Antonio P Gonçalves | Instituto Superior Técnico (original) (raw)
Identification:
António Cândido Lampreia Pereira Gonçalves
(born in September 20, 1961, Lisbon, Portugal)
President of Center for Nuclear Sciences and Technologies (C2TN), Instituto Superior Técnico, Universidade de Lisboa
Education:
2013 Habilitation (Agregação) in Chemistry, IST, Technical University of Lisbon, Portugal.
Lesson title: "Thermoelectric compounds and materials".
1996 Ph. D. in Chemistry, IST, Technical University of Lisbon, Portugal.
Thesis title: "Study of UFe12-xMx intermetallic compounds".
1991 Senior Research Assistant degree , ICEN, National Laboratory for Engineering and Industrial Technology (LNETI).
Lesson title: "Introduction to the single crystal growth techniques".
1985 Graduation in Chemical Engineering, IST, Technical University of Lisbon, Portugal.
Positions:
Full Researcher (Investigador Coordenador), IST, 2017-
Senior Researcher, IST, 2006-2017
Researcher, Instituto Tecnológico e Nuclear (ITN), 1996-2006
Senior Research Assistant, LNETI (ITN since 1993), 1991-1996
Research Assistant, LNETI, 1988-1991
Research Grant Holder, LNETI, 1986-1988
Research Interests
Solid State Chemistry, Inorganic Chemistry, Materials Science, Phase diagram studies, Exploratory synthesis, Design of new materials, Nanostructured materials, Actinide and Rare Earth Intermetallics, Pnictide and Chalcogenide compounds, Strongly Correlated Electronic Systems, Thermoelectric materials, Nuclear materials for peaceful applications
Phone: (+351)21 994 6182
Address: C2TN, Department of Nuclear Sciences and Engineering (DECN) of Instituto Superior Técnico (IST), Universidade de Lisboa.
Address: Estrada Nacional 10, Km 139.7, 2695-066 Bobadela LRS, Portugal.
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Papers by Antonio P Gonçalves
Trabajos de Prehistoria
La excavación de la necrópolis prehistórica de Galeria da Cisterna (1988-1989) recuperó los resto... more La excavación de la necrópolis prehistórica de Galeria da Cisterna (1988-1989) recuperó los restos de varios individuos. La datación de cuatro de ellos demuestra que la cavidad fue usada con fines funerarios en época campaniforme. No se ha encontrado ningún fragmento de la característica cerámica del periodo, pero un pequeño fragmento de espiral en oro y un conjunto de botones con perforación en V justifican la asignación cultural del contexto. Su asociación con los restos humanos fechados puede considerarse segura. La observación macroscópica de los botones concluyó que la materia prima usada había sido el marfil de cachalote, lo que confirmó el análisis de densidad. Este indicador se eligió debido a que el análisis es no destructivo y discrimina bien los diferentes tipos de marfil conocidos en el Calcolítico de la península ibérica. La densidad media obtenida para los 13 botones de Galeria da Cisterna es de 2,32 ± 0,12, claramente por encima del rango de variación de los marfiles ...
Boletim da Sociedade Portuguesa de Química, 2012
Sustainable Chemistry, 2021
Ionic liquids are critical reagents for science and technical processes nowadays. Metals are the ... more Ionic liquids are critical reagents for science and technical processes nowadays. Metals are the most used reagents in the industry. It is crucial to have a deeper understanding of how ionic liquids and metals could interact. In this article the interaction of those two families of compounds is accessed. The dissolution (reaction) of metals with ionic liquids is studied, namely the influence of temperature, redox potential, and availability of an oxidant in the process. The final state achieved by the iron metal samples was also addressed by Mössbauer spectroscopy.
RSC Advances, 2016
Tetrahedrite formation is influenced positively by selenium and negatively by bismuth and nickel.... more Tetrahedrite formation is influenced positively by selenium and negatively by bismuth and nickel. However, selenium decreases the skinnerite formation temperature.
Intermetallics, 2006
UFe 6 Ga 6 polycrystalline samples were prepared by arc-melting, and single crystals were grown b... more UFe 6 Ga 6 polycrystalline samples were prepared by arc-melting, and single crystals were grown by the Czochralski method. This compound crystallizes in the orthorhombic ScFe 6 Ga 6-type structure (space group Immm, aZ5.0560(4), bZ8.5484(7) and cZ8.6914(7) Å), an ordered variant of the ThMn 12-type structure. A ferromagnetic-type transition at T C Z530(5) K is seen in the magnetization and A.C.-susceptibility measurements, and no other magnetic anomaly is observed down to 5 K. Single crystal magnetization measurements along the three different crystallographic axes indicated a as the easy direction, with a spontaneous magnetization M S Z12.3 m B /f.u. at 5 K. The analysis of the 57 Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, B hf , significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFe x Al 12Kx , where the average B hf were found to increase with the iron-iron interatomic distances.
Journal of Electronic Materials, 2018
Tetrahedrites are widespread minerals with Cu10M2Sb4S13 (M = Cu, Mn, Fe, Co, Ni, Zn) general form... more Tetrahedrites are widespread minerals with Cu10M2Sb4S13 (M = Cu, Mn, Fe, Co, Ni, Zn) general formula, whose thermoelectric properties can be tuned through proper doping and reach zT values as high as 1, being considered promising low-cost materials for thermoelectrics. However, for their practical applications in thermoelectric devices it is necessary to establish their ability to operate for long periods under the working temperatures and atmospheres. Here we present the oxidation studies in air of the Cu12Sb3.9Bi0.1S10Se3 tetrahedrite at four different temperatures, between 230ºC and 375ºC, together with preliminary corrosion studies in aggressive NaCl electrolytes. Surface oxidation already occurs at the lower studied temperatures, but a strong decrease of the oxidation rate is observed in materials treated at medium temperatures (275ºC), where a continuous surface layer of Cu2-xS forms, pointing to the protector effect of this layer that could be used in devices at those temperatures. For the materials treated at higher temperatures (350ºC and 375ºC) no tetrahedrite phases are seen after 1500 h, which can be related to the (Tetrahedrite + Chalcostibite + Antimony → Skinnerite) reaction that occurs above 280ºC. Corrosion studies indicate that increasing the oxidation temperature leads unfortunately to a decrease of the corrosion resistance of tetrahedrite-based phases.
Materials
As the search continues for novel, cheaper, more sustainable, and environmentally friendly thermo... more As the search continues for novel, cheaper, more sustainable, and environmentally friendly thermoelectric materials in order to expand the range of applications of thermoelectric devices, the tetrahedrite mineral (Cu12Sb4S13) stands out as a potential candidate due to its high abundance, low toxicity, and good thermoelectric performance. Unfortunately, as most current thermoelectric materials achieve zTs above 1.0, ternary tetrahedrite is not a suitable alternative. Still, improvement of its thermoelectric performance has been achieved to zTs ≈ 1 via isovalent doping and composition tuning, but most studies were limited to a single doping element. This project explores the effects of simultaneous doping with nickel and selenium in the thermoelectric properties of tetrahedrite. Simulated properties for different stoichiometric contents of these dopants, as well as the measured thermoelectric properties of the correspondent materials, are reported. One of the samples, Cu11.5Ni0.5Sb4S1...
Estudos Arqueológicos de Oeiras é uma revista de periodicidade anual, publicada em continuidade d... more Estudos Arqueológicos de Oeiras é uma revista de periodicidade anual, publicada em continuidade desde 1991, que privilegia, exceptuando números temáticos de abrangência nacional e internacional, a publicação de estudos de arqueologia da Estremadura em geral e do concelho de Oeiras em particular. Possui um Conselho Assessor do Editor Científico, assim constituído:
Solid State Sciences, 2014
Abstract Uranium copper aluminide, UCu6.68Al4.32, has been synthesized by arc-melting, followed b... more Abstract Uranium copper aluminide, UCu6.68Al4.32, has been synthesized by arc-melting, followed by annealing at 600 °C. The phase belongs to the tetragonal BaCd11-type (space group I41/amd, Pearson symbol tI48, Z = 4, a = 10.2471(4) and c = 6.5883(3) A, V = 691.78(4) A3). Electrical resistivity, specific heat and magnetic susceptibility data, measured from room temperature down to ∼3 K do not show any magnetic phase transition. The compound stays in its paramagnetic state, and at high temperatures can be adjusted according to the modified Curie–Weiss model (μeff ∼ 2.7 μB/U-atom). The Sommerfeld value of the specific heat, γ ∼ 98 mJ/molK2, is well above the values derived for simple metallic systems. In this context, with the overall shape of the temperature dependent electrical resistivity, spin fluctuations can be concluded, dominating the ground state behaviour in UCu6.68Al4.32.
Diffusion and Defect Data Pt.B: Solid State Phenomena, 2013
Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are s... more Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are synthesized for the first time. Their crystal structures are solved on basis of X-ray powder diffraction data. The above mentioned compounds belong to the BaAl4 (space group I4/mmm) and Rb5Hg19 (space group I4/m) structure types. Details of the structure of the Ce5Zn2Ga17 compound and relationship with RZn2-xGa2+x (BaAl4 type) and R3Zn8-xGa3+x (La3Al11 type) are briefly discussed.
