KR102301893B1 - MANUFACTURING METHOD Of LOW SODA ALUMINA POWDER - Google Patents

Abstract

The present invention comprises the steps of adding and mixing a diluted hydrofluoric acid solution to a raw material containing aluminum hydroxide; stirring the mixture to obtain an alumina powder by washing and drying; and calcining the alumina powder to obtain alumina (α-Al ₂ O ₃ ).
According to the manufacturing method of the present invention, it is possible to produce alumina powder with very low soda content and silicon and iron content in the final alumina and low cost, and also to significantly lower impurities such as _{Fe 2} O ₃ and SiO _{2 to increase whiteness.} There are advantages.
In addition, the alumina produced by the method of the present invention has few impurities and thus has excellent electrical insulation as well as mechanical strength, heat resistance, abrasion resistance, corrosion resistance, etc. It can be widely used.

Description

Low soda alumina powder manufacturing method {MANUFACTURING METHOD Of LOW SODA ALUMINA POWDER}

The present invention relates to a method for producing alumina powder having a low soda content.

Most alumina is manufactured by using bauxite mineral as a raw material to obtain aluminum hydroxide manufactured through the Bayer process, and then calcining the aluminum hydroxide at a high temperature. However, in the Bayer process, since bauxite is eluted with an aqueous sodium aluminate solution at a high temperature using NaOH (caustic soda) as a solvent and then precipitated to obtain aluminum hydroxide, soda (soda, Na _{2 ) in aluminum hydroxide} O, etc.) will remain in the powder. As a result, alumina obtained by high-temperature calcination of sodium hydroxide obtained through the Bayer process exhibits unsuitable properties for use in electrical and electronic fields due to its high soda content. _{Alkali components such as Na 2} O and K ₂ O contained in the alumina made in this way deteriorate the electrical insulation performance.

Most alumina is manufactured by firing at high temperature using aluminum hydroxide as a raw material. Referring to the attached Na2O reduction technology 4Page, the raw material, aluminum hydroxide, is naturally present in the form of gibbsite (Al(OH) ₃ ), boehmite (γ-AlOOH), or diaspore (α-AlOOH). When the site loses water molecules when heated to a temperature of 200°C or higher, it is changed to AlOOH form, and when heated to a temperature of 500°C or higher, it is converted into a transition type alumina (γ,η-Al ₂ O _3, etc.), and then at a temperature of about 1100°C or higher Further heating with a furnace produces the most chemically stable alumina (α-alumina) (see formula below):

Al(OH) ₃ + heating (1100~1800℃) → α-Al ₂ O ₃ + 3H ₂ O↑

Aluminum hydroxide used as a raw material may be prepared through a conventional Bayer process.

As such, aluminum hydroxide produced by the Bayer process generally contains trace amounts of impurities. For example, the aluminum hydroxide may include soda in an amount of 0.2 wt% or more. In addition, the aluminum hydroxide _{may further include Fe 2} O ₃ , SiO ₂ and the like as other impurities, and may include these in an amount of 0.1 wt% or less.

_{Alkali components such as Na 2} O and K ₂ O contained in the alumina made in this way deteriorate the electrical insulation performance.

Accordingly, a technique for producing low-sodium alumina by performing a de-soda process during sintering of aluminum hydroxide is used. As a conventional technique for producing low soda alumina, a method of removing soda through heat treatment and washing with water from aluminum hydroxide as a raw material is known, but such a method has insufficient soda removal effect and is uneconomical.

In addition, there is known a method of removing soda using an inorganic acid such as dilute hydrochloric acid instead of using water as described above (refer to Korean Patent Application Laid-Open No. 2001-0046015), but in this method, the hydrochloric acid solution reacts with aluminum hydroxide There is a problem in that aluminum is dissolved. In addition, a method of reducing soda by adding chamotte during sintering of aluminum hydroxide is known, but there is a problem in that the iron content in the final alumina increases due to the iron contained in the chamotte.

In addition, other known general acid treatment methods, Cl ₂ gas reduction methods, etc. have problems such as corrosion of process equipment, process inefficiency, environmental pollution, harm to human body, and deterioration of alumina purity.

It is an object of the present invention to provide a method for manufacturing low-sodium alumina having a low impurity content in order to solve the above problems of the prior art.

