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Title: Fabrication and properties of oxide nanocomposites containing uniformly dispersed second phases
Author: Mukhopadhyay, Amartya
ISNI:       0000 0004 2683 1283
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2009
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available