Materials Science Forum Vols. 727-728

Abstract: The growing concern with the global environmental issues has resulted in a constant demand for the production of clean fuels. Therefore, researches were carried out in order to improve the gas-to-liquids technology, well represented by the Fischer-Tropsch synthesis. This synthesis is able to produce liquid fuels from syngas, a mixture of carbon monoxide and hydrogen which is obtained through the processing of the methane gas. Based on literature data, this paper suggests a kinetic model developed by making use of the Matlab® commercial application. The goal was to predict the production of hydrocarbons such as paraffins and olefins with up to six carbons in each chain. The Fischer-Tropsch synthesis was conducted with the catalyst 20% Co/ MCM-41 in fixed bed reactor at the temperature of 270 °C and atmospheric pressure. The results obtained by the model for both paraffins and olefins were compared with experimental data found in the literature.

Abstract: Containerless solidification of 300 to 850 µm diameter droplets of PbSn eutectic alloy was achieved by using a 3m length drop tube, which is one of the most suitable and low cost option to provide a microgravity environment on the ground. Phase morphology and composition were investigated, respectively, by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). It was found that the microstructure of the droplets depends on their sizes, where in larger diameters (>500µm) consists of both regular lamellar and irregular structures, and on other hand, for the smaller ones (<500µm) the structure is only irregular with higher lead concentration.

Abstract: Titanium and Ti alloys have been widely used as biomaterial due to their mechanical properties and high in vitro and in vivo cytocompatibility. Studies have showed that the acceleration of the osseointegration process is associated to the modification of the surface morphology. The aim of this work is to study the influence of the operating parameters of titanium electropolishing to obtain nanostructured titanium surfaces. The titanium electropolishing was carried out with different temperatures (7°C, 18°C and 25°C), current density of 0.19 A/cm² and electropolishing time of 8 minutes. After the electropolishing process the titanium samples were characterized by Atomic Force Microscopy, profilometry (mechanical profilometer) and contact angle measurements. Preliminary results showed that the Ti nanostructured surfaces formation, strongly depends on the control of operating parameters.

Abstract: This study aimed to evaluate the characteristics of virgin and regenerated filter media and their relation with filtration efficiencies for particles with aerodynamic diameter up to 20 µm. The permeability of the filter media was determined and their fibers were observed in a scanning electron microscope. Filtration efficiency was obtained from the dust cake formed. The particulate matter used was phosphate concentrate and the filter media were cellulose fiber filters. The results showed that regenerated filter media presented higher air permeability due to the opening of the fibers observed in the microphotographs obtained; lower removal efficiencies were observed for particles smaller than 2.5 µm; and for particles larger than 2.5 µm, the efficiencies were nearly the same as those of the virgin filter, which was approximately 100%. It was verified that the regenerated filter media lost their initial characteristics, but continued to be efficient for particles larger than 2.5 µm.

Abstract: This study aimed to examine the behavior of different filter media used in gas filtration at high pressure. Trials were carried out having phosphate concentrate as the particulate matter and compressed air as fluid. Operating conditions were evaluated at the following absolute pressures of the system: 193, 393 and 693 kPa, and the gas velocity was kept constant at 0.05 m/s. The results indicated that, for a given pressure drop at the filter, the highest absolute pressure applied to the system (693 kPa) yielded the highest powder mass deposited on the filter medium. An analysis of the porosity of dust cakes revealed that the increase in pressure resulted in cakes which were more porous and less resistant to gas flow. It was also verified that the increase in the pressure of the system provided an increase in the fractional efficiency of the filters for particles smaller than 5 μm.

Abstract: The machines and equipment has required increasing performance of lubricating fluids and coolants which plays important role on reducing friction with the metal parts and heat extraction. Viscosity and thermal conductivity are the most important properties of lubricants, in relation to the friction between the fluid molecules. This paper presents two useful models to predict this properties and their relation with the particles volume fraction and temperature in the nanofluid formed by adition of iron or particles produced by friction. Nanofluids are innovative heat transfer fluids with superior potential for enhancing the heat transfer performance of conventional fluids. In this paper the Unit Cell Model (UCM) which considers the Brownian movement experienced by the nanoparticles are adapt to predict the increment of thermal conductivity of iron nanopowders and standard lubrication oil. The viscosity of the nanofluids was adapt from a model usually suitable for predict the effective viscosity of emulsions. Model results indicated a strong effect of the particle size and volume fractions on the increment of thermal conductivity.

Abstract: The production of metallurgical coke and carbo chemicals generates residues that evaporate several persistent organic pollutants. Among them, the so-called BTX (benzene, toluene and xylene) are of special concern due to their accumulation into sources of vegetal and animal foods. Owing to the surface properties, large number of porosities and activated sites, activated carbon has been successfully used as a selective adsorbent material. In this study a theoretical model is proposed to analyze the rate of adsorption on the surface of activated carbon compacted produced from powders of micrometer size. The model considers the inner diffusion of BTX into the agglomerate particles. The model results confirm that the agglomerate produced by micro particles of activated carbon increases the amount of adsorption not only by the mechanism of surface action of the agglomerate but is enhanced by the gas diffusion into the pores and subsequent adsorption into the surfaces of the inner particles.

Abstract: ntrinsically Conducting Polymers (ICPs) are of increasing interest, especially in areas such as electronic devices. PANI is one of the most intensively investigated of the ICPs due to its easy chemical synthesis, easy doping process by protonic acids and also because it is chemically stable at room temperature conditions. PANI is used as sensor for many gases that are responsive for air pollution The applicability of these materials as sensors is based on their selectivity over a wide range of analyte molecules and low level of gas concentration, the potential to operate at or near room temperature and also its response time. The present work studies the influence of different synthesis conditions of PANI-HF in its electrical resistance when subjected to the presence of ammonia gas. The PANI-HF was chemically synthesized and it was submitted to electrical and physical characterization. The preview results showed that the synthesis conditions change significantly the response of PANI-HF to ammonia gas.

Abstract: We have proposed the growth of ultrananocrystalline diamond (UNCD) thin films on p-type (100) silicon etched with 27wt. % KOH in H₂O. To get homogeneous distribution of micro pyramids on the silicon surface we have varied temperature (62 to 77 °C), etching time (1 to 35 min) and exposition diameter area (5 to 18 mm). For UNCD growth we have used hot filament chemical vapor deposition (HFCVD).The gas mixture have used 1 vol.% methane, 9 vol.% hydrogen and 90 vol.% argon, with the total flow rate of 200 sccm, at work pressure of 30 Torr. Images of Scanning Electron Microscopy (SEM) showed UNCD covered the silicon surface following the micro pyramidal morphology. Raman spectra (514.5 nm) showed all feature bands of UNCD such as: transpolyacethylene (1150 cm^-1) and graphite (1350-1575 cm^-1). The X-ray diffraction confirmed Raman spectroscopy. These results showed the silicon micro pyramidal structures obtained at 20 min, 75°C and 10 mm exposition diameter area as the more satisfactory for UNCD growth.

Abstract: In this work, we use x-ray fluorescence and x-ray diffraction methods to investigate the chemical and mineralogical composition of drilled cuttings at different points throughout the solids control process. Cuttings coated or contaminated with drilling fluid are the result of drilling. Over the past twenty years, studies have been conducted to assess the effects that these contaminated cuttings have on the environment, in both offshore and onshore scenarios. A more restrictive environmental legislation and the need to reduce drilling costs (exploration and production) has led to the optimization of solid-liquid separation. Knowledge of the chemical and mineralogical composition of drilled cuttings will assist in finding a dispersant and in determining an appropriate procedure for carrying out particle size analysis of these solids.