Materials Science Forum Vols. 498-499

Abstract: Among the industrial solid residues, the galvanic wastes have been received special attention, due to the nature of its components. These residues in general present a high concentration of alkaline and transition metals. When discarded or stored inadequately, they can be released for the environment, causing ecological and health damages. An interesting alternative to recycle those wastes is to remove them from the environment, through its incorporation in silicate glasses matrices. This work proposes the obtaining of amorphous structures, glasses or frits, from formulations with industrial solid galvanic wastes, with good chemical stability. A characterization study of the residue and primary materials, as commercial silica and feldspar and investigations about the formation of amorphous phases, galvanic wastes incorporation and chemical stability of the obtained products, were made. With these results, it was possible to formulate compositions that allow the obtaining of frits for ceramic enamels, with 23 % in weight of solid galvanic waste incorporated and good coating characteristics.

Abstract: CeO2- ZrO2 ceramics are considered a candidate material for applications as structural high performance ceramics. In this work are presented and discussed the tetragonal-to-monoclinic stress-induced transformation influence on the mechanical properties in these ceramics. Sintered ceramics were fabricated from powders mixtures containing ZrO2 and 8 to 14 CeO2 % mol. SEM observations were used to study de ceramic microstructures and X-rays diffraction to identification and determination of tetragonal and monoclinic phases. It was adopted the 4-point bending tests, Vickers surface hardness and fracture toughness technique to the determination of the mechanical parameters. The results showed that the mechanical properties were strongly dependent of the CeO2 content, the microstructure and the fraction of tetragonal-to-monoclinic stress-induced transformation.

Abstract: In Campos oil Basin (Brazil), which is responsible for more than 80 % of the national petroleum production, it is generated a great amount of wastes from deep crude oil extraction related activities. Particularly, the oil sludge waste has been intensely studied in order to search alternatives for the reuse of the waste in treated form in the ceramic industry. the present work focuses on the photoacoustic thermal characterization of sintered ceramic bodies containing up to 5 wt.% added waste. Specimens were uniaxially pressed at 25 MPa, and sintered between 850 °C and 1000 °C. The results of thermal diffusivity indicate that the use of petroleum waste in structural ceramic up to 5 wt.% does not cause significant changes in the structure or composition of the clay/waste system, resulting in great advantages in waste minimization.

Abstract: The industry of ornamental stones processing from Espírito Santo State produces high amounts of powder waste from sawing and polishing of granite. This waste is a non-biodegradable material that when disposed generates pollution and environmental damage. Clay/waste mixtures were prepared with a kaolinitic clay and waste additions up to 10 wt.%. Various bodies were prepared by uniaxial pressing and sintered in air between 850°C and 1150°C. Emphasis is given on the drying and firing properties. The results revealed that the ceramic bodies containing granite powder waste are adequate for manufacture of structural ceramic. In addition, the employed methodology is environmentally correct and can contribute to the sustainable development.

Abstract: In the present era, high technology wireless communication and mobile communication systems require advanced ceramics as high frequency dielectric resonators. In the present work we have produced Ba2MgWO6 (BMW) ceramics and studied its structural, microstructural and mechanical properties. Ba2MgWO6 (BMW) ceramics belong to the Ba2MgTaO6 (BMT) and Ba2ZnTaO6 (BZT) ceramics family, which is well known ceramic material for the communication technology. There is little information available on materials characteristics of BMW ceramics. Structural characteristics of BMW ceramics were studied by X-ray diffractometry. Microstructural characteristics were studied by scanning electron microscopy and mechanical behavior was tested by Vickers micro-hardness tests on sintered BMW bodies. This article reports these characteristics of BMW ceramics and discusses its implications on application viability.

