High-grade MWCNT/ZrO₂ composites prepared by sol–gel method and high-pressure technique (4.0 GPa): mechanically resistant, porous, and conductive

Preparation of bulk samples with high content of carbon nanotubes and still maintaining their impressive properties is not usual because the connection between them is very difficult. Several attempts to obtain carbon nanotube bulk samples have been made; however, the samples presented insufficient mechanical properties being brittle and difficult to handle. In the present work, multiwalled carbon nanotube/zirconia (MWCNT/ZrO₂) composite compacted samples, containing nearly 40% of multiwalled carbon nanotubes or functionalized carbon nanotubes (MWCNT or f-MWCNT) dispersed in a zirconia matrix (ZrO₂), were prepared for the first time. The sol–gel method was applied to warrant the connection between the MWCNT, associated with the high-pressure technique to impart mechanical properties. The samples that present the best characteristics in compaction and handling were the ones made with composite powders heat-treated at 300 °C. Subsequently, these powders were processed under high pressure (4 GPa) and high pressure/temperature (4 GPa/400 °C). These samples maintain significant content of MWCNT even after heat treatments. The physical and morphological integrity of the MWCNT were retained and yielded samples with impressive properties, such as high surface area (near 150 m² g⁻¹), load resistance (load/mass ratio >8000) and electrical conductivity (3 × 10¹ S m⁻¹).