Design and testing of a 9.5 kWe proton exchange membrane fuel cell–supercapacitor passive hybrid system

The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling.     

Dynamic versus static behaviour of a masonry structure under lateral loads

A set of physical models of masonry structures was tested at the Politecnico of Milan. Static lateral loads simulate seismic excitation. As a start to this research the meaningfulness of a static approach for seismic studies is discussed. A nonlinear dynamic numerical model is worked out.It is shown that, in general, a dynamic approach offers greater margins of safety than a static approach. It is then shown that the out-of-plane resistance and ductility may be the weak point of the walls. In this field no experimental measures of ductility are so far available, and only one on resistance.     

A polymer gel electrolyte composed of a poly(ethylene oxide) copolymer and the influence of its composition on the dynamics and performance of dye-sensitized solar cells

A polymer gel electrolyte composed of a poly(ethylene oxide) derivative, poly(ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether), mixed with gamma-butyrolactone (GBL), LiI and I₂ is employed in dye sensitized solar cells (DSSC). The electrolyte is characterized by conductivity experiments, Raman spectroscopy and thermal analysis. The influence of the electrolyte composition on the kinetics of DSSC is also investigated by transient absorption spectroscopy (TAS). The electrolyte containing 70 wt.% of GBL and 20 wt.% of LiI presents the highest conductivity (1.9 × 10⁻³ S cm⁻¹). An efficiency of 4.4% is achieved using this composition. The increase in I_SC as a function of GBL can be attributed an increase in the mobility of the iodide (polyiodide) species. The increase in the yield of the intermediate species, I₂⁻, originating in the regeneration reaction, is confirmed by TAS. However, the charge recombination process is faster at this composition and a decrease in the V_oc is observed. Photovoltage decay experiments confirm an acceleration in charge recombination for the DSSC assembled with the electrolyte containing more GBL. Raman investigations show that in this electrolyte the I₅⁻/I₃⁻ ratio is higher. Theoretical calculations also indicate that the I₅⁻ species is a better electron acceptor.     

Mean stress and plasticity effect prediction on notch fatigue and crack growth threshold,combining the theory of critical distances and multiaxial fatigue criteria

In the present work, we propose a robust calibration of some bi‐parametric multiaxial fatigue criteria applied in conjunction with the theory of critical distances (TCD). This is based on least‐square fitting fatigue data generated using plain and sharp‐notched specimens tested at two different load ratios and allows for the estimation of the critical distance according to the point and line method formulation of TCD. It is shown that this combination permits to incorporate the mean stress effect into the fatigue strength calculation, which is not accounted for in the classical formulation of TCD based on the range of the maximum principal stress. It is also shown that for those materials exhibiting a low fatigue‐strength‐to‐yield‐stress ratio σ_fl,R = ?1/σ_YS, such as 7075‐T6 (σ_fl,R = ?1/σ_YS = 0.30), satisfactorily accurate predictions are obtained assuming a linear‐elastic stress distribution, even at the tip of sharp notches and cracks. Conversely, for any materials characterized by higher values of this ratio, as quenched and tempered 42CrMo4 (σ_fl,R = ?1/σ_YS = 0.54), it is recommended to consider the stabilized elastic‐plastic stress/strain distribution, also for plain and blunt‐notched samples and even in the high cycle fatigue regime still with the application of the TCD.     

In situ wide angle X-ray scattering (WAXS) study of bimetallic Au–Pd catalysts

Aim of the paper is to apply a modified version of the Rietveld method to two Au–Pd/C catalysts prepared by successive impregnation and reduced in situ by a special holder in order to show that a suitable WAXS analysis, performed in routine lab and using an X-ray conventional generator, can be very detailed and rich of information especially when a bimetallic catalyst has to be considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Depth-dependent magnetic characterization of Fe films on NiO(0 0 1)

We used nuclear hyperfine spectroscopies and a ⁵⁷Fe probe layer approach to study the depth-dependent magnetic properties of ultrathin Fe films on NiO(0 0 1), a system exhibiting exchange bias. Conversion electron Mössbauer spectroscopy and nuclear resonance scattering of synchrotron radiation were employed. The samples were two Fe films with a thickness (8–10 ML) slightly above the critical thickness for the onset of ferromagnetism at room temperature, in which a 2 ML-thick probe layer, enriched in the ⁵⁷Fe Mössbauer isotope, was embedded at different depths from the Fe/NiO interface. Both techniques indicate that inside the film Fe has a metallic character, while at the interface with NiO different Fe phases are present. The main conclusion is that already a few monolayers from the interface with NiO the magnetic properties of Fe are bulk-like.     

Influence of iron addition on the microstructure and the electrochemical corrosion of Al–Zn–Mg alloys

The effect of Fe addition on the microstructural properties and the corrosion resistance of Al–Zn–Mg alloys submitted to different heat treatments (cast, annealed and aged), has been studied in chloride solutions using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), cyclic polarization (CP) and open circuit potential (o.c.p.) measurements. The presence of 0.3% Fe in the alloy limited the growth of the MgZn₂ precipitates, both in the annealed and in the quenched specimens. No effect of Cr on the grain size in the presence of Fe was found because of the accumulation of Cr in the Fe-rich particles. Fe in the Al–Zn–Mg alloys also made them more susceptible to pitting. Pitting occurred mainly near the Fe-rich particles both, under o.c.p. conditions in O₂-saturated solutions and during the CP.     

High-temperature compressive creep of novel fine-grained orthorhombic ZrO2 ceramics stabilized with 12 mol% Ta doping

A novel fine-grained orthorhombic ZrO₂ ceramic stabilized with 12?mol% Ta doping was fabricated by spark-plasma sintering from home-made powders, and its high-temperature mechanical properties evaluated for the first time by compressive creep tests in both Ar and air. It was found that the high-temperature plasticity of the ceramic deformed in Ar, under which the Ta-doped orthorhombic ZrO₂ is a black suboxide with abundant oxygen vacancies in its crystal structure, is controlled by grain boundary sliding (stress exponent ～2, and activation energy ～780–800?kJ/mol). However, the high-temperature plasticity of the ceramic deformed in air, under which the Ta-doped orthorhombic ZrO₂ is a white oxide due to the elimination in situ of oxygen vacancies, is controlled by recovery creep (stress exponent ～3, and activation energy ～750?kJ/mol). It was also observed that black Ta-doped orthorhombic ZrO₂ is more creep resistant than its white counterpart with the same grain size, and that the former deforms as the more conventional Y₂O₃-stabilized ZrO₂ does.