Iron carbonyl powder and manufacturing method thereof

Abstract

To provide an industrially practicable manufacturing method of an iron carbonyl powder from which deposits on a surface have been removed and an iron carbonyl powder from which deposits on a surface have been removed by this method, and to provide a magnetic particle comprising an iron carbonyl powder with a surface uniformly coated with a titanium oxide film by the removal of deposits on the surface of the iron carbonyl powder.SOLUTION: A manufacturing method of an iron carbonyl powder includes a step of subjecting an iron carbonyl powder to vacuum treatment at a pressure of 50 Pa or under for 6 hrs or over in a vacuum deaeration atmosphere, followed by a step of atmosphere opening until the pressure of the vacuum deaeration atmosphere becomes at an atmospheric pressure of 1.0×105 Pa in 1 hr or over.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to carbonyl iron powder and a method for producing the same. [Background technology]

[0002] Microsized carbonyl iron particles (hereinafter referred to as "carbonyl iron powder") are widely used as magnetic particles for a variety of purposes, including magnetic inks, magnetic toner pigment powders, magnetic filler powders for plastics and paper, cosmetic powders, magnetorheological fluids, and photocatalytic powders. Magneto-magnetic fluids (MRFs), suspensions of magnetic particles, are also used in dampers, brakes, clutches, valves, and other applications due to their unique rheological properties. However, carbonyl iron powder easily oxidizes when exposed to air or moisture, resulting in a loss of magnetic and magnetorheological properties. To prevent surface oxidation, a method has been developed in which carbonyl iron particles are coated with an inert material. Examples of such inert materials include titanium dioxide, silicon oxide, zinc oxide, aluminum phosphate, and graphene oxide, which are stable in air and moisture. Methods for coating metal powder with a titanium oxide film include a method using a tetraisopropoxytitanium solution (Patent Document 1: Japanese Patent No. 4804720), and a method in which base particles are suspended in a buffer solution of pH 7.0 to 12.0 to form a suspension, and a hydrogen peroxide-ammonia mixture containing peroxotitanic acid is added dropwise to the suspension to cause a reaction that produces titanium oxide in the suspension (Patent Document 2: Japanese Patent No. 4205582).

[0003] The methods described in Patent Documents 1 and 2 were able to coat carbonyl iron powder with a titanium oxide film, but some carbonyl iron powder could not be uniformly coated with the titanium oxide film, and these methods left room for improvement. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4804720 [Patent Document 2] Patent No. 4205582 [Non-patent literature]

[0005] [Non-Patent Document 1] Hideyuki Yamamoto, "Degreasing and Cleaning Technology in Plating Pretreatment", Surface Technology, Vol. 69, No. 9, 376-379 (2018) [Non-patent document 2] "The crystal sttuctures of carbonyl iron powder revised using in situ synchrotron XRPD", Zeitschrift fur Kristallographie - Crystalline Materials 232(12), (January 2017) Summary of the Invention [Problem to be solved by the invention]

[0006] One possible reason for the inability to form a uniform titanium oxide film is the presence of deposits or oxides on the surface of the carbonyl iron powder, and the surface deposits are thought to be volatile impurities containing nitrogen derived from the carbonyl iron powder synthesis process (Non-Patent Document 2). Carbonyl iron powder is generally synthesized by decomposing iron pentacarbonyl Fe(CO)5 using carbon monoxide (CO) gas at high temperatures (250-300°C) and high pressures (e.g., 200 bar). Because the disproportionation of CO to CO2 or graphite occurs simultaneously with the decomposition, NH3 gas is used as an inhibitor to minimize the disproportionation of CO. Therefore, it was thought that nitrogen components from the NH3 gas used as an inhibitor adhere to the surface of the carbonyl iron powder.

[0007] The cleaning treatment (degreasing treatment) of the metal surface of raw iron powder and the like is generally carried out using an aqueous sodium hydroxide solution (Non-Patent Document 1). However, with the general degreasing treatment of metal surfaces, it is difficult to remove the small amount of deposits on the surface of carbonyl iron powder.

[0008] As mentioned above, previous metal surface cleaning processes have had difficulty removing deposits from the surface of carbonyl iron powder. This has made it difficult to uniformly coat carbonyl iron powder with a titanium oxide film on the surface of carbonyl iron powder with deposits. Furthermore, the particle size of the carbonyl iron powder base material is very small, with a median diameter of approximately 5 μm, which poses a high risk of fire and heat generation when surface deposits are removed by heating, making this method unsuitable for industrial application. Therefore, there has been a demand for carbonyl iron powder from which surface deposits have been removed, and an industrially feasible method for producing carbonyl iron powder from which surface deposits have been removed. Based on the above, the present invention provides an industrially practicable method for producing carbonyl iron powder from which surface deposits have been removed, and carbonyl iron powder from which surface deposits have been removed by said method. The present invention also provides magnetic particles that use carbonyl iron powder from which surface deposits have been removed as a base material, and that have the surface of the carbonyl iron powder uniformly coated with a titanium oxide film. [Means for solving the problem]

