Materials Science Forum Vols. 591-593

Abstract: Titanium is an attractive material for structural and biomedical applications because of its excellent corrosion resistance, biocompatibility and high strength-to-weight ratio. Power metallurgy was used in this work to prepare 3D porous titanium. The powders became fragile from hydrogenation process and were able to be used to obtain compacts with different porosities by uniaxial pressing and sintering without applied pressure. Since hydrogen dissolves easily in titanium to form titanium hydrides which have a strong influence on the microstructure coarsening and mechanical properties, the study of the porous compacts hydrogenation was carried out by hydrogenation at different temperatures (870 K up to 1070 K) in a hot filament reactor. Titanium surface morphology changes were investigated by scanning electron microscopy. High resolution x-ray was used to characterize the present phases. Evaluation of the porous titanium hydrides mechanical behavior was realized by flexion assay performed at three points.

Abstract: Sintered stainless steel has a wide range of applications mainly in the automotive industry. Properties such as wear resistance, density and hardness can be improved by addition of nanosized particles of refractory carbides. The present study compares the behavior of the sintering and hardness of stainless steel samples reinforced with NbC or TaC (particles size less than 20 nm) synthesized at UFRN. The main aim of this work was to identify the effect of the particle size and dispersion of different refractory carbides in the hardness and sintered microstructure. The samples were sintered in a vacuum furnace. The heating rate, sintering temperature and times were 20°C/min, 1290°C and 30, 60 min respectively. We have been able to produce compacts with a relative density among 95.0%. The hardness values obtained were 140 HV for the reinforced sample and 76 HV for the sample without reinforcement.

Abstract: Atmosphere control in a continuous sintering furnace is one of the most important variables in a successful sintering process. This statement becomes even more weight when sintering of high chromium containing powders at elevated temperatures is applied. Depending on the sintering atmosphere, de-carburization at the surface of a product is almost impossible to avoid. The production of more highly loaded PM parts by sintering requires higher sintering temperatures, which in turn increases the need for controlling the carbon level, and limiting surface decarburization. One way to control the carbon level is to add CO to the sintering atmosphere and increase the carbon activity of the atmosphere. This idea has been used in conventional carburizing for decades. But is it applicable for sintering processes at temperatures up to 1250°C The presented paper shows results of tests on Astaloy CrM bodies with additions of up to 0.6% carbon that were sintered at 1250°C in carbon monoxide containing atmospheres with and without hydrogen additions. Finally, an outlook of how this technology could be implemented in industrial scale sintering furnaces will be given.

Abstract: Hardmetal alloys are processed by liquid phase sintering, which consist of one refractory carbide, embebided in to a tough matrix of Co. These alloys extensively are used in applications that demand abrasion resistance and high hardness. The present work has as objective to analyze the sintering of ultrafine powders of tungsten carbide (WC) with the addition of 10%wtCo. The alloys had been prepared by using high pressure and high temperature technique. The sintering of the WC/10%pCo alloy was processed at the 3, 4 and 5 GPa, in temperatures of 1300,1400 and 1500°C, during 2 and 4 minutes. The analysis was made by microstructure, densification, structure, Vickers hardness and fracture toughness. The best results was density = 98.9%, hardness HV30 =10,77GPa and fracture toughness KIC = 15,57 MPa.m1/2.

Abstract: Silicon-iron alloys with silicon content about 6.5wt.%Si offer a great potential for applications aiming reduction of core loss in electric parts. Deposits of the Fe-6.5wt%Si alloy produced by spray forming were annealed at temperatures between 400 and 1300oC, during 1h in vacuum. The grain size has a great importance to the magnetic properties. In the present work, it was analyzed the influence of the metallography parameters in order to get the best accuracy to determine the grain size according to ASTM 112-96. Chemical composition, time and temperature of specific etchings were modified and tested in different conditions of observation in light microscopy. Bright field, polarized light and dark field were used in the samples aiming to measure the grain size. The best etchings were Nital 10% and Marshall, both at room temperature. The results of grain measurement are presented in their relationship with the magnetic properties.

