铁过量M型钡铁氧体的放电等离子体烧结合成

SYNTHESIS OF M-TYPE BARIUM FERRITE WITH EXCESS IRON BY THE SPARK PLASMA SINTERING METHOD

采用并加共沉淀法制备了名义组成为BaFe_(12.4)O_(19.6)的铁过量M型钡铁氧体前驱体,研究了该前驱体在放电等离子体烧结条件下的结晶行为和烧结体的磁性能。结果表明:700～850℃,烧结体均是单相M型钡铁氧体,没有BaFe_2O_4和γ-Fe_2O_3中间相结晶。晶粒分布随温度升高而显著变化,700℃时呈随机分布:700℃以上表现出择优取向。饱和磁化强度在700℃时显著增大:700～850℃时基本不变,这与烧结体的相组成随温度升高的变化规律相吻合。矫顽力随温度升高先增加后降低,与M型钡铁氧体含量增加和择优取向程度提高有关。

The precursor of M-type barium hexaferrite with iron excess, which the nominal composition was BaFe12.4O19.6, was pre- pared by a so-called co-dump coprecipitation method. The crystallization behavior of the precursor under the spark plasma sintering （SPS） conditions and the magnetic properties of the SPS samples were investigated. The results show that the samples obtained at 700-850 ℃ were composed of single-phase M-type barium hexaferrite, and that the crystallization of intermediates such as BaFe2O4 and γ-Fe2O3 did not occur. The distribution of crystal grains obviously changed with the increase of temperature; the distribution was random at 700 ℃ and became preferential orientation when the temperature was more than 700 ℃. The saturation magnetization significantly increased at 700 ℃ and remained almost constant in the range of 750 ℃ to 850 ℃. This accorded with the evolution characteristics of the phase composition of the SPS samples with the increase of temperature. The coercivity first increased and then decreased with the increase of the temperature, which was attributed to the corresponding increases in the content of M-type barium ferrite and the degree of preferential orientation of crystal grains.