S. Eugénio

Hydrogen evolution on nanostructured Ni-Cu foams

Three-dimensional (3D) nickel–copper (Ni–Cu) nanostructured foams were prepared by galvanostatic electrodeposition, on stainless steel substrates, using the dynamic hydrogen bubble template. These foams were tested as electrodes for the hydrogen evolution reaction (HER) in 8 M KOH solutions. Polarisation curves were obtained for the Ni–Cu foams and for a solid Ni electrode, in the 25–85 °C temperature range, and the main kinetic parameters were determined. It was observed that the 3D foams have higher catalytic activity than pure Ni. HER activation energies for the Ni–Cu foams were lower (34–36 kJ mol−1) than those calculated for the Ni electrode (62 kJ mol−1). The foams also presented high stability for HER, which makes them potentially attractive cathode materials for application in industrial alkaline electrolysers.

One-step process to form a nickel-based/carbon nanofoam composite supercapacitor electrode using Na2SO4 as an eco-friendly electrolyte

In this work, NiOx is anodically electrodeposited onto carbon nanofoam (CNF) to form a composite electrode devoted to supercapacitor applications. The use of NiSO4 as precursor in electrodeposition results in the formation of NiO and NiOOH species, as confirmed by XPS analysis, by means of a one-step anodic process. The presence of both NiO and NiOOH suggests the existence of pseudocapacitance, as observed in MnO2 and RuO2 materials. By employing Na2SO4, an eco-friendly electrolyte, the resulting composite delivers a specific capacitance of 150 F g−1 at 1 A g−1 considering the total mass of the electrode (deposit plus substrate). In addition, this composite electrode can operate in a very broad potential window, as high as 2.2 V, suggesting its application in high energy density electrochemical supercapacitors.

Three-dimensional nanostructured Ni–Cu foams for borohydride oxidation

Three-dimensional (3D) nanostructured nickel–copper (Ni–Cu) foams have been prepared by electrodeposition using a dynamic hydrogen template. These 3D materials were tested as electrodes for the borohydride oxidation reaction (BOR) in alkaline media for possible application as anodes of direct borohydride fuel cells. Their activity in BOR was studied using cyclic voltammetry, chronoamperometry, and chronopotentiometry and main reaction parameters and electrodes’ stability were evaluated.

Osteoblast Proliferation and Morphology Analysis on Laser Modified Hydroxyapatite Surfaces: Preliminary Results

Biocompatibility has long been associated with surface microtopography, microtexture and microchemistry. The surface topography ultimately affects the nature and the strength of the interactions that occur at biomaterial-biological environment (cell adhesion, mobility, spreading and proliferation). Thus, it is necessary to produce and work with controlled microtopographical surfaces that present reproducible microdomains of a dimension similar to that of the biological elements of interest (for instance, cells). [1] There are a number of substrates that already have been studied (such as silicone, polystyrene, poly-L-lactic acid and titanium coated polystyrene) in terms of surface topography. [2] However, few studies are related to hydroxyapatite substrates. As it is well established, hydroxyapatite is a well known ceramic that is extremely used in medical applications, namely implants and coatings. In this work, the surface topography of dense hydroxyapatite substrates was altered by using KFr excimer laser. Excimer lasers produce high-intensity, pulsed ultraviolet radiation and are especially well suited for materials processing due to their large beam cross-section area, which permits using mask projection technologies to process relatively large areas in a single step.[3]

Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO2 electrochemical capacitor electrodes

The use of room temperature cathodic electrodeposition to produce MnO2 electrochemical capacitor electrodes is demonstrated. By employing a permanganate-based bath, birnessite-type MnO2 electrodes are directly obtained with no further heat treatment. Moreover, a crystalline/amorphous structural transition is observed as the applied current density is increased up to 50 mA cm−2.

KrF laser treatment of human dentin

The present paper summarizes the results of a study of the morphological, structural and compositional changes caused on dentin by processing with KrF excimer laser (λ= 248 nm). Different surface textures are achieved depending on the structure of the samples and on the processing parameters. Independently of the radiation fluence used, a significant reduction of the organic material content is observed in a surface layer a few nanometers thick, but no significant changes in the mineral phase occur.

Potential anti-cancer and anti-Candida activity of Zn-derived foams

Zinc (Zn)-derived foams have been prepared from an alkaline electrolyte solution by galvanostatic electrodeposition under different conditions. A detailed physico-chemical characterization was performed by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A pioneer application of these foams in medical implant-related applications was investigated. The in vitro behaviour of these Zn-derived foams in simulated physiological conditions was studied. The results revealed that the presence of zinc oxide was important enough to change the in vitro behaviour of these materials. The potential of these Zn-derived foams in inhibiting bone cancer cell proliferation - osteoscarcoma cells - and important pathogenic fungi responsible for implant-related infections -Candida albicans- was examined. Furthermore, the foams were evaluated for cytocompatibility with normal human osteoblasts. The results obtained allowed us to conclude that Zn-derived foams have an interesting potential for anti-cancer and anti-Candida activity, targeted for bone-related implant applications, suggesting that this novel material may have potential for further clinical studies.

