Abstract: The main purpose of this paper is to present a spray dryer device developed to synthesize ammonium niobium-oxalate precursor powder with controlled grain size. The dryer device is manufactured using stainless steel 304 and measures 0,48m in outside diameter and 1,9m in height. The spray dryer has a cylindrical shape assembled on a conical base. The central chamber is heated by three 4 KW resistances and is equipped with serpentine coil heaters placed around its main body. This configuration guarantees that the air is at the same temperature of the chamber walls and the adherence of the powder particles on the wall is prevented. The precursor solution is atomized on the air stream downwards from the top to the bottom, at low rates. Powder particles are collected on a 0,4m diameter horizontal plate placed at the bottom portion of the dryer and the wet air is released from the chamber by the opening located under the collecting plate. The synthesis of the niobium oxalate precursor and the results of the decomposition process are described.
Abstract: A complete description of the parts of a centrifugal atomizer, with geometries and dimensions are shown. Tests of atomization were carried out by using pure tin metal in air atmosphere. Mathematical simulation of the thermodynamics of the process was successful to describe the centrifugal atomization, showing a maximum experimental correspondence mismatch of 14%.
Abstract: This work aims at the study of the behavior of the powder systems Fe-Cu e Fe- Cu-Diamond under compaction, using the stoichiometries Fe-20Cu (wt%) e Fe-20Cu-4 Diamond (wt%). It was applied pressures at the interval 100 to 600 MPa, and it was used the Balshin and Rong-De’s equations to establish the exact behavior of the systems under pressing: accommodation, plastic deformation and particle’s rearrangement.
Abstract: The deposition of Sn-5wt.%Al alloy onto pure aluminum powder in its self-convective motion by magnetron DC sputtering was examined in order to prepare Al-Sn composite particles, aiming not only at the development of highly uniform sintered binary compact materials but also at the improvement of the bonding between the aluminum particles after sintering at low temperature such as 250°C. The self-convection phenomenon of the aluminum powder in the vacuum chamber occurred when a perpendicular vibration was applied to the powder. The sputter-deposition of the Sn-Al alloy was carried out during the self-convection of the aluminum powder. Under SEM and according to EPMA analysis, as well as according to thermal analysis with DSC, it was confirmed that the obtained particles were coated with the Sn-Al deposits. Therefore it was found that Sn-Al composite powder could be produced by this processing, and thereby not only the development of highly uniform sintered binary compact materials but also the improvement of the bonding between the aluminum particles after sintering at low temperature were expected.
Abstract: Explosion study in an iron powder reduction furnace was performed. Pressurized gaseous hydrogen was used as reductive atmosphere to convert iron powder in the interior of the furnace. Hydrogen was fed to the pre-chamber of the iron powder reduction furnace. The furnace was located inside a brick building. Explosion potential causes were determined by the fault tree technique. The impact effects to people, environment and materials were also analyzed by using Chem-Plus software. The consequences and vulnerability analyzes were performed considering a confined explosion inside the furnace pre-chamber, resulting from formation of a hydrogen cloud within the H2 explosion limits. The vent area criteria recommended by NFPA 68 to confined spaces were employed to the reduction furnace and to the vulnerability calculations; probit equations of the Eisenberg model were used. As results, safety measures to enhance safety on the reduction of iron powder operation inside the furnace installation were recommended.
Abstract: Abstract: Titanium and titanium alloys present the highest biocompatibility among metallic biomaterials. The ideal titanium alloy for orthopedic applications should have low modulus of elasticity (near the bone), excellent mechanical strength, high corrosion resistance, formability and no potential toxic elements. Among titanium alloys, the Ti-35Nb-7Zr-5Ta alloy, due its high biocompatibility and lower Young’s modulus is a promising candidate for implants material. The titanium alloys production by powder metallurgy, starting from the elementary powders, is a viable route due at the smaller costs and larger operational facilities. The Ti-35Nb-7Zr-5Ta samples were manufactured by blended elemental method from a sequence of uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 at 1700 °C, in vacuum, under a heating rate of 20 °C×min-1 for 1h. The objective of this work is the analysis of alloy microstructural evolution from the powders dissolution under the increase of the sintering temperature. For the alloy microstructural characterization, scanning electron microscopy and Vickers microhardness measurements, were used. Density was measured by Archimedes method. The samples presented high densification, an homogeneous microstructural development, with complete dissolution of alloying elements in the titanium matrix with the temperature increase.
Abstract: With the prolonged average duration of life, there is an increase concern for repair of bone, joints and teeth which deteriorated and lose their functions. Thus, research of artificial materials for implants has assumed an important role in the implants development. The trend of the current research in orthopedic implants is based in the development of titanium alloys with low modulus of elasticity, next to the bone, and toxic elements free. In this work, results of the Ti-13Zr- 13Nb alloy sintering are presented. This alloy due its high biocompatibility and lower modulus of elasticity is a promising candidate for implants fabrication. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 800 at 1500 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. It was shown that the samples were sintered to high densities and presented homogeneous microstructure from the elements dissolution. Processing parameters were optimized in order to reduce the interstitial pick-up (O, C, N and H) and to minimize grain growth during sintering.
Abstract: The behavior of an isothermal and non-reaction solid-liquid system can be model using a mathematical model based on the Mixtures’ Theory of Continuum Mechanics. The knowledge of the constitutive equations of this phenomenon, as pressure on the solids and medium permeability, is very important in the design and performance evaluation of the continuous thickeners or filters. In this work the batch sedimentation phenomena of a kaolin aqueous suspensions was investigated. The technique consists on measuring of the gamma rays attenuation when they cross the physical media as a function of the local concentration at several vertical positions in a reservoir. Using the experimental data and local concentration as a function of the attenuation curve, it is possible to determine the constitutive equations. The results were satisfactory, allowing simulations of this phenomenon for steady and transient regimes in future papers.
Abstract: The alpha-beta Ti-5%Al-2.5Fe (wt-%) alloy was developed as a cost-effective option to replace the traditional Ti-6%Al-4%V alloy in the manufacture of surgical implants because of its larger biocompatibility (V-free alloy). Samples of this alloy were prepared using the blended elemental (BE) technique. The isochronal sintering of the cold pressed compacts was carried out at 700, 1000, and 1400°C in vacuum. In this work, the preliminary results of the behavior of elementary powders during sintering and the corresponding microstructural evolution are shown. The alloy was characterized by means of scanning electron microscopy (SEM) in the backscattered mode, X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), and density measurements. The results indicate that the homogenization of the alloy is diffusion-controlled. Non-equilibrium Ti-Al phases as well as Fe-Al compounds were identified in samples sintered at lower temperatures (700oC). With increasing temperature, homogenization of the alloy takes place and a structure consisting of coarse plate-like alpha and intergranular beta is present.
Abstract: The determination of the grade distribution of solid particles is fundamental for the performance analysis of several pieces of equipment promoting the solid-fluid separation. The main objective of this work is to compare the results obtained for two traditional methodologies for determination of the sized grade distribution of powdery solids: the gamma rays attenuation technique (GRAT) and LADEQ test tube technique. The influence of draining of suspension in the two used techniques was also analyzed. The gamma rays attenuation technique can supply the grade distribution of solids through the monitoring of solid concentration in experiments of batch settling of diluted suspensions. The results show that the usage of the peristaltic pump in GRAT and LADEQ methodologies presented a significant difference among the values obtained for the parameters of the particles size model.