JPS61263202A - Magnetic fluid and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the chemical stability and hydrophobic nature by employing perfluoro compound except polar group of surfactant compound as surfactant and base oil. CONSTITUTION:Aqueous alkaline solution is added to mixed aqueous solution of 2-valency ferrous salt and 3-valency ferric salt or aqueous solution mixture produced by adding 2-valency metal salt to the mixed solution, and matured to prepare an aqueous suspension of fine magnetic powder. After the fine powder is cleaned, the powder is once substituted for the form of suspension of organic solvent. Then, perfluoroether base oil is added to the suspension, the solvent is hen removed to obtain fine magnetic powder dispersed in base oil. In this case, to improve the dispersibility, perfluoroether surfactant is added. A freezing drying method may be used instead of the above solvent substituting method.

Description

[Detailed description of the invention] [Industrial application field] TECHNICAL FIELD The present invention relates to magnetic fluids and methods of manufacturing the same.

More specifically, the present invention relates to a magnetic fluid exhibiting good dispersion stability and a method for producing the same.

[Conventional technology]

In an aqueous suspension of magnetic particles prepared by a wet method,
A surfactant having a carboxyl group derived from an alkali metal salt of a perfluorocarboxylic acid having 8 or more carbon atoms or a perfluorosulfonic acid having a fluorocarbon chain having 8 or more carbon atoms is added and adsorbed, and then dehydrated and dried. , a method for producing magnetic fluid by dispersing it in fluorocarbon base oil was published in Japanese Patent Publication No. 53-13437.
It is stated in the No.

However, for this type of fluorine-based magnetic fluid.

(1) The perfluoro compound used is unstable and easily undergoes hydrofluorination, resulting in the formation of unsaturated hydrocarbon groups in the molecule, which prevents the perfluoro compound from fully demonstrating its properties (2) Due to the strong interaction between fluorine atoms and carbon atoms due to the strong electronegativity of fluorine atoms, perfluoro compounds have poor interaction with other molecules, that is, low affinity, so fluorocarbon base oils are not used. (3) Since the adsorption of surfactants onto magnetic fine particles takes place in an aqueous liquid, it is difficult to disperse the fine particles in base oil. In order to achieve this, a long dehydration and drying process under heating is required.
This not only causes problems in process operation, but also causes oxidation and aggregation of the generated magnetic particles. (4) In general water- or oil-based magnetic fluids, the dispersion concentration of magnetic particles can easily be several 10% by volume, but in fluorine-based systems, it is at most several % by volume. .

This means that the saturation magnetization of the magnetic fluid is limited to a small value [problem to be solved by the invention]. As a result of various studies in search of a dispersion state that exhibits a large saturation magnetization, this problem was effectively solved by using perfluoroether compounds for both the surfactant as a dispersant and the base oil. I discovered that.

[Means for Solving the Problem] and [Operation] Accordingly, the present invention relates to a magnetic fluid, which uses a perfluoroether surfactant as a dispersant and has magnetic properties in a perfluoroether base oil. It is made by dispersing body particles.

The present invention also relates to a method for producing such a magnetic fluid, in which the magnetic particles prepared as an aqueous suspension by a wet method are replaced with an organic solvent suspension;
After adding a perfluoroether surfactant and a perfluoroether base oil, the organic solvent is removed, or to an aqueous suspension of magnetic particles prepared by a wet method, a perfluoroether interface is added. Add a mixture of activator and base oil;
This is done by dispersing magnetic particles therein and then freeze-drying them.

The first step in this production method is to prepare an aqueous suspension of magnetic fine particles using a wet method. ,nitrate,
chloride, etc.) or a mixture solution in which divalent metal salts (sulfates, nitrates, chlorides, etc. of cobalt, nickel, manganese, zinc, etc.) are further added to these.
This is done by adding and aging an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide. This results in
Ferrite fine particles 1 For example, magnetite (Fa, 0
4), nickel ferrite (NiO-Fe, O,
), manganese ferrite (MnO・Fa, O,), cobalt ferrite (Coo # Fe, 03),
Nickel-zinc ferrite (Ni-2nO・Fe, O
), manganese-zinc ferrite (Mn-2nO-Fe
203), cobalt-zinc ferrite (Co・ZnO・
Fe, O, ), etc. are obtained in particle sizes of approximately 50-100 particles.

The generated magnetic particles are dispersed in perfluoroether base oil using a solvent substitution method or a freeze-drying method.

In the solvent substitution method, magnetic fine particles prepared in the form of an aqueous suspension are washed with water, preferably hot water, and then treated with a hydrophilic solution such as acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, n-butanol, dioxane, or tetrahydrofuran. The organic solvents were washed with organic solvents, and the organic solvents were once substituted in the form of a suspension, and then added thereto in a perfluoroether base oil, and then the organic solvent was removed by distillation and dispersed in the base oil. Obtain magnetic fine particles. At this time, if a perfluoroether surfactant is added as a dispersant together with the perfluoroether base oil, the surfactant will be adsorbed to the surface of the magnetic fine particles to form a magnetic fluid with good dispersibility.

In the freeze-drying method, magnetic fine particles prepared in the form of an aqueous suspension are washed with water, preferably warm water, and then solid-liquid separation is performed using a permanent magnet, and the supernatant liquid is removed to form an aqueous suspension. Then, a mixture of a perfluoroether surfactant and base oil is added thereto, and the magnetic fine particles are uniformly dispersed therein using a homogenizer or the like.

Magnetic fine particles dispersed in base oil can be obtained by rapidly cooling to −50° C. or lower and gradually returning the temperature to room temperature under reduced pressure conditions to sublimate water.

