Process for producing a magnetic fluid and composition therefor

• US 6,056,889 A
• Filed: 10/10/1997
• Issued: 05/02/2000
• Est. Priority Date: 03/26/1996
• Status: Expired due to Term

• Current Assignee: Ferrotec Corporation (Ferrotec Holdings Corporation)
• Original Assignee: Ferrotec Corporation (Ferrotec Holdings Corporation)
• Inventors: Tsuda, Shiro, Hirota, Yasutake, Borduz, Lucian, Heckman, Kacey Wiley, Borduz, Stefan
• Primary Examiner(s): KOSLOW, CAROL M
• Application Number:
  US08/948,951
• Time in Patent Office: 935 Days
• Field of Search: 252/62.52, 252/62.51 R, 252/62.54
• US Class Current: 252/62.52
• CPC Class Codes: H01F 1/44 of magnetic liquids, e.g. ferrofluids particles in a bonding agent H01F1/28, H01F1/36, H01F1/37

Abstract

The invention relates to a composition and a process for producing a chemically stable magnetic fluid comprising finely divided magnetic particles covered with surfactants. A surface modifier is also employed which is added to cover thoroughly the free oxidizable exterior surface of the outer layer of the particles to assure better chemical stability of the colloid under different environmental conditions.

Claims

1. A chemically stable magnetic fluid composition comprising:

0.1 to 40 parts by volume of magnetic particles;

0.1 to about 30 parts by volume of at least one surfactant;

10 to about 99 parts by volume of an organic carrier fluid; and

0.01 to 30 parts by volume of a surface modifier to improve resistance against the chemical oxidation of said composition,

wherein said surface modifier is a non-dispersant and has a molecule tail which contains no more than 10 carbon atoms.

2. The composition according to claim 1, wherein said surface modifier comprises one of an acid based additive, an amine based additive and a silane based surface modifier;

which contains no more than 10 carbon atoms.

3. The composition according to claim 2, wherein said surface modifier is represented by the formula

4. The composition according to claim 1 wherein said magnetic particles are ferrite particles which have a diameter size ranging from about thirty (30) to about one hundred fifty (150) angstroms.

5. The composition according to claim 1, wherein said surfactant is chosen from the class of surfactants consisting of cationic surfactants, anionic surfactants and nonionic surfactants.

6. The composition according to claim 1, wherein said surfactant has a molecular weight of at least 150.

7. The composition according to claim 1, wherein said carrier fluid is an organic molecule compatible with the surfactant and comprises a concentration of between ten percent to ninety-five percent by volume of said composition.

8. A process for preparing an improved chemically stable magnetic fluid comprising 0.1 to 40 parts by volume of magnetic particles;

0.1 to about 30 parts by volume of at least one surfactant;

10 about 99 parts by volume of an organic carrier fluid; and

0.01 to about 30 parts by volume of a surface modifier, wherein said surface modifier is a non-dispersant and has a molecule tail which contains no more than 10 carbon atoms, and said process comprising the steps of;

preparing a solvent base magnetic fluid containing at least one of a cationic, an anionic and a nonionic surfactant, whereby said surfactant is attached to the outer surface of the magnetic particles of the fluid, in order to disperse the particles in a compatible solvent base;

adding said surface modifier to cover an exposed area of the outer layer of the magnetic particle previously uncovered by the surfactant, and said surface modifier being one of an acid based surface modifier, an amine based surface modifier, and a silane based surface modifier;

adding said organic carrier; and

increasing the temperature of the mixture to evaporate the solvent carrier and to disperse the magnetic particles in the carrier fluid.

9. A chemically stable magnetic fluid composition comprising:

0.1 to 40 parts by volume of magnetic particles;

0.1 to about 30 parts by volume of at least one surfactant;

10 to about 99 parts by volume of an organic carrier fluid; and

,

0.01 to 30 parts by volume of a surface modifier selected from the group consisting of acetic acid, benoic acide, allantoin, triproply amine, and methacryloxypropyl trimethoxysilane to improve resistance against the chemical oxidation of said composition.

10. The composition according to claim 9 wherein said magnetic particles are ferrite particles which have a diameter size ranging from about thirty (30) to about one hundred fifty (150) angstroms.

11. The composition according to claim 9, wherein said surfactant is selected from the group consisting of cationic surfactants, anionic surfactants and nonionic surfactants.

12. The composition according to claim 9, wherein said surfactant has a molecular weight of at least 150.

13. The composition according to claim 9, wherein said carrier fluid is an organic molecule compatible with the surfactant and comprises a concentration of between ten percent to ninety-five percent by volume of said composition.