JPS60177098A - Magnetic fluid - Google Patents

Abstract

PURPOSE:To obtain a magnetic fluid of improved heat resistance, suitable for sealing, screening by specific gravity, fixation of fluid, printing, recording, sensor, etc., by dispersing in a low-melting point alloy constituted by Zn, Gd, etc. high-permeability fine powder having surface of good wetting with Zn, etc. CONSTITUTION:(A) High-permeability Fe-, Ni-, Co-based fine powder having surface of good wetting with Zn, Sn and In is dispersed in (B) a low-melting point alloy constituted by Ga and at least one sort of metal selected from Zn, Sn and In to obtain the objective magnetic fluid with the component (A) dispersed as stable particles coated with Zn, Sn, In, etc. The material for the component (A) is pref. pure iron, pure cobalt, pure nickel, silicon steel plate, 78 permalloy, supermalloy, mumetal, 45-25 perminvar, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic fluid that can be used in various application fields such as seals, ratio selection, fluid fixing, printing, recording, sensors, and bearings.

Prior Art Magnetic fluids that have been used in practical use have high magnetic permeability, such as magnetite or various ferrites, and have a particle size of 1.
A colloidal solution in which the surface of microparticles of 00 to 200 people is coated with long-chain unsaturated fatty acids such as oleic acid or linoleic acid and dispersed in a dispersion medium such as hydrocarbon or water in the presence of a surfactant. be.

This magnetic fluid has both fluidity and ferromagnetism.
It is an extremely useful material that has been used in a variety of applied fields in recent years and is being further developed.

However, since these magnetic fluids all contain organic compounds and water as one of their components, they have the disadvantage that they cannot be used at temperatures and pressures that would cause thermal decomposition or evaporation of these substances.

In addition, ferrofluid powders dispersed in liquid metals such as mercury have also been developed. However, mercury is toxic, has a high vapor pressure, and boils at 350°C, so there are considerable restrictions on the temperature and method of use.

Purpose This invention solves the above-mentioned drawbacks of conventionally used magnetic fluids.
In particular, this objective was achieved by using a metal, especially a Ga-based low alloy alloy, as a dispersion medium to improve heat resistance.

Structure The structure of the present invention is that fine powder having a high magnetic permeability and a surface that is easily wetted with Zn13n, ln, ln, 3n, and ln.
The magnetic fluid is characterized in that it is dispersed in a dispersion medium that is a low melting point alloy consisting of Ga and one or more of the group consisting of n.

We will discuss the low melting point alloy, high magnetic permeability material, and manufacturing method that are the components of this magnetic fluid.

A. Low melting point alloy Ga, which is the main component of the low melting point alloy in the present invention, is a low melting point metal having the following properties.

m, p, 29.8°C b, p, 2071°C (estimated) Assuming that the vapor pressure is a monoatomic molecule, logp = -16280/T -1,27ioa T
+14.123p:mmH! J T:' K Comparing this with H(] using specific numerical values, it is clear from the above explanation that Ga melts at 30°C and 2000°C.
It is liquid up to 500°C, has a low vapor pressure even at 500°C, and is non-toxic. Therefore, Qa can be used from room temperature to considerably higher temperatures than H(+).

By the way, the viscosity of liquid Ga is as follows.

Temperature °C Viscosity poise (dyne am/a1)5
2.9 0,019 97.4 0.016 149 0.014 200 0.013 301 0.01 402 0.009 soo o, ooa Goo ,,0.007 806 0.00 It seems obvious It is a very flowing liquid,
Its viscosity can be said to be close to that of water.

Further, the thermal conductivity of the liquid Qa is 30 to 100'C.

This (
10 is 1710 which is 3.85 (0° C.) of Cu, which is large compared to the heat transfer liquid of the following material.

Material Thermal conductivity J/Cm-3° mercury 0.09
(0℃) Water 6.05x 10-3 (30℃) Organic oil 1.
5~2x10' Air 0.24xlO-8 Examples of low melting point eutectic alloys in which Ga is formed with Zn, 3n, In, etc. are as follows.

Composition Melting point (℃) 95Ga -521125 92Ga -83n 20 76Ga -24I n 15.7 82Ga -123n -6Zn 15.7Ga, Sn
The magnetic properties of , Zn, and In are expressed as magnetic susceptibility χ(10-'emu'/a) and Q
a: -0,31, In: -0,11 3n knee 0.25, Zn knee 0.14, both of which are diamagnetic and are virtually unaffected by the II field.

zn 13n and ln, which are components of Qa-based low alloy alloy, are Fe
, Ni, GO, and strongly coats their surfaces to prevent oxidation.

Therefore, in the present invention, Fe, Ni.

GO-based high magnetic permeability fine particles are Zn, S, etc. in the above-mentioned low melting point alloy.
It is dispersed as stable particles coated with n, In, etc., and does not aggregate or become coarse.

B. High magnetic permeability materials Substances with high magnetic permeability and a high Curie point are generally Fe, co,
There are many highly magnetic materials useful as constituents of the material of the present invention, such as Ni alone or alloys thereof.

For example, pure iron, pure cobalt, pure nickel, silicon steel plate,
Examples include Alperm, Sendust, 78 Permalloy, Supermalloy, Mumetal, 45-25 Perminvar, and the like.

