Materials Science Forum Vols. 514-516

Abstract: Stereolithography is a rapid manufacturing process that builds objects layer-by-layer based on the photo polymerization of a liquid resin. Due to the good geometric precision, this process has been used in Rapid Tooling for injection moulding. These tools are suitable for the production of short runs of parts and prototypes, where without resorting to the manufacture of a conventional metallic mould. The mechanical and thermal properties of the stereolitography resins, used in the manufacture of hybrid moulds, differ substantially from those of the conventional metallic materials. Particularly they must be known for guaranteeing the structural integrity and the thermal performance of the mould. Also the chemistry behaviour of the resin in contact with the polymer is important when tribological aspects are involved, especially during the ejection of the moulding. In this work, the behaviour of hybrid moulds with SL Vantico 5260 resin moulding cores was assessed. Several thermoplastics (iPP, ABS, PET and PA 6.6) were moulded, and their mechanical, thermal and chemical properties considered and related to the performance of the moulding process. Also, the friction properties of the SL resin in contact with the moulded thermoplastic in moulding conditions were observed and considered in the context of the performance of hybrid moulds.

Abstract: The Hotbird is a state of the art X-ray laboratory for advanced materials characterisation, installed at ITN since 1999. Several major improvements in its capabilities have been implemented. On the one hand, new hardware developments have extended the applications that can be studied and on the other hand, new software has enabled both enhanced automated control of the system, and improved data analysis that leads to extraction of further precise information from the data. One improvement was the implementation of the x-ray reflectometry (XRR) technique, which is a major expansion of the Hotbird capabilities. XRR is well-suited to characterise film thickness and roughness with high resolution. Furthermore, several optics improvements, such as a Göbel mirror and monochromators were introduced. The combination of this optics allows one to use either a higher intensity beam (orders of magnitude better) or a higher resolution beam configuration. A new high-temperature chamber was developed, which allows one to perform in-situ experiments with excellent temperature control up to 800 °C, in all possible configurations. Data simulation/fitting analysis software for XRR was developed. Also, to control the diffractometer and perform experiments, a new user-friendly software package was developed. In order to illustrate the Hotbird capabilities improvements, several experimental examples will be described.

Abstract: Bi-Sn-Zn is one of the systems being used as substitute of the traditional lead solders. Therefore a deeper knowledge of its phase diagram is a priority. Due to the lack of data about the thermodynamic properties of terminal solid solutions as well as on their phase boundaries, only binary contributions were utilized and the ternary terms were ignored on the published assessments [1, 2]. Samples corresponding to several vertical sections were prepared and DTA, SEM/EDS and XRD at room and high temperatures were performed. It was concluded that ternary terms should be held in consideration in a future assessment of the system.

Abstract: Preservation of our Historical Cultural Heritage built in stone requires studies on the material itself, on the environment where the monument is located, and even on the microclimate affecting a particular stone in the building. The knowledge of the decay processes, as well as mechanisms governing these processes, and the real effect of factors depending on the intrinsic properties of the material to be studied, and external agents of decay, will allow a rationale use of these materials and to anticipate their behaviour beforehand, in order to success in restoration

Abstract: Previous studies had shown that a promising material could be obtained by mixing aluminium-rich sludge with slate powder (with Al2O3:SiO2 molar proportion of 2:1), shaping by uniaxial pressing and sintering at 1300oC, in order both to detoxify the sludge by fixing the metals in a leach-resistant ceramic matrix and to yield a new material from the reactions of the above compounds at high temperature. In view of potential applications, since this material was also found to be inert after leaching tests, a further systematic study, reported in the present paper, was carried out, in order to determine its mechanical properties and discuss them in function of the microstructure. The average values of Vickers hardness HV3 (683), bend strength (126 MPa), Young's modulus (161GPa) and fracture toughness (3.35 MPa.m1/2) are significantly higher than those found for the as sintered slate powders, which is attributed to the increased fraction of α- alumina and reduced content of glassy phase in the microstructure of the material with sludge addition.

