EP0343934A2
Expired / Lapsed
EP
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Magnetically attractable particles and method of preparation
Assignee: Alfa Wasserman SpA
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Filing: 1989-05-23
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Granted: —
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Expires: 2009-05-23
Abstract
Abstract Magnetically attractable particles comprise a core of magnetic material encapsulated in a metal oxide coating. They may be made by emulsifying an aqueous solution or dispersion of the magnetic material or precursor, and an aqueous solution or sol of a coating inorganic oxide or precursor, in an inert water-immiscible liquid. The aqueous droplets are gelled, e.g. by ammonia or an amine, recovered, and heated at 250 - 2000 o C. The resulting particles are generally smooth spheres below 100 microns in diameter and often of sub-micron size.
Inventors
- 👤 Jean Victor Sang
- 👤 Paul Groves
- 👤 Robert Edward Burrell
- 👤 Gerard Flynn
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 08:34
CPC Classifications
G; G01; G01N; G01N33/00; G01N33/48; G01N33/50; G01N33/53; G01N33/543; G01N33/54313; G01N33/54326; G01N33/5434; B; B03; B03C; B03C1/00; B03C1/005; B03C1/01; H; H01; H01F; H01F1/00; H01F1/01; H01F1/03; H01F1/12; H01F1/34; H01F1/36; H01F1/44; H01F1/445; G01N2446/00; G01N2446/20; G01N2446/80; Y; Y10; Y10T; Y10T428/00; Y10T428/29; Y10T428/2982; Y10T428/2989
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
91 words
A method of making magnetically attractable particles by the use of: a) a precursor salt solution or sol or dispersion of magnetic material, b) a precursor salt solution or sol of a coating inorganic oxide, and c) an inert liquid immiscible with the solvent used in a) and b), which method comprises emulsifying a) and b) either together or separately in c), converting droplets of the emulsion to a gel, and heating the resulting gel droplets to form magnetically attractable particles comprising the magnetic material encapsulated in the coating inorganic oxide.
Claim 2
Independent Claim
91 words
A method of making magnetically attractable particles by the use of: a) a precursor salt solution or sol or dispersion of magnetic material, b) a precursor salt solution or sol of a coating inorganic oxide, and c) an inert liquid immiscible with the solvent used in a) and b), which method comprises emulsifying a) and b) either together or separately in c), converting droplets of the emulsion to a gel, and heating the resulting gel droplets to form magnetically attractable particles comprising the magnetic material encapsulated in the coating inorganic oxide.
Claim 3
Dependent Claim
30 words
A method as claimed in claim 1, wherein the magnetic material of a) is dispersed throughout the solution or sol b) and the resulting mixture in then emulsified in c).
Claim 4
Dependent Claim
22 words
A method as claimed in claim 2, wherein a particulate non-magnetic refractory oxide is also dispersed in the solution or sol b).
Claim 5
Dependent Claim
33 words
A method as claimed in claim 1, wherein a solution of the magnetic material precursor a) is mixed with the solution or sol b) and the resulting mixture in then emulsified in c).
Claim 6
Dependent Claim
76 words
A method as claimed in claim 1, wherein a solution of the magnetic material precursor a) is emulsified in c) and the droplets of the emulsion converted to a gel, then the resulting gel droplets are dispersed in the solution or sol b), and the resulting mixture is emulsified in c), the droplets of the emulsion are converted to a gel, and the resulting gel droplets are heated to form the water dispersable magnetically attractable particles.
Claim 7
Dependent Claim
35 words
A method as claimed in claim 5, wherein the solution or sol b) containing the dispersed gel droplets is emulsified in c) in the presence of a surfactant havng an HLB number greater than 10.
Claim 8
Independent Claim
18 words
A method as claimed in any one of claims 1 to 6, wherein the magnetic material is superparamagnetic.
Claim 9
Independent Claim
21 words
A method as claimed in any one of claims 1 to 6, wherein the magnetic material is a "soft" magnetic material.
Claim 10
Independent Claim
21 words
A method as claimed in any one of claims 1 to 6, wherein the magnetic material has a low Curie temperature.
Claim 11
Independent Claim
30 words
A method as claimed in any one of claims 1 to 9, wherein ammonia or an amine is added to the emulsion to convert aqeuous droplets thereof to a gel.
Claim 12
Independent Claim
27 words
A method as claimed in any of claims 1 to 10, wherein the gel droplets are heated at a temperature of 250 o - 2000 o C.
Claim 13
Dependent Claim
55 words
Water-dispersable magnetically attractable particles comprising a mass of finely divided superparamagnetic material encapsulated in an inorganic oxide or hydrated oxide formed by a gel technique, the particles having the property of being readily brought down out of dispersion by application of a magnetic field and of being readily re-dispersed after removal of the magnetic field.
Claim 14
Dependent Claim
55 words
Water-dispersable magnetically attractable particles comprising a mass of finely divided superparamagnetic material encapsulated in an inorganic oxide or hydrated oxide formed by a gel technique, the particles having the property of being readily brought down out of dispersion by application of a magnetic field and of being readily re-dispersed after removal of the magnetic field.
Claim 15
Dependent Claim
16 words
Particles as claimed in claim 12, wherein the superparamagnetic material comprises a ferrite such as Fe₃O₄.
Claim 16
Dependent Claim
20 words
Particles as claimed in claim 12 or claim 13, having a magnetic material content of 1 to 95% by weight.
Claim 17
Dependent Claim
22 words
Particles as claimed in any one of claims 12 to 14, wherein the average particle diameter is from 0.25 - 100 microns.
Claim 18
Dependent Claim
77 words
A coated ferrimagnetic particle having a diameter in the range of 0.1 to 100 micrometers and comprising a discrete core of magnetic material coated with a metal oxide selected from the group consisting of Al₂O₃. SiO₂, TiO₂, ZrO₂, hydroxy-apatite and mixtures thereof, said coating weighing in the range of 1% to 95% of said core weight and providing a continuous coating over the entire surface of said core to prevent exposure of said core to surrounding media.
Claim 19
Dependent Claim
77 words
A coated ferrimagnetic particle having a diameter in the range of 0.1 to 100 micrometers and comprising a discrete core of magnetic material coated with a metal oxide selected from the group consisting of Al₂O₃. SiO₂, TiO₂, ZrO₂, hydroxy-apatite and mixtures thereof, said coating weighing in the range of 1% to 95% of said core weight and providing a continuous coating over the entire surface of said core to prevent exposure of said core to surrounding media.
Claim 20
Dependent Claim
24 words
A particle of claim 15 having a diameter in the range of 0.5 to 2 micrometers and being spherical in shape with smooth surfaces.
Claim 21
Dependent Claim
26 words
A particle of claim 16 or 17, wherein said magnetic material is a ferrite such as magnetite, lithium ferrite, nickel zinc ferrite, or manganese zinc ferrite.
Claim 22
Dependent Claim
18 words
A dispersion of the particles claimed in any one of claims 12 to 18 in an aqueous medium.
References Cited (Backward Citations)
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