Dense fine-grained biphasic calcium phosphate (BCP) bioceramics designed by two-step sintering

In this study, dense, fine-grained biphasic calcium phosphate bioceramics were designed via the two-step sintering method. The starting powder was nanosized calcium-deficient hydroxyapatite, whose phase composition, average particle size and morphology were characterized by XRD, FTIR, Raman spectroscopy, laser diffraction and FE-SEM. The phase transformations of the initial powder during heating up to 1200 °C were examined using TG/DSC. At first, conventional sintering was performed and the recorded shrinkage/densification data were used to find out the appropriate experimental conditions for two-step sintering. The obtained results show that two-step sintering yields BCP ceramics, consisting of hydroxyapatite and β-TCP, with full dense, homogeneous structure with average grain size of 375 nm. Furthermore, BCP ceramics obtained by the two-step sintering method exhibit improved mechanical properties, compared to conventionally sintered BCP.     

Phosphorus dynamics in permanent pastures: differential fertilizing and the animal effect

The general objective of this study was to evaluate the deviation between measured and estimated soil phosphorus (P) content, over 3 years, in a permanent bio-diverse pasture system in Southern Portugal with grazing sheep, and subjected to annual, differential P fertilization. The results can be a contribution to the development of practical and effective site-specific management strategies to minimize pasture yield variation. The soil and pasture samples were taken from a 6 ha field and were geo-referenced with RTK GPS. This procedure was carried out, each year, from March to May, according to the vegetative growth of the pasture. In October of each year the field was fertilized in a differential manner, as a function of soil P concentration measured at the end of the pasture growth cycle (May–June). Maps were developed in ARCGIS 9.3 considering: (1) the soil P concentration and pH; (2) the average P plant uptake; (3) the differential P application; and (4) the extractable P. The significant temporal variability of soil P concentration and pasture dry matter yield confirm the complexity of soil P dynamics in pastures involving two biological systems: plant and animal, under Mediterranean conditions and the consequent difficulties in implementing precision agriculture techniques. The results of this work indicate that 3 years of P variable-rate application rate were not sufficient to obtain homogeneous and adequate levels of P in the whole field for crop production. Despite differential P fertilization with the objective of obtaining homogenous values of soil P content in experimental field, the undulating topography of the experimental field associated with the presence of grazing animals adds a notable short-range spatial variation in nutrients that generally arises from heterogeneous excreta depositions. The small and positive final deviation between measured and estimated P levels suggests the irregular and gradual release of P by the fertilizer over years, contributing to an increase in soil P concentration. P input in fertilizer and removal in the crop greatly exceed all other inputs and outputs. However, the pH effect on extractable P, the estimation of amounts of export/import by livestock, atmospheric deposition or erosion/leaching losses are complex and justify more experiments to evaluate the confidence of long-term estimated P dynamic balance before sustained decision making is possible for differential pasture fertilization and site-specific management strategy implementation.     

In‐line optical techniques to characterize the polymer extrusion

In the past 15 years our research group has been creating new optical devices to characterize in real time the extrusion process. These detectors are made of a slit‐die fitted at the extruder exit from where the molten polymer flows, with a pair of transparent windows that allows a light beam to pass orthogonally through the molten flow. Following the reduction of the transmitted light intensity one is able to quantify the turbidity, which is a function of the type, concentration and particle size and shape of the second phase present in the flow. By evaluating the scattering pattern of a laser beam (LALLS) it is possible to get information upon the morphology of the molten polymeric system in real time during the extrusion. With the interposition of a pair of crossed polarizers in the optical beam, rheo‐polarimetry, it is possible to evaluate quantitatively the flow birefringence, which is a function of the degree of the polymer matrix orientation. POLYM. ENG. SCI., 54:386–395, 2014. © 2013 Society of Plastics Engineers     

Photocatalytic oxidation of oxalic acid in dilute aqueous solution,in a fully illuminated fluidized bed reactor

A comprehensive kinetic model for the photooxidation of oxalic acid (C₂O₄H₄) in a fluidized bed (FB) of a TiO₂/quartz sand composite, in a UV-fully illuminated photoreactor, was developed and correlated with experimental results. A proper solution for the mass balance of the reacting system was achieved by combining the complete radiation field profile and the most recent and updated pathway for the adsorption and photodecomposition of oxalic acid onto TiO₂ (Mendive et al., 2007), which was employed to determine the kinetic expression and model parameters.     

Effect of stoichiometry and milling processes in the synthesis and the piezoelectric properties of modified KNN nanoparticles by solid state reaction

Nanoparticles in the system (K,Na,Li)(Nb,Ta,Sb)O₃, modified KNN, were synthesized following a solid state reaction procedure. Milling of the individual carbonate and oxide raw materials was carried out before mixing of the components to optimize particle size. These mixtures were calcined at 700 °C for 2 h, obtaining nanoparticles with size ranging between 50 and 200 nm. The optimization of the raw materials particle size and the particle refinement of the carbonates during their decomposition play a key role in the formation of the modified KNN nanoparticles by solid state route. The obtained nanoparticles show tetragonal and orthorhombic phases coexistence that could be attributed in part to the lack of homogeneity of cations distribution confirmed by EDS analysis. The K⁺ cation excess on the modified KNN system produces a displacement of Li⁺ cations from the perovskite structure that is the origin of the stabilization of the orthorhombic symmetry. These nanoparticles are used to sintered ceramics with good piezoelectric properties without needing of anisotropic preparation methods. The sintered ceramics show resistance to hygroscopicity and deliquescence.     

The carbonization of colloidal polyaniline nanoparticles to nitrogen‐containing carbon analogues

The carbonization of nanostructures afforded by conducting polymers represents a new route to the preparation of functional nanostructured carbons. The exposure of colloidal polyaniline particles stabilized with poly(N‐vinylpyrrolidone) or silica nanoparticles at 650 °C in inert atmosphere led, in both cases, to nitrogen‐containing carbonaceous materials with specific surface areas of 200 and 205 m² g^?1, respectively, and conductivities of 8.3 × 10^?7 and 1.9 × 10^?10 S cm^?1, respectively. The latter material contained 77 wt% of silica. The original particulate nanostructure of the samples was preserved after carbonization. The carbon‐to‐nitrogen atomic ratio was 7.2 and 7.9; the nitrogen content in the carbonized polyaniline–poly(N‐vinylpyrrolidone) particles was 10.8 wt%. Thermogravimetric analysis in air revealed their stability to be up to 500 °C. This is comparable with commercial multi‐wall carbon nanotubes, which have similar areas of application. The nitrogen‐containing carbons are potentially useful as supports for catalysts and in applications where carbon of higher hydrophilicity would be of benefit. Copyright © 2010 Society of Chemical Industry