Materials Science Forum Vol. 802

Abstract: The study of compressibility in deformable porous media is of interest in many industrial processes, such as, filtration, thickening and during oil well drilling processes in the petrochemical sector. In this work the compressibility of porous media was evaluated by the comparison of solid concentration profiles in sediments using fluids with Newtonian and non-Newtonian behavior. For this, consolidation tests in distillated water, solutions of xanthan and glycerol were performed in a vertical column from the gravitational settling of suspensions. The porosity distribution in the formed sediment was obtained after the complete settling of particulate material. The local porosity measurements were performed using the ionizing radiation emitted by americium-241. The gamma-ray attenuation technique used in this study allowed the realization of nondestructive measurements for achieving local concentration of solids. The results showed that the rheological behavior of the fluid does not change significantly the compressibility of the porous matrix.

Abstract: Solid-state reactions were used to synthesize pure and doped barium titanate powder. Barium titanate formation with tetragonal perovskite structure was detected by X-ray diffraction and occurred at a temperature above 700°C for pure powder and 500°C for doped powder. However, quite crystalline samples were observed only at 800oC and 600°C for pure and doped barium titanate, respectively, what made the refinement of the synthesized powders possible. They were characterized by X-ray diffraction and Fourier transform infrared spectroscopy and scanning electron microscopy. X-ray diffraction data was analyzed by using the Fullprof Rietveld refinement approach, Thompson-Cox-Hastings pseudo-Voigt with function. The refinement method was effective in the study of the temperature influence on the microstructure of the analysis of pure and doped barium titanate.

Abstract: For a Soderberg Technology, paste production process consists of four basic steps: raw material handling; dry aggregate preparation; mixing; and briquettes loading at electrolytic cells for aluminum production. Dry aggregate is prepared from calcined petroleum coke, where the grains are crushed and separated between 3 different fractions of pre-determined sizing and a dust component. Petroleum pitch blended with the finest particles from dry aggregate forms the binder used for wetting, lubricating and filling open pores of larger coke grains, resulting into a higher anode paste quality with adequate mechanical properties, higher density, oxidation resistance and lower electrical resistivity. Raw materials recent trends showed significant quality degradation and cost raise, pushing up industry to look forward for untraditional suppliers, in addition to process optimization. This paper describes enablers chosen to improve paste properties, through dry aggregate particle size distribution using two of the most traditional particle packing models: Andreasen and Alfred. The formulations developed in this work were compared to the formulation originally used by an industry through measures flowability and apparent baked density. The results have shown that both the equations of Alfred and Andreasen, for distribution coefficient 0.30 and 0.52 respectively, can be applied to the Aluminum Industry, resulting into products significantly different from the point of view of quality.

Abstract: Several studies on removal of nanosized particles are being developed with the aim of minimizing the adverse effects nanoaerosols can cause to the environment and human health due to poor air quality. Moreover, scientific and technological studies have developed in the application of nanosized particles. In academy and industry there are many mechanisms to remove nanoparticles from aerosols, such as fiber filters. Thus, this study aims to analyze the performance of fibrous filters, such as polyester filters (porosity is 0.82 and thickness is 2.2 mm and fiber mean diameter of 26 μm. A nanoparticle generator constitutes an atomizer that was used to generate nanoaerosols of monodisperses polystyrene latex) in a size distribution from 20 nm to 200 nm. The performance of the fibrous media was evaluated through the analysis of removal efficiency of nanoaerossols, using a particle counter TSI model 3007 before and after the filtering device. The experimental system consists of a compressor, which generates air current; high efficiency filters, in order to generate ultra-pure air; an atomizer and a container of polystyrene solution to generate aerosol; diffusion dryer to remove silica humidity from the gas stream; a filtration device; and, a counter to particles. The results obtained showed that the efficiency of a filter decreases with increasing filtration rate and diameter in the range in work. The diffusion mechanism is dominant in the separation process.

