Materials Science Forum Vols. 660-661

Abstract: Polycrystalline SiC-diamond composites have been fabricated by high pressure and high temperature, HPHT, sintering conditions using a Si infiltration method. However, infiltration of liquid Si around the diamond particles results not only in SiC but also in free Si, which causes deterioration of the composite properties. In this work, a novel sintering procedure was developed to avoid the formation of free Si in the composite structure. A disk composed of a mixture of graphite and Si was first press-molded at room temperature. The disk was then placed above the diamond powder inside a high pressure chamber used for the HPHT sintering process. This arrangement permitted to preferentially form liquid SiC, which infiltrates in between the diamond particles. Using this procedure, free Si formation is inhibited and the SiC-diamond composite forms a rigid structure with improved properties.

Abstract: The spray forming technology combines in a single step the advantages of the rapid solidification techniques and high the productivity of the conventional casting processes, allowing obtention of preforms with a refined microstructure, almost without porosity and macrosegregation free. The development and research efforts are leading to interesting alloys and materials production. The rapid solidification processes inherent to the spray forming allow the production of alloys with different compositions from those obtained by conventional ingot processes. The aim of this work was to carry out mechanical properties characterization of a spray formed AA-6082 alloy. The hardness results are presented in different sections related to the height of the spray formed preform (in a three-dimensional arrangement). The material was evaluated in the as sprayed formed condition and after heat treatments of solution at 525 °C for 1 h and aging for 1 h, 10 h, 100 h and 500 h periods at 125 °C. It is showed that the spray formed AA 6082 aluminum alloy is very stable regarding hardness variation during aging.

Abstract: Gas cyclone separators are widely used in industrial processes for separation of dust from gas streams or for product recovery. Their design normally has tangential entrance inlets and the cyclones are defined as funnel-shaped industrial inertial devices. Cyclones are particularly well suited for high temperature and pressure conditions because of their rugged design and flexible components materials. Cyclone collection efficiencies can reach 99% for particles bigger than 5 μm, and can be operated at very high dust loading. One of the aims of this research was simulate, through computational fluid dynamics (CFD), the operation of the cyclones with different geometrics and to analyze the influence its different geometrics in the performance of the cyclones. The numerical solutions were carried out using commercial CFD. A two-dimensional computational fluid dynamics (CFD) Reynolds stress model (RSM) was used to describe the gas–solid flow in cyclones.

Abstract: The new environmental laws, as well as the search for technologies of accuracy production, have leaded companies to search for more and more efficient equipment. Regarding the emission of particulate material, the fabric filter is the most used equipment in the industry, for presenting a high efficiency and low operational costs, essential in any project of this type. In the search for a more efficient and economic filtering operation, this work studied, by techniques of CFD, the modification of the traditional way of feeding a filtering box (usually accomplished by the side of the system) by another in which the feeding was accomplished through the bottom of the equipment, in order to review the distribution of volumetric outflows in the bags and pressure drop. The fluid dynamic simulations had shown that the feeding fluid - through the bottom of the filtering box - provides an inferior operational pressure drop and a better distribution of fluids between the bags.

Abstract: Hydrocyclones are centrifugal devices widely used in chemical industries and they are used to the solid or liquid particles separation of a fluid according to the density and size distribution of the dispersed phase. In order to maximize the separation in these devices, this work had as objective to study the influence of the filtration during the process of separation in hydrocyclones. Thus, experimental data were used to predict the behavior of a hydrocyclone having a porous cylinder in the same operating conditions of a conventional hydrocyclone (impermeable cylinder). The experimental studies showed that the filtration interferes directly in the performance of the separator, so the filtering hydrocyclone required a higher pumping power. Moreover, the experimental data also indicated that the presence of the porous cylinder in the hydrocyclone was able to increase the number of dragged particles in the underflow, increasing therefore the efficiency of separation.

