Papers by Author: Adilson Luiz Chinelatto

Abstract: Triaxial ceramics are multiphased materials produced from natural raw material. That a small modification as much concerning in the composition from raw material a ceramic mass, may change several properties from ceramics. Thus, was included into the ceramic mass Al₂O₃ and Fe₂O₃, however both originated from pectin citrus plus salt the intended respective metal source. These oxides have a particular physical characteristic as high softness and high porosity. In addition to the ceramic mass containing 10% of clay, 25% kaolin, 35% feldspar and 30% of alumina (Ind. Alcoa) was inserted 6% of Fe₂O₃ and the full replacement of commercial alumina by Al₂O_3(pec). The result from these oxides are satisfactory mainly. Influencing in thermal contraction, in the reduction of the residual porosity and changing the final color inthe product.

Abstract: Structural ceramics, such as alumina, are widely used in industrial applications due to their properties such as hardness, chemical resistance and thermal stability in high temperatures. However, low fracture toughness has limited applications of these materials. One way to overcome the low fracture toughness is to control the microstructure, seeking a refined and homogeneous microstructure. In this way, the aim of this study was to investigate the effect of unconventional methods sintering based on two steps and microwaves sintering methods on the microstructure of a commercial alumina ceramic. From two-steps sintering method, the samples are first heated to a high temperature and then cooled down to a lower than one temperature to suppress grain-boundary migration. Ceramics obtained by microwave sintering method were produced after 1100, 1300 and 1350°C for 1 hour. The microwave heating method reduces the time and temperature processing, which results in energy saving. The sintered samples were characterized by apparent density, scanning electron microscopy and measurements of grain size. The results showed that two-steps sintering and microwave were effective to control the microstructure of alumina and that in two steps sintering it is essential to control the sintering steps to inhibit grain growth.

Abstract: Ceramic materials have limited use due to their brittleness. The inclusion of nanosized particles in a ceramic matrix, which are called nanocomposites, and ceramic processing control by controlling the grain size and densification can aid in obtaining ceramic products of greater strength and toughness. Studies showed that the zirconia nanoinclusions in the matrix of alumina favor an increase in mechanical properties by inhibiting the grain growth of the matrix and not by the mechanism of the transformation toughening phase of zirconia. In this work, the microstructural evolution of alumina nanocomposites containing 15% by volume of nanometric zirconia was studied. From the results it was possible to understand the sintering process of these nanocomposites.

Abstract: Two-step sintering has been able to produce fully dense bodies and with controlled grain size, without pressure during sintering. In this study, it was studied the sintering behavior of alumina-5% vol zirconia powders submitted to high energy milling. For this, the mixture of 5% vol of Y₂O₃ partially stabilized zirconia and 95% vol alumina powder was performed by high-energy ball milling (Spex 8000) with a ball ratio: mass of material at 7:1, in a steel vial with balls of steel, in milling times from 0 to 7 hours. The milled powders were characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD). After milling, the powders were uniaxially pressed and two-step sintered with heating at a temperature of 1500 oC for 5 minutes, cooling until 1450°C and then sintering at this temperature for 2 hours. The sintered composites were analyzed by X-ray diffraction, apparent density and scanning electron microscopy. The results were compared with the conventional sintering and showed that the microstructure of the nanocomposites appears more refined and homogeneous when they are sintered in steps.

Abstract: Green sand molds are used in metal casting process. However, after heating, activated bentonite present in green sand loses the binding properties, and part of the foundry sand has to be discarded from the process. The ABNT NBR 15.984/2011 standard establishes the management of waste foundry sand (WFS) avoiding disposal in landfills. The objective of this work was to investigate the possibility of reusing the WFS from the study of its interaction with sodium silicate binder. Studies with silica sand and new green sand were performed in order to compare the results obtained with the WFS. The characterization of the samples was performed by measuring compressive strength, by X-ray diffraction, by optical microscopy and by scanning electron microscopy. The results showed that there is an interaction of the sodium silicate with the WFS as well as with the silica sand and green sand.

