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.