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.% Fe<sub>2</sub>O<sub>3</sub> in Al<sub>2</sub>O<sub>3</sub> 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 FeAl<sub>2</sub>eO<sub>4</sub> as second phase particles throughout the bulk of the samples. The optimum aging schedules resulted in a final microstructure comprising nanosized (~ 100 nm) intragranular FeAl<sub>2</sub>eO<sub>4</sub> 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 Al<sub>2</sub>O<sub>3</sub>. 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 10<sup>6</sup>) with respect to the unreinforced ABS glass/ceramic. Furthermore, 40% improvement in thermal conductivity (~ 1.8 W m<sup>-1</sup> K<sup>1</sup>) over that of unreinforced ABS glass/ceramic was recorded with ABS-15 wt.% MWCNT nanocomposite.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:510191 |
| Date | January 2009 |
| Creators | Mukhopadhyay, Amartya |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:094c8b45-49b8-4518-8257-c1fd3ebbd8b2 |
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