CN103359764B - A kind of preparation method of flaky α-alumina - Google Patents

Abstract

The invention relates to a preparation method of sheet-shaped alpha-Al2O3. The preparation method is characterized by specifically comprising the following steps of: adding alpha-Al2O3 and amorphous Al2O3 into a ball grinding mill for ball grinding to obtain nanometer Al2O3 powder; mixing Na2SO4 with K2SO4, dissolving obtained mixed salt in deionized water, and adding the nanometer Al2O3 to prepare a sizing agent; carrying out ultrasonic treatment on the obtained sizing agent for 0.5-5 hours, and distilling the obtained sizing agent to obtain a mixed material of the Al2O3, the Na2SO4 and the K2SO4; calcining the mixed material of the Al2O3, the Na2SO4 and the K2SO4, and carrying out furnace cooling to room temperature after calcining; and washing the obtained composition with the deionized water to remove the Na2SO4 and the K2SO4 in the composition and finally filtering and drying to obtain the sheet-shaped alpha-Al2O3. According to the preparation method, the sheet-shaped alpha-Al2O3 is prepared by a fused salt method. The preparation method is simple in process and easy in industrial production. The sheet-shaped alpha-aluminium oxide prepared by the invention can be applied to industries of pearlescent pigment, cosmetics and the like and also can be used as a filler of composite material wild phase, advanced abrasives and high polymer materials.

Description

A kind of preparation method of flaky α-alumina

technical field

The invention relates to a preparation method of flaky α-alumina, which can be used in coatings, cosmetics, wallpaper, printing and other industries, and can also be used as a composite material reinforcing phase, high-grade abrasive, base material of pearlescent pigments and polymer materials filler.

Background technique

The structure of flaky alumina is characterized by its particle shape being hexagonal flakes with a small thickness and a large aspect ratio, each particle having an aspect ratio of at least 10:1. Therefore it is a powder with a two-dimensional planar structure. Flaky alumina has excellent intrinsic properties and special structural features, so it has many excellent properties:

(1) Compared with other flaky powders, flaky alumina has excellent comprehensive properties, such as high melting point, high hardness, high mechanical strength, good wear resistance, chemical corrosion resistance, oxidation resistance and heat resistance, etc. .

(2) Flaky alumina has a small thickness and a large diameter-to-thickness ratio, which can reach the nanometer level in the thickness direction and micron level in the radial direction. Therefore, it has the dual effects of nanometer and micron powder technology; The surface activity is moderate, which can effectively combine with other active groups, and is not easy to agglomerate so as to facilitate effective dispersion.

(3) Flaky alumina has good adhesion, significant shielding effect and ability to reflect light.

(4) Flaky alumina powder is almost transparent, colorless, and has a flat and smooth surface, and the well-crystallized crystals are regular hexagonal.

Flaky alumina powder is widely used in pearlescent pigments, cosmetics and other industries, and can also be used as a reinforcing phase for composite materials, advanced abrasives, and fillers for polymer materials.

1) Used in the field of pearlescent pigments

Although the matrix of pearlescent pigments can be artificially synthesized mica flakes, it is difficult to artificially synthesize mica flakes, and its cost is high, and the prepared pearlescent pigments are not resistant to high temperatures. Therefore, artificially synthesized mica flakes have not been widely used in the field of pearlescent pigments.

In recent years, people have synthesized powders such as flaky alumina and silica, and applied them to the field of pearlescent pigments. Artificially synthesized flaky alumina not only has the excellent performance of natural mica flakes, but also has its own advantages: the introduction of impurities can be controlled or eliminated during the preparation process of flaky alumina; the flaky alumina is colorless and has a smooth Flat surface; the synthetic flaky alumina powder has a narrow particle size and thickness distribution range; good dispersion in water and good streamlined shape. It is the flaky alumina that has many excellent properties, so it can replace mica flakes for the preparation of pearlescent pigments. At present, there have been studies abroad on using flake alumina as the matrix of pearlescent pigments, but there are few domestic studies.

2) Used in the field of cosmetics

Flaky alumina has stable chemical properties and is not easy to be absorbed by the human body, and has good chemical properties, high gloss and bright color. After testing, flake alumina has good spreadability and adsorption capacity, and is easy to adhere to the skin surface And prevent makeup from falling off, so it can be used as an additive in the field of cosmetics. Not any particle size of flaky alumina can be used in cosmetics, and cosmetics propose a specific structure for the flaky alumina used. Generally speaking, the ideal thickness of flake alumina flakes is 0.2-1pm, and the particle size is 2-40pm. If the thickness of the film is greater than 2pm, the reflective effect of the film will be poor. If the thickness is less than 0.01pm, the mechanical properties of the film will be poor, thereby affecting the makeup effect and the adhesion of cosmetics.

