JPH05159917A - Fluorosilicon ferromagnetic fine particle and its manufacture, and magnetic fluid and its manufacture - Google Patents

Abstract

PURPOSE:To elevate dispersion stability, and improve low torque, cold resistance, chemical resistance, and insulation property, and besides, remove the compatibility with water, etc., by silicifying ferromagnetic substance fine particles with fluorosilicon oligomer. CONSTITUTION:A fluorosilicon group is introduced into the surface of a ferromagnetic substance fine particle by silicifying a ferromagnetic fine particle such as magnetite, etc., with specified fluorosilicon oligomer. Next, this fluorosilicon ferromagnetic substance fine particle obtained is thrown in a low boiling point fluoric solvent so as to do cracking with a crusher. Next, a perfluoro solvent such as a kind of perfluoropolyether, etc., is added and is agitated and dispersed. Then, the low boiling point fluoric solvent is removed by heating the dispersed solution. Here, at need, an interface activator is added. Hereby, dispersion stability ups, and besides heat resistance and mechanical strength increases, and mechanical strength also increases, and besides compatibility to water and hydrocarbon oil can be removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to novel fluorosilicon-based ferromagnetic fine particles, magnetic fluid, and a method for producing them.

[0002]

2. Description of the Related Art A magnetic fluid is an extremely stable colloidal solution in which ferromagnetic fine particles such as magnetite, ferrite, iron, cobalt, etc. are dispersed in a liquid, and the solution itself has a characteristic that it exhibits strong magnetic properties. .. Therefore, even though it is a liquid, its behavior can be freely controlled by a magnet or the like, and therefore it is applied in various fields such as a damping agent, a sealing agent in a sealing mechanism of a magnetic disk or a sealing agent for aerospace.

However, in the above-mentioned fields, in addition to low torque, cold resistance, chemical resistance and insulation,
Although it is required that they are incompatible with water and hydrocarbon-based oils, it is said that the above-mentioned requirements cannot be sufficiently satisfied in magnetic fluids that are conventionally used as a dispersion solution of a hydrocarbon-based solvent. There's a problem. Therefore, there has been proposed a magnetic fluid in which ferromagnetic fine particles are dispersed in the presence of a fluorocarbon surfactant, using a perfluoro solvent as a dispersion solution (US Pat. No. 3,784,471). In the magnetic fluid, there is a problem that the affinity between the surfactant and the perfluoro solvent decreases with time, and the dispersion stability of the magnetic fluid deteriorates.

Accordingly, ferromagnetic fine particles having high dispersion stability in a perfluoro solvent and high dispersion stability, low torque, cold resistance, chemical resistance, and insulation properties, and a phase for water and hydrocarbon oils. At present, there is a strong demand for the development of magnetic fluids that are not soluble.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide fluorosilicone ferromagnetic fine particles having a high dispersion stability in a perfluorosolvent and the like, and a method for producing the same.

Another object of the present invention is low torque, cold resistance,
It is an object of the present invention to provide a magnetic fluid having excellent chemical resistance and insulating properties, having no compatibility with water and hydrocarbon oils, and having excellent dispersion stability, and a method for producing the same.

[0007]

According to the present invention, a ferromagnetic silicon fine particle is obtained by silylating ferromagnetic fine particles with a fluorosilicon oligomer represented by the following general formula 3 (hereinafter referred to as fluorosilicon oligomer 1). Magnetic particles are provided.

[0008]

[Chemical 3]

Further, according to the present invention, there is provided a method for producing fluorosilicone-based ferromagnetic fine particles, which comprises reacting the fluorosilicone oligomer 1 with ferromagnetic fine particles.

Further, according to the present invention, there is provided a magnetic fluid containing the fluorosilicon-based ferromagnetic fine particles as a main component.

Further, according to the present invention, there is provided a method for producing a magnetic fluid, characterized in that the fluorosilicon-based ferromagnetic fine particles are dispersed in a perfluoro-based solvent.

The present invention will be described in more detail below.

The fluorosilicon-based ferromagnetic fine particles of the present invention are ferromagnetic fine particles obtained by subjecting the ferromagnetic fine particles to a silylation treatment with a specific fluorosilicon oligomer to introduce a fluorosilicon group on the surface of the ferromagnetic fine particles. ..

