E. Salernitano

Carbon Nanotube Growth on PAN‐ and Pitch‐Based Carbon Fibres by HFCVD

Abstract Carbon nanotubes (CNT) were grown on carbon fibres, both PAN‐ and pitch‐based, by hot filament chemical vapour deposition (HFCVD) using H2 and CH4 as precursors. Nickel clusters were electrodeposited on the fibre surfaces to catalyse the growth, and uniform CNT coatings were obtained on both PAN‐ and pitch‐based carbon fibres. Ni cluster features varied, depending on the deposition parameters, showing on average larger dimensions and denser distribution on pitch fibres. Multi‐walled CNTs with smooth walls and low impurity content were grown. The morphological features, both before and after the growth process, were characterised by SEM. This novel material based on carbon fibres coated with CNT, shows a potential for applications in polymeric matrix composites.

Nanomaterials-Based PEM Electrodes by Combining Chemical and Physical Depositions

The real market penetration of polymer electrolyte fuel cells is hindered by the high cost of this technology mainly due to the expensive platinum catalyst. Two approaches are followed to reduce the cost: one way is to increase the Pt utilization efficiency reducing at the same time the total load and the other way is to increase the catalytic activity of the catalyst/support assembly. In this work, the increase of utilization efficiency is addressed by optimizing the catalyst distribution on the uppermost layer of the electrode via electrodeposition and sputter deposition, while the improvement of the catalyst activity is pursued by nanostructuring the catalysts and the carbon-based supports. A very low Pt loading 0.006 mg cm 2 was obtained by sputter deposition on electrodes that exhibited a mass specific activity for methanol oxidation reaction better than a commercial product. Carbon nanofibers used as catalyst support of electrodeposited platinum nanoparticles resulted in improved mass specific activity and long term stability compared to conventional carbon-based supports. Finally, PtAu alloys developed by sputter deposition were found more efficient than commercial PtRu catalyst for the methanol oxidation reaction. In conclusion, polymer electrolyte membrane fuel cell electrode based on nanomaterials, developed by combining physical and chemical deposition processes, showed outstanding electrochemical performance. DOI: 10.1115/1.4003629

A Comparison between Conventional Thermal Treatment and Excimer Laser Irradiation Performed on Alumina/PEEK Composite Coatings

Poly(etherether-ketone)-alumina coating were deposited by EPD. In order to densify the coatings, conventional thermal treatments were performed at a temperature equal or higher than the melting point of the polymer. The samples treated at the lower temperature showed an increase in the quality of crystallinity of the polymer. As an alternative method, an excimer laser was used to treat the surface of the composite coatings. The laser beam irradiation did not induce any modification in the crystalline structure of the polymer and at the same time did not produce strong degradation of the polymer molecule, also when the laser beam fluence was higher than the ablation limit. The most relevant modification induced by both the treatments was a change in the morphology and the porosity.

Synthesis of Graphene Films on Copper Substrates by CVD of Different Precursors

In the present work, graphene films of the order of \(1\,\hbox{cm}^{2}\) were grown on copper foil substrates by CVD using hydrogen/methane or hydrogen/argon/ethanol mixtures as gas precursors. The growth processes were performed near \(1\hbox{,}000^{\circ}\hbox{C}\) both at atmospheric and low pressures. A system for the fast cooling of the sample, based on the fast extraction from the hot zone of the furnace, was implemented allowing for rapid decrease of the temperature below \(600^{\circ}\hbox{C}\) in few seconds. Samples grown under different conditions were analyzed by SEM, Raman spectroscopy and XPS with the aim to assess their characteristics and to refine the growth process.

Nanocrystalline Diamond Films by Bias Enhanced Nucleation and Argon Assisted Growth in a HFCVD System

The achievement of nanosmooth, ultrathin diamond coatings with nanosized grains is mandatory for the successful utilization of diamond in areas such as microelectromechanical systems, field emission and surface acoustic waves devices. The bias enhanced nucleation technique (BEN) allows to achieve high nucleation density diamond films, where the average distance between diamond nuclei can be as low as 10-20nm. Moreover by diluting the gas precursors (H2 and CH4) into noble gas (Ar, He) during growth, the formation of larger crystals can be inhibited, giving rise to nanocrystalline films without a degradation of the film quality, such as the presence of more graphitic bonds. In this paper we report the growth of ultrathin, smooth, high quality nanodiamond films obtained by combining the two techniques in a HFCVD reactor. A variety of nanocrystalline diamond films with a grain size as low as 10nm and thickness up to 1μm were obtained. The nucleation process and ensuing growth of the film were monitored by SEM observation. Spectroscopic measurements were also performed to study the microstructure and to assess the quality of the deposited material.

