2006

Advances in gas turbine technology place an increasing demand on thermal protection systems of nickel-base superalloys in turbine blades. Current strategies for performance improvements are focused on thermal barrier coatings (TBC).

Nano-sized particles of ceria with high surface area were processed by solution combustion synthesis (SCS) and their catalytic activity towards combustion of carbonaceous materials was compared with that obtained by simple thermal decomposition of cerium nitrate, exhibiting the same specific surface area.

A wide series of carbon nanostructures (ranging from fullerenes, through carbon nanotubes, up to carbon nanofibers) promise to change several fields in material science, but a real industrial implementation depends on their availability at reasonable prices with affordable and reproducible degrees of purity. In this study we propose simple instrumental approaches to efficiently characterize different commercial samples, particularly for qualitative evaluation of impurities, the discrimination of their respective spectral features and, when possible, for quantitative determination.

Co-continuous ceramic-metal composites (C4) were prepared by reactive metal penetration of cordierite-based ceramics used as oven refractory. A compositional and physical characterisation of both precursors and composites was carried out to understand how the choice of the starting material affects the reactive metal penetration. Mechanical behaviour was then compared with that of composites obtained from silica glass or fully sintered cordierite ceramics.

Co-continuous metal–ceramic composites synthesised by the reactive metal penetration method, starting from silica preforms and a 99.5% pure aluminium alloy, were characterised in high cycle tension–compression fatigue. The tests were performed at ambient temperature, in load control and with R = −1; the fracture surfaces were observed in a scanning electron microscope. The Wöhler curve is rather flat, suggesting that these composites behave similarly to ceramics, and the fatigue limit at 107 cycles is 91 MPa.

Nanostructured zirconia toughened alumina composite has been prepared by solution combustion synthesis. Urea has been used as sacrificial fuel and metal nitrates as precursor reagents. A traditional composition for the final ceramic–ceramic composite has been chosen: 20 vol.% of t-zirconia partially stabilized with 3 mol% of yttria dispersed in alumina matrix.