Ferrofluid compositions and process of making same

Claim 2

A PROCESS FOR PREPARING AN IMPROVED FERROFLUID COMPOSITION WHICH PROCESS COMPRISES IN COMBINATION: A. PREPARING FIRST FERROFLUID COMPOSITION COMPRISING A DISPERSION OF COLLOIDAL-SIZE MAGNETIC PARTICLES IN A DISPERSANT IN A POLAR LIQUID CARRIER, B. ADDING A FLOCCULATING AGENT TO THE FIRST FERROFLUID COMPOSI-, TION TO PRECIPITATE THE MAGNETIC PARTICLES FROM THE FIRST COMPOSITION SEPARATING THE PRECIPATE FROM THE SUPERNATANT LIQUID TO OBTAIN FLOCKED PRECIPITATED MAGNETIC PARTICLES WHICH ARE CHARACTERIZED IN THAT SUCH FLOCKED PARTICLES WILL NOT REDISPERSE IN THE POLAR LIQUID CARRIER WITHOUT THE ADDITION OF A DISPERSANT, C. RECOVERING ESSENTIALLY DISPERSANT-FREE MAGNETIC PRECIPITATED PARTICLES, D. COATING THE SURFACE OF THE FLOCCULATED PRECIPITATED MAGNETIC PARTICLES WITH SECOND DISPERSANT, AND E. REDISPERSING SAID COATED PARRTICLES IN A SECOND CARRIER LIQUID TO PROVIDE A SECOND FERROFLUID COMPOSITION OF IMPROVED PROPERTIES AND CHARACTERISTICS.

Claim 3

The process of claim 1 which includes drying the recovered magnetic precipitated particles.

Claim 4

The process of claim 1 wherein the second dispersant employed to obtain the second ferrofluid composition is different from the dispersant in the first ferrofluid composition.

Claim 5

The process of claim 1 wherein the second liquid carrier in the second ferrofluid composition is different from the liquid carrier in the first ferrofluid composition.

Claim 6

The process of claim 1 wherein both the second dispersant and the second carrier liquid are different from the first dispersant and the first carrier liquid of the first ferrofluid composition.

Claim 7

The process of claim 1 wherein the first and second carrier liquids comprise water.

Claim 8

The process of claim 1 wherein the first carrier liquid of the first ferrofluid composition comprises water, and the second carrier liquid of the second ferrofluid composition comprises a nonaqueous liquid.

Claim 9

The process of claim 1 wherein the step of coating the flocked particles and redispersing such particles in the second carrier liquid is accomplished by grinding the recovered flocked particles in a ball mill in the presence of the second dispersant and the second carrier liquid.

Claim 10

The process of claim 1 which includes the step of washing the dispersant-free particles to remove residual traces of the dispersant from the surface of the particles, and, thereafter, drying the magnetic particles.

Claim 11

The process of claim 1 wherein the first carrier liquid is water, and wherein the flocculating agent added to the first ferrofluid composition comprises a polar solvent.

Claim 12

The process of claim 1 wherein the second carrier liquid comprises a liquid fluorocarbon.

Claim 13

The process of claim 11 wherein the fluorocarbon comprises a perfluorinated polyether liquid.

Claim 14

The process of claim 1 wherein the second carrier liquid comprises a diester liquid.

Claim 15

The process of claim 1 wherein the magnetic particles of the first ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.

Claim 16

The process of claim 1 wherein the magnetic particles comprise magnetite or gamma iron oxide.

Claim 17

The process of claim 1 wherein the second disperssant comprises, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume.

Claim 18

The process of claim 1 wherein the second ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.

Claim 19

The process of claim 1 wherein the first liquid carrier is water, and the second flocculating agent is a ketone, ester or alcohol.

Claim 20

The process of claim 1 wherein the magnetic particles of the second ferrofluid composition have an average particle size of about 120 Angstroms.

Claim 21

The process of claim 1 which includes: a. drying the essentially dispersant-free magnetic precipitated particles; and b. ball milling the dry magnetic particles with the second carrier liquid and second dispersant to provide the second ferrofluid composition.

Claim 22

The process of claim 1 wherein the first carrier liquid is water, and the second carrier liquid is a mineral oil.

