The Influence of the Distributor Plate on the Bottom Zone of a Fluidized Bed Approaching the Transition from Bubbling to Turbulent Fluidization

The dynamics of the bottom zone of a narrow fluidized bed, from bubbling to turbulent regimes, was studied in a cold model of 0.1 m i.d. and 1.3 m high. Tested distributor types were perforated perspex plates, with six different perforation grids, metallic mesh and porous ceramic, with pressures drops ranging from 0.05 to 350 kPa, corresponding to superficial air velocities from 0.1 to 2.3m s-1. Group B silica ballotini, within the range 0.355-0.425 mm, were used as bed material. The experimental data consisted of pressure drop and absolute pressure fluctuating signals, together with visual observations. The bottom zone presented a dynamic condition that produced higher pressure drop values than those expected with the incipient fluidization condition, particularly for the distributor plates with a higher open area. A simple model is used to describe the axial solids distribution and the dynamics characteristics of the voids created in that zone, and an attempt is made to differentiate the bubble voidage from that of the dense phase, with a value of through flow estimated in a systematic way.http://www.sciencedirect.com/science/article/B8JGF-4RT04WJ-5/1/35ae43b23db71e43caf98b5be93bab0

Estimating the sustainability of carbon nanotube composites: reprocessing studies

Polylactide (PLA) has attracted particular attention in the area of environmentally degradable polymer materials. Some applications require the incorporation of a reinforcement material to produce a composite with specific properties. It was observed that PLA /carbon nanotube (CNT) composites present adequate properties for liquid sensing. The health risks involved in the use of carbon nanotubes are still under study, and thus the application of these materials must be planned with caution. From the point of view of environmental protection, recycling the CNT composites is the way to reduce these problems to the lower level possible, by maximizing they life cycle. The work presented reports the processing of PLA/CNT composite monofilaments, produced for sensing applications, and their reprocessing to form new monofilament composites. The monofilaments were reprocessed three times, and the tensile properties and electrical resistivity was measured. The melt flow index of the nanocomposites after each reprocessing step was measured. The thermal stability was evaluated by thermogravimetric analysis. It was observed that, although the melt flow index increased with reprocessing cycles, the tensile and electrical properties of the monofilaments produced after reprocessing were not affected, even after the fourth processing cycle. The thermal stability of the filaments was comparable after each processing cycle.Project Inteltex, FP

Functionalized carbon nanotubes-polyamide composites produced by microinjection moulding

Polymer composites containing carbon nanotubes (CNT) have attracted much attention due to the possibility to obtain electrically conductive and reinforcing materials at relatively low CNT concentrations, and for their potential applications in electronics, and chemical and biological sensing. Microinjection molding (μIM) is an emerging efficient and cost-effective process for the large-scale production of thermoplastic nanocomposite microparts. The present work reports the dispersion of CNT in polyamide 6 (PA 6) for the production of nanocomposites with different amounts of functionalized and non-functionalized CNT. The nanocomposites were microinjection molded under specific conditions and the electrical and mechanical properties of the specimens obtained were measured.Fundação para a Ciência e a Tecnologia (FCT) - POCI/QUI/59835/2004, bolsa de doutoramento T. Ferreira (SFRH/BD/39119/2007)

Dispersion and re-aggregation phenomena in carbon nanotube polymer composites

The preparation of polymer nanocomposites is usually carried out in twin-screw extruders or internal batch mixers. Previous studies have extensively shown that the resulting filler dispersion is strongly dependent on the characteristics of the melt mixing equipment. It is also known that the dispersion level of nanofillers strongly affects the final nanocomposite properties. The present work focuses on the study of the dispersion of carbon nanotubes (CNT) in polypropylene using a prototype mixer that develop high thermomechanical stress. The distribution and dispersion of the CNT was evaluated by optical and electron microscopy. The level of dispersion achieved was analysed, and the electrical resistivity of the composite, along the mixing cycles, was measured. The enhancement of the CNT dispersion along the mixing process correlated with a large decrease in electrical resistivity of the composite. A “percolation time”, defined as the time, or number of mixing cycles, required to achieve electrical conductivity, was measured, and correlated with mixing conditions. The composite formed was re-heated and reprocessed using the same mixing system. Re-agglomeration and loss of electrical conductivity was observed, and the final dispersion level varied with the mixing conditions imposed. Agglomerate size and electrical resistivity increased when reprocessing was performed at lower shear rate, as compared to the first processing cycle

