Surface Optimization of Commercial Porous Ti Substrates by EPD of Titanium Nitride.

In this work, the infiltration of TiN powders by electrophoretic deposition (EPD) in aqueous media was considered as alternative method to reduce the size craters and the roughness of commercial porous Ti substrates. Ti substrates can be used as suitable supports for the deposition of dense hydrogen separation TiNx-based membranes by physical vapor deposition (PVD) techniques. The influence of various EPD deposition parameters on surface morphology and roughness of TiN-infiltrated substrates were investigated in order to optimize their surface properties. The results suggest that a multi-step EPD procedure is an effective technique for reducing substrate surface defects of commercial porous Ti substrates which could then be successfully used as proper supports for the deposition of dense and defect-free TiNx layers, also aligning the thermal mismatch between the active layer and the porous substrate.

Production Strategies of TiNx Coatings via Reactive High Power Impulse Magnetron Sputtering for Selective H2 Separation.

This scientific work aims to optimize the preparation of titanium nitride coatings for selective H2 separation using the Reactive High Power Impulse Magnetron Sputtering technology (RHiPIMS). Currently, nitride-based thin films are considered promising membranes for hydrogen. The first series of TiNx/Si test samples were developed while changing the reactive gas percentage (N2%) during the process. Obtained coatings were extensively characterized in terms of morphology, composition, and microstructure. A 500 nm thick, dense TiNx coating was then deposited on a porous alumina substrate and widely investigated. Moreover, the as-prepared TiNx films were heat-treated in an atmosphere containing hydrogen in order to prove their chemical and structural stability; which revealed to be promising. This study highlighted how the RHiPIMS method permits fine control of the grown layer's stoichiometry and microstructure. Moreover, it pointed out the need for a protective layer to prevent surface oxidation of the nitride membrane by air and the necessity to deepen the study of TiNx/alumina interface in order to improve film/substrate adhesion.

Surface oxidation of single wall carbon nanohorns for the production of surfactant free water-based colloids.

In this work, powders of Single Wall Carbon Nanohorns (SWCNHs), a typical hydrophobic material, were oxidized with concentrated HNO3 with the aim of surface carboxylation and consequent improved hydrophilicity and dispersibility in polar solvents. Dynamic Light Scattering and ζ-potential measurements demonstrated that very stable colloidal suspensions of SWCNH in water were obtained in total absence of stabilizers. By properly optimizing the reaction parameters, the suspensions achieved stability even higher than colloids with similar composition but prepared with the use of surfactants. Surface damage and oxidation degree of SWCNHs were evaluated by SEM microscopy, Thermogravimetric Analysis, Residual Gas Analysis, XPS and UV-visible spectroscopy.

Microturbine and Thermoelectric Generator Combined System: A Case Study.

Waste heat recovery is one of the suitable industrial applications of thermoelectrics. Thermoelectric generators (TEG) are used, commonly, only for low-mid size power generation systems. The low efficiency of thermoelectric modules generally does not encourage their combination with high power and temperature sources, such as gas turbines. Nevertheless, the particular features of thermoelectric technology (no moving parts, scalability, reliability, low maintenance costs) are attractive for many applications. In this work, the feasibility of the integration of a TE generator into a cogeneration system is evaluated. The cogeneration system consists of a microturbine and heat exchangers for the production of electrical and thermal energy. The aim is to improve electric power generation by using TE modules and the "free" thermal energy supplied by the cogeneration system, through the exhaust pipe of the microturbine. Three different solutions for waste heat recovery from the exhausts gas are evaluated, from the fluid dynamics and heat transfer point of view, to find out a suitable design strategy for a combined power generation system.

Nanostructured Tetrahedrite Synthesis for Thermoelectric Applications.

Nowadays, a big challenge in the thermoelectric field is the identification of efficient thermoelectric materials but inexpensive, easy to synthesize, and comprised of Earth-abundant elements. On this basis, tetrahedrite mineral family (Cu(12−x)Tr(x)Sb4S13 where Tr = Cu, Mn, Fe, Co, Ni, Zn) seems to be an attractive p-Type Pb-free thermoelectric material, showing a relatively high conversion efficiency. In this work, a solvothermal synthesis method was developed for undoped tetrahedrite Cu12Sb4S13 and the introduction of Zn and Ni as substituents of copper was also tested. The influence of the stoichiometry and the synthesis conditions on the tetrahedrite phase content and density of the samples were investigated by X-ray diffraction (with profile Rietveld refinements) and scanning electron microscope (equipped with energy dispersive X-ray spectroscopy). Preliminary sintering test were performed by Open Die Pressing.

Thermal Shock and Oxidation Behavior of HiPIMS TiAlN Coatings Grown on Ti-48Al-2Cr-2Nb Intermetallic Alloy.

