JPS61124502A - Stable magnetic metallic powder and its production - Google Patents

Abstract

PURPOSE:To form a film on the particles of magnetic metallic powder with easy control and to provide high ignition preventive powder thereto without decreasing satd. magnetization with a safe and simple stage by coating the surfaces of said particles with a fluoride. CONSTITUTION:The magnetic metallic powder consisting essentially of iron and contg. Co, Ni, Cr, etc. is treated with hydrogen fluoride and/or hydrogen fluoride-cong. compd., fluorine and/or fluorine compd. at a prescribed temp. (for example, by passing a gas for the above-mentioned fluorination for a prescribed period, etc.). The film of the fluoride of the above-mentioned metal is thus formed nearly stoichiometrically and extremely easily on the surface of the metallic powder particles. The magnetic metallic powder is preferably treated with hydrogen fluoride or fluorine-contg. gas and further an inert gas or reducing gas for diluting said gases in a 200-820 deg.C range.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a stabilized metal magnetic powder and a method for producing the same. More specifically, by coating the particle surface of metal magnetic powder with fluoride, it suppresses ignitability and makes handling and storage safer. It has been used as a magnetic material in a variety of fields, including materials for magnetic cores, recording materials for magnetic tapes, and materials for copying machines. However, in the case of a component mainly composed of metal,
As the grain size becomes finer, it becomes flammable, so extreme care has been required in handling and storage.

Regarding the stabilization of metal magnetic powders, acicular metal iron and iron alloys are attracting attention as recording materials for magnetic tapes for audio or video, and various methods for producing surface coatings have already been published. . For example, JP-A-53-11
No. 4769 discloses a method in which metal powder is suspended in an aqueous sodium hydroxide solution and then oxygen-containing gas is aerated therein, and according to JP-A-59-59801, metal powder impregnated with an organic solvent is stirred and elevated. Most of the methods involve covering the surface with an oxide film, such as a method of contacting the material with an inert gas containing a trace amount of oxidizing gas while heating it.

However, with the conventional method of covering with an oxide film, the ignition point is 15
The temperature is about 0 to 160℃, so it will not ignite in the atmosphere, and it is not completely safe from external shocks and vibrations during transportation.Also, when covering with an oxide film, the oxide is dense, It is difficult to control the thickness of the coating.

Furthermore, if an organic solvent or the like is used, it is necessary to handle a mixture of flammable metal powder and flammable organic solvent), which poses a safety problem in the manufacturing process itself.

In addition, in terms of manufacturing quality, this meant that the high saturation magnetization, which is a characteristic of metals, was reduced by surface oxidation, and it was necessary to develop an improved surface treatment method.

"Problems to be Solved by the Invention" The present invention provides a stabilized metal magnetic powder with high ignition prevention ability, a process for obtaining the same that is safe and simple, and a controllable film formation on the metal magnetic powder particles. The purpose is to provide a manufacturing method that is easy and can provide high ignition prevention ability without reducing saturation magnetization.

The present inventors have been researching methods for producing stable films in place of oxide films, and found that fluorides, especially iron fluoride, are relatively thermally stable (Inorgani
c Th@or@tical Chsmlstry v
The present invention was achieved as a result of various tests regarding the conditions for fluoridizing the surface of iron powder or iron alloy.

"Means for Solving the Problems" That is, the present invention provides a stable metal magnetic powder characterized in that the surface of metal particles is coated with a fluoride of the metal and the average particle size is 8 μm or less.

Furthermore, the present invention is a method for producing a stable metal magnetic powder, which is characterized in that a surface-active metal magnetic powder is treated with hydrogen fluoride and/or a hydrogen fluoride-containing compound.

The present invention will be explained in more detail below.

In the stable magnetic metal powder of the present invention, the surfaces of the particles of metal magnetic powder having an average particle size of 8 μm or less are coated with a film made of a metal fluoride constituting the magnetic powder particles. The thickness of this coating is determined by balancing the requirements for stability, such as imparting ignition prevention ability to the metal magnetic powder, and the requirement not to reduce the saturation magnetism of the metal.

However, the thickness is preferably such that the fluorine content in the nine-stabilized metal magnetic powder obtained is 0.1 inch or more.

If it is less than 0.1 inch, it is difficult to completely form a fluoride film that is sufficiently effective.

In the present invention, stabilization is achieved with such a thin coating layer, and the thickness of the coating layer is extremely easy to control, making it possible to produce extremely fine stabilized metal magnetic powder of 0.1 μm or less, which was previously difficult. It is also possible to realize this.

As is well known, the metal magnetic powder of the present invention has iron as its main component,
Co+Ni+TI, V, Cr, Mn, Zn, Mo
, Cu, and other metals.