Science-religion dialogue in education: religion teachers’ perceptions in a roman-catholic context

This paper examines the relationship between science and religion in the education system of Roman-Catholic Portuguese society. In particular, we explored perceptions of the relationship between science and religion for religious education teachers. We surveyed 198 Portuguese religious education teachers about how they view science and religion. The questionnaires’ results revealed a number of similarities: religious education teachers are highly involved in religious practices and exposed to science; they perceived a compatibility between science and religion; and they have an openness to dialogue between both. They do not adhere to anti-scientific perspectives, but they simultaneously try to limit what can be explained by science. Thus, an interpretative view of dialogue and/or integration seems to best explain the perceptions of religious education teachers of the relationship between science and religion. These findings allow a space of discussion, enabling teachers to possibly foster the science-religion dialogue in their contexts of pedagogical activity.info:eu-repo/semantics/acceptedVersio

Comparação entre folíolo central nos diferentes nós do feijoeiro.

O objetivo do trabalho foi observar se o índice foliar de diferentes nós do talo principal em vários estados de desenvolvimento guarda semelhança entre si

Dispersion of carbon nanotubes in poly(lactic acid)

Carbon nanotubes (CNT) present excellent mechanical, electrical and thermal properties, and are expected to impart these properties into their composites. However, the CNT are grown as entangled bundles that are difficult to disperse in polymer matrices, or even in solvents. Several approaches have been tried for the efficient dispersion of CNT in polymer matrices, ranging from the CNT chemical modification to the use of different mixing methods. Previous studies have shown that the resulting filler dispersion is strongly dependent on the characteristics of the melt mixing equipment [1]. It is also known that the dispersion level of nanofillers strongly affects the final nanocomposite properties [2]. The present work reports the optimization of the CNT dispersion in poly (lactic acid) (PLA) using a small-scale twin-screw extruder. The CNT were chemically modified for improved interaction with PLA. The effect of varying the mixing parameters on the dispersion level of the CNT and functionalized CNT was evaluated using optical and electron microscopy. The electrical resistivity and mechanical properties of the composites were measured. It was observed that the incorporation of 1% (weight) of CNT reduced the electrical resistivity of the composite to 400 Ohm.m, and that 3% CNT rendered the composite conductive, with an electrical resistivity of 0.6 Ohm.m.Fundação para a Ciência e a Tecnologia (FCT) - POCI/QUI/59835/2004, bolsa de doutoramento SFRH/BD/32189/2006

Dispersion and re-agglomeration of graphite nanoplates in polypropylene melts under controlled flow conditions

The kinetics of GnP dispersion in polypropylene melt was studied using a prototype small scale modular extensional mixer. Its modular nature enabled the sequential application of a mixing step, melt relaxation, and a second mixing step. The latter could reproduce the flow conditions on the first mixing step, or generate milder flow conditions. The effect of these sequences of flow constraints upon GnP dispersion along the mixer length was studied for composites with 2 and 10 wt.% GnP. The samples collected along the first mixing zone showed a gradual decrease of number and size of GnP agglomerates, at a rate that was independent of the flow conditions imposed to the melt, but dependent on composition. The relaxation zone induced GnP re-agglomeration, and the application of a second mixing step caused variable dispersion results that were largely dependent on the hydrodynamic stresses generated.Project Matepro – Optimizing Materials and Processes (NORTE-07-0124-FEDER-000037) by Programam Operacional Regional do Norte (ON.2

A comparative study of the dispersion of carbon nanofibres in polymer melts

The dispersion of carbon nanofibres (CNF) in a polymer matrix using two melt mixing methods is studied. Distributive and dispersive mixing were evaluated by optical and electron microscopy. The CNF were chemically modified to improve the interface with the matrix. The results showed that the two methods produced good distribution of the filler, but extensional stresses induced higher dispersion. The latter correlated well with a decrease in electrical resistivity. Also, the chemical modification largely improved the CNF/polymer interfaceFundação para a Ciência e a Tecnologia (FCT