Materials Science Forum Vol. 802

Abstract: The deposition of TiO₂ nanoparticles in the environment has been systematically investigated; this is due to the use of nanosized titanium dioxide (TiO₂) in a variety of consumer products such as sunscreens, cosmetics, paints and surface coatings as well as the environmental decontamination of air, soil and water. It is the generalized use which increases the concern that the nanoparticle TiO₂ could pose a risk to ecosystems and humans. In this context, this paper aims to characterize different suspensions of nanoparticles of titanium dioxide. Although these particles are already incorporated in a wide range of products, the evaluation of their behavior and its effects on the environment and health start to grow now. So this paper aims to conduct a study of the behavior of TiO₂ nanoparticles in aqueous suspensions. The study encompasses TiO₂ solutions with ultra pure water with and without added NaCl, landfill leachate and tap water. The results obtained showed that the addition of NaCl in the solution increases the size of the TiO₂ nanoparticles, showing that the sodium chloride functions as a binding agent when in contact with nanoparticles of titanium dioxide.

Abstract: This is a comparative experimental study of the micro, nanoand ultranano-crystalline diamond deposition. The Hot Filament Chemical Vapor Deposition (HFCVD) reactor deposits the films using different deposition parameters. Scanning Electron Microscopy and Field Emission Scanning Electron Microscopy let morphology inspection. Visible-Raman scattering loaded to estimating relative induced stress, by the graphite peak shift and associated with the defect incorporation and sp² bond enhancement. The x-ray diffraction confirmed the diamond crystallinity, where Scherrer ́s equations estimate crystallite size and diamond renucleation rates. In this work we propose a defect increasing relative graphite incorporation with the transition of micro, nanoto ultranano-crystalline diamond deposition. Besides this, we propose that this increase defects follows the increase diamond renucleation rates and decreases in the induced stress films. Included is a discussion of the possible reasons for these observations.

Abstract: This study aimed to evaluate the deposition of NaCl nanoparticles during filtration in a cellulose filter medium (HEPA). The diameter of the generated polydisperse particles was between 6 and 800nm. Deposition was evaluated with the curves of pressure drop as a function of time. The permeability of the filter medium was determined and, after the deposition of particles, specific resistance of the formed cake was obtained. Filter performance was evaluated by counting particles before and after the filter medium and the pressure drop was monitored in order to obtain the filtration curve. Filtration velocity was kept at 0.06 m/s, and the concentration of the solution generated at a rate of 0.0042 L /min in a commercial inhaler was of 5 g/L. The results showed that this filter showed two steps during the deposition of particles, an internal filtration stage and a surface filtration stage. Although this filter is highly efficient in removing particles in the range evaluated, roughly 100%, particle penetration was observed in the range between 50 and 200nm.

Abstract: The purpose of this work is to study the structural and morphological modification of the surface of the n-type diamond electrodes as a function of nitrogen doping. The characterizations of these electrodes were made using Raman Spectroscopy, Contact Angle, X-ray diffraction and Scanning Electron Microscopy (SEM). The nitrogen-doped diamond (NDD) electrodes were produced using Hot Filament-assisted Chemical Vapor Deposition method (HFCVD) from methane, hydrogen and nitrogen in the gas mixture. The results from Raman spectroscopy show that the diamond films obtained with nitrogen addition presented one large band at 1100-1700 cm^-1. The SEM images showed that the variation in the nitrogen doping influenced the growth rate of films by promoting changes in the sizes of grains from microcrystalline to nanocrystalline texture. This behavior supported the results obtained from X-ray diffraction analyses. It was possible to verify a decrease in the crystallite size as a function of the nitrogen increase.

Abstract: Carbon nanotubes (CNT) are a material with unique properties (mechanical, electrical, electrochemical, etc) allied with low density and high specific area. The present paper studied the electrochemical properties of carbon nanotubes growth by Chemical Vapor Depostion (CVD) technique. The samples were characterized by SEM, Raman Spectroscopy and the double layer capacitance of the powders was evaluated in a Teflon capacitor system with a Ag/AgCl (3M) as reference electrode. The catalyst remotion is provided in Hydrochloric acid washing and the wet oxidative treatments promotes the CNT oxidation and increase the pseudocapacitive response.

