A preservation study of carbon nanotubes in alumina-based nanocomposites via Raman spectroscopy and nuclear magnetic resonance

Raman spectroscopy was used to study the preservation of the carbon nanotube structure in nanotube-reinforced alumina nanocomposites consolidated via spark plasma sintering (SPS). A series of Raman spectroscopy experiments was used to identify the thermal breakdown temperature of single-walled carbon nanotubes (SWCNTs) embedded in nanocrystalline alumina. It was found that the carbon nanotube structure remains intact after sintering at 1150 °C, but almost completely breaks down by 1350 °C after only 5 min. Also, ²⁷Al nuclear magnetic resonance (NMR) was used to study the chemical and structural effects of high-energy ball milling (HEBM) and SPS consolidation on pure alumina and SWCNT-alumina nanocomposites. HEBM does not change the mixed coordination number of the as-received alumina, but slight peak shifts indicate residual stresses. No Al₄C₃ was detected in any of the consolidated samples - even up to 1550 °C for 10 min. Thus, it is concluded that consolidation of carbon nanotube-reinforced composites should be completed at temperatures below ∼ 1250 °C in order to preserve the carbon nanotube structure.