Ambient-temperature synthesis of metal-bearing ferrites : how and why?
Ambient-temperature synthesis of metal-bearing ferrites : how and why?
复制标题
含金属铁氧体的常温合成：如何以及为什么？
DOI：
10.1016/s0925-8388(99)00238-8
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Y. Umetsu
中科院分区：
文献类型：
--
作者：
O. Perez;K. Tohji;Y. Umetsu
通过同时控制氧化条件和pH值，在25℃的水溶液中直接制备了各种金属铁氧体。为了弄清相关的机理，本工作研究了铁氧体类化合物形成的反应条件与它们的结晶度、结合水的性质和发展的磁性之间的对应关系。含锌铁氧体的形成被认为是第一个案例。用X射线衍射仪(XRD)、傅里叶变换红外光谱(FT-IR)和扩展X射线吸收精细结构谱(EXAFS)对其进行了表征。结果表明：(I)增加Fe/Zn摩尔比，(Ii)在pH值为11.0(接触阶段)时适当延长悬浮液的曝气时间，或(Iii)母液中的沉淀物在25℃下陈化，可促进铁氧体类沉淀物的结晶度、中间产物的脱水和硫酸盐含量的减少，这些作用归因于Fe(II)实体的氧化-水解反应的适当进展和中间化合物中分子水的损失，这也解释了观察到的沉淀物的饱和磁化强度(Ms)的增强。此外，EXAFS对铁氧体和锌原子局域结构的分析表明，常温铁氧体具有与陶瓷法(1000℃以上)相似的结构，锌原子充分结合到铁氧体骨架中，占据最稳定的位置，即四面体位置。
Various metal-bearing ferrites were produced directly from aqueous solutions at 25°C by simultaneous control of the oxidizing conditions and pH. In order to make clear the involved mechanisms, this work investigated the correspondence between the reaction conditions of formation of ferrite-type compounds and their crystallinity, nature of incorporated water and developed magnetic characteristics. The formation of a Zn-bearing ferrite was considered as a first-case study. X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) and extended X-ray absorption fine structure spectroscopy (EXAFS) measurements were undertaken. It was found that the crystallinity, the dehydration of the intermediate and the diminution of the sulfate contents in the ferrite-type precipitates could be promoted by: (i) increasing the Fe/Zn mole ratios; (ii) a suitable duration of the aeration of the suspensions at pH 11.0 (contact stage) or, (iii) by aging of the precipitates in their mother liquors at 25°C. These effects were attributed to the suitable progress of the oxidation–hydrolysis reactions of Fe(II) entities and the loss of molecular water from the intermediate compound, which also explained the observed enhancement in the saturation magnetization (Ms) of the precipitates. Furthermore, the analysis of the local structure of Fe and Zn atoms by EXAFS evidenced that the ambient temperature ferrite exhibited a similar structure than the one produced by the ceramic method (above 1000°C) and Zn atoms were fully incorporated into the ferrite frameworks occupying the most stable position; i.e. the tetrahedral sites.