The particle size of the ferromagnetic fine particles of the present invention is from 50 to 50.
It is preferably in the range of 1000Å. The particle size is 50
If it is less than Å, the production is difficult, and if it exceeds 1000 Å, the particles settle and the stability decreases, which is not preferable.

In the fluorosilicon-based ferromagnetic fine particles of the present invention, the specific fluorosilicon oligomer used when the ferromagnetic fine particles are subjected to the silylation treatment is the fluorosilicon oligomer 1 represented by the general formula 3. .. In the fluorosilicone oligomer 1, when R ₂ or R ₃ has 5 or more carbon atoms, it is difficult to produce, and when n ₁ exceeds 10, or n ₂ is 8
If it exceeds, the solubility in the solvent decreases, and therefore it cannot be used. Further, when m exceeds 10, the production is difficult. Furthermore, the average molecular weight of the fluorosilicone oligomer 1 is preferably in the range of 500 to 10,000. When the average molecular weight is out of the above range, the production is difficult, which is not preferable.

In the fluorosilicone oligomer 1, the applicable RF, namely,-(CF ₂ ) n ₁ X or the following general formula 4 is specifically listed. F ₃ C-, F
(CF ₂ ) ₂ −, F (CF ₂ ) ₃ −, F (CF ₂ ) ₄ −, F
(CF ₂ ) ₅ −, F (CF ₂ ) ₆ −, F (CF ₂ ) ₇ −, F
(CF ₂ ) ₈ −, F (CF ₂ ) ₉ −, F (CF ₂ ) ₁₀ −, H
_{CF 2 -, H (CF 2} ) 2 -, H (CF 2) 3 -, H (C
F ₂ ) ₄ −, H (CF ₂ ) ₅ −, H (CF ₂ ) ₆ −, H (CF
_{2) 7 -, H (CF} 2) 8 -, H (CF 2) 9 -, H (C
F ₂ ) ₁₀ −, ClCF ₂ −, Cl (CF ₂ ) ₂ −, Cl (C
_{F 2) 3 -, Cl (} CF 2) 4 -, Cl (CF 2) 5 -, Cl
(CF ₂ ) ₆ −, Cl (CF ₂ ) ₇ −, Cl (CF ₂ ) ₈ −,
Cl (CF ₂ ) ₉ −, Cl (CF ₂ ) ₁₀ −, the following chemical formulas 5, 5, 6, 7, 8, 9, 10, 11, and 1
2 and 13

[0017]

[Chemical 4]

[0018]

[Chemical 5]

[0019]

[Chemical 6]

[0020]

[Chemical 7]

[0021]

[Chemical 8]

[0022]

[Chemical 9]

[0023]

[Chemical 10]

[0024]

[Chemical 11]

[0025]

[Chemical 12]

[0026]

[Chemical 13]

Specific examples of the fluorosilicone oligomer 1 include those represented by the following general formulas 14, 15, 15, 16, 17, 18, 19, 20, 21, and 2.
2, 23, 24, 25, 26, 27, 2
8, Chemical 29, Chemical 30, Chemical 31, Chemical 32, Chemical 33, Chemical 3
4, Chemical formula 35, Chemical formula 36, Chemical formula 37, Chemical formula 38, Chemical formula 39 and the like can be mentioned (where m is an integer of 1 to 10).

[0028]

[Chemical 14]

[0029]

[Chemical 15]

[0030]

[Chemical 16]

[0031]

[Chemical 17]

[0032]

[Chemical 18]

[0033]

[Chemical 19]

[0034]

[Chemical 20]

[0035]

[Chemical 21]

[0036]

[Chemical formula 22]

[0037]

[Chemical formula 23]

[0038]

[Chemical formula 24]

[0039]

[Chemical 25]

[0040]

[Chemical formula 26]

[0041]

[Chemical 27]

[0042]

[Chemical 28]

[0043]

[Chemical 29]

[0044]

[Chemical 30]

[0045]

[Chemical 31]

[0046]

[Chemical 32]

[0047]

[Chemical 33]

[0048]

[Chemical 34]

[0049]

[Chemical 35]

[0050]

[Chemical 36]

[0051]

[Chemical 37]

[0052]

[Chemical 38]

[0053]

[Chemical Formula 39]

To prepare the fluorosilicone oligomer 1, for example, a difluoroalkanoyl peroxide represented by the following general formula 40 and a vinyl group-containing organosilicon compound represented by the following general formula 41 are preferably used in a molar ratio. In the range of 1: 1.0 to 10.0, particularly preferably 1:
Charged in the range of 1.2 to 5.0, and the reaction temperature is preferably in the range of -20 to + 150 ° C, particularly preferably 0 to 10.
The reaction can be performed at 0 ° C. for a reaction time of preferably 30 minutes to 20 hours, particularly preferably 3 to 10 hours.

