Characterization of barium hexaferrite produced by varying the reaction parameters at the mixing-points in a supercritical water crystallization process

Abstract

Barium hexaferrite (BaFe12O19) was synthesized from a Ba(NO3)2, Fe(NO3)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 ‡C 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 ‡C 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 BaFe12O19 nanocrystals could be easily obtained.