It is preferable that the perfluoroether surfactant and the base oil have the same structure other than the polar group, and are used in the following combinations, for example.

゛ Base oil RO (CF, 0) n (CF2) Q (CH,) kX
RO(CF,O)mR'RO(CF,0)n(CF
,) Q (CH,)kX, RO(C2F,O)
mR'RO(C,F,0)n(CF,) Q (C)1
2) kX RO(C,F,O)mR'm≦n: All positive integers fl, to: 0.1 or 2 R, R': Perfluoroalkyl group surfactant completely removes magnetic particles. The base oil is generally used in an amount about 1.5 times the amount required to coat the magnetic fluid with a single molecule, and the base oil is used depending on the concentration of the magnetic fine particles in the magnetic fluid.

〔Effect of the invention〕

Regarding the magnetic fluid according to the present invention, the following effects can be achieved.

(1) Since the surfactant and base oil are completely perfluorinated compounds, except for the polar group portion of the surfactant compound, chemical stability and lyophobicity can be improved (2) Moreover, since both of them have the same chemical structure except for the polar group part of the surfactant compound, they have a high affinity, and therefore the magnetic fine particles can be stably dispersed at a higher concentration. (3) Effectively eliminates alterations such as oxidation that cause the magnetic properties of magnetic fine particles to deteriorate, and agglomeration that causes unstable dispersion of fine particles. (4) Due to the above effects, the magnetic fluid according to the present invention can be used in chemically active environments such as liquid seals, corrosive gas seals, etc. The present invention can be effectively applied to use in a wide temperature range [Examples] Next, the present invention will be described with reference to Examples.

Example 1 A 1.5 molar ferrous chloride aqueous solution 50 ra Q and a 3.0 molar ferric chloride aqueous solution 50+w n were mixed in a nitrogen stream, and a 6 N sodium hydroxide aqueous solution was added to the mixture at a pH of 11.5.
The mixture was added dropwise while stirring until the mixture was dissolved. Thereafter, the particles were refluxed at 100°C for 30 minutes, aged, and then cooled to about 50°C. The generated fine particles were washed with warm water (four times) and then with acetone, and finally, the fine particles were washed with acetone containing 9 g of magnetic fine particles. A suspension was prepared.

Perfluoroether carboxylic acid C,F,O(C,F,O)n CF(CF,)COOH
(n: 10-12) 4.28 g of perfluoroether C,F,O(C,FsO)+nC,F, (I
l: average 17) Add the above acetone suspension to a solution dissolved in 10 mfl of base oil, irradiate it with ultrasonic waves to perform dispersion treatment, and then use a rotary evaporator to
C. for 2 hours to remove acetone and adsorb the surfactant onto the magnetic fine particles.

As a result, a magnetic fluid containing 12% by volume of magnetic fine particles and stably dispersed therein was obtained. This magnetic fluid is
It exhibits the characteristics of a fluorine-containing compound, and even when strongly shaken in an organic solvent such as water or alcohol, the surfactant does not desorb from the magnetic fine particles and does not cause poor dispersion that causes solid-liquid separation. It was confirmed that it exists stably.

Example 2 A 1.5 molar ferrous sulfate aqueous solution 50mQ and a 3.0 molar ferric sulfate aqueous solution 50IIIQ were mixed in a nitrogen stream,
A 6N aqueous sodium hydroxide solution was added dropwise to this while stirring until the pH reached 11.5. Thereafter, the mixture was refluxed at 100° C. for 30 minutes, aged, and then cooled to about 50° C., and the resulting fine particles were washed with hot water in which dissolved oxygen was replaced with nitrogen. This aqueous suspension was placed on a permanent magnet to perform solid-liquid separation, and the supernatant was removed to obtain an aqueous suspension containing 8.4 g of magnetic fine particles.

Perfluoroether phosphate C, F, O (C, F,
0)nCF(CF,)C284PO(OH)z(n:
10-12) 4.0g of perfluoroether C in advance
,F,0(C3F,O)mc2F, (m: average 17)
The above aqueous suspension was added to a solution dissolved in base oil 10111Q, and the magnetic fine particles were uniformly dispersed therein using a homogenizer, and then rapidly cooled to below -50°C.
While maintaining the pressure at 0.2 Torr or less, the temperature was gradually returned to room temperature to sublimate water. After removing water by such a freeze-drying method, it was heat-treated at 80° C. for 2 hours while cutting off oxygen. the result.

A magnetic fluid containing 11% by volume of magnetic fine particles was obtained.

Claims (1)

[Claims] 1. A magnetic fluid made by using a perfluoroether surfactant as a dispersant and dispersing magnetic fine particles in a perfluoroether base oil. 2. The magnetic fluid according to claim 1, wherein a perfluoroether surfactant and a base oil are used, which have the same structure except for the polar group. 3. Magnetic particles prepared as an aqueous suspension by a wet method are replaced with an organic solvent suspension, and after adding a perfluoroether surfactant and a perfluoroether base oil, the organic solvent is removed. A method for producing a magnetic fluid characterized by: 4. The method for producing a magnetic fluid according to claim 3, wherein a perfluoroether surfactant and base oil having the same structure except for the polar group are used. 5. Add a mixture of perfluoroether surfactant and base oil to an aqueous suspension of magnetic particles prepared by a wet method, disperse the magnetic particles therein, and then freeze-dry. A method for producing a magnetic fluid characterized by: 6. The method for producing a magnetic fluid according to claim 5, wherein a perfluoroether surfactant and base oil having the same structure except for the polar group are used.