[0009] To solve the above problems, the present invention employs the following means. (1) A process of subjecting carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 50 Pa or less for 6 hours or more, and a process of subjecting the carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 1.0 × 10 atmospheric pressure or less for 6 hours or more. 5 and exposing the mixture to the atmosphere for at least one hour until the temperature reaches a temperature of 1 Pa. <2> Carbonyl iron powder obtained by the method described in <1>. <3> The carbonyl iron powder according to <2>, wherein the N fraction on the surface of the carbonyl iron powder is 2.0 atm% or less. <4> The carbonyl iron powder according to <2> or <3>, wherein the particle size of the carbonyl iron powder is 0.5 to 70 μm. <5> The carbonyl iron powder according to <2> or <3>, wherein the coefficient of variation (CV) of the carbonyl iron powder is 0.3 to 0.6. <6> A powder composition in which the surface of carbonyl iron powder is coated with an inert material. <7> The powder composition according to <6>, wherein the inert material is at least one of titanium oxide, silicon oxide, zinc oxide, aluminum phosphate, and graphene oxide. <8> A copy toner made of carbonyl iron powder as described in <2>. <9> A magnetic ink made of carbonyl iron powder as described in <2>. <10> An MR fluid made of carbonyl iron powder as described in <2>. <11> Magnetic particles having a titanium oxide film on the surface of the carbonyl iron powder according to <2>. <12> Magnetic particles having a titanium oxide film according to <11>, which have an oxidation onset temperature of 437.1°C or higher. <13> A process of subjecting carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 50 Pa or less for 6 hours or more, and a process of subjecting the carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 1.0 × 10 atmospheric pressure or less for 6 hours or more. 5 The method for producing magnetic particles comprises the steps of: exposing the mixture to the atmosphere for at least one hour until the temperature reaches a temperature of 1 Pa to obtain carbonyl iron powder; and further coating the surface of the carbonyl iron powder with a titanium oxide film to obtain magnetic particles. [Effects of the Invention]

[0010] According to the present invention, it is possible to industrially remove deposits from the surface of carbonyl iron powder and provide carbonyl iron powder from which surface deposits have been removed. Furthermore, by removing deposits from the surface of carbonyl iron powder, the present invention makes it possible to uniformly coat the surface of the carbonyl iron powder with a titanium oxide film. This improves the antioxidant stability compared to carbonyl iron powder that is not sufficiently coated with a titanium oxide film. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are SEM photographs of the carbonyl iron powder of the example. [Figure 2] 2A and 2B are SEM photographs of the carbonyl iron powder of the comparative example. [Figure 3]Figure 3 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of the carbonyl iron powder surfaces of the Examples, Comparative Examples, and Reference Examples. Figure 3A shows an XPS survey spectrum. Figure 3B shows the results of XPS surface elemental analysis of the carbonyl iron powders of the Examples, Comparative Examples, and Reference Examples in the N 1s region and Figure 3C shows the results of XPS surface elemental analysis in the Fe 2p region. [Figure 4] Figure 4 shows the results of XPS depth profiles (depth direction analysis). Figure 4A shows the results of XPS depth direction analysis of the carbonyl iron powder of the comparative example in the Fe 2p region. Figure 4B shows the peak intensity ratio of Fe / Fe oxide calculated from the depth profile. [Figure 5] 5A and 5B are cross-sectional TEM images of the carbonyl iron powder of the comparative example. [Figure 6] Figure 6 shows the results of X-ray photoelectron spectroscopy (XPS) analysis of the chemical composition of the surface of the titanium oxide film-coated carbonyl iron powders of the Example, Comparative Example, and Reference Example. Figure 6A shows the results of XPS analysis of the surface elemental state of the titanium oxide film-coated carbonyl iron powders of the Example, Comparative Example, and Reference Example in the Ti 2p region, Figure 6B shows the results of XPS analysis of the surface elemental state of the titanium oxide film-coated carbonyl iron powders of the Example, Comparative Example, and Reference Example in the Fe 2p region, and Figure 6C shows the results of XPS analysis of the surface elemental state of the titanium oxide film-coated carbonyl iron powders of the Example, Comparative Example, and Reference Example in the O 1s region. [Figure 7] 7A and 7B are SEM photographs of the carbonyl iron powder of the example coated with a titanium oxide film. [Figure 8] 8A and 8B are SEM photographs of the carbonyl iron powder of the comparative example coated with a titanium oxide film. [Figure 9] Figure 9A is a cross-sectional TEM image of the carbonyl iron powder coated with a titanium oxide film according to the present invention. Figures 9B, 9C, and 9D are the results of elemental mapping by EDX, with Figure 9B showing titanium, Figure 9C showing iron, and Figure 9D showing oxygen. [Figure 10] FIG. 10 shows the magnetic hysteresis loops of the carbonyl iron powder of the Examples and the carbonyl iron powder of the Examples, Comparative Examples, and Reference Examples coated with a titanium oxide film. [Figure 11] FIG. 11 shows TG curves of the carbonyl iron powder of the Examples and the carbonyl iron powder of the Examples, Comparative Examples, or Reference Examples coated with a titanium oxide film. [Figure 12]12A and 12B are SEM photographs of the carbonyl iron powder of the reference example. [Figure 13] FIG. 13 is a cross-sectional TEM image of the carbonyl iron powder of the reference example. [Figure 14] 14A and 14B are SEM photographs of the carbonyl iron powder of the reference example coated with a titanium oxide film. [Figure 15] Fig. 15 is a cross-sectional TEM image of the carbonyl iron powder of the reference example coated with a titanium oxide film, and Fig. 15B is a high-magnification visual field observation result of Fig. 15A. [Figure 16] Figure 16A is a cross-sectional TEM image of a reference carbonyl iron powder coated with a titanium oxide film. Figures 16B, 16C, and 16D are the results of elemental mapping by EDX, with Figure 16B showing titanium, Figure 16C showing iron, and Figure 16D showing oxygen. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below with reference to embodiments, but the present invention is not limited to the following embodiments. [Method for producing carbonyl iron powder from which surface deposits have been removed] The method for producing carbonyl iron powder from which surface deposits have been removed according to the embodiment includes the steps of: (A) subjecting the carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 50 Pa or less for 6 hours or more; (b) The pressure of the vacuum degassing atmosphere is 1.0 x 10 atmospheric pressure. 5 and a step of opening the container to the atmosphere for at least one hour until the temperature reaches 1 Pa.

