F. Agresti

The Synthesis and Effect of Copper Nanoparticles on the Tribological Properties of Lubricant Oils

Cu nanoparticles (NPs) are widely studied to understand how they work in lubricant oils to improve its tribological properties. This paper describes the synthesis and characterization of Cu NPs of different size (φ = 60 and 130 nm) carried out in EG and the dispersion procedure used to prepare nanolubricants containing different amounts of NPs (0.005 vol% -0.01 vol% -0.02 vol%). The base oil was a commercially available lubricant oil for internal combustion engines. In order to study the influence of different parameters such as particles size and concentration on tribological properties of nanolubricants, the Stribeck curves were recorded at 25°C in the three lubrication regions (elasto-hydrodynamic, mixed lubrication, and boundary lubrication) and the results discussed. It was found that Cu NPs with a 130-nm mean diameter were more effective in reducing the coefficient of friction in all the lubrication regimes with respect to smaller ones.

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.

Tuning the thermal diffusivity of silver based nanofluids by controlling nanoparticle aggregation

With the aim of preparing stable nanofluids for heat exchange applications and to study the effect of surfactant on the aggregation of nanoparticles and thermal diffusivity, stable silver colloids were synthesized in water by a green method, reducing AgNO₃ with fructose in the presence of poly-vinylpyrollidone (PVP) of various molecular weights. A silver nanopowder was precipitated from the colloids and re-dispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-visible spectroscopy, combined dynamic light scattering and ζ-potential measurements, and laser flash thermal diffusivity. The Ag nanopowders were characterized by scanning electron microscopy and thermal gravimetric analysis. It was found that the molecular weight of PVP strongly affects the ζ-potential and the aggregation of nanoparticles, thereby affecting the thermal diffusivity of the obtained colloids. In particular, it was observed that on increasing the molecular weight of PVP the absolute value of the ζ-potential is reduced, leading to increased aggregation of nanoparticles. A clear relation was identified between thermal diffusivity and aggregation, showing higher thermal diffusivity for nanofluids having higher aggregation. A maximum improvement of thermal diffusivity by about 12% was found for nanofluids prepared with PVP having higher molecular weight.

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.