Polymer-Derived Silicon Carbide and Boron Nitride Nanotube Composites with High Thermal Shock Resistance

Ceramic composite manufacturing typically requires high temperatures and a long duration of sintering or pyrolysis and has a low yield. Efforts to accelerate manufacturing, especially in the case of emerging polymer-derived ceramics, can result in void and crack formation or even catastrophic failure of the ceramic product. Research findings reveal that boron nitride nanotube networks effectively reinforce polymer-derived silicon carbide ceramics, enabling them to withstand substantial volume changes during pyrolysis. This reinforcement results in the production of high-quality ceramics characterized by extremely low porosity and enhanced mechanical and thermal properties, encompassing improvements in the elastic modulus, fracture strength, ductility, and thermal shock resistance. No degradation of mechanical properties was observed after 100 thermal shock cycles with a sudden temperature drop of about 1100 degrees C at a rate of about 2190 degrees C s(-1). By increasing the nanotube weight concentration to 40%, highly flexible ceramic thin films were obtained that can be bent to a small radius without failure. With the addition of nanotubes, pyrolysis can also proceed with a much faster temperature ramping rate for both heating and cooling cycles, enabling much faster manufacturing throughput than conventional pyrolysis for dense-structure ceramics.