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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.

富硼硼化合物如碳化硼（B_4C）由于其高的化学稳定性和高的热电优值（ZETA）而成为高温热电材料的候选材料。由于B_4C的Seebeck系数（α）强烈地依赖于结构缺陷，因此，在B_4C基体中分散第二相将增大α值。通过用高导电材料制成复合材料也可以提高电导率（siguma）。在本研究中，我们选择了SiB_4、SiB_6、SiB_4<14>、SiC作为高α材料，W_2B_5、TiB_2、YB_6作为高siguma材料。我们已经成功地提高了热电性能，通过控制的微观结构的分散体使用的共晶和过氧化氢反应在凝固过程中从熔融复合材料。在B-C-Si系中，熔态试样含有SiB_2<14>和Si三相。试样经热处理后，Si固溶于SiB_2中<14>，形成SiB_4或SiB_6。σ一般随热处理时间的延长而减小，但α在某一特定热处理时间出现最大值。在1100 K时，包晶系统的ZT值最大，为0.4。B_4C-W_2 B_5，_4C-SiC，B_4C-Ti B_2系均为准二元系，其共晶成分分别为20，50-55，60和75 mol%B_4C，表现出细小的片层结构。少量YB_6、TiB_2等第二相的加入使ZT值显著提高。B_4 C-Ti B_2和B_4 C-Y B_6共晶系在1100 K时ZT值最大，为0.55。本研究制备的B 4 C基复合材料的ZT值（ZT=0.55）是文献报道的富硼硼化物中最高的。