CN110182834B - Method for preparing flaky alpha-alumina and flaky alpha-alumina - Google Patents
Method for preparing flaky alpha-alumina and flaky alpha-alumina Download PDFInfo
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Abstract
A preparation method of flaky alpha-alumina and flaky alpha-alumina are provided, wherein the preparation method of flaky alpha-alumina adopts pseudo-boehmite directly as an aluminum source to prepare flaky alpha-alumina; the pore volume of the pseudoboehmite is 0.5ml/g-1.2ml/g, and the specific surface area of the pseudoboehmite is 250m2/g‑360m2(ii) in terms of/g. The preparation method can reduce energy consumption, and the prepared flaky alpha-alumina has good performance as a base material of pearlescent pigment.
Description
Technical Field
The invention belongs to the field of inorganic powder materials, relates to alpha-alumina, and relates to application of the alpha-alumina in paint (paint), industrial coating, automobile coating, printing ink and cosmetic preparation, in particular to a transparent substrate (substrate) used as an effect pigment, and especially relates to a preparation method of flaky alpha-alumina.
Background
The base material of conventional pearlescent pigments is typically natural mica. Natural mica, as a substrate for pearlescent pigments, needs to be screened, pulverized, ground and classified. The impurities of natural mica and the unevenness of the thickness and diameter of the ground mica cause some disadvantages in the performance of the conventional pearlescent pigments, such as: the color is not bright, the color saturation is not high, and the like. With the continuous improvement of the requirements of people on the pearlescent pigment, the traditional pearlescent pigment taking mica as a base material can not meet the requirements of people.
Artificially synthesized flaky alpha-alumina (Al)2O3) A substrate having design freedom and physicochemical properties not obtainable with natural mica substrates. In the process of synthesizing the flaky alpha-alumina, the introduction of impurities can be eliminated or controlled, and simultaneously, the product has narrow particle size distribution and large diameter-thickness ratio, and can be almost completely colorless and have a smooth and flat surface, and the flaky alumina has good dispersibility in water. Therefore, it is an ideal substrate for high-quality pearlescent pigments.
The preparation method of the flaky alpha-alumina is various, and the most common methods mainly comprise a molten salt method, a high-temperature sintering method, a hydrothermal (alcohol-thermal) method, a coating method, a sol-gel method, a mechanical method and the like. However, except for the molten salt method, other methods cannot be used as a base material for synthesizing pearlescent pigments because the prepared flaky alumina has small particle size, small aspect ratio, unsmooth surface and poor dispersibility.
The flaky alumina powder prepared by the molten salt method has unique properties. Because the migration rate of substances in the molten salt is far higher than that of solid-phase reaction, the molten salt method can obviously reduce the reaction temperature and shorten the reaction time; secondly, the molten salt method can effectively control the size and the shape of the flaky alumina by adjusting the dosage and the type of the molten salt, the reaction temperature and the reaction time, adding a proper amount of crystal growth regulator and the like, and can synthesize the flaky alumina with uniform particle size distribution, large diameter-thickness ratio and smooth surface.
US5702519 adopts molten salt method to prepare sheet-like alumina powder. The method comprises the steps of taking water-soluble inorganic aluminum salt as an aluminum source, taking sulfate as molten salt, taking a small amount of phosphate and titanyl sulfate as crystal growth regulators, dissolving the phosphate and titanyl sulfate in a large amount of water, neutralizing with a carbonic acid salt aqueous solution with the same chemical quantity to prepare an aluminum hydroxide sol, heating and drying, removing a large amount of water, and sintering at the high temperature of 1200 ℃ for 5 hours to prepare the aluminum oxide powder with the hexagonal flaky structure. The obtained flaky alumina powder has the particle size of 3-22 μm, the thickness of about 200-300nm and the ratio of diameter to thickness of more than 40. The method needs a large amount of water to dissolve inorganic aluminum salt, sulfate, carbonate and crystal growth regulator, so that a large amount of water needs to be removed in the subsequent drying and dehydration process, and a large amount of energy needs to be consumed in the front and the back. And. The combination between the crystal growth regulator and the aluminum hydroxide is not uniform, so that the migration efficiency of the crystal growth regulator to the aluminum oxide in the molten salt is not high, the grain diameter of the prepared flaky aluminum oxide is small, the grain diameter distribution is not uniform, and the scintillation degree of the pearlescent pigment prepared by taking the flaky aluminum oxide as the base material is not high.
US2016046812a1 discloses another method for preparing flake alumina, and a method for making pearlescent pigments using the same as a substrate. It also uses inorganic aluminum salts as the aluminum source and inorganic salts of zinc and tin as the crystal growth regulators. The method also needs a large amount of water to dissolve the inorganic salt, and needs a curing stage of 4 to 30 hours after the aluminum hydroxide colloid is obtained, so that the energy consumption is high, and the production period is long.
