Preparation and Characterization of B4C-HfB2 Composites as Material for High-Temperature Thermocouples

Boron carbide shows high thermoelectric power. Therefore, it is an interesting material for thermoelectric applications. In the past, there were already successful uses of boron carbide as a thermocouple material together with graphite. However, more reliable, cost-efficient, and long-term stable solutions are required for practical benefit. Boron carbide and hafnium boride composites were prepared by pressureless sintering of B4C and HfC powder mixtures. The effect of HfC addition on the sinterability of boron carbide was studied. Highly densified ceramic with a relative density of 95.4% was obtained at a sintering temperature of 2250 °C. The composition and the microstructure of the dense composites are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). In addition, the correlation between the composition, Seebeck coefficient, and the electrical conductivity was investigated. The Seebeck coefficient of the composite is decreased and the electrical conductivity is increased with the increasing addition of HfC, and a change in conduction behavior from semiconducting to a metallic mechanism is observed. Functional thermocouples based on the prepared composites were tested and showed potential for temperature measurement application.