ME - Artigos em revistas internacionais
Permanent URI for this collection
Browse
Browsing ME - Artigos em revistas internacionais by Issue Date
Now showing 1 - 10 of 162
Results Per Page
Sort Options
- Effect of vanadium and carbon content on the sinterability of water atomised high speed steel powdersPublication . Mascarenhas, João; Oliveira, M. Manuela; Wright, C. S.This paper presents the results of an investigation into the sintering behaviour of three vanadium enriched variants of T42 high-speed steel. Powders were prepared by water atomization with vanadium and carbon contents of 6-8 wt% and 2.2 -2.7 wt%, respectively. These were annealed, die pressed and sintered in vacuum. All three alloys were sintered to full density giving "as-sintered" microstructures comprising globular MC carbides dispersed in a martensitic matrix. Optimum sintering temperatures were in the range 1240-1250 degrees C with lower optimum temperatures associated with higher carbon levels. Sintering characteristics are correlated with phase diagrams calculated using ThermoCalc (TM) software and TCFe2000 database. The implications for the design of sinterable vanadium containing high-speed steels are discussed.
- Manufacture of cordierite foams by direct foamingPublication . Silva, Elisabete Ribeiro; Correia, N.; Silva, J. M.; Oliveira, Fernando Almeida Costa; Ribeiro, F. R. M. C.; Bordalo, J. C.; Ribeiro, M. F.Open cell cordiereti fosms were prepared by a direct foaming two-component polyurethane (PUR)/ceramic system. Throught optimization of several experimental parameters such as contents of catalysts and ceramic cordiereti precursor, as well as plasticizer presence, foams with porosites 85-95&% and densities ranging from 130-410 kg/m3 were obtained. Thse foams characteristics make them attractive to be used as catalyst supports. The new two-component PUR/ceramics system developped allows the high solid's loading (higher than 40 wt. %). Finer ceramic particles in this system provide better particles packaged and cohesion upon sintering, favouring the cordiereti foam stability.
- Macrostructural changes of polymer replicated open cell cordierite based foams upon sinteringPublication . Matos, Maria José; Dias, Susana; Oliveira, Fernando Almeida CostaThe goal of this work was to clarify the macrostructural changes that take place upon sintering of open cell cordierite based foams. A methodology, based on optical image analysis, was developed to assess the structure of open-cell foams, which allowed evaluating the macrostructure of both cordierite based foams obtained by the replication process and their polymeric templates. The parameters used to describe the structures were the size of the cell and the window, the window shape factor, the strut thickness and the volume fraction of the material. The experimental evidence gathered opened the way to understand the physical/chemical transformations involved in the polymer burnout and the ceramic sintering processes, as well as their influence on the ceramic final structure. The observed trends provide guidance for tailoring ‘replicated’ cordierite based foams, in view of the required application.
- Life Cycle Assessment of a Multi-Material Car ComponentPublication . Ribeiro, Catarina; Ferreira, José V.; Partidário, Paulo JorgeBackground, Aims and Scope. In recent years, the automotive industry has been experiencing an increasing concern with environmental requirements. A particular focus is being given to light-weighting of cars, to reducing fuel consumption and to the use of different recycling materials. Consequently, decisions on product design and development must involve economic and technological as well as environmental considerations. In adequate conditions, the LCA methodology enables one to assist an effective integration of the environmental considerations in the decision- making process [1]. In this paper, a multi-material car component which is part of the current automotive brake system, has been modified by its original manufacturer. Such a modification included the use of a new multi-material injection moulding process and the consumption of recyclable materials. The new and the current component were comparatively assessed throughout their life cycles in order to evaluate their respective environmental impacts and, thus, to verify if the new component offers a lower environmental load. The results described in this paper are part of the outcome of a broader research project involving industrial companies, university, technological centres and research institutes based in Portugal, Spain and Germany.
- Nano-meter size WC whiskers grown over a compacted pellet of praphite: tungsten powder mixture heated with an ultra-fast heating rate by a concentrated solar beamPublication . Dias, Susana; Oliveira, Fernando Almeida Costa; Granier, Bernard; Badie, Jean Marie; Fernandes, Jorge Cruz; Rosa, Luís Guerra; Shohoji, NobumitsuIn equilibrium binary W-C system, mono-carbide WC is acknowledged as the stable phase under presence of excess free carbon up to temperature 2700 C whereas sub-carbideW2C would form between 1250 C and 2700 C under the carbon-deficiency condition. In unique setup of solar furnace at PROMES-CNRS in Odeillo (France), temperature of specimen is raised from the ambient temperature to target temperature up to 2000 C within fractions of a second. In the recent experimental attempts of W2C phase synthesis using this unique experimental facility starting from compacted pellet consisted of graphite and tungsten powders at ratios smaller than 0.50, we detected growth of nano-meter size WC whisker at the top surface directly exposed to the concentrated solar beam. The presence of WC was confirmed also by X-ray diffraction (XRD) of the top surface but, when the specimen as a whole was subjected to powder XRD analysis, WC became indiscernible being masked by principal W2C phase. Mechanism of formation of the detected WC nano-whisker over sub-stoichiometric C/W pellet during ultra-fast heating by concentrated solar beam is discussed.