CN101541681A, CN1150165A, CN1936114A, CN101660204A and CN104925843A, disclose methods in which inorganic aluminum salt or composite aluminum salt is mostly selected as an aluminum source, a mixture of sodium sulfate and potassium sulfate is used as a molten salt, and titanium salt, tin salt, zinc salt or phosphate is selected as a crystal growth regulator. These methods also require large amounts of water, are high in energy consumption, and the resulting flake alumina has a small particle size and does not meet the requirements as a substrate for pearlescent pigments.
The realization of a preparation method of flaky alpha-alumina with less water consumption and low energy consumption is a strong demand in the industry, and meanwhile, the prepared flaky alpha-alumina is expected to have better performance.
Disclosure of Invention
The invention aims to provide a preparation method of flaky alpha-alumina and the flaky alpha-alumina.
The preparation method of the flaky alpha-alumina provided by the invention adopts pseudo-boehmite as an aluminum source directly to prepare the flaky alpha-alumina.
The method for preparing flaky alpha-alumina instead of other alumina by directly using pseudo-boehmite as an aluminum source is a novel method, the flaky alpha-alumina with the particle size of micron grade is suitable for being used as a base material of a pearlescent pigment, and the flaky alpha-alumina prepared by the corresponding preparation method has the particle size of micron grade and large average particle size (namely the particle size distribution D)50Large), uniform particle size distribution, large diameter-thickness ratio, no twin crystal, easy dispersion and the like. To achieve the preparation of such alpha-alumina in the form of flakes and having a particle size on the micrometer scale, the present invention is carried out in accordance with the following conditions and procedures.
In the selected pseudoboehmite, the pore volume of the pseudoboehmite is preferably 0.5ml/g-1.2ml/g, and the specific surface area of the pseudoboehmite is preferably 250m2/g-360m2(ii) in terms of/g. If the pore volume and specific surface area indexes of the pseudo-boehmite are smaller than the corresponding ranges, the corresponding crystal growth regulators such as titanyl sulfate, sodium phosphate and the like cannot cover the possibly large number of pseudo-boehmite surfaces to the maximum extent, which is not beneficial to the production of the flaky alpha-alumina. If the pore volume and specific surface area indexes of the pseudo-boehmite are larger than the corresponding ranges, the internal pore diameter is very small, and the corresponding aqueous solution is not easy to wet the small pore inner wall, so that the crystal growth regulators such as titanyl sulfate, sodium phosphate and the like are unevenly distributed, and the particle size distribution of the obtained final flaky alumina product is uneven.
Wherein, the pore volume generally refers to the micropore volume inside the material powder particles, i.e. the pore volume inside the unit solid matter, and is also an important index for measuring the activity of the material. The specific surface area, i.e., the total area (including the outer surface area and the inner pore area) per unit solid matter, is one of the technical indicators representing the active size of the material.
As mentioned above, the corresponding preparation steps are important, and in the present invention, the following steps are included:
dispersing the pseudoboehmite in water to prepare a first mixed solution with the mass fraction of 20-40%;
adding a crystal growth regulator (the crystal growth regulator can be in a solution state) into the first mixed solution to prepare a second mixed solution;
drying the second mixed solution to obtain powder;
mixing the powder with molten salt, and calcining the mixed powder at the temperature of 1000-1400 ℃ to generate alpha-alumina crystals;
and preserving the temperature and cooling the alpha-alumina crystal.
In the steps of the preparation method, the pseudoboehmite is dispersed in water as little as possible when dispersed in the water, and the solid mass fraction is very high in the corresponding first mixed solution. This step, unlike the first step of the prior processes, is usually a complete dissolution of the corresponding molten salt and aluminium salt with a large amount of water. According to the method, the corresponding water is only required to ensure that the pseudoboehmite can be dispersed in water.
In the steps of the preparation method, the first mixed solution can be stirred for a first time at a first temperature, wherein the first temperature is 60-80 ℃, and the first time is 15-30 min. This stirring step is intended to fully wet the corresponding pseudoboehmite.
In the steps of the preparation method, the second mixed solution can be stirred for a second time at a second temperature, wherein the second temperature is 20-80 ℃, and the second time is 30-90 min. This stirring step is intended to mix the second mixed solution sufficiently and uniformly.
In the steps of the preparation method, the crystal growth regulator solution is soluble titanium salt (the soluble titanium salt can be added in a solution state), the addition amount of the soluble titanium salt solution is calculated by the mass of titanium dioxide, and the mass of the titanium dioxide accounts for 0.1-4% of the mass of aluminum oxide in the pseudo-boehmite.
The soluble titanium salt solution may be, for example: titanyl sulfate solution, titanium tetrachloride solution or titanium trichloride solution. The soluble titanium salt solution has the functions of regulating the shape and thickness of the flaky alumina to reduce twinning and agglomeration and improve the product dispersibility.
Or, in the steps of the preparation method, the crystal growth regulator solution is soluble phosphate (the soluble phosphate can be in a solution state), the addition amount of the soluble phosphate solution is calculated by the mass of phosphorus pentoxide, and the mass of the phosphorus pentoxide accounts for 0.1-3% of the mass of the aluminum oxide in the pseudo-boehmite.
