Manufacturing method of silica-coated iron oxide powder

Abstract

The present invention relates to a method for manufacturing iron oxide powder coated with SiO2 by performing the synthesis of iron oxide and SiO2 coating in a one-step process, comprising the steps of adding an acid to an iron (Fe) precursor solution to cause a hydrothermal 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 oxide powder, wherein the iron oxide powder has a core-shell structure in which α-Fe2O3 constitutes a core and SiO2 constitutes a shell surrounding the α-Fe2O3. According to the present invention, by performing the synthesis of iron oxide (α-Fe2O3) 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 oxide powder, and more specifically, to a method for manufacturing iron oxide (α-Fe2O3) powder coated with SiO2 by performing the synthesis of α-Fe2O3 powder and SiO2 coating in a one-step process. Background Technology

[0003] Iron oxides, which are abundant on Earth, exist in more than 15 phases composed of oxygen and iron. Among the iron oxides found in nature, γ-Fe2O3, Fe3O4, and α-Fe2O3 are the most common phases.

[0004] Iron oxide is applied in pigments and other materials due to its low cost and eco-friendly properties. Among iron oxides, α-Fe2O3 is useful as a red and purple pigment. α-Fe2O3 has a stable corundum-type crystal structure and is a material that deviates very little from its stoichiometric composition among iron oxides.

[0005] α-Fe2O3 exhibits a vivid red color when at the nano size, but at high temperatures, it aggregates into micro sizes and loses its original red color. Prior art literature

[0007] Republic of Korea Published Patent Application No. 10-2006-0097845 The problem to be solved

[0008] The problem that the present invention aims to solve is to provide a method for manufacturing iron oxide powder in which the synthesis of iron oxide (α-Fe2O3) 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

[0010] The present invention provides a method for manufacturing iron oxide powder coated with SiO2 by performing the synthesis of iron oxide and SiO2 coating in a one-step process, comprising the steps of adding an acid to an iron (Fe) precursor solution to cause a hydrothermal 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 oxide powder, wherein the iron oxide powder has a core-shell structure in which α-Fe2O3 constitutes a core and SiO2 constitutes a shell surrounding the α-Fe2O3.

[0011] The above iron (Fe) precursor solution may contain FeCl3.

[0012] The above iron (Fe) precursor solution may include an aqueous FeCl3 solution in which FlCl3 is dissolved in water (H2O).

[0013] The above acid may include NaH2PO4.

[0014] It is preferable to mix the above iron (Fe) precursor solution and the above acid in a molar ratio of 0.1:1 to 10:1.

[0015] The above SiO2 precursor may include tetraethylorthosilicate.

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

[0017] It is preferable to mix the above SiO2 precursor and the above basic solution in a volume ratio of 0.1:1 to 10:1.

[0018] The SiO2 forming the shell above can have a thickness of 10 to 50 nm. Effects of the invention

[0020] According to the present invention, the synthesis of iron oxide (α-Fe2O3) 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.

[0021] The synthesis of iron oxide (α-Fe2O3) and SiO2 coating can be carried out as a one-step process, and the effect of improving thermal stability can be achieved.

[0022] In addition, by coating SiO2 on the surface of iron oxide (α-Fe2O3), thermal instability issues such as color change can be resolved, and by coating SiO2 on α-Fe2O3 powder, thermal stability can be increased, and color control by changes in reflectance is possible compared to the case where SiO2 is not coated. Brief explanation of the drawing

[0024] Figure 1 is a diagram showing a two-step process for manufacturing iron oxide powder coated with SiO2. Figure 2 is a diagram showing a process flow for synthesizing α-Fe2O3 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 oxide powder according to a preferred embodiment of the present invention is a method for manufacturing iron oxide powder coated with SiO2 by performing the synthesis of iron oxide and SiO2 coating in a one-step process, comprising the steps of adding an acid to an iron (Fe) precursor solution to cause a hydrothermal 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 oxide powder, wherein the iron oxide powder has a core-shell structure in which α-Fe2O3 constitutes a core and SiO2 constitutes a shell surrounding the α-Fe2O3.

[0028] The above iron (Fe) precursor solution may contain FeCl3.

[0029] The above iron (Fe) precursor solution may include an aqueous FeCl3 solution in which FlCl3 is dissolved in water (H2O).

[0030] The above acid may include NaH2PO4.

[0031] It is preferable to mix the above iron (Fe) precursor solution and the above acid in a molar ratio of 0.1:1 to 10:1.

[0032] The above SiO2 precursor may include tetraethylorthosilicate.

[0033] The above basic solution may include water ammonia (NH4OH).

[0034] It is preferable to mix the above SiO2 precursor and the above basic solution in a volume ratio of 0.1:1 to 10:1.

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

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

[0037] Iron oxide is being applied in pigments and other materials due to its low cost and eco-friendly properties. Among iron oxides, α-Fe2O3 is useful as a red and purple pigment. α-Fe2O3 exhibits a vivid red color when at the nanoscale, but at high temperatures, it aggregates into microscale and loses its original red color.

[0038] The inventors of the present invention have researched a method to make α-Fe2O3 powder easier to manufacture and to further enhance its thermal and chemical stability so that it can be widely used for various purposes, such as pigments. The present invention provides a method for producing iron oxide (α-Fe2O3) powder coated with SiO2 by performing the synthesis of α-Fe2O3 powder and SiO2 coating in a one-step process.

