Research of crystal changing of barium hexaferrite prepared by citric acid sol-gel method

Barium hexaferrite was synthesized by combining citric acid sol-gel process with self-propagating at high temperature, relationship between the forming temperature of barium ferrite, and crystal phase was investigated in the experiment. The thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used in the analysis to discuss the influence of different amounts of citric acid additives on the calcination product crystal phase, and relationship of transformation of gamma-Fe2O3 to alpha-Fe2O3 between W-type and M-type of the crystal phase of barium hexaferrite. The results revealed that the crystal phase of barium hexaferrite was W-type when the value of CA/MN <= 1.2, and if CA/MN = 2, the crystal phase became M-type. With the increase in the amount of citric acid, the crystallization temperature of product rose. The excessive citric acid additive changed the existing form of Fe, which contributed to the transformation of gamma-Fe2O3 to alpha-Fe2O3. The latter had greater thermal stability, resulting in an increase in the formation temperature of the W-type barium hexaferrite, and finally obtaining the M-type.