Soluble phosphate solutions are a generic term which may include phosphate solutions, metaphosphate solutions, or phosphoric acid solutions, etc., and may be, for example: sodium phosphate solution, sodium dihydrogen phosphate solution, sodium hexametaphosphate solution, phosphoric acid solution, or the like. When the soluble phosphate solution acts, the thickness of the flaky alumina is reduced, and the diameter-thickness ratio is improved. The soluble phosphate salt may also be a solid, such as sodium phosphate dodecahydrate.
In addition, the soluble titanium salt (solution or solid) and the soluble phosphate salt (solution or solid) can be used as the crystal growth regulator (solution or solid) at the same time, and the beneficial effects of the two can be added.
In other cases, the soluble titanium salt can be replaced by one or more of zirconium salt, zinc salt or tin salt, or the crystal growth regulator is selected from one or more of titanium salt, zirconium salt, zinc salt and tin salt.
In the above steps of the preparation method, the drying manner may be drying. For example, the second mixture may be dried in an oven at 100 ℃ to 130 ℃ (e.g., 120 ℃) for 2 to 5 hours to obtain a dry powder. Other drying means may be used as long as the moisture is dried. For another example, vacuum drying at 70 ℃ may be employed.
In the steps of the preparation method, the calcination specifically comprises the steps of fully mixing the powder with molten salts such as sodium sulfate, potassium sulfate and the like, and then putting the mixture into a corundum crucible. The crucible is then placed in a muffle furnace and calcined at the corresponding temperature.
According to the process, the pseudoboehmite is used as the aluminum source, and the corresponding molten salt is added in the next step after the aluminum source is mixed with the crystal growth regulator, so that a large amount of water can be saved, and meanwhile, the energy consumed in the subsequent drying step can be saved.
In the steps of the preparation method, the temperature adopted for heat preservation is 1000-1400 ℃. The holding time can be 2h-5 h. The incubation is to allow the crystal to grow stably.
In the above steps of the preparation method, the cooling mode may be natural cooling. The cooling mode of program control cooling can also be adopted, the cooling speed can be slow, a slow cooling environment for crystal growth can be provided, the crystal can grow more uniformly, the particle size is larger, and the distribution is narrower.
In the above steps of the preparation method, the molten salt may be one or more of sodium sulfate, potassium sulfate (sodium sulfate and potassium sulfate are described above), sodium chloride, potassium chloride, and lithium sulfate, lithium chloride, sodium fluoride, and potassium fluoride.
The above steps of the preparation method may further comprise washing after the cooling. Corresponding to the calcination process described above, the corresponding washing process may be: scraping the product after high-temperature calcination from the crucible, dissolving the product with a large amount of distilled water, filtering, washing with distilled water to remove residual molten salt, and drying the insoluble substances in an oven to obtain the flaky alpha-alumina.
The technical scheme of the invention directly adopts the pseudoboehmite as the aluminum source, and the pseudoboehmite can be suitable for preparing the flaky alpha-alumina through special selection.
Meanwhile, in the technical scheme of the invention, the steps of preparing the powder firstly and then adding the corresponding molten salt are adopted, so that the water consumption is low, and the water required for drying in the drying process is also low, thereby the energy consumption is low.
According to the technical scheme, the large-pore-volume pseudo-boehmite is used as an aluminum source, and the pseudo-boehmite specific surface area is large, so that the crystal growth regulator can be more uniformly adsorbed on the surface of the pore structure of the pseudo-boehmite, and the efficiency of regulating the growth of alumina crystals into sheets is improved.
The invention also obtains the flaky alpha-alumina prepared by the preparation method, namely the flaky alpha-alumina is prepared by the preparation method. The flaky alpha-alumina prepared by the preparation method does not simply emphasize the improvement of each parameter index of the monolithic flaky alpha-alumina, and simultaneously, more means the improvement of the overall parameter performance of the powder as a product.
The flaky alpha-alumina particle size distribution D5018 μm to 28 μm, particle size distribution D50Also referred to as median diameter or median value of the particle size distribution, which is the value of the diameter of the particles at 50% in the cumulative distribution and is one of the important parameters characterizing the particle size of the pigment. The thickness of the flaky alpha-alumina is 0.3-0.5 μm. From this, it is understood that the flaky α -alumina of the present invention has a large aspect ratio.
The flaky alpha-alumina of the present invention has an average particle diameter (particle size distribution D)50) Large size, uniform particle size distribution, large diameter-thickness ratio, no twin crystal and easy dispersion.
The flaky alpha-alumina provided by the invention also has corresponding application in cosmetics, such as a cosmetic functional filler pigment, and is applied and used in decorative and personal care products.
Due to the parameters and properties of the corresponding flaky alpha-alumina, the flaky alpha-alumina has good smoothness, can be used for preparing cosmetics with good skin touch, and has good and durable adhesion to the skin.
The filler pigment using the flaky alpha-alumina can have good transparency to improve skin color, cover uneven skin color, provide light and natural finish, and realize more natural makeup.
Particle size, thickness, aspect ratio, shape, surface properties, refractive index, etc., affect the properties of the flaky alpha-alumina. The particle size significantly affects the coloration of flaky alpha-alumina as a filler pigment. The smaller the particle size, the larger the surface area of the flaky alpha-alumina, thereby improving colorability and enhancing reflectivity, as well as providing a more vivid color.
