METHOD FOR PRODUCING ALUMINUM OXIDE POWDER BY ELECTROCHEMICAL DISSOLVING ALUMINUM SALT

Abstract

Provides a method for producing aluminum oxide powder by electrochemical dissolving aluminum salt, comprise: (A) providing an electrochemical device with an aluminum material as an anode and an acidic solution as an electrolyte; (B) accelerating the dissolution of the aluminum material by current pulse method to form an acidic aluminum salt solution; (C) neutralizing the acidic aluminum salt solution with a basic solution to form an aluminum hydroxide sol; (D) adding an additive in the aluminum hydroxide sol, filtering the aluminum hydroxide sol and drying to obtain aluminum hydroxide powder; (E) roasting the aluminum hydroxide powder to form micron scale γ-aluminum oxide powder. Combines the acidic aluminum salt method and the electrochemical dissolution method to improve the dissolving rate of the aluminum material and increase the output efficiency of the acidic aluminum salt, and obtaining micron scale γ-aluminum oxide powder.

Claims

1. A method for producing aluminum oxide powder by electrochemical dissolving aluminum salt, steps comprising: (A) providing an electrochemical device with an aluminum material as an anode and an acidic solution as an electrolyte; (B) accelerating the dissolution of the aluminum material by current pulse method to form an acidic aluminum salt solution; (C) neutralizing the acidic aluminum salt solution with a basic solution to form an aluminum hydroxide sol, a particle size of the aluminum hydroxide sol is in the range of 1 to 10 μm; (D) adding an additive in the aluminum hydroxide sol to control the particle size of the aluminum hydroxide sol to the nanoscale, filtering the aluminum hydroxide sol and drying to form aluminum hydroxide powder, a particle size of the aluminum hydroxide powder is in the range of 30 to 300 nm; (E) roasting the aluminum hydroxide powder at a high temperature to form micron scale γ-aluminum oxide powder.

2. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the aluminum material of the step (A) is an aluminum scrap or aluminum sheet with a purity of 3N grade or above; the electrochemical device is an electrochemical dual electrode system with one of platinum, gold and graphite as a cathode material.

3. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the acidic electrolyte of the step (A) is selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H.sub.2SO.sub.4) and nitric acid (HNO.sub.3), a concentration of the acidic electrolyte is between 0.5M and 3M.

4. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the current pulse method of the step (B) sets constant current pulse by a power supply, the constant current pulse is 0.1 to 1.0 A/cm.sup.2 and 10 seconds, 0 A/cm.sup.2 and 15 seconds for a cycle, number of pulse current cycles is more than 20 times, the total electrolysis time is more than 500 seconds.

5. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the basic solution of the step (C) is selected from the group consisting of sodium hydroxide (NaOH), ammonia water (NH.sub.4OH) and potassium hydroxide (KOH), the basic solution is used to perform the acid-base neutralization of the acidic aluminum salt solution, and the pH is neutralized between 6 and 8 to form an aluminum hydroxide (Al(OH).sub.3) sol.

6. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the additive of the step (D) is selected from the group consisting of sodium chloride (NaCl), ammonium chloride (NH.sub.4Cl), 3-mercapto-1-propanesulfonic acid sodium salt (MPS) and 4-dodecylbenzenesulfonic acid (DBSA).

7. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 6, wherein a concentration of the additive is between 0.01M and 0.5M, and the acid-base value is controlled at pH value between 6 and 8.

8. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein the filtering and drying process of the step (D) is allowing the aluminum hydroxide sol to carry out suction filtration, and then is dried at a low temperature by oven or a heating plate with temperature set 80 to 100° C. to form nanoscale aluminum hydroxide powder.

9. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 1, wherein a temperature of the high temperature roasting of the step (E) is between 600° C. and 1000° C., and a temperature holding time is 1 to 5 hours.

10. The method for producing aluminum oxide powder by electrochemical dissolving aluminum salt according to claim 9, wherein the temperature of the high temperature roasting of the step (E) is between 600° C. and 1000° C., and the temperature holding time is 1 to 5 hours to form the micron scale γ-aluminum oxide powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a flow chart of a method for producing aluminum oxide powder by electrochemical dissolving aluminum salt of the present disclosure.

[0028] FIG. 2 shows photos of the aluminum hydroxide sol after electrochemical dissolving the acidic aluminum salt and the neutralization with the basic solution according to an embodiment of the present disclosure.

[0029] FIG. 3 show photos of aluminum hydroxide powder obtained by the aluminum hydroxide sol after suction filtration and drying according to the embodiment of the present disclosure.

