Materials Science Forum Vols. 591-593

Abstract: The interest in porous ceramics has increased concurrently with new processes and new applications. This material has been used in several industrial applications such as filters, catalysis and sensors. The objective of the present investigation was to produce porous alumina with 3 % mol yttria stabilized zirconia in tetragonal crystalline structure (Y-TZP). This material will be used in cooling systems of satellites, due to its mechanical properties and chemical inertia. To obtain the porous ceramics was used the direct foaming technique, which is a method based on the preparation of a stable foam slurry and a slurry of alumina and zirconia that are later mixed and blended for incorporation of air in the mixture. The sintered ceramics was characterized by scanning electronic microscopy, mercury porosimetry and permeability measurements. The porous Al2O3–ZrO2 ceramics obtained showed high porosity and uniform microstructure with 20–100 ,m open pores. The results from these alumina zirconia composites showed a potential to apply in heat pipes.

Abstract: A procedure that comes being studied for the exploitation of powder waste rejected from the sanitary ware production is the incorporation in mass for red ceramics. Objective of this work is to present the results gotten in the incorporation of this rejects. The used clay was from ceramics industries of the Jundiai region, SP. Spherical bodies test samples had been conformed incorporating 1%, 5%, 10%, 20% and 30% of the powder waste in mass. These bodies had been evaluated on compression resistance after dried to 110°C and to color after burns to 950°C. The composition that presented better results had been conformed by extrusion in prismatic bodies test samples. Again, the dried to 110°C and burnt to 950°C bodies test samples had been evaluated on flexion resistance but to linear retraction too. It was measured the ceramic properties of the burnt bodies test samples. Results indicate that there is a great potential in the formula with 30% incorporation of powder waste in mass. Comparative assays were made being used a mixture without incorporation of the denominated white reject.

Abstract: Microstructures and chemical compositions of some commercial La-Mg based alloys have been investigated. The hydrogen storage alloys can be represented by the formulae La2Mgx, La2Mgx-1Ni and LaMg2Ni9 (x=12 or 17). The determination of the microstructures and phase compositions of these alloys has been carried out using scanning electron microscopy and energy dispersive X-ray analysis.

Abstract: Sintered magnets have been produced with powder obtained using the hydrogenation, disproportionation, desorption and recombination process (HDDR). The new processing procedure for the production of the sintered magnets has been adopted in an attempt to reduce the milling time. Commercial cast ingot alloys based on the compositions Pr14Fe75.9Co4B6Nb0.1 and Pr20.5FebalB5Cu2.0 have been employed in this investigation. The HDDR powder was used to produce sintered magnets using a mixture of these alloys, in very distinct proportions. Only a small amount (20 wt. %) of the copper-containing alloy has been added as a sintering aid. Standard hydrogen decrepitation (HD) magnets have also been included in this work for a comparison. The effect of a reduced milling time on the magnetic properties of the HDDR sintered magnets has been investigated. Sintering temperature and time of were kept constant for all magnets (1050°C for 60 minutes). The microstructures of the permanent magnets have been investigated by scanning electron microscopy and energy dispersive X-ray analysis.

Abstract: It is discussed the difference between the magnetic reversal mechanisms: i) coherent rotation, ii) nucleation, iii) unpinning of domain walls. The main argument to suggest pinning as the coercivity mechanism of Sm(CoFeCuZr)z magnets is the low initial susceptibility of magnetization curves of thermally demagnetized magnets. However, coherent rotation also implies in low initial susceptibility, since the grain size of the magnets is near the single domain particle size. It is unlikely that pinning could be the coercivity mechanism in this case, since the anisotropy field of Sm2Co17 phase is 65 kOe, whereas the coercivity of magnets can be higher than 40 kOe. Such coercive field of 60% of the anisotropy field indicates coherent rotation as mechanism. A model for describing the abnormal coercivity behavior in Sm(CoFeCuZr)z magnets is proposed.

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 size and the size distribution of the droplets inside the equipment are therefore of great importance in the equipment performance. In the present work, the liquid jet penetration is visualized and the study of the droplet formation in a rectangular Venturi is carried out. The liquid injection is made through multiple orifices and the interaction of multiple jets is taken into account. In the experimental tests, the gas velocity in the throat, the liquid flow rate and the number of orifices for liquid injection were varied. A Malvern Spraytec aerosol analyzer was used for measuring of the droplet size and size distribution. The results showed that the liquid jet penetration influences significantly the size of the formed droplet.

Abstract: The electrostatic precipitator (ESP) is usually employed by industries for the removal of aerosol particles from gaseous streams. The behavior of the particles inside the collection duct is of great interest as a tool for optimizing precipitator design and performance. In this work, a laboratory scale ESP (0.6m long, 0.3m high and 0.2m wide) was tested with electric fields of 250, 350 and 450 kV/m at a gas velocity of 1.0 m/s. The discharge electrode was located at 0.30 m from the beginning of the collector plate. The test aerosol was constituted of a phosphatic concentrate dispersed in air. Particles were sampled isokinetically in situ in the duct, at five different longitudinal positions. The experimental results for the aerosol studied show that concentration profile of particles are affected by the electrical field at considerable upstream distances from the charging electrode. The particle collection starts well before the charging electrode, characterizing a strong entrance effect, often disregarded in the existing correlations for predicting ESP performance.

Abstract: There is considerable industrial potential for aluminium alloys and aluminium metal matrix composites fabricated via net shape press-and-sintering powder metallurgy using low-cost, elemental premixed powder. In this work, the compressibility and sinterability of premixed Al– 4.5Cu–0.7Si–0.5Mg powder alloy reinforced with Al2O3 particles was analyzed. The powders reinforced with increasing ceramic particle content were cold-pressed under increasing pressure and sintered at 600 oC for 40 minutes, in nitrogen atmosphere. The powders showed the typical compressibility curves and the presence of hard ceramic particles decreased the powder deformation capacity and, consequently, the powder compressibility. The sintering produced swelling of the parts, due to the poor wettability of liquid phase on the aluminium particles and to the Kirkendall effect caused by the difference in diffusivity of aluminium in copper and copper in aluminium. The presence of Al2O3 particles increased the swelling during sintering probably due to the sooner formation of liquid phase.