JP2556013B2 - Manufacturing method of magnetic fluid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a magnetic fluid. More specifically, it relates to a method for producing a magnetic fluid from an aqueous suspension of magnetic ultrafine particles prepared by a wet method.

[Conventional technology]

Magnetic ultrafine particles prepared by a wet method or those obtained by stabilizing it with a surfactant are conventionally prepared by drying an aqueous suspension thereof by a vacuum drying method, etc. It is manufactured into a magnetic fluid by a method of dispersing in a base oil, a peptization method of introducing the above-mentioned aqueous suspension into heated kerosene, or the like. However, the former method is exposed to a heated aqueous solution that is relatively susceptible to chemical changes for a long time, and the latter method is
There is a problem that it involves a danger in the process.

[Problems to be solved by the invention]

Therefore, the present inventors have conducted various investigations on a method for producing a magnetic fluid without causing the problems found in the conventional methods for producing a magnetic fluid, and as a result, have isolated magnetic ultrafine particles from an aqueous suspension. It was found that the method of concentrating the aqueous suspension without performing the above and then performing the solvent replacement by the base oil by the freeze-drying method is extremely effective.

[Means for solving the problem]

Therefore, the present invention relates to a method for producing a magnetic fluid, which is produced by adding a base oil to a concentrated aqueous suspension of ultrafine magnetic particles surface-treated with a surfactant, and freeze-drying this. Done.

The concentrated aqueous suspension of magnetic ultrafine particles surface-treated with a surfactant used in the method of the present invention is prepared by a wet method, and an aqueous suspension of magnetic ultrafine particles to which a surfactant is added is prepared. For example, the one concentrated by the freeze-drying method is used.

In the preparation of such a concentrated aqueous suspension, first, an aqueous suspension of magnetic ultrafine particles is prepared by a wet method, which has the advantage that particle size control is easy. Preparation of an aqueous suspension of magnetic ultrafine particles by this wet method is performed by using divalent ferrous salt (sulfate, nitrate, chloride, etc.) and trivalent ferric salt (sulfate, nitrate, chloride, etc.) An aqueous alkaline solution such as sodium hydroxide or potassium hydroxide is added to a mixed aqueous solution of or with a divalent metal salt (sulfate such as cobalt, nickel, manganese, zinc, etc., nitrate, chloride, etc.) added thereto. It is done by aging.

Thus, ferrites ultrafine particles, for example magnetite (Fe ₃ 0 _4), nickel ferrite (Ni0-Fe
₂ 0 _3), manganese ferrite (Mn0-Fe ₂ 0 _3), cobalt ferrite (CO0-Fe ₂ 0 _3), nickel - zinc ferrite _{(Ni · Zn0 · Fe 2 0} 3), manganese - zinc ferrites (Mn _{· Zn0 · Fe 2 0 3)} , cobalt - zinc ferrite (Co ·
Zno · Fe ₂ 0 ₃₎ and the like, obtained with particle size of about 50 to 100 Å.

In this way, the aqueous suspension of the magnetic ultrafine particles prepared and aged is provided with higher unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid or their alkali metal salts, sodium stearate and dodecylamine. Acetate, morphophosphate, sodium dodecylbenzene sulfonate, polyoxyethylene octylphenol ether, sodium di (tridecyl) sulfosuccinate, di [tridecyltri (ethylene oxide)] phosphate ester, 2-penta (perfluoropropylene oxide) peroxide Various surfactants such as fluoropropionic acid are added in an amount sufficient to disperse the ultrafine particles, followed by washing to remove excess surfactant.

The aqueous suspension of magnetic ultrafine particles to which the obtained surfactant is added is concentrated until the occupied volume becomes approximately 25 to 60% by volume with the ultrafine particles of the surface treated with the surfactant by, for example, freeze-drying. To be done. Freeze-drying is performed by conventional methods according to the pressure and temperature conditions used to remove water.

The concentrated aqueous suspension of the ultrafine magnetic particles surface-treated with the surfactant thus obtained contains a base oil as a dispersion medium such as kerosene, dodecane, eicosylnaphthalene, and synthetic polyolefin. It was added at a ratio of at least about 25% by volume to the suspension, and after dispersing it by means such as mechanical stirring method or application of ultrasonic waves, freeze-drying was performed again and dispersed in base oil. A magnetic fluid composed of ultrafine magnetic particles can be obtained.

〔The invention's effect〕

According to the method of the present invention, the solvent substitution from the aqueous suspension directly to the base oil suspension is carried out without separating the magnetic ultrafine particles, and since the freeze-drying is carried out in the presence of the base oil, Before the fine particles agglomerate with each other, the base oil infiltrates between the super-particulate particles, and a magnetic fluid in which agglomeration does not occur between the particles, that is, a sol state is maintained is obtained.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 1N FeS0 ₄ aqueous solution 100 ml and 1N Fe ₂ (S0 ₄ ) ₃ aqueous solution 10
The required amount of 6N Na0H aqueous solution is added to 0 ml of the mixed solution at a rate of 6 ml per minute with stirring until the pH becomes 11.5, and then aged at 90 ° C for 30 minutes. To this, 200 ml of a 3 wt% oleic acid aqueous solution is added, and the mixture is heated at 80 ° C. for 30 minutes and cooled. Then 1N HCl
Is slowly added until the pH is 5-6 and then washed to remove excess oleic acid liberated. Next, this is -50 ℃
Rapidly cool to below, gradually return to room temperature while maintaining the pressure below 0.2 Torr, sublimate the water to about 1/3, concentrate liquid of magnetic ultrafine particles (fine particle occupied volume 35% by volume)
Get.

Add kerosene 20 as a base oil to this concentrated suspension.
After adding ml and dispersing under stirring, it was rapidly cooled again to -50 ° C or less and freeze-dried under reduced pressure in the same manner to obtain a magnetic fluid having a diameter of about 100Å and uniformly dispersed in the base oil. .

Example 2 In Example 1, 12 g of sodium di (tridecyl) sulfosuccinate was used as a surfactant, and the dispersion after addition of kerosene was carried out by ultrasonic irradiation. As a result, a magnetic fluid uniformly dispersed in the base oil was obtained.

Example 3 In Example 1, 4.6 g of laurylamine hydrochloride was used as a surfactant, and n-dodecane 20 was used as a base oil.
ml was used. However, after adding the surfactant, 1 at 90 ℃
After being heated for an hour and cooled, 1N NaOH was added to adjust the pH to 9.
As a result, a magnetic fluid uniformly dispersed in the base oil was obtained.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area C10N 20:06 40:14 70:00

Claims (3)

(57) [Claims] 1. A method for producing a magnetic fluid, which comprises adding a base oil to a concentrated aqueous suspension of ultrafine magnetic particles surface-treated with a surfactant and freeze-drying the base oil. 2. The concentrated aqueous suspension used is prepared by a wet method, and the aqueous suspension of magnetic ultrafine particles to which a surfactant is added is concentrated by a freeze-drying method. 2. The method for producing a magnetic fluid according to claim 1. 3. The method for producing a magnetic fluid according to claim 2 or 3, wherein an aqueous suspension liquid is used which is concentrated until the occupied volume of the magnetic ultrafine particles becomes about 25 to 60% by volume. .