Effect of melting pressure and superheating on chemical composition and contamination of yttria coated ceramic crucible induction melted titanium alloys

When melting reactive alloys, chemical composition and alloy homogeneity strongly depend on processing conditions, especially if melting is performed in ceramic crucibles. In this case, the nature of crucible materials, the melting stock composition and the melting parameters (atmosphere, pressure, superheating time and temperature) are critical processing variables. In this work, a Ti–48Al alloy was induction melted in a ZrO2 SiO2-based crucible with Y2O3 inner layer using different superheating temperatures (1600 and 1650 C) and times (0, 60 and 90 s) and poured into a graphitemould. The influence of different temperature/time combinations in the alloy composition, Al loss by evaporation and metal/crucible interaction was studied for different melting pressures. Al loss was found to increase significantly for melting pressures below 10-2 mbar and increases with increasing superheating time and temperature. The experimental results concerning to Al loss are in agreement with theoretical (and experimentally validated) models available for induction skullmelting of TiAl.Metal/crucible interaction directly increased with melting pressure, superheating time and temperature, leading to alloy contamination withYand O. For the experimental set-up used in this work, optimal temperature/ superheating time/pressure combinations that lead to acceptable alloy composition have been identified.FCT - Fundação para a Ciência e Tecnologi

Evaluation of functionally graded ceramic crucible for induction melting of TiAl based alloys

During the last years a very significant effort to develop a melting crucible for induction melting of Ti based alloys at competitive cost has been carried out by many researchers, where the authors are included. Results obtained so far have shown that no material accomplishes the melting crucibles two main demands: inertness facing titanium alloys and suitable/enough thermal-shock resistance. Until now, yttrium and calcium oxides were those materials that performed best on what concerns to thermodynamic stability. However, in both cases, crucibles thermal-shock resistance was very poor, and there are references to crucibles that cracked during melting. Besides, calcium oxide reveals manipulation problems, due to its high higroscopicity. This paper concerns to the evaluation of zircon based crucibles with Y2O3 inner layer for induction melting of TiAl based alloys. A novel multi layered crucible production technique based in a centrifugally assisted slip casting process followed by a sintering operation is described, and results concerning to crucibles porosity and wall composition and morphology are presented. Crucibles obtained in different processing conditions were used to melt a Ti48Al alloy which was poured in graphite moulds. Experimental results include alloy chemical contamination with residual elements, mainly yttrium and oxygen, microhardness measurement and the presence of yttrium oxide and zircon inclusions in the cast samples. Results concerning to the crucibles behaviour are also presented with particular attention to cracks development. The Y2O3 crucible layer was found to suffer some erosion and be slightly dissolved by the molten alloy and the extent of those phenomena depends on the porosity of the layer surface, for fixed experimental melting conditionsFCT - Fundação para a Ciência e Tecnologi

Aluminium evaporation during ceramic crucible induction melting of titanium aluminides

Melting TiAl based alloys in ceramic crucibles often leads to chemical contamination, alloy heterogeneity and non-metallic inclusions. The severity of such phenomena usually depends on the nature of crucible materials, the melting stock composition and the melting parameters, namely superheating time and temperature and melting pressure. Among the referred drawbacks, Al loss during melting is a critical aspect, as its concentration in TiAl based alloys has a very strong effect in their mechanical properties. Although a few studies of critical factors affecting the evaporation behaviour of Al during electron beam and induction skull melting of Ti-Al alloys had been carried out, until now no information was released on this subject for the ceramic crucible induction melting process. In this work a Ti-48Al alloy was induction melted in a zircon crucible with Y2O3 inner layer, using 50 and 100 ºC superheating temperatures and 0, 60 and 90 second holding times, and poured into a graphite mould. The effect of different temperature/time combinations in the alloy composition, Al loss by evaporation and extent of the metal/crucible interaction was studied for different melting pressures. Al loss was found to increase significantly for melting pressures below around 10-1 mbar, at a rate that increases as melting pressure decreases, until a maximum rate is reached, remaining constant for lower pressure levels. Metal/crucible interaction increased directly with the melting pressure and superheating time, leading to alloy contamination with yttrium and oxygen. For the experimental set-up and conditions used on this work, optimal superheating time/pressure combinations that lead to acceptable alloy composition and sanity have been identified.FCT - Fundação para a Ciência e Tecnologi

