Disclosure of Invention
It is an object of the present invention to provide a flaky alumina having a particle size distribution D which is superior to the prior art10~D9010 to 500 μm, preferably 20 to 200 μm, more preferably 50 to 100 μm; the median thickness is 50nm to 5000nm, preferably 100nm to 1000nm, more preferably 200 to 500 nm; the thickness deviation is less than or equal to 20 percent, and the thickness deviation is preferably less than or equal to 10 percent.
Preferably, the particle size distribution D of the tabular alumina10~D90The particle size is in the range of 10 to 500 μm, 300 to 400 μm, or 400 to 450 μm.
Preferably, the tabular alumina has a median thickness of any of 50nm, 110nm, 215nm, 530nm, 985nm, 5020nm, and ranges therebetween.
Preferably, the thickness deviation of the tabular alumina is 21% or less, 20.8% or less, 15.6% or less, 12.9% or less, 10.1% or less, 10% or less, 8.3% or less, 5.7% or less, and ranges therebetween.
In the present invention, the particle diameter distribution D10Diameter value representing cumulative 10% point, particle size distribution D90Representing the cumulative 90% point diameter value.
"median thickness" refers to the median of all statistical point thickness values.
"thickness variation" refers to the thickness (H) at any one statistical point and the median thickness (H)Median value) The deviation ratio between them; the calculation formula is (H-H)Median value)/HMedian value×100%。
Another object of the present invention is to provide a method for preparing flake alumina, which comprises the following steps:
s1: taking a solution containing sulfuric acid as an electrochemical solution, an electrode containing aluminum foil as a positive electrode, a conductive electrode as a negative electrode, applying current between the positive electrode and the negative electrode, and preparing an aluminum oxide film on the surface of the electrode containing aluminum foil;
s2: cutting off the edge or cutting the aluminum foil with the surface containing the aluminum oxide film prepared in the step S1 into a certain size;
s3: dipping the aluminum foil sheared in the step S2 in a solution containing copper salt, and dispersing by ultrasonic waves to prepare a suspension containing an aluminum oxide film;
s4: the suspension containing the aluminum oxide film of step S3 is separated to prepare the flaky alumina.
In the present invention, in order to make the flaky alumina undergo crystal transformation and improve the acid and alkali resistance thereof, the flaky alumina is calcined after step S4, the calcination temperature is 800 to 1200 ℃, for example, any temperature of 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃ and the range value between the two, preferably the calcination temperature is 900 to 1000 ℃; the calcination time is 1 to 12 hours, for example, any time of 1 to 4 hours, 6 to 8 hours, 10 to 12 hours, and a range therebetween, and preferably 2 to 4 hours.
In the invention, an aluminum oxide film is prepared on the surface of aluminum by an electrochemical method commonly called anodic oxidation, the corrosion dissolution of aluminum and the generation of the aluminum oxide film are simultaneously carried out, sulfuric acid is a strong corrosive acid, the aluminum oxide film cannot be generated when the concentration is lower than 5 wt%, the aluminum oxide film becomes brittle when the concentration is higher than 15 wt%, and the mass fraction of the sulfuric acid in the electrochemical solution is 5-15 wt%, such as 5 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 15 wt%, preferably 7-9 wt%; any mass fraction of 5 wt% to 15 wt% and the range value between the two, preferably 8 wt% to 10 wt%. In the preparation process of the aluminum oxide film, aluminum ions in the sulfuric acid solution gradually increase, when the concentration of the aluminum ions exceeds 10 wt%, the oxide film is difficult to further form, and in order to improve the compactness and thickness uniformity of the aluminum oxide film, the electrochemical solution of the step S1 further comprises an auxiliary acid consisting of at least one of citric acid, boric acid and oxalic acid; the mass fraction of the auxiliary acid is 0.5 wt% to 3 wt%, such as any mass fraction of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt% and a range value therebetween. Adding citric acid as an auxiliary acid to be complexed with aluminum ions to reduce the content of the aluminum ions in the sulfuric acid solution; or boric acid is added to prevent the alumina film from becoming loose after the temperature of the sulfuric acid solution is increased, or oxalic acid is added to improve the toughness of the alumina film, and preferably, a small amount of each of the three auxiliary acids is added.
Step S1 of the present invention includes a solution temperature of sulfuric acid of 15 to 35 ℃, more preferably, a solution temperature of 19 to 25 ℃; preferably, a current of 0.5A/dm is applied between the positive electrode and the negative electrode2~1A/dm2For example 0.5A/dm2、0.6A/dm2、0.7A/dm2、0.8A/dm2、0.9A/dm2、1.0A/dm2Preferably 0.6A/dm and the range value between the two2~0.8A/dm2(ii) a The time for applying the current between the positive electrode and the negative electrode is 120s to 3600s, preferably 600s to 1800 s.
