JP3412189B2 - Method for producing iron nitride particles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic paint,
The present invention relates to a method for producing iron nitride magnetic particles that can be used for a powder magnetic material such as a magnetic toner or a magnetic carrier. 2. Description of the Related Art Magnetic fluids have been attracting attention as new functional materials. For example, powder magnetic materials such as magnetic paints, magnetic toners or magnetic carriers for image forming apparatuses,
Magnetization value is large, isotropic shape (needle, rod, plate,
Flat, etc., refers to shapes other than anisotropic shapes, spheroids whose major axis and minor axis do not differ so much, cuboids and polyhedrons whose major and minor sides do not differ so much, or irregular shapes similar thereto), And uniform size, in particular, a particle size of 20 nm to 100
Fine particles of about μm are required. [0004] Therefore, conventionally, spherically sintered ferrite particles or carbonyl iron powder has been used. However, ferrite has a small magnetization and is not very suitable for an image forming apparatus. On the other hand, carbonyl iron powder has good spherical shape as it is and its magnetization is large, but is not stable against oxidation. In addition, it has the disadvantage that it is difficult to obtain a powder having a size of 1 μm or less suitable for an image forming apparatus. Therefore, iron nitride has attracted attention as a magnetic material that is chemically stable and has a large magnetization. [0008] At present, methods for producing iron nitride fine particles include:
The following are known: That is, disclosed in JP-B-59-34125 and the like,
A method of heating and nitriding iron powder at a temperature of 500 ° C. or more in an ammonia gas atmosphere (ammonia nitriding method), which is disclosed in JP-A-2-164443 and the like;
Method of causing decomposition reaction of iron carbonyl Fe (CO) ₅ vapor in glow discharge plasma of N ₂ gas (plasma CVD)
Method), a hydrocarbon oil solution of iron carbonyl and ammonia gas, which are disclosed in JP-A-3-187907,
A method of reacting at 00 ° C. (gas-liquid phase reaction method) and a method of heating and evaporating iron in a reduced-pressure ammonia gas atmosphere (gas evaporation method) are known. In the ammonia nitriding method, the size of the iron nitride particles to be formed is determined by the size of the iron particles as a raw material, and at present, the minimum particle size is 1 μm. In the gas evaporation method, several particles are linked in a chain, so that it is difficult to obtain a single particle, energy efficiency in the production process is low, and productivity is poor. The plasma CVD method and the gas-liquid phase reaction method have been developed for the production of iron nitride magnetic fluid, and ultrafine particles of about 10 nm, which are optimal for the magnetic fluid, can be obtained. At present, particles of 20 nm or more have not been obtained from these methods, and the plasma CVD method has a wide range of application, but a reaction apparatus for performing the method is complicated and expensive. And it requires advanced techniques for its operation, so it is not always technically and economically efficient. Therefore, it is possible to synthesize iron nitride particles of a desired particle size from a gas-liquid reaction method. It is expected to be. [0010] However, as described above, powder magnetic materials such as magnetic paints, magnetic toners and magnetic carriers for image forming apparatuses, and the like, have not been disclosed.
While fine particles of about nm to 100 μm are required, conventional gas-liquid reaction methods cannot produce isotropically shaped iron nitride particles having a particle diameter of 20 nm or more. [0011] The present inventors have, as a result of intensive studies iron nitride particles forming process, the formation of iron nitride, iron ammine carbonyl complex Fe ₂ is a precursor of the iron nitride by reaction of iron carbonyl and ammonia gas (CO) ₅ (N
As long as H ₂ ) ₂ and Fe ₃ (CO) ₉ (NH) ₂ continue to maintain their concentrations above their critical concentration, they are preferentially and more easily at the surface of the fine particles of iron nitride. As a result, the iron nuclei were grown one by one without erasing the fine particle nuclei of iron nitride once generated, and succeeded in growing the iron nitride. As described above, according to the new production method, it is possible to produce isotropically shaped iron nitride particles having a particle size of about 20 nm to 1 μm, which could not be produced by the conventional ammonia nitriding method. However, the present invention provides such a material having excellent properties as a magnetic material.
It is an object of the present invention to provide a new method for producing isotropically shaped iron nitride particles having a particle size of about 0 nm to 100 μm. [0013] The present invention solves the above-mentioned problems by mixing a surfactant and an iron nitride colloid prepared under a lipophilic solvent by a gas-liquid phase reaction with water , The problem was solved by drying and sintering the emulsion in an ammonia gas or inert gas atmosphere. In the method of increasing the size of the iron nitride fine particles one by one on the surface of the once formed iron nitride fine particles, since the growth rate is limited by the layer thickness, the particle size of the obtained iron nitride fine particles is drastically increased. For this reason, the fine particles were granulated isotropically and sintered. For example, if the powder is packed in an isotropic mold or the like and baked as particles, isotropic particles having a desired particle diameter can be obtained. Granulation is performed by applying the relationship between the raw material and the mold to the relationship between a solution containing iron nitride fine particles and an emulsion in which the solution droplets are present in the non-solvent. Further, by sintering the granulated fine particles, particles having a desired particle diameter can be produced. In the present invention, iron carbonyl is used as a raw material of iron nitride, and ammonia is used as a raw material gas. Instead of ammonia, an arbitrary nitrogen compound such as amines which can be introduced into the reaction system as a liquid or solid is used. You can also. As the organic solvent, for example, hydrocarbons, or mixtures thereof, ketones, ethers, esters, amines, and the like are preferable, and as the surfactant added to the solvent, amines are preferable. However, the present invention is not limited to these. The iron nitride colloid formed as a seed crystal is
