THE PREPARATION OF MAGNETIC IRON-OXIDE

Two methods for the preparation of magnetic iron oxide starting from F eSO4 . 7H(2)O are described. The traditional method involves preparati on of Fe(OH)(2) seed material, conversion of the seed to acicular gamm a-FeOOH crystals, dehydration of the crystals to alpha-Fe2O3, hydrogen reduction of Fe2O3 to magnetite, and finally reoxidation of magnetite particles to gamma-Fe2O3. Magnetic iron oxide particles thus obtained , after a total processing time of about 25 h, have a coercivity betwe en 330 and 380 Oe. The other method, known as the direct method, invol ves fewer steps, a shorter overall processing time, and yields magneti c iron oxide having an equivalent or higher coercivity value. A sample from the seed preparation solution is recrystallized at 250 degrees C , yielding a product, gamma-Fe2O3, which has a coercivity value of 320 Oe. In another procedure the seed is prepared in the presence of H2O2 as the oxidizing agent and recrystallized at 300 degrees C for 2 h to yield gamma-Fe2O3 having 390 Oe coercivity.