[0030] FIG. 4 is a spectrum of graph of scanning electron microscope of aluminum hydroxide powder according to the embodiment of the present disclosure.

[0031] FIG. 5 is a spectrum of graph of x-ray diffraction of aluminum oxide powder after high temperature roasting according to the embodiment of the present disclosure.

[0032] FIG. 6 is a spectrum of graph of scanning electron microscope of γ-aluminum hydroxide powder after the high temperature roasting synthesis of 700° C. according to the embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The implementation of the disclosure is further described by the specific embodiments as below, and a person having ordinary skill in the art can easily understand other advantages and effects of the present disclosure by the content of the specification. However, the implementation of the disclosure is not limited by the following embodiments.

[0034] Referring to FIG. 1, FIG. 1 is a flow chart of a method for producing aluminum oxide powder by electrochemical dissolving aluminum salt of the present disclosure, steps comprising: providing an electrochemical device with an aluminum material as an anode and an acidic solution as an electrolyte, S101; accelerating the dissolution of the aluminum material by current pulse method to form an acidic aluminum salt solution, S102; neutralizing the acidic aluminum salt solution with a basic solution to form an aluminum hydroxide sol, S103; then, adding an additive in the aluminum hydroxide sol to control the particle size of the aluminum hydroxide sol to the nanoscale, filtering the aluminum hydroxide sol and drying to form aluminum hydroxide powder, S104; finally, roasting the aluminum hydroxide powder at a high temperature to form micron scale γ-aluminum oxide powder, S105.

[0035] As to the aluminum material described in step S101, an aluminum sheet with a purity of 3N grade or above is preferable in the embodiment, the size is 5 cm×2 cm, the thickness is about 2.5 to 3 mm, and a reaction area is defined by an acid and alkali-resistant tape as 6.6 cm.sup.2; the electrochemical device is an electrochemical dual electrode system with an aluminum sheet having a purity of 3N grade or above as an anode, a platinum sheet as a cathode, and an acidic solution as an electrolyte, and the electrochemical dissolution of the aluminum sheet is performed.

[0036] The aforementioned aluminum sheet needs to go through a pretreatment process to remove the oil stain and oxidation layer on the surface. First, the aluminum sheet is soaked into a detergent, and washed with ultrasonic cleaning for 10 minutes; after the aluminum sheet is cleaned with acetone, then the aluminum sheet is soaked with deionized water, and placed in an ultrasonic cleaner for 10 minutes; the aluminum sheet is soaked with 2M H.sub.2SO.sub.4, and placed in the ultrasonic cleaner for 5 minutes; after the aluminum sheet is cleaned with deionized water, the aluminum sheet is placed in 1M NaOH, and stirred thoroughly for 1 minute; after the aluminum sheet is cleaned with deionized water, the aluminum sheet is baked, and the pretreatment process of the aluminum sheet is completed.

[0037] As to the acidic electrolyte described in step S102, 0.5M hydrochloric acid (HCl) is preferable in the embodiment, it is preferable that the electrochemical method used is current pulse method, the current pulse method sets constant current pulse by a power supply, the constant current pulse is 0.1 to 1.0 A/cm.sup.2 and 10 seconds, 0 A/cm.sup.2 and 15 seconds, the anode is the aluminum sheet, the cathode is the platinum sheet, and the dissolution of the aluminum material is accelerated to form an acidic aluminum salt (AlCl.sub.3) solution.

[0038] Only considering the chemical dissolution, the chemical dissolution rate of basic aluminum salt system is high, but it is easy to retain sodium, potassium and other metal ions, which affect the purity of synthetic powder and subsequent electronic-grade applications. In contrast, although the acidic aluminum salt system has no sodium, potassium and other metal ion impurities, the chemical dissolution rate is very poor. Therefore, the present disclosure uses electrochemical dissolution (electrodissolution) to improve the solution rate, adding a small positive bias to the acidic dissolving system, which promotes the oxidation reaction of aluminum to increase the dissolution rate of aluminum.

[0039] However, under the condition of electrolyzing aluminum in a state of the constant current for a long time, the problem of electrode surface polarization becomes more and more serious, which will cause the problem of overpotential rise of electrode surface or surface temperature rise. In the electrochemical dissolution reaction is accompanied by an electrolytic reaction of water at the same time, so there will be oxygen accumulation on the surface. Although stirring can be used to increase mechanical disturbances in the solution to take away the gas generated on the surface of the electrode, it is still easy to produce by-products with the increase of reaction time, so the electrochemical dissolution performed by current pulse method is attempted. The advantage of the method is that when the pulse current is 0 or a small reverse current, the polarization of the electrode surface that is caused by the constant current reaction continuing a long time can be carried out depolarization, so that an overpotential produced by the polarization of the electrode surface is reduced. Accordingly, it provides an effective and stable method for an electrochemical process that has a large number of reactions and continues a long time.