The magnetic heat resistance of Fe, Co, and Ni is as shown in FIG. 1, for example, and the meanings of the symbols in the figure are as follows.

is Magnetic efficiency at 1o OoK Value extrapolated to OoK θf Curie temperature Fe: 1041.8'K Co; 1388.2°K Ni; 629,5'K The temperature in degrees Celsius corresponding to the values in Figure 1 is It is shown below.

In addition, the numerical values of each substance at room temperature (20°C, 293,2°K) show that these materials approach Curie humidity as the striking part approaches, and the magnetic efficiency decreases, but Fe1GO has I
The decrease in S is small.

Production of C0 magnetic fluid The method of producing the magnetic fluid of this invention includes the following method. To explain them, a low melting point alloy of Qa and 7n, 3n, In, etc. is first prepared, and then the following method is performed.

b) Electrolytic method This low melting point alloy is used as an anode in a molten state, and Fe1CO
An aqueous solution of a 1Ni compound is electrolyzed to diffuse the metal deposited on the anode surface into the interior.

Immediately after precipitation, the deposited metal becomes Zn 1811, ' I
The surface is coated with n and dispersed as stable particles.

) Zinc reduction method Zn is added to this low melting point alloy for reduction, and Fe, Go
, the following reaction is caused while shaking the aqueous solution of the Ni compound vigorously.

Fe 2++ + Zn − + Fe + Zn 2 + The reduced iron contains Zn, 3
n,in and exist as stable particles.

C) Grinding method This method can be applied to Fc, Qo, and Ni alone or to their alloys, and these metals are ground in the above-mentioned low melting point alloy. The surface of the metal produced by pulverization comes into preferential contact with 3n, zn, and In in the low melting point alloy and is coated with these metals. The same phenomenon occurs even when pulverization progresses and becomes ultra-fine.

There are various types of crushing equipment, but any type that can crush in molten alloy will suffice.

A hydrophilic colloid can be obtained by using the above methods A), D), and C) alone or in combination.

D. Properties of magnetic fluid The rheology of the dispersion The dispersion particles are pulverized to 1 culm, and industrially the particle size is 100 to 200.
It is finely pulverized to the size of a person (10-20I11μ), but 50
It is said that when the particle size reaches 0.00 people (500 mμ), it already behaves as a colloidal particle. Although it varies depending on the shape of the particles,
As the concentration of dispersed particles increases, the properties change from Newtonian fluid properties to thixotropic fluid properties. Rinawara,
Although it does not flow when it is at rest, it becomes a fluid with a yield point that easily flows when an external force is applied.

, if this is shown qualitatively in a diagram, the properties will be as shown in Figure 2.

(2) Flow rate p...External force When this dispersion is placed in a magnetic field, a change is observed, not shown in Figure 3. That is, without the action of a magnetic field, the liquid 3 in the container 1 is simply dispersed as shown in Figure 3-a, but the magnet 2
When a magnetic field is applied, as shown in Fig. 3-b, when the edge of the dispersoid is small, there is a part A with a large concentration of the component (dispersoid) attracted to the magnet 2, and a part A that is not affected by the magnet ( It is separated into part B, which mainly contains dispersion medium). When the concentration of the dispersoids is high, they are hardly separated and are attracted to the magnet 2 as shown in Figure 3-0. Part A can be said to be a part where highly permeable particles are concentrated with a minimum amount of dispersion medium, and part B can be said to be a part consisting of surplus dispersion medium. The particle concentration in the concentrated part is determined by the shape and size of the particles and the strength of the magnetic field.

Therefore, after the particle shape and particle size reach target values, it can be placed in a sufficiently high magnetic field and applied as a means for separating and removing excess dispersion medium.

Example 82Ga-12Sn-6Zn alloy (m, p are 1
A dispersion in which iron is ground and suspended at a concentration of 7% at 5.7°C) exhibits thixotropic properties reliably at 18°C, and at 500°C.
The magnetic fluid remained unchanged even after heating.

The fact that this dispersion medium is electrically conductive is a feature not found in other magnetic fluids.

Other materials that can compete with the Qa-based low alloy used in the present invention include alloys of mercury and Na -. It is presumed that similar magnetic fluids can be produced using similar methods using these as dispersion media, but as already explained, mercury has a high vapor pressure and is highly toxic, and its alloys with Na - are extremely unstable. Because it is an open substance, it cannot be used in an open state. Therefore, these metals have significant practical limitations. Compared to those, Q used in this invention
A-based alloys are practical dispersion media.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between T/θf and Is/Io of Fe, co, and Ni. Fig. 2 is a graph showing the properties of dixotropic fluid. Fig. 3-a-C is a graph showing the relationship between T/θf and Is/Io of Fe, co, and Ni. An explanatory diagram showing properties of fluid is shown. 1... Container, 2... Magnet, 3... Magnetic fluid, Patent applicant Yoshu Taketo Poka 2 agents Patent attorney Hide Komatsu Gaku agent Patent attorney Hiroshi Asahi Figure 1 Figure 2-Side 23 i4 Fang31”dl-o-Fang3 E-c2ノ

Claims (1)

[Claims] A fine powder with high magnetic permeability and a surface that is easily wetted with Zn, 3n1)n is dispersed in a dispersion medium that is a low melting point alloy consisting of one or more of the group consisting of Zn, Sn and In and Qa. A magnetic fluid characterized by: