Application of boron carbide-based composite ceramics to thermoelectric conversion materials

碳化硼基复合陶瓷在热电转换材料中的应用

基本信息

批准号：
09450255
负责人：
GOTO Takashi
金额：
$ 0.64万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

Boron rich borides such as boron carbide (B_4C) are a candidate for the high-temperature thermoelectric material because of their high chemical stability and high thermoelectric figure-of-merit (ZETA). Since the Seebeck coefficient (alpha) of B_4C strongly depends on the structural defects, the a values would increase by dispersing second phases in the B_4C matrix. The electrical conductivity (siguma) may also increase by making composite with highly conductive materials, In the present research, we have chosen SiB_4, SiB_6, SiB_<14>, SiC as high alpha materials, and W_2B_5, TiB_2, YB_6 as high siguma materials. We have successfully improved the thermoelectric performance by controlling the microstructure of dispersoids using the eutectic and pertectic reactions during the solidification process from the melted composites. In the case of B-C-Si pertectic system, as-melted specimens contained three phases of SiB_<14> and Si. Heat-treatments of the specimens caused the solid solution of Si into SiB_<14> and the formation of SiB_4 or SiB_6. The siguma decreased with the heat-treatment in general, but the a indicated the maximum at a specific heat-treatment time. The greatest ZT value in the peritectic system was 0.4 at 1100K.The B_4C-W_2B_5, _4C-SiC, B_4C-Tib_2 systems were all quasi-binary, whose eutectic compositions were 20, 50-55, 60 and 75 mol%B_4C, respectively, indicating fine lamella structures. The addition of small amount second phases such as YB_6 and TiB_2 resulted in the significant increase of ZT values. The greatest ZT values in the eutectic system were 0.55 at 1100K for the B_4C-TiB_2 and B_4C-YB_6 systems. This value (ZT=0.55) of the present B_4C-based composites are the highest level among the boron-rich borides reported in the literatures.

富含硼的硼化物，例如碳化氢（B_4C），是高温热电材料的候选者，因为它们具有较高的化学稳定性和高热电图（Zeta）。由于B_4C的Seebeck系数（Alpha）在很大程度上取决于结构缺陷，因此A值将通过将第二阶段分散在B_4C矩阵中来增加。电导率（Siguma）也可以通过用高导电材料制成复合材料来增加，在本研究中，我们选择了SIB_4，SIB_6，SIB_ <14>，SIC作为高α材料，W_2B_5，TIB_2，TIB_2，YB_6，YB_6作为高siguma材料。我们通过在熔化的复合材料的凝固过程中使用共晶和骨骼反应来控制分散体的微观结构，从而成功地改善了热电性能。在B-C-SI特性系统的情况下，熔融的标本包含SIB_ <14>和Si的三个阶段。样品的热处理导致Si的固体解决方案sib_ <14>以及SIB_4或SIB_6的形成。 Siguma通常随热处理而降低，但A表示在特定的热处理时间的最大值。在1100K时，脑观察系统中最大的ZT值为0.4。B_4C-W_2B_5，_4C-SIC，B_4C-TIB_2系统都是准二进制的，其Eutectic构图分别为20、50-55、60和75 mol％B_4C，表明高细层层。添加少量第二阶段（例如YB_6和TIB_2）导致ZT值的显着增加。对于B_4C-TIB_2和B_4C-YB_6系统，共晶系统中最大的ZT值在1100K时为0.55。目前基于B_4C的复合材料的该值（ZT = 0.55）是文献中报道的富含硼的硼化物中的最高水平。