JP3933366B2 - Method for producing metal oxide nanoparticles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, ultrafine particles (hereinafter, abbreviated as nano particles) Water oxide by a wet process method for producing metal oxide nanoparticles from the hydroxide nanoparticles obtained by the process and the method of manufacturing.
[0002]
[Prior art]
Particles having a size of 0.1 μm or less, that is, nm order are called ultrafine particles. Conventional metal ultrafine particles have been obtained mainly by a dry process (dry method) such as a sputtering method or a vacuum evaporation method, but the particle size is as large as 10 nm or more.
[0003]
In JP-A-8-100201, a material represented by TM · RE (TM = Fe, Co, Ni, RE = rare earth element) is dissolved in a reaction gas atmosphere composed of N, O, or hydrocarbon, A method is disclosed in which the evaporated material is reacted with a reaction gas to produce nano-order composite particles.
[0004]
As a wet method replacing the dry method as described above, a method of producing magnetic ultrafine particles of about 10 nm or less such as iron-based oxide by a coprecipitation method is known (Japanese Patent Publication No. 3-21510, No. 7-77963 and JP-B No. 7-115876). Japanese Patent Laid-Open No. 6-262061 discloses a method of obtaining metal oxide ultrafine particles by firing a precipitate obtained by dropping a dilute solution of a metal inorganic acid salt into a dilute alkaline solution near the crystallization temperature. However, the diameter of the fine particles is about several tens of nanometers. There is also known a method in which a transition metal carbonyl is thermally decomposed under a surfactant to form an ultrafine particle colloid, but the diameter of the obtained fine particle is about 6 nm. In addition, a method is known in which a metal-containing solution and a precipitating agent are pressurized and a high shear force is applied to produce nanoparticles having a size of 1 to 30 nm (Japanese Patent Publication No. 8-500289).
[0005]
[Problems to be solved by the invention]
Ultrafine particles provide new and unique physical properties that have never been seen before, and various materials are being explored as materials that can be expected to improve the performance of functional materials. Manufacturing of solid-phase methods, gas-phase methods, liquid-phase methods, etc. Although a method has been developed, no means has yet been established for inexpensively producing fine particles smaller than 10 nm. For example, with the recent development of an advanced information society, high-density recording of information has been demanded, and ultrahigh-density magnetic recording using fine particles of ferromagnetic iron oxide has been developed. However, conventional practical magnetic recording ferromagnetic fine particles have a diameter of 10 nm or more, and it has been impossible to achieve high density at the TB (terabyte) level for magnetic recording. Fine particles, for example, CoCrTa fine particles, in a magnetic recording tape by a conventional manufacturing method have a diameter of about 30 nm.
[0006]
[Means for Solving the Problems]
The present inventors have found a method of manufacturing nanometer-sized ultrafine particles that overcome the above-mentioned problems in the process of preparing a sample for studying the ferromagnetic phase transition of magnetic fine particles.
[0007]
The hydroxide nanoparticles obtained by the production method of the present invention are MX _p · nH ₂ O (M: Fe or Ni ; X: halogen element selected from F, Cl, Br, I, p = 2 or 3, n is a hydroxide particles produced precipitated by wet mixing with an integer) from 0 to _{9 Na 2 SiO 3 · mH 2} O (m = 9 or 0), that have a network of amorphous SiO _2.
[0008]
Amorphous SiO ₂ + M _i O _j oxide by calcining hydroxide nanoparticles above SL (i, j is an integer from 1 to 9) Ru obtained nano particles.
[0009]
Oxide nanoparticles of above SL are useful as ultra-high density magnetic recording material. The individual oxide nanoparticles form a single ferromagnetic domain, and the coercive force Hc at room temperature is larger than that of the conventional one. Further, the addition of heterogeneous atoms such as Si, Co, Os, or Fe ²⁺ can increase the Hc by about twice.
