Manufacturing method of silica-coated iron hydroxide powder

Abstract

The present invention relates to a method for producing iron hydroxide powder coated with SiO2 by performing the synthesis of iron hydroxide and SiO2 coating in a one-step process, comprising the steps of adding iron chloride hydrate to a solvent to cause a solution reaction, adding a SiO2 precursor and a basic solution to cause an atmospheric pressure reaction, and selectively separating a precipitate formed by the reaction to obtain iron hydroxide powder, wherein the iron hydroxide powder has a core-shell structure in which β-FeOOH constitutes a core and SiO2 constitutes a shell surrounding the β-FeOOH. According to the present invention, by performing the synthesis of iron hydroxide (β-FeOOH) and SiO2 coating in a one-step process, the process is simple, requiring less time, increasing productivity, and lowering production costs.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing iron hydroxide powder, and more specifically, to a method for manufacturing iron hydroxide (β-FeOOH) powder coated with SiO2 by performing the synthesis of β-FeOOH powder and SiO2 coating in a one-step process. Background Technology

[0003] Iron hydroxide is applied in pigments and other materials due to its characteristics as a low-cost and eco-friendly material. Since α-FeOOH and β-FeOOH undergo a phase transition to α-Fe2O3 at specific temperatures, they are useful as yellow and red pigments, respectively. However, β-FeOOH undergoes a phase transition to α-Fe2O3 at 500°C, which presents problems of thermal instability, such as color change.

[0004] The inventor of the present invention has disclosed a method for manufacturing iron hydroxide in Korean Registered Patent Publication No. 10-1771005. However, the method for manufacturing iron hydroxide disclosed in Korean Registered Patent Publication No. 10-1771005 consists of a two-step process, and such a two-step process has the disadvantage of requiring a long manufacturing time and having a high production cost. Prior art literature

[0006] Republic of Korea Registered Patent Publication No. 10-1771005 The problem to be solved

[0007] The problem that the present invention aims to solve is to provide a method for manufacturing iron hydroxide powder in which the synthesis of iron hydroxide (β-FeOOH) and SiO2 coating are performed as a one-step process, thereby simplifying the process, reducing the time required, increasing productivity, and lowering production costs. means of solving the problem

[0009] The present invention provides a method for producing iron hydroxide powder coated with SiO2 by performing the synthesis of iron hydroxide and SiO2 coating in a one-step process, comprising the steps of adding iron chloride hydrate to a solvent to cause a solution reaction, adding a SiO2 precursor and a basic solution to cause an atmospheric pressure reaction, and selectively separating a precipitate formed by the reaction to obtain iron hydroxide powder, wherein the iron hydroxide powder has a core-shell structure in which β-FeOOH constitutes a core and SiO2 constitutes a shell surrounding the β-FeOOH.

[0010] The above solvent may include distilled water.

[0011] The above iron chloride hydrate may contain FeCl3·6H2O.

[0012] The above SiO2 precursor may include tetraethylorthosilicate.

[0013] It is preferable to carry out the above solution reaction at a temperature of 60 to 95°C, which is lower than the boiling point of the solvent.

[0014] It is preferable to add 0.1 to 20 g of the above iron chloride hydrate based on 100 g of the above solvent.

[0015] It is preferable to adjust the weight ratio of the above iron chloride hydrate and the above SiO2 precursor to be in the range of 1:0.01 to 10.

[0016] The above basic solution may include water ammonia (NH4OH).

[0017] The SiO2 forming the shell above can have a thickness of 10 to 50 nm. Effects of the invention

[0019] According to the present invention, the synthesis of iron hydroxide (β-FeOOH) and SiO2 coating can be carried out in a one-step process. Compared to a two-step process, this one-step process is simpler, requiring less time, increasing productivity, and lowering production costs.

[0020] The synthesis of iron hydroxide (β-FeOOH) and SiO2 coating can be carried out as a one-step process, and the effect of improving thermal stability can be achieved.