[0013] (A) (Vacuum degassing treatment of carbonyl iron powder) The upper limit of the pressure of the vacuum degassing atmosphere is preferably 50 Pa or less, more preferably 10 Pa or less. The lower limit is preferably 0.1 Pa or more, more preferably 0.6 Pa or more. Pressures below 0.1 Pa are in a pressure range called a high vacuum range, and generally, degassing cannot be achieved using an inexpensive oil rotary vacuum pump, making industrial processing difficult. The pressure of the vacuum degassing atmosphere is preferably maintained in the range of 50 Pa to 0.1 Pa. In this case, the range of 10 Pa to 0.6 Pa is more preferable. The reduced pressure treatment time for carbonyl iron powder is preferably 6 hours or more. If it is less than 4 hours, it is not possible to sufficiently remove deposits from the surface.

[0014] (b) (Open to the atmosphere) After reducing the pressure of carbonyl iron powder in a vacuum degassed atmosphere, the pressure was reduced to 1.0 × 10 5 It is preferable to expose the apparatus to the atmosphere for at least one hour until the pressure reaches Pa. If the pressure is less than one hour, the iron powder may burn due to the sudden introduction of oxygen, causing a dust explosion inside the apparatus, so it is preferable to expose the apparatus to the atmosphere for at least one hour.

[0015] [Carbonyl iron powder] According to the present embodiment, in addition to the method for producing carbonyl iron powder from which surface deposits have been removed, carbonyl iron powder produced by the production method is also provided. The carbonyl iron powder preferably has a surface N fraction of 2.0 atm % or less. The particle size of the carbonyl iron powder is preferably 0.5 to 70 μm, more preferably 0.5 to 20 μm, and even more preferably 0.5 to 10 μm. The CV value, which is the coefficient of variation of the particle size of the carbonyl iron powder, is preferably 0.1 to 0.3. The particle size of the carbonyl iron powder can be measured using various devices, and is not particularly limited. For example, it can be measured using the laser light diffraction scattering method (Microtrac MT3300EXII, Nikkiso Co., Ltd.) described below.

[0016] The raw materials used to produce carbonyl iron powder are not particularly limited, and various materials can be used. Commercially available raw materials may be used. For example, EM grade carbonyl iron powder manufactured by BASF can be used.

[0017] (Inert material coated powder composition) The carbonyl iron powder described above has had all of its surface deposits removed, allowing various films to be uniformly coated on the surface of the carbonyl iron powder, which makes it less susceptible to oxidation even when exposed to air without impairing its magnetic properties. Due to these properties, in addition to the above-mentioned production method, this embodiment provides a powder composition in which the surface of carbonyl iron powder is coated with an inert material, such as titanium oxide, silicon oxide, zinc oxide, aluminum phosphate, or graphene oxide. Specifically, magnetic particles are provided in which the surface of carbonyl iron powder is coated with a titanium oxide film. As will be explained in the Examples section below, these magnetic particles have the advantageous effect of having higher antioxidative stability than carbonyl iron powder before being coated with a titanium oxide film. When these magnetic particles are exposed to a heated atmosphere, their oxidation onset temperature is 437.1°C or higher.

