Grain growth in barium ferrite

Abstract

Section I. Kinetics of the Formation of Barium Ferrite. A study has been made on the thermal decomposition reaction $$BaCO_3+6Fe_2O_3\;\;\;BaO.6Fe_2O_3 + CO_2$$ between 900$^\circ$C and 1100$^\circ$C. The reaction kinetic was monitered by a X-ray diffraction technique after the preparation of a standard calibration curve. In the latter stages of the formation the reaction is controlled by a diffusion-process with an experimental activation energy of about 14 $\pm$ 10Kcal/mole. A different mechanism is operating in earlier stages of the reaction. Section II. Grain Growth in Barium Ferrite Isothermal grain growth in the solid-state reaction was investigated in undoped and $SiO_2$-doped polycrystalline barium ferrite. Sintering was run over the temperature range 1150$^\circ$C to 1300$^\circ$C, at 25$^\circ$C intervals for various time in air atmosphere. An electron microscope was used to study the growth-phenomena. Between 1150$^\circ$C and 1200$^\circ$C the grain growth can be described by an equation $$D^2-D_0^2=Kt$$ where D is the average grain size after heat-treatment time t, $D_0$ the initial grain size at t = 0, and K a reaction rate constant. At higher temperatures, there is an indication that a vapor transport mechanism is also taking place. The activation energy for the grain growth was 130 + 20 Kcal/mole and there were no significant difference in the activation energies between the undoped and doped barium ferrite.