[0010]
That is , the present invention relates to y mol MX _p · nH ₂ O (M: transition metal or rare earth metal; X: halogen element selected from F, Cl, Br, I, p = 2 or 3, n is from 0 (Integer up to 9) and y-mole Na ₂ SiO ₃ .mH ₂ O (m = 9 or 0) aqueous solution are wet-mixed at room temperature and allowed to stand to form a precipitate, which is washed and a method of producing a water-oxide nanoparticles you and obtaining a hydroxide nanoparticles having a network of amorphous SiO ₂ by drying.
[0011]
In addition, the present invention converts the hydroxide nanoparticle obtained by the above method into an oxide by firing in air, thereby converting amorphous SiO ₂ + M _i O _j oxide (i, j is 1 to 9). (Integer) is a method for producing metal oxide nanoparticles, characterized in that nanoparticles are produced.
[0012]
In the present invention, as described above, an aqueous solution of metal halide and an aqueous solution of sodium (meth) silicate are mixed and stirred at room temperature (wet mixing) to produce a precipitate of hydroxide nanoparticles, which is dried, glass The process consists of crushing the lumps and then firing them in an air atmosphere to convert them into oxides to form nano-particles. Good. Moreover, when producing a thin film, direct baking is performed.
[0013]
Nanometer-sized ultrafine particles of hydroxide surrounded by amorphous SiO ₂ can be generated by wet mixing of a metal halide and sodium silicate or metametasilicate. The network of amorphous SiO ₂ thinly surrounds individual nanoparticles with a monomolecular layer, and the number density of the nanoparticles is about 10 ¹⁸ to 10 ¹⁹ particles / cm ^{2 on} the surface, compared to the conventional 10 nm diameter particles. 10 to 100 times.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The metal oxide and hydroxide nanoparticle production process of the present invention is as follows. First, y moles of MX _p · nH ₂ O aqueous solution (M:: Fe or Ni, X F, Cl, Br , integers halogen element selected from I, p = 2 or 3, n is from 0 to 9) And y moles of an aqueous solution of Na ₂ SiO ₃ .mH ₂ O (m = 9 or 0) are wet-mixed and stirred at room temperature. When this is left standing, a precipitate is formed. At this stage, M (OH) _x nanoparticles surrounded by amorphous SiO ₂ are generated. The supernatant solvent is removed and the precipitate is washed with pure water. This cleaning is preferably repeated over about the 10th order.
[0015]
Next, the precipitate is dried. Drying may be natural drying at room temperature. After this drying, a glassy mass of amorphous SiO ₂ + M (OH) _p nanoparticles is obtained. The glassy mass is pulverized to obtain a powder.
[0016]
Furthermore, this powder is converted into an oxide by firing in an electric furnace in air to produce amorphous SiO ₂ + M _i O _j oxide (i, j is an integer of 1 to 9) nanoparticle.
[0017]
The powder having the intended properties and functions obtained by the method of the present invention can be solidified with an appropriate medium and formed into an arbitrary shape for use. Instead of the above powder manufacturing method, after wet mixing, it is also possible to insert a flat plate into an undried mixed solution, attach the liquid in a thin film shape, and dry it in the thin film state to obtain a thin film It is easy to form an arbitrary shape.
[0018]
【Example】
Example 1
At room temperature, 1 mol of FeCl ₂ · 4H ₂ O and 1 mol of Na ₂ SiO ₃ · 9H ₂ O are mixed in a glass container with stirring with a stirrer (wet mixing) and allowed to stand for about 20 hours. As a result, a precipitate of the iron hydroxide nanoparticle population was generated. This precipitate was washed 10 times with pure water. After washing and standing at room temperature and drying, a glassy mass was obtained. This glassy lump was put into a mortar and pulverized with a mortar to obtain a powder.