Bond Strength of an Etch-and-Rinse Adhesive to KrF Excimer Laser-Treated Dentin

OBJECTIVE The aim of this work was to evaluate the effect of KrF excimer laser treatment on the bond strength between dentin and an etch-and-rinse adhesive system. MATERIALS AND METHODS Polished dentin surfaces were subjected to the following treatments: (1) 35% phosphoric acid etching for 15 s; (2) laser surface treatment using KrF excimer laser radiation (1 J/cm(2)); and (3) laser treatment under the same conditions followed by acid etching. After treating the dentin, an etch-and-rinse adhesive (Adper Scotchbond 1 XT, 3M ESPE) was applied and composite (Esthet-X, Dentsply Caulk, Konstanz, Germany) build-ups were incrementally constructed. After 24 h of water storage at 37 degrees C, 1 mm(2) beams were longitudinally cut from the samples. Microtensile sticks were loaded in tension at a crosshead speed of 0.5 mm/min. Bond strength data were analyzed with one-way ANOVA and the Student-Newman-Keuls test (p < 0.05). The dentin surfaces resulting from each surface treatment and the fracture surfaces originated by the bond-strength tests were observed under a scanning electron microscope. RESULTS Laser-treated surfaces exhibited a cone-shaped topography with a frank occlusion of dentinal tubules, while acid etching produced a smoother surface with open tubules. Application of 35% phosphoric acid on laser-treated dentin surfaces resulted in the partial dissolution of the surface cones. Mean microtensile bond strengths for acid-etched dentin was significantly higher (33.7 +/- 8.7 MPa) than for laser-treated (13.8 +/- 5.1 MPa) and laser-treated and etched surfaces (19.7 +/- 6.9 MPa). A higher percentage of cohesive failures at the base of the cones occurred in the laser-treated group, whereas mixed failures were predominant on acid-etched samples. CONCLUSION The cone-shaped texture produced by treating dentin with KrF laser radiation does not improve the bond strength of the tested etch-and rinse adhesive system when compared to the traditional acid-etching technique.

Surface Treatment of Human Dentin by KrF Laser

In the present work, dentin samples extracted from human molar teeth were treated with 248 nm wavelength pulsed laser radiation at fluences between 0.5 and 20 J/cm2. The surfaces were characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and x-photoelectron spectroscopy (XPS). Two distinct behaviours were observed in what concerns the evolution of surface morphology with fluence and number of pulses. In some samples the surface remained flat, independently of the fluence and covered by a layer of resolidified material and redeposited ablation particles, which often occluded the dentinal structure. In other samples the surface topography depended on radiation fluence. For fluences below 1 J/cm2, intertubular dentin was preferentially removed, originating a columnar structure where columns were centred on the dentinal tubules and constituted by peritubular dentin. The height of the columns increased with the number of laser pulses. When fluence exceeded 1 J/cm2 the processed surface remained flat, covered with a fine resolidified layer. These distinct behaviours of dentin can be explained by differences in the constitution of this composite biological material. Despite the topographic changes observed, the mineral phase of dentin (apatite) remained unaltered and collagen was removed only from the outermost superficial layers of the processed material. This fact is explained by the constitution and structure of dentin and by the physical properties and electronic structure of its main constituents. Taking into consideration the results obtained and the bond type and properties of the constituents of dentin, it is suggested that the ablation of collagen occurs by a photochemical mechanism while the ablation of apatite is photothermal.

Laser cladding of Cu-NbC nanocomposite coatings

Cu-matrix composites are interesting materials to be used as coatings in applications where efficient heat transfer and good wear resistance are simultaneously necessary, like mould repair, electric sliding contacts, high temperature seals, etc.In this work, Cu-NbC nanocomposite powder was synthesized in-situ by mechanical alloying from elemental mixtures of Cu, Nb and graphite powders and used to produce Cu-10% NbC coatings on CK45 steel substrate by laser cladding. The coatings have an average thickness of 800 Pm and present some porosity due to the oxidation of the powder and consequent incorporation of oxygen in the coating. Their microstructure was characterized by SEM, EDS, XRD, and TEM analysis. It consists of very fine (submicron sized) NbC particles uniformly distributed in the Cu matrix.The coatings present an average microhardness of 180 HV. The wear behavior of the coatings was investigated through microscale wear tests performed under dry sliding conditions against a steel counterbody. The influence of load on the prevailing wear mechanisms was analyzed and related to the microstructure of the coatings. Two wear regimes were identified. At low loads the predominant wear mechanism is abrasion, while at high loads adhesion and material transfer are the main mechanisms. However, the wear coefficients are relatively low (10−13 m2/N) and wear remains in the moderate regime.Cu-matrix composites are interesting materials to be used as coatings in applications where efficient heat transfer and good wear resistance are simultaneously necessary, like mould repair, electric sliding contacts, high temperature seals, etc.In this work, Cu-NbC nanocomposite powder was synthesized in-situ by mechanical alloying from elemental mixtures of Cu, Nb and graphite powders and used to produce Cu-10% NbC coatings on CK45 steel substrate by laser cladding. The coatings have an average thickness of 800 Pm and present some porosity due to the oxidation of the powder and consequent incorporation of oxygen in the coating. Their microstructure was characterized by SEM, EDS, XRD, and TEM analysis. It consists of very fine (submicron sized) NbC particles uniformly distributed in the Cu matrix.The coatings present an average microhardness of 180 HV. The wear behavior of the coatings was investigated through microscale wear tests performed under dry sliding conditions against a steel counterbody. The in...