Marta C. Ferro

Production of glass-ceramics from coal ashes

Abstract Coal fly ashes produced by an extinguished power plant in the north of Portugal have been melted with addition of CaCO 3 and Na 2 CO 3 to obtain glasses. One of the formulated compositions was selected for further studies and it was possible to manufacture glass-ceramics by crystallising the parent glass through adequate time–temperature schedules. The macroscopic appearance, microstructure, mechanical, thermal and chemical properties indicated that these materials are quite attractive for cladding applications, exhibiting in some cases better performances than the conventional ceramic tiles.

The fluorapatite–anorthite system in biomedicine

Glasses and glass ceramics of fluorapatite-anorthite (eutectic composition) were produced and characterized in order to evaluate their potential application in biomedicine. Bio-reactivity was determined by in vitro tests by immersion of powders in simulated plasma liquids as well as by in vivo experiments by implantation in rabbits. According to the results, the investigated materials are bio-acceptable since no toxic or other harmful evidence was detected. Glass-ceramics showed remarkable inertness, whereas glasses spontaneously dissolved in SBF and after 1 week moderate formation of apatite was observed, that however ceased within a month.

Synthesis, texture, and photoluminescence of lanthanide-containing chitosan-silica hybrids

Three different types of photoluminescent hybrid materials containing trivalent lanthanide (Ln(3+) = Eu(3+), Tb(3+)) ions, chitosan, and silica have been prepared with different structural features. The different silica sources lead to diverse microstructures of hybrid materials, with silica being homogeneously dispersed in the chitosan materials (LnChS-H), or forming a core-shell morphology. Postsynthesis treatment is necessary for embedding the luminescent probe. The Ln(3+)-based materials have been investigated by photoluminescence spectroscopy (12-300 K). The chitosan-Eu(3+)-related local environment is maintained in the EuChS-H hybrid material. The emission features of the core-shell materials are characterized by the presence of two Eu(3+) distinct local environments, one associated with the chitosan core and the other with the silica shell.

Labeling and monitoring the distribution of anchoring sites on functionalized CNTs by atomic layer deposition

The chemical inertness of graphite and, in the case of tubes, of rolled up few layer graphene sheets, requires some degree of “defect engineering” for the fabrication of carbon based heterostructured materials. It is shown that atomic layer deposition provides a means to specifically label anchoring sites and can be used to characterize the surface functionality of differently treated carbon nanotubes. Direct observation of deposited titania by analytical transmission electron microscopy reveals the location and density of anchoring sites as well as structure related concentrations of functional groups on the surface of the tubes. Controlled functionalization of the tubes therefore allows us to tailor the distribution of deposited material and, hence, fabricate complex heterostructures.

Synthesis and characterization of reduced graphene oxide/spiky nickel nanocomposite for nanoelectronic applications

The surface modification of graphene oxide (GO) sheets with Ni nanoparticles has been a subject of intense research in order to develop new preeminent materials with increased performance for different application areas. In this work, we develop a new hydrothermal one-step method for the simple and controllable synthesis of reduced GO/nickel (GO/Ni) nanocomposites. Different reaction parameters have been investigated in order to control the synthetic process: reaction temperature, concentration of the nickel precursor and reducing agent. It was observed that the critical parameter for effective control of nickel particle size, morphology, crystalline structure and distribution at the GO surface during the reaction process was the concentration of hydrazine. The results obtained showed that control of hydrazine concentration allows obtaining crystalline metallic Ni nanoparticles, from spherical to spiky morphologies. For nanocomposites with spiky Ni nanoparticle, the reaction time allows controlling the growth of the nanothorn. The electrical properties of reduced graphene nickel nanocomposites containing spiky nickel particles showed a large resistive switching, which is essentially due to the switchable diode effect that can be used as a built-in part of graphene-based embedded electronics.

