Alpha-aluminum oxide as well as preparation method and application thereof

Abstract

The invention provides alpha-aluminum oxide and a preparation method and application thereof, the preparation method comprises the following steps: 1) providing a first emulsion in which first micelles are formed, and the first micelles are surfactant micelles adsorbed with aluminum hydroxide; 2) mixing ammonium fluoride with the first emulsion to form a second emulsion; and 3) dewatering and roasting. According to the method for preparing the alpha-aluminum oxide, the porous alpha-aluminum oxide can be prepared, the specific surface area of the alpha-aluminum oxide is increased to 10-235 m < 2 > / g, the pH is reduced to 8.3-9.6, and the preparation method is simple, low in cost, free of waste liquid generation and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum oxide preparation, in particular to alpha-aluminum oxide and a preparation method and application thereof. Background Art

[0002] Alumina has many phases, including α-alumina, γ-alumina, η-alumina, δ-alumina, θ-alumina, χ-alumina, and κ-alumina. Different crystal forms exhibit varying properties due to their structure and are used in diverse fields. α-alumina, as the most stable crystalline phase of alumina, boasts a range of excellent properties, including high strength, hardness, high temperature resistance, corrosion resistance, and wear resistance. It is widely used in aviation, metallurgy, machinery, sensors, bioceramics, catalyst supports, and other fields.

[0003] Currently, α-alumina is commonly prepared using mechanical grinding, combustion, precipitation, sol-gel, and chemical vapor deposition methods. These existing methods for preparing porous alumina are complex, costly, and difficult to handle. Furthermore, the heteroatoms introduced during modification can significantly impact its application.

[0004] Chinese patent CN1331605C discloses a modified alumina support containing titanium and silicon additives and its preparation method. The silicon additive in the modified alumina support is introduced during the aluminum hydroxide gelation process, significantly increasing the alumina's specific surface area, pore size, and pore volume. The titanium additive is added after gelation and before aging to further improve the support's surface acidity, significantly increasing the surface acidity and Brønsted acid content. To adjust the alumina's surface acidity and alkalinity, this invention introduces metal cations for surface modification. However, since these metal cations tend to form coordination bonds, this could potentially affect the modified alumina's application. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide an α-alumina and a preparation method and use thereof, aiming to creatively propose a new concept of a preparation method of α-alumina to solve the problems of the prior art preparation method being complex, costly, and generating a large amount of industrial waste liquid.

[0006] To achieve the above-mentioned purpose and other related purposes, the present invention is achieved through the following technical solutions.

[0007] The present invention discloses a method for preparing α-alumina, comprising the following steps:

[0008] 1) providing a first emulsion, wherein first micelles are formed in the first emulsion, and the first micelles are surfactant micelles adsorbed with aluminum hydroxide;

[0009] 2) Ammonium fluoride is mixed with the first emulsion to form a second emulsion;

[0010] 3) Water is removed and then calcined.

[0011] Preferably, in step 1), the first emulsion is formed by dispersing aluminum hydroxide and a surfactant in water.

[0012] More preferably, the first emulsion is obtained by stirring and mixing, and the mixing and stirring time is 0.5 - 1 h, further preferably 0.5 h.

[0013] Preferably, in step 2), the mixing and stirring time is 0.5 - 3 h, further preferably 1 - 2 h.

[0014] Preferably, in step 1), the surfactant is selected from one or more of stearic acid, palmitic acid, and oleic acid.

[0015] Preferably, in step 1), the mass fraction of the surfactant in the first emulsion is 0.1% - 0.3%.

[0016] Preferably, the purity of the aluminum hydroxide is 99%.

[0017] Preferably, the mass ratio of the surfactant to the aluminum hydroxide is (0.01 - 0.3):1. For example, it can be 0.05:1, 0.1:1, 0.2:1, 0.3:1. If the amount of the surfactant is too small, the aluminum hydroxide cannot be well dispersed in water, and the aluminum hydroxide cannot be completely adsorbed inside the micelles, which will reduce the specific surface area and pH change amount of the prepared α-aluminum oxide; if the amount of the surfactant is too large, it will cause waste of raw materials; therefore, the mass ratio of the surfactant to the aluminum hydroxide is preferably (0.2 - 0.3):1.

[0018] Functions of the surfactant: First, it makes the aluminum hydroxide evenly dispersed in water; second, it wraps the aluminum hydroxide to avoid reacting with ammonium fluoride.

[0019] Preferably, the mass ratio of the ammonium fluoride to the aluminum hydroxide is (0.01 - 10):1. For example, it can be 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.5:1, 1:1, 5:1, 10:1.

[0020] If the amount of ammonium fluoride is too small, it will reduce the specific surface area and pH change amount of the prepared α-aluminum oxide; if the amount of ammonium fluoride is too large, it will cause waste of raw materials; therefore, the mass ratio of ammonium fluoride to the aluminum hydroxide is more preferably (0.05 - 1):1, further preferably (0.5 - 1):1.