- Statistical thermodynamic approach to molten Fe–Cr–PPublication . Shohoji, Nobumitsu; Marques, Sofia FigueiredoStatistical thermodynamic analysis was applied to the available phosphorus solubility data set for molten Fe1 –yCryPx given as functions of Cr composition y, temperature T and phosphorus activity a(P) under the assumption that the solubility limit x of P in the molten Fe1-yCry was 0.50 irrespective of y. The evaluated values of the energy parameter representing the extent of stability of P atoms in the molten Fe1– yCryPx showed an apparently realistic variation pattern with y for the level of y up to 0.465. Further, it was demonstrated by an interpolating estimation using the obtained statistical thermodynamic parameter values at two known levels of y that a(P) vs. x relationships for arbitrary y at specified T could be derived with acceptable accuracy.
- Mechanical properties of dense cordierite discs sintered by solar radiation heatingPublication . Oliveira, Fernando Almeida Costa; Shohoji, Nobumitsu; Martinez, Diego; Fernandes, Jorge Cruz; Rodriguez, Jose; Rosa, Luís Guerra; Cañadas, InmaculadaConsolidation of cordierite disc specimens was undertaken under concentrated solar beam in a solar furnace at PSA (Plataforma Solar de Almerıá). Satisfactory extent of densification was achieved by the present solar-sintering experiment. The mechanical properties measured for the solar-sintered cordierite test pieces were; density ¼ 2:45 0:02 g/cm3, Vickers microhardness HV ¼ 7:31 0:29 GPa, Young’s modulus E ¼ 97 5 GPa, shear modulus G ¼ 38 2 GPa, Poisson ratio ¼ 0:27 0:01, fracture toughness KIC ¼ 1:50 0:15 MPa m1=2 and modulus of rupture evaluated by ring-on-ring test MORROR ¼ 57:8 13:7 MPa which were comparable to those of the counterparts sintered by conventional industrial gas furnace.
- EFSA Compendium of botanicals that have been reported to contain toxic, addictive, psychotropic or other substances of concernPublication . Anton, Robert; Abolina, Ilze; Muller, Judith Amberg; Sundh, Ulla Beckman; Dusemund, Birgit; Lulergue, Marie Helene; Lugasi, Andrea; Martena, Martijn; Nogueira, Maria Teresa; Pilegaard, Kirsten; Serafini, Mauro; Toth, Jaroslav; Vlietinck, Arnold; Zika, MagdaliniThe Compendium is intended to facilitate the implementation of the EFSA guidance for the safety assessment of botanicals and botanical preparations intended for use as food supplements. The Compendium aims at flagging plants or part of plants or compounds of possible concern for human heath naturally present in the listed botanicals and that therefore require specific attention while assessing the safety of the product(s) containing such botanical(s). For some botanicals in the compendium adverse (toxic) effect(s) are known even though the constituent(s) of concern are not elucidated in the literature. In some cases the whole genus was flagged because of the likely presence of substances of concern characteristic for the toxicity of that genus. The presence of a substance of concern in a given botanical does not mean that this substance will also be present in the botanical preparation. This depends largely on the plant part used, as well as the preparation method. The Compendium contains also an “insufficient information” list regrouping botanicals that appear in one of the sources of information, but for which the working group could not find enough information on possible substances of concern, or for which the information present could not be verified. The Compendium is a living list which should be periodically updated by EFSA. As a consequence, the absence of a given species in this Compendium cannot be interpreted as this species devoid of compounds hazardous for human health. In the same way, not mentioning a specific part of plant, does not imply absence of substance(s) of concern in this part.
- Novel 1-hydroxy-1,1-bisphosphonates derived from indazole: synthesis and characterizationPublication . Teixeira, Fatima; Antunes, Inês F.; Curto, Maria João Marcelo; Neves, M.; Teixeira, António P. S.Bisphosphonates (BPs) are an important class of drugs used in the treatment of abnormal calcium metabolism diseases. The first syntheses of bisphosphonates derived from indazole, substituted at the N-1, N-2 and C-3 positions are reported. The 1-hydroxy-1,1-bisphosphonates were synthesized from the corresponding carboxylic acid or acyl chloride compounds, by two different methods. These BPs have a side chain with different lengths ((CH2)n, n = 0-5) between the indazole ring and the bisphosphonate group.
- Carbide phases synthesised from C/Mo powder compacts at specified sub-stoichiometric ratios by solar radiation heating to temperatures between 1600 C and 2500 CPublication . Granier, Bernard; Shohoji, Nobumitsu; Almeida Costa Oliveira, Fernando; Magalhães, Teresa; Fernandes, Jorge Cruz; Rosa, Luís GuerraThere are a number of distinguishable carbide phases in the binary Mo-C system depending on C/Mo ratio as well as on temperature. In a preceding work published in this journal, carbide formation performance for graphite/molybdenum powder mixtures at specified levels of substoichiometric C/Mo atom ratio (C/Mo = 1/1, 3/4, 2/3 and 1/2) by exposure to concentrated solar radiation in a solar furnace at PROMESCNRS in Odeillo (France) was reported at a target temperature 1900 C. In the present work, the similar carbide synthesis experiments were carried out at 1600 C as well as at temperature exceeding 2500 C. The target temperature setting was adjusted by controlling the downward deviation of the test piece top surface position from the exact focal spot of the parabolic mirror concentrator located above. In this solar furnace at PROMES-CNRS, temperature of the test piece was raised from ambient temperature to the target temperature within fractions of a second. Reaction products detected were hexagonal -MoC1 x and -Mo2C (high temperature sub-carbide phase) depending on the C/Mo ratio in the starting material as well as on the processing temperature. No evidence of formation of cubic -MoC1 x was detected by X-ray diffraction analysis for any test piece examined.