A. Maddalena

Electrical conductivity of tin oxide films prepared by the sol-gel method

Abstract A preliminary study concerning the electrical conductivity of tin oxide films obtained by a procedure of dipping sol-gel technique onto glass substrate is reported. The tin oxide-sol solution was prepared starting from stannous chloride. Crystallization of amorphous tin oxide was followed by means of XRD and DTA analyses. The morphology of the coatings was observed by SEM. By this method, it has been verified that tin oxide can be easily doped by means of zirconium and titanium oxides, giving films, in which electrical conductivity is strongly increased.

Mechanical Properties of 3-Glycidoxypropyltrimethoxysilane Based Hybrid Organic-Inorganic Materials

Hybrid organic-inorganic materials were synthesized from acid catalysed sols of tetraethyl orthosilicate, 3-glycidoxypropyltrimethoxysilane and titanium or zirconium alkoxides. The mechanical properties of these materials were measured in different conditions of preparation. The elastic modulus E was determined by a resonance method and by Knoop microindentation. After a thermal treatment at 125°C for 120 h, E was around 3–5 and 1–2 GPa for the samples synthesized with titanium butoxide or zirconium butoxide, respectively. An increase in E in the samples cured for longer times was observed. Knoop microhardness also increased with the heating time and was larger in samples synthesized from titanium alkoxides than zirconium alkoxides. The two methods gave results in good agreement when applied to samples treated for shorter times. In the other samples Knoop microindentation gave a larger value of E compared to the resonance vibration method. Hardness to elastic modulus ratio, H/E, was evaluated by Knoop microindentation. The elastic recovery at the longest heat treatment time was similar to that of soda-lime glasses. Fracture toughness was measured by three points flexural test, a KIc in the range of 0.4–0.5 MPa m1/2 was evaluated for samples treated during 168 h.

Preparation of silver nanoparticles in silica films by combined thermal and electron-beam deposition

Thin films of silica containing Ag particles, grown by a co-deposition technique, have been studied by optical absorption, X-ray diffraction and low-frequency Raman scattering. Particle sizes were estimated from the vibrational frequencies of the quadrupolar spheroidal modes. Laser annealing increases the size of the particles and smoothes their surfaces.

Structural evolution and the kinetics of Cu clustering in the amorphous phase of Fe-Cu-Nb-Si-B alloy

An attempt has been made to investigate the evolution of the structure of the amorphous phase of Fe73.9 Cu0.9 Nb3.1 Si13.2 B8.9 (finemet) alloy by a combination of wide-angle x-ray scattering, small angle x-ray scattering (SAXS), Mossbauer spectroscopy and X-ray absorption near edge spectroscopy on the supposition that they would provide complementary information. Before the onset of nanocrystallization, the amorphous phase undergoes a structural relaxation resulting in small increase in the hyperfine field and a decrease in the width of the first diffraction maxima. There is an increase in the topological ordering in the system, though chemical inhomogeneity sets-in due to the clustering of Cu atoms in the pure amorphous state of this alloy. Annealing at 400 °C (well below the crystallization temperature) for different time durations results in occurrence of Cu clusters having fcc structure. Kinetics of Cu clustering is studied using SAXS. The incubation time for the clustering at 400 °C is ∼120 min. Wit...

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.

Fe–Mn mechanically alloyed powders characterised by local probes

Abstract High-energy ball milling of Fe–Mn elemental powder mixtures has been carried out for Mn atomic concentrations in the range 10–90%. X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and perturbed angular correlations (PAC) have been used to investigate the crystalline structure in the milled samples. It is found that ball milling gives rise to concentration ranges of existence of terminal solid solutions more extended than in the equilibrium phase diagram. Particular attention has been paid to the environment of 57Fe (MS) and 111In (PAC) probe atoms: 57Fe atoms are a constituent of the system, while 111In atoms have been implanted at 400 keV into pills made from the milled powders. The PAC spectra of milled Fe show the ferromagnetic α-phase with a high fraction of a single vacancy next to the probe. Accordingly, the Mossbauer spectrum is a sextet with the characteristic splitting of α-Fe and a broadening which indicates a certain degree of atomic structure disorder. With an amount of Mn up to 15% PAC probes with one and two Mn next neighbours are identified by their smaller magnetic hyperfine field, corresponding to two distinct magnetic components in the Mossbauer spectra. At 20 and 30% of Mn the PAC magnetic signal of the a-phase disappears in favour of a distorted cubic apparently non-magnetic signal. From 40 to 70% of Mn a broad distribution of hyperfine magnetic fields is observed by PAC. Mossbauer spectra in the 20–70% of Mn range can be fitted with an unresolved low field magnetic sextet. Finally, the PAC spectra at 80 and 90% are quite similar to the one which is obtained after milling pure Mn, while the corresponding Mossbauer data can be roughly approximated to those of the α-Mn(Fe) solid solution.

Nanocrystallisation of amorphous alloys: comparison between furnace and current annealing

Abstract The mechanism of nanocrystallisation of the amorphous Fe72Cu1Nb4.5Si13.5B9 alloy has been studied with particular attention to the early stages of crystallisation. The specimens have been nanocrystallised by furnace (FA) and current (CA) annealing and analysed by Mossbauer spectroscopy. X-ray scattering, using the beamline 5.2L at Elettra Synchrotron Source, Trieste, has been carried out on the same FA and CA samples, as well as on a previously untreated sample current heated in situ. It is found that for the same amount of nanocrystalline phase, the crystallite size in CA samples does not differ significantly from that in FA samples. Analysis of the Mossbauer spectra shows that in FA and CA samples the nanocrystalline grains consist of non-stoichiometric partially disordered Fe3Si phase, and that there is an indication of the presence of boron atoms in the nanocrystals of CA samples. This implies a lower segregation of boron atoms or of borides at the boundaries of nanocrystallites of CA samples and can be connected to their lower brittleness.

Nanoconfinement in activated mesoporous carbon of calcium borohydride for improved reversible hydrogen storage

Mesoporous carbon frameworks were synthesized using the soft-template method. Ca(BH(4))(2) was incorporated into activated mesoporous carbon by the incipient wetness method. The activation of mesoporous carbon was necessary to optimize the surface area and pore size. Thermal programmed absorption measurements showed that the confinement of this borohydride into carbon nanoscaffolds improved its reversible capacity (relative to the reactive portion) and performance of hydrogen storage compared to unsupported borohydride. Hydrogen release from the supported hydride started at a temperature as low as 100 °C and the dehydrogenation rate was fast compared to the bulk borohydride. In addition, the hydrogen pressure necessary to regenerate the borohydride from the dehydrogenation products was reduced.

Influence of the dipping coating procedure on the mechanical strength of soda-lime glass rods

Abstract In order to investigate the effect of sol-gel coatings on the mechanical behavior of a high strength glass substrate, HF etched glass rods were used. Coatings with different compositions (SiO 2 , ZrO 2 and 20%ZrO 2 80%SiO 2 ) and different thicknesses were produced to study the influence of these parameters on strength. Functions of integral probability versus strength were used to analyze data. Coated glass rods exhibit higher strength in comparison with uncoated control rods that have undergone the same treatment. It seems evident that there is an effect of composition on strengthening. SiO 2 coated rods displayed higher strength. A lowering in strength at thickness higher than 0.2 μ was observed, independently of composition. The effect of a saturated Ca(OH) 2 solution was also studied.

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.