Materials Science Forum Vols. 660-661

Abstract: Catalysts supported on SBA-15 were obtained by wet impregnation using aqueous solution of cobalt nitrate, where different contents of cobalt (5 wt% and 10 wt%) were prepared. The molecular sieve SBA-15 was synthesized using tetra ethyl ortho silicate (TEOS) as silicate source, and triblock copolymer, poly-(ethylene oxide)-poly (propylene oxide)-poly-(ethylene oxide) PEO-PPO-PEO as the organic structure directing agent. These materials were characterized by X-ray diffraction (XRD), X-ray energy dispersion spectrophotometer (EDX) and Nitrogen adsorption–desorption isotherms (BET). The results from the XRD showed that the molecular sieve mesoporous (SBA-15) was identified by X-ray diffraction, especially from the (210) and (300) peaks, which represent a typical spectrum for the SBA-15. Characterization of catalysts by Nitrogen adsorption–desorption isotherms (BET) made it possible to verify the the samples had been of type IV with hysteresis of corresponding the H2 type the porous materials.

Abstract: In this work the layered precursor of zeolite MCM-22 was synthesized as per the hydrothermal synthesis method, the length of crystallization varying from 8 to 9 days. The preparation of the lamellar precursor of MCM-22 zeolite broke the hydrogels with the following molar composition: 0.511 SiO2: 0.039 NaOH: 0.024 Al2O3: 23.06 H2O. The hydrothermal crystallization occurred in a preheated oven at 150 °C for different periods of 8-9 days. The originality of the work consists in the synthesis of lamellar precursor of MCM-22 zeolite with a variation in the crystallization time from 8 to 9 days, since the literature is used longer times. The materials were characterized by X-ray diffraction (XRD), chemical analysis by atomic energy dispersive X-ray (EDX) and scanning electron microscopy (SEM). The achievement conversion the precursor of MCM-22 zeolite was confirmed by diffracting X-ray, indicating that these materials are crystalline, with typical properties of the samples free of amorphous materials and also that the material became more crystalline as the crystallization increased. From the micrographs, it was observed that the lamellar precursor of MCM-22 zeolite consist of clusters of particles of spherical shape.

Abstract: The coating and encapsulating of particles presents many applications in the chemical, pharmaceutical, food and agricultural products industries. Among the many applications of seeds coating, the enlargement of small seeds is included in order to facilitate the planting, the addition of herbicides, fungicides, fertilizers, micronutrients and inoculation. The spouted bed has often been used in studies related to the coating of particles, due to the cyclical motion of the material, which promotes a fast axial mixture of particles and an excellent gas-particle contact. In this work, the coating of soybean seeds with inoculum and micronutrients in spouted bed has been studied. The different flow regimes were investigated using the pressure fluctuations and power spectrum. The results of the present work showed that it was possible to identify the main flow regimes and to analyze the influence of the coating in the stability of those regimes.

Abstract: The objective of this work is to study the dynamics of nanoparticle formation by atomization of saline solutions at different concentrations. The nanoparticles were generated by a two fluid particle atomizer. Saline solutions were atomized and, with the immediate evaporation of the dispersion liquid in the droplets, resulted in an aerosol of solid nanoparticles. Test replicates were performed with aqueous solutions of sodium chloride (NaCl) at concentrations ranging from 0.01 to 50.0 g/L. The solutions were characterized as for density, viscosity and surface tension. The size and concentration distributions of the particles were measured utilizing a TSI Scanning Mobility Particulate Sizer, SMPS, and the sampling was directly performed in the aerosol cloud. The results showed that, as expected, the increase of the saline solution concentration caused an increase in particle mean diameter. Also, and less obvious, it resulted in an increase in the number of particles. The results, when compared to theoretical prediction, indicate that particle formation and deposition after atomization is responsible for this phenomenon.

Abstract: Containerless solidification of Bi32.5In51Sn16.5 eutectic alloy under microgravity conditions was investigated by using a 3 m length drop tube. The Bi-In-Sn system is an important material for lead-free solder and fuse element for electrical protection. It has a low eutectic melting temperature of 60°C, which is suitable for experiments in restricted environments like the International Space Station (ISS), where the security requirements are very strict. Droplets, with diameters in the range of 200 to 400 m, solidified under microgravity, were obtained consistently with irregular ternary eutectic structure, whereas, previous results under normal gravity presented both regular lamellar and irregular structures.