The present invention comprises the steps of adding and mixing 3 to 6% by weight of an aqueous hydrofluoric acid solution to dissolving aluminum in a raw material containing aluminum hydroxide; obtaining an alumina powder by stirring the mixture for 1 to 12 hours while heating the mixture from room temperature to ~ 60°C, washing and drying the mixture; and calcining the alumina powder to obtain alumina (α-Al ₂ O ₃ ).

Since dilute hydrofluoric acid has little solubility in aluminum, washing with dilute hydrofluoric acid in aluminum hydroxide can produce alumina with a very low content of impurities such as soda, which is an impurity in aluminum hydroxide, and has the advantage of low manufacturing cost.

In addition, in the hydrofluoric acid aqueous solution, hydrofluoric acid is 1 to 20 wt%, and it is characterized in that it is a dilute hydrofluoric acid aqueous solution. When the hydrofluoric acid concentration is lower than the above range, it is difficult to remove impurities, and when the hydrofluoric acid concentration is too high, aluminum fluoride is generated in addition to alumina.

In addition, as the hydrofluoric acid aqueous solution, it is characterized in that at least one of nitric acid, sulfuric acid, hydrochloric acid, and organic acids such as citric acid, formic acid, and succinic acid is mixed and used together with hydrofluoric acid.

In addition, the calcination temperature of the alumina powder is characterized in that 1100 ℃ or more. In order to lower the content of soda in the alumina powder, it is preferable to calcinate at a temperature above the above temperature (refer to FIG. 8).

_{The alumina (α-Al 2} O ₃ ) powder prepared by the manufacturing method of the present invention has a Na ₂ O content of 0.1 wt% or less, Fe ₂ O ₃ content of 0.05 wt% or less, and a whiteness of 95% or more. . Alumina produced by the method of the present invention has few impurities and thus has excellent electrical insulation as well as mechanical strength, heat resistance, abrasion resistance, corrosion resistance, etc. can be used

According to the method of the present invention, it is possible to produce alumina with a significantly lowered content of soda, an impurity in aluminum hydroxide, by a simple process of washing aluminum hydroxide with dilute hydrofluoric acid having low aluminum solubility.

In addition, Fe ₂ O ₃ , SiO ₂ It has the advantage of increasing the whiteness by significantly lowering impurities, and the soda content and the silicon and iron content in the final alumina are very small compared to the prior art, and the cost is low.

In addition, the alumina produced by the method of the present invention has few impurities and thus has excellent electrical insulation as well as mechanical strength, heat resistance, abrasion resistance, corrosion resistance, etc. It can be widely used.

1 is a comparison of the whiteness of the conventional aluminum hydroxide powder and the pickling product of the present invention.
2 is a graph showing the SEM and color difference values of SG-ALO-L500 (500 nm grade α-Al ₂ O _{3 );}
3 is a graph showing the SEM and color difference values of SG-ALO-L1000 (1 μm grade α-Al ₂ O _{3 );}
Figure 4 is a graph showing the SEM and color difference values of SG-ALO-L4000 (4㎛ grade α-Al ₂ O _{3 );}
5 is a graph showing the SEM and color difference values of SG-ALO-L500UP (500 nm grade α-Al ₂ O _{3 );}
6 is a graph showing the SEM and color difference values of SG-ALO-L1000UP (1 μm grade α-Al ₂ O _{3 );}
7 is a graph showing the SEM and color difference values of SG-ALO-L4000 (4 μm grade α-Al ₂ O _{3 );}
8 is a graph confirming the crystal phase control for each heat treatment temperature,
9 is an XRF showing the change _{in the Na 2} O content according to the heat treatment temperature of the ATH raw material,
10 is an XRF showing the _{Na 2} O content change through the ATH pickling process,
11 is an XRF showing the _{Na 2} O content change through the α-Al ₂ O _{3 pickling process.}

In order to solve the above problem, the present invention comprises the steps of adding and mixing a dilute hydrofluoric acid solution having little reactivity in dissolving aluminum to a raw material containing aluminum hydroxide; and drying it after washing; It provides a method for producing low-sodium alumina, comprising the step of calcining the obtained powder to obtain alumina (α-Al ₂ O _{3 ).}

According to the method of the present invention, it is possible to produce alumina with a significantly lowered content of soda, an impurity in aluminum hydroxide, by a simple process of washing aluminum hydroxide with dilute hydrofluoric acid having low aluminum solubility.