The flaky alpha-alumina of the present invention can be used in inks, coatings, preferably automotive coatings and plastics, and may contain suitable dopants, some of which may contribute as modifiers for particle size, thickness, optical properties and surface morphology, and may function to inhibit color, promote thickness reduction and particle growth and prevent agglomeration.
The flaky alpha-alumina of the present invention may be coated with one or more metal oxide layers, wherein some of the metal oxide layers may serve as high refractive index layers, the thickness depending on the desired interference color. May also be coated with a suitable colorless low refractive index material.
The flaky alpha-alumina of the present invention may also have a translucent metal layer as an outer layer. The metal layer may be one or more layers. It may also be coated with an organic dye as a top layer.
The flaky alpha-alumina of the present invention may be coated with one or more of the following layers: TiO 22Layer, Fe2O3Layer, Fe3O4Layer, SiO2Layer of Al2O3Layer and SnO2. The coating can be carried out by wet-chemical coating (wet-chemical coating methods developed for pearlescent pigment preparations can be used), or by CVD or PVD methods.
The flaky alpha-alumina of the present invention is used in effect pigments and is suitable for use in all types of compositions, including plastics, cosmetics, and in particular in automotive paints.
Flaky alpha-alumina and effect pigments based on flaky alpha-alumina are compatible with a variety of color systems, including color systems in the fields of paints, automotive coatings, industrial coatings, printing inks, and cosmetic formulations. In order to prepare printing inks for, for example, gravure, flexographic, offset and offset lacquering, various binders are, in particular, water-soluble grades.
The flaky alpha-alumina of the present invention is used in the form of a blend with: organic dyes, organic pigments or other pigments, e.g. transparent and opaque white, colored and black pigments, flake-form oxidesIron, organic pigments, holographic pigments, liquid-crystalline polymers and mica and SiO based on metal oxide coatings2Conventional transparent, colored and black luster pigments for flakes and the like.
The flaky alpha-alumina of the present invention can be used for coloring coating materials, agricultural plastic films, button pastes, for seed coatings, for food coloring, coating of pharmaceutical or cosmetic preparations.
The flaky alpha-alumina of the invention can be used in paints and binder systems for printing inks for gravure, offset or screen printing. Such as in formulations in the field of paints, coatings, automotive finishes, industrial coatings, paints, powder coatings, printing inks, security printing inks, plastics, ceramic materials.
The flaky alpha-alumina of the present invention can be used as an absorber in glass, paper coatings, toners for electrophotographic printing processes, seeds, greenhouse coatings, thermally conductive, self-supporting, electrically insulating, flexible sheets for machine or device insulation, in laser marking of paper and plastics, in laser welding of plastics, in pigment pastes containing water, organic and aqueous solvents, in pigment preparations and dry preparations, e.g. particles, such as clear coats in the industry and the automotive industry, in sunscreens, as a filler, especially in automotive coatings and automotive finishes.
Drawings
FIG. 1 is a graph showing the particle size distribution of flaky alpha-alumina in the first example;
FIG. 2 is a graph showing the particle size distribution of flaky alpha-alumina in example two;
FIG. 3 is a graph showing the particle size distribution of flaky alpha-alumina in the third example;
FIG. 4 is a graph showing the particle size distribution of flaky alpha-alumina in the fourth example;
FIG. 5 is a graph showing the particle size distribution of flaky alpha-alumina in example V;
FIG. 6 is a graph showing the particle size distribution of flaky alpha-alumina in example six;
FIG. 7 is a scanning electron micrograph of flaky alpha-alumina in the sixth example;
FIG. 8 is a photograph of another scanning electron microscope of flaky alpha-alumina in the sixth example;
fig. 9 is a graph showing a particle size distribution of the flaky alpha-alumina in the comparative example.
Detailed Description
The invention provides a novel preparation method of flaky alpha-alumina and flaky alpha-alumina prepared correspondingly, and the invention is explained in detail below by combining with the attached drawings for clearer representation.
Example one
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 0.5ml/g, and the specific surface area of the pseudoboehmite was 250m2/g。
Dispersing 22g of the pseudo-boehmite in 88g of water to prepare a first mixed solution with the corresponding mass fraction of 25%; in the first mixed solution preparation process, the first mixed solution was stirred at 60 ℃ (first temperature) for 15min (first time).
Adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution; in the second mixed solution preparation process, the second mixed solution was stirred at 60 ℃ (second temperature) for 30min (second time).
In this embodiment, the crystal growth regulator solution is a soluble titanium salt solution, the addition amount of the soluble titanium salt solution is calculated by the mass of titanium dioxide, and the mass of the titanium dioxide accounts for 0.5% of the mass of alumina in the pseudo-boehmite. Specifically, in this embodiment, the crystal growth regulator solution is a titanyl sulfate aqueous solution, and the concentration is 30% by mass. In order to add titanium dioxide accounting for 0.5 percent of aluminum oxide, 0.57g of the 30 percent by mass aqueous solution of the titanyl sulfate is added in the embodiment.