Structural Interpretation of the In Vitro Reactivity of SiO2-MgO-Na2O Glasses

The in vitro reactivity of different glasses, with 55mol% SiO2 and MgO/Na2O molar ratios ranging from 1/8 to 8/1, was investigated. Despite the same amount of SiO2, the glasses exposed different reactivities, from very reactive (low MgO/Na2O ratio) to inert (high MgO/Na2O ratio). These results are interpreted in terms of a cross-link disruption by Na2O. Introduction Since the pioneer studies of Prof. L.Hench on bioactive glasses, numerous compositions have been investigated, both in vitro and in vivo. However, most of studies usually rely on the results rather than the thorough interpretation. Hill has underlined this issue, when meeting difficulties in calculating the glass “network connectivity” for several bioactive glasses, due to inadequate information provided in the published reports [1]. The present work aims at providing an insight into the influence of glass structure on their in vitro reactivity, on the basis of preliminary results in the system SiO2-MgO-Na2O. Glass. Our previous investigations on SiO2-P2O5-CaO-Na2O-MgO glasses added new perception to the relationship between glass structure and properties, namely amorphous phase separation and in vitro reactivity in simulated body fluids [2-5]. Oliveira et al. have reviewed the most important studies done when MgO is incorporated in bio-glasses in ref.[5]. In general, MgO has been attributed an inhibiting effect on surface activity, although our experimental evidence supported rather a structural role, whereby MgO may actually improve mineralisation. In the present study, we have selected the ternary system 55SiO2-(45-x)MgO-xNa2O (mol%) with x=5 to 40. The SiO2 concentration chosen is that generally accepted as a threshold for bioactive behaviour in monolithic glasses [6]. Figure 1 and Table 1 present the eight compositions produced. Structural Characteristics. Structurally, silica glasses are networks of Si-centred SiO4 tetrahedra linked by oxygen corners. Tetrahedra can be either found isolated or connected with others by one, two, three or four binding oxygens, being identified, respectively, as Q, Q, Q, Q or Q structural units. Techniques, such as Raman spectroscopy or NMR [2, 3], can be employed to determine the structural configurations. A related concept is the degree of cross-linking, i.e. the average number of bridging oxygens per tetrahedron. Several indexes aim at quantifying the crosslinking. Among them, Stevel’s number Y [7], which anticipates that if Y>3 then the glass is nonbioactive. For all the investigated glasses (Table 1), Stevel’s number was calculated as Y=2.36. Materials and experimental procedure Glass blocks were prepared in 50g batches using reagent–grade MgO, Na2CO3 and SiO2 powders, homogenized in an agate mill for 30 minutes. The mixtures were then melted in Pt-crucibles in air between 1350-1550°C (depending on composition), for 3h. The melts were cast into metal moulds and annealed at ~500°C for 1h, in air. Raman spectroscopy was applied to small prismatic glass blocks (Jobin Yvon SPEX, T64000, Ar-laser source 514.5 nm). Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 217-220 doi:10.4028/www.scientific.net/KEM.240-242.217

Fine-Grained Glass-Ceramics Obtained by Crystallisation of Vitrified Coal Ashes

Coal fly ashes have been vitrified by melting with Na2O and CaO as fluxing additives. Adequate heat treatments on the fly ash derived glass produced attractive dark green glass-ceramics. These glass-ceramics exhibited fine-grained microstructures consisting of esseneite and nepheline crystals, with average size below 200 nm, homogeneously dispersed in a residual glassy matrix. Several properties, such as density, thermal expansion coefficient, bending strength, hardness and brittleness index were determined and the correlation microstructure-properties is discussed. The results suggest that these coal ash-based glass-ceramics have potential applications as structural materials or as cladding materials.

Pulsed laser deposition of SiO2 - P2O5 - CaO - MgO glass coatings on titanium substrates

Thin films of bioactive glass-ceramic have been deposited on titanium substrates by the Pulsed Laser Deposition (PLD) technique under different experimental conditions. The effect of parameters such as deposition pressure and temperature of heat treatments was studied. The microstructure and the crystalline phases of the coatings were characterized using SEM, EDX and XRD analysis; the phases present were titanium oxides, calcium magnesium silicates and phosphates. The adhesion of the as-deposited films has been examined by scratch tests. The interfacial adhesion of the coatings was better when the deposition was performed at low pressure. Samples were immersed in simulated body fluid (SBF), and a calcium-phosphate precipitate was observed on the surface of less crystallized samples, suggesting that there is some relationship between surface reactivity and crystallinity.

Carbon nanotube-based bioceramic grafts for electrotherapy of bone

Bone complexity demands the engineering of new scaffolding solutions for its reconstructive surgery. Emerging bone grafts should offer not only mechanical support but also functional properties to explore innovative bone therapies. Following this, ceramic bone grafts of Glass/hydroxyapatite (HA) reinforced with conductive carbon nanotubes (CNTs) - CNT/Glass/HA - were prepared for bone electrotherapy purposes. Computer-aided 3D microstructural reconstructions and TEM analysis of CNT/Glass/HA composites provided details on the CNT 3D network and further correlation to their functional properties. CNTs are arranged as sub-micrometric sized ropes bridging homogenously distributed ellipsoid-shaped agglomerates. This arrangement yielded composites with a percolation threshold of pc=1.5vol.%. At 4.4vol.% of CNTs, thermal and electrical conductivities of 1.5W·m(-1)·K(-1) and 55S·m(-1), respectively, were obtained, matching relevant requisites in electrical stimulation protocols. While the former avoids bone damaging from Joules heat generation, the latter might allow the confinement of external electrical fields through the conductive material if used for in vivo electrical stimulation. Moreover, the electrically conductive bone grafts have better mechanical properties than those of the natural cortical bone. Overall, these highly conductive materials with controlled size CNT agglomerates might accelerate bone bonding and maximize the delivery of electrical stimulation during electrotherapy practices.

Tailoring gold and silver colloidal bimetallic nanoalloys towards SERS detection of rhodamine 6G

Nanoparticles of gold, silver and their bimetallic alloys have been prepared by an adapted method of reduction of the aqueous salts using sodium borohydride. It is demonstrated that the temperature and order of addition of the corresponding salt solutions influence the nanoalloys chemical arrangement giving different surface plasmon resonance behavior. The colloidal dispersions show very good Surface-Enhanced Raman Spectroscopy (SERS) signal towards rhodamine 6G. The obtained nanoparticles were then successfully deposited onto glass supports by evaporation of the respective colloids and also used as functional SERS sensors with efficient detection of trace amounts of the analyzed dye. These spectroscopic studies demonstrated that both mono and bimetallic nanoparticles show very good SERS sensitivity with the advantage of being prepared using a straightforward synthetic method in the absence of an additional stabilizer as needed for commonly used core–shell systems.