[0021] In addition, by coating SiO2 on the surface of iron hydroxide (β-FeOOH), thermal instability issues such as color change can be resolved, aggregation and oxidation of β-FeOOH powder can be minimized, and color control through changes in reflectance is possible compared to the case where SiO2 is not coated.

[0022] The silica-coated iron hydroxide powder produced by the present invention can be used as a yellow pigment that stably expresses color. Brief explanation of the drawing

[0024] Figure 1 is a diagram showing a two-step process for manufacturing iron hydroxide powder coated with SiO2. Figure 2 is a diagram showing a process flow for synthesizing β-FeOOH powder and SiO2 coating in one step according to Experimental Example 2. Specific details for implementing the invention

[0025] Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. However, the following embodiments are provided to enable those skilled in the art to fully understand the present invention and may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0026] When a component is described as "comprising" another component in the detailed description of the invention or the claims, this shall not be interpreted as being limited to being composed solely of said component unless specifically stated otherwise, but shall be understood as potentially including additional components.

[0027] A method for manufacturing iron hydroxide powder according to a preferred embodiment of the present invention is a method for manufacturing iron hydroxide powder coated with SiO2 by performing the synthesis of iron hydroxide and SiO2 coating in a one-step process, comprising the steps of adding iron chloride hydrate to a solvent to cause a solution reaction, adding a SiO2 precursor and a basic solution to cause an atmospheric pressure reaction, and selectively separating a precipitate formed by the reaction to obtain iron hydroxide powder, wherein the iron hydroxide powder has a core-shell structure in which β-FeOOH constitutes a core and SiO2 constitutes a shell surrounding the β-FeOOH.

[0028] The above solvent may include distilled water.

[0029] The above iron chloride hydrate may contain FeCl3·6H2O.

[0030] The above SiO2 precursor may include tetraethylorthosilicate.

[0031] It is preferable to carry out the above solution reaction at a temperature of 60 to 95°C, which is lower than the boiling point of the solvent.

[0032] It is preferable to add 0.1 to 20 g of the above iron chloride hydrate based on 100 g of the above solvent.

[0033] It is preferable to adjust the weight ratio of the above iron chloride hydrate and the above SiO2 precursor to be in the range of 1:0.01 to 10.

[0034] The above basic solution may include water ammonia (NH4OH).

[0035] The SiO2 forming the shell above can have a thickness of 10 to 50 nm.

[0036] Hereinafter, a method for manufacturing iron hydroxide powder according to a preferred embodiment of the present invention will be described in more detail.

[0037] Iron hydroxide is applied in pigments and other materials due to its characteristics as a low-cost and eco-friendly material. Since α-FeOOH and β-FeOOH undergo a phase transition to α-Fe2O3 at specific temperatures, they are useful as yellow and red pigments, respectively. However, β-FeOOH undergoes a phase transition to α-Fe2O3 at 500°C, which presents problems of thermal instability, such as color change.

[0038] The inventors of the present invention have investigated a method to make β-FeOOH powder easier to manufacture and to further enhance its thermal and chemical stability so that it can be widely used as a pigment for various purposes. The present invention provides a method for producing iron hydroxide (β-FeOOH) powder coated with SiO2 by performing the synthesis of β-FeOOH powder and SiO2 coating in a one-step process.

[0039] A solution reaction is carried out by adding ferric chloride hydrate (e.g., FeCl3·6H2O) to a solvent such as deionized water. It is preferable to add 0.1 to 20 g, more specifically 1 to 15 g, of the ferric chloride hydrate per 100 g of solvent. β-FeOOH is synthesized through the solution reaction. It is preferable to carry out the solution reaction for 1 to 72 hours at a temperature of approximately 60 to 95°C, which is lower than the boiling point of the solvent. To prevent a rapid reaction and maintain a constant temperature, it is preferable to carry out the solution reaction by placing a container holding the ferric chloride hydrate solution into a bath containing oil and using an oil bath method. In the present invention, β-FeOOH powder is synthesized using a low-temperature solution reaction rather than a hydrothermal reaction. By utilizing a low-temperature solution reaction, there are advantages such as ease of manufacturing and reduced manufacturing costs.