A High Power Impulse Magnetron Sputtering (HiPIMS) method for depositing TiAlN environmental barrier coatings on the surface of Ti-48Al-2Cr-2Nb alloy was developed in view of their exploitation in turbine engines. Three differently engineered TiAlN films were processed and their performance compared. Bare intermetallic alloy coupons and coated specimens were submitted to thermal cycling under oxidizing atmosphere up to 850 °C or 950 °C, at high heating and cooling rates. For this purpose, a burner rig able to simulate the operating conditions of the different stages of turbine engines was used. Microstructures of the samples were compared before and after each test using several techniques (microscopy, XRD, and XPS). Coating-intermetallic substrate adhesion and tribological properties were investigated too. All the TiAlN films provided a remarkable increase in oxidation resistance. Good adhesion properties were observed even after repeated thermal shocks. HiPIMS pretreatments of the substrate surfaces performed before the coating deposition significantly affected the oxidation rate, the oxide layer composition and the coating/substrate adhesion.

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.

Cathodoluminescence evaluation of oxygen vacancy population in nanostructured titania thin films for photocatalytic applications.

Room-temperature results of cathodoluminescence (CL) spectroscopy investigations are presented for nanostructured titanium dioxide (anatase) thin films (500 nm thick) deposited via RF magnetron sputtering on high-purity silica substrates. The collected CL bands of the anatase thin films, as deposited and after different annealing cycles, showed a broad morphology consisting of three Voigtian bands located at 500, 550, and 610 nm that were partially overlapping. The overall CL emission increased with increasing temperature and time of the annealing cycle as a consequence of the increased crystallinity of the thin film. A clear trend was found for the oxygen-vacancy-related band (located at 610 nm), whose relative intensity decreased, as compared with the as-grown sample, after annealing in air; the higher the annealing temperature, the lower the relative intensity. We evaluated the photoactivity of the nanostructured thin film samples by measuring their photocatalytic activity in aqueous solution toward the degradation of phenol. A relationship between the decrease in oxygen vacancy concentration as a consequence of the annealing and the increase in the photoactivity was highlighted.

Sims characterization of La0.7Sr0.3MnO3 films for solid oxide fuel cell applications.

Among solid oxides exploited to prepare efficient fuel cells, La(1-x)SrxMnO3 manganites have been widely studied and used as cathodes, because of their high conductivity at the working temperatures, good thermal stability and compatibility with other cell components. A fundamental goal in solid oxide fuel cells technology consists in lowering the normal operating temperatures, e.g. increasing the surface/volume ratio of electrodic materials, so as to enhance their catalytic performances. In this work, the preparation of high surface area La(1-x)SrxMnO3 (x approximately 0.3) films on silicon wafers by the nitrate-citrate Pechini process is described. The films were characterized by X-ray diffraction, Atomic Force Microscopy and Secondary Ion Mass Spectrometry. Good quality nanostructured perovskite-type films were obtained. SIMS methodology enabled to show the surface and in-depth coatings composition and residual contaminants. Moreover, it allowed defining the best synthesis conditions for complete in-depth decomposition of precursors and obtaining homogeneously thick coatings.

3-methylthiophene self-assembled monolayers on planar and nanoparticle Au surfaces.

In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent.

Surface chemistry study of RuO2/IrO2/TiO2 mixed-oxide electrodes.

DSA metal oxide electrodes such as the RuO(2)/IrO(2)/TiO(2) mixed system are widely studied for their excellent electrocatalytic activity. In order to understand their catalytic properties, the comprehension of the surface chemistry involved during electrochemical treatments is crucial. With this aim, RuO(2)/IrO(2)/TiO(2) mixed-oxide electrodes having various noble metal contents were studied by means of secondary ion mass spectrometry (SIMS). In particular, cathodic and anodic polarization and O(2) evolution reactions were carried out to test the electrode behaviour and SIMS analyses were performed after all these treatments. In this way, surface changes induced by electrochemical treatments and depending on electrode composition were widely investigated by SIMS, revealing, for example, the presence of hydration or preferential dissolution phenomena induced by electrochemical processing.

Secondary ion mass spectrometry and X-ray photoelectron spectroscopy investigation on chemical vapor deposited CeO(2-)ZrO(2)-TiO(2) thin films.

Mixed CeO(2)-ZrO(2) systems have attracted widespread interest for their use in three-way catalyst (TWC) technology for automotive exhaust conversion to non-toxic products. In this work, CeO(2)-ZrO(2) thin films were deposited, via chemical vapor deposition, in order to obtain nanoscale materials with a high surface-to-volume ratio, with precise control of system properties. The addition of TiO(2) as buffer layer was also investigated. Cordierite was chosen as substrate, being the usual refractory material for catalytic mufflers. The multilayers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). In particular, the combination of SIMS and XPS allowed us to investigate both surface and in-depth chemical composition, studying also film-intermixing phenomena induced by annealing processes.