In addition, the alumina produced by this method has few impurities and thus has excellent electrical insulation as well as excellent mechanical strength, heat resistance, abrasion resistance, corrosion resistance, etc., so it can be widely used in various fields such as ceramics, electricity, electronics, optics, machinery, and chemistry. .

In the present invention, 3 to 6% by weight of a dilute hydrofluoric acid aqueous solution is mixed with aluminum hydroxide, stirred for 1 to 12 hours, washed and dried, and then calcined to obtain low-soda alumina powder. In addition, after the aluminum hydroxide is calcined to obtain alumina powder, 3 to 6% by weight of a dilute hydrofluoric acid aqueous solution is mixed, stirred for 1 to 12 hours, and then washed and dried to obtain alumina powder with low soda.

Hereinafter, it will be described in more detail through examples.

Example 1

2 kg of 1㎛ grade aluminum hydroxide powder is added to 5 kg of a dilute 4% by weight aqueous solution of hydrofluoric acid, and the mixture is stirred for 4 hours. After that, it is washed with ultrapure water five times and dried to obtain low-soda aluminum hydroxide powder. This is again heat-treated at 1200° C. for 4 hours to obtain α-phase alumina.

Example 2

After heat-treating 1㎛ grade aluminum hydroxide at 1200°C for 4 hours to obtain α-phase alumina, 2 kg of α-phase alumina powder obtained by heat treatment in 5 kg of a dilute 4 wt% hydrofluoric acid aqueous solution is added and stirred for 4 hours. After that, it is washed with ultrapure water 5 times and dried to obtain a low-soda α-alumina powder.

Example 3

2 kg each of α-alumina powder of 500 nm, 1 μm, and 4 μm was added to 5 kg of a dilute 4 wt% hydrofluoric acid aqueous solution and stirred for 4 hr. After that, it is washed with ultrapure water 5 times and dried to obtain a low-soda α-alumina powder.

Comparative Example 1

2 kg of 1㎛ grade aluminum hydroxide powder is heat treated at 1200°C for 4 hours to obtain α-phase alumina.

<Alumina properties and content>

1. Soda (Na ₂ O) content (using the same lot of aluminum hydroxide raw material)

1) Aluminum hydroxide powder: 0.4455 wt%

2) Aluminum hydroxide heat treatment powder: 0.2495 wt% (see Fig. 9)

3) Aluminum hydroxide acid treatment: 0.2502 wt% (see Fig. 10)

4) Powder treated with acid after aluminum hydroxide heat treatment: 0.0535% (see FIG. 11)

The alumina produced by the above method may have a soda content of 0.1 wt% or less, preferably 0.05 wt% or less, and more preferably about 0.01 to 0.04 wt%.

2. Iron content

The iron content, particularly Fe ₂ O ₃ content, may be 0.05% by weight or less, preferably 0.03% by weight or less. In addition, _{it was confirmed that the silicon (SiO 2} ) content was also slightly reduced in the pickled powder compared to the raw powder.

3. Comparison of whiteness (Comparison of whiteness according to pickling, Example 3)

500nm 1㎛ 4㎛ before pickling 96.84 95.58 93.58 after pickling 98.26 97.33 97.06

As shown in Table 1 and FIGS. 1 to 7, the alumina produced according to the manufacturing method of the present invention may have a whiteness of 95% or more, preferably 97% or more, and more preferably 98% or more. .

Claims (5)

adding and mixing an aqueous hydrofluoric acid solution to a raw material containing aluminum hydroxide, wherein the hydrofluoric acid content in the aqueous hydrofluoric acid solution is 1-20 wt%;
obtaining an alumina powder by stirring the mixture from room temperature to ~60°C while stirring for 1 to 12 hours, washing and drying; and
A method of producing a low-sodium alumina powder, including; calcining the alumina powder at a temperature of 1100° C. or higher to obtain alumina (α-Al ₂ O _{3 ).} delete According to claim 1, wherein the hydrofluoric acid aqueous solution, nitric acid, sulfuric acid, hydrochloric acid, and at least one selected from organic acids (Citric acid, Formic acid, Succinic acid) with hydrofluoric acid, characterized in that the production of low-soda alumina powder Way. delete The low-soda alumina powder prepared by the method according to claim 1 or 3, characterized in that the Na ₂ O content is 0.1 wt% or less, the Fe ₂ O _{3 content is 0.05 wt% or less, and the whiteness is 95% or more.}

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