According to the invention, copper ions and aluminum are subjected to a displacement reaction, so that the aluminum reacts into aluminum ions, and the aluminum oxide does not react with the copper ions, thereby separating the aluminum from the aluminum oxide film. In order to make the solution of the copper compound sufficiently contact with the aluminum foil, the aluminum foil having an aluminum oxide film on the surface thereof is cut to remove the edge, preferably to a certain size, so that not only the contact area between the copper compound and the aluminum foil is increased, but also the particle size of the aluminum oxide film to be peeled off is made more uniform. The solution of at least one copper compound selected from copper sulfate, copper chloride, copper nitrate and copper acetate is generally used, and copper chloride is preferred because of the small radius of chloride ion. The concentration of the copper compound influences the dissolution rate of the aluminum foil and the particle size uniformity of the flaky alumina, and the copper compound in the step S3 is selected from at least one of copper sulfate, copper chloride, copper nitrate and copper acetate, preferably copper chloride; the mass fraction of the copper compound in the copper compound solution is 0.5 wt% to 10 wt%, such as any mass fraction of 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt% and a value ranging therebetween, preferably 1 wt% to 8 wt%, more preferably 2 wt% to 6 wt%; the temperature of the copper compound solution is 25-60 ℃, preferably 35-50 ℃; the dipping time is 4-24 h, preferably 8-12 h; preferably, the aluminum foil is immersed in the copper compound solution while applying 50 to 100W of power for ultrasonic dispersion.
The copper compound solution of step S3 in the present invention further comprises 0.1 wt% to 1 wt% hydrochloric acid, such as any mass fraction of 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1.0 wt% and the range value therebetween, preferably 0.2 wt% to 0.6 wt%; in order to improve the adhesion and permeability of the copper compound solution on the surface of the aluminum foil, 0.01 to 0.5 weight percent of surfactant is preferably added, and 0.05 to 0.1 weight percent of surfactant is preferably included; preferably, the surfactant is at least one selected from the group consisting of alkylphenol ethoxylates, sodium dodecylbenzenesulfonate and sodium dodecylbenzenesulfonate.
In the present invention, the peeled oxide film is dispersed by ultrasonic oscillation in step S4 to reduce the particle size and improve the uniformity of the particle size, the power of the ultrasonic wave is generally 300W to 500W, preferably 200W to 400W; if the power is not too high, the alumina film is easy to shatter. The time for ultrasonic dispersion is 1 h-24 h, preferably 4 h-8 h.
According to another aspect of the invention, the flake alumina and the flake alumina prepared by the preparation method are applied to functional coatings, pigments, fillers, toughening agents and refractory materials.
The invention has the beneficial effects that:
1) the flaky alumina has uniform thickness and large particle size, and can be applied to functional coatings, fillers, toughening agents, refractory materials and the like.
2) The preparation method of the flaky alumina has the advantages of simple process, simple reaction, easy control, low cost and wide application prospect.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
According to the present invention, there is provided a flaky alumina having a median thickness of 50 to 5000nm, preferably 100 to 1000nm, more preferably 200 to 500 nm; the thickness deviation is less than or equal to 20 percent, and preferably, the thickness deviation is less than or equal to 10 percent; particle size distribution D10~D90From 10 μm to 500. mu.m, preferably from 20 μm to 200. mu.m, more preferably from 50 μm to 100. mu.m. The flaky alumina has high thickness uniformity and large particle size, and can be applied to functional coatings, fillers, toughening agents, refractory materials and the like.
The present invention will be described in further detail below with reference to examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Examples 1 to 6: using 1060 aluminum foil as a raw material, immersing an effective area of 100mm x 50mm into a sulfuric acid solution with the temperature of 21 ℃ and the weight percent of 15 mm, using 1060 aluminum foil as a positive electrode to be connected with a power supply positive electrode, using 316 stainless steel sheet as a negative electrode to be connected with a power supply negative electrode, applying constant current for a period of time, washing 1060 aluminum foil with pure water for 2 times, cutting four edges of the aluminum foil by using a cutting machine, immersing the aluminum foil into a copper chloride solution with the temperature of 25 ℃ and the weight percent of 10% for 8 hours, filtering out an aluminum oxide film by using an 80-mesh filter screen, dispersing the aluminum oxide film in pure water, placing the aluminum oxide film in an ultrasonic cleaning machine, dispersing the aluminum oxide film under 200W power of ultrasonic waves for 24 hours, testing the particle size distribution of the flaky aluminum oxide by using an optical microscope, and testing the thickness of the flaky aluminum oxide by using a scanning probe microscope. The experimental parameters and properties of examples 1-6 are shown in Table 1.
TABLE 1 Experimental parameters and Performance of examples 1-6
Example 7: unlike example 4, the 10 wt% sulfuric acid solution was replaced with 10 wt% sulfuric acid and 3 wt% boric acid, and the same operation as in example 4 was performed.
Example 8: unlike example 4, the 10 wt% sulfuric acid solution was replaced with a mixed solution of 8 wt% sulfuric acid and 2 wt% citric acid, and the same operation as in example 4 was performed.
Example 9: the same operation as in example 4 was carried out except that the 10 wt% copper chloride solution at 25 ℃ was replaced with a mixed solution of 1 wt% copper sulfate and 0.1 wt% hydrochloric acid at 35 ℃.
Example 10: unlike example 4, the same operation as in example 4 was carried out except that the 25 ℃ 10 wt% copper chloride solution was replaced with a mixed solution of 50 ℃ 2 wt% copper chloride and 0.1 wt% sodium dodecylbenzenesulfonate.
The performance of examples 7-10 was similar to that of example 4.
Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.