And drying the second mixed solution to obtain powder. The drying mode is drying, and specifically, the second mixed solution is put into a 120 ℃ drying oven for drying.
The powder was mixed with molten salts, sodium sulfate and potassium sulfate being added in this example. And after mixing, putting the mixture into a corundum crucible, putting the crucible into a muffle furnace, and calcining at 1200 ℃ for 2h to generate alpha-alumina crystals.
And (3) carrying out heat preservation and natural cooling on the alpha-alumina crystal for 2 hours. The temperature adopted for heat preservation is 1200 ℃.
Washing is performed after the cooling. Specifically, a product after high-temperature calcination is scraped from a crucible, the product is dissolved by distilled water, then the product is filtered and washed by distilled water to remove residual molten salt in the product, and after washing, insoluble substances are placed in an oven for drying to obtain the flaky alpha-alumina.
The flaky alpha-alumina particle size distribution D5018-28 μm and 0.3-0.5 μm in thickness.
The invention also provides the flaky alpha-alumina prepared by the method, namely the flaky alpha-alumina prepared by the preparation method. That is, the flaky alpha-alumina obtained in example one has a large average particle size, a uniform particle size distribution, a large aspect ratio, no twins, and is easily dispersed.
The Particle Size information of the flaky alpha-alumina obtained in the first example is measured by using a laser Particle sizer Mastersizer2000 (water is used as a dispersing agent), and the corresponding measurement results are shown in fig. 1, that is, fig. 1 is a Particle Size distribution graph (Particle Size measurement result graph) of the flaky alpha-alumina in the first example, and the ordinate of the Particle Size distribution graph is the corresponding Volume percentage (Volume) and the abscissa of the Particle Size (Particle Size, in μm).
As can be seen from fig. 1, in this example, the flaky α -alumina had a uniform particle size distribution and a large particle size. Specific flaky alpha-alumina related parameters may be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 0.359 | 16.733 | 23.734 |
TABLE 1
In this example, the particle size distribution D5021.780 μm.
The product has large diameter-thickness ratio, which is reflected in that the product has no agglomeration and twin crystal.
The product is easy to disperse, and when the product is dispersed in water and stirred, smooth streamline can be generated (the streamline is a special phenomenon caused by light reflected by the surface of the flaky material when flaky powder is dispersed and flows in liquid).
The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
Example two
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 0.6ml/g, and the specific surface area of the pseudoboehmite was 270m2/g。
Dispersing 22g of the pseudo-boehmite in 88g of water to prepare a first mixed solution with the mass fraction of 25%; in the first mixed solution preparation process, the first mixed solution was stirred at 65 ℃ (first temperature) for 20min (first time).
Adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution; in the second mixed solution preparation process, the second mixed solution was stirred at 50 ℃ (second temperature) for 35min (second time).
The crystal growth regulator is soluble titanium salt solution and soluble phosphate, the addition amount of the soluble titanium salt solution and the soluble phosphate is calculated by the mass of titanium dioxide and phosphorus pentoxide, and the mass of the titanium dioxide and the phosphorus pentoxide accounts for 1.5% of the mass of aluminum oxide in the pseudo-boehmite. Specifically, in this example, 1.0g of 34.4% by mass aqueous solution of titanyl sulfate and 0.45g of solid sodium phosphate dodecahydrate (with titanium dioxide and phosphorus pentoxide added in an amount of 1.5% by mass based on aluminum oxide) were used as the soluble titanium salt.
And drying the second mixed solution to obtain powder, and referring to the corresponding content of the previous embodiment.
The powder was mixed with molten salts, lithium chloride and potassium chloride being used in this example. And calcining after mixing, wherein the calcining temperature is 1000 ℃, the calcining time is 5h, and alpha-alumina crystals are generated by calcining.
And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1000 ℃, and the heat preservation is carried out for 5 hours.
After the cooling, washing is carried out, and reference is made to the corresponding contents of the preceding examples.
The flaky alpha-alumina obtained in the final example II has large average particle size, uniform particle size distribution, large aspect ratio, no twin crystals and easy dispersion.
The flaky alpha-alumina obtained in example two was measured by a laser particle sizer Mastersizer2000 (water as a dispersant), and the results are shown in fig. 2, in which the particle size distribution was uniform and the particle size was large. Specific platy α -alumina parameters can be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 0.315 | 19.051 | 25.810 |
TABLE 2
In this example, the particle size distribution D5023.447 μm.
The product has large diameter-thickness ratio, which is reflected in that the product has no agglomeration and twin crystal. The product is easy to disperse, and when the product is dispersed in water and stirred, a smooth streamline can be generated. The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
EXAMPLE III
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 0.7ml/g, and the specific surface area of the pseudoboehmite was 280m2/g。
Dispersing 22g of the pseudo-boehmite in water to prepare a first mixed solution with the mass fraction of 25%; in the first mixed solution preparation process, the first mixed solution was stirred at 70 ℃ (first temperature) for 15min (first time).
Adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution; in the second mixed solution preparation process, the second mixed solution was stirred at 40 ℃ (second temperature) for 40min (second time).
The crystal growth regulator solution is a soluble titanium salt solution, the addition amount of the soluble titanium salt solution is calculated by the mass of titanium dioxide, and the mass of the titanium dioxide accounts for 0.5 percent of the mass of aluminum oxide in the pseudo-boehmite. Specifically, in this example, the soluble titanium salt solution used was an aqueous titanium tetrachloride solution, and a 1.0mol/L aqueous titanium tetrachloride solution was used, and the amount added was 1.08 mL.
And drying the second mixed solution to obtain powder, and referring to the corresponding content of the previous embodiment.
Mixing the powder with two molten salts of lithium sulfate and lithium chloride, and calcining the mixture at 1150 ℃ for 4h to generate alpha-alumina crystals.
And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1150 ℃, and the heat preservation is carried out for 3 hours.
After the cooling, washing is carried out, please refer to the corresponding content of the previous embodiment.
The flaky alpha-alumina obtained in the first final embodiment has the advantages of large average particle size, uniform particle size distribution, large aspect ratio, no twin crystals and easy dispersion.
The invention also provides the flaky alpha-alumina prepared by the method, namely the flaky alpha-alumina prepared by the preparation method. That is, the flaky alpha-alumina obtained in example three had a large average particle size, a uniform particle size distribution, a large aspect ratio, no twins, and easy dispersion.
The flaky alpha-alumina obtained in example three was measured for particle size information using a laser particle sizer Mastersizer2000 (dispersant using water), and the corresponding results of the measurement are shown in fig. 3. In this example, the flaky α -alumina had a uniform particle size distribution and a large particle size. Specific flaky alpha-alumina related parameters may be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 0.408 | 14.706 | 20.390 |
TABLE 3
In this example, the particle size distribution D5018.744 μm.
The product has large diameter-thickness ratio, which is reflected in that the product has no agglomeration and twin crystal. The product is easy to disperse, and when the product is dispersed in water and stirred, a smooth streamline can be generated. The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
Example four
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 0.8ml/g, and the specific surface area of the pseudoboehmite was 290m2/g。
The pseudoboehmite is dispersed in water to prepare a first mixed solution with the mass fraction of 20-40%, and the corresponding content of the previous embodiment is referred.
And adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution, referring to the corresponding content of the previous embodiment.
The crystal growth regulator solution is a soluble titanium salt solution, the addition amount of the soluble titanium salt solution is calculated by the mass of titanium dioxide, and the mass of the titanium dioxide accounts for 0.1-4% of the mass of aluminum oxide in the pseudo-boehmite. Specifically, in this embodiment, an aqueous titanium tetrachloride solution is selected as the soluble titanium salt solution, and the amount of titanium dioxide added is calculated to be 1.0% of aluminum oxide, in this case, 2.16mL of an aqueous titanium tetrachloride solution of 1.0mol/L is added.
And drying the second mixed solution to obtain powder, wherein the drying adopts vacuum drying.
Mixing the powder with molten salts such as sodium fluoride and potassium fluoride, and calcining the mixture after mixing, wherein the calcining temperature is 1250 ℃, the calcining time is 3h, and alpha-alumina crystals are generated by calcining.
And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1250 ℃, and the heat preservation time is 2.5 h.
After said cooling, washing is carried out, the process can be referred to the corresponding content of the previous embodiment.
The invention also provides the flaky alpha-alumina prepared by the method, namely the flaky alpha-alumina prepared by the preparation method. That is, the flaky alpha-alumina obtained in example four had a large average particle size, a uniform particle size distribution, a large aspect ratio, no twins, and easy dispersion.
The flaky alpha-alumina obtained in example four was measured for particle size information using a laser particle sizer Mastersizer2000 (dispersant using water), and the corresponding results of the measurement are shown in fig. 4. In this example, the flaky α -alumina had a uniform particle size distribution and a large particle size. Specific flaky alpha-alumina related parameters may be found in the following table:
TABLE 4
In this example, the particle size distribution D5024.508 μm.
The product has large diameter-thickness ratio, which is reflected in that the product has no agglomeration and twin crystal. The product is easy to disperse, and when the product is dispersed in water and stirred, a smooth streamline can be generated. The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
EXAMPLE five
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 1.0ml/g, and the specific surface area of the pseudoboehmite was 320m2/g。
Dispersing 22g of the pseudo-boehmite in 88g of water to prepare a first mixed solution with the mass fraction of 25%; in the first mixed solution preparation process, the first mixed solution was stirred at 75 ℃ (first temperature) for 15min (first time).
Adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution; in the second mixed solution preparation process, the second mixed solution was stirred at 35 ℃ (second temperature) for 45min (second time).
The crystal growth regulator solution is soluble phosphate solution, the addition amount of the soluble phosphate solution is calculated by the mass of phosphorus pentoxide, and the mass of the phosphorus pentoxide accounts for 0.1-3% of the mass of alumina in the pseudo-boehmite. Specifically, in this example, the solid sodium phosphate dodecahydrate was added directly in an amount of 0.5% of the aluminum oxide in the pseudo-boehmite (based on the amount of phosphorus pentoxide in the sodium phosphate dodecahydrate), and specifically 0.45g of sodium phosphate dodecahydrate was added.
