2009

Deagglomeration of a nanocrystalline transition alumina performed using different techniques was first demonstrated to be active in the achievement of a better powder compaction ability under uniaxial pressing and consequently in the development of a highly dense and homogeneous microstructure during pressureless sintering. A major effect, however, was associated to the heating rate chosen during the densification cycle.

The main focus of this paper is on materials for radiant burners application. Two advanced metallic alloys, a Ni and Fe-based alloy are studied and compared to a reference ferritic stainless steel. Oxidation kinetics of such alloys at different temperatures are reported. Oxide formation mechanisms are discussed. Furthermore, thermo-mechanical resistance and eventual strengthening mechanism in temperature are studied. Finally, technical and brief tentative economical analysis of different alloys as potential candidates for the fabrication of radiant burners are given.

In this work, a nanocomposite (Cr,Al)xN1−x/Si3N4 coating system was deposited on H11 hot work tool steel, using the Lateral Arc Rotating Cathodes (LARC®) deposition system and modulating the chemical composition of the chromium and aluminium–silicon content. Structural characterizations were performed using scanning electron microscopy, equipped with energy dispersive spectroscopy probe, and applying x-ray diffraction, for the evaluation of phase constitution and crystallite size.

High surface area MgAl2O4 has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl2O4 was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate.

Silicon carbide multilayered composites containing short carbon fibres were prepared by tape casting followed by pressureless sintering. The dispersion of fibres into the SiC slurry was studied either by ultrasonics or by mechanical agitation, choosing the best solvent-dispersant couple that was compatible with the requirements of the tape casting technique. The effect of sintering temperature was studied, using carbon and boron as sintering aids, and mechanical properties were measured on composites containing from 5 vol.% to 25 vol.% of short carbon fibres.

Reactive metal penetration was used to prepare intermetallic–ceramic composites with co-continuous structure, starting from silica glass preforms. Two subsequent metal penetrations were performed: first, the silica was immersed in a liquid Al bath, obtaining an Al(Si)/Al2O3 composite, then Ni was put in contact with the composite at high temperature, bringing to the substitution of Al with a Ni–Al intermetallic. The obtained composites present both phases continuous, and the whole process is a near net-shape one.

Mesoporous alumina has been synthesised by the solution combustion synthesis method. While often the synthesis of mesoporous materials with a relatively narrow pore distribution requires the use of a template, this technique allows a simple and rapid synthesis of pure alumina without the use of any templating agent: by regulating the synthesis conditions is possible to obtain from relatively low surface area α-alumina to high surface mesoporous γ-alumina. The porosity of the latter was assessed chiefly by density functional method and was found to be in the range 2.8–3.5 nm.

Two experimental aluminium alloys (belonging to 2000 and 7000 series respectively) were welded using the laser beam welding (LBW) technique and an Al–Si alloy as filler. Different combinations of pre- and post-welding thermal treatments were proposed. The change of strength during aging treatments was investigated by microhardness measurements carried out on the weld and on the regions of the alloys not affected by the LBW process. The microstructure of the welded specimens was studied by scanning electron microscopy and energy dispersive X-ray spectroscopy.

In the present work, TiO2 films deposited on polyethylene terephthalate substrates by dip coating technique were subsequently treated by DC glow discharge plasma as a function of discharge potential. Hydrophilicity of these TiO2 film surfaces was analyzed by contact angle measurements. Atomic force microscopy (AFM) revealed changes in surface morphology of the plasma treated TiO2 films. Modifications in structural and chemical composition of the TiO2 films were detected by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).