Thermochimica Acta, 2004
In our laboratories we have been studying the synthesis and reactivity of binary actinide and lan... more In our laboratories we have been studying the synthesis and reactivity of binary actinide and lanthanide intermetallic compounds. In this work, the air-oxidation of ThCu 2 and AnNi 2 (An = Th, U) was followed by thermogravimetry (TG) and the products were characterized by X-ray powder diffraction (XRD). The heterobimetallic oxides obtained are described by the formulas 2MO•ThO 2 (M = Cu, Ni) and 2NiO•UO 3. The thermogravimetric analysis under hydrogen of these heterobimetallic oxides show one mass loss for 2MO•ThO 2 and two mass losses for 2NiO•UO 3 over a wide range of temperature (293-1273 K). The characterization by XRD shows that the reduction products are 2M•ThO 2 (M = Cu, Ni) and 2Ni•UO 2 , with all the actinides in the 4+ oxidation state. The actinide heterobimetallic oxides were described as copper or nickel supported catalysts.
Journal of Alloys and Compounds, 2001
Isoprene hydrogenation on LnNi (Ln5Pr, Gd, Tm) rare earth intermetallic compounds has been studie... more Isoprene hydrogenation on LnNi (Ln5Pr, Gd, Tm) rare earth intermetallic compounds has been studied. The effect of rare earth elements on nickel catalytic behaviour was investigated. The results at steady state indicate that the compounds are all more active than pure nickel. The main reaction products are 2M2B (2-methyl-2-butene) and 2M1B (2-methyl-1-butene) with a selectivity greater than 90%. The activity at t (initial time reaction) and the selectivity at isoprene isoactivity clearly indicate the promotion of nickel's catalytic o behaviour by the rare earth element.
Journal of Alloys and Compounds, 2010
ABSTRACT Novel RZn2Ga2 intermetallics with R=La, Ce, Pr, Nd, Sm have been synthesized and charact... more ABSTRACT Novel RZn2Ga2 intermetallics with R=La, Ce, Pr, Nd, Sm have been synthesized and characterized with regards to their crystal structures and magnetic properties. The compounds form with a tetragonal structure of the BaAl4 type (space group I4/mmm). Except for LaZn2Ga2, they exhibit localised magnetism due to the presence of magnetic moments on the respective trivalent rare earth ions. The Pr-, Nd- and Sm-based compounds order antiferromagnetically at low temperatures with likely contribution of some ferromagnetic components.
Journal of Alloys and Compounds, 2009
High temperature oxidation-reduction studies were undertaken on binary intermetallic compounds Ln... more High temperature oxidation-reduction studies were undertaken on binary intermetallic compounds LnCu 2 (Ln = La, Ce, Pr, Nd, Eu, Gd, Dy, Tm, Yb). A two steps cycle was optimized by O 2-TG and H 2-TG or H 2-TPR studies along the lanthanide series. The oxidation mass uptake occurs over a wide range of temperature (200-900 • C), leading to two bimetallic copper-lanthanide oxides families according to the lanthanide: 3CuO•Ln 2 CuO 4 (Ln = La, Pr, Nd, Eu, Gd) and 2CuO•Ln 2 Cu 2 O 5 (Ln = Dy, Tm, Yb), except for CeCu 2 that gives 2CuO•CeO 2. Under hydrogen, all systems exhibit two reduction steps accompanied by mass losses in the 150-600 • C temperature range. The first mass loss is linked to the reduction of CuO, whereas the second mass loss corresponds to copper reduction in the Ln 2 CuO 4 or Ln 2 Cu 2 O 5 phase with concomitant formation of Ln 2 O 3. The reduction products were characterized by XRD and different stoichiometries were obtained according to the lanthanide: 2Cu/CeO 2 , 3Cu/Ln 2 CuO 4 or 2Cu/Ln 2 Cu 2 O 5 , after the first reduction step, and 4Cu/Ln 2 O 3 after the second reduction one. Therefore, the binary intermetallic compounds LnCu 2 decompose into a copper-rare earth oxide phase that after reduction leaves their surface highly enriched on the copper. The structure of the oxidized and reduced intermetallics can best be described as copper embedded in lanthanide oxides (Ln 2 O 3) or "type supported catalysts" and exhibited activity for the 2-propanol oxidative dehydrogenation-dehydration reaction, which was also used to characterize their acid-base properties.
