Vittoria Contini

Li4Ti5O12 as anode in all-solid-state, plastic, lithium-ion batteries for low-power applications

Abstract Spinel Li 4 Ti 5 O 12 was prepared and tested as alternative anode for lithium-ion batteries. The electrochemical performance of the material was evaluated in liquid electrolyte at C/25 rate. The material delivered 150 mA h g −1 with a very satisfactory capacity retention. The electrochemical performance of commercial LiMn 2 O 4 was also tested. These materials were used to prepare polymer electrodes on aluminium foil substrate by using a screen-printing deposition technique. The transport properties of symmetrical polymer-electrode/polymer-electrolyte cells were evaluated by AC impedance. All-solid-state, plastic, lithium-ion batteries were fabricated with the cell configuration Li 4 Ti 5 O 12 /polymer electrolyte/LiMn 2 O 4 . The electrochemical performance of such a cell was evaluated at various temperatures.

Ordering kinetics of disordered Ni3Al synthesized by mechanical alloying

The Ni[sub 3]Al compound belongs to that class of intermetallics whose virtual critical temperature for the order-disordered transformation is higher than the melting temperature. Chemically disordered Ni[sub 3]Al can be prepared by several methods including high energy ball milling (BM) of the ordered compound. Another possibility is offered by mechanical alloying (MA) of elemental Ni and Al powders. Aluminum and nickel powders in the 3:1 atomic ratio were mechanically alloyed in an air-cooled SPEX mill for times up to 40 hours. EDS microanalysis after MA showed an Fe contamination of about 2 and 4 at.% in the powders milled for 20 and 40 hours respectively. The structural characterization of the samples was performed by x-ray diffraction and their thermal stability was tested in a Perkin-Elmer DSC7 calorimeter. The diffraction patterns of the samples milled for at least 10 hours were very similar and showed the presence of a supersaturated fcc Ni(Al) solid solution whose diffraction peaks were considerably broadened with respect to those of the starting Ni powder.

Mechanical alloying of immiscible elements : experimental results on Ag-Cu and Co-Cu

Abstract Equimolar solid solutions of Ag[sbnd]Cu and Co[sbnd]Cu were prepared by mechanical milling of the elements. The structure and the thermodynamic properties of the resulting phases were analysed by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Large mixing enthalpies (ΔH = 6–8kJg-atom−1 and ΔH = 4–8kJg-atom−1 for Ag-Cu and Co-Cu respectively) were measured in the alloyed phases. It is clear that the solid solution forms through a process of grain refinement down to the nanometre scale and is assisted by an atomic-scale dissolution. The possible role played by coherent interfaces in substantially increasing the energy of the solid solutions is discussed.

Nanocrystalline Al‒Fe alloys synthesized by high-energy ball milling

Abstract This study describes the effect of ball milling and heat treatment on the phases synthesized in a Spex mill starting from mixtures of Al and Fe powders containing 71, 75, 80 and 90 at.% A1. In the 71 and 75 at.% Al mixtures we observed the formation of the Al5Fe2 phase. At the 80 at.% Al concentration we observed the formation of an Al-rich ultrafine phase with a coherent domain size of the order of 1 nm. At the 90 at.% Al concentration, no new phase is observed to nucleate for milling times up to 50 hs. The thermal behaviour of the samples depends on the time of the milling. At all compositions, we observed the nucleation of the metastable A16Fe compound at about 320°C on heating of samples milled for short times (10 h or less) and the formation of the equilibrium phase(s) upon heating to 600°C.

Arc-discharge synthesis of carbon nanohorns and multiwalled carbon nanotubes

Carbon nanohorns and multiwalled carbon nanotubes have been synthesized by DC arcdischarge carried out at room pressure in air and Ar-enriched environment, by a specially designed experimental device. The resulting nanostructured material, characterized by electron microscopy and X-ray diffraction, shows different structures according to the condensation channels through which the sublimated carbon atoms are re-condensed in the solid state. Multi-Walled Carbon Nano- Tubes are mainly found in the hard crust formed at the cathode, while nano-horned particles can be recovered from a cylindrical collector surrounding the discharge. Further material, rag-like shaped and with an amorphous structure, can be collected in the reaction area. When the discharge occurs under Ar atmosphere, a larger quantity of this latter phase is synthesized. This suggests that the atmospheric oxygen could play an active role by burning the most reactive among the synthesized phases, like amorphous carbon contributing so to an “in situ” purification of the raw material.

Quantitative evaluation of nanotube content produced by arc discharge in a raw material

The amount of carbon nanotube in a raw material grown by electric arc discharge, ignited in different liquid environments, has been evaluated by combined use of X-ray diffraction, electron microscopy and differential thermal analysis (TG-DTA) in a reactive environment. X-ray diffraction was used to discriminate the various carbon microstructures utilizing the difference in lattice parameter between curved and planar graphite structures. The results are repeatable and in good agreement with TG-DTA measurements carried out in a reactive environment, where the relative amount of carbon nanostructures is evaluated on the basis of the difference in the reaction kinetics with atmospheric oxygen. In analyzed specimens, SEM and TEM show the presence of only two allotropic forms of carbon, namely nanotubes and globular particles, the relative amounts of which depend on the nature of the liquid surrounding the discharge and on the voltage applied to the electric arc.

Solid-state reactions in mechanically alloyed Al-V powders

Abstract High-energy ball milling has been performed on Al x V1−x powder mixtures in the Al-rich range of composition (x = 0.61, 0.70, 0.75, 0.85 and 0.90). The structural evolution and the thermal stability of the samples was followed by X-ray diffraction and differential scanning calorimetry. We have observed that, similar to other Al-transition metal binary systems, the reaction rate decreases with increasing Al content and that milling promotes diffusion of both elements into each other; in fact for short times of milling Al(V) and V(Al) solid solutions have been observed at all investigated compositions. With the exception of the Al-richest composition, several metastable phases have been observed to nucleate in the early stages of milling. In a broad range of composition around the stoichiometric ratio extended milling promotes the formation of the Al3V intermetallic compound in a heavily strained nanocrystalline state. Upon heating of pre-milled samples to 360°C the disappearance of the metastable ...

Preparation of Titanium Oxide and Metal Titanates as Powders, Thin Films, and Microspheres by Novel Inorganic Sol-Gel Process

Titanium oxide and titanates based on Ba, Sr and Ca were prepared from commercial solutions of TiCl 4 and HNO 3 . The main preparation steps for the sols consisted of elimination of chloride anions by distillation with nitric acid and addition of metal hydroxides for the titanates. Resulting sols were gelled and used to (1) prepare irregularly shaped powders by evaporation; (2) produce by a dipping technique thin films on glass, Ag, or Ti substrates; and (3) produce spherical powders (diameters

Purification of Multi-Walled Carbon Nanotubes Grown by Thermal CVD on Fe-Based Catalyst

Aiming at the purpose of using carbon nanotubes as secondary phase in composite materials, removal of metal catalyst, catalyst support and amorphous carbon is crucial to make the most of the required properties. A purification method was developed to remove the metal catalyst from multi-walled nanotubes grown by thermal CVD. A nanosized Fe-based catalyst, prepared by coprecipitation of iron and aluminum ions, followed by solid state reaction, was used to catalyze the growth. Carbon nanotubes were subjected to acid purification and a comparison between nitric acid and a mixture of nitric and hydrochloric acid for the removal of Fe and Fe oxides is provided. Morphological and spectroscopic analyses of the materials were performed, both before and after the purification processes.