[0018] (Titanium oxide coating treatment)

[0019] The buffer solution used in the titanium oxide coating treatment to suspend the base particles is not particularly limited as long as it is neutral or weakly alkaline with a pH of 7.0 to 12.0, but specific examples include Tris-based, boric acid-based, borate-based, phosphoric acid-based, phosphate-based, glycine-based, and carbonate-based solutions.

[0020] The hydrogen peroxide-ammonia mixed solution containing peroxotitanic acid used in the titanium oxide coating treatment is not particularly limited, but it is preferable that the pH be higher than that of the buffer solution in which the base particles are suspended. The method for preparing the mixture is not particularly limited, but the following method may be mentioned. (1) A method of directly preparing titanium hydroxide by mixing a raw material (hereinafter also referred to as a titanium source) such as titanium alkoxide, titanium chloride solution, titanium sulfate solution, etc., which produces titanium hydroxide when mixed with ammonia water alone, with ammonia water and hydrogen peroxide water. The valence of Ti in the titanium source used in this method may be not only tetravalent but also trivalent. For example, titanium chloride (III) may be used. (2) A method of preparing the product by mixing aqueous ammonia and aqueous hydrogen peroxide with a yellow transparent solution product that already contains peroxotitanic acid, such as "New TAS Fine" manufactured by Furuuchi Chemical Co., Ltd., or "PTA Solution" manufactured by Tanaka Transcription Co., Ltd. based on Patent No. 2938376.

[0021] In the titanium oxide coating treatment, the reaction temperature when a hydrogen peroxide-ammonia mixture containing peroxotitanic acid is dropped into a suspension of base particles to cause a titanium oxide deposition reaction by decomposition of peroxotitanic acid is not particularly limited. Rather, as an advantage, by maintaining the base particle suspension at a neutral or weakly alkaline pH of 7.0 to 12.0, the film formation reaction can be carried out at room temperature of 5 to 50°C. Furthermore, the titanium oxide film formed by the decomposition reaction of the peroxotitanium complex can be used as a transparent film and can be combined with other transparent metal hydroxide films or metal oxide films to form a multilayer structure. In this case, special functions can be imparted by adjusting the thickness of each layer of the multilayer coating film (layers of films that coat the base particles and can be involved in light interference). For example, by coating the powder with multiple layers of the above-mentioned titanium oxide film or other materials, a light interference multilayer thin film can be formed, and by wavelength-selective light reflection, the powder can be vividly colored in a desired color system without using pigments or dyes.

[0022] In this case, it is necessary to select in advance the material of the base particles, the shape of the base particles, the particle size of the base particles, the number of coating layers, the coating order of each coating layer, the material of each coating layer, and the desired wavelength of reflected light. In particular, selecting the materials of the base particles and each coating layer naturally specifies their complex refractive indices. The determination of the complex refractive index of the base particle and each coating layer is involved in the calculation of the Fresnel reflection coefficient and amplitude reflection intensity between each layer. By selecting the shape of the base particles, correction based on the particle shape, which will be described later, may be required. By selecting the particle size of the base particles, the curvature of the base particles and the multilayer film is specified. If the curvature is not specified, it becomes difficult to correct the spectrophotometric characteristics for film thickness monitoring, which will be described later. The selection of the number of coating layers contributes to the determination of the Rflat value, which will be described later. The reflection intensity Rflat of a multilayer film when the base particle is flat can be determined by applying the preselected base particle material (complex refractive index), the number of coating layers, the coating order of each coating layer, the material (complex refractive index) of each coating layer, and the desired reflected light wavelength to the following recurrence formula 1 and solving it.

[0023]

number

[0024] (where Rj+1,j is the amplitude reflection intensity between the jth layer from the bottom and the layer immediately above it, j: an integer of 1 or more (j-1=0 indicates the base), i: imaginary unit, rj+1,j: Fresnel reflection coefficient of the interface between the jth layer from the bottom and the layer immediately above it, Rj,j-1: Amplitude reflection strength between the j-1th layer from the bottom and the layer immediately above it, 2δj: phase difference in the jth layer from the bottom, λ: desired reflected light wavelength, nj: complex refractive index of the jth layer from the bottom, dj: thickness of the jth layer from the bottom, φj: The angle of incidence of light on the jth layer from the bottom.

[0025] The method for correcting the multilayer film reflection intensity Rflat obtained as described above based on the shape of the base particles is not particularly limited. When the particle shape is spherical, semi-spherical, or irregular, the Rflat value can be further calculated by the following formula 2.

[0026]

number

[0027] (where θ is the angle of incidence onto the outermost layer) and find the film thickness of each coating layer so that the R(λ) value becomes maximum or minimum at the desired wavelength. Applying the Rflat value to the above equation 2 means correcting the solution of the above equation 1 by approximating the angular distribution of the light incident angle onto the multilayer-coated powder to the light incident angle distribution onto one coated hemisphere. When determining the thickness of each coating film, it is efficient to use a computer simulation.

