JPH0477689B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Industrial Application" This invention is applicable to pigments, abrasives, catalysts, conductive fillers, magnetic materials, microcapsules, adsorbents, moisture absorbers, catalyst supports, column packing materials for liquid chromatography or gas chromatography, etc. This invention relates to a method for producing iron oxide porous microspheres that are used in a wide range of applications. "Prior Art and its Problems" Conventionally, iron oxide powder has been used in many fields as pigments, abrasives, raw materials for powder metallurgy, catalysts, magnetic materials, conductive materials, electrodes, and the like. As methods for producing such iron oxide powder, the following methods are known. α-FeO is obtained by air oxidation of iron sulfate () suspension.
A method of generating (OH) and heating and dehydrating it to α-Fe ₂ O ₃ . The precipitate of iron hydroxide () is dispersed in distilled water, heated and dehydrated in a pressure tube or autoclave, and α-
Method to make Fe ₂ O ₃ . A method of reducing α-Fe ₂ O ₃ to generate Fe ₃ O ₄ , which is then gently oxidized at low temperatures to form γ-Fe ₂ O ₃ . A method in which Fe ₂ O ₃ and iron powder are heated in argon gas and reduced to FeO. _{FeO _ _}
How to do it. However, when iron oxide powder is produced by these methods, the shape of the powder particles becomes irregular and non-spherical, so there are problems as shown in (i) to (vi) below. . (i) Powder particles tend to aggregate and form flocs. (ii) Poor dispersibility when mixed with other substances. (iii) When used as a filler, the filling rate is low. (vi) The bulk of the powder increases, resulting in poor transportation and storage efficiency. (v) When made into a composite material, it causes a decrease in strength. (vi) It is difficult to obtain powder particles with uniform shape and size. Therefore, a method described in Japanese Patent Publication No. 57-55454 is known as a method capable of solving the above-mentioned problems. This method involves mixing an aqueous solution of at least one water-soluble inorganic compound (compound) selected from alkali metal silicates and alkaline earth metal halides or nitrates with an organic solvent having a solubility in water of 5% or less. to form a W/O emulsion, and then an aqueous solution of a water-soluble inorganic compound (compound) that reacts with the inorganic compound in the emulsion to form a water-insoluble precipitate is mixed with the emulsion. . In this method, the emulsion constituting the emulsion is broken by mixing an emulsion obtained by emulsifying an aqueous solution of the compound with an aqueous solution of the compound, and droplets of the aqueous solution of each compound are liberated in the aqueous solution of the compound. At the same time, the compound and the ions generated by the dissociation of the compound immediately react on the surface of the free droplet, and a thin film of the water-insoluble compound corresponding to the shape and size of the droplet is formed on the surface, Subsequently, the reaction proceeds so as to grow this thin film, and the desired spherical shell-like particles of the water-insoluble compound are produced. By the way, when iron oxide porous microspheres are used for various applications as mentioned above, the particle size of the particles (microspheres) required is often different depending on the application, and in such cases, the manufacturing method in the above manufacturing method is It is possible to change the conditions. Therefore, as a result of intensive research by the present inventors,
An aqueous solution of iron nitrate () is used as the aqueous solution of the above compound, and the concentration of this aqueous iron nitrate () solution is 1 to 3 mol/
The average particle size of the produced iron oxide porous microspheres can be controlled within the range of 0.4 to 1 μm by appropriately selecting the iron oxide porous microspheres. It has been found that it can be controlled so that the higher the concentration, the larger the value, and the lower the concentration, the smaller the value. This invention was made based on the above findings, and an object of the present invention is to provide a method for producing iron oxide porous microspheres, which allows the average particle size of the particles to be easily controlled. In addition, the iron oxide porous microspheres produced by the conventional method described above have poor dispersibility, packing ratio, etc. due to variation in particle size, which often causes problems when used for the various applications described above. . "Means for Solving the Problems" In order to achieve the above object, the method for producing iron oxide microspheres of the present invention involves mixing an aqueous solution of iron nitrate () with a solution of a surfactant dissolved in an organic solvent. Te W/
A method for producing iron oxide porous microspheres by preparing an O-type emulsion and then mixing the W/O-type emulsion with an aqueous sodium bicarbonate solution, the method comprising: The average particle size of the iron oxide porous microspheres can be adjusted to a range of 0.4 to 1 μm by appropriately selecting the amount of nitric acid () in the range of 1 to 3 mol/
It is characterized in that the average particle size is controlled to increase as the concentration of the aqueous solution increases. Further, the iron oxide porous microspheres of the present invention are composed of iron oxide, exhibit a nearly perfect spherical shape with an average particle size in the range of 0.4 to 1 μm, and have a porous structure, and
It is in a dry state with a pore size of approximately 2-60 nm. "Function" In the present invention, an aqueous solution of iron nitrate () is dispersed as droplets in an organic solvent using a surfactant,
By mixing this organic solvent and an aqueous sodium bicarbonate solution, a precipitation reaction is caused to occur at the interface of a droplet of an aqueous iron nitrate solution, and a water-insoluble wall film is formed on the surface of the droplet. Microspheres made of this wall film are manufactured. In this case, the average particle diameter of the microspheres can be controlled within the range of 0.4 to 1 μm by appropriately selecting the concentration of the iron nitrate () aqueous solution within the range of 1 to 3 mol/. The above concentration is 1~
The reason why it was set at 3 mol/ is that if it is less than 1 mol/ it is difficult to form a stable wall film, and if it exceeds 3 mol// it exceeds the solubility. In addition, the iron oxide porous microspheres produced by the above method have an average particle size in the range of 0.4 to 1 μm,
Since there is little variation in particle size, it has excellent dispersibility and filling rate. ``Example'' Hereinafter, an example of the manufacturing process for manufacturing iron oxide porous microspheres according to the present invention will be described in detail step by step. First, an aqueous iron nitrate solution and a benzene surfactant solution are mixed at a volume ratio of 1:3 to 1:5,
Emulsify with a shaker or stirrer to form a W/O emulsion. As a result of this operation, as shown in Figure 1, the surfactant molecules S surround the droplet A of the iron nitrate () aqueous solution, and many droplets of the iron nitrate () aqueous solution are generated. It will be in a dispersed state. At this time, the concentration of iron nitrate () aqueous solution is 1 mol/
It is difficult to form a stable wall film below 3 mol/
If this exceeds the solubility, 1 to 3 mol/
A range of is optimal. Furthermore, as the surfactant used for emulsification, a nonionic surfactant having an HLB value of about 4 to 7 is used. Specifically, they are sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate, and the concentration thereof is 1 to 2%. These conditions for the surfactant were determined in order to prepare a stable W/O type emulsion. When an activator is used, a stable W/O emulsion cannot be prepared, and a large amount of amorphous particles that have collapsed during wall film formation are mixed in. Furthermore, if the concentration of the surfactant is 2% or more, a large amount of the surfactant remains on the particle surface, making it impossible to completely remove the surfactant by water washing in post-treatment. . Next, the W/O emulsion is mixed with an aqueous sodium hydrogen carbonate solution and stirred or shaken. In this way, benzene is separated from the W/O emulsion and the droplet A is dispersed in an aqueous sodium bicarbonate solution, and this aqueous sodium bicarbonate solution absorbs the surfactant S around the droplet A. It passes through and reacts with the iron nitrate aqueous solution at the interface of the droplet A, and as shown in FIG. 2, a water-insoluble wall film C is formed on the surface of the droplet A to form spherical particles. In this case, if the concentration of the sodium hydrogen carbonate aqueous solution is lower than the saturated solution, it is difficult to form a stable and strong wall film, so the sodium hydrogen carbonate aqueous solution is
A saturated solution of sodium bicarbonate mixed with 1.5 mol of sodium bicarbonate is used. Further, the reaction temperature is set at 20 to 40°C, since the reaction rate is slow at 20°C or lower, and the W/O emulsion is easily destroyed and it is difficult to obtain spherical particles at 40°C or higher. In addition, in order to completely form a wall film and prevent particles from collapsing in the post-processing stage described below,
The reaction time should be approximately 80-100 minutes. In addition,
It is thought that the following reaction proceeds on the surface of the droplet A. NaHCO ₃ →Na ⁺ +OH ^- +CO ₂ ↑ Fe ₃ ⁺ +OH ^- →Fe(OH) ₃ ↓ →FeO(OH)↓ After the above reaction is completed, add to the above W/O emulsion.
