Repositório Institucional da Universidade de Aveiro
Not a member yet
41903 research outputs found
Sort by
Electrophoretic bilayer deposition of zirconia and reinforced bioglass system on Ti6Al4V for implant applications: An in vitro investigation
No full textThe physical, chemical and biological properties of the bioglass reinforced yttria-stabilized composite layer on Ti6Al4V titanium substrates were investigated. The Ti6Al4V substrate was deposited with yttria stabilized zirconia - YSZ as the base layer of thickness approximate to 4-5 mu m, to inhibit metal ion leach out from the substrate and bioglass zirconia reinforced composite as the second layer of thickness approximate to 15 mu m, which would react with surrounding bone tissue to enhance bone formation and implant fixation. The deposition of these two layers on the substrate was carried out using the most viable electrophoretic deposition (EPD) technique. Biocompatible yttria-stabilized zirconia (YSZ) in the form of nano-particles and sol gel derived bioglass in the form of micro-particles were chosen as precursors for coating. The coatings were vacuum sintered at 900 degrees C for 3 h. The biocompatibility and corrosion resistance property were studied in osteoblast cell culture and in simulated body fluid (SBF) respectively. Analysis showed that the zirconia reinforced bioglass bilayer system promoted significant bioactivity, and it exhibited a better corrosion resistance property and elevated mechanical strength under load bearing conditions in comparison with the monolayer YSZ coating on Ti6Al4V implant surface. (C) 2013 Elsevier B.V. All rights reserved
Influence of sol counter-ions on the visible light induced photocatalytic behaviour of TiO2 nanoparticles
No full textTitanium dioxide (TiO2) nanoparticles are attracting increasing interest because of their superior photocatalytic and antibacterial properties. Here, aqueous titanium oxy-hydroxide sols were made, using a green synthesis method, from the controlled hydrolysis/peptisation of titanium isopropoxide. Three different mineral acids were used to peptise the sol (HNO3, HBr and HCl), and provide counter-ions. The influence of nitrate or halide sol counter-ions on size distributions of the starting sols were measured via photon correlation spectroscopy (PCS). Semi-quantitative phase composition analysis (QPA), on the gels thermally treated at 450 and 600 degrees C, was carried out via Rietveld refinement of the X-ray powder diffraction (XRD) patterns. Photocatalytic activity of the prepared samples was also assessed, in the gas-solid phase, monitoring NOx degradation using both solar and white lamps (artificial indoor lightning). Both halides (chlorine or bromine) encouraged the anatase-to-rutile phase transition (ART), resulting in powders containing up to 77 wt% rutile and only 5 wt% brookite after heating to only 450 degrees C, with particle sizes similar to 50 nm, and these produced 100% rutile at 600 degrees C. Photocatalytic tests in the gas phase, using a white lamp, showed that the halide-stabilised sols, thermally treated at 450 degrees C, gave titania with the highest NOx conversion rate - twice that of Degussa P25
Production of adsorbents by pyrolysis of paper mill sludge and application on the removal of citalopram from water
No full textThis work describes the production of alternative adsorbents from industrial residues and their application for the removal of a highly consumed antidepressant (citalopram) from water. The adsorbents were produced by pyrolysis of both primary and biological paper mill sludge at different temperatures and residence times. The original sludge and the produced chars were fully characterized by elemental and proximate analyses, total organic carbon, specific surface area (BET), N-2 isotherms, FTIR, C-13 and H-1 solid state NMR and SEM. Batch kinetic and equilibrium experiments were carried out to describe the adsorption of citalopram onto the produced materials. The fastest kinetics and the highest adsorption capacity were obtained using primary sludge pyrolysed at 800 degrees C during 150 min. The use of pyrolysed paper mill sludge for the remediation of contaminated waters might constitute an interesting application for the valorization of those wastes. (C) 2014 Elsevier Ltd. All rights reserved
Synthesis, Structural Aspects and Catalytic Performance of a Tetrahedral Cobalt Phosphonate Framework
No full textA new phosphonate-based metal organic framework has been synthesized. The structure determined by X-ray crystallography reveals that it has an interesting 8-ring channel 3D structure having the Co-2-dimers as the secondary building unit. Topological analysis shows that it has 10-c uninodal 3D net structure with the Schlafli symbol 3(15).4(22).5(8). The magnetic measurement reveals the tetrahedral coordinated Co-II ion. The compound is highly active towards epoxidation in the presence of air and IBA (isobutyraldehyde). It catalyses almost all types of olefinic substrates with equal efficiency. The compound is highly stable thermally (370 degrees C) and under the reaction conditions as well. After the reaction it can be recovered quite easily and can be used for further reaction without any loss of activity over several cycles
A combined thermodynamics and first principles study of the electronic, lattice and magnetic contributions to the magnetocaloric effect in La0.75Ca0.25MnO3
