Coated magnetizable microparticles, reversible suspensions thereof, and processes relating thereto
OwnerGeorge H. Czerlinskiinventor
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Abstract
Coated magnetizable particles of sub-micron size are used to form reversible suspensions in which the particles may be magnetically aggregated and thereafter resuspended as desired. Each microparticle comprises a core composed essentially of a magnetically-responsive material having a Curie temperature within the range of about 5.degree. to 65.degree. C. and a magnetic moment at saturation of at least 2.0 .mu..sub.B at 4.2.degree. K., and a coating about the core formed of a solid cross-linked polymeric material having chemically reactive groups at the surface thereof.
Claims18
Magnetically-responsive discrete microparticles suitable for use in preparing selectively reversible suspensions thereof;
- each such microparticle having a core, a coating thereabout, and a diameter no greater than about one micron;
- said core being formed of a single particle of magnetically-responsive material having a Curie temperature within the range of about 5 to 65.degree. C., a magnetic moment at saturation of at least 2.0 .mu..sub.B at 4.2.degree. K, and a specific gravity above 3.0;
- said coating comprising a water-insoluble cross-linked polymeric material having reactive groups at the surface thereof.
A method for magnetically aggregating and thereafter suspending sub-micron-sized magnetizable particles, comprising the steps of forming each of said particles to have (a) a core of magnetically-responsive material with a Curie temperature within the range of about 5 to 65.degree. C. and a saturation magnetic moment of at least 2.0 .mu..sub.B at 4.2.degree. K and (b) a cross-linked polymeric coating about said core having reactive sites on the surface thereof;
- mixing said particles at a temperature not substantially below said Curie temperature with a first liquid medium containing a component capable of reacting with said coating;
- then exposing said particles to a magnetic field at a temperature not substantially exceeding said Curie temperature to cause magnetic aggregation of said particles;
- then separating the particles so aggregated magnetically from said first liquid medium, introducing said magnetically-aggregated particles into a second fluid medium, and subjecting the same to a temperature in excess of said Curie temperature in the absence of a magnetic field and with agitation to resuspend said particles in said second medium.
A method of preparing a reversible suspension of coated magnetically-responsive microparticles, in which a magnetically-responsive core material is pulverized to produce core particles of a size substantially under 1.0 micron and said core particles are then each coated with a nonmagnetic polymeric material to form discrete coated magnetic microparticles having reactive groups at the surface thereof, wherein the improvement comprises
- forming said core particles of a magnetically-responsive material having a Curie temperature within the range of about 5 to 65.degree. C., a magnetic moment at saturation of at least 2.0 .mu..sub.B at 4.2.degree. K, and a specific gravity above 3.0;
- and carrying out said pulverizing and coating steps in a liquid medium at temperatures above the Curie temperature of said material.
Dependencies are inferred from the claim text.