The particles are collected by centrifugation at 7000 rpm for 10 minutes, and then washed with water and methanol in order to remove water-soluble byproducts such as sodium nitrate remaining on the particle surface, and the particles. Remove surfactant etc. remaining on the surface.
Through this series of operations, as shown in FIG. 3, porous microspheres or porous hollow microspheres made of wall membrane C are produced. The iron oxide porous microspheres thus obtained are made of amorphous iron oxide, and by firing them at 500 to 900°C for about 20 hours,
Porous microspheres made of hematite are obtained. In addition, in normal firing, the porous microspheres become hematite (α-Fe ₂ O ₃ ), but by reducing or oxidizing them, they can be transformed into wustite (FeO), magnetite (Fe ₃ O ₄ ), and maghemite ( γ-
It is also possible to obtain porous microspheres made of Fe ₂ O ₃ ) or the like. Next, an example will be described in which an experiment was actually conducted in the above production method in which the concentration of the iron nitrate () aqueous solution was changed in steps of 1 mol/in the range of 1 to 3 mol/in. Experimental example 1 Add 2.5 ml of a 3 mol iron nitrate () aqueous solution to 12.5 ml of a 1% benzene solution of surfactant (sorbitan monostearate) and emulsify with a stirrer for 3 minutes to form a W/O emulsion. Prepared. The above W/O emulsion was added to 1.5 mol/100 ml of aqueous sodium hydrogen carbonate solution, and
Stir for a minute. After completion, the benzene phase and water bath were removed by centrifugation (×7000 rpm, 10 minutes), and the precipitate was collected. The precipitate was washed with methanol and water to remove the surfactant and water-soluble inorganic salt. The product was obtained by drying at 110°C for 17 hours. Through the above operations, about 0.4 g of porous microspheres made of amorphous iron oxide with an average particle diameter of 0.932 μm, a pore diameter of 2 to 55 nm, and a specific surface area of 396.6 m ² /g were obtained. FIG. 4 is a scanning electron micrograph of this porous microsphere, and FIG. 5 is a graph showing the pore distribution of this porous microsphere. Experimental Example 2 Add 2.5 ml of a 2 mol iron nitrate () aqueous solution to 12.5 ml of a 1% benzene solution of surfactant (sorbitan monostearate) and emulsify with a stirrer for 3 minutes to form a W/O emulsion. Prepared. ~ Same as Experimental Example 1. Through the above operations, about 0.3 g of porous microspheres made of amorphous iron oxide and having an average particle diameter of 0.762 μm, a pore diameter of 2 to 55 nm, and a specific surface area of 365.2 m ² /g were obtained. Experimental Example 3 Add 2.5 ml of a 1 mol iron nitrate () aqueous solution to 12.5 ml of a 1% benzene solution of surfactant (sorbitan monostearate) and emulsify with a stirrer for 3 minutes to form a W/O emulsion. Prepared. ~ Same as Experimental Example 1. By the above operations, about 0.2 g of porous microspheres made of amorphous iron oxide with an average particle diameter of 0.489 μm, a pore diameter of 2 to 55 nm, and a specific surface area of 259.8 m ² /g were obtained. As is clear from the above experimental examples 1 to 3, the concentration of the iron nitrate () aqueous solution is 1 mol/, 2 mol/,
3mol/, and by keeping all other manufacturing conditions the same, the average particle diameters of the produced iron oxide porous microspheres were 0.498μm, 0.762μm, and 0.762μm, respectively.