Abstract: The pore structure and the presence of open and close porosity has always made difficult the study of the interaction between fluids and porous materials, being complicated the analysis of liquids wettability and permeability, capillarity or speed of wetting, among others. This work tries to deal with these problems in a simple way, from a theoretical point of view, applying hydrostatic laws and the effect of capillarity to address the effect of open porosity. Moreover, surface roughness of these materials is the consequence of surface finishing (e.g. polishing) and porosity. This work also faces this aspect of wettability of surfaces, important to understand sealing conditions or lubricant retention in powder metallurgical components. From a practical point of view, the speed of fluids through metallic filters is compared to that through metallic meshes.

Abstract: In order to develop a composite for future applications as self-lubricating material, samples with iron matrix and contents of hexagonal boron nitride (hBN) of 0, 2.5, 5, 7.5 and 10 vol%. were produced by conventional powder metallurgy, varying the compacting pressures. It was observed a decrease of mixture flowability and apparent density when increasing hBN content. Moreover, the samples showed an increment of green densification with the increase of applied pressures and hBN contents, suggesting that hBN particles accommodate into the voids during pressing. As known, hBN has low shear strength and is insoluble in the iron matrix, which hinder the formation of necks between the particles of iron during sintering. To improve matrix continuity the double pressing technique was used, and this technique presented increments of 3 to 5% of densification and up to 95% of tensile strength when compared with the composites produced by single pressing.

Abstract: Powder forming involves fabrication of a preform by conventional press-and-sinter processing, followed by various forming processes, citing as examples, rolling, compaction, forging, extrusion, among others, of the porous preform into a final shape through substantial densification. This work makes a finite element analysis for porous metals. The finite element model was applied to simulating the case of compaction of nanocristalline copper under uniaxial compression conditions in order investigate the densification behavior. The model was simulated using explicit integration method as applied to the evolution variation of the relative density and the dislocation density of the compact. Finite element analysis program used was Abaqus. Finite element calculations were compared with literature data. The agreements between finite element model and literature results for densification of nanocristalline copper were good.

Abstract: Titanium is found in its raw form in nature mainly in rutile, ilmenite, and anatase which appears in abundant quantities in the earth crust. However, its extraction through the conventional process is still very expensive. Powder metallurgy has been used as an alternative technique for production of titanium alloys parts due to its low cost compared with conventional melting techniques. The process involves the use of powders under high pressure and temperature. Using this technique, Ti-10V-2Fe-3Al samples were produced from Ti-Al pre-alloyed powder with additions of different contents of aluminum in order to study the influence of aluminum particles on the formation of residual porosity. After cold uniaxial and isostatic pressing and sintering at 1100°C and 1400oC, samples were characterized by SEM (Scanning Electron Microscopy), XRD (X-ray Diffraction), EDS (Energy Dispersive Spectrometry) and density analyses. Sintered samples presented homogeneous microstructure and increased densification due to increased content of Ti-Al pre-alloyed powder.

Abstract: This paper presents the microstructural characterization of particle systems used in equipment for selective laser sintering. Three distinct commercial metal powders, with chemical composition based on Co-Cr-alloy, were characterized by X-ray diffraction, scanning electron microscopy and particle size distribution. The powders showed regular spherical particles with varying sizes and crystalline phase of Co-solid solution. Different powders present particle size among 55nm and 245 nm. This behavior affects the sinterability of samples submitted to the selective laser sintering.

Abstract: This study shows the influence of the temperature in the Direct Forming Laser process (DFL) of 316L stainless steel metal powder. Results shows that an increasing in the sample surface temperature can improve the laser beam absorption in the DFL process. A pre-heating in the substrate and in the powder contributed to decrease the time to reach the melting point and to improve the surface roughness. This effect was investigated with constant lasers parameters (scanning speed and intensity) and a heating in the samples in the temperature range of 20^o to 200^o C. It was possible to evaluate the DFL process and to optimize the quality of the sample surface roughness. These results will benefit the knowledge of the DFL technology that can be applied in the development of turbine blades.