THERMOELECTRIC PROPERTIES OF CALCIUM HEXABORIDE SINTERED BODY

摘要

Calcium hexaboride (CaB_6) is one of the hardest (Hv=～27Gpa) and stiffest (Young's modulus E=～460GPa) ceramics known with moderate electric conductivity (10~1～10~4 S). Recently, studies have been carried out to determine the feasibility of using CaB_6 as an additional material for improvement of the abrasion resistance of bricks for converter. In this study, CaB_6 was prepared by hot pressing. The influence of sintering temperature on thermoelectric properties and Vickers hardness of CaB_6 sintered bodies were investigated. CaB_6 powders with about 13μm and 20 μm in size were used in this experiment. The samples were at sintered of 1823K to 1923K for 3.6ks in vacuum under a pressure of 40MPa. The relative density of sintered body at 1923K was approximately 100%. The electrical conductivity and Seebeck coefficient were measured using a D.C. four-terminal method. The electrical conductivity of CaB_6 decreased with increasing temperature. The Seebeck coefficient of CaB_6 was showed-40 × 10~(-6) V/Kat 1073K. The figure of merit Z of CaB_6 increased with increasing temperature. The Z of CaB_6 sintered at 1923K by hot pressing reached 22.5 × 10~(-6) /K at 1273K. The Vickers hardness showed 17GPa at room temperature and showed 4GPa at 1373K using a powder with 13 μ m.