MATERIALS BASED ON MAGNETIC NANOPARTICLES OF MAGNETITE-TYPE, COVERED WITH A DOUBLE INORGANIC LAYER AND PROCESS FOR PREPARING THE SAME

The invention relates to a process for preparing magnetic nanoparticles used as pigments for manufacturing security paper. According to the invention, the process comprises the magnetite-forming reaction, after which the magnetic nanoparticles are covered with a layer of barium sulphate, resulting in nanoparticles of the type FeO/BaSOwhich are magnetically dispersed from the reaction mass, are successively washed with ethanol and water and are subjected to reaction with tetraethyl orthosilicate in a ratio of 1:2 in a mixture of ethanol, water and ammonia, at room temperature, for 3 h, while continuously stirring, the formed particles being magnetically separated, washed with water and ethanol and dried, resulting in magnetic nanoparticles of magnetite type covered with a doube inorganic layer of barium sulphate and silicon dioxide.