Compositional effects on the restoration behaviour in Mg-Zn-Re alloys

Additions of rare earth elements to magnesium alloys are qualitatively reported in the literature to retard recrystallisation. However, their effect in the presence of other (non-rare earth) alloy additions has not been systematically shown nor has the effect been quantified. The microstructural restoration following the hot deformation of Mg-xZn-yRE (x = 2.5 and 5 wt.%, y = 0 and 1 wt.%, and RE = Gd and Y) alloys has been studied using double hit compression testing and microscopy. It was found that, in the absence of rare earth additions, increases in zinc level had a negligible influence on the kinetics of restoration and the microstructure developed both during extrusion and throughout double hit testing. Adding rare earth elements to Mg-Zn alloys was found to retard restoration of the microstructure and maintain finer recrystallised grains. However, in the Mg-Zn-RE alloys, increasing the zinc concentration from 2.5 wt.% to 5 wt.% accelerated the restoration process, most likely due to a depletion of rare earth elements from solid solution and modification of the particles present in the matrix.

Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy

Surface passivation of AZNd Mg alloy with Pr(NO3)3 is studied using scanning electrochemical microscopy (SECM) in surface generation/tip collection (SG/TC) and AC modes. Corrosion protection afforded by the Pr treatment and the degradation mechanism in a simulated biological environment was examined on a local scale and compared with non-treated AZNd. SG/TC mode results revealed a drastic decrease in H2 evolution due to the Pr treatment. Mapping the local insulating characteristics using AC-SECM showed higher conductivity of the surface where H2 evolution was most favorable.

Estudo dos óxidos A2B2O7 e ABO3 a base de terras raras, para aplicações térmicas e catalíticas a altas temperaturas

Rare earth elements have recently been involved in a range of advanced technologies like microelectronics, membranes for catalytic conversion and applications in gas sensors. In the family of rare earth elements like cerium can play a key role in such industrial applications. However, the high cost of these materials and the control and efficiencies associated processes required for its use in advanced technologies, are a permanent obstacle to its industrial development. In present study was proposed the creation of phases based on rare earth elements that can be used because of its thermal behavior, ionic conduction and catalytic properties. This way were studied two types of structure (ABO3 and A2B2O7), the basis of rare earths, observing their transport properties of ionic and electronic, as well as their catalytic applications in the treatment of methane. For the process of obtaining the first structure, a new synthesis method based on the use of EDTA citrate mixture was used to develop a precursor, which undergone heat treatment at 950 ° C resulted in the development of submicron phase BaCeO3 powders. The catalytic activity of perovskite begins at 450 ° C to achieve complete conversion at 675 ° C, where at this temperature, the catalytic efficiency of the phase is maximum. The evolution of conductivity with temperature for the perovskite phase revealed a series of electrical changes strongly correlated with structural transitions known in the literature. Finally, we can establish a real correlation between the high catalytic activity observed around the temperature of 650 ° C and increasing the oxygen ionic conductivity. For the second structure, showed clearly that it is possible, through chemical processes optimized to separate the rare earth elements and synthesize a pyrochlore phase TR2Ce2O7 particular formula. This "extracted phase" can be obtained directly at low cost, based on complex systems made of natural minerals and tailings, such as monazite. Moreover, this method is applied to matters of "no cost", which is the case of waste, making a preparation method of phases useful for high technology applications

Petrologia do plúton Serra da Macambira, neoproterozóico da faixa seridó, província Borborema (NE do Brasil)