Journal of Alloys and Compounds, 2009
The phase relations in the ternary system Yb-Zn-In have been established for the partial isotherm... more The phase relations in the ternary system Yb-Zn-In have been established for the partial isothermal section in the 0-33.3 at.% ytterbium concentration range at 400 • C, by researching of more than forty alloys. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to study the microstructures, identify the phases and characterize their crystal structures and compositions. The phase equilibria of this Yb-Zn-In partial section at 400 • C are characterized by the presence of three extended homogeneity ranges, indium solubility in Yb 13 Zn 58 and YbZn 2 and of zinc solubility in YbIn 2 , and the existence of one ternary intermetallic compound, YbZn 1−x In 1+x , x = ∼0.3. This new compound crystallizes in the UHg 2 structure type (space group P6/mmm), with a = 4.7933(5) Å, c = 3.6954(5) Å. The studied partial isothermal section has eight ternary phase fields at 400 • C.
Journal of Alloys and Compounds, 2008
The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi 2 and UNi 2 was un... more The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi 2 and UNi 2 was undertaken and the effect of the 5f element on nickel catalytic behavior investigated. At nearly steady state, the reaction products were isopentane and isopentenes (2-methyl-2-...
Journal of Alloys and Compounds, 2012
ABSTRACT We have studied a ternary phase of the CePt3 +/- xGe composition, with the maximum value... more ABSTRACT We have studied a ternary phase of the CePt3 +/- xGe composition, with the maximum values of x = 0.2. A series of samples was prepared by arc melting, Czochralski method and splat cooling, and characterized by scanning electron microscopy and X-ray diffraction. The arc-melted samples are well-crystalline and single-phase with slightly varying stoichiometry close to the nominal CePt3Ge, while the splat-cooled samples form an amorphous or a nanocrystalline constitution of the similar to CePt3Ge composition. Detailed measurements of magnetization, specific heat and electrical resistivity were performed in the temperature range 0.40-300 K, and magnetic fields up to 9 T. In addition, a delicate neutron diffraction experiment down to 70 mK was done, which excluded long-range magnetic order in the CePt3Ge compound. The specific heat data were tested to anisotropic Kondo model, and the resistivity behavior has been treated by means of electron localization effects. The experiments evidenced that the CePt3Ge compound can be considered as a Kondo lattice with low-temperature magnetic correlations, and the size effect seems to have minor role in control of the Kondo scattering phenomena in this compound. (C) 2011 Elsevier B. V. All rights reserved.
Intermetallics, 2013
ABSTRACT The phase relations in the U-Cu-Al and U-Cu-Ga systems have been studied at 600 degrees ... more ABSTRACT The phase relations in the U-Cu-Al and U-Cu-Ga systems have been studied at 600 degrees C in concentration region of 0-45/75 at.% Al and 0-40/75 at.% Ga, respectively. X-ray diffraction techniques, optical microscopy and scanning electronic microscopy, complemented with energy dispersive X-ray spectroscopy (EDS), were used to identify the phases and characterize their crystal structures and compositions. Five new ternary phases have been identified for the first time: UCu6+xAl5-x (x similar to 0-0.2) (TbCu6.4Al4.6 structure type), UCu6+xAl5-x (x similar to 0.38-0.68) (BaCd11 structure type), U2-epsilon(Cu7+xGa10-x)(1+delta) (epsilon similar to 0.5, delta similar to 0.03, x similar to 0.5-1) (related to Th2Ni17 structure type), UCu5+xGa1-x(x similar to 0-0.7) (CeCu6 structure type) and U14Cu44+xGa7-x (x similar to 0.5-2.5) (related to Gd14Ag51 structure type). The crystal structure of the UCu5+xGa1-x and U14Cu44+xGa7-x intermetallics has been determined from X-ray single crystal counter data.
Materials
High electrical and thermal contact resistances can ruin a thermoelectric device’s performance, a... more High electrical and thermal contact resistances can ruin a thermoelectric device’s performance, and thus, the use of effective diffusion barriers and optimization of joining methods are crucial to implement them. In this work, the use of carbon as a Cu11Mn1Sb4S13 tetrahedrite diffusion barrier, and the effectiveness of different fixation techniques for the preparation of tetrahedrite/copper electrical contacts were investigated. Contacts were prepared using as jointing materials Ni and Ag conductive paints and resins, and a Zn-5wt% Al solder. Manual, cold- and hot-pressing fixation techniques were explored. The contact resistance was measured using a custom-made system based on the three points pulsed-current method. The legs interfaces (Cu/graphite/tetrahedrite) were investigated by optical and scanning electron microscopies, complemented with energy-dispersive X-ray spectroscopy, and X-ray diffraction. No interfacial phases were formed between the graphite and the tetrahedrite or ...
