass percentage concentration of 15.5%, adding 0.75 g of lauric acid into the mixed material, stirring for 1 hour, transferring the mixed material into an autoclave, sealing, heating at 140 ℃ for 6 hours, drying the carrier at 110 ℃ for 6 hours, roasting at 600 ℃ for 4 hours to obtain an alumina product, wherein a high-power scanning electron microscope photograph is shown in figure 1, a low-power scanning electron microscope photograph is shown in figure 2, and the specific surface area of the product is 179m 2 Per g, pore volume 0.78mL/g, average pore diameter 17.5nm.
Example 2
As in example 1, except that the firing temperature of pseudo-boehmite was 550 ℃. The ammonium bicarbonate solution is 650 g and the mass percentage concentration of the solution is 17.5%. The heat treatment temperature was 120℃and the treatment time was 5 hours. Lauric acid is added in an amount of 1 gram to prepare a hexagonal flaky alumina product, and the specific surface area of the product is 185m 2 Per g, pore volume 0.82mL/g, average pore diameter 18nm.
Example 3
The same as in example 1, except that the ammonium bicarbonate solution was used in an amount of 450 g, the mass percentage concentration of the solution was 12.5%. The heat treatment temperature was 130℃and the treatment time was 6 hours. Lauric acid is added in an amount of 1.25 g, and the hexagonal flaky alumina product is prepared, and the specific surface area of the product is 193m 2 Per g, pore volume 0.83mL/g, average pore diameter 17nm.
Example 4
As in example 1, except that the ammonium bicarbonate solution was used in an amount of 750 g, the mass percentage concentration of the solution was 20%. The heat treatment temperature was 110℃and the treatment time was 6 hours. Lauric acid is added in an amount of 0.5 gram to prepare a hexagonal flaky alumina product with a specific surface area of 171m 2 Per g, pore volume 0.79mL/g, average pore diameter 18.5nm.
Comparative example 1
As in example 1, the ammonium bicarbonate solution was changed to the ammonium carbonate solution. No flaky alumina was found in the alumina product.
Comparative example 2
The same as in example 1, except that the ammonium bicarbonate solution was changed to sodium bicarbonate solution. No flaky alumina was found in the alumina product.
Comparative example 3
As in example 1, except that no surfactant was added to the hydrothermal treatment, no flaky alumina was found in the alumina product.
Comparative example 4
As in example 1, except that the heat treatment temperature was 220 ℃, no flaky alumina was found in the alumina product.
Comparative example 5
As in example 1, except that the heat treatment temperature was 80 ℃, no flaky alumina was found in the alumina product.
Comparative example 6
As in example 1, except that the mass percentage concentration of the ammonium bicarbonate aqueous solution was 5%, no flaky alumina was found in the alumina product.
Comparative example 7
As in example 1, except that the mass percentage concentration of the ammonium bicarbonate aqueous solution was 35%, no flaky alumina was found in the alumina product.