The final stage of Brasiliano/Pan-African orogeny in the Borborema Province is marked by widespread plutonic magmatism. The Serra da Macambira Pluton is an example of such plutonism in Seridó Belt, northeastern Borborema Province, and it is here subject of geological, petrographic, textural, geochemical and petrogenetic studies. The pluton is located in the State of Rio Grande do Norte, intrusive into Paleoproterozoic orthogneisses of the Caicó Complex and Neoproterozoic metassupracrustal rocks of the Seridó Group. Based upon intrusion/inclusion field relationships, mineralogy and texture, the rocks are classified as follows: intermediate enclaves (quartz-bearing monzonite and biotite-bearing tonalite), porphyritic monzogranite, equigranular syenogranite to monzogranite, and late granite and pegmatite dykes. Porphyritic granites and quartz-bearing monzonites represent mingling formed by the injection of an intermediate magma into a granitic one, which had already started crystallization. Both rocks are slightly older than the equigranular granites. Quartz-bearing monzonite has K-feldspar, plagioclase, biotite, hornblende and few quartz, meanwhile biotite-bearing tonalite are rich in quartz, poor in K-feldspar and hornblende is absent. Porphyritic and equigranular granites display mainly biotite and rare hornblende, myrmekite and pertitic textures, and zoned plagioclase pointing out to the relevance of fractional crystallization during magma evolution. Such granites have Rare Earth Elements (REE) pattern with negative Eu anomaly and light REE enrichment when compared to heavy REE. They are slight metaluminous to slight peraluminous, following a high-K calc-alkaline path. Petrogenesis started with 27,5% partial melting of Paleoproterozoic continental crust, generating an acid hydrous liquid, leaving a granulitic residue with orthopyroxene, plagioclase (An40-50), K-feldspar, quartz, epidote, magnetite, ilmenite, apatite and zircon. The liquid evolved mainly by fractional crystallization (10-25%) of plagioclase (An20), biotite and hornblende during the first stages of magmatic evolution. Granitic dykes are hololeucocratic with granophyric texture, indicating hypabissal crystallization and REE patterns similar to A-Type granites. Preserved igneous textures, absence or weak imprint of ductile tectonics, association with mafic to intermediate enclaves and alignment of samples according to monzonitic (high-K calcalkaline) series all indicate post-collisional to post-orogenic complexes as described in the literature. Such interpretation is supported by trace element discrimination diagrams that place the Serra da Macambira pluton as late-orogenic, probably reflecting the vanishing stages of the exhumation and collapse of the Brasiliano/Pan-African orogen.

Phosphate functionalization of spongiolite surface

Spongiolite from Mato Grosso do Sul (Brazil), natural inorganic composite constituted of silica needles, was treated with concentrated phosphoric acid at high temperatures. Superficial coating of the needles was proved to be constituted of silicon diphosphate, a compound offering six-coordinated silicon sites. Owing to the affinity of three charged ions to phosphate groups, this coating acts as specific adsorbent for the rare earth elements which prefer octahedral coordination (starting from samarium, yttrium included). The uptake of lanthanum and neodymium are significantly lower due to different coordination tendencies. Lanthanide fixation upon silica with PO4 groups anchored on its surface may be useful in the manufacturing of special phosphate-silicate glasses. (C) 2003 Elsevier B.V. All rights reserved.

Sm-Nd system in total rock open versus closed isotopic composition in zones of high deformation

High strain shear zones of Brasiliano age, developed in Paleoproterozoic basement gneiss of the Caicó region, Borborema Province, NE Brazil, were associated with medium- to low-grade metamorphism and deformational processes that transformed porphyritic augen gneiss into muscovite quartzite, modifying their original mineralogy and chemical properties. During the last hydrothermal event mobility of major, minor and trace elements was great, whereas the pattern of Rare Earth Elements was not changed. We carried out a Sm-Nd isotopic study in these rocks in order to understand the behavior of Nd isotopes during mylonite generation. TDM model ages at around 2.6 Ga and εNd (t) values for both protolith and transformed rock suggest that the Nd isotopic system remained closed, recording the original source rock signature, despite undergoing two superposed metamorphic events. These new Sm-Nd results provide important information on the geologic evolution of basement rocks in the central Rio Grande do Norte Terrane of the Borborema Province, NE Brazil.

Red, green, and blue upconversion luminescence in ytterbium-sensitized praseodymium-doped lead-cadmium-germanate glass

Blue, green, red, and near-infrared upconversion luminescence in the wavelength region of 480 - 740 nm in Pr3+/Yb3+-codoped lead-cadmium-germanate glass under 980 nm diode laser excitation, is presented. Upconversion emission peaks around 485, 530, 610, 645, and 725 nm which were ascribed to the 3P0 - 3HJ (J=4, 5, and 6), and 3P0 - 3FJ (J=2, and 3,4), transitions, respectively, were observed. The population of the praseodymium upper 3P0 emitting level was accomplished through a combination of ground-state absorption of Yb3+ ions at the 2F7/2, energy-transfer Yb3+(2F 5/2) Pr3+(3H4), and excited-state absorption of Pr3+ ions provoking the 1G4 - 3P0 transition. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, is also examined, in order to subsidize the proposed upconversion excitation mechanism.