CVD SYNTHESIS OF CARBON NANOTUBES ON DIFFERENT SUBSTRATES

Carbon nanotubes (CNTs) were grown using three different chemical vapor deposition (CVD) processes. Optimized conditions were studied. CNTs were grown on differently supported Ni catalytic nanoparticles on flat and bulk substrates using H2 and CH4 as precursors. The different behavior of the same metal catalyst in the presence of the same precursor varying the gas activation by different energy sources, using Hot Filament, Plasma Enhanced (PE), and pure Thermal CVD processes, was studied. By properly choosing the process parameters, dense CNTs were grown by HFCVD on 3 nm Ni thin film deposited by Evaporation and Radio-frequency (RF) Sputtering onto flat Si substrates coated with an intermediate SiO2 layer 3 (Fig. 1a). Prior to the growth, the samples were heated in H2 atmosphere and the Ni clusters distribution shown in Fig. 2a was obtained. No CNT growth was obtained on the same sample in the thermal CVD reactor, but only cluster coalescence was observed (Fig. 2b). CNT grew sparsely in the PE CVD reactor. The different results were ascribed to: i) the catalytic decomposition of the precursors was more efficient where an additional activation source was present; ii) weak interaction between the Ni cluster and the SiO2 substrate could favour cluster coalescence, which was the dominant effect in the thermal CVD process. Flat Al2O3 substrate coated by a 3nm Ni film, deposited by RF Sputtering, were subjected to the same clustering and CNT growth process in Thermal and PE CVD. The thermal process failed as in the previous case giving rise to

Eco-friendly Leather: Chromium Reduction in the Tanning Cycle

The leather manufacturing is traditionally responsible for high environmental pollution. Tannery effluent contains, indeed, large amounts of lime sludge, sulfides, acids, toxic metals salts, in particular chromium salts, which are toxic, non-biodegradable and hardly disposable. For this reason, great research efforts are addressed to establish a significantly eco-sustainable and convenient business for companies and to produce high quality leather products. The replacement of current commercial chemical and toxic products with innovative natural/naturalized products and technologies in some crucial phases of the tanning cycle (mainly bating and defatting), can induce an eco-friendly reduction of the needed chromium amount. Leather samples, treated with innovative bating and defatting products and tanned by several different Cr contents, were characterized by SEM-EDS (Scanning Electron Microscopy equipped with Energy Dispersive X-Ray Spectroscopy) and TGA (Thermogravimetric Analysis). SEM-EDS was used to observe the surface and cross-section morphology and to provide a semi-quantitative elemental analysis, while TGA to evaluate the thermal stability and decomposition phases. The compatibility of the innovative products was demonstrated and the environmental impact of the process, performed by the effluents characterization, was effectively improved as a result of a 20% Cr lowering. The use of innovative products and the chromium reduction did not affect the thermal stability, leather morphology and not involve significant differences in the composition.

15-15Ti(Si) austenitic steel: Creep behaviour in hostile environment

This work aims at studying the creep behaviour of 15-15Ti(Si) austenitic steel, under uniaxial stress (range of 300-560 MPa), and its interaction with liquid lead. The steel was tested to verify its sensitivity to Liquid Metal Embrittlement (LME) and to simulate its behaviour in operating thermal and mechanical stress conditions of the IV generation Lead-cooled fast reactor. The experimental results permitted to plot the time-strain creep curve and the characteristic Norton-based curve, simulating the creep behaviour at all stress values. The comparison between the creep curves in air and in lead showed that the LME produces a decrease of creep-rupture time, a reduction of creep strain and then the loss of steel ductility. Moreover, the raw material and fracture surfaces were analyzed by Optical Microscope and Scanning Electron Microscope (SEM). SEM micrographs highlighted that lead changes both the mode and the type of specimen fracture. In addition, it was analyzed the lead action time, as the time after which the corrosion appears with macroscopic effects. Although some tests are still ongoing, it can be assumed that at high stresses, LME takes place after a long time of steel/lead contact while at low stresses, LME tends to prevail on creep effect.

Pt Alloys on Carbon Nanostructures as Electrocatalysts for Direct Methanol Fuel Cell

Extensive efforts are focused on the development of Direct Methanol Fuel Cells, due to the intrinsic advantages of this type of devices for mobile power supply system. One of the major drawback of the DMFC resides in the easy poisoning of the anode electrocatalyst (platinum) by COlike reaction intermediates, which implies the need of high platinum load in order to obtain reasonable performances. The development of platinum alloys is considered one of the promising routes for overcoming this problem: the second metal in fact acts as inhibitor of the Pt poisoning. In this work we have combined the use of unconventional methods to deposit the electrocatalyst nanoparticles with unconventional carbon supports. PtAu alloys have been deposited by sputter deposition process on carbon nanofibers with platelet morphology grown by plasma enhanced chemical vapour deposition on carbon paper. Cyclic voltammetry in H2SO4 was used to determine the electrochemical active surface and the electrocatalytic performance for methanol oxidation reaction. Even at lower Pt load, respect to the ones prepared with commercial catalysts supported on carbon black, the innovative electrodes showed higher performance and stability.

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.