[0028] Next, each coating film is formed on the base particles so as to have the film thickness determined as above. However, as mentioned above, in the actual film-forming operation of a multilayer coated powder, it is impossible to directly monitor the actual film thickness until the film thickness reaches the designed value. Therefore, one way to monitor the film thickness during the film-forming operation is to use a spectrophotometer to measure the wavelength at which the reflection intensity of the coated object coated with each coating layer reaches its maximum or minimum value, and to terminate the film-forming operation when the maximum or minimum reflection wavelength value corresponding to the film thickness is reached. However, when the substrate is a powder, the curvature of each coating layer, which depends on the particle shape and particle diameter, can cause distortions in the relationship between the measured maximum or minimum reflection wavelength and the film thickness.If a film is formed so that the maximum or minimum reflection wavelength measured by a spectrophotometer is the desired value, the final multilayer-coated powder will not have the desired reflection intensity at the desired wavelength.

[0029] Therefore, correction is required based on the curvature of each coating layer, which depends on the shape and particle diameter of the base particle. The correction method is not particularly limited, but it is preferable to coat selected coating layers on selected base particles with several different film thicknesses in stages to form particle size correction film-coated powders, measure the actual film thickness (dM) of each coating layer of the particle size correction film-coated powders, measure each of the film-coated powders with a spectrophotometer to determine the optical film thickness (nd) of each coating layer of each particle size correction film-coated powder, determine the ratio (nd / ndM) of the optical film thickness (nd) of each coating layer to the product (ndM) of the actual film thickness of each coating layer of each particle size correction film-coated powder and the real term (n) of the complex refractive index, multiply 2δj in the above recurrence formula 1 for determining the multilayer film reflection intensity by the above ratio (nd / ndM) to correct the spectrophotometric characteristics of the powder having each coating layer, and form each coating layer so as to achieve the corrected spectrophotometric characteristics.

[0030] The method for measuring the actual film thickness (dM) of each coating layer of the particle size correction film-coated powder is not particularly limited, but it is preferable to cut each of the particle size correction film-coated powders and measure from the cut surface. When cutting the particle size correction film-coated powder, it is preferable to use focused ion beam (FIB) processing, as this makes the cut surface clear and is suitable for measuring the actual film thickness (dM) of each coating layer.

[0031] Next, a multilayer coated powder is produced so that each coating film has the corrected spectrophotometric characteristics determined as described above. In order to obtain a bright colored powder of a desired color system by coating with an optical interference multilayer thin film, it is preferable to perform multilayer coating as described above. However, if the thickness of a single layer coated on a base particle is simply calculated from the spectrophotometric characteristics with an error of approximately 10%, the imaginary term of the complex refractive index in the above formula 1 can be set to 0, and the following formula 3 can be used, which is derived by setting j=1 and φ≡0.

[0032]

number

[0033] (where n is the real term of the complex refractive index of the single layer film, k is the interference order, and λ is the peak or valley wavelength.) [Example]

[0034] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0035] (1) Sample The raw material carbonyl iron powder used was EM grade carbonyl iron powder manufactured by BASF (hereinafter referred to as "untreated carbonyl iron powder"). The median diameter of the untreated carbonyl iron powder was 4.6 μm. The untreated carbonyl iron powder had an ammonia-like odor, suggesting that the surface was covered with impurities.

[0036] (2) Preparation of carbonyl iron powder (Example) Untreated carbonyl iron powder (100 kg to 200 kg per unit) was loaded into the vacuum degassing equipment, and the equipment was then sealed. The oil rotary vacuum pump [GLD-202, manufactured by ULVAC] attached to the equipment was then operated, and the pressure inside the equipment was reduced until the value (internal pressure value) displayed on the vacuum gauge [CC-10, manufactured by Tokyo Electronics Co., Ltd.] was 50 Pa or less. The reduced pressure state was continued for 6 hours, starting from the time when the internal pressure value reached 50 Pa. During this time, the internal pressure value of the equipment was maintained between 50 Pa and 0.6 Pa. After that, the pressure inside the treatment device was reduced to atmospheric pressure (1.0 × 10 5 These steps resulted in a degassed carbonyl iron powder (hereinafter referred to as "vacuum degassed carbonyl iron powder").

[0037] (Comparative Example) Untreated carbonyl iron powder served as a comparative example.

[0038] (Reference example) To oxidize the surface of the untreated carbonyl iron powder, 49 g of the untreated carbonyl iron powder was suspended in 500 ml of a 0.10 M boric acid solution (pH 5.0) at 50°C for 30 minutes with stirring, and the particles were then recovered. The resulting oxidized carbonyl iron powder was used as a reference example.

[0039] (3) Titanium oxide film formation on carbonyl iron powder Deionized water, ammonia water, and tetraisopropoxytitanium (Ti[OCH(CH3)2]4) as a Ti raw material were placed in a beaker and stirred and mixed for 5 minutes using a Teflon-coated magnetic stirrer bar. Next, hydrogen peroxide water was added and stirred and mixed for an additional 10 minutes to prepare a peroxotitanic acid solution, which is a titanium oxide film coating raw material solution. The concentrations of ammonia water, titanium, and hydrogen peroxide water in the peroxotitanic acid solution were approximately 4.3 M, 0.29 M, and 2.0 M, respectively, and the volume of the mixture was 27.6 ml. Separately, a Clark & Lubs buffer solution at pH 9.0 was prepared by mixing 0.40 M boric acid, potassium chloride solution, and 0.40 M sodium hydroxide solution. 122.5 g of the carbonyl iron powder from each of the Examples, Comparative Examples, and Reference Examples was added to 140 ml of the buffer solution weighed into a beaker, dispersed using a SUS304 stirring rod and impeller, and stirred and suspended in a water bath at 50°C. The peroxotitanic acid solution was added dropwise to the stirred and suspended solution over 24 minutes using a tube pump set at a feed rate of 1.15 g / min. The mixture was then stirred for 2 hours as a post-crystallization aging treatment. The resulting slurry was rinsed with deionized water and dried at 110°C for 2 hours, resulting in a titanium oxide film coating on the carbonyl iron powder.

[0040] (4) Evaluation of carbonyl iron powder before and after surface coating with titanium oxide film (particle size) The particle size of the carbonyl iron powder was measured using a laser light diffraction scattering method (Microtrac MT3300EXII, Nikkiso Co., Ltd.). (Surface morphology) The surface morphology was observed using a field emission scanning electron microscope (FE-SEM; SU-8000, Hitachi High-Technologies Corporation) and a transmission electron microscope (TEM; JEM-ARM200F, JEOL Ltd.). An energy dispersive X-ray analyzer (EDX) (Figure 9: On-chip SDD detector, HD-2700A, Hitachi High-Technologies Corporation; Figure 16: Dual SDD detector, JEM-F200, JEOL Ltd.) was used to acquire EDX images at an accelerating voltage of 200 kV. (crystal structure) The samples were analyzed by X-ray diffraction (XRD; Smart Lab., Cu Kα, Rigaku Corporation) and TEM. (Surface chemical composition) The samples were evaluated by X-ray photoelectron spectroscopy (XPS; K-Alpha, Thermo Fisher Scientific Inc.) equipped with a monochromated Al Kα X-ray source, a flood gun, and an Ar ion gun. In calculating the peak intensity ratio of Fe / Fe oxide from the depth profile, the etching rate in the depth direction was 1.18 nm / sec when Ta2O5 was used as the standard sample, and the peak intensity ratio of Fe / Fe oxide was calculated based on this. (specific surface area) Measurements were made using an automatic surface area and pore size analyzer (BELSORP MINI X, MicrotrackBell Corporation). (magnetic properties) The samples before and after surface coating were evaluated by hysteresis loop measurement using a vibrating sample magnetometer (TM-VSM101483N7-MRO, Tamagawa Seisakusho Co., Ltd.). (Antioxidant stability) Thermogravimetric analysis (Thermo plus TG-DTA8122, Rigaku) was performed with an air purge of 300 mL / min and a heating rate of 2 K / min to evaluate the antioxidant stability.

[0041] The results obtained are shown in Table 1 and Figures 1 to 16. Table 1 shows the results of calculating the proportions of the chemical composition on the surface of the carbonyl iron powders of Examples, Comparative Examples, and Reference Examples from the results of analysis by X-ray photoelectron spectroscopy.

[0042] [Table 1]

[0043] 1B and 2B, the surface morphology of the carbonyl iron powder of the Example was almost the same as that of the Comparative Example. Furthermore, a comparison of Fig. 12B and Fig. 1B and Fig. 2B revealed that the surface irregularities of the carbonyl iron powder of the Reference Example were greater than those of the Example and Comparative Example.

[0044] The specific surface areas of the carbonyl iron powders of the Examples, Comparative Examples, and Reference Examples are 0.420, 0.424, and 1.151 m, respectively. 2 / g. The oxidation treatment increased the specific surface area by more than four times compared to vacuum-deaerated or untreated carbonyl iron powder. These results suggest that the oxidation treatment increased the surface roughness, resulting in an increase in the specific surface area.

[0045] The XPS survey spectra in Figure 3A show peaks in the C 1s, O 1s, and Fe 2p regions for all carbonyl iron powders in the Examples, Comparative Examples, and Reference Examples. For the Examples and Comparative Examples, a peak (399.7 eV) was detected in the N 1s region, as shown in Figure 3B. This N 1s peak originates from surface impurities, and the peak intensity of the Examples was attenuated compared to the Comparative Examples. Table 1 also shows that the N fraction calculated from the XPS peaks of the Examples was smaller than that of the Comparative Examples. These results demonstrate that vacuum degassing treatment reduced the amount of impurities on the surface of the untreated carbonyl iron powder.