And drying the second mixed solution to obtain powder, and referring to the corresponding content of the previous embodiment.
Mixing the powder with molten salts such as potassium sulfate, potassium chloride and the like, and calcining the mixture at 1300 ℃ for 5h to generate alpha-alumina crystals.
And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1300 ℃, and the heat preservation is carried out for 3 hours.
Washing is performed after the cooling.
The invention also provides the flaky alpha-alumina prepared by the method, namely the flaky alpha-alumina prepared by the preparation method. That is, the flaky alpha-alumina obtained in example five had a large average particle size, a uniform particle size distribution, a large aspect ratio, no twins, and easy dispersion.
The flaky alpha-alumina obtained in example five was measured for particle size information using a laser particle sizer Mastersizer2000 (dispersant using water), and the corresponding results of the measurement are shown in fig. 5. In this example, the flaky α -alumina had a uniform particle size distribution and a large particle size. Specific flaky alpha-alumina related parameters may be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 0.314 | 19.090 | 25.789 |
TABLE 5
In this example, the particle size distribution D5024.071 μm.
The product has large diameter-thickness ratio, which is reflected in that the product has no agglomeration and twin crystal. The product is easy to disperse, and when the product is dispersed in water and stirred, a smooth streamline can be generated. The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
EXAMPLE six
A method for preparing flaky alpha-alumina.
22g of pseudo-boehmite (containing 17.2g of alumina) was used as an aluminum source directly to prepare flaky alpha-alumina. In this example, the pore volume of the pseudoboehmite was 1.2ml/g, and the specific surface area of the pseudoboehmite was 360m2/g。
Dispersing the pseudoboehmite in water to prepare a first mixed solution with the mass fraction of 25%; in the first mixed solution preparation process, the first mixed solution was stirred at 80 ℃ (first temperature) for 30min (first time).
Adding a crystal growth regulator solution into the first mixed solution to prepare a second mixed solution; in the second mixed solution preparation process, the second mixed solution was stirred at 50 ℃ (second temperature) for 60min (second time).
The crystal growth regulator solution is soluble phosphate solution, the addition amount of the soluble phosphate solution is calculated by the mass of phosphorus pentoxide, and the mass of the phosphorus pentoxide accounts for 1.0% of the mass of alumina in the pseudo-boehmite. Specifically, in this embodiment, the solid of sodium phosphate dodecahydrate is directly added, and no solution is prepared in advance, and in order to achieve that the mass of the phosphorus pentoxide accounts for 1.0% of the mass of the aluminum oxide in the pseudo-boehmite, 0.90g of sodium phosphate dodecahydrate is added in this embodiment.
And drying the second mixed solution to obtain powder.
Mixing the powder with molten salts such as sodium sulfate, potassium sulfate, sodium chloride, potassium chloride and the like, and calcining the mixture at 1400 ℃ for 5 hours to generate alpha-alumina crystals.
And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1400 ℃, and the heat preservation is carried out for 2 hours.
Washing is performed after the cooling.
The invention also provides the flaky alpha-alumina prepared by the method, namely the flaky alpha-alumina prepared by the preparation method. That is, the flaky alpha-alumina obtained in example six had a large average particle size, a uniform particle size distribution, a large aspect ratio, no twins, and easy dispersion.
The flaky alpha-alumina obtained in example six was measured for particle size information using a laser particle sizer Mastersizer2000 (water was used as a dispersant), and the corresponding results of the measurement are shown in fig. 6. In this example, the flaky α -alumina had a uniform particle size distribution and a large particle size. Specific flaky alpha-alumina related parameters may be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 0.306 | 19.614 | 28.584 |
TABLE 6
In this example, the particle size distribution D5026.341 μm.
Referring to fig. 7, a scanning electron micrograph of a portion of the particle size of the flaky alpha-alumina prepared in this example is shown, from which it can be seen that the particle size distribution (particle size distribution) of the flaky alpha-alumina is at a more understood level (three particle sizes of 13.98 μm, 7.26 μm and 28.52 μm are shown in the figure).
Referring to FIG. 8, a SEM image of the thickness of the flaky alpha-alumina prepared in this example is shown, wherein the flaky alpha-alumina is 0.3 μm to 0.5 μm (both 0.332 μm and 0.327 μm are shown).
As can be seen from the combination of FIG. 7 and FIG. 8, the product obtained in this example has a large aspect ratio, and is free from agglomeration and twinning.
The product is easy to disperse, and when the product is dispersed in water and stirred, a smooth streamline can be generated. The other concrete expression of easy dispersion of the product is that the corresponding flaky alpha-alumina is dispersed in the coating and subjected to card scraping, and the prepared paint film has smooth surface, high glossiness and no coarse particles.
Some steps between embodiments of the present invention may be referred to and replaced with each other.