[0055]

[Chemical 40]

[0056]

[Chemical 41]

RF in the difluoroalkanoyl peroxide used at this time is the fluorosilicone oligomer 1
Are the same as RF specifically listed in the above, and specific examples of the difluoroalkanoyl peroxide include diperfluoro-2-methyl-3-oxahexanoyl peroxide and diperfluoro-2,5-dimethyl peroxide. −
3,6-dioxanonanoyl, diperfluoro peroxide
Preferable examples include 2,5,8-trimethyl-3,6,9-trioxadodecanoyl, diperfluorobutyryl peroxide, diperfluoroheptanoyl peroxide, and the like. Further, as the vinyl group-containing organosilicon compound,
Preferable examples include trimethoxyvinylsilane, 3-methacryloxypropyltrimethoxysilane, triethoxyvinylsilane, triisopropoxyvinylsilane, and 3-methacryloxypropyldiethoxymethylsilane.

In the fluorosilicone ferromagnetic fine particles of the present invention, the ferromagnetic fine particles to be silylated with the fluorosilicone oligomer 1 are not particularly limited as long as they are normally used ferromagnetic fine particles. None, specifically, for example, ferrous ion and ferric ion in an arbitrary ratio, preferably in a weight ratio of 1: 0.01-1.
Magnetite mixed in the range of 00; general formula MO.Fe ₂ O ₃
Or RO.6Fe ₂ O ₂ (where M is cobalt, nickel,
An iron compound represented by manganese, copper, zinc, etc., and R represents barium, strontium, etc.), nickel sulfate, zinc sulfate, manganese zinc ferrite, nickel zinc ferrite, cobalt ferrite, nickel ferrite, manganese ferrite, iron, Preferable examples include ferromagnetic metals such as cobalt and rare earths.

In the method for producing fluorosilicon-based ferromagnetic fine particles according to the present invention, the fluorosilicon oligomer 1 and the ferromagnetic fine particles are reacted with each other, and the surface of the ferromagnetic fine particles is subjected to silane coupling treatment to obtain the ferromagnetic material. It is characterized in that a fluorosilicone group is introduced into the surface of the body particles.

To carry out the reaction, for example, an aqueous solution or an aqueous slurry of the ferromagnetic fine particles is preferably added with an alkali such as aqueous ammonia, sodium hydroxide or potassium hydroxide with respect to 100 parts by weight of the aqueous slurry. 0.01 ~
100 parts by weight of organic solvent such as toluene is preferably added in an amount of 0.01 to 1000 parts by weight, and unsaturated fatty acid such as oleic acid, linoleic acid, or linoleic acid is added in an amount of preferably 0.1 to 1000 parts by weight as a dispersant. Then, aging is preferably carried out at 0 to 200 ° C. with stirring to obtain a dispersion solution. At this time, the content ratio of the ferromagnetic fine particles in the dispersion solution is preferably 0.1 to 1000 g / liter. Then, after water in the obtained dispersion solution is separated and removed, the fluorosilicone oligomer 1 is added, and the temperature is not lower than the boiling point of the organic solvent used, preferably for 10 minutes to
Heat and reflux for 100 hours to react. At this time, if necessary, ammonia water or the like may be further added and the mixture may be heated and stirred. Then, the fluorosilicon ferromagnetic fine particles of the present invention can be obtained by washing and filtering with water or the like.

When carrying out the reaction, the dispersion solution containing the ferromagnetic fine particles and the fluorosilicone oligomer 1 are used.
It is preferable that the charging ratio of the above is in the range of 1: 0.01 to 100 in terms of volume ratio. When the charging ratio of the fluorosilicone oligomer 1 is less than 0.01, the surface performance brought about by the fluorosilicone oligomer is lowered, and when it exceeds 100, the particles are precipitated and the stability is lowered, which is not preferable.