Abstract: Carbon fibers have been studied for electrochemical applications. Recently, carbon nanotubes present a wide potential uses in electric, mechanic, electrochemical and materials science field. At present study, vertically aligned carbon nanotubes were produced over carbon fibers. The process occurs catalytically by chemical vapor deposition (CVD) using mixture with camphor and ferrocene. After that, the VACNT/CF composite are treated by oxygen plasma for oxygen functionalization. Prior the electrochemical analysis, CNT/Carbon fibers are treated by hydrochloric acid to remove residual catalyst. The electrodes were tested in a usual electrolyte (with H₂SO₄ 0.5M) in a conventional electrochemical cell. The specific capacitance was tested in a separate device. The configuration of carbon fibers and VACNT presents a high potential application for electro analytical application and energy storage.

Abstract: The nanotechnology has become an important area, either because the special features of nanometric particles confer to products, or due to a maximum limit of emission of such particles in air. However, the reduced size of this kind of particle limit them to be separated by conventional techniques, and a good way to ensure an aerosol stream with monodispersed particles is to use the electrical mobility technique. This theory is based on the ability of a charged particle to cross an electrical field, thus depending of the size of particles, the bigger ones will arrive later in the central electrode than the smaller ones, and only a narrow band of sizes will be collected in a slit located in the bottom of the equipment. This work aimed to project and construct a Differential Mobility Analyzer (DMA) in order to produce an aerosol containing NaCl nanoparticles monodispersed, from a aerosol polydispersed produced by an atomizer. The operating principle is to charge NaCl nanoparticles with a neutralizer so that they can be collected according to the voltage applied to the DMA in a specific range of size distribution. The unit comprises a compressor for generating air current, high efficiency filters in order to generate ultrapure air, atomizer, reservoir of NaCl solution to generate aerosol, a diffusion dryer to remove moisture silica current gas, a source of X-rays to charge nanoparticles, a source of high voltage to be applied to the DMA, a DMA to classify the nanoparticles and a particle counter to perform the counting of particles before and after DMA. Preliminary results indicated the dependence of the particle size with the applied electric field. The results were very promising.

Abstract: Rotary dryers are a significant capital item for many industrial plants. Many potential benefits can be obtained through a greater understanding of the rotary drying process. In order to improve drying efficacy, a novel version of the rotary dryer, known as the rotoaerated dryer, was evaluated in previous studies. This work has studied the effect of the configuration and arrangement of mini-pipes in the rotoaerated dryers by experimental and CFD techniques. The results obtained showed that it was possible to predict the effect of variations in the configuration of the rotoaerated dryer and obtain the more appropriate arrangement of mini-pipes.

Abstract: The study of the sedimentation of particulate materials is of interest in several industrial processes, such as in the design and optimization of operating conditions of thickeners and during the operational stages of drilling oil wells. In this context, this work aims to study the sedimentation of particles in viscous Newtonian fluids. For the tests, aqueous solutions of glycerol were used in the volumetric concentration of 80% and 92%. The suspensions were prepared using sand with the size range of 150-212 μm. The settling of particles was studied by using a nondestructive technique based upon the measurement of gamma-ray attenuation for achieving the local concentration of solids. The results showed that the sedimentation velocity of particles was changed significantly with increasing fluid viscosity. Moreover, the dynamic behavior of the particles settling in both glycerol solutions showed similar, with two regions of varying concentration of solids very defined: one in which the solids concentration remained constant until the transition from descending clarified interface; and the other in which the concentration remained constant until the formation of sediment.

Abstract: This paper aims to investigate the particle dynamic behavior in a rotating drum operating in a rolling regime under different rotating velocity, based on experimental results and simulations. Simple superphosphate fertilizer (SSP) was used as particulate matter in the current study. The Eulerian–Eulerian multiphase model along with the kinetic theory of granular flow was used in the simulations. In order to evaluate the simulation results, velocity distributions of the particulate phase were compared with experimental data. The experimental particle velocity distribution was obtained by using a high speed video camera. The numerical simulation results showed significant insights towards understanding of the particle dynamic in a rotating drum. The simulated results of particle velocity were in good agreement with the experimental data.