The above-mentioned stabilized metal magnetic powder can be obtained by the following method for producing stabilized metal magnetic powder, but the range of stabilized metal magnetic powder obtained by this production method is limited to the above-mentioned stabilized metal magnetic powder. isn't it.

The method for producing a stabilized magnetic metal powder of the present invention involves treating magnetic metal powder with hydrogen fluoride and/or a hydrogen fluoride-containing compound at a predetermined temperature, thereby very easily removing the fluoride coating of the metal from the metal powder. It forms almost stoichiometrically on the particle surface.

The magnetic metal particles used in the present invention can be obtained, for example, by reducing an oxide of a magnetic metal with a reducing substance such as hydrogen gas by a known method. It can also be obtained by vacuum evaporation or gas phase reduction. In this case, ultrafine powder is obtained.

Hydrogen fluoride, hydrogen fluoride-containing compounds, and fluorine compounds used in the present invention include hydrogen fluoride itself and hydrofluoric acid that generates hydrogen fluoride, as well as NH4F and NH4H.
F2. KHF2. These include hydrogen fluoride-containing compounds such as NaHF2, and fluorine compounds such as bromine fluoride, iodine fluoride, and horonine fluoride.

The treatment of metal magnetic powder with hydrogen fluoride, hydrogen fluoride-containing compound fluorine, or a fluorine compound is, for example, a metal magnetic powder obtained by reduction with a reducing substance such as hydrogen gas by a known method, and then treated with fluorine at a predetermined temperature. A method in which a chemical gas (hydrogen fluoride, hydrogen fluoride-containing compound, fluorine, fluorine compound, etc.) is passed in a predetermined amount for a predetermined period of time.
A method in which hydrogen fluoride-containing compounds such as H4F and NH4HF2 and/or fluorides such as bromine fluoride and iodine fluoride) is mixed in advance with the substance to be reduced and reduction is performed, or when the reduction is completed, This is carried out by a method such as supplying a compound capable of generating hydrogen fluoride and then maintaining it at a predetermined temperature and for a predetermined time in an inert or reducing atmosphere.

The fluoride production reaction is considered to be based on the following reaction formula.

Fe + 2H possible g) = FeF2 + N2 (g) The standard free energy ΔG of this reaction is ΔG = 33.7
T-36,800 (cal), and the limit on the high temperature side is 820℃, and on the low temperature side, the reaction rate is almost zero below 200℃, so the temperature conditions for fluoride production are 200℃~200℃. In the range of 820°C, preferably 350°C
~600°C.

In addition, fluorinating gas is generally a hazardous substance and is
It is considered more desirable to dilute it with an inert gas such as r. It is also possible to add reducing gases to control the rate of fluorination.

Furthermore, instead of using fluoride gas directly, this can also be achieved by mixing a compound capable of generating hydrogen fluoride (for example, N14F, NH41'2) with the substance to be reduced in advance or supplying it during reduction. At this time, a fluoride film can be formed by setting the temperature conditions during the reduction to be in the range of 200 to 960°C.

For submicron particles of metal magnetic powder, the specific surface area value is 10.
m"/Ji' or less, but when finer particles equivalent to 0.01 μm (100X) are obtained by vacuum evaporation or gas phase reduction, the particle size reaches nearly 100 m"/Ji', and in order to stabilize it, currently A surface oxide film is used, and for this reason,
The high saturation magnetization of the iron powder is inhibited, and at the same time, very delicate control of the atmosphere is required to control the thickness of the coating, and the productivity is not high. In this respect, the present method is expected to enable industrial mass production of ultrafine powder with improved stability.

"Example" Hereinafter, a more detailed explanation will be given based on examples.

Example 1 Iron oxide (Fe304) with an average particle size of 0.7 μm was placed in a rotary retort furnace with an effective length of 250 mφ/250 wLt.
650I was charged, and while flowing N2 gas at a rate of 3°C per minute, the temperature was raised from room temperature to 450°C, and while keeping the temperature inside the furnace at the same temperature, N2 gas was flowing at 33°C per minute. Aerate at a rate of
After 2 hours and 30 minutes, switch to N2 gas again, with N2 gas at 2.21/min and hydrogen fluoride gas at 0.8/min.
After mixing at a ratio of 1:1 and aerating for 15 minutes, the supply of hydrogen fluoride gas was stopped and the N2 gas was increased to 3:3 per minute. After cooling to room temperature, about 470I of metal magnetic powder A-1 was obtained.