The magnetic fluid of the present invention is characterized by containing the fluorosilicon-based ferromagnetic fine particles as a main component, and the fluorosilicon-based ferromagnetic fine particles dispersed in a dispersion medium.

As the dispersion medium, CF ₃ -[-(OCF (CF ₃ ) C
F ₂ ) n- (OCF ₂ ) m] -OCF ₃ , CF ₃ -[-(OCF (CF ₃ ) CF ₂ ) n- (OCF ₂ ) m]-
OCF ₂ COOH, CF ₃ -[-(OCF (CF ₃ ) CF ₂ ) n- (OCF ₂ ) m] -OCF ₂ CH ₂ O
H, CF ₃ -[-(OCF (CF ₃ ) CF ₂ ) n- (OCF ₂ ) m] -OCF ₂ SO ₃ OH, CF ₃ -[-
(OCF (CF ₃ ) CF ₂ ) n- (OCF ₂ ) m] -OCF ₂ PO ₃ H, CF ₃ -[-(OCF (CF ₃ ) C
F ₂ ) n- (OCF ₂ ) m] -OCF ₂ OH, CF ₃ -[-(OCF (CF ₃ ) CF ₂ ) n- (OCF ₂ )
m] -OCF ₂ NH ₂ , F-[(CF ₃ ) CFCF ₂ O] m-CF ₂ (CF ₃ ), F-[(CF ₃ ) CFC
Compounds represented by F ₂ O] m-CFH (CF ₃ ),-(CF ₂ CFCl) n-, and the like; preferred are perfluoro solvents such as perfluoropolyethers obtained by oligomerization of hexafluoropropene oxide. Alternatively, a commercially available product can be used.

The mixing ratio of the dispersion medium and the fluorosilicon-based ferromagnetic fine particles is 1: 0.0 by weight.
It is preferably 1 to 100. If the compounding ratio of the fluorosilicone ferromagnetic fine particles is less than 0.01, the desired magnetic fluid cannot be obtained, and if it exceeds 100, the dispersion stability decreases, which is not preferable.

In the magnetic fluid of the present invention, the fluorosilicon-based ferromagnetic fine particles and the dispersion medium further contain an anionic, cationic, or nonionic surfactant, and particularly preferably a fluorine-based surfactant. Agents may be added.

The method for producing a magnetic fluid according to the present invention is characterized in that the fluorosilicon-based ferromagnetic fine particles are dispersed in a perfluoro-based solvent.

The perfluoro-based solvent is the same as the perfluoro-based solvent specifically listed as the dispersion medium.

In order to carry out the dispersion, for example, the fluorosilicon-based ferromagnetic particles are first added to the flon 113.
{"DAIFLON 113" (Brand name, Daikin Industries, Ltd.
)}, Etc., and crush with a crusher such as a planetary ball mill. Then, the perfluoro-based solvent is added and dispersed by stirring, and then the resulting dispersion solution is heated to remove the low-boiling fluorine-based solvent or crushed by the pulverizer, and then the low-boiling fluorine is added. The system solvent can be removed by heating, and then the perfluoro system solvent can be added to disperse the system solvent, or the system can be dispersed directly in the perfluoro system solvent without using the low boiling point fluorine system solvent. At this time, if necessary, a surfactant such as a fluorine-based agent may be added for dispersion.

[0069]

EFFECT OF THE INVENTION The fluorosilicon-based ferromagnetic fine particles of the present invention are ferromagnetic fine particles whose surface is surface-modified with a specific fluorosilicon, and the fluorosilicon group is introduced by a chemical bond. Also, the properties attributed to silicon can be maintained for a long period of time, and it has a high affinity for perfluoro solvents and the like.

Further, since the magnetic fluid of the present invention uses the above-mentioned fluorosilicon-based ferromagnetic fine particles, it has excellent stability and heat resistance as compared with the conventional magnetic fluid using a hydrocarbon oil as a dispersant. Excellent properties such as abrasion resistance, chemical stability and oil repellency can be imparted. Therefore, it is useful as a damping agent, a sealing agent in a sealing mechanism of a magnetic disk, a sealing agent for aerospace and the like.