Abstract: Waste porcelain tile polishing sludges result from sediments of the treatment plants of tile manufacturing industrial wastewater. These polishing by-products are essentially a mix of fine residues of the specific ceramic body and a coarse residue of the abrasive used for polishing the surface of the tiles. In the present work, it was studied the use of porcelain tile polishing sludges, as a raw material in manufacturing of aluminosilicate fireclay bricks to be used in fireplaces. In order to establish the feasibility of the process and to develop the addition conditions, a set of appropriate ceramic compositions of white and red fireclays was studied. Results showed that up to 10 % in weight of the basic raw materials could be preplaced by tile polishing dry sludges, without significant changes in the ceramic process and the resulting materials properties.

Abstract: Sewage sludge consists of a solid mixture of biological and mineral origin. It is the main byproduct of Effluent Treatment Stations. Its final draining has been a relevant environmental problem in several countries. In Brazil, due to the growth of the urban population and the requirements of environmental agencies, efficient ways for sludge disposal or effluent treatment have been investigated. Possible discarding solutions include incineration, pelletization, energy production and addition to fertilizers. This work focuses on the use of sludge in the ceramic industry for the production of light ceramic blocks, since this residue is basically composed of organic substances which volatilize during high temperature sintering. Mixtures containing different contents residue and clayed materials were prepared. For each mixture, after processing, the physical and mechanical properties of the burned pieces were measured, with emphasis on water absorption and linear shrinkage tests carried out as a function of the sintering temperature. Gresification diagrams were plotted for the temperature range of 850 °C to 1150 °C. The addition of the residue provided an increase in the porosity of the material. Light blocks were sintered and presented adequate mechanical resistance for application as building material.

Abstract: Fly ash from Tapada do Outeiro, a coal power plant in the north of Portugal, has been processed by a powder technology route in order to obtain durable and mechanical resistant ceramics. Dolomite (CaCO3.MgCO3) was added in different proportions to the waste material, from zero up to 10 wt%, and the effect of this addition on the densification behaviour of the fired samples was investigated by measuring the apparent density, the open porosity and the linear shrinkage. The powder mixtures were uniaxially dry pressed in a steel die and fired at temperatures ranging from 950 to 1150°C. XRD and SEM were used to identify the phases present in the sintered materials and the degree of densification. The results revealed that added dolomite was responsible for the appearance of anorthite, an extra phase besides mullite and quartz, for an increase in the amount of liquid phase and for the swelling of closed pores at the highest firing temperatures. Significant morphological changes and phase transformations occurred during sintering and their effects on the physical-mechanical and leaching characteristics of the sintered materials were analyzed.

Abstract: Hydrated alumina Al2O3.3H2O was produced from spent alkaline baths resulting from aluminium transformation industry. Batch and continue laboratory and pilot tests were performed in order to assess technical viability of producing reactive alumina directly from the baths by a precipitation/crystallization process and at the same time of recovering and recycling the associated sodium hydroxide to the extrusion process. The influence of three parameters: time, seed quantity and dilution were evaluated using a statistical method. It was found that time and dilution are the factors which have more influence on aluminium precipitation yield, allowing to reach values greater than 45%. The hydrated aluminas obtained were characterized by granulometric analysis, scanning electron microscopy and x-ray diffraction. Therefore, apart from minimizing the environmental impact of the aluminium transformation industry by reducing a waste quantity, it is obtained a marketable sub-product and recovered a raw material (NaOH), which can be recycled within the aluminium transformation process.

Abstract: Additions of γ-Al2O3 and Al(OH)3 powders produced at INETI from spent baths resulting from the aluminium transformation industry were made to a commercial cordierite batch formulation (without Al2O3 addition), known as DC4, developed by Rauschert Portuguesa Lda., in order to evaluate the possibility of replacing with benefits the conventional α-Al2O3 source used. The resulting samples were found to be denser than the commercial ones. This is related to the higher reactivity of these particular sources of alumina as compared to that added to the commercial product. Consequently, higher Young’s modulus (100-114 GPa) and flexural strength (80-98 MPa) were achieved for the developed materials in comparison to those obtained for commercial cordierite (96±2 GPa and 67±5 MPa, respectively). In addition, slightly lower thermal expansion coefficients were observed (3.6x10-6 K-1) and the thermal shock resistance was found to increase from 325 K to 350 K. The developed technology can be regarded as suitable for reducing the environmental impact of deposition of wastes from the aluminium transformation industry.