Abstract: Orifice Meters are mechanical devices used to measure gases and liquids flows. Due to manufacturing, installation and operation simplicity, the orifice meters are widely used in the industrial processes in which there is flow of gases or liquids. Moreover, their acquisition and operation costs are smaller than the ones verified for other flow meters (Venturi, flowmeter). However, before the utilization of any calibration orifice meters, they demand an experimental calibration procedure. Thus, in order to suppress this laborious experimental procedure, this work objectified to apply computational fluid dynamics techniques (CFD) to numerically predict the Calibration Coefficient of the orifice meter. The adopted numerical methodology was able to satisfactorily predict the discharge coefficients, presenting an economic alternative when compared to traditional experimental approaches.

Abstract: A Pease-Anthony Venturi scrubber is a relatively simple and very efficient device used for gas cleaning. This paper presents photographic images of the atomization of a liquid jet in the throat of a Pease-Anthony Venturi scrubber, obtained through the development and use of an electronic flash of short duration. This new evidence was used to improve the parameters of the model of Gonçalves et al. (2000) [1]. The experimental conditions used were: throat gas velocities between 59 and 74m/s, jet velocities between 3.18 and 19.10m/s and liquid injected into the throat through different orifices.

Abstract: Zeolite ZSM-5 have been synthesized by hydrothermal method, using tetrapropylammonium bromide as template. This work aims to evaluate the preparation and characterization structural and morphology of zeolite ZSM-5 resulting in a pure and crystalline material. The ZSM-5 zeolite was prepared by hydrothermal synthesis at 170 °C, using silica, deionized water and structure-directing salt (tetrapropylammonium bromide-TPABr). Several techniques like X ray diffraction (XRD), scanning electron microscopy (SEM) and X ray energy dispersion spectrophotometer (EDX) have been utilized to characterize the framework structure and morphology of the sample. Obtaining ZSM-5 zeolite could be confirmed by X ray diffratograms. The result X ray diffraction showed that the synthesized sample presented typical peaks of the ZSM-5 zeolite. According to the XRD, it is possible to observe intense and well defined peaks. The acquired X ray patterns identified the product as highly-crystalline materials, without the presence of impurities. From the images obtained by SEM, it was possible are composed of showed that the crystal accumulations of ZSM-5 zeolite, without the presence secondary phases on the crystals.

Abstract: The Venturi scrubber, equipment frequently used in the removal of particles from gases, is constituted basically by a duct with a convergent section followed by a constriction, or throat, and a divergent section. A liquid, usually injected in the throat, is atomized by the flowing air at high speed. The formed droplets act as collectors of particles from the gas. The process of droplet formation from an injected liquid can be described as follows: the liquid enters the gas stream in the form of a jet, perpendicular to the gas flow. As the jet penetrates the gas stream, it is bent by the gas drag. After a given penetration distance, a burst occurs, and the remaining jet is disintegrated as a droplet cloud. Depending on the liquid and gas flow rates, the penetration on the jet into the gas stream may reach the walls of the equipment, and a fraction of liquid deposits in the form of a film. This film contributes little for the removal of particles from the dust laden gas. Few studies have analyzed the formation of film at the scrubber walls and its influence in the droplet size inside the Venturi scrubber. For this reason, the present study is focused on the experimental measurement of the deposition of the liquid film on the walls of a rectangular Venturi scrubber and, simultaneously, the estimation of the droplet size measured in the Venturi throat. The experiments were carried out varying the liquid flow rate, the gas velocity and the number of orifices of liquid injection. A correlation, using a dimensionless number, was proposed to quantify the influence of each experimental condition. The results indicate that film fraction has a significant influence in the droplet size measured inside of Venturi scrubber.

Abstract: Froth flotation is an adsorptive-bubble separation method based on the selective attachment of particles on the surfaces of gas bubbles passing through a suspension. Reagents as collectors, frothers and pH modifiers are added to perform specific roles to facilitate and to improve the separation. In the present work the process of apatite flotation in column has been investigated experimentally. The influence of the reagents (collector and frother dosages and interactions), percentage of solids and pH value on the column flotation of coarse particles of apatitic ore was analyzed. Percentage of solids was the variable that more influenced on the apatite recovery and the P2O5 grade was more affected by varying pH. The best results were achieved by using lower pH values and lower pulp density. Frother addition only had significant effect for lower collector dosage.