3) Used as toughening agent

Because flaky alumina has good toughness, a certain amount of flaky alumina can be added to ceramics as a toughening agent. This strengthening behavior is due to the generation of microcracks in the crack tip region when the crack tip stress and thermal expansion anisotropy tensile stress interact. It can deflect the crack along the interface between the matrix and the flaky grains, thereby consuming the energy that promotes the crack expansion, and produces a toughening effect through the bridging effect, and finally plays a role in improving the fracture toughness of the ceramic. Yoshizawa et al. successfully prepared Al ₂ O ₃ ceramics by using flaky alumina as seeds under hot pressing conditions. The fracture strength of the ceramics is 600MPa, and the fracture toughness is 7.9MPa·m. Using flake alumina as a toughening agent can not only strengthen alumina ceramics but also toughen other ceramics.

4) Used as filler

One of the earliest uses of flaky alumina was as a filler. The thermal conductivity of alumina is much higher than that of organic matter, so flaky alumina is often used as a filler for polymers to enhance the thermal conductivity of polymers. A certain amount of flaky alumina is added to the polymer to form an alumina network in the polymer. This network can successfully transfer most of the heat. The larger the particle size of the flaky alumina, the formed network The fewer the nodes, the better the thermal conductivity, so the use of this polymer-ceramic composite to prepare electronic components can greatly improve its service life.

5) For refractory materials

Tabular alumina has the following advantages when used as refractory aggregate or used together with other refractory materials: (1) high refractoriness; (2) good thermal load strength-low creep type; (3) high density, breathable (4) Good thermal shock resistance; (5) Good wear resistance; (6) Good corrosion resistance; (7) Low thermal shrinkage; (8) High purity, reducing the impact of impurities on the system Influence. Plate-shaped alumina refractories have been used in the iron and steel industry with increasingly harsh smelting conditions, almost including blast furnaces, hot blast stoves, mixed iron furnaces, torpedo tanks to converters, secondary refining furnaces, die casting and continuous casting steel drums, All parts of the tundish, hot furnace and heating furnace are made of alumina refractory materials.

At present, the methods for preparing flaky α-alumina particles are: (1) hydrothermal method, that is, in a sealed pressure vessel, water (or alcohol) is used as a solvent, and a chemical reaction is carried out under high temperature and high pressure conditions; (2) ) Coating method, that is, using the precursor to prepare a sol, coating the sol on a base material with a smooth surface, drying and peeling off, to obtain a flake powder material; (3) Mechanical method, that is, using mechanical force The powder is mechanically mixed according to a certain proportion. During the long-term operation, the powder undergoes repeated extrusion, cold welding and crushing under the repeated impact of the grinding medium, and becomes dispersed ultrafine particles; (4) Gel- Combustion method: This method organically combines the sol-gel wet chemical synthesis method and the self-propagating combustion synthesis method, and prepares the metal nitrate of the oxide (as the oxidant in the combustion process) as the precursor, and an organic fuel (as the reducing agent in the combustion process) to form a gel. During the lower temperature heat treatment process, the gel ignites rapidly and burns rapidly, thereby obtaining metal oxide ceramic powder; (5) molten salt method: it is to combine the reactants of the required components with one or two salts according to the A certain proportion of phases are mixed, and then calcined at a temperature higher than the melting point of the salt to form a flux containing salt components. After cooling, the salt content is removed by washing with deionized water to obtain a powder material. Among them, the hydrothermal method has a long reaction cycle and high temperature and high pressure steps, so it has a strong dependence on production equipment; the powder obtained by the coating method has low mechanical strength and a wide particle size distribution range, which requires classification treatment to achieve The user's requirements; the powder produced by the mechanical method has low purity and takes a long time. Due to the action of mechanical force, the particle structure and physical and chemical properties will change, making the crystal structure difficult to control; the gel-combustion process is complicated. The resulting powder is prone to agglomeration, and the shape is not easy to control. Compared with the above methods, the molten salt method has simple equipment, and its reaction can be carried out at a lower temperature and completed in a shorter time. When preparing flake powder, it can also be added by adding seeds or additives, The change of process parameters such as the type and amount of molten salt can control the shape of the powder, so it has been favored by scholars from all over the world.