The fluorosilicon-based ferromagnetic fine particles and the magnetic fluid manufacturing method of the present invention can easily obtain the desired fluorosilicon-based ferromagnetic fine particles and magnetic fluid in a short time.

[0072]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0073]

Example 1 7.6 g (0.06 mol) of ferric chloride and 14.6 g (0.09 mol) of ferric chloride were dissolved in 50 ml of distilled water. Next, 2 ml of 28 wt% ammonia aqueous solution was added to the resulting solution while stirring to adjust the solution to be alkaline, and a water slurry of magnetite was prepared. Next, a solution prepared by dissolving 5 ml of oleic acid in 50 ml of toluene was heated to 90 ° C., and while rapidly stirring, the resulting water slurry of magnetite was added, stirring was stopped, heating was performed while maintaining the same temperature, and water was added. Separated into layers and oil layer. After removing the aqueous layer, toluene was added to the obtained oil layer to adjust the volume to 100 ml to obtain a magnetite dispersion liquid.

Then, 10 m of the obtained magnetite dispersion liquid
l was weighed out under a nitrogen atmosphere, 2.0 ml of a fluorosilicone oligomer represented by the following chemical formula 42 was added, and the mixture was heated under reflux at 120 ° C. for 3 hours, and then 1 ml of a 28 wt% ammonia solution was added. The mixture was heated and refluxed at the same temperature for 30 minutes. Then, after cooling to room temperature, 100 ml of distilled water was added and stirred, and the obtained fluorosilicone magnetite was dispersed in the aqueous layer. Then, after separating into a water layer and a toluene layer, the toluene layer was removed and unreacted oleic acid-adsorbed magnetite was removed. While stirring the obtained aqueous layer, a 3N-HCl aqueous solution was added until the pH became 5.5, and the mixture was allowed to stand, then the supernatant was removed, and washing with water was repeated 3 times. Further, the oily oleic acid was removed by washing with methanol, and the mixture was heated at 120 ° C. for 1 hour and then dried to obtain 2.8 g of fluorosilicone ferromagnetic fine particles of the present invention.

[0075]

[Chemical 42]

The IR spectrum of the obtained fluorosilicon-based ferromagnetic fine particles was measured and found to be 1335 cm to ^{1
_{(CF 3), 1240cm ~ 1}} (CF 2), 1200cm ~ 1
Absorption was observed in (SiO), and it was confirmed that a fluoroalkyl group was introduced.

Further, 2.8 g of the obtained fluorosilicone-based ferromagnetic fine particles was added to chlorofluorocarbon 11310 ml,
Crushing was performed for 10 minutes using a planetary ball mill and dispersed in Freon 113. 5 ml of the resulting dispersion solution
Was mixed with 2 ml of a perfluoro solvent “Daifloyl” (trade name, manufactured by Daikin Industries, Ltd.) and heat-treated at 40 ° C. to remove CFCs 113 having a low boiling point to obtain the magnetic fluid of the present invention. .. The obtained magnetic fluid was a black-brown uniform dispersion, and was stable without being separated even when left standing at 40 ° C. for 1 month. Furthermore, it was stable even in a magnetic field.

[0078]

Example 2 The compound represented by the chemical formula 42
2.3 g of the fluorosilicon-based ferromagnetic fine particles of the present invention was obtained in the same manner as in Example 1 except that the compound represented by the following chemical formula 43 was used.

[0079]

[Chemical 43]

The IR spectrum of the obtained fluorosilicon-based ferromagnetic fine particles was measured and found to be 1335 cm to ^{1
_{(CF 3), 1245cm ~ 1}} (CF 2), 1200cm ~ 1
Absorption was observed in (SiO), and it was confirmed that a fluoroalkyl group was introduced.

Dispersion was performed in the same manner as in Example 1 except that 2 g of the obtained fluorosilicone-based ferromagnetic fine particles were used to obtain a magnetic fluid of the present invention. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0082]

Example 3 The compound represented by the chemical formula 42
In the same manner as in Example 1 except that the compound represented by the following chemical formula 44 was used, 3.1 g of the fluorosilicon-based ferromagnetic fine particles of the present invention was obtained.

[0083]

[Chemical 44]

The IR spectrum of the obtained fluorosilicon-based ferromagnetic fine particles was measured and found to be 1330 cm to ¹
(CF ₃ ), 1240 cm to ¹ (CF ₂ ), 1200 cm
Absorption was observed in ¹ (SiO), and it was confirmed that a fluoroalkyl group was introduced.

