Bi_2Te_3基热电材料的湿化学还原法合成反应机制

The Reaction Mechanism for the Synthesis of Bi_2Te_3-Based Thermoelectric Materials by Aqueous Chemical Method

以BiCl_3、Te为初始原料,在NaOH所提供的碱性环境中利用EDTA包裹Bi^(3+),采用NaBH_4作为还原剂,由此通过湿化学还原法制备高纯Bi_2Te_3基粉体材料。利用X射线衍射(XRD)对粉体材料进行相组成分析,利用扫描电镜(SEM)和电子探针(EPMA)进行了形貌观察和元素成分表征。通过研究反应温度、还原剂NaBH_4的含量以及EDTA的包裹效应对产物化学组分和显微形貌的影响规律,阐明了制备过程中的反应机制。结果显示:NaBH_4加入量的适当改变以及EDTA的包裹效应可起到调节Bi^(3+)、Te^(4+)被还原速度的作用,从而有利于产物纯度的提高.并可获得晶粒尺度约为100～200 nm的圆球状Bi_2Te_3基粉体材料。

Bi2Te3-based nano-powders were synthesized from BiCl3 and Te through an aqueous chemical reduction method, by using EDTA to capsulate Bi^3＋ and NaBH4 as reduction. The phase purity was analyzed by XRD and the morphology and chemical composition were characterized by SEM and EPMA. The reaction mechanism was illustrated through the influence of temperature, amount of NaBH4, capsulation of Bi^3＋ by EDTA on purity and morphology of the powders. The results showed that Te could be gradually broken down to form reO3^2- in an alkaline solvent. The higher reduction rate of TeO3^2- at high temperatures caused an improvement in purity for the product. Meanwhile, the grain size increased and irregular polyhedral shaped powders were obtained. The addition of NaBH4 and capsulation of Bi^3＋ by EDTA could adjust the reduction rate of Bi3^＋ and Te4^＋, and spherical-shaped powders with diameters of 100-200 nm was obtained.