Comparative example
Preparation of solution A: 111.9g of aluminum sulfate octadecahydrate (containing 17.2g of alumina) as aluminum source, dissolved in 300g of water, and 57.3g of sodium sulfate and 46.9g of potassium sulfate were added, and 1.0g of 34.4% aqueous solution of titanyl sulfate was added, and stirred at 60 ℃ until complete dissolution.
Preparing a solution B: 54g of anhydrous sodium carbonate, 0.45g of dodecahydrate and sodium phosphate, 150g of water was added, and the mixture was dissolved by heating and stirring.
And dropwise adding the solution B into the solution A, and drying the white colloid or suspension (wherein at least 504g of water in the system comprises about 450g of water added during preparation of the solution A and the solution B and about 54g of water in aluminum sulfate octadecahydrate) to obtain powder, and calcining the powder at 1200 ℃ for 4 hours to generate alpha-alumina crystals. And preserving the temperature and cooling the alpha-alumina crystal. The temperature adopted for heat preservation is 1200 ℃, and the heat preservation is carried out for 4 hours.
The finally obtained flaky alpha-alumina is measured for particle size information by a laser particle sizer Mastersizer2000 (water is used as a dispersing agent), the corresponding measurement result is shown in fig. 9, and as seen from the curve in fig. 9, the flaky alpha-alumina has uneven particle size distribution, small particle size and large volume ratio. Specific flaky alpha-alumina related parameters may be found in the following table:
| specific surface area (m)2/g) | Surface area average particle diameter (. mu.m) | Volume average particle diameter (μm) |
| 1.07 | 5.610 | 20.373 |
TABLE 7
In comparative example, particle size distribution D5016.203 μm and less than 18 μm, and the product has a low aspect ratio and dispersibility as in the previous examples.
Comparing the first to sixth examples with the comparative example, it can be seen that, when an aluminum source containing 17.2g of alumina is used to prepare the flaky alpha-alumina, the water consumption of the examples of the present invention is significantly reduced, and the amount of water required for drying is correspondingly reduced, so the energy consumption of the method of the present invention is lower. Meanwhile, the large-pore-volume pseudo-boehmite is adopted as an aluminum source in each embodiment of the invention, and the pseudo-boehmite specific surface area is large, so that the crystal growth regulator can be more uniformly adsorbed on the surface of the pore-size structure of the pseudo-boehmite, the efficiency of regulating the aluminum oxide crystal to grow into a flaky shape is improved, and the average particle size (particle size distribution D) of the flaky alpha-aluminum oxide finally obtained in each embodiment is ensured50) The flake alpha-alumina has the advantages of large size, uniform particle size distribution, large diameter-thickness ratio, no twin crystal and easy dispersion, namely the flake alpha-alumina obtained by the embodiment of the invention has good performance as a base material of pearlescent pigment.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. A preparation method of flaky alpha-alumina is characterized in that pseudo-boehmite is directly used as an aluminum source to prepare flaky alpha-alumina; the pore volume of the pseudoboehmite is 0.5ml/g-1.2ml/g, and the specific surface area of the pseudoboehmite is 250m2/g-360m2(ii)/g; particle size distribution D of the prepared flaky alpha-alumina5018-28 μm and 0.3-0.5 μm thick;
the method specifically comprises the following steps:
dispersing the pseudoboehmite in water to prepare a first mixed solution with the mass fraction of 20-40%;
adding a crystal growth regulator into the first mixed solution to prepare a second mixed solution;
drying the second mixed solution to obtain powder;
mixing the powder with molten salt, and calcining after mixing, wherein the calcining adopts the temperature of 1000-1400 ℃ and the calcining time of 2-5 h, and alpha-alumina crystals are generated by calcining;
keeping the temperature of the alpha-alumina crystal and cooling;
the crystal growth regulator is soluble titanium salt, the addition amount of the soluble titanium salt is calculated by the mass of titanium dioxide, and the mass of the titanium dioxide accounts for 0.1-4% of the mass of aluminum oxide in the pseudo-boehmite; or the crystal growth regulator is soluble phosphate, the addition amount of the soluble phosphate is calculated by the mass of phosphorus pentoxide, and the mass of the phosphorus pentoxide accounts for 0.1-3% of the mass of aluminum oxide in the pseudo-boehmite.
2. The method of preparing flaky alpha-alumina according to claim 1, further comprising stirring the first mixed solution at a first temperature of 60 ℃ to 80 ℃ for a first time of 15min to 30 min.
3. The method of preparing flaky alpha-alumina according to claim 2, further comprising stirring the second mixed solution at a second temperature of 20 ℃ to 80 ℃ for a second time of 30min to 90 min.
4. The method of preparing flaky alpha-alumina according to claim 1, wherein the temperature for the heat preservation is 1000 ℃ to 1400 ℃.
5. The method of preparing flaky alpha-alumina according to claim 1, wherein the molten salt is one or more combinations of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, lithium sulfate, lithium chloride, sodium fluoride and potassium fluoride.
6. The method of preparing flaky alpha-alumina according to claim 1, further comprising washing after the cooling.
7. A flaky alpha-alumina prepared by the production method according to any one of claims 1 to 6.
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