The Effect of CNTs on the Sintering Behaviour and Properties of Structural Ceramic Composites

PhDThis research provides a comprehensive investigation into the effects of carbon nanotubes (CNTs) on the sintering behaviour, grain growth and properties of ceramics. Contradictory results reported in the literature on the effect of CNTs on sintering behaviour indicated the need for a systematic investigation under reproducible, controllable conditions. The sintering studies were performed using instrumented spark plasma sintering (SPS). It is a rapid sintering process that allows sintering to be studied in real time under isothermal conditions, enabling accurate calculation of time exponents and activation energies. A study into the effects of CNTs on the sintering behaviour of PSZ and B4C has shown that the presence of CNT content above the percolation threshold significantly reduces the sintering activation energies by 62 and 38% respectively. In both systems, the CNTS were also found to enhance the grain boundary diffusion mechanism of consolidation. Below the percolation threshold there was no significant effect on the activation energy. As well as the sintering behaviour, the grain growth of the PSZ and PSZ CNT composites was investigated. This research found that the CNTs acted as a grain growth inhibitor through a solute drag like mechanism both below and above the percolation threshold although with a high CNT content the solute drag effect was enhanced further with no significant change to the activation energy. The degradation of the CNTs was examined to determine whether they maintain their structural integrity during sintering. It was found that in both matrices with increasing temperature the CNTs were degraded to a greater extent. In the case of the PSZ-CNT composite the degradation was measured with respect to time at a series of temperatures to investigate the mechanism of degradation. Abstract ii The thermal properties of the ceramic CNT composites and porous ceramics were examined to determine the effect of CNTs on the transport properties of the matrix. It was found that the inclusion of CNTs in a PSZ matrix could enhance the thermal diffusivity and the residual porosity caused by burning them out causes a reduction