一步合成法制备镁硅基热电材料及其热电性能研究

发布时间：2018-03-25 20:33

本文选题：MgH2　切入点：FAPAS　出处：《太原理工大学》2015年硕士论文

【摘要】：热电材料是一种能够利用材料内部载流子运动将电能和热能直接转换的新型功能材料，具有质量轻、寿命长、体积小、清洁环保等许多优点，在汽车尾气回收和工业余热、废热的再利用方面得到了初步的推广。热电材料的种类多种多样，其中镁硅基热电材料以其原料丰富、无毒、安全可靠的特点得到了人们的广泛关注。本文主要针对传统制备方法制备镁硅基热电材料过程中容易造成Mg的挥发和氧化等问题，设计了以MgH2代替Mg，并结合电场激活压力辅助合成（Field-Activated and Pressure-Assisted Synthesis，简称FAPAS）技术实现了Bi掺杂的Mg2Si和Mg2Si1-xSnx（0.3≤x≤0.5）镁硅基热电材料的快速烧结成型（一步合成法），并对其热电性能和热稳定性进行了表征。该方法工艺简便，制备时间短，样品具有纳米片层结构，且纯净致密。主要研究结果总结如下：以MgH2粉、Si粉和Bi粉为原料，运用一步合成法制备出不同配比且不同Bi含量的Mg2Si块体材料，实验结果表明，改变MgH2与Si配比和Bi含量对材料的热导率和电导率均有一定的影响。当MgH2与Si配比为1.95:1且掺入1at.%-Bi时，所得Mg2Si样品在775K获得最佳ZT值，ZTmax=0.77。以MgH2粉、Si粉、Sn粉和Bi粉为原料，运用一步合成法制备出不同Bi含量的Mg2Si1-xSnx基热电材料，实验结果表明，当x=0.4时，，Mg2Si1-xSnx热电材料的性能达到最佳，同时在此基础上通过掺入不同含量的Bi进一步提高材料的热电性能。当温度为770K时，Mg2Si0.6Sn0.4Bi0.01的样品获得了最大ZT值，为1.29。将制备的样品进行自然时效处理和退火处理。自然时效处理后的Mg2Si0.6Sn0.4Bi0.02的样品在整个测温区间的性能为最佳，当温度在775K时ZTmax=1.29。退火处理的样品ZT值在700K之后上升趋势都趋于平缓，且三者ZT值较为接近，说明热电性能趋于稳定。当温度在775K时，Mg2Si0.6Sn0.4Bi0.01样品退火后ZTmax=0.9。
[Abstract]:Thermoelectric material is a kind of carrier material will be able to use within the new functional material electrical and thermal energy conversion, has the advantages of light weight, long life, small size, clean and environmental protection and many other advantages, in the automobile exhaust gas recycling and industrial waste heat, waste heat recycling has been popularized. Various types of thermoelectric materials among them, magnesium and silicon based thermoelectric materials with its rich raw materials, non-toxic, safe and reliable characteristics has been widespread concern.
In this paper, the volatilization of Mg and oxidation problems caused by traditional preparation method of magnesium silicon based thermoelectric materials in the process of design, using MgH2 instead of Mg, and combined with the field activated pressure assisted synthesis (Field-Activated and Pressure-Assisted Synthesis, referred to as FAPAS) technology to achieve the Bi doped Mg2Si and Mg2Si1-xSnx (x = 0.3 ~ 0.5 rapid sintering of silicon) magnesium based thermoelectric materials (one-step synthesis method), and the thermoelectric properties and thermal stability were investigated. The method has the advantages of simple process, short preparation time, samples with nano lamellar structure, dense and pure. The main results are as follows:
Using MgH2 powder, Si powder and Bi powder as raw material, using one step synthesis of different ratio and different Bi content Mg2Si bulk materials, the experimental results show that the change of the MgH2 and Si ratio and Bi content on the thermal conductivity and electrical conductivity have a certain impact. When the ratio of MgH2 and Si for 1.95:1 and doped in 1at.%-Bi, the Mg2Si ZT 775K in the sample to obtain the best value, ZTmax=0.77.
Using MgH2 powder, Si powder, Sn powder and Bi powder as raw material, using one step synthesis of Mg2Si1-xSnx based thermoelectric materials with different Bi content, the experimental results show that when x=0.4, the performance of Mg2Si1-xSnx thermoelectric materials to achieve the best, and on this basis through adding different content of Bi to further improve the thermoelectric properties of materials when the temperature is 770K, Mg2Si0.6Sn0.4Bi0.01 sample obtained the maximum ZT value, natural aging treatment and annealing treatment for 1.29. prepared samples. After natural aging treatment of Mg2Si0.6Sn0.4Bi0.02 samples in the whole range of ZTmax=1.29. is the best, when the temperature in the 775K annealed sample ZT value increased in 700K after the trend is flat, and the three ZT values are close to that of thermoelectric performance tends to be stable. When the temperature at 775K, Mg2Si0.6Sn0.4Bi0.01 after annealing ZTmax=0.9.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

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