The thermal properties of the obtained metal magnetic powder were measured in the atmosphere using a differential thermal balance, and the results are as shown in FIG. Note that the chart speed was 2.5 μ/min, the program rate was 5° C./min, and the DTA was 50 μV. The ignition point is estimated to be 350°C, indicating that it is sufficiently stable. FIG. 2 shows a scanning electron micrograph of the metallic magnetic powder used for thermal analysis at a magnification of 6400 times. This powder was further subjected to an X-ray photoelectron analyzer for surface diffraction, and the results are shown in FIG. The samples used in the above measurements were obtained by repeatedly washing with ethyl alcohol and drying in vacuum.

Therefore, it has become possible to safely measure fine metal magnetic powder whose flammability has virtually disappeared due to the fluoride coating on its surface.

Example 2 In the apparatus used in Example 1, 650 pieces of iron oxide (Fe203) with an average particle size of 0.8 μm were added! i' was charged with a mixture of 130F ammonium fluoride (NI (4F)) and heated to room temperature while flowing N2 gas at a rate of 31/min.
While raising the temperature to 500℃ and keeping the temperature inside the furnace at the same temperature,
N2 gas was aerated at a rate of 301/min, and after 2 hours, the N2 gas was switched again, and after cooling to room temperature while aerating at a rate of 31/min, metal magnetic powder A-2 was obtained. .

Example 3 Cobalt-containing iron oxide (average particle size 0.
5 μm) 650.9 was charged into the apparatus of Example 1, and N2.
While flowing ff gas at a rate of 31/min,
t:, and while keeping the furnace temperature at the same temperature, N2
Gas was passed through at a rate of 301/min, and after 2 hours, it was switched to N gas again, and the N2 gas was mixed with hydrogen fluoride at a rate of 0.61/min. After ventilation for one minute, the supply of hydrogen fluoride gas was stopped, and the N2 gas was returned to a rate of 31/min, and after cooling to room temperature, metal magnetic powder A-3 was obtained.

Example 4 Manganese sulfate and ferrous sulfate solution were mixed so that the molar ratio of F+s/Mn was 2, neutralized with caustic soda, and then subjected to aerobic oxidation to produce manganese ferrite (average particle size 0.
4μm) 650.9, acidic ammonium fluoride (NH4
After adding 130 g of HF'2) and mixing well, the mixture was charged into the apparatus of Example 1, and while flowing N2 gas at a rate of 3 mm per minute, the temperature was raised from room temperature to 9400''C. Aeration was carried out at a rate of 301/min, and after 2 hours and 30 minutes, the switch was again made to N2 gas, and metal magnetic powder A-4 was obtained while aerating N2 gas at a rate of 31/min.

Example 5 Nickel sulfate and ferrous sulfate solution were mixed so that the Pa/Ni molar ratio was 5, neutralized with caustic soda, the resulting precipitate was thoroughly washed, and then dried powder 55ON was prepared. It was placed in the apparatus of Example 1, and heated from room temperature to 500° C. while flowing N21f gas at a rate of 31/min.

While keeping the temperature inside the furnace at the same temperature, N2 gas is supplied at 301 m/min.
After 2 hours, the gas was switched to N2f gas at a rate of 2.41% per minute. Hydrogen fluoride gas was mixed at a rate of 0.31 per minute, and NH gas was mixed at a rate of 0.31 per minute, and the mixture was aerated for 15 minutes. Thereafter, the hydrogen fluoride, NH, and gases were stopped, and the mixture was cooled to room temperature while flowing N2 gas at a rate of 3j to obtain metal magnetic powder A-5.

Example 6 After neutralizing a ferrous sulfate solution with caustic soda, sodium silicate was hydrolyzed into needle-shaped α-F OOH crystals with a major axis of 0.5 μm and a uniaxial ratio of 10 obtained by aerobic oxidation. by 0.5
% of silicic acid and heated and heated by a known method.
Iron oxide 300.9% obtained by dehydration was charged into the apparatus of Example 1, and the temperature was raised from room temperature to 400° C. while flowing N2 gas at a rate of 31% per minute. After that, while keeping the temperature inside the furnace at the same temperature, N2 gas was vented at a rate of 221°/min. After 2 hours and 20 minutes, the switch was again switched to N2 gas, and the N2 gas was introduced at a rate of 2.2°/min. 51, hydrogen fluoride at 0.5 per minute
7 parts and aerated for 300 minutes. Thereafter, the hydrogen fluoride was stopped and the mixture was cooled to room temperature while flowing N2 gas at a rate of 31% to obtain metal magnetic powder A-6.