[0046] As shown in Figure 3C, the positions, shapes, and widths of the peaks observed in the Fe 2p region of the samples of the Example, Comparative Example, and Reference Example were almost identical. The Fe 2p3 / 2 and Fe 2p1 / 2 peaks at 710.5 and 724.1 eV, respectively, are attributed to Fe3O4, while a peak extending toward higher binding energies and a satellite peak were detected at approximately 718.8 eV.

[0047] 4B, the Fe / Fe oxide ratio of the carbonyl iron powder of the Example was almost the same as that of the Comparative Example. Furthermore, the thickness of the oxide layer of the carbonyl iron powder of the Reference Example gradually increased with the etching time, and the oxide layer thickness was significantly thicker than that of the carbonyl iron powders of the Example and Comparative Example.

[0048] 5A and 5B, the surface of the untreated carbonyl iron powder of the comparative example was smooth, whereas Fig. 13 shows that the surface of the carbonyl iron powder of the reference example after oxidation treatment was very rough. As shown in Figure 5B, in the untreated carbonyl iron powder (comparison example), Fe oxide crystal planes [e.g., FeO(200), d = 0.215 nm and Fe2O3(116), d = 0.169 nm] were observed at a depth of approximately 15 nm from the surface. Furthermore, Fe crystal planes [e.g., Fe(110), d = 0.203 nm] were observed at a depth of 15 nm or more from the surface, indicating that the thickness of the Fe oxide layer was approximately 15 nm. 13, the measurement result of the oxide layer thickness of the carbonyl iron powder after oxidation treatment of the reference example was approximately 35 nm. From these results, it can be said that the thickness of the oxide layer on the surface of the untreated carbonyl iron powder increased from 15 nm to 35 nm by the oxidation treatment.

[0049] As shown in Figure 6A, the carbonyl iron powders coated with titanium oxide films in the Examples, Comparative Examples, and Reference Examples exhibited peaks in the Ti 2p region, and the peak positions and shapes were similar. The two peaks at binding energies of 458.6 eV and 464.3 eV in the XPS analysis corresponded to Ti with a tetragonal structure. 4+ It matched. As shown in Figure 6B, iron oxide peaks were observed in the Fe 2p region of the titanium oxide-coated carbonyl iron powders of the Comparative and Reference Examples, but almost no iron oxide peaks were detected in the titanium oxide-coated carbonyl iron powders of the Examples. Therefore, the O 1s peak of the titanium oxide-coated carbonyl iron powders of the Examples, shown in Figure 6C, is believed to be primarily due to Ti compounds. The peaks detected in the O 1s region were separated by waveform analysis into a main peak at 530.1 eV, representing the Ti-O and OH components of TiO2 and Ti-OH, respectively, and a minor peak at 532.2 eV. Figures 6B and 6C indicate that TiO2, including hydroxides, was formed on the carbonyl iron powder surface from the peroxotitanic acid solution. This suggests that the surface coating is a TiO2-OH film.

[0050] Comparing Figures 7B and 8B, the surface of the titanium oxide-coated material using carbonyl iron powder as a base material in the Example was uniformly and sufficiently coated with titanium oxide, whereas the surface of the titanium oxide film-coated material using carbonyl iron powder as a base material in the Comparative Example was not entirely and sufficiently covered with titanium oxide. 14B, plate-like particles were formed on the surface of the titanium oxide film-coated object using carbonyl iron powder as a base material during the Ti coating process, resulting in flower-like particles. These results demonstrate that removing surface impurities through vacuum degassing treatment enables a uniform titanium oxide film to be coated on the surface of carbonyl iron powder. Furthermore, as can be seen from FIG. 9, the uniform shell structure film of the titanium oxide film coating using the carbonyl iron powder of the example had a thickness of about 20 nm.

[0051] As can be seen from FIG. 15A, the surface of the titanium oxide film coated object using carbonyl iron powder as a base material in the reference example was significantly eroded, and plate-like particles were observed.

[0052] Furthermore, from Figure 16, EDX element mapping revealed that the plate-like structure coating portion (shell portion) of the flower-like particles is composed of Ti and O, and the plate-like structure (core portion) that serves as the base is composed of Fe and O. Furthermore, Figure 15B shows that the crystal plane of the platelet-like core coincided with γ-FeOOH [(200), d = 6.270]. These results suggest that γ-FeOOH was deposited on the carbonyl iron powder surface and subsequently coated with TiO2-OH, leading to the formation of plates. The oxidation treatment increased not only the thickness of the surface oxide layer but also the specific surface area, resulting in an active surface. The peroxotitanic acid solution contained Cl ions, which likely dissolved the active surface, leading to the deposition of plates on the surface. In conclusion, the removal of surface impurities inhibited the adsorption of Ti complexes on the carbonyl iron powder surface, and passivating the carbonyl iron powder surface was found to be important for the formation of a uniform surface coating using peroxotitanic acid solution.

