The ferroferric
oxide nano magnetic fluid prepared with the method has the particle size of 8-17 nm. The ferroferric
oxide particles modified by
trisodium citrate have negative
electricity on the surfaces, and the
Zeta potential measurement shows that the potential on the surfaces of the ferroferric
oxide particles is -8.6 mV to -23.9 mV. The ferroferric oxide particles modified by
nitric acid have positive
electricity on the surface, and the
Zeta potential measurement shows that the potential on the surfaces of the ferroferric oxide particles is +6.7 mV to +18.5 mV. Compared with the prior art, because the invention adopts lower synthesis temperature, and the
nitrogen protection prevent the oxidation of
divalent iron salt, the prepared magnetic particles have small and even size and
electricity on surfaces, can disperse stably for a long time without agglomerating and are super
paramagnetic particles which can move directionally under the condition that the
magnetic field exists. The method for preparing the improved ferroferric oxide magnetic fluid comprises the following steps: adjusting the pH value of solution containing trivalent iron salt and bivalent iron
salt solution to 9-10 with aqueous
ammonia under the
nitrogen protection, stirring the aqueous
ammonia to the solution to make the aqueous
ammonia react with the solution at 70-100 DEG C for 1-4h, washing the product of reaction with
ethanol and deionized water repeatedly until the pH value of the product of reaction being neutral, dispersing the prepared nano magnetic ferroferric oxide in the
trisodium citrate solution or the
nitric acid solution, and washing the product of reaction with
acetone and deionized water repeatedly to obtain the ferroferric oxide nano magnetic fluid with negative electricity or positive electricity.