Claim 23

A ferrofluid composition which comprises a solution of a low-volatility liquid diester carrier and a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of between about 300 to 800 gauss, and having a viscosity of from about 100 to 2000 cps, the magnetic particles comprising magnetite or gamma iron oxide, the dispersant comprising, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume, and the composition comprising from abOut 2 to 15% by volume of magnetic particles, the magnetic particles having a particle size of about 120 Angstroms.

Claim 24

A ferrofluid composition which comprises a solution of a low-volatility liquid diester carrier and a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of between about 300 to 800 gauss, and having a viscosity of from about 100 to 2000 cps, the magnetic particles comprising magnetite or gamma iron oxide, the dispersant comprising, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume, and the composition comprising from abOut 2 to 15% by volume of magnetic particles, the magnetic particles having a particle size of about 120 Angstroms.

Claim 25

The flocked dispersant-free magnetic particles having a particle size of from about 20 to 300 Angstroms produced by the process of claim 1, the particles essentially free of adsorbed surfactant and incapable of being redispersed in the first carrier liquid without the addition of a dispersant.

Claim 26

A process of preparing an improved ferrofluid composition of low viscosity and high magnetization saturation, which process comprises in combination: a. grinding in a ball mill coarse magnetic solids, a water-soluble dispersant, and a water carrier liquid to provide a first ferrofluid composition of colloidal-size stable magnetic particles; b. adding a polar solvent as a flocculating agent to the first ferrofluid composition to precipitate the magnetic particles from the first ferrofluid composition separating the precipitate from the supernatant liquid to obtain flocked, dispersant-free magnetic particles which are characterized in that such flocked particles will not redisperse in the polar liquid carrier without the addition of a dispersant; c. washing the dispersant-free precipitated particles with water to remove the flocculating polar solvent and any residual traces of the dispersant; d. heating the washed precipitated particles to a temperature not in excess of about 200*F to remove moisture, and to produce dry, flocculated dispersant-free, magnetic particles; and e. grinding in a ball mill the dry flocked particles in the presence of an alternate and different dispersing agent and a second carrier liquid to provide a second ferrofluid composition.

Claim 27

A process of preparing an improved ferrofluid composition of low viscosity and high magnetization saturation, which process comprises in combination: a. grinding in a ball mill coarse magnetic solids, a water-soluble dispersant, and a water carrier liquid to provide a first ferrofluid composition of colloidal-size stable magnetic particles; b. adding a polar solvent as a flocculating agent to the first ferrofluid composition to precipitate the magnetic particles from the first ferrofluid composition separating the precipitate from the supernatant liquid to obtain flocked, dispersant-free magnetic particles which are characterized in that such flocked particles will not redisperse in the polar liquid carrier without the addition of a dispersant; c. washing the dispersant-free precipitated particles with water to remove the flocculating polar solvent and any residual traces of the dispersant; d. heating the washed precipitated particles to a temperature not in excess of about 200*F to remove moisture, and to produce dry, flocculated dispersant-free, magnetic particles; and e. grinding in a ball mill the dry flocked particles in the presence of an alternate and different dispersing agent and a second carrier liquid to provide a second ferrofluid composition.

Claim 28

A ferrofluid composition which comprises a solution of a diester liquid carrier, a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of over 300 gauss, and having a viscosity of from about 100 to 2000 cps.

Claim 29

A ferrofluid composition which comprises a solution of a diester liquid carrier, a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of over 300 gauss, and having a viscosity of from about 100 to 2000 cps.

Claim 30

The composition of claim 25 wherein the liquid carrier comprises a nonaqueous carrier, and the average particle size is about 120 Angstroms.

Claim 31

The composition of claim 25 wherein the dispersant is a polyisobutene succinic acid derivative.

Claim 32

The composition of claim 25 wherein the composition comprises a ratio of dispersant-to-magnetic particles of about 1: 2 to 10:1 by volume.

Claim 33

The composition of claim 25 wherein the magnetic particles comprise magnetite or gamma iron oxide.

Claim 34

The composition of claim 25 wherein the magnetic particles of the ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.

Claim 35

The composition of claim 25 wherein the ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.

Claim 36

The composition of claim 25 wherein the composition has a magnetic saturation of between about 300 to 800 gauss.