[0040] While carrying out a solution reaction, an SiO2 precursor and a basic solution are added to carry out an atmospheric pressure reaction. Through the above solution reaction, β-FeOOH is synthesized, and SiO2 can be coated on the surface through reaction with the SiO2 precursor. The thickness of the SiO2 coating varies depending on the reaction time, and silica (SiO2) growth occurs on the β-FeOOH surface due to the SiO2 precursor over time. A core-shell structure is formed by coating SiO2 on the β-FeOOH surface. It is preferable to perform the above atmospheric pressure reaction at a temperature of 60 to 95°C. In the case of a hydrothermal reaction, the reaction is carried out using vapor pressure resulting from the evaporation of H2O in an aqueous solution, requiring high temperature and high pressure conditions; whereas the atmospheric pressure reaction is carried out at a relatively low temperature and low pressure at a temperature below 100°C, where water boils, making the reaction easier compared to the hydrothermal reaction. Unlike hydrothermal reactions, atmospheric pressure reactions have the advantage of allowing silica precursors to be added during the reaction for processes such as SiO2 coating and surface modification.

[0041] The above SiO2 precursor may be tetraethyl orthosilicate (TEOS), and it is preferable to adjust the weight ratio of iron chloride hydrate to the SiO2 precursor to be in the range of 1:0.01 to 10. The hydration reaction of tetraethyl orthosilicate (TEOS) occurs in a basic atmosphere. The thickness of the SiO2 can be controlled by adjusting the amount of the SiO2 precursor, but the thickness of the SiO2 can be precisely controlled by adjusting the reaction time. It is preferable to coat the above SiO2 onto the surface of the β-FeOOH with a thickness of 10 to 50 nm.

[0042] The above basic solution may be ammonia water (NH4OH), etc. SiO2 coating may be achieved by coating using a SiO2 precursor in a basic solution (e.g., ammonia water (e.g., pH 8 or higher)).

[0043] SiO2 (silica) is coated on the surface of the synthesized β-FeOOH to form a core-shell type structure. SiO2 has the advantages of being thermally stable, having good permeability, easy thickness control, and easy surface modification. In addition, it is non-toxic and colorless, physically and chemically stable, and has good weather resistance and durability. The SiO2 coated on the surface of β-FeOOH exhibits transparency and does not affect the color expression of the core material (β-FeOOH).

[0044] β-FeOOH powder coated with SiO2 can be obtained by selectively separating the precipitate from the reaction product and drying it. Selective separation can be performed using a centrifuge, for example, by centrifuging at 8,000 rpm for 10 minutes using a centrifuge to selectively separate the precipitate.

[0045] The precipitate selectively separated may undergo washing and drying processes, for example, by washing with distilled water, ethanol, etc., and drying in an oven at 30 to 80°C to obtain β-FeOOH powder coated with SiO2.

[0046] When SiO2 is coated on the surface of β-FeOOH, the aggregation and oxidation of the β-FeOOH powder can be minimized. Compared to the case where SiO2 is not coated, color control through changes in reflectance is possible. The present invention has the advantage of reducing manufacturing time and increasing productivity by simultaneously performing SiO2 coating after the synthesis of β-FeOOH powder in a one-step process without a separation process. According to the present invention, β-FeOOH synthesis and SiO2 coating can be carried out in a one-step process by adjusting the pH without adding additional surface modifiers.

[0047] According to the present invention, compared to a method that requires performing a two-step process in which β-FeOOH is synthesized, a precipitate is selectively separated, and then the precipitate is washed and dried to obtain β-FeOOH, and then an SiO2 precursor and a basic solution are added and reacted to coat SiO2, the synthesis of β-FeOOH and SiO2 coating are performed in a one-step process, so the production cost can be lowered, and the process is simple, requiring less time and increasing productivity.

