2FeCl3·6H2O+FeCl2·4H2O+8NH3·H2O= Fe3O4+8NH4Cl+24H2O (1)

In the dissolution process, FeCl2·4H2O blue-green crystals and FeCl3·6H2O yellow crystals are weighed according to the mass ratio of 0.37:1, and then dissolved in water according to the mass ratio of FeCl2·4H2O and FeCl3·6H2O to water of 0.68:1. Place in a beaker, stir with a glass rod to dissolve it, and prepare a mixed solution. In order to speed up the dissolution rate, the beaker containing the solution can be placed in a hot water bath, and then fully dissolved before being cooled in cold water. The filtration process is to filter the mixed solution of FeCl2 and FeCl3 after cooling to remove impurities, and after filtration, a brown oily solution is obtained. The reaction process is to add ammonia water dropwise in a mixture of filtered FeCl2 and FeCl3 with a rubber cap pipette to cause a chemical reaction like formula (1). Immediately after the addition of ammonia water, the formation of blue-black Fe3O4 colloidal particles was observed, and it should be stirred with a glass rod or a stirrer to make it disperse uniformly without agglomeration to form a large particle precipitate. Until the formation of Fe3O4 is no longer seen, it indicates that the ammonia has been excessive, and the ammonia water is stopped. At this time, the blue-black liquid is obtained. In the heating process, the activator oleic acid and the base liquid kerosene are added to the blue-black solution formed by the above reaction, and the mixture is uniformly stirred to obtain a black shiny liquid. Place it in a water bath above 80 ° C to remove excess ammonia water. Use a glass rod to stir to speed up the removal of ammonia water during heating. To check whether the ammonia water is removed, use PH test paper to place the beaker mouth to see its color change, such as Neutrality proves that ammonia has been basically removed. 

In the process of removing ammonia, it is necessary to heat in a water bath instead of directly heating to prevent evaporation of water and kerosene. The purpose of removing ammonia is to separate water and kerosene. The separation process is The above solution is transferred to a measuring cylinder or a test tube. After ten minutes of standing, it can be observed that the solution is divided into two layers. The upper layer of black shiny colloidal solution is Fe3O4 kerosene-based magnetic fluid, which is composed of Fe3O4 magnetic particles and activator oleic acid. And the base liquid kerosene composition. The lower layer is colorless (or slightly colored) transparent is water and a small amount of unreacted aqueous solution of FeCl2 or FeCl3. The upper layer of black colloidal solution is sucked by a pipette to obtain the desired kerosene of Fe3O4. Base magnetic fluid. If the heated solution does not stratify after ten minutes of standing, it indicates that ammonia is still not removed and can be returned to the beaker relay and continuous heating.