[0019]
FIG. 1 shows a powder X-ray diffraction pattern of the powder obtained by pulverization. The vertical axis of the graph is the X-ray diffraction intensity, and the horizontal axis is twice the diffraction angle. This pattern shows that amorphous SiO ₂ and Fe (OH) ₃ nanoparticles coexist. Next, the powder was fired in air at 200 ° C., 430 ° C., 650 ° C., and 860 ° C. for 10 hours using an electric furnace.
[0020]
FIG. 2 shows a powder X-ray diffraction pattern after firing at 650 ° C. The symbols in the graph are the same as those in FIG. This pattern shows the coexistence of amorphous SiO ₂ and γ-Fe ₂ O ₃ (maghemite) nanoparticles.
[0021]
FIG. 3 shows magnetization curves at room temperature (300 K) of powders fired at 200 ° C., 430 ° C., 650 ° C., and 860 ° C., respectively. The vertical axis of the graph represents the intensity of magnetization per lg, and the horizontal axis represents the magnitude of the applied magnetic field. As the firing temperature increases, the powder is strongly magnetized. The powder fired at 860 ° C. has a history in the magnetization curve and exhibits a coercivity (Hc) of about 1500 Oersted. Since ferromagnetism can be strengthened with an increase in the firing temperature, the temperature and time may be appropriately selected according to the properties and functions of the target powder. The firing temperature is preferably 600 ° C. or more, more preferably Is 800 ° C. or higher.
[0022]
Example 2
A precipitate of Ni (OH) ₂ ultrafine particles surrounded by amorphous SiO ₂ was obtained in the same manner as in Example 1 except that NiCl ₂ .6H ₂ O was used instead of FeCl ₂ .4H ₂ O as a raw material. Formed. FIG. 4 is an electron microscope image of the powder obtained by drying and pulverizing the precipitate. In FIG. 4, many black dots shown in a circle represent ultrafine particles having a diameter of about 3 nm. It seems that most of the parts that appear large in diameter are superfine particles. This is a raw material for producing NiO ultrafine particles having the potential as an ultrasensitive temperature sensor.
[0023]
【The invention's effect】
The production method of the present invention can supply ultrafine particles having a particle size of 2 to 3 nm smaller than conventional particles by a wet process (wet method). If ultrafine particles obtained by the production method of the present invention are processed into a magnetic tape or a magnetic disk as a raw material for magnetic recording, it becomes possible to realize ultrahigh density recording as an ultrahigh density recording medium of a high density magnetic recording / reproducing apparatus. . The production method of the present invention is not limited to magnetic recording materials, and can be applied to the production of oxide-based magnetic materials, giant magnetoresistive materials, superconducting materials, and the like.
[Brief description of the drawings]
FIG. 1 is a graph showing a powder X-ray diffraction pattern of a precipitate dried at room temperature in Example 1. FIG.
FIG. 2 is a graph showing a powder X-ray diffraction pattern after the powder was fired in Example 1.
FIG. 3 is a graph showing magnetization curves at room temperature (300 K) of powders having different firing temperatures in Example 1.
FIG. 4 is an electron microscopic image in place of a drawing of Ni (OH) ₂ ultrafine particles obtained by pulverizing a precipitate dried at room temperature in Example 2.

Claims (2)

y moles of _{MX p · nH 2 O (M} : Fe or Ni; X: F, Cl, Br, a halogen element selected from I, p = 2 or 3, n is an integer from 0 to 9) aqueous solution with y An aqueous solution of molar Na ₂ SiO ₃ .mH ₂ O (m = 9 or 0) is wet-mixed at room temperature and allowed to stand to form a precipitate. The precipitate is washed and dried to obtain amorphous SiO _2. method of producing a water-oxide nanoparticles you and obtaining a hydroxide nanoparticles having a mesh. The hydroxide nanoparticle obtained by the method according to claim 1 is converted into an oxide by firing in air, and amorphous SiO ₂ + M _i O _j oxide (i, j is an integer of 1 to 9). A method for producing metal oxide nanoparticles, characterized by producing nanoparticles.

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