Thermal studies of solid 2-methoxybenzylidenepyruvate of lighter trivalent lanthanides

Solid-state compounds with a general formula of LnL3· nH2O, where Ln stands for lighter trivalent lanthanides (lanthanum to samarium), L is 2-methoxybenzylidenepyruvate and n=1.5, 2, 2, 1.5 and 2, respectively, have been synthesized. On heating these compounds are decompose in two or three steps. They lose their hydration water in the first step and the thermal decomposition of the anhydrous compounds occurs with the formation of the respective oxide, CeO2, Pr6O11 and Ln 2O3 (Ln=La, Nd, Sm) as final residue. The dehydration enthalpies found for these compounds (La to Sm) were: 222.7, 163.6, 497.7, 513.9 and 715.4 kJ mol-1, respectively. © 2005 Akadémiai Kiadó, Budapest.

Thermal studies on solid 2-chlorobenzylidenepyruvate of lighter trivalent lanthanides

Solid compounds of general formula LnL3 for La and Ce and LnL3·nH2O for Pr, Nd and Sm where Ln stands for trivalent lanthanides, L is 2-chlorobenzylidenepyruvate and n=2, 3 and 2 respectively, have been synthesized. On heating these compounds decompose in two or five steps. They lose the hydration water in the first step and the thermal decomposition of the anhydrous compounds occurs with the formation of the respective oxide, CeO2, Pr6O11 and Ln 2O3 (Ln=La, Nd, Sm) as final residue. The dehydration enthalpies found for these compounds (Pr, Nd and Sm) were: 140.1, 148.2 and 221.3 kJ mol-1, respectively. © 2005 Akadémiai Kiadó, Budapest.

Synthesis, characterization and thermal behavior of solid state compounds of heavy trivalent lanthanide succinates

Solid-state Ln-L compounds, where Ln stands for heavy trivalent lanthanides or yttrium(III) (Tb-Lu, Y) and L is succinate, have been synthesized. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), infrared spectroscopy, TG-DTA coupled to FTIR, elemental analysis, X-ray powder diffractometry and complexometry were used to characterize and study the thermal behavior of these compounds. For the terbium to thulium and yttrium compounds, the dehydration, as well the thermal decomposition of the anhydrous compound occurs in two consecutive steps, while ytterbium and lutetium the dehydration occurs in a single step. The results also led to information about the ligand's denticity, thermal stability and thermal decomposition of these compounds. © 2013 Elsevier B.V.

Thermoanalytical study of heavier trivalent lanthanides fumarates

Solid-state heavier lanthanides fumarates compounds have been synthesized, and the compounds were characterized by employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), TG coupled to FTIR, elemental analysis, and complexometry. On heating, the dehydration occurs in a single and two consecutive steps and the thermal decomposition of the anhydrous compounds occurs in consecutive and/or overlapping steps, with formation of the respective oxides: Tb4O7 and Ln2O3 (Ln=Dy to Lu). The results also led to information about composition, thermal behavior, and the type of coordination of the isolated compounds. © 2012 Akadémiai Kiadó, Budapest, Hungary.

Caracterização dos diamantes da província kimberlítica de Juína (MT), e distritos diamantíferos de Espigão D'Oeste (RO), Cacoal (RO) e Diamantina (MG)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Geoquímica das águas do médio e baixo rio Madeira e seus principais tributários - Amazonas - Brasil

Este trabalho teve como objetivo estudar as águas do rio Madeira e seus principais tributários entre a cidade de Humaitá e sua foz no rio Amazonas. Foram analisados pH, condutividade, turbidez, íons maiores, elementos traço e isótopos de Sr nos períodos de seca, cheia e transição para a seca entre 2009 e 2010. As águas do Madeira, classificadas com brancas, são bicarbonatadas-cálcicas, têm pH entre 5 e 6 e são mais concentradas que as dos tributários. Estes têm águas de cor preta, mais ácidas e quimicamente heterogêneas, os da margem esquerda são quimicamente mais semelhantes as do Madeira, enquanto os da margem direita têm alta concentração em SiO2. Os cátions, Cl- e NO3- são mais concentrados na cheia o que sugere influência do solo, da vegetação e da composição da água da chuva (Cl-), enquanto HCO3-, SO42-, Al, Br e P, com maiores concentrações na seca, devem estar relacionados com a química das rochas. A SiO2 e os elementos terras raras (ETR) com concentrações elevadas na seca e na cheia, estão associados tanto a vegetação e ao solo como as rochas. A interação desses fatores é a causa da heterogeneidade química das águas. Contudo, a semelhança entre as águas dos tributários da margem esquerda e as do Madeira são consequência das rochas dos Andes serem a fonte dos sedimentos cenozóicos percolados por elas, enquanto a química das águas dos tributários da margem direita retrata a estabilidade tectônica, o intenso intemperismo e a baixa taxa de erosão das rochas do cráton Amazônico.

