Fabrication and properties of oxide

Thesis

The present research addresses some of the major problems pertaining to two different types of ceramic nanocomposite; viz. participate reinforced polycrystalline alumina-based nanocomposites and multiwalled carbon nanotube (MWCNT) reinforced aluminoborosilicate glass/ceramic (ABS) nanocomposites. With respect to the former, a novel and economical processing route based upon solid solution-precipitation technique is explored. Dense and homogeneous solid solutions of 10 wt.% Fe₂O₃ in Al₂O₃ were produced by pressureless sintering at 1450°C in air. Aging of the solid solutions in a reducing atmosphere at temperatures in the range 1250°C-1550°C for different durations (up to 50 h) resulted in the precipitation of FeAl₂eO₄ as second phase particles throughout the bulk of the samples. The optimum aging schedules resulted in a final microstructure comprising nanosized (~ 100 nm) intragranular FeAl₂eO₄ particles, along with coarser micro-sized particles along the matrix grain boundaries and triple point corners. The hybrid nano/micro composites possessed improved fracture toughness (by ~ 40%), flexural strength (by ~ 50%) and abrasive wear resistance (by a factor of ~ 2.5) with respect to monolithic Al₂O₃.

With respect to the ABS - MWCNT nanocomposites, we report here the ability to develop dense nanocomposites, containing uniformly dispersed nanotubes up to a content of 10 wt.%, by an ultrasonication-assisted sol-gel technique followed by hot pressing. The optimised ABS - 10 wt.% MWCNT nanocomposite possessed nearly double the strength, and a fracture toughness improvement of ~ 150% with respect to the unreinforced ABS. The carbon nanotubes have been observed to bridge crack openings of the order of ~ 100 nm which provides the major contribution towards the improvement in fracture toughness. The nanocomposites, showed an electrical percolation threshold of between 2.5 to 5 wt.% MWCNT and possessed significantly higher electrical conductivities (by a factor of 10⁶) with respect to the unreinforced ABS glass/ceramic. Furthermore, 40% improvement in thermal conductivity (~ 1.8 W m^-1 K¹) over that of unreinforced ABS glass/ceramic was recorded with ABS - 15 wt.% MWCNT nanocomposite.

Authors: Mukhopadhyay, A

• DOI: 10.5287/ora-n65no2vrn
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford