Sergio Lo Russo

Improvement of dehydrogenation kinetics of LiBH4 dispersed on modified multi-walled carbon nanotubes

The dehydrogenation kinetics of LiBH(4) dispersed on multi-walled carbon nanotubes (MWCNTs) by the solvent infiltration technique has been studied. Commercial MWCNTs were ball-milled for different milling times in order to increase the specific surface area (SSA) as measured by the BET technique. Thermal programmed desorption measurements have been performed using a Sieverts apparatus on samples with different SSA of MWCNTs and different LiBH(4) to MWCNT ratio. Pressure composition isotherms (PCI) have been obtained at different temperatures in order to estimate the DeltaH and DeltaS of dehydrogenation. It has been observed that the dispersion of LiBH(4) on MWCNTs leads to a lower dehydrogenation temperature compared to pure LiBH(4). Moreover, the dehydrogenation temperature further decreases with increasing MWCNT surface area. An interpretation of the kinetic effect is proposed.

The structural change of graphene oxide in a methanol dispersion

Graphene oxide is a derivative of graphene which contains oxygen domains. Its debatable structure depends on the specific functional groups bonded to the graphene basal plane which have an impact on its reactivity. Here, we report the influence of methanol which affects the functionalization of pristine graphene differently to water.

Thermodynamic effects in the ion‐beam mixing of Fe‐Al and Mo‐Cr multilayers

Ion‐beam mixing of Fe‐Al and Mo‐Cr multilayers was studied by alternately sputtering with 5 keV Ar+ and then analyzing with Auger electron spectroscopy. The target temperature was variously room temperature, 450, 525, or 600 K. The two systems were chosen on the basis of having heats of mixing (ΔHm) which were opposite in sign, namely H1:1m=−0.25 eV for solid Fe‐Al and ΔH1:1m=+0.075 eV for solid Mo‐Cr. (ΔH1:1m applies to a 1:1 composition.) With Fe‐Al a well‐defined peak broadening was observed as the profiling temperature increased, while with Mo‐Cr there was a slight narrowing of the peaks with increasing temperature. The results were analyzed in terms of numerical solutions of a diffusion equation which contained terms appropriate not only to ballistic motion but also to the motion of bombardment‐induced residual defects. The latter were assumed to be in part ‘‘chemically guided,’’ as quantified with the parameter ‘‘qp’’ (qp∼∝ΔHm). A major difference between Fe‐Al and Mo‐Cr was found. The peak changes ...

Irradiation effects at the Ni-Fe interface

Abstract Layered thin film samples of 100 nm 56 Fe/3 nm 57 Fe/43 nm Ni (coating) or 100 nm 56 Fe/3 nm 57 Fe/63 nm Ni (coating) have been irradiated with 100 keV Ar + or 200 keV Kr 2+ ions, respectively, at doses up to 6 × 10 16 ions/cm 2 . In order to study the effects of irradiation at the Ni/Fe interface, the samples have been analyzed before and after ion bombardment by means of Rutherford backscattering spectrometry, conversion electron Mossbauer spectroscopy and nuclear reaction analysis. For the first time the resonant 58 Ni(p, γ) 59 Cu reaction at E p = 1424 keV has been used to obtain Ni concentration depth profiles at a Ni/Fe interfac Three distinct Fe-Ni phases have been identified by their hyperfine field in the ion beam mixed region after irradiation: a solid solution of Ni in bcc α-Fe, an fcc Fe-Ni alloy (possibly either Ni 3 Fe or Fe 0.64 Ni 0.36 invar alloy), and a nonmagnetic Fe-rich fcc Fe (γ-Fe) phase. The mixing efficiency for fcc Fe-Ni phase formation and for Ni migration into the Fe-rich region as a function of dose has been determined quantitatively indicating that Kr 2+ is more effective than Ar + , as expected and that saturation occurs at higher Ar + doses.

On the question of whether ion-beam mixing of Fe-Al and Mo-Cr multilayers is governed more nearly by ballistic effects, residual defects, or thermal-spike effects

Abstract Metallic multilayers were profiled by alternately sputtering and analyzing thin films of Fe-Al in one case, and Mo-Cr in the other. The two systems have heats of mixing ( ΔH m 1:1 ) that are opposite in sign, namely −0.23 eV for Fe-Al and +0.075 eV for Mo-Cr. Sputtering was carried out with 5 keV Ar + and Auger electron spectroscopy was used for the analysis, the target temperature being variously room temperature, 450, 525, or 600 K. With Fe-Al a well-defined peak broadening was observed as the profiling temperature increased, while with Mo-Cr there was a slight narrowing of the peaks under similar profiling conditions. The results are analyzed in terms of numerical solutions of a diffusion equation which contains terms appropriate not only to ballistic motion but also to the motion of chemically guided residual defects. It is argued that the mixing is fully understandable without invoking an explicit role for thermal spikes. This follows, firstly, from the fact that Fe-Al and Mo-Cr show an opposite response to increasing temperature. Secondly, it follows from the fact that the mixing shows different aspects by changing the temperature by only 75 K (i.e. 450 to 525 to 600 K). A similar conclusion can be reached from other work in which increasing extents of mixing of Fe-Al were observed at 77, 200, 300, 400 and 500 K, as well as in the case of Ag-Ni where a decreasing extent of mixing was observed when passing from 300 to 400 to 600 K. Other examples of important temperature effects include Cr-SiO 2 , Ni-SiO 2 and Ti-SiO 2 . We conclude that thermal spike effects, if they exist, are contained implicitly within the ballistic component.

Recent achievements on materials for hydrogen storage

After a brief introduction on the problems related to hydrogen storage, recent trends of the research on hydrogen storage materials are presented and discussed: metal hydrides; nanostructured magnesium-based hydrides; nanocomposites based on mixtures of amides and hydrides, amides and alanates, and borohydrides and hydrides; chemical hydrides; and nonhydride systems. The aim of the paper is to show that, even if none of these studied materials satisfies all the requirements for a very wide practical use, some niche applications are already feasible.

ION BEAM INDUCED PHASE TRANSFORMATION IN FE-MN BILAYERS : A MOSSBAUER STUDY

Ion‐beam mixing of Fe–Mn bilayers induced by 100 keV krypton ions in the dose range (0.1-15)×1015 ions/cm2has been studied by means of conversion electron Mössbauer spectroscopy and X‐ray diffraction. The results indicate that a dose of about 1 ×1015 Kr+/cm2 is sufficient to induce an appreciable mixing between the two atomic species. The α-Fe(Mn)solid solution presents a maximum at this dose, while at higher doses also the ɛ and γFe–Mn phases are formed in an appreciable amount. Heating of irradiated samples evidences the metastable character of ɛ phase and favours the growth of the terminal structures γ-Fe(Mn) and α-Mn(Fe) of the Fe–Mn equilibrium phase diagram.

Innovative Systems for Hydrogen Storage

One of the main challenges in the perspective of a hydrogen economy is the development of a storage system both safe and with high weight capacity. Among the most promising systems are the storage in metals and chemical hydrides and the high pressure storage in tanks made of composite materials. Both these technologies allow volumetric densities equal or higher than that of liquid hydrogen. The present work deals with the results obtained in a Italian national project, whose objectives have been the development of innovative technologies in specific applications: large scale energy storage, stationary applications in distributed generation, and automotive (with a particular attention to the fluvial and the sea transportation in protected areas). The theoretical, modellistic and experimental activities have been oriented to the development of innovative high capacity metal hydrides, the study of a regeneration method for chemical hydrides, the integration of intermediate pressure electrolyzers with advanced compressors and, finally, the development of thermomechanical models for executive design of storage systems. A number of prototypes has been realised and installed in a test facility in the Fusina (Venezia) power plant. The activity has been completed with an executive feasibility evaluation, in the perspective of industrial applications.