Prepare flakes by the molten salt method. In the preparation process of alumina powder, Al ₂ (SO ₄ ) ₃ and Al(OH) ₃ are commonly used as raw materials to obtain alumina precursor by calcining. Among them, when aluminum sulfate is used as a raw material to prepare an alumina precursor, toxic gases such as SO ₂ and SO ₃ will be emitted during the calcination process. When aluminum hydroxide is used as a raw material to prepare an alumina precursor, although the synthesis temperature is low, the process is simple, and there is no pollution, aluminum hydroxide is usually prepared from sodium aluminate as a raw material. The present invention directly uses α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as raw materials to prepare flaky alumina, which not only saves raw materials, simplifies the process, but also has no harmful gas and liquid emissions, and is safe in production. It can be used in the industrial production of flaky α-alumina powder Promoted use.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing flaky alumina with simple production process, easy implementation, low cost, no harmful gas and liquid discharge, high product purity, uniform particle size, regular shape and good stability .

In order to solve the above problems, the present invention provides a preparation method of flaky α- _Al2O3 , characterized _in that the specific steps include:

Step 1: adding α-Al ₂ O ₃ and amorphous Al ₂ O ₃ to a ball mill at a mass ratio of 1:1 to 1:20 and ball milling to obtain nano-Al ₂ O ₃ powder;

Step 2: Mix Na ₂ SO ₄ and K ₂ SO ₄ at a mass ratio of 1:1 to 1:5, dissolve the resulting mixed salt in deionized water, and add the nano-Al ₂ O ₃ powder obtained in Step 1 to make Slurry, the mass ratio _of nanometer _Al2O3 powder and mixed salt in the slurry is 1:1～1:5;

Step 3: ultrasonically treat the slurry obtained in step 2 for 0.5-5 hours, and distill the obtained slurry to obtain a mixture of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ;

Step 4: Heat the mixture of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ to 700-1350°C for calcination. After calcination for 1-7 hours, cool down to room temperature with the furnace; Wash with water to remove Na ₂ SO ₄ and K ₂ SO ₄ in the composition, and finally filter and dry to obtain flaky α-Al ₂ O ₃ .

Preferably, the filtrate obtained by filtering in step 4 is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

The present invention uses α-Al ₂ O ₃ and amorphous Al ₂ O ₃ as raw materials, adds Na ₂ SO ₄ and K ₂ SO ₄ as molten salt, and obtains flaky α-Al ₂ O ₃ through high-temperature calcination.

The invention has the advantages of simple process and easy industrial production. The flaky alumina prepared by the invention can be used in industries such as pearlescent pigments and cosmetics, and can also be used as a reinforcing phase of composite materials, a high-grade grinding material, and a filler of high-molecular materials.

Description of drawings

Fig. 1 is the X-ray diffraction pattern of the flaky α-Al of embodiment ₁ gained O ₃ ;

Fig. 2 is the scanning electron micrograph of the flaky α-Al ₂ O ₃ gained in embodiment 1;

Fig. 3 is the scanning electron micrograph of the flaky α-Al ₂ O ₃ gained in embodiment 2;

Fig. 4 is the scanning electron micrograph of the flaky α-Al of embodiment 3 gained ₂ O ₃ ;

Fig. 5 is the scanning electron micrograph of the flaky α-Al of embodiment 4 gained ₂ O ₃ ;

FIG. 6 is a scanning electron microscope image of the flaky α-Al ₂ O ₃ obtained in Example 5.

Detailed ways

In order to make the present invention more comprehensible, preferred embodiments are described in detail below with accompanying drawings.

Example 1

α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as starting materials, and the purity is above 99.6%. Weigh 10g of α-Al ₂ O ₃ into a ball mill, and press α-Al ₂ O ₃ and amorphous The mass ratio of Al ₂ O ₃ is 1:9. Weigh 90g of amorphous Al ₂ O ₃ into a ball mill and mill for 30 hours to obtain nano Al ₂ O ₃ powder; mix Na ₂ SO ₄ and K ₂ SO ₄ in a mass ratio of 1:1 Mix and prepare 200g of mixed salt, and dissolve the mixed salt in 1000ml of deionized water to obtain a salt solution; add 100g of nanometer Al ₂ O ₃ powder to the salt solution to make a slurry, ultrasonically treat the slurry for 2 hours, and dissolve the resulting slurry The material is distilled to obtain a mixed material of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; the above mixed material is placed in a corundum crucible with a cover and calcined in a high temperature furnace at a speed of 10°C/min Heat up to 1000°C for calcination, calcine for 4 hours, and then cool to room temperature with the furnace to obtain the synthetic product; rinse the above calcined synthetic product with deionized water 8 times to remove residual Na ₂ SO ₄ , K ₂ SO ₄ , Finally, the flaky α-Al ₂ O ₃ single crystal was obtained after filtration and drying. The filtered filtrate is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

