2000

High-conductivity and high-density samples with new compositions in the NASICON-type electrolyte series, i.e., the Na3Zr2-(x/4)Si2-xP1+xO12 system, with x = 0(A), 0.667(B), and 1.333(C) were synthesized using a mixed inorganic-organic sol-gel process. The sinterability was improved with increasing the x value, but the conductivity decreased. Highly dense samples were obtained by sintering at 1100 °C. The conductivity decreased with decreasing the c lattice parameter of the hexagonal structure.

The activation energy of carbon combustion catalysed by alkali vanadates or alkali vanadates/chlorides mixtures is assessed by the Ozawa method. The most active catalyst, Cs4V2O7, entails more than 50% decrease of the activation energy compared to non-catalytic combustion (from 157 down to 75 kJ/mol). The catalyst performance is enhanced when the catalyst is dissolved in a eutectic liquid (e.g., AgCl + CsCl), which likely improves the catalyst/carbon contact conditions.

This paper concerns the development of catalytic traps for diesel particulate removal from the exhaust gases of light-duty vehicles. The studied traps were realised with ceramic (ZTA and mullite) foam structure, on which two different kinds of catalysts, one based on caesium metavanadates and the other on pyrovanadates, were deposited.

Thermal fatigue behaviour of a 2014/Saffil composite has been investigated. This composite was produced by infiltration of preforms of Saffil fibers (Al2O3-SiO2 fibers) with a 2014 aluminium alloy (Al-4.7Cu-1.0Si-0.6Mg). The composite samples, containing 13 vol.% of fibers, were sectioned and their microstructure was investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Tensile tests, hardness and microhardness measurements were carried out. The fracture surfaces were examined by SEM.

The high temperature behaviour of a Ti-6Al-4V/TiCp composite (10% Vol. of TiC) was investigated. A composite produced by Dynamet Technology according to the blended-elemental-cold-hot isostatic pressing (BE-CHIP) method was used. The stress-strain properties of the material were tested at 25, 200, 400, 500, 600 and 800°C. Composite specimens were aged in air at 500 and 700°C or under vacuum at 500, 700 and 1050°C, for periods ranging between 100 and 500 hours.

Brake discs of (Al-Si-Mg)/SiC composite were produced by gravity casting. To this purpose ingots, containing 50 vol.-% of SiC particles, produced by pressureless metal infiltration at Lanxide Corp., were melted, diluted with an unreinforced alloy (thus achieving a SiC content of 30 vol.-%), and cast in permanents moulds. The possibility of repeating the casting process using recycled material was investigated. Brake discs were fabricated by using 50 or 100% of recycled composite.

The thermal stability of a 2D-Nicalon/C/SiC composite was studied through the variation of both mechanical properties and microstructure occurring during heat treating. The composite was processed by infiltration of SiC preforms according to SICFILL® method. The material toughness was enhanced by a carbon interphase put between the fibers and the matrix. In order to improve the thermal stability a CVI layer was deposited on the carbon interphase and the specimen surfaces were CVD covered by an external SiC seal coating about 165 μm thick.