[0040] As to the basic solution described in step S103, ammonia water (NH.sub.4OH) is preferable in the embodiment, the basic ammonia water (NH.sub.4OH) is used to perform the acid-base neutralization of the acidic aluminum salt solution, and the pH is neutralized between 6 and 8 to form an aluminum hydroxide (Al(OH).sub.3) sol. Referring to FIG. 2, FIG. 2 shows photos of the aluminum hydroxide sol after electrochemical dissolving the acidic aluminum salt and the neutralization with the basic solution according to an embodiment of the present disclosure.

[0041] As to the additive described in step S104, sodium chloride (NaCl) or ammonium chloride (NH.sub.4Cl) salt is preferable in this embodiment, the concentration is between 0.01M and 0.5M, and the acid-base value is controlled at pH value between 6 and 8, and then the aluminum hydroxide sol is carried out suction filtration, dried by oven with temperature set 80 to 100° C., or dried at a low temperature by a heating plate with temperature set 80 to 100° C. to obtain nanoscale aluminum hydroxide powder. Referring to FIGS. 3 and 4, they show photos of aluminum hydroxide powder obtained by the aluminum hydroxide sol after suction filtration and drying, and a spectrum of graph of scanning electron microscope of aluminum hydroxide powder according to the embodiment of the present disclosure, it can be seen from the results of electron micrograph that the particle size of aluminum hydroxide powder is about 100 nm, and the particle size of aluminum hydroxide powder without the addition of the additive is about 10 μm, showing the particle size control effect of the additive.

[0042] As to the high temperature roasting described in step S105, temperature control is carried out by heating up to 100° C. at a rate of 10° C./min, holding the temperature for 30 minutes, then heating up to a roasting temperature TA at the rate of 20° C./min, holding the temperature for t hour(s), and finally the furnace is cooled to normal temperature, the roasting temperature TA is between 600° C. and 900° C., and the temperature holding time t is 1 to 5 hours. After the aluminum hydroxide powder is carried out the high temperature roasting, micron scale γ-aluminum oxide powder can be obtained.

[0043] Referring to FIG. 5, FIG. 5 is a spectrum of graph of x-ray diffraction of aluminum oxide powder after high temperature roasting according to the embodiment of the present disclosure, it can be found that aluminum hydroxide can be converted to γ-aluminum oxide under the condition of holding the temperature of 700° C. for 1 hour, but is completely converted to θ-aluminum oxide under the condition of 1000° C. Referring to FIG. 6, FIG. 6 is a spectrum of graph of scanning electron microscope of γ-aluminum hydroxide powder after the high temperature roasting synthesis of 700° C. according to the embodiment of the present disclosure, it can be found from the electron micrograph that the particle size of γ-aluminum hydroxide powder synthesized by the embodiment of the present disclosure is about 5 to 10 μm.

[0044] According to the description of the above-mentioned embodiments, a method for producing aluminum oxide powder by electrochemical dissolving aluminum salt of the present disclosure can improve the dissolving rate of aluminum material and increase the output efficiency of aluminum salt, using aluminum metal as the starting raw material, combined with acidic aluminum salt method and electrochemical dissolution method, and going with the current pulse design. The aluminum salt is carried out the acid-base neutralization to produce an aluminum hydroxide sol, and an additive is added to the sol to control the particle size of the aluminum hydroxide sol, producing nanoscale aluminum hydroxide powder, reducing the roasting temperature of subsequent synthetic aluminum oxide powder, and finally obtaining high-quality micron scale γ-phase aluminum oxide powder after roasting at 600° C. to 900° C. The purpose of the disclosure is to develop γ-phase aluminum oxide powder with characteristics of high purity and low cost, which can be used as a starting material for carbothermic reduction process and can be used for the synthesis of high-purity aluminum nitride powder.

[0045] The above embodiments of the disclosure made only by way of example to describe the feature and effect of the disclosure, and it should not be considered as the scope of substantial technical content is limited thereby. Various possible modifications and alternations of the embodiments could be carried out by the those of ordinary skill in the art without departing from the spirit and scope of the disclosure. Therefore, the scope of the disclosure is based on the appended claims.