[0021] The role of ammonium fluoride: First, it creates pores during calcination to form a porous structure of α-alumina, thereby increasing the specific surface area of α-alumina; second, fluoride ions are doped into the unit cell structure of α-alumina during the formation of α-alumina crystals, increasing the acid content of α-alumina and lowering the pH of α-alumina.

[0022] Preferably, in step 3), the dehydration is carried out by low-temperature drying or high-temperature drying to completely remove the moisture.

[0023] More preferably, the temperature of high temperature drying is <120°C.

[0024] More preferably, the drying is low-temperature drying, and further preferably freeze drying.

[0025] Preferably, in step 3), the calcination temperature is 1000-1200° C., and the calcination time is 1-5 hours.

[0026] Preferably, the heating rate of the calcination is (3-5)°C / min, more preferably 3°C / min.

[0027] More preferably, the calcination process is as follows: the first stage calcination temperature is 300-500°C, the first stage calcination time is 1-2 hours; the second stage calcination temperature is 1000-1200°C, the second stage calcination time is 1-3 hours. Further preferably, the first stage calcination temperature is 500°C, the first stage calcination time is 2 hours; the second stage calcination temperature is 1200°C, the second stage calcination time is 1 hour.

[0028] The invention also discloses alpha-alumina.

[0029] Preferably, the specific surface area of the α-alumina is 10 to 235 m 2 / g. For example, it can be 10m 2 / g, 10.65m 2 / g, 13.15m 2 / g, 15.37m 2 / g, 20m 2 / g, 25.29m 2 / g, 40.58m 2 / g, 50m 2 / g、70m 2 / g、90m 2 / g, 110.68m 2 / g, 150m 2 / g, 200m 2 / g, 230.96m 2 / g.

[0030] Preferably, the pH of the α-aluminum oxide is 8.3 to 9.6. It can be, for example, 9.53, 9.48, 9.33, 9.21, 9.03, 9.0, 8.78, 8.34, 8.3.

[0031] The present invention also discloses the use of the α-aluminum oxide as an adsorbent, a catalyst carrier, and a battery coating material.

[0032] The present invention provides a preparation method of α-aluminum oxide, which has the following beneficial effects: In this application, a micelle method is creatively adopted to protect aluminum hydroxide to avoid reacting with ammonium fluoride. Thus, ammonium fluoride can play a role in pore formation and reducing the pH of α-aluminum oxide during calcination. By using the preparation method in this application, not only can porous α-aluminum oxide be prepared, increasing the specific surface area of α-aluminum oxide to 10 - 235 m 2 / g and reducing the pH to 8.3 - 9.6, but also the preparation method is simple, low-cost, and no waste liquid is generated, making it suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shown are the XRD patterns of the α-aluminum oxide prepared in Examples 1 - 7 and Comparative Examples 1 - 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] It should be noted that the process equipment or devices not specifically specified in the following examples are all conventional equipment or devices in the art.

[0036] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these clearly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbers of the method steps are only convenient tools for identifying the method steps, rather than limiting the arrangement order of the method steps or the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0037] In a specific embodiment, the preparation method of α-aluminum oxide includes the following specific steps:

[0038] (1) Uniformly disperse aluminum hydroxide and a surfactant in water by stirring to form a first emulsion.

[0039] The mass ratio of the surfactant to aluminum hydroxide is (0.01 - 0.3):1, the mass fraction of the surfactant in water is 0.1% - 0.3%, and the mixing and stirring time is 0.5 - 1 h.

[0040] (2) Mix the first emulsion and ammonium fluoride uniformly to form a second emulsion.

[0041] The mass ratio of ammonium fluoride to aluminum hydroxide is (0.01 - 10):1, and the mixing and stirring time is 0.5 - 3 h.

[0042] (3) Dry the second emulsion B.

[0043] (4) Calcinate in a muffle furnace to obtain α-aluminum oxide.

[0044] The calcination temperature is: the initial calcination temperature is 300 - 500 °C, and the initial calcination time is 1 - 2 h; the later calcination temperature is 1000 - 1200 °C, and the later calcination time is 1 - 3 h. The heating rate of the calcination temperature is (3 - 5) °C / min.

[0045] Example 1

[0046] This example provides a more specific method for preparing α-aluminum oxide.

[0047] In step (1), the mass ratio of stearic acid to aluminum hydroxide is 0.2:1, the mass fraction of the surfactant in water is 0.2%, and the mixing and stirring time is 0.5 h.

[0048] In step (2), the mass ratio of ammonium fluoride to aluminum hydroxide is 1:1, and the mixing and stirring time is 1 h.

[0049] In step (3), freeze-dry.

[0050] In step (4), the calcination temperature is: the initial calcination temperature is 500 °C, and the initial calcination time is 2 h; the later calcination temperature is 1200 °C, and the later calcination time is 1 h. The heating rate of the calcination temperature is 3 °C / min.

[0051] Example 2

[0052] This example provides a more specific method for preparing α-aluminum oxide.

[0053] The difference from Example 1 is that in step (2), the mass ratio of ammonium fluoride to aluminum hydroxide is 0.5:1.

[0054] Example 3

[0055] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0056] The difference from Embodiment 1 is that in step (2), the mass ratio of ammonium fluoride to aluminum hydroxide is 0.2:1.