Crystals
CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between... more CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between the plasma-facing tungsten tiles and the copper-based heat sink in the first wall of fusion nuclear reactors. These novel materials were prepared by ball milling and consolidated by Upgrade Field Assisted Sintering Technology at 1873 K under an applied pressure of 90 MPa for 10 min. In this work, the structural and mechanical properties of these materials were evaluated. Consolidated samples presented a major phase with a bcc-type structure with lattice parameter value of 0.316 nm for CrNbTaVW and CrNbTaVW1.7 compositions. Moreover, observation of the microstructures evidences also two minor phases: Ta-Nb-Cr and Ta-V rich (in which carbon is detected). Despite the similarity in the structural properties of these two alloys, their mechanical properties are distinct. The flexural stress for the sample with higher amount of W (CrNbTaVW1.7) is higher by 50% in the 298–873 K range, with an i...
Trabajos de Prehistoria
La excavación de la necrópolis prehistórica de Galeria da Cisterna (1988-1989) recuperó los resto... more La excavación de la necrópolis prehistórica de Galeria da Cisterna (1988-1989) recuperó los restos de varios individuos. La datación de cuatro de ellos demuestra que la cavidad fue usada con fines funerarios en época campaniforme. No se ha encontrado ningún fragmento de la característica cerámica del periodo, pero un pequeño fragmento de espiral en oro y un conjunto de botones con perforación en V justifican la asignación cultural del contexto. Su asociación con los restos humanos fechados puede considerarse segura. La observación macroscópica de los botones concluyó que la materia prima usada había sido el marfil de cachalote, lo que confirmó el análisis de densidad. Este indicador se eligió debido a que el análisis es no destructivo y discrimina bien los diferentes tipos de marfil conocidos en el Calcolítico de la península ibérica. La densidad media obtenida para los 13 botones de Galeria da Cisterna es de 2,32 ± 0,12, claramente por encima del rango de variación de los marfiles ...
Boletim da Sociedade Portuguesa de Química, 2012
Sustainable Chemistry, 2021
Ionic liquids are critical reagents for science and technical processes nowadays. Metals are the ... more Ionic liquids are critical reagents for science and technical processes nowadays. Metals are the most used reagents in the industry. It is crucial to have a deeper understanding of how ionic liquids and metals could interact. In this article the interaction of those two families of compounds is accessed. The dissolution (reaction) of metals with ionic liquids is studied, namely the influence of temperature, redox potential, and availability of an oxidant in the process. The final state achieved by the iron metal samples was also addressed by Mössbauer spectroscopy.
RSC Advances, 2016
Tetrahedrite formation is influenced positively by selenium and negatively by bismuth and nickel.... more Tetrahedrite formation is influenced positively by selenium and negatively by bismuth and nickel. However, selenium decreases the skinnerite formation temperature.
Intermetallics, 2006
UFe 6 Ga 6 polycrystalline samples were prepared by arc-melting, and single crystals were grown b... more UFe 6 Ga 6 polycrystalline samples were prepared by arc-melting, and single crystals were grown by the Czochralski method. This compound crystallizes in the orthorhombic ScFe 6 Ga 6-type structure (space group Immm, aZ5.0560(4), bZ8.5484(7) and cZ8.6914(7) Å), an ordered variant of the ThMn 12-type structure. A ferromagnetic-type transition at T C Z530(5) K is seen in the magnetization and A.C.-susceptibility measurements, and no other magnetic anomaly is observed down to 5 K. Single crystal magnetization measurements along the three different crystallographic axes indicated a as the easy direction, with a spontaneous magnetization M S Z12.3 m B /f.u. at 5 K. The analysis of the 57 Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, B hf , significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFe x Al 12Kx , where the average B hf were found to increase with the iron-iron interatomic distances.
Journal of Electronic Materials, 2018
Tetrahedrites are widespread minerals with Cu10M2Sb4S13 (M = Cu, Mn, Fe, Co, Ni, Zn) general form... more Tetrahedrites are widespread minerals with Cu10M2Sb4S13 (M = Cu, Mn, Fe, Co, Ni, Zn) general formula, whose thermoelectric properties can be tuned through proper doping and reach zT values as high as 1, being considered promising low-cost materials for thermoelectrics. However, for their practical applications in thermoelectric devices it is necessary to establish their ability to operate for long periods under the working temperatures and atmospheres. Here we present the oxidation studies in air of the Cu12Sb3.9Bi0.1S10Se3 tetrahedrite at four different temperatures, between 230ºC and 375ºC, together with preliminary corrosion studies in aggressive NaCl electrolytes. Surface oxidation already occurs at the lower studied temperatures, but a strong decrease of the oxidation rate is observed in materials treated at medium temperatures (275ºC), where a continuous surface layer of Cu2-xS forms, pointing to the protector effect of this layer that could be used in devices at those temperatures. For the materials treated at higher temperatures (350ºC and 375ºC) no tetrahedrite phases are seen after 1500 h, which can be related to the (Tetrahedrite + Chalcostibite + Antimony → Skinnerite) reaction that occurs above 280ºC. Corrosion studies indicate that increasing the oxidation temperature leads unfortunately to a decrease of the corrosion resistance of tetrahedrite-based phases.
