Thermo-Physical Properties and Characterization Studies on Vacuum Hot-Pressed Boron Carbide Ceramics

Boron carbide (B4C) ceramic has attracted fusion communities worldwide due to its high neutron shielding capabilities and other satisfactory thermal, chemical, physical, and mechanical properties. It is receiving wide attention for the ITER diagnostics ports for neutron shielding and for protecting maintenance personnel against radiation exposure. B4C ceramic blocks were developed using vacuum hot pressing of B4C powder at a process temperature of ~2100 °C and 30 MPa pressure by ITER-India through Indian Industry. Considering the need for reduced contamination, no sintering aid was used during the process. Inside the diagnostics port of Tokamak, B4C will be subjected to high radiation, ultrahigh vacuum, and high-temperature (HT) environments. Therefore, it is necessary to study temperature-dependent properties along with its other properties and vacuum compatibility. Toward the qualification of this vacuum hot-pressed B4C ceramic, its phase purity and surface microstructure were analyzed using X-ray diffraction (XRD) techniques and scanning electron microscopy (SEM). XRD data confirmed the presence of the B4C phase. Helium pycnometry was applied to determine the true density of the powder and hot-pressed B4C pellets, which were 2.55 and 2.52 g/cc, respectively. The thermal expansion is estimated to be 0.6% up to 1200 °C, with a mean coefficient of thermal expansion of $5.28\times 10^{-6}\,\,\text{K}^{-1}$ between room temperature (RT) and 700 °C. Thermal expansion data were used to calculate temperature-dependent densities up to 1200 °C. The Differential scanning calorimetry sensor (DSC) measures phase stability up to 700 °C and calculates specific heat capacity. It was observed experimentally that the thermal conductivity drops by 45% between 50 °C and 500 °C. The experimental results are compared with the published data and are discussed in depth in this work.