| M-type hexagonal ferrite magnet firmly accounts for most of the permanent magnetic materials market, not only due to its low price, but also the relatively excellent performance, high Curie temperature(Tc) and good corrosion resistance. The booming market, which consists of fashionable hybrid and electric vehicles, more and more intelligent and portable office/home appliances, brings both opportunities and challenges to the further development of M-type hexagonal ferrite. Ion substitution and preparation-technology innovation are two of numerous effective methods to improve the performance of M-type hexagonal ferrite magnets.Based on the fundamental theories of Ca La Co-substituted strontium hexaferrite, Sr1-x-y Lax Cay Fe2n-z Coz O19 permanent ferrites were prepared by the conventional ceramic process, and their magnetic properties, such as the remanence Br and the intrinsic coercivity Hc J, were discussed in several aspects including the key process, ion substitution, additives and so on.Firstly, the influence of the calcination temperature, the sintering temperature and the holding time on Ca La Co-substituted strontium hexaferrite were investigated systematically in some aspects of the composition, morphology and magnetic properties. The results show that:(1) Within a reasonable range, the calcination temperature, the sintering temperature and the holding time are favorable to the improvement of remanence Br, and harmful to the intrinsic coercivity Hc J.(2) The sintered magnets can achieve the relatively greatest performance on the condition that the calcination temperature and the holding time are 1250? and 1.5 hours, respectively. Besides, the remanence Br is higher when the samples are sintered at 1190?, but the intrinsic coercivity Hc J is different that it achieves the maximum value at 1170?. So, it depends that the sintering temperature can be variable on which to be preferred, the remanence or intrinsic coercivity.In the next section, a series of experiments about the milling process optimization were conducted to deal with the problem that the particle size distribution is poor after milling and amounts of micropowder would be harmful while molding to a cylindrical specimen in magnetic field. The effect of heat-treatment process on Ca La Co-substituted strontium hexaferrite were studied in several aspects of heat-treatment temperature and time, rotation speed and grinding time, and so on. The results show that appropriate heat-treatment process could improve the poor particle size distribution and decrease the amount of micropowder. In addition, the secondary grinding process should be mild so that the particle size and magnetic properties of sintered samples are better than before when the powder is treated at 900? for 1 hour, then ground in a 200r/min rotation speed for 1.5 hours.Moreover, on the basis of preparation process innovation, the influence of Zn2+ substitution on Ca La Co-substituted strontium hexaferrite. The results indicate that:(1) The composition of the calcined samples remains a single phase of M-type hexagonal ferrite with an appropriate amount of Zn2+. However, with the Zn2+ substitution increasing, the grain size becomes larger, the microstructure gets worse, and both the remanence Br and maximum magnetic energy product(BH) max increases, but the intrinsic coercivity Hc J decreases sharply.(2) The magnetic properties of sintered samples reach the maximum value, Br =434m T and Hc J =412.5k A/m, when the Zn2+ substitution amount is 0.1.At last, certain additive groups are introduced to obtain uniform and dense microstructure and small enough grain size so as to improve the magnetic properties. The optimum additive combination, including 0.5wt% Ca CO3, 0.5wt% La2O3, 0.3wt% Co O and 0.25% H3BO3, contributes positively to the magnetic properties of Ca La Co-substituted strontium hexaferrite which could reach the maximum value: Br=441m T, Hc J=437k A/m,(BH)max=38.5k J/m3 with Zn substitution. |
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