[0057] Embodiment 4

[0058] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0059] The difference from Embodiment 1 is that in step (2), the mass ratio of ammonium fluoride to aluminum hydroxide is 0.1:1.

[0060] Embodiment 5

[0061] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0062] The difference from Embodiment 1 is that in step (2), the mass ratio of ammonium fluoride to aluminum hydroxide is 0.05:1.

[0063] Embodiment 6

[0064] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0065] The difference from Embodiment 3 is that in step (1), the mass ratio of stearic acid to aluminum hydroxide is 0.1:1.

[0066] Embodiment 7

[0067] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0068] The difference from Embodiment 3 is that in step (1), the mass ratio of stearic acid to aluminum hydroxide is 0.05:1.

[0069] Embodiment 8

[0070] This embodiment provides a more specific method for preparing α-aluminum oxide.

[0071] The difference from Embodiment 1 is that in step (1), stearic acid is replaced by palmitic acid.

[0072] Comparative Example 1

[0073] This comparative example is a comparative example of Embodiment 1, and the difference is that it does not contain ammonium fluoride.

[0074] Comparative Example 2

[0075] This comparative example is a comparative example of Embodiment 1, and the difference is that it does not contain stearic acid.

[0076] Comparative Example 3

[0077] This comparative example is a comparative example of Example 1, except that the mass ratio of stearic acid to aluminum hydroxide is 0.1:1.

[0078] Comparative Example 4

[0079] This comparative example is a comparative example of Example 1, except that ammonium chloride is used instead of ammonium fluoride.

[0080] XRD test was performed on the α-alumina prepared in Examples 1 to 7 and Comparative Examples 1 to 2. The test spectra are shown in FIG. Figure 1 .

[0081] The specific surface area and pH value of the α-alumina prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were measured using a specific surface area analyzer (model SSA-7000) and a pH meter (model PHS-3E), respectively. The test results are shown in Table 1.

[0082] The particle size distribution and magnetic metal content of the α-alumina prepared in Examples 1 and 2 were measured using a Better Laser Particle Size Analyzer and a JJCC Magnetic Metal Content Analyzer. The test results are shown in Table 2.

[0083] The pH test method is: dissolve 3g of α-alumina in 20ml of water, stir evenly and immediately measure with a pH meter, wait until the reading stabilizes, and record the pH value.

[0084] The test method for particle size distribution is: after debugging the instrument, directly add the powder into the sample cell so that the refractive index is 5%-10%, and then measure its particle size.

[0085] The method for testing magnetic metal content is as follows: Place the instrument horizontally and securely, pour the prepared sample into the container, apply magnetism, start the motor, and adjust the flow control gate to ensure that the sample flows evenly through the flow channel into the sample container. After the sample has flowed out, stop the motor, connect the small cup, and then disconnect the magnetism. Sweep away any adsorbed material from the flow channel.

[0086] Table 1

[0087]

[0088]

[0089] Table 2

[0090] Serial number Particle size distribution D50 Content of magnetic metal Example 1 3.52 microns 0.13 ppm Example 2 4.72 microns 0.15 ppm

[0091] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing α-aluminum oxide, characterized in that , including the following steps: 1) Provide a first emulsion in which first micelles are formed, and the first micelles are surfactant micelles adsorbed with aluminum hydroxide; 2) Mix ammonium fluoride with the first emulsion to form a second emulsion; 3) Remove water and calcine.

2. The preparation method according to claim 1, wherein The first emulsion is formed by dispersing aluminum hydroxide and a surfactant in water.

3. The preparation method according to claim 1, wherein In step 1), the surfactant is selected from one or more of stearic acid, palmitic acid and oleic acid; And / or, in step 1), the mass fraction of the surfactant in the first emulsion is 0.1% - 0.3%.

4. The preparation method according to claim 1, characterized in that, The purity of the aluminum hydroxide is 99%.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the surfactant to the aluminum hydroxide is (0.01 - 0.3):1; And / or, the mass ratio of the ammonium fluoride to the aluminum hydroxide is (0.01 - 10):

1.

6. The preparation method according to claim 1, characterized in that The temperature of the calcination is 1000 - 1200 °C, and the calcination time is 1 - 5 h; And / or, the heating rate of the calcination is (3 - 5) °C / min.

7. The preparation method according to claim 6, characterized in that, The calcination adopts the following procedure: the temperature of the first stage of calcination is 300 - 500 °C, and the time of the first stage of calcination is 1 - 2 h; the temperature of the second stage of calcination is 1000 - 1200 °C, and the time of the second stage of calcination is 1 - 3 h.

8. An α-aluminum oxide prepared by the preparation method according to any one of claims 1 - 7.

9. The α-aluminum oxide according to claim 8, characterized in that, The specific surface area of the α-aluminum oxide is 10 to 235 m 2 / g; And / or, the pH of the α-aluminum oxide is 8.3 - 9.

6.

10. Use of the α-aluminum oxide according to any one of claims 8 - 9 as an adsorbent, a catalyst carrier and as a battery coating material.

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