Detect the obtained alumina powder with an X-ray diffraction analyzer; as shown in Figure 1, there is only the peak of α-Al ₂ O ₃ in the diffraction pattern; as shown in Figure 2, through scanning electron microscopy, the average The particle size is 1~2um.

Example 2

α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as starting materials, and the purity is above 99.6%. Weigh 10g of α-Al ₂ O ₃ into a ball mill, and press α-Al ₂ O ₃ and amorphous The mass ratio of Al ₂ O ₃ is 1:9, and 90 g of amorphous Al ₂ O ₃ is weighed and added into a ball mill for 30 h of ball milling to obtain nanometer Al ₂ O ₃ powder. Na ₂ SO ₄ and K ₂ SO ₄ were formulated into 200 g of mixed salt at a mass ratio of 1:1, and the mixed salt was dissolved in 1000 ml of deionized water to obtain a salt solution. Add 100g of nano Al ₂ O ₃ powder into the salt solution to make a slurry, ultrasonically treat the slurry for 2 hours, and distill the resulting slurry to obtain a mixed material of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; put the above mixed material in a corundum crucible with a cover, put it in a high temperature furnace for calcination, and heat up to 1100 ℃ at a speed of 10 ℃/min for calcination, and the calcination time is 3 hours. Cool to room temperature with the furnace to obtain the synthesized product. The calcined synthetic product was rinsed eight times with deionized water to remove residual Na ₂ SO ₄ , K ₂ SO ₄ , and finally filtered and dried to obtain a flaky α-Al ₂ O ₃ single crystal. The filtered filtrate is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

The obtained alumina powder was detected by an X-ray diffraction analyzer. There are only α-Al ₂ O ₃ peaks in the diffraction pattern. As shown in FIG. 3 , observed by scanning electron microscope, the average particle size of the flake-shaped alumina is 1-3 um.

Example 3

α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as starting materials, and the purity is above 99.6%. Weigh 10g of α-Al ₂ O ₃ into a ball mill, and press α-Al ₂ O ₃ and amorphous The mass ratio of Al ₂ O ₃ is 1:9, and 90 g of amorphous Al ₂ O ₃ is weighed and added into a ball mill for 30 h of ball milling to obtain nanometer Al ₂ O ₃ powder. Na ₂ SO ₄ and K ₂ SO ₄ were formulated into 200 g of mixed salt at a mass ratio of 1:1, and the mixed salt was dissolved in 1000 ml of deionized water to obtain a salt solution. Add 100g of nano Al ₂ O ₃ powder into the salt solution to make a slurry, ultrasonically treat the slurry for 2 hours, and distill the resulting slurry to obtain a mixed material of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; Put the above mixed material in a corundum crucible with a cover, put it in a high-temperature furnace for calcination, and heat up to 1200 ℃ at a rate of 10 ℃/min for calcination, and the calcination time is 2 hours. Cool to room temperature with the furnace to obtain the synthesized product. The calcined product was rinsed eight times with deionized water to remove residual Na ₂ SO ₄ , K ₂ SO ₄ , and finally filtered and dried to obtain a flaky α-Al ₂ O ₃ single crystal. The filtered filtrate is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

The obtained alumina powder was detected by an X-ray diffraction analyzer. There are only α-Al ₂ O ₃ peaks in the diffraction pattern. As shown in FIG. 4 , observed by scanning electron microscope, the average particle size of the flake-shaped alumina is 1-3 um.