Example 7 An aqueous solution of zinc sulfate aqueous salt of 22rn9 was prepared for iron oxide (Fe304) 1.9, the solution was neutralized using caustic soda, the resulting precipitate was washed, and then dried. In addition, 0.3 μm of ZnO-coated iron oxide (Fe, 04)
Particles 650I were charged into the apparatus of Example 1, and the temperature was raised from room temperature to 400° C. while flowing N2 gas at a rate of 31 per minute.

While keeping the furnace temperature at the same temperature, N2 gas is supplied at 331 m/min.
Aeration was performed at a rate of did. Thereafter, the hydrogen fluoride gas was stopped, and the mixture was cooled in a room @o while flowing N2 gas at a rate of 31 per minute to obtain metal magnetic powder A-7.

Comparative Example 1 Reduction was carried out in exactly the same manner as in Example 1 except that the flow rate of hydrogen fluoride was changed, and while maintaining the same temperature, N2 gas was supplied at 2.91/min and hydrogen fluoride gas was supplied at 0/min. .1A! After stirring for 6 minutes, the hydrogen fluoride gas was stopped and the N
2. It was cooled to room temperature while flowing ff gas at a rate of 31/min. After confirming that it had completely cooled to room temperature, it was taken out into the air, where it partially ignited and partially changed its color from reddish brown to black.

A sample for analysis was taken from the black-gray unignited part, and the F content was found to be 0.1%.

Comparative Example 2 Similar to Comparative Example 1, except for the conditions for forming a fluoride film, reduction was carried out in the same manner as in Example 1, and then the N2 gas was switched to gas at a rate of 31/min. The temperature inside the furnace was lowered to 19°O 0 C while venting. While keeping the same temperature, N
The two gases were mixed at a rate of 2.51 per minute and hydrogen fluoride gas was mixed at a rate of 0.51 per minute, and the mixture was aerated for 24 hours. Thereafter, the hydrogen fluoride gas was stopped, and the mixture was cooled to room temperature while flowing N2 gas at a rate of 31/min. After confirming that it had completely cooled down to room temperature, the sample was taken out into the air, whereupon a flame was generated and the entire sample turned reddish-brown.

Comparative Example 3 Similar to Example 1, iron oxide (F@, 04) 65011 was reduced with N2 gas, then switched to -N2 gas without performing the stabilization treatment of the present invention, and after cooling to room temperature. ,
To prevent ignition, take it out in an organic solvent and dry it naturally.
Metal magnetic powder B-3 approx. 4701! I got it.

Comparative Example 4 As in Example 6, α-FeOOH needle crystals 3001 were reduced with N2 gas, then switched to N2 gas without performing the stabilization treatment of the present invention, and after cooling to room temperature,
To prevent ignition, take it out in an organic solvent and dry it naturally.
Metal magnetic powder B-4 was obtained.

All of the magnetic metal powders obtained in the above examples were black to gray powders that were stable in the air. Table 1 shows various properties of each magnetic powder together with the results of comparative examples.

"Effects of the Invention" As is clear from the above, according to the present invention, fine fluoride-coated metal magnetic powder with an average particle size of 8 μm or less has sufficient stability such as ignition prevention ability in various handling and storage conditions. can be obtained. In addition, metal magnetic powder having such excellent properties can be produced in a safe and simple process, with easy control over the formation of a fluoride film, and without reducing saturation magnetization.

[Brief explanation of drawings]

FIG. 1 shows the metal magnetic powder A-1 obtained in Example 1.
Figure 2 shows the results of differential thermal analysis of the metal magnetic powder A-1 obtained in Example 1.
FIG. 3 is a scanning electron micrograph at 6400 times magnification, and FIG. 3 is an X-ray photoelectron analysis result of metal magnetic powder A-1 obtained in Example 1.

Claims (5)

[Claims] (1) A stable metal magnetic powder characterized in that the surface of the metal particles is coated with a fluoride of the metal and the average particle size is 8 μm or less. (2) The amount of fluoride is 0 in stable metal magnetic powder as fluorine.
．． The stable magnetic metal powder according to claim 1, which has a content of 1% or more. (3) A method for producing stable metal magnetic powder, which comprises treating metal magnetic powder with hydrogen fluoride and/or a hydrogen fluoride-containing compound, fluorine and/or a fluorine compound. (4) Claim 3, in which the metal magnetic powder is treated with hydrogen fluoride or a fluorine-containing gas at a temperature range of 200 to 820°C, and further with an inert gas or reducing gas for diluting these gases. A method for producing the described stable metal magnetic powder. (5) The method for producing stable magnetic metal powder according to claim 3, wherein the metal magnetic powder is obtained by reducing an oxide of the metal mixed in advance with a hydrogen fluoride-containing compound with a reducing gas. .