Materials
As the search continues for novel, cheaper, more sustainable, and environmentally friendly thermo... more As the search continues for novel, cheaper, more sustainable, and environmentally friendly thermoelectric materials in order to expand the range of applications of thermoelectric devices, the tetrahedrite mineral (Cu12Sb4S13) stands out as a potential candidate due to its high abundance, low toxicity, and good thermoelectric performance. Unfortunately, as most current thermoelectric materials achieve zTs above 1.0, ternary tetrahedrite is not a suitable alternative. Still, improvement of its thermoelectric performance has been achieved to zTs ≈ 1 via isovalent doping and composition tuning, but most studies were limited to a single doping element. This project explores the effects of simultaneous doping with nickel and selenium in the thermoelectric properties of tetrahedrite. Simulated properties for different stoichiometric contents of these dopants, as well as the measured thermoelectric properties of the correspondent materials, are reported. One of the samples, Cu11.5Ni0.5Sb4S1...
Estudos Arqueológicos de Oeiras é uma revista de periodicidade anual, publicada em continuidade d... more Estudos Arqueológicos de Oeiras é uma revista de periodicidade anual, publicada em continuidade desde 1991, que privilegia, exceptuando números temáticos de abrangência nacional e internacional, a publicação de estudos de arqueologia da Estremadura em geral e do concelho de Oeiras em particular. Possui um Conselho Assessor do Editor Científico, assim constituído:
Solid State Sciences, 2014
Abstract Uranium copper aluminide, UCu6.68Al4.32, has been synthesized by arc-melting, followed b... more Abstract Uranium copper aluminide, UCu6.68Al4.32, has been synthesized by arc-melting, followed by annealing at 600 °C. The phase belongs to the tetragonal BaCd11-type (space group I41/amd, Pearson symbol tI48, Z = 4, a = 10.2471(4) and c = 6.5883(3) A, V = 691.78(4) A3). Electrical resistivity, specific heat and magnetic susceptibility data, measured from room temperature down to ∼3 K do not show any magnetic phase transition. The compound stays in its paramagnetic state, and at high temperatures can be adjusted according to the modified Curie–Weiss model (μeff ∼ 2.7 μB/U-atom). The Sommerfeld value of the specific heat, γ ∼ 98 mJ/molK2, is well above the values derived for simple metallic systems. In this context, with the overall shape of the temperature dependent electrical resistivity, spin fluctuations can be concluded, dominating the ground state behaviour in UCu6.68Al4.32.
Diffusion and Defect Data Pt.B: Solid State Phenomena, 2013
Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are s... more Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are synthesized for the first time. Their crystal structures are solved on basis of X-ray powder diffraction data. The above mentioned compounds belong to the BaAl4 (space group I4/mmm) and Rb5Hg19 (space group I4/m) structure types. Details of the structure of the Ce5Zn2Ga17 compound and relationship with RZn2-xGa2+x (BaAl4 type) and R3Zn8-xGa3+x (La3Al11 type) are briefly discussed.
Thermochimica Acta, 2004
In our laboratories we have been studying the synthesis and reactivity of binary actinide and lan... more In our laboratories we have been studying the synthesis and reactivity of binary actinide and lanthanide intermetallic compounds. In this work, the air-oxidation of ThCu 2 and AnNi 2 (An = Th, U) was followed by thermogravimetry (TG) and the products were characterized by X-ray powder diffraction (XRD). The heterobimetallic oxides obtained are described by the formulas 2MO•ThO 2 (M = Cu, Ni) and 2NiO•UO 3. The thermogravimetric analysis under hydrogen of these heterobimetallic oxides show one mass loss for 2MO•ThO 2 and two mass losses for 2NiO•UO 3 over a wide range of temperature (293-1273 K). The characterization by XRD shows that the reduction products are 2M•ThO 2 (M = Cu, Ni) and 2Ni•UO 2 , with all the actinides in the 4+ oxidation state. The actinide heterobimetallic oxides were described as copper or nickel supported catalysts.
