Super paramagnetic fluids and methods of making super paramagnetic fluids

Claim 2

A magnetic fluid comprising: (a) a carrier liquid; (b) a dispersing agent comprising a salt of an aromatic sulfonic acid which disperses coated magnetic particles in said carrier liquid; and (c) coated magnetic particles coated with a combination of organic acids which renders said magnetic particles hydrophobic, wherein said combination of acids comprises from about 1% to about 70% of a first acid selected from the group consisting of arachidic acid, behenic acid and a mixture of arachidic and behenic acids and from about 30% to about 99% of a second acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid and isostearic acid, said combination of organic acids being capable of peptizing said magnetic particles into a fugitive solvent for said dispersing agent.

Claim 3

A magnetic fluid as recited in claim 1 wherein said first acid is a mixture of arachidic and behenic acids.

Claim 4

A magnetic fluid as recited in claim 2 wherein said second acid is oleic acid.

Claim 5

A magnetic fluid as recited in claim 2 wherein said second acid is isostearic acid.

Claim 6

A magnetic fluid as recited in claim 3 wherein said mixture of arachidic and behenic acids comprises from about 10% to about 40% of said combination of acids and said oleic acid comprises from about 60% to about 90% of said combination of acids.

Claim 7

A magnetic fluid as defined in claim 5 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 8

A magnetic fluid as defined in claim 3 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 9

A magnetic fluid as defined in claim 1 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 10

A magnetic fluid as defined in claim 8 wherein said salt of an alkylated aromatic sulfonic acid has at least one alkyl substituent containing from 1 to 25 carbon atoms.

Claim 11

A magnetic fluid as defined in claim 8 wherein said magnetic particles have an average magnetic particle diameter from about 80 Å to about 90 Å.

Claim 12

A magnetic fluid as recited in claim 8 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 13

A magnetic fluid as recited in claim 6 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 14

A magnetic fluid as recited in claim 1 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 15

A process for making a magnetic fluid comprising: (a) providing an aqueous suspension of coated magnetic particles coated with a combination of organic acids which renders said magnetic particles hydrophobic, wherein said combination of acids comprises from about 1% to about 70% of a first acid selected from the group consisting of arachidic acid, behenic acid and a mixture of arachidic and behenic acids and from about 30% to about 99% of a second acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid and isostearic acid; (b) separating said coated magnetic particles from said aqueous suspension; (c) treating said coated magnetic particles with a solution of a dispersing agent in a fugitive solvent wherein said fugitive solvent peptizes said coated magnetic particles into a stable colloidal suspension; and (d) adding a carrier liquid to said colloidal suspension to form a stable magnetic liquid.

Claim 16

A process for making a magnetic fluid comprising: (a) providing an aqueous suspension of coated magnetic particles coated with a combination of organic acids which renders said magnetic particles hydrophobic, wherein said combination of acids comprises from about 1% to about 70% of a first acid selected from the group consisting of arachidic acid, behenic acid and a mixture of arachidic and behenic acids and from about 30% to about 99% of a second acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid and isostearic acid; (b) separating said coated magnetic particles from said aqueous suspension; (c) treating said coated magnetic particles with a solution of a dispersing agent in a fugitive solvent wherein said fugitive solvent peptizes said coated magnetic particles into a stable colloidal suspension; and (d) adding a carrier liquid to said colloidal suspension to form a stable magnetic liquid.

Claim 17

A process as recited in claim 14 wherein said first acid is a mixture of arachidic and behenic acids.

Claim 18

A process as recited in claim 15 wherein said second acid is oleic acid.

Claim 19

A process as recited in claim 15 wherein said second acid is isostearic acid.

Claim 20

A process as recited in claim 16 wherein said mixture of arachidic and behenic acid comprises from about 10% to about 40% of said combination of acids and said oleic acid comprises from about 60% to about 90% of said combination of acids.

Claim 21

A process as recited in claim 18 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 22

A process as recited in claim 16 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 23

A process as recited in claim 14 wherein said dispersing agent is a salt of an alkylated aromatic sulfonic acid.

Claim 24

A process as recited in claim 19 wherein said salt of an aromatic sulfonic acid has at least one alkyl substituent containing from 1 to 25 carbon atoms.

Claim 25

A process as recited in claim 21 wherein said magnetic particles have an average magnetic particle diameter from about 80 Å to about 90 Å.

Claim 26

A process as recited in claim 14 wherein said magnetic particles have an average magnetic particle diameter from about 80 Å to about 90 Å.

Claim 27

A process as recited in claim 24 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 28

A process as recited in claim 23 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 29

A process as recited in claim 14 wherein said carrier liquid is an 8 cst. non-polar poly(alpha olefin) oil.

Claim 30

A process for making a magnetic fluid comprising: (a) precipitating magnetic particles from an aqueous solution; (b) contacting said precipitated magnetic particles in an aqueous suspension with a combination of organic acids to provide coated magnetic particles coated with said combination of organic acids, wherein said combination of organic acids comprises from about 1% to about 70% of a first acid selected from the group consisting of arachidic acid, behenic acid and a mixture of arachidic and behenic acids and from about 30% to about 99% of a second acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid and isostearic acid; (c) adding a fugitive solvent to said coated magnetic particles in an amount sufficient to coagulate said coated magnetic particles into a water repellant granular mass and separating said coated magnetic particles from said suspension; (d) rinsing said coated magnetic particles with water to remove by-product inorganic salts; (e) adding additional fugitive solvent to said coated magnetic particles to form a stable suspension of magnetic particles in said additional fugitive solvent; (f) heating said stable suspension to evaporate residual water and water associated with the surfaces of said magnetic particles; (g) removing from said stable suspension coated magnetic particles with a particle diameter greater than that which can be stabilized by said combination of organic acids in said fugitive solvent; (h) treating the coated magnetic particles remaining in said stable suspension with a salt of an aromatic sulfonic acid dispersing agent to form a stable colloid of said remaining coated magnetic particles; (i) removing excess dispersant from said stable colloid; (j) adding a carrier liquid to said stable colloid; and (k) removing said fugitive solvent from said stable colloid.

Claim 31

A process for making a magnetic fluid comprising: (a) precipitating magnetic particles from an aqueous solution; (b) contacting said precipitated magnetic particles in an aqueous suspension with a combination of organic acids to provide coated magnetic particles coated with said combination of organic acids, wherein said combination of organic acids comprises from about 1% to about 70% of a first acid selected from the group consisting of arachidic acid, behenic acid and a mixture of arachidic and behenic acids and from about 30% to about 99% of a second acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid and isostearic acid; (c) adding a fugitive solvent to said coated magnetic particles in an amount sufficient to coagulate said coated magnetic particles into a water repellant granular mass and separating said coated magnetic particles from said suspension; (d) rinsing said coated magnetic particles with water to remove by-product inorganic salts; (e) adding additional fugitive solvent to said coated magnetic particles to form a stable suspension of magnetic particles in said additional fugitive solvent; (f) heating said stable suspension to evaporate residual water and water associated with the surfaces of said magnetic particles; (g) removing from said stable suspension coated magnetic particles with a particle diameter greater than that which can be stabilized by said combination of organic acids in said fugitive solvent; (h) treating the coated magnetic particles remaining in said stable suspension with a salt of an aromatic sulfonic acid dispersing agent to form a stable colloid of said remaining coated magnetic particles; (i) removing excess dispersant from said stable colloid; (j) adding a carrier liquid to said stable colloid; and (k) removing said fugitive solvent from said stable colloid.