Patent ID: 7591960

Claim:
A preparation method for magnetic fluid comprising the steps of: adding a diamino compound of urea into an oleaginous material of an organic oil to form an oil-based compound containing a diamino group; adding a carboxyl compound selected from the group consisting of undecenoic acid, oleic acid, lauric acid and caproic acid into the oil-based compound containing said diamino group to obtain an oil-based compound having a carboxyl group and said diamino group; mixing an iron solution with another carboxyl compound to obtain a magnetic iron oxide with said another carboxyl group; and adding the oil-based compound having said carboxyl group and said diamino group into the magnetic iron oxide with said carboxyl group to obtain an oil-based magnetic fluid, wherein in the step of mixing the iron solution with said carboxyl compound to obtain the magnetic iron oxide with said carboxyl group, the carboxyl compound is undecenoic acid, the step of mixing the iron solution with the carboxyl compound further comprising the steps of: dissolving ferrous chloride and ferric chloride in deoxidized water to obtain a solution of the ferrous and ferric chlorides, wherein the molecular ratio between ferrous chloride and ferric chloride ranges from 1/2 to 1/3; heating said solution to 80 Celsius degrees inside a reflux condenser, adding the heated solution into the undecenoic acid and continuingly heating a resulting solution; diluting ammonia water with alcohol and ethyl acetate, thereby obtaining a dilution, pouring the dilution into the reflux condenser to obtain a mixture, and heating the mixture at 80 Celsius degrees for thirty minutes; cooling down the mixture to 65 Celsius degrees for 5 hours and thirty minutes to obtain the precipitation of undecenoic acid-magnetic iron powder; and decanting clear supernatant to obtain the undecenoic acid-magnetic iron powder, containing the magnetic iron oxide with said carboxyl group.