Abstract: The pyrolysis kinetics of sugarcane bagasse in nitrogen flow was studied by thermogravimetric analysis from room temperature to 1173 K at different heating rates (1.5, 3, 5, 10, 15, 20, 30 and 50 K/min). As there are three distinct devolatilization peaks in the DTG curve, each peak was associated to thermal decomposition of an individual biomass subcomponent (hemicellulose, cellulose and lignin). The kinetic model adopted was a consecutive reactions model. The kinetic parameters of the pyrolysis process, such as activation energy and pre-exponential factor, were calculated by least squares non-linear method and Scilab are used as the simulation tool. The simulated results showed a good agreement with the experimental data and the parameters found are similar to reported by the literature.

Abstract: Stearic acid is treated in a DC Ar-O2 plasma created by a cathode-anode confined system. The influence of the most important process parameters (gas flow rate, sample temperature, output power and exposure time) on the acid modification is studied. The evaluation of the influence of these parameters on grafting and etching of stearic acid was done by measuring the mass variation rate (MVR). The results show that when charged and chemically active species increase in density, what is directly connected with plasma parameters, the MVR increases too. In all experimental conditions, a negative MVR was obtained, due to the etching of the sample. The etching rate decreases with processing time, probably because of the formation of a product which is more resistant to plasma etching.

Abstract: Currently, new and uncommon materials are being more used in automotive components, such as the manufactured by Powder Metallurgy due to new cost reduction strategies adopted by carmakers. The companies are searching more and with stronger aggressiveness the ways of finding cost reduction opportunities of a product and/or process. With this intention and for being it tracked by technical and commercial interests, new departments are being created with different names and structures. The ways to find out a reduction of viable cost are discussed in different ways of approaching of this question, which may be originated from the standardization of an item utilized in similar products, in the removal of components with questionable importance, in the change of manufacture processes, in the localization of items and finally, in the change of material and/or project. Starting from known approaches, the present work relates the most different ways of proposals and characterizes and quantifies them in graphical forms, adopted procedures, and by descriptions of ways pursued to reach a financial goal of reduction, mentioning typical examples of proposals with potential of implementation after a technical and critical analysis. Finally, the focus of this study is the approach of materials and specifications, said currently as the most complex and difficult field; however, with inexhaustible ways in the last instance in the field of Cost Reductions, and then the acquired knowledge should be used in sintered material.

Abstract: - Ferromagnetic stainless steels (SS) produced by powder metallurgy (PM) techniques have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. Two SS were investigated: SS 17-4 PH produced by powder injection (PIM) and SS PM2000 obtained by mechanical alloying. In vitro cytotoxicity analysis of the two SS showed no cytotoxic effects. The magnetic retention force of both tested SS was also evaluated and they were comparable to noble commercially available material that is in use at the moment. The corrosion resistance of both SS was evaluated by electrochemical techniques in sodium phosphate buffer solution (PBS) at 37°C. The AISI 316L SS was also tested under the same conditions for comparison reasons. SS samples tested showed passive behaviour in the electrolyte, but they also presented susceptibility to pitting. The best pitting resistance was associated to the PM2000 whereas the 17-4PH PIM showed the highest pitting susceptibility among the tested steels. The results pointed out that the PM2000 SS might be considered a potential candidate for substitution of high cost magnetic alloys used in dental prosthesis.

Abstract: The use of pressed and sintered aluminum, obtained by the powder metallurgy route, to produce large quantities of near-net-shaped components is increasing rapidly in the automobile industry. The production of lightweight pieces of Al by powder metallurgy has attracted increasing attention due to its unique properties. Sintering helps develop mechanical strength and other properties in commercial alloys obtained by powder metallurgy. Sintering of Al can be achieved only upon formation of a liquid phase capable of destroying the extremely stable oxide layer on the surface of the Al particles. The aim of this investigation was to analyze the effect of compaction pressure on sintering of atomized ASTM 2124 type alloy. Powder characterization was carried out using scanning electron microscopy (SEM). The specimens were axially compacted at pressures of 500, 600 and 700 MPa. Differential scanning calorimetry (DSC) was carried out to determine the sintering temperature of the alloy powder. The specimens were sintered at 570° C. Characterization of the sintered material consisted of density measurements and optical as well as SEM examinations. Nevertheless, even the low recycling cost of Al , what increases its useful time and stabilizes its value, the large amount of energy required to obtain it reduce its application.