No full textManganites with the formula La1-xCaxMnO3 for 0.2 < x < 0.5 undergo a magnetic field driven transition from a paramagnetic to ferromagnetic state, which is accompanied by changes in the lattice and electronic structure. An isotropic expansion of the La0.75Ca0.25MnO3 cell at the phase transition has been observed experimentally. It is expected that there will be a large entropy change at the transition due to its first order nature. Doped lanthanum manganite (LMO) is therefore of interest as the active component in a magnetocaloric cooling device. However, the maximum obtained value for the entropy change in Ca-doped manganites merely reaches a moderate value in the field of a permanent magnet. The present theoretical work aims to shed light on this discrepancy. A combination of finite temperature statistical mechanics and first principles theory is applied to determine individual contributions to the total entropy change of the system by treating the electronic, lattice and magnetic components independently. Hybrid-exchange density functional (B3LYP) calculations and Monte Carlo simulations are performed for La0.75Ca0.25MnO3. Through the analysis of individual entropy contributions, it is found that the electronic and lattice entropy changes oppose the magnetic entropy change. The results highlighted in the present work demonstrate how the electronic and vibrational entropy contributions can have a deleterious effect on the total entropy change and thus the potential cooling power of doped LMO in a magnetocaloric device
Compositional and chromatic properties of strontium hexaferrite as pigment for ceramic bodies and alternative synthesis from wiredrawing sludge
No full textThis paper reports a new black pigment based on strontium M-type hexaferrite (SrM) obtained from pure reagents or by the inclusion of Fe-rich wiredrawing sludge. The fired powders show a clear predominance of SrFe12O19. Also, haematite (alpha-Fe2O3) and iron spinel were detected in variable amounts. These two phases are present in higher amounts (57 wt.%) in the sludge-based pigment, due to the interference of contaminants. The optical measurements illustrated that the prepared pigments displayed good colorimetric properties, close to those shown by a black commercial pigment. However, the addition of Fe-rich sludge slightly reduced this black colour by increasing the L* and b* colour coordinates. Since the variance is slight, further trials were carried out by minor addition of chromophores (Co, Mn and Ni). The chromatic measurements showed that the best pigment was obtained by adding cobalt. Nevertheless, in ceramic porcelainized bodies, the combination of Co and Mn assured the nearest hue to the commercial pigment. Nickel was not effective in the colouration because it was mostly assimilated by the spinel (trevorite) phase and was not inserted in the hexaferrite phase. Other trials with non-stoichiometric formulations showed a bleaching of the black colouration in stoneware supports, especially on sludge-containing formulations, along with an apparent increasing of the green hue. (C) 2012 Elsevier Ltd. All rights reserved
Copper wettability on tungsten carbide surfaces
No full textThe wetting behavior of copper on tungsten carbide surfaces was investigated through the sessile drop method, at 1080 degrees C, in vacuum atmosphere. Tests were performed on three different types of substrates: (i) commercial sample of WC-Co with 3.5 wt% of cobalt; (ii) WC thin film sputter-deposited on the aforementioned commercial WC-Co sample and (iii) WC sample processed by hot pressing. The lowest final contact angle was achieved on the WC-Co surface (6), followed by those of WC thin film (13) and WC (25). The contact angle values were inversely correlated with the wetting behavior, i.e. the highest wettability was found for the WC-Co and the lowest for the WC surfaces. Structural, microstructural and elemental characterizations of the interface region between the molten copper and the substrate were performed, using low angle X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). The wettability behavior was discussed taking into consideration the effect of minor phases, such as cobalt. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved
Tuning of azine derivatives for selective recognition of Ag plus with the in vitro tracking of endophytic bacteria in rice root tissue
No full textSeveral azine derivatives have been prepared and structurally characterized by spectroscopic and single-crystal X-ray diffraction analysis. Two of them, viz. naphthalene based (A10) and anthracene based (A11) show fluorescence enhancement in the presence of Ag+ in aqueous-methanol. Moreover, A11 efficiently tracks Ag+ in vitro endophytic bacteria infected rice root tissue. Experimental results have been substantiated by theoretical DFT calculations
Smart electroconductive bioactive ceramics to promote in situ electrostimulation of bone
No full textBiomaterials can still be reinvented to become simple and universal bone regeneration solutions. Following this roadmap, conductive CNT-based \"smart\" materials accumulate exciting grafting qualities for tuning the in vitro cellular phenotype. Biphasic electrical stimulation of human osteoblastic cells was performed in vitro on either dielectric bioactive bone grafts or conductive CNT-reinforced composites. The efficiency of the electrical stimuli delivery, as well as the effect of stimulation on cellular functions were investigated. Conductive substrates boosted the local culture medium conductivity and the confinement of the exogenous electrical fields. Hence, bone cell proliferation, DNA content and mRNA expression were maximized on the conductive substrates yielding superior stimuli delivering efficiency over dielectric ones. These findings are suggestive that bioactive bone grafts with electrical conductivity are capable of high spatial and temporal control of bone cell stimulation