【作者】 张德华；

【导师】 孟庆森；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 热电材料具有直接将热能和电能转换的功能,能够提供环保安全、安全节能的固态发电和制冷方式,具有极其广泛的应用前景。Mg2Si基热电材料具有载流子有效质量大、迁移率高、晶格热导率低、原料丰富、环境友好等特点,是一种应用于中温区域的优良热电材料。近十几年来大量的理论研究表明,低维热电材料可显著提高热电性能,纳米结构有望大幅度提高Mg2Si基热电材料的热电性能。本文采用反应法+电场激活压力辅助合成(Field-Activated and Pressure-Assisted Synthesis,简称FAPAS)技术,制备了碳纳米管、纳米Si02和纳米La203掺杂的Mg2Si基纳米复合热电材料,研究了三种纳米添加物对热电性能的影响,同时对使纳米添加物更均匀的分布在Mg2Si基体中进行了工艺改进。研究结果表明,碳纳米管在低掺量的条件下能提高复合材料的电导率,掺杂0.3wt.%MWCNTs的试样表现了最好的电性能,其功率因子在427K时最高,达到了1.09×10-3Wm-1k-2,相对于未掺杂试样的1.01×10-3Wm-1k-2有了一定的提高。纳米SiO2、La2O3的掺杂同时增强了Seebeck值。纳米级SiO：的掺杂成功的降低了热导率,使得复合材料的热导率大大降低,进而提升了整体热电性能,复合热电材料1wt.%Si02/Mg2Si0.8Sn0.2在573K时ZT=0.25。更多还原

【Abstract】 As one of the options for the energy conversion between thermal and electrical energy, thermoelectric(TE) materials are widely used in environmental, reliable and all-solid-state electricity generation and refrigeration. Magnesium Silicide is a kind of middle temperature thermoelectric material with the advantages of large effective carrier mass and mobility, abundant raw materials, low cost and environment friendly. For a decade or more, lots of theoretical studies have shown that low-dimensional TE materials could improve the thermoelectric properties remarkably. Thus the introduction of nanostructures is expected to improve the thermoelectric properties of Mg2Si-based alloys largely.In this paper, the low-temperature reaction method combined with the Field Activated and Pressure Assisted Synthesis process was used to successfully prepare MWCNTs, nano-SiO2and nano-La2O3doped Mg2Si based thermoelectric bulk nanocomposite. The effects of three types of nano-additives on the microstructure and thermoelectric properties of Mg2Si were studied. At the same time, the process of how to make the nano-additives disperse more homogeneously in Mg2Si matrix was improved.The electrical performance testing results of samples doped with SWCNTs indicate that the carbon nanotubes can improve the conductivity of the composites under low dosage. Among them, the sample with an addition of0.3wt.%SWCNT exhibits the best electrical property. Its power factor reaches1.09×10-3Wm-1K-2at the temperature of427K, which is higher than that of the sample without SWCENs (1.01×10-3Wm-1k-2). Both the addition of nano-SiO2and nano-La2O3improve the Seebeck coefficient of the composites. Lattice thermal conductivity decreases greatly as a result of the presence of the homogeneously dispersed nano-SiO2, which reduce the thermal conductivity of the composites largely and then enhance the thermoelectric properties. Among all of the samples,1wt.%SiO2/Mg2Si0.8Sn0.2exhibits the best figure of merit (ZT=0.25at573K), which is24%higher than that of the sample without SiO2. Thus, the adoption of low-temperature reaction and FAPAS method and the addition of nanometer-sized SiO2provide a new way of improving the thermoelectric properties of Mg2Si based materials.更多还原