Journal of Alloys and Compounds, 2001
Isoprene hydrogenation on LnNi (Ln5Pr, Gd, Tm) rare earth intermetallic compounds has been studie... more Isoprene hydrogenation on LnNi (Ln5Pr, Gd, Tm) rare earth intermetallic compounds has been studied. The effect of rare earth elements on nickel catalytic behaviour was investigated. The results at steady state indicate that the compounds are all more active than pure nickel. The main reaction products are 2M2B (2-methyl-2-butene) and 2M1B (2-methyl-1-butene) with a selectivity greater than 90%. The activity at t (initial time reaction) and the selectivity at isoprene isoactivity clearly indicate the promotion of nickel's catalytic o behaviour by the rare earth element.
Journal of Alloys and Compounds, 2010
ABSTRACT Novel RZn2Ga2 intermetallics with R=La, Ce, Pr, Nd, Sm have been synthesized and charact... more ABSTRACT Novel RZn2Ga2 intermetallics with R=La, Ce, Pr, Nd, Sm have been synthesized and characterized with regards to their crystal structures and magnetic properties. The compounds form with a tetragonal structure of the BaAl4 type (space group I4/mmm). Except for LaZn2Ga2, they exhibit localised magnetism due to the presence of magnetic moments on the respective trivalent rare earth ions. The Pr-, Nd- and Sm-based compounds order antiferromagnetically at low temperatures with likely contribution of some ferromagnetic components.
Journal of Alloys and Compounds, 2009
High temperature oxidation-reduction studies were undertaken on binary intermetallic compounds Ln... more High temperature oxidation-reduction studies were undertaken on binary intermetallic compounds LnCu 2 (Ln = La, Ce, Pr, Nd, Eu, Gd, Dy, Tm, Yb). A two steps cycle was optimized by O 2-TG and H 2-TG or H 2-TPR studies along the lanthanide series. The oxidation mass uptake occurs over a wide range of temperature (200-900 • C), leading to two bimetallic copper-lanthanide oxides families according to the lanthanide: 3CuO•Ln 2 CuO 4 (Ln = La, Pr, Nd, Eu, Gd) and 2CuO•Ln 2 Cu 2 O 5 (Ln = Dy, Tm, Yb), except for CeCu 2 that gives 2CuO•CeO 2. Under hydrogen, all systems exhibit two reduction steps accompanied by mass losses in the 150-600 • C temperature range. The first mass loss is linked to the reduction of CuO, whereas the second mass loss corresponds to copper reduction in the Ln 2 CuO 4 or Ln 2 Cu 2 O 5 phase with concomitant formation of Ln 2 O 3. The reduction products were characterized by XRD and different stoichiometries were obtained according to the lanthanide: 2Cu/CeO 2 , 3Cu/Ln 2 CuO 4 or 2Cu/Ln 2 Cu 2 O 5 , after the first reduction step, and 4Cu/Ln 2 O 3 after the second reduction one. Therefore, the binary intermetallic compounds LnCu 2 decompose into a copper-rare earth oxide phase that after reduction leaves their surface highly enriched on the copper. The structure of the oxidized and reduced intermetallics can best be described as copper embedded in lanthanide oxides (Ln 2 O 3) or "type supported catalysts" and exhibited activity for the 2-propanol oxidative dehydrogenation-dehydration reaction, which was also used to characterize their acid-base properties.
Journal of Alloys and Compounds, 2009
The phase relations in the ternary system Yb-Zn-In have been established for the partial isotherm... more The phase relations in the ternary system Yb-Zn-In have been established for the partial isothermal section in the 0-33.3 at.% ytterbium concentration range at 400 • C, by researching of more than forty alloys. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to study the microstructures, identify the phases and characterize their crystal structures and compositions. The phase equilibria of this Yb-Zn-In partial section at 400 • C are characterized by the presence of three extended homogeneity ranges, indium solubility in Yb 13 Zn 58 and YbZn 2 and of zinc solubility in YbIn 2 , and the existence of one ternary intermetallic compound, YbZn 1−x In 1+x , x = ∼0.3. This new compound crystallizes in the UHg 2 structure type (space group P6/mmm), with a = 4.7933(5) Å, c = 3.6954(5) Å. The studied partial isothermal section has eight ternary phase fields at 400 • C.
Journal of Alloys and Compounds, 2008
The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi 2 and UNi 2 was un... more The study of isoprene (2-methyl-1,3-butadiene) gas phase hydrogenation on ThNi 2 and UNi 2 was undertaken and the effect of the 5f element on nickel catalytic behavior investigated. At nearly steady state, the reaction products were isopentane and isopentenes (2-methyl-2-...