In addition to the emulsifying solvent (water), the mixture is emulsified with a high-speed stirrer such as an ultrasonic disperser or a homogenizer. At this time, in order to avoid oxidation of iron nitride, it is preferable to perform the treatment in contact with an inert gas atmosphere so that oxygen is not mixed into the solution to be stirred. Although the particle diameter varies depending on the apparatus, the particle diameter of the colloid droplets becomes constant after a certain period of time for various rotational speeds of the stirring. Therefore, it is preferable to continue the stirring for a little longer than that period. When mixing, the specific gravity of the iron nitride colloid is
The specific gravity of the emulsifying solvent should be as close as possible,
In order to further stabilize the emulsion, it is preferable to use a surfactant having an HLB of 7 or more. In particular, by forming droplets in the form of microcapsules and fixing the interface with the solvent, the droplets can be made completely spherical. The emulsion thus obtained is
Heat drying or spray drying in an atmosphere of ammonia gas or an inert gas, or vacuum drying to powder. The obtained dry iron nitride powder is a loosely aggregated ultrafine particle as it is. Then, the powder is sintered by performing a heat treatment. The sintering conditions are as follows: inert gas or nitrogen gas atmosphere, temperature of 200
The temperature is preferably set to 400 ° C. A solvent such as acetone, xylene, benzene, petroleum benzine, or cyclohexane is used to remove a surfactant or the like attached to the surface of the obtained single crystal iron nitride particles. The present invention will be described in more detail with reference to the following examples. (1) Seed Crystal Forming Step The apparatus for synthesizing a metal nitride magnetic fluid shown in FIG. 1 has a lid having a plurality of airtight introduction flanges in a heat-resistant pyrolysis reaction tank 1 having a heating device 2 attached to the bottom. 3 is formed by airtight connection. A stirring device 6 is attached to one introduction flange 5 so that the solution 4 in the reaction tank 1 can be stirred. The raw material gas is introduced into the solution 4 through the introduction pipe 7. Raw material 9 is introduced through a conduit provided in another introduction flange 8, and for example, a surfactant 11 is introduced through an introduction port 10. Another inlet 1
2 is branched, one is connected to a reflux cooling device 13 for performing a production reaction of metal nitride fine particles, and the other is connected to a condenser 14 as a distillation cooling device. ing. As a raw material, iron carbonyl having a purity of 96.5% manufactured by Aldrich Co. is used as a solvent, kerosene manufactured by Wako Pure Chemical Industries, Ltd. is used, and a surfactant is used by KAO Corporation.
N-diethyleneisobutenylsuccinimide (amine) manufactured by Nippon Sanso Corporation and 99.99% ammonia gas manufactured by Nippon Sanso Corporation were used. First, in a reaction tank 1 of the synthesis apparatus shown in FIG. 1, ammonia gas was introduced into a mixed solution 4 consisting of 200 g of iron carbonyl, 11.3 g of amine and 53.1 g of kerosene through an introduction pipe 7 at a flow rate of 390 ml / m Mix well while bubbling for min, heat to 90 ° C. by heating device 2, hold mixed solution 4 at that temperature for 1 hour, then raise the temperature to 185 ° C. and hold again for 1 hour. This two-stage heating operation was periodically repeated until all of the iron carbonyl in the reaction tank 1 was consumed, to obtain 86 g of iron nitride colloid as a seed crystal. The average particle size of the obtained magnetic iron nitride particles was determined from a high magnification photograph of a transmission electron microscope and found to be 10.4 nm. (2) Step of Emulsifying Iron Nitride Colloid An example of granulating the iron nitride colloid thus obtained will be described. Water is used as the emulsifying solvent. When water is used, the specific gravity of the iron nitride colloid is adjusted to 1 according to the water.
To The colloid and water are put in a container at a volume ratio of 1:10, and the container is replaced with nitrogen gas and sealed. Thereafter, the mixture is emulsified by irradiation with ultrasonic waves. By this operation, 950 g of an emulsion in which colloid droplets having an average particle size of about 1 to 3 μm were emulsified in water was obtained. On this occasion,
To maintain the emulsion for an extended period of time,
g. (3) Dry powder sintering step The obtained emulsion is heated and dried in an inert gas atmosphere to make a powder. Then, 5.8 g of this dry powder of iron nitride was sintered at 200 ° C. for 1 hour in a nitrogen gas atmosphere. Table 1 shows the physical properties of the obtained iron nitride particles. [Table 1] According to the production method of the present invention, isotropic iron nitride particles having a large magnetization value and a uniform particle diameter are obtained. The particle surface can be appropriately changed to lipophilic or hydrophilic, and can be suspended in an aqueous solvent or an oil solvent, and can be stored, transported, and otherwise handled, so that the particles burn. It is safe and easy to handle.

[Brief description of the drawings] FIG. 1 is a schematic view of a known apparatus for synthesizing iron nitride particles. [Explanation of symbols] 1 Pyrolysis reaction tank 2 Heating device 6 stirrer 13 Reflux cooling device 14 Condenser

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-188704 (JP, A) JP-A-4-283275 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 21/06

Claims (1)

(57) [Claim 1] An iron nitride colloid prepared under a surfactant and a lipophilic solvent by a gas-liquid reaction is mixed with water , and the emulsion is treated with ammonia gas or A method for producing iron nitride particles dried and sintered in an inert gas atmosphere.