Abstract: The suspended particles in the air are a factor that causes chronic illnesses to the respiratory system, which go from allergy to severe pulmonary damage. Particulary, breathable particles (from 0,5 μm to 5,0 μm sizes) cause damages to the respiratory system. The penetration and the deposition are the reason for the damages to the pulmonary alveolus. The industrial activity is the main responsible for the most part of the breathable particles emission. Because of that, Venturi scrubbers have been incorporated to the industrial process due to their high efficiency for particle collection. Venturi scrubbers are gas-atomizing devices. They are mechanical devices which rely on shearing and impaction forces to break water into fine droplets. Those droplets in contact with the particles, will collected them. This work consists of a Venturi scrubber of circular section operating horizontally, with liquid injection through a single orifice located in the scrubber throat. The experiments will analyse the influence of the length throat, gas velocity, liquid flow and particles sizes on the Venturi´s collection efficiency.

Abstract: The particle circulation rate and gas–solid contacting efficiency are important parameters for the project of spouted beds, applied in many industrial processes. Due to the restrictions found in the identification of flow regimes through visual observation, new techniques have been developed to obtain a better gas and particle dynamics description, necessary for the evaluation of these parameters. One of these techniques has been the CFD simulation. In this work the pattern of solids and gas flows in a spouted bed was numerically simulated using a 3D Eulerian multiphase model. Soybean particles had been used in the attainment of data of pressure drop fluctuation and power spectrum as a function of gas velocity in an experimental apparatus. The 3D simulated solids volume fraction profiles allow the identification of the flow regimes showing a good agreement with the experimental data.

Abstract: The minimum fluidization velocity is an important parameter in the design and operation of an industrial unit of fluidization. In the present work the minimum fluidization velocities of fine particles were obtained through two experimental methodologies. The first one is the classic procedure to determine that parameter analyzing the diagram of medium pressure drop in the bed in function of the superficial gas velocity, during the defluidization of the bed. And the second is the technique of identifying the minimum fluidization velocity interpreting the behavior of the normalized standard deviation of the pressure drop in the bed. A cylindrical bed of transparent acrylic was used in the process and the used particles were glass spheres, FCC and zinc powder. To compare the precision of the two methodologies some equations that predict the minimum fluidization velocity were used.

Abstract: The filtering hydrocyclone is a solid-liquid separation device patented by the Chemical Engineering School of the Federal University of Uberlândia, which consists of a hydrocyclone whose conical section was replaced by a conical filtering wall. During the operation of these separators, besides underflow and overflow streams, the existence of a filtrate stream generated by the filtering process is found in the permeable conical region of the hydrocyclones. Vieira et al. (2006) got a filtering hydrocyclone that simultaneously presented low Euler Number and cut size diameter because its geometric relationships has been optimized. The objective of this work was to analyze the behavior of this optimized filtering hydrocyclone through computational fluid dynamics and experimental studies. In the same operational conditions of the conventional hydrocyclone, the performance of this optimized filtering hydrocyclone was significantly influenced by the filtration. The filtration caused decreases in the Euler number and increment in the total efficiency.

Abstract: The centrifugal technique was used to investigate the influence of particle size, applied compression and substrate materials (stainless steel, glass, Teflon® and PVC) on particle-surface adhesion force. Phosphate rock and manioc starch particles were used in a microcentrifuge that contained specially designed centrifuge tubes and reached a maximum rotation speed of 14,000 rpm. The profile of adhesion force followed a log-normal distribution and adhesion force increased linearly with particle size and the increment of the compression force. The manioc starch particles presented adhesion forces greater than those for the phosphate rock particles for all particle sizes studied. The glass substrate showed a higher adherence than other materials, most probably due to its hardness and polishing.