Further, dispersion was performed in the same manner as in Example 1 except that 2 g of the obtained fluorosilicone ferromagnetic fine particles were used to obtain a magnetic fluid of the present invention. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0086]

Example 4 The compound represented by the chemical formula 42
In the same manner as in Example 1 except that the compound represented by the following chemical formula 45 was used, 3.1 g of the fluorosilicone ferromagnetic fine particles of the present invention was obtained.

[0087]

[Chemical 45]

The IR spectrum of the obtained fluorosilicon-based ferromagnetic fine particles was measured and found to be 1330 cm.
¹ (CF ₃ ), 1245 cm to ¹ (CF ₂ ) and 1740c
Absorption was observed in m- ¹ (> C = O) and 1200 cm- ¹ (SiO), and it was confirmed that a fluoroalkyl group and a methacryloxy group were introduced.

Further, dispersion was performed in the same manner as in Example 1 except that 2 g of the fluorosilicone-based ferromagnetic particles thus obtained were used to obtain a magnetic fluid of the present invention. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0090]

Example 5 The compound represented by the chemical formula 42
2.7 g of the fluorosilicon-based ferromagnetic fine particles of the present invention was obtained in the same manner as in Example 1 except that the compound represented by the following chemical formula 46 was used.

[0091]

[Chemical 46]

The IR spectrum of the obtained fluorosilicon-based ferromagnetic fine particles was measured and found to be 1330 cm to ^{1
_{(CF 3), 1235cm ~ 1}} (CF 2), 1200cm ~ 1
Absorption was observed in (SiO), and it was confirmed that a fluoroalkyl group was introduced.

Further, dispersion was performed in the same manner as in Example 1 except that 2 g of the obtained fluorosilicone-based ferromagnetic fine particles were used to obtain a magnetic fluid of the present invention. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0094]

[Example 6] The perfluoro solvent "Daifloyl" (trade name, manufactured by Daikin Industries, Ltd.) used in Example 1 was
"Galden Mono Acid" (trade name, manufactured by Enimonte Co., Ltd.)
The magnetic fluid of the present invention was prepared in the same manner as in Example 1 except that the amount was 2 ml. The obtained magnetic fluid was blackish brown, stable, and stable even in a magnetic field.

[0095]

[Example 7] The perfluoro solvent "Daifloyl" (trade name, manufactured by Daikin Industries, Ltd.) used in Example 1 was
"Galden HT" (manufactured by Montefluos Co., Ltd., trade name) 2
The magnetic fluid of the present invention was prepared in the same manner as in Example 1 except that the amount was changed to ml. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0096]

[Example 8] The perfluoro solvent "Daifloyl" (trade name, manufactured by Daikin Industries, Ltd.) used in Example 1 was
The magnetic fluid of the present invention was prepared in the same manner as in Example 1 except that "BARRIERTA J60" (trade name, manufactured by NOK Clewer Co., Ltd.) was 2 ml. The obtained magnetic fluid was blackish brown, stable, and stable in a magnetic field.

[0097]

Comparative Example 1 The compound represented by the chemical formula 42 is
"TSL8257" (Toshiba Silicon Co., Ltd., trade name, C ₆ F ₁₃ CH
₂ CH ₂ Si (OCH ₃ ) ₃ )
Ferromagnetic fine particles were prepared.

When the obtained ferromagnetic fine particles were dispersed in a perfluoro solvent in the same manner as in Example 1, they were not dispersed at all.

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Claims (4)

[Claims] 1. Fluorosilicon-based ferromagnetic fine particles obtained by silylating ferromagnetic fine particles with a fluorosilicon oligomer represented by the following general formula 1. [Chemical 1] 2. A method for producing fluorosilicon-based ferromagnetic fine particles, which comprises reacting a fluorosilicon oligomer represented by the following general formula 2 with ferromagnetic fine particles. [Chemical 2] 3. A magnetic fluid containing the fluorosilicon-based ferromagnetic fine particles according to claim 1 as a main component. 4. A method for producing a magnetic fluid, which comprises dispersing the fluorosilicon-based ferromagnetic fine particles according to claim 1 in a perfluoro-based solvent.