[0048] In the following, specific experimental examples according to the present invention are presented, but the present invention is not limited to the experimental examples presented below.

[0049] <Experimental Example 1>

[0050] A two-step process diagram for preparing SiO2-coated iron hydroxide powder is shown in Fig. 1. Referring to Fig. 1, 0.2 mol of FeCl3·6H2O was dissolved in 100 ml of distilled water with stirring, and then stirred for 12 hours at a water bath temperature of 80°C. The reaction product was washed several times using centrifugation and dried in a 60°C dryer for 24 hours to obtain β-FeOOH.

[0051] The obtained β-FeOOH was added to a mixed solution of 9 mL of distilled water and 21 mL of ethanol and dispersed. 300 µL of NH4OH and 150 µL of TEOS (tetraethylorthosilicate) were added sequentially to the solution in which β-FeOOH was dispersed, and the mixture was stirred for 24 hours to coat the β-FeOOH with SiO2. After the reaction was complete, the precipitate was obtained by centrifugation at 8000 rpm, washed several times with distilled water and ethanol, and dried in a 60°C dryer for 24 hours to obtain SiO2-coated β-FeOOH.

[0052] <Experimental Example 2>

[0053] Figure 2 shows a process flowchart for the one-step synthesis of β-FeOOH powder and SiO2 coating. Referring to Figure 2, 5.4 g of FeCl3·6H2O was dissolved in 100 g of distilled water by stirring, and then stirred for 12 hours at a water bath temperature of 80°C. 10 ml of NH4OH and 14 ml of TEOS (tetraethylorthosilicate) were added sequentially to the reacting solution and stirred for 24 hours to synthesize SiO2-coated β-FeOOH. After the reaction was complete, the precipitate was obtained by centrifugation at 8000 rpm, washed several times with distilled water and ethanol, and dried in a 60°C dryer for 24 hours to obtain SiO2-coated β-FeOOH.

[0054] SiO2 could be coated on the surface of β-FeOOH powder through a one-step process.

[0055] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible by those skilled in the art.

Claims

Claim 1 A method for producing iron hydroxide powder coated with SiO2 by performing the synthesis of iron hydroxide and SiO2 coating in a one-step process, comprising: a step of adding iron chloride hydrate to a solvent to cause a solution reaction while adding a SiO2 precursor and a basic solution to cause an atmospheric pressure reaction; and a step of selectively separating a precipitate formed by the reaction to obtain iron hydroxide powder, wherein 1 to 15 g of the iron chloride hydrate is added based on 100 g of the solvent, the atmospheric pressure reaction is performed at a temperature of 60 to 95°C, the basic solution contains ammonia water (NH4OH), and the iron hydroxide powder is characterized by having a core-shell structure in which β-FeOOH constitutes a core and SiO2 constitutes a shell surrounding β-FeOOH. Claim 2 A method for manufacturing iron hydroxide powder according to claim 1, wherein the solvent comprises distilled water. Claim 3 A method for manufacturing iron hydroxide powder according to claim 1, characterized in that the iron chloride hydrate comprises FeCl3·6H2O. Claim 4 A method for manufacturing iron hydroxide powder according to claim 1, characterized in that the SiO2 precursor comprises tetraethylorthosilicate. Claim 5 A method for manufacturing iron hydroxide powder according to claim 1, characterized in that the solution reaction is performed at a temperature of 60 to 95°C, which is lower than the boiling point of the solvent. Claim 6 delete Claim 7 A method for manufacturing iron hydroxide powder according to claim 1, characterized in that the iron chloride hydrate and the SiO2 precursor are adjusted to have a weight ratio in the range of 1:0.01 to 10. Claim 8 delete Claim 9 A method for manufacturing iron hydroxide powder according to claim 1, characterized in that the SiO2 forming the shell has a thickness of 10 to 50 nm.

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