Kinetic study of crystallization titanium substituted barium hexaferrite in a glassy matrix of the system BaO-Fe2O3-TiO2-B2O3
P. Quiroz and B. Halbedel
Differential thermal analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallization behavior of the rapid cooled melt compositions (mole-%): 40 BaO + 33 B2O3 + (27-x) Fe2O3 + x TiO2 with x = 0, 1.8, 3.6, 4.6 and 6.4 mole-% TiO2 for the production of electromagnetic absorber powders in the microwave range. After annealing of these cooled melts the crystalline phases BaB2O4, BaFe12-xTixO19 and from melt substitutions of x >4.6 mole-% TiO2 a dielectric phase BaTi6O13 were determined by XRD. The Netzsch Thermokinetics® program was used in order to understand the phase transformations through the analysis of the kinetic parameters. Thereby the influence of temperature and heating rate was investigated. Overall activation energy of 311.74 ± 3 kJ mol-1 was obtained for the crystallization of barium hexaferrite with the ASTM E698® method. A slightly decreasing tendency in this energy was observed when the TiO2 content was increased, but it is not a significant variation despite the substitution. In addition, the Friedmann method was used to calculate the activation energy, because it is not constant throughout the crystallization process.
Keywords: barium hexaferrite, phase transformation, kinetics, substitution, X-ray diffraction.