Evaluation of thermal conductivities and thermal expansion coefficients of TiSi2 and Ti5Si3 ceramics prepared from Ti- and Si-rich wastes

Abstract

TiSi2 and Ti5Si3 ceramics are high-temperature coating materials that are mainly synthesized using high-purity Ti and Si. In this study, to determine the application potential of TiSi2 and Ti5Si3 ceramics prepared through Al reduction-electromagnetic directional crystallization (AR-EDC) from Ti-bearing blast furnace slag (TBFS), spent SCR catalysts (SSCs), and diamond wire saw Si powder (DWSSP) for high-temperature coating, the thermal conductivity of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics was measured. In addition, the effect of dissolved W and Al on the thermal conductivities of TiSi2 and Ti5Si3 ceramics was investigated. Meanwhile, the thermal conductivities of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics were compared with those of commercial TiSi2 and Ti5Si3 ceramics and typical high-temperature coating materials. Additionally, the thermal coefficient expansions of AR-EDC-prepared TiSi2 and Ti5Si3 ceramics were compared with those of typical high-temperature Ti alloys. The results showed that the heat transfer mode of TiSi2 ceramics was phonon heat transfer, while that of the Ti5Si3 ceramics was radiation heat transfer, and dissolved W and Al reduced their thermal conductivities. At the temperature range of 298–873K, the thermal conductivities of the TiSi2 and Ti5Si3 ceramics were 29–35 W/(m·K) and 6–11 W/(m·K), respectively, and their thermal expansion coefficients were 8 × 10−6–12 × 10−6 K−1 and 5 × 10−6 –10 × 10−6 K−1, respectively. These results indicate that the thermal conductivity and thermal expansion coefficient of AR-EDC-prepared TiSi2 and Ti5Si3 meet the requirements for high-temperature coating. This study shows that Ti5Si3 and TiSi2 ceramics prepared from Ti- and Si-rich wastes are promising high-temperature coating materials.