Geoffrey Otieno

Geoffrey Otieno

Rhodes Scholar

BSc, MEng.


Aligned Carbon nanotubes / ceramic composites

Previous attempts to produce carbon nanotube (CNT) ceramic composites have usually resulted in poorly dispersed, unaligned and/or non-continuous CNTs in the composites. Consequently, property improvements have been limited. To avoid this, we produce dense composites by infiltration of aligned multiwalled carbon nanotube (MWCNT) preforms using aluminoborosilicate (ABS) glass sol. The preforms are produced by aerosol chemical vapour deposition, without further processing infiltrated with the sol, which fills the interstices of the preforms. Aligned MWCNT preforms of up to 5mm in length are produced for composite fabrication. When pressurelessly sintered, composite sheets containing continuous CNTs are obtained. The electrical and thermal conductivities of the composites through thickness are 5-8 x 102 S m-1 and 16 W m-1 K-1 which are 2 and 1 order better than randomly oriented CNT/ABS composites. When hot pressed, the microstructure of the composites shows no residual porosity. Toughening mechanisms familiar from fibre reinforced composites, notably CNT pullout are observed. The pullouts are longer (~ 500 nm) compared to randomly oriented CNT/ABS composites suggesting weak interfacial bonding. Microcantilever bend tests show "graceful failure". Strengths and toughnesses are currently being investigated.