[0039] To produce iron oxide powder coated with SiO2 by performing the synthesis of iron oxide and SiO2 coating in a one-step process, an acid is added to an iron (Fe) precursor solution to carry out a hydrothermal reaction. The iron (Fe) precursor solution may contain FeCl3. The iron (Fe) precursor solution may contain an aqueous solution of FeCl3 in which FlCl3 is dissolved in water (H2O). The acid may contain NaH2PO4. It is preferable to mix the iron (Fe) precursor solution and the acid in a molar ratio of 0.1:1 to 10:1. α-Fe2O3 is synthesized by the hydrothermal reaction. It is preferable to add the acid and carry out the hydrothermal reaction under conditions of pH less than 7.

[0040] An SiO2 precursor and a basic solution are added to a solution formed by a hydrothermal reaction, and an atmospheric pressure reaction is carried out. α-Fe2O3 is synthesized by the above hydrothermal reaction, 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 α-Fe2O3 surface due to the SiO2 precursor over time. A core-shell structure is formed by coating SiO2 on the α-Fe2O3 surface. It is preferable to perform the above atmospheric pressure reaction at a temperature ranging from room temperature to about 80°C. In the case of a hydrothermal reaction, high temperature and high pressure conditions are required because the reaction is carried out by vapor pressure resulting from the evaporation of H2O in an aqueous solution, whereas the atmospheric pressure reaction is performed at a relatively low temperature and low pressure at a temperature of 100°C or lower, where water boils. 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). The hydration reaction of tetraethyl orthosilicate (TEOS) occurs in a basic atmosphere. The thickness of SiO2 can be controlled by adjusting the amount of SiO2 precursor, but the thickness of SiO2 can be precisely controlled by adjusting the reaction time. It is preferable that the above SiO2 be coated on the surface of the α-Fe2O3 to 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 α-Fe2O3 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 α-Fe2O3 exhibits transparency and does not affect the color expression of the core material (α-Fe2O3).

[0044] α-Fe2O3 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 α-Fe2O3 powder coated with SiO2.

[0046] Coating α-Fe2O3 powder with SiO2 can improve thermal stability. Color control is possible through changes in reflectance compared to the case without SiO2 coating. The present invention has the advantage of reducing manufacturing time and increasing productivity by simultaneously performing SiO2 coating without a separation process after the synthesis of α-Fe2O3 powder in a one-step process. According to the present invention, α-Fe2O3 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 of synthesizing α-Fe2O3, selectively separating precipitates, washing and drying the precipitates to obtain α-Fe2O3, adding a SiO2 precursor and a basic solution to the α-Fe2O3 and reacting them to coat SiO2, the synthesis of α-Fe2O3 and SiO2 coating are performed in a one-step process, which has the advantage of lowering production costs, simplifying the process to save 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 α-Fe2O3 powder is shown in Fig. 1. Referring to Fig. 1, 0.4 mmol of NaH2PO was added to a 0.2 mol FeCl3 aqueous solution and stirred at 300 rpm for 1 hour. After the hydrothermal reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000 rpm to obtain a precipitate. The precipitate was then washed several times with distilled water and ethanol, and dried in a 60°C dryer for 24 hours to obtain α-Fe2O3 powder.

[0051] The obtained α-Fe2O3 powder 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 were added sequentially to the dispersed solution and stirred for 24 hours to synthesize SiO2-coated α-Fe2O3 powder. After the reaction was finished, 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 α-Fe2O3 powder.

[0052] <Experimental Example 2>

[0053] Figure 2 shows a process flowchart for the one-step synthesis of α-Fe2O3 powder and SiO2 coating. Referring to Figure 2, 0.4 mmol of NaH2PO4 was added to a 0.2 mol FeCl3 aqueous solution and stirred at 300 rpm for 1 hour. After stirring, the solution was subjected to a hydrothermal reaction at 100°C for 48 hours. Subsequently, 300 µL of NH4OH and 150 µL of TEOS were added sequentially to the obtained solution, and the mixture was stirred at room temperature for 4 hours to synthesize SiO2-coated α-Fe2O3 powder. After the reaction, 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 α-Fe2O3 powder.

[0054] SiO2 could be coated on the α-Fe2O3 surface 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 SiO2-coated iron oxide powder by performing the synthesis of iron oxide and SiO2 coating in a one-step process, comprising the step of adding an acid to an iron (Fe) precursor solution to cause a hydrothermal reaction and adding a SiO2 precursor and a basic solution to cause an atmospheric pressure reaction; A method for manufacturing iron oxide powder comprising the step of obtaining iron oxide powder by centrifuging a precipitate formed by a reaction, wherein the iron (Fe) precursor solution and the acid are mixed in a molar ratio of 0.1:1 to 10:1, and the acid is added to carry out a hydrothermal reaction under conditions of pH less than 7, wherein the acid includes NaH2PO4, and the atmospheric pressure reaction is performed at a temperature of 100°C or lower at which water boils, and the iron oxide powder is characterized by having a core-shell structure in which α-Fe2O3 constitutes the core and SiO2 constitutes the shell surrounding the α-Fe2O3. Claim 2 A method for manufacturing iron oxide powder according to claim 1, characterized in that the iron (Fe) precursor solution comprises FeCl3. Claim 3 A method for producing iron oxide powder according to claim 1, characterized in that the iron (Fe) precursor solution comprises an aqueous FeCl3 solution in which FlCl3 is dissolved in water (H2O). Claim 4 delete Claim 5 delete Claim 6 A method for manufacturing iron oxide powder according to claim 1, characterized in that the SiO2 precursor comprises tetraethylorthosilicate. Claim 7 A method for manufacturing iron oxide powder according to claim 1, characterized in that the basic solution comprises ammonia water (NH4OH). Claim 8 A method for manufacturing iron oxide powder according to claim 1, characterized in that the SiO2 precursor and the basic solution are mixed in a volume ratio of 0.1:1 to 10:

1. Claim 9 A method for manufacturing iron oxide 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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