Characterization of Barium Hexaferrite Produced by Varying the Reaction Parameters at the Mixing-Points in a Supercritical Water Crystallization Process

摘要

Barium hexaferrite (BaFe_(12)O_(19)) was synthesized from a Ba(NO_3)_2, Fe(NO_3)_3 and KOH mixed solution by hydrothermal treatment of the solution using a supercritical water flow apparatus. The first step is the hydrolysis of the nitrates of barium and iron in potassium hydroxide; the pressure and temperature were adjusted in the respective range of 25-40 MPa and 100-250℃ in tee reactor (MP2). The second one is the dehydration of the formed hydrolytic products, under the supercritical state of the solvent in the range of 25-40 MPa, 300-450℃ and 40-100 s in tubular flow reactor (MP3). All samples of barium hexaferrite were prepared without calcination of the dehydrated products. Using this method, smaller, uniform-size and single-phase BaFe_(12)O_(19) nanocrystals could be easily obtained.