A multi-criteria model to define intervention priority levels for traffic signs

Traffic signs are only effective when they are visible and perceptible. Improving traffic safety cannot be achieved without properly applying and maintaining traffic signs. An integrated approach combining GIS-based multi-criteria analysis with risk assessment is proposed to evaluate the physical and operational characteristics of traffic signs and to define a level of intervention reflecting the need/urgency to improve their performance and compliance. The multi-criteria analysis is based on the identification and weighting of physical and operational criteria. One of the criteria, sign visibility, was evaluated through GIS tools. The method was applied in Guimarães, a Portuguese medium-sized city, by analysing the characteristics of 35 regulatory traffic signs. Results show that 51% of the signs analysed have physical and operational problems (level of intervention 2), requiring actions to improve their condition. Besides the compact urban structure, with narrow and non-linear streets, the trees planted on the pavements were identified as the main cause of obstruction. Since the obstructed signs are hardly visible within the braking and stopping distances, road users are exposed to significant accident risk. Removing and maintaining regularly the vegetation and replacing some signs are important actions to improve their physical and operational characteristics. The proposed method can help transportation entities in improving traffic safety

Balanço hídrico e a distribuição geográfica dos anfíbios

Given the high cutaneous permeability of amphibians, their inter-specific variation in aspects of water balance could be associated to patterns of distribution in environments that differ in water availability. Comparative studies including species from different biomes evidence adaptations of several variables associated to water balance, such as dehydration tolerance, skin resistance to water loss, and rates of water uptake. However, to understand the underlying mechanisms of amphibian geographical distribution and sensitivity to environmental change, ecological and behavioral aspects must be integrated to physiology under a historical approach of clade diversification and environmental occupancy.Dado que os anfíbios são geralmente caracterizados por uma elevada permeabilidade tegumentar, a variação interespecífica em aspectos do balanço hídrico poderia estar associada a padrões de distribuição dos anfíbios em ambientes que diferem quanto à disponibilidade hí- drica. Análises comparativas de espécies que habitam diferentes biomas fornecem evidências de adaptações em diversas variáveis fisiológicas associadas ao balanço hídrico, tais como tolerância à desidratação, resistência da pele à perda de água e taxas de reidratação. Entretanto, aspectos ecológicos e comportamentais devem ser integrados aos fisiológicos, sob um enfoque histórico da diversificação dos clados e de sua ocupação ambiental, para o entendimento das bases funcionais da distribuição geográfica e da tolerância às alterações ambientais dos anfíbios

Discurso do recipiendário António Ribeiro Gomes na sessão solene do "elogio histórico" do académico

info:eu-repo/semantics/publishedVersio

Notes on fauna associated with an opportunistic artificial reef near cold-water corals

This short communication provides a sporadic insight on the importance of a hard three-dimensional structure for deepwater fish near CWC. Fish size and behaviour inside the structure and in the surrounding area are described. Additionally, a list of biofouling macroorganisms found on the structure after one year of deployment is presented

Forecasting seasonal peaks in roadkill patterns for improving road management

For several species, roadkill is not spatially aggregated on hotspots, having instead a more diffuse pattern along the roads. For such species, management measures such as road passages may be insufficient for effective mitigation, since a large part of the road crossings is likely to occur outside the influence of those structures. One complementary approach could be to implement temporary mitigation actions, such as traffic calming. This requires understanding when roadkill peaks may occur. We tested the feasibility of predicting seasonal peaks of roadkill using data from a 3-year systematic monitoring (78 surveys over ca. 960 km of roads) from eight non-flying vertebrate species from Mato Grosso do Sul, Brazil, with different body size and life history traits (ca. 6400 records from focal species). We modelled the time-series of the roadkill of these species at large scale (state level) using generalized additive mixed models (GAMMs). We used the data of the first 2 years as training datasets, and the information from the third year of surveys as testing datasets to evaluate the prediction performance of models. Overall, the models of species feed with a higher number of records were able to follow reasonably well the variations of roadkill over time, although they were not able to correctly predict the number of collisions. For species with fewer observations, the models presented a poorer goodness-of-fit and prediction ability. Our results suggest that, at least for those species with higher roadkill rates, it can be possible to forecast periods of higher probability of occurring hot-moments of mortality. Such models can provide valuable information to implement seasonal management actions.info:eu-repo/semantics/publishedVersio

First in situ observations of soft bottom megafauna from the Cascais Canyon head

We report the first in situ observations of soft bottom megafauna from the Cascais Canyon head. Observations were collected opportunistically during three technical dives with the ROV Luso between 460-805 m at two locations distanced 1,230 m. The habitats were clas-sified as upper bathyal fine mud. The soft bottom fauna was dominated by burrows of Nephrops norvegicus reaching up to 2.9 burrows/m2, a common habitat along the Portu-guese continental margin. To our knowledge, densities are the highest ever reported for depths below 300 m. The ichthyofauna at the upper Cascais Canyon is a mixture of lower shelf and upper bathyal species, including Phycis blennoides, Scyliorhynus canicula, Coe-lorhynchus labiatus/occa and Chimaera monstrosa. Bait release attracted Myxine glutinosa. Surveys in other geological settings of the Cascays Canyon are required to understand more comprehensively the diversity of its sessile and vagile biodiversity