0.932 μm. Therefore, the average particle size of the produced iron oxide porous microspheres can be controlled by the concentration of the iron nitrate () aqueous solution. Note that this average particle size becomes larger as the concentration of the iron nitrate () aqueous solution becomes higher, and becomes smaller as the iron nitrate () aqueous solution becomes thinner. Furthermore, the specific surface area of the produced iron oxide porous microspheres can be controlled by the concentration of the iron nitrate () aqueous solution. Experimental Example 4 The porous microspheres obtained in Experimental Example 1 were fired at 500° C. for 20 hours in an air atmosphere, and then subjected to X-ray diffraction measurement (CuKα rays). The results are shown on the next page.

[Table] The above measurement values almost coincide with the diffraction peak of hematite (α-iron oxide) listed in ASTM card 33-664, and from this, it can be seen that by firing, porous microscopic particles made of hematite It was confirmed that the ball was obtained. "Effects of the Invention" As explained above, according to the present invention, iron oxide porous microspheres produced by appropriately selecting the concentration of iron nitrate () aqueous solution in the range of 1 to 3 mol/ The average particle size can be controlled within the range of 0.4 to 1 μm, and the average particle size can be controlled to increase as the concentration of the iron nitrate () aqueous solution increases. Therefore, iron oxide porous microspheres having a desired particle size can be easily supplied depending on the application. Moreover, the following effects can also be achieved. (i) The raw material iron nitrate () is cheap and easily available. (ii) Since the solubility of iron nitrate () is high, it is easy to prepare an aqueous solution. (iii) Since the iron nitrate () aqueous solution is relatively stable and difficult to deteriorate, raw material preparation and reaction can be performed in air. Therefore, iron oxide porous microspheres can be manufactured without using special equipment, and can be manufactured at low cost. (iv) Nitrate produced as a by-product during manufacturing is easy to decompose at relatively low temperatures and is easy to remove. In addition, the iron oxide porous microspheres produced by this production method are lightweight due to their porosity, and
Because it has a uniform spherical shape, it has excellent powder fluidity. For this reason, the iron oxide porous microspheres of the present invention are
When used in place of conventional iron oxide powder as pigments, abrasives, powder metallurgy raw materials, catalysts, magnetic materials, conductive materials, electrodes, etc., it can improve dispersibility, increase filling rate, and reduce product size. It is possible to reduce the weight, increase the strength, and improve the transportation efficiency and storage efficiency. Furthermore, this iron oxide porous microspheres can be used as adsorbent,
It can also be used as a moisture absorbent, a column filler for liquid chromatography or gas chromatography, a catalyst carrier, or as a microcapsule for particles exhibiting a hollow structure. In particular, when used as microcapsules, the wall material is composed of water-insoluble inorganic substances, so compared to microcapsules composed of ordinary organic substances, they have better heat resistance, nonflammability, water resistance, and resistance to organic solvents. It has excellent properties and high strength.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams illustrating the method for producing porous iron oxide microspheres of the present invention. FIG. 4 is a scanning electron micrograph of the iron oxide porous microspheres, and FIG. 5 is a graph showing the pore distribution of the iron oxide porous microspheres.

Claims (1)

[Claims] 1. A dry powder composed of iron oxide, exhibiting an almost perfect spherical shape with an average particle size in the range of 0.4 to 1 μm, and having a porous structure and a pore size of about 2 to 60 nm. Iron oxide porous microspheres. 2 Prepare a W/O emulsion by mixing an aqueous solution of nitrate () and a solution of a surfactant dissolved in an organic solvent, and then mix this W/O emulsion with an aqueous sodium bicarbonate solution. A method for producing porous iron oxide microspheres by appropriately selecting the concentration of the iron nitrate () aqueous solution in the range of 1 to 3 mol/ 0.4
A method for producing porous iron oxide microspheres, characterized in that the average particle size is controlled to be within the range of ~1 μm and to increase as the concentration of the iron nitrate () aqueous solution increases.