Journal of Alloys and Compounds, 2012
ABSTRACT We have studied a ternary phase of the CePt3 +/- xGe composition, with the maximum value... more ABSTRACT We have studied a ternary phase of the CePt3 +/- xGe composition, with the maximum values of x = 0.2. A series of samples was prepared by arc melting, Czochralski method and splat cooling, and characterized by scanning electron microscopy and X-ray diffraction. The arc-melted samples are well-crystalline and single-phase with slightly varying stoichiometry close to the nominal CePt3Ge, while the splat-cooled samples form an amorphous or a nanocrystalline constitution of the similar to CePt3Ge composition. Detailed measurements of magnetization, specific heat and electrical resistivity were performed in the temperature range 0.40-300 K, and magnetic fields up to 9 T. In addition, a delicate neutron diffraction experiment down to 70 mK was done, which excluded long-range magnetic order in the CePt3Ge compound. The specific heat data were tested to anisotropic Kondo model, and the resistivity behavior has been treated by means of electron localization effects. The experiments evidenced that the CePt3Ge compound can be considered as a Kondo lattice with low-temperature magnetic correlations, and the size effect seems to have minor role in control of the Kondo scattering phenomena in this compound. (C) 2011 Elsevier B. V. All rights reserved.
Intermetallics, 2013
ABSTRACT The phase relations in the U-Cu-Al and U-Cu-Ga systems have been studied at 600 degrees ... more ABSTRACT The phase relations in the U-Cu-Al and U-Cu-Ga systems have been studied at 600 degrees C in concentration region of 0-45/75 at.% Al and 0-40/75 at.% Ga, respectively. X-ray diffraction techniques, optical microscopy and scanning electronic microscopy, complemented with energy dispersive X-ray spectroscopy (EDS), were used to identify the phases and characterize their crystal structures and compositions. Five new ternary phases have been identified for the first time: UCu6+xAl5-x (x similar to 0-0.2) (TbCu6.4Al4.6 structure type), UCu6+xAl5-x (x similar to 0.38-0.68) (BaCd11 structure type), U2-epsilon(Cu7+xGa10-x)(1+delta) (epsilon similar to 0.5, delta similar to 0.03, x similar to 0.5-1) (related to Th2Ni17 structure type), UCu5+xGa1-x(x similar to 0-0.7) (CeCu6 structure type) and U14Cu44+xGa7-x (x similar to 0.5-2.5) (related to Gd14Ag51 structure type). The crystal structure of the UCu5+xGa1-x and U14Cu44+xGa7-x intermetallics has been determined from X-ray single crystal counter data.
Materials
High electrical and thermal contact resistances can ruin a thermoelectric device’s performance, a... more High electrical and thermal contact resistances can ruin a thermoelectric device’s performance, and thus, the use of effective diffusion barriers and optimization of joining methods are crucial to implement them. In this work, the use of carbon as a Cu11Mn1Sb4S13 tetrahedrite diffusion barrier, and the effectiveness of different fixation techniques for the preparation of tetrahedrite/copper electrical contacts were investigated. Contacts were prepared using as jointing materials Ni and Ag conductive paints and resins, and a Zn-5wt% Al solder. Manual, cold- and hot-pressing fixation techniques were explored. The contact resistance was measured using a custom-made system based on the three points pulsed-current method. The legs interfaces (Cu/graphite/tetrahedrite) were investigated by optical and scanning electron microscopies, complemented with energy-dispersive X-ray spectroscopy, and X-ray diffraction. No interfacial phases were formed between the graphite and the tetrahedrite or ...
Crystals
CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between... more CrNbTaVWx with (x = 1 and 1.7) high entropy alloys have been devised for thermal barriers between the plasma-facing tungsten tiles and the copper-based heat sink in the first wall of fusion nuclear reactors. These novel materials were prepared by ball milling and consolidated by Upgrade Field Assisted Sintering Technology at 1873 K under an applied pressure of 90 MPa for 10 min. In this work, the structural and mechanical properties of these materials were evaluated. Consolidated samples presented a major phase with a bcc-type structure with lattice parameter value of 0.316 nm for CrNbTaVW and CrNbTaVW1.7 compositions. Moreover, observation of the microstructures evidences also two minor phases: Ta-Nb-Cr and Ta-V rich (in which carbon is detected). Despite the similarity in the structural properties of these two alloys, their mechanical properties are distinct. The flexural stress for the sample with higher amount of W (CrNbTaVW1.7) is higher by 50% in the 298–873 K range, with an i...