Time resolved X-ray diffraction and thermal imaging studies of magnesium zinc ferrites.

摘要

Self-propagating high temperature synthesis (SHS) reactions have been carried out on mixtures to form MgFe2O4, Mg0.5Zn0.5Fe2O4 and ZnFe2O4. Reactions were carried out in zero and applied magnetic fields of 0.2 T in order to determine the effects the field had on the reaction process and the structure of the spinel formed. Time Resolved X-Ray Diffraction experiments (TRXRD) were carried out at the European Synchrotron Radiation Facility (ESRF) on all three samples. Rietveld refinement of the MgFe2O4 zero and applied field samples were completed. From the calculated weight fractions the applied field was found to reduce the reaction time from 875 ms to 250 ms and led to a reduction in the lattice parameter value for the MgFe2O4. Similar observations were made for the Mg0.5Zn0.5Fe2O4 and ZnFe2O4 samples. The temperature and velocity of the MgFe2O4 reaction were measured using the Thermal Imaging technique. This allowed real time observations of the SHS wave moving through the sample. The applied field was found to lead to ca 50°C hotter and 0.79 mm s-1 faster reactions. It also appeared to influence the method of wave propagation, zero field reactions followed a steady mode of propagation with the applied field making the wave front more oscillatory. The first SHS bulk reactions studied using the thermal imaging technique were carried out and offered an explanation for the surface cracking and heat islands formed as the reaction occurred. Conventional X-Ray analysis was carried out on the three samples, to determine the differences between as made SHS and sintered products. The applied field was observed to influence the atomic site occupancies of the SHS and sintered products with the inversion parameter at 0.26 for the applied field when compared to 0.06 in zero field. Reduction of the magnesium content, resulted in less of the spinel forming in the SHS stage of the reaction. This was attributed to the lower temperatures reached in the reaction measured in the thermal imaging experiments. Finally the development of the new mount allowed identical experiments to be carried out on zero and applied field samples. The TRXRD and Thermal imaging results could directly compared helping to understand the influence of the applied field.