Abstract: The aim of this study was to obtain 4.5%mol Y₂O₃-doped ZrO₂ dense with submicrometer grain size and studying the effects of using oxygen flow during calcination in the electrical properties of bodies sintered. The powders were synthesized by the Pechini method. After synthesis, the resins were dried and the calcinations were performed in air and in oxygen flow at 600°C for 2 h. The powders were pressed with 1600 MPa and sintered by Two Step Sintering (TSS) at 1500°C / 5 min and 1200°C, 1300oC, 1400°C, remaining at these temperatures for 2 and 10 hours. The sinterized samples were characterized by X-ray diffraction, apparent density, scanning electron microscopy and impedance spectroscopy. The apparent densities were greater than 94% for all conditions of calcination and sintering. The value of the activation energy was 0.7eV for the grain and 0.9 eV for the grain boundaries.

Abstract: The solid oxide fuel cell are an alternative of production clean and efficient energy, because converts chemical energy in electrical energy. A fuel cell is formed basically by an electrolyte, a cathode and an anode. The main electrolyte used for SOFC manufacturing is the ZrO₂-Y₂O₃. The materials for electrode manufacturing must possess thermal expansion characteristics close to electrolyte and have high electrical conductivity in operating temperature. Recently, the perovskite LaNi_0,6Fe_0,4O_3-δ, has attracted interest for application as cathode in SOFC ́s for has a high electronic conductivity and a thermal expansion coefficient whish for the zirconia electrolyte. This work aimed to LaNi_0,6Fe_0,4O_3-δ obtained by Pechini method. The powders were characterized by differential thermal analysis, thermogravimetric analysis, x-ray diffraction, energy dispersion X-ray fluorescence spectroscopy, helium pycnometry and scanning electron microscopy. The results showed powders obtained with perovskite formation when calcined 600°C during 2 hours.

Abstract: The traditional Ni-based anodes are capable of providing a good power output using H₂ and CO fuels, but sulfur contamination in any hydrocarbon fuel is a problem. Thus, perovskite structure materials containing lanthanum have been widely studied as electrodes for solid oxide fuel cells (SOFCs), due to its electrical properties. In this work was investigated the obtain of the perovskite structure LaCr_0.5Ni_0.5O₃, by Pechini method, and its suitability as SOFC anode. The choice of this composition was based on the stability provided by chromium and the catalytic properties of nickel. After preparing the resins, the samples were calcined at 300oC, 600oC, 700oC and 850oC. The resulting powders were characterized by X-ray, X-ray fluorescence spectroscopy, He pycnometry, specific surface area by BET isotherm and scanning electronic microscopy. The obtaining of the powders of LaCr_0.5Ni_0.5O₃ through the Pechini method proved to be effective for temperatures above 850oC.

Abstract: Alumina has been studied as a substitute for quartz triaxial porcelain formulations, but the high cost of the alumina raises the cost of production. The use of aluminum hydroxide from the Bayer process for obtaining aluminum, a source of alumina, is an alternative to alumina. In this work we used two aluminum hydroxides to replace the quartz composition of triaxial porcelain. The raw materials used were characterized by analysis of particle size distribution, scanning electron microscopy, diffraction and X-ray fluorescence. The compositions sintered were characterized by apparent density, apparent porosity, water absorption, flexural strength, and X-ray diffraction and scanning electron microscopy. Both the total and partial replacement of quartz by aluminum hydroxide showed good results with high flexural strength, low water absorption and low porosity.

Abstract: The microstructures of solid electrolytes play an important role in the level of ionic conductivity of these materials. Thus join the mechanical properties of partially stabilized tetragonal phase and the ionic conductivity displayed by the large area of the grain boundaries of polycrystalline zirconia nanometric is an advantage. The objective of this work is to study the densification of ultrafine particles of yttria stabilized zirconia in the tetragonal phase (Y-TSZ) obtained by chemical routes using the unconventional method of sintering the Two Steps Sintering (TSS). The nanocrystalline powders Y-TSZ (4.5 mol%) were prepared by Pechini method and were characterized by X-ray diffraction and scanning electronic microscopy (SEM). The powders were pressed and sintered per TSS. The density of sintered samples was measured by Archimedes method, the crystalline structure was determinate by X-ray diffraction and the grain size and microstructure were observed by SEM. The TSS prevented the grain growth keeping your submicrometer grain size.