Improving the thermoelectric properties of silicon carbide and boron carbide based ceramics with segregated network structures

Expensive and rare element contents of high-temperature thermoelectric (TE) materials bring a need for developing cost-effective materials such as carbides, as they have naturally abundant low-cost constituents. In this regard, this dissertation covers the production and characterisation of the TE properties of B4C, SiC and TiC, and their composites. TiC and SiC particles were coated on B4C granules with a dry particle coating method, then spark plasma sintered (SPS), forming segregated network structures (SNS) of in-situ TiB2 and SiC which simultaneously increased the electrical and decreased thermal conductivities with TiC-SNS and increased the Seebeck coefficient and decreased thermal conductivity of B4C with SiC-SNS. Maximum ZT of 8.02x10-2 was achieved with in-situ TiB2-SNS, improving the ZT of B4C by ≈120%. Maximum ZT of 0.12 was achieved with SiC-SNS, improving the ZT of monolithic B4C by ≈230%. To investigate the effects of porosity on the TE properties of carbides, monolithic B4C, SiC, and TiC powders and their SNS-composites were partially sintered by SPS and then TE characterisation was utilised. ZT of SiC with TiC-SNS was improved by a significant ≈38% to a value of 6.69x10-3. On the other hand, ZT of B4C with SiC-SNS was improved by a slight ≈3%, to a value of 0.123. Compositions with insufficient thermoelectric performance despite having high electrical conductivities were utilised as EDM (electrical discharge machining) machinable armour ceramics. Different approaches of particulate composite, SNS, and a combination of these were studied to increase the electrical conductivity of SiC in this respect.