2009

The paper deals with the surface hardening of stainless steels trough the application of suitable plasma nitriding cycle to different austenitic and martensitic grades. The cylindrical shaped samples, 18 to 30 mm in diameter and 50 mm long, have been plasma nitrided in an industrial plant, performing the heating in hydrogen based plasma up to 420 °C for 2 h, then the temperature has been elevated at 530 °C in plasma obtained by H2 - N2 (80% and 20% respectively), the cooling has been done in nitrogen based atmosphere.

Al-based alloy, produced by a patented, namely Liquid forging, process is studied for automotive application. The patented procedure leads to produce high resistance and high toughness components with the possibility to realise T6 heat treatment. The influence of some process parameter (filling rate and time) on the alloy properties is investigated. The benefits of T6 heat treatment on the performance of Al-based components is considered. The alloy morphological and mechanical characterization has been realised in different conditions and a comparison of these data has been carried out.

Preliminary results on Pt-based electrocatalysts prepared with CMK3 mesoporous carbons are presented. The electrocatalytic performance towards the oxygen reduction reaction (ORR) was compared to that of commercial Pt/C-Vulcan catalysts with the same Pt content. Polarisation tests were carried out with a single PEM fuel cell containing the Pt/OMC cathodes. The analysis of these tests, based on a semi-empirical determination of the various polarisation terms, showed an interesting catalytic activity for ORR for the cathodes prepared with mesoporous carbon supports.

Pt–Co alloys prepared by high energy ball milling synthesis were tested as electrocatalysts for hydrogen fueled Polymer Electrolyte Membrane Fuel Cells (PEMFC). In the present contribution we report on the first results regarding the electrochemical behaviour of two samples of Pt–Co alloys. One sample contains 20 wt.% alloy Pt:Co in the molar ratio 0.25:0.75 and C 80 wt.% and the second one Pt:Co in the molar ratio 0.75:0.25 and C 80 wt.%.

For mobile applications, performance of polymer electrolyte membrane fuel cells (PEM-FCs) should be maintained with being exposed to subzero temperatures in winter time. To simulate such a situation, a single cell PEM-FC was operated at 70{degree sign}C, stopped, kept at -10{degree sign}C for 8 h, and heated to 80{degree sign}C for the next operation. The cell was unable to work. The degradation was attributed to freezing of water present inside the MEA, produced during operation, and remained in the PEMFC after the operation.

The influence of inorganic precursors on phase evolution and powder sinterability of YAG has been investigated. YAG powders were synthesised by reverse-strike precipitation, from yttrium and aluminium chlorides or nitrates aqueous solution. The powders were characterised by thermal analysis and XRD measurements. Pure-YAG was obtained after calcination at high temperature from both precursors, but the chlorides-derived materials yield mixtures of YAG and metastable YAlO3 phases from 800°C to 1100°C.

UV-cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV-vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photo-degradation.

De-agglomeration of a nanocrystalline transition alumina powder was performed in distilled water at its natural pH under magnetic stirring for 170 h or by ball milling for 3 h. Gibbsite appeared near transition aluminas in the magnetic stirred sample. In addition, a relevant lowering of the α-Al2O3 crystallization temperature was observed in the dispersed materials with respect to the as-received powder. However, the activation energy of the above transformation, determined by the Kissinger method, was in any case about 480–500 kJ/mol and unaffected by the dispersion route.

The composite powders 90 vol.% Al2O3–5 vol.% YAG–5 vol.% ZrO2 were produced by doping commercial alumina powders with zirconium and yttrium chloride aqueous solutions. Both a nanocrystalline transition alumina and a pure α-phase powder were used as starting materials. The obtained materials were characterized by DTA-TG, XRD and dilatometric analyses and compared to the respective biphasic systems developed by the same procedure.

Doping of commercial alumina nanopowders by using aqueous solutions of metal salts was exploited to prepare alumina-based nanocomposites. The same procedure was applied to produce a composite made of immiscible phases, that is an alumina–zirconia material, by doping an α-alumina powder with a zirconium chloride solution, as well as to produce an alumina–YAG (yttrium aluminium garnet) system by doping alumina with a yttrium chloride solution and promoting YAG formation by solid-state reaction at high temperature. For this latter case, the difference in reactivity between two commercial po