[0053] 10, the saturation magnetization (Ms) of the carbonyl iron powder of the example was 205 emu / g (see the dashed line in FIG. 10), but the Ms value after TiO2-OH coating for each substrate was 204 emu / g when the carbonyl iron powder of the comparative example was used (see the dashed line in FIG. 10), 203 emu / g when the carbonyl iron powder of the example was used (see the two-dot chain line in FIG. 10), and 198 emu / g when the carbonyl iron powder of the reference example was used (see the solid line in FIG. 10). These results demonstrate that when a thin TiO2-OH film is coated on the surface of carbonyl iron, it has almost no effect on the magnetic properties of the carbonyl iron powder.

[0054] Figure 11 shows that as the temperature increased, the weight increased due to the conversion of Fe to Fe oxide. The oxidation onset temperatures (extrapolated onset temperatures) calculated from the thermogravimetric analysis results were 369.8°C for the carbonyl iron powder of the Example (see the dashed-dotted line in Figure 11 ), 437.1°C for the carbonyl iron powder of the Example coated with a titanium oxide film (see the dashed-two-dot line in Figure 11 ), 434.4°C for the carbonyl iron powder of the Comparative Example coated with a titanium oxide film (see the dashed line in Figure 11 ), and 425.7°C for the carbonyl iron powder of the Reference Example coated with a titanium oxide film (see the solid line in Figure 11 ). The TiO2-OH surface coating on each substrate significantly increased the oxidation onset temperature. Furthermore, the carbonyl iron powder of the Example coated with a titanium oxide film had the highest oxidation onset temperature. It is believed that the carbonyl iron powder of the Example exhibited the highest oxidation onset temperature compared to the carbonyl iron powders of the Comparative Example and Reference Example because it was more thoroughly coated with a titanium oxide film. 10 and 11 show that the carbonyl iron powder of the example coated with a titanium oxide film had improved oxidation stability without impairing the magnetic properties.

[0055] These results indicate that the surface of untreated carbonyl iron powder contains a thin oxide layer approximately 15 nm thick and volatile impurities, resulting in partial and insufficient TiO2-OH surface coverage. However, vacuum degassing treatment reduces the surface impurities of untreated carbonyl iron powder, resulting in a uniform and sufficient TiO2-OH film coating. Furthermore, vacuum degassing treatment was shown to remove surface impurities without increasing the specific surface area of carbonyl iron powder, contributing to the formation of a uniform TiO2-OH film. This uniform surface coating with a TiO2-OH film significantly improved the antioxidant stability of carbonyl iron powder from 369.8°C (before coating) to 437.1°C (after coating), without impairing its saturation magnetization. [Industrial Applicability]

[0056] The carbonyl iron powder obtained by the present invention has surface deposits removed, allowing a uniform coating of a titanium oxide film to be formed on the surface of the carbonyl iron powder. This allows for the provision of a titanium oxide film-coated product based on carbonyl iron powder that is resistant to oxidation even when exposed to air or moisture without impairing its magnetic properties. This titanium oxide film-coated product based on carbonyl iron powder is expected to be used in magnetic inks, magnetic toners, and MR fluids.

Claims

1. a step of subjecting the carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 50 Pa or less for 6 hours or more; The pressure of the vacuum degassing atmosphere is atmospheric pressure 1.0 × 10 ５ and exposing the mixture to the atmosphere for at least one hour until the temperature reaches Pa.

2. Carbonyl iron powder obtained by the method of claim 1.

3. 3. The carbonyl iron powder according to claim 2, wherein the N fraction on the surface of the carbonyl iron powder is 2.0 atm % or less.

4. The carbonyl iron powder according to claim 2 or 3, wherein the particle size of the carbonyl iron powder is 0.5 to 70 μm.

5. The carbonyl iron powder according to claim 2 or 3, wherein the carbonyl iron powder has a CV value of 0.3 to 0.

6.

6. A powder composition in which the surface of the carbonyl iron powder is coated with an inert material.

7. The powder composition according to claim 6, wherein the inert material is at least one of titanium oxide, silicon oxide, zinc oxide, aluminum phosphate, and graphene oxide.

8. A copying toner comprising the carbonyl iron powder according to claim 2.

9. A magnetic ink comprising the carbonyl iron powder according to claim 2.

10. 3. An MR fluid comprising the carbonyl iron powder according to claim 2.

11. Magnetic particles having a titanium oxide film on the surface of carbonyl iron powder according to claim 2.

12. 12. Magnetic particles having a titanium oxide film according to claim 11, having an oxidation onset temperature of 437.1°C or higher.

13. a step of subjecting the carbonyl iron powder to a vacuum degassing atmosphere at a pressure of 50 Pa or less for 6 hours or more; The pressure of the vacuum degassing atmosphere is atmospheric pressure 1.0 × 10 ５ and a step of exposing the mixture to the atmosphere for at least one hour until the pressure reaches Pa to obtain carbonyl iron powder. The method for producing magnetic particles comprises a step of coating the surface of the carbonyl iron powder with a titanium oxide film to obtain magnetic particles.

Images