Example 4

α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as starting materials, and the purity is above 99.6%. Weigh 10g of α-Al ₂ O ₃ into a ball mill, and press α-Al ₂ O ₃ and amorphous The mass ratio of Al ₂ O ₃ is 1:9, and 90 g of amorphous Al ₂ O ₃ is weighed and added into a ball mill for 50 h of ball milling to obtain nanometer Al ₂ O ₃ powder. Na ₂ SO ₄ and K ₂ SO ₄ were formulated into 200 g of mixed salt at a mass ratio of 2:1, and the mixed salt was dissolved in 1000 ml of deionized water to obtain a salt solution. Add 100g of nano Al ₂ O ₃ powder into the salt solution to make a slurry, ultrasonically treat the slurry for 2 hours, and distill the resulting slurry to obtain a mixed material of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; put the above mixed material in a corundum crucible with a cover, put it in a high temperature furnace for calcination, and heat up to 1100 ℃ at a rate of 10 ℃/min for calcination, and the calcination time is 3 hours. Cool to room temperature with the furnace to obtain the synthesized product. The calcined product was rinsed eight times with deionized water to remove residual Na ₂ SO ₄ , K ₂ SO ₄ , and finally filtered and dried to obtain a flaky α-Al ₂ O ₃ single crystal. The filtered filtrate is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

The obtained alumina powder was detected by an X-ray diffraction analyzer. There are only α-Al ₂ O ₃ peaks in the diffraction pattern. As shown in FIG. 5 , observed by scanning electron microscope, the average particle size of the flake-shaped alumina is 1-3 um.

Example 5

α-Al ₂ O ₃ and amorphous Al ₂ O ₃ are used as starting materials, and the purity is above 99.6%. Weigh 10g of α-Al ₂ O ₃ into a ball mill, and press α-Al ₂ O ₃ and amorphous The mass ratio of Al ₂ O ₃ is 1:9, and 90 g of amorphous Al ₂ O ₃ is weighed and added into a ball mill for 50 h of ball milling to obtain nanometer Al ₂ O ₃ powder. Na ₂ SO ₄ and K ₂ SO ₄ were formulated into 200 g of mixed salt at a mass ratio of 3:1, and the mixed salt was dissolved in 1000 ml of deionized water to obtain a salt solution. Add 100g of nano Al ₂ O ₃ powder into the salt solution to make a slurry, ultrasonically treat the slurry for 2 hours, and distill the resulting slurry to obtain a mixed material of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; Put the above mixed material in a corundum crucible with a cover, put it in a high temperature furnace for calcination, raise the temperature to 1100 ℃ at a rate of 10 ℃/min, and calcine for 3 hours. Cool to room temperature with the furnace to obtain the synthesized product. The calcined product was rinsed eight times with deionized water to remove residual Na ₂ SO ₄ , K ₂ SO ₄ , and finally filtered and dried to obtain a flaky α-Al ₂ O ₃ single crystal. The filtered filtrate is distilled to recover Na ₂ SO ₄ and K ₂ SO ₄ for recycling.

The obtained alumina powder was detected by an X-ray diffraction analyzer. There are only α-Al ₂ O ₃ peaks in the diffraction pattern. As shown in FIG. 6 , observed by scanning electron microscope, the average particle size of the flake-shaped alumina is 1-2 um.

The flaky alumina powder of the present invention is widely used, and can be used in industries such as pearlescent pigments and cosmetics, and can also be used as a reinforcing phase of composite materials, high-grade abrasives, fillers for polymer materials, and the like.

Claims (1)

1. A preparation method of flaky α-Al ₂ O ₃ is characterized in that, the specific steps comprise: Step 1: Add α-Al ₂ O ₃ and amorphous Al ₂ O ₃ to a ball mill at a mass ratio of 1:9 to obtain nano-Al ₂ O ₃ powder; Step 2: Mix Na ₂ SO ₄ and K ₂ SO ₄ at a mass ratio of 2:1 or 3:1, dissolve the resulting mixed salt in deionized water, and add the nano-Al ₂ O ₃ powder obtained in Step 1 to make Slurry, in the slurry, the mass ratio of nanometer Al ₂ O ₃ powder and mixed salt is 1:2; Step 3: ultrasonically treat the slurry obtained in step 2 for 0.5-5 hours, and distill the obtained slurry to obtain a mixture of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ ; Step 4: Heat the mixture of Al ₂ O ₃ , Na ₂ SO ₄ and K ₂ SO ₄ to 1000-1200°C for calcination. After calcination for 2-4 hours, cool to room temperature with the furnace; Washing with water to remove Na ₂ SO ₄ and K ₂ SO ₄ in the composition, and finally filtering and drying to obtain hexagonal flaky α-Al ₂ O ₃ .