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.

碳化硼（B_4C）等富硼硼化物因其高化学稳定性和高热电品质因数（ZETA）而成为高温热电材料的候选者。由于 B_4C 的塞贝克系数 (alpha) 强烈依赖于结构缺陷，因此通过在 B_4C 基体中分散第二相，a 值会增加。通过与高导电材料复合也可以提高电导率（siguma），在本研究中，我们选择SiB_4、SiB_6、SiB_<14>、SiC作为高α材料，以及W_2B_5、TiB_2、YB_6作为高siguma材料。我们通过利用熔融复合材料凝固过程中的共晶和共晶反应来控制弥散体的微观结构，成功地提高了热电性能。在B-C-Si 晶系的情况下，熔融态样品包含SiB_ 14 和Si 三相。样品的热处理引起Si固溶到SiB_14中并形成SiB_4或SiB_6。一般来说，西格玛随着热处理的进行而降低，但α在特定的热处理时间处达到最大值。包晶体系在1100K时ZT值最大为0.4。B_4C-W_2B_5、_4C-SiC、B_4C-Tib_2体系均为准二元体系,其共晶成分分别为20、50-55、60和75 mol%B_4C ，表明精细的层状结构。添加少量YB_6和TiB_2等第二相导致ZT值显着增加。对于 B_4C-TiB_2 和 B_4C-YB_6 系统，共晶系统中的最大 ZT 值在 1100K 时为 0.55。目前B_4C基复合材料的这一值（ZT=0.55）是文献报道的富硼硼化物中最高水平。