Abstract: In high technology industries ceramics have several uses, especially at high temperature, e.g. inert crucibles, electrodes and catalysts. We are working on production and development of new oxide ceramics, based on complex cubic perovskite structure, for fabrication of crucibles for metallurgical applications. In the present work, we have produced and studied sintering behavior of a new ordered complex cubic perovskite oxide ceramic Ba2HoWO5.5. Microstructural characteristics of the Ba2HoWO5.5, sintered between 1200 to 1400°C for 48h, were studied by scanning electron microscopy. The mechanical behavior was studied by Vickers microhardness tests. Our studies show a gradual improvement in microstructural characteristics of sintered Ba2HoWO5.5, both on polished and fractured surface. This homogeneity of grain sizes and particle size distribution increases with the increasing of the sintering temperature, which results in higher sintered density and increased mechanical hardness.

Abstract: This work deals with the synthesis and thermal decomposition of complexes of general formula: Ln(ß-dik)3L (where Ln=Tb+3, ß-dik=4,4,4-trifluoro-1-phenyl-1,3- butanedione(btfa) and L=1,10-fenantroline(phen) or 2,2-bipiridine(bipy). The powders were characterized by melting point, FTIR spectroscopy, UV-visible, elemental analysis, scanning differential calorimeter(DSC) and thermogravimetry(TG). The TG/DSC curves were obtained simultaneously in a system DSC-TGA, under nitrogen atmosphere. The experimental conditions were: 0.83 ml.s-1 carrier gas flow, 2.0±0.5 mg samples and 10°C.min-1 heating rate. The CHN elemental analysis of the Tb(btfa)3bipy and Tb(btfa)3phen complexes, are in good agreement with the expected values. The IR spectra evinced that the metal ion is coordinated to the ligands via C=O and C-N groups. The TG/DTG/DSC curves of the complexes show that they decompose before melting. The profiles of the thermal decomposition of the Tb(btfa)3phen and Tb(btfa)3bipy showed six and five decomposition stages, respectively. Our data suggests that the thermal stability of the complexes under investigation followed the order: Tb(btfa)3phen < Tb(btfa)3bipy.

Abstract: Titanium dioxide (rutile) has a lot of interesting and useful features and hence is widely utilized for application. It has been used as white pigment, photocatalyst, biocompatible material and semiconductor material used in solar battery. In semiconducting TiO2 oxygen vacancies are said to play an important role in the electrical conduction. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occur in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in TiO2 samples using a torsion pendulum operating in frequencies around 40Hz, in the temperature range between -173 oC to 330 oC with heating rate of 1 oC/min. The results shown a reduction in the elasticity modulus with the increase in the corn starch content used for this consolidation.

Abstract: Thermomechanical and electrical properties of zirconia-based ceramics have led to a wide range of advanced and engineering ceramic applications like solid electrolyte in oxygen sensors, fuel cells and furnace elements and its low thermal conductivity has allowed its use for thermal barrier coatings for aerospace engine components. In this work, PSZ (partially stabilized zirconia) was studied to analyze the behavior during sintering in low oxygen partial pressure. Zirconia was partially stabilized with yttria 8 wt%. The sintering temperatures used were 1600, 1700, 1800 and 1900°C. The study of PSZ sintered in low oxygen partial pressure was done using Scanning Electron Microscope, X Ray Diffraction and density analysis. The values of samples density showed that the increasing in sintering temperature was favorable to the material densification. The monoclinic phase converted in tetragonal and cubic phases. The tetragonal phase maintains constant in all sintering temperatures, but the cubic phase increased at 1700 and 1800°C. The lattice parameters werecalculated and showed similar in all sintering temperature.

Abstract: This work studies the influence of the granulometry of organic matter ashes from the municipal solid waste (MOL) on the mechanical properties of vitrified ceramics. Mixtures of clay with additions of the MOL ashes were prepared as vitrified ceramics. The degree of immobilization of the potentially toxic metals (PTM) contained in the ashes was then evaluated. Samples of a sedimentary clay with 13.5% of MOL ashes with granulometry, 35 and 200 mesh, were uniaxially pressed at 18 MPa and sintered at 1200°C. Results from 3- point flexural resistance and water absorption tests showed that the reduction in the particle size of the MOL ashes increased the mechanical resistance to 45 MPa while the water absorption reached 0.8%. These results and the high degree of immobilization of the PTM qualify the ceramic vitrification as an alternative to the final disposal of the MOL.