Opalas gemológicas do Piauí: gênese revelada por microtermometria e minerais associados

As opalas de Pedro II e Buriti dos Montes, no estado do Piauí, constituem as mais importantes ocorrências brasileiras dessa gema, tanto em termos de volume quanto pela qualidade gemológica, que é comparável à das famosas opalas australianas. No entanto, a informalidade na extração e comercialização destas opalas, assim como a falta de informações quanto à gênese destes depósitos não permitem a prospecção por novas jazidas e o estabelecimento de um certificado de procedência para as opalas do Piauí que permitisse sua inserção formal no mercado gemológico internacional. Alguns autores têm se dedicado ao estudo dessas opalas, revelando fortes evidências de sua origem hidrotermal, mas até então, nenhum trabalho abordou as características físico-químicas dos fluidos que teriam originado esses depósitos de opalas. Diante disso, o principal objetivo deste trabalho foi entender o sistema hidrotermal responsável pela gênese das opalas do Piauí, ou seja, caracterizar os fluidos que originaram a mineralização e mostrar sua relação com o contexto geológico da região. Os municípios de Pedro II e Buriti dos Montes se localizam na porção nordeste do estado do Piauí, a aproximadamente 230 km a leste da capital Teresina, e as ocorrências de opala se encontram na porção basal da Bacia do Parnaíba, constituindo veios e vênulas nos arenitos dos grupos Serra Grande (Buriti dos Montes) e Canindé (Pedro II), os quais são seccionados por soleiras e diques de diabásio da Formação Sardinha. Elas também ocorrem cimentando brechas e como depósitos coluvionares e de paleocanal. Associados às opalas, localmente encontram-se veios de quartzo, calcedônia, barita e hematita (ou goethita). De maneira geral, as opalas de Pedro II apresentam jogo de cores, são predominantemente brancas ou azuladas com aspecto leitoso, semitranslúcidas a opacas e com inclusões sólidas pouco aparentes. Em contrapartida, as opalas de Buriti dos Montes não apresentam jogo de cores, a cor varia entre amarelo claro e vermelho amarronzado, são semitransparentes a translúcidas e contêm grande variedade de inclusões sólidas. Os dados obtidos revelam que as opalas de Pedro II são tipicamente do tipo amorfo (opala-A), enquanto as opalas de Buriti dos Montes variam entre amorfas e cristobalita-tridimita (opala-CT). Na opala preciosa, o típico jogo de cores é causado pelo arranjo regular das esferas de sílica que as constituem. A ausência de cimento opalino entre as esferas reforça a beleza desse efeito. Em contrapartida, as opalas laranja não apresentam jogo de cores, mas têm maior transparência devido ao diminuto tamanho das esferas. As inclusões sólidas também produzem belos efeitos nas opalas estudadas, principalmente na variedade laranja, que é mais transparente. Além disso, o conjunto de inclusões sólidas revela características intrínsecas aos processos hidrotermais que originaram as opalas estudadas. Agregados botrioidais, dendríticos e nodulares são exemplos de inclusões formadas por fragmentos dos arenitos hospedeiros carreados pelos fluidos hidrotermais que geraram as opalas. As inclusões sólidas também têm relação direta com a cor das opalas. Nas opalas de Buriti dos Montes, os tons de vermelho, laranja e amarelo são produzidos pela dissolução parcial das inclusões constituídas por oxihidróxidos de Fe. De maneira semelhante, a cor verde nas opalas preciosas está relacionada aos microcristais de Co-pentlandita inclusos nas mesmas. O conjunto de minerais associados às opalas conduz a uma assinatura mineralógicogeoquímica marcada pelos elevados teores de Fe e Al nas opalas com inclusões de hematita/goethita e caulinita, e assim também com aumento considerável dos teores de elementos terras raras nas opalas em que se concentram as inclusões de caulinita e apatita. Entre os elementos-traço, Ba é o mais abundante, e provavelmente foi incorporado pelo fluido hidrotermal, tendo em vista que veios de barita são encontrados com frequência nessa região da Bacia do Parnaíba. Várias feições como estruturas de fluxo nas opalas, corrosão e dissolução parcial dos cristais de quartzo hialino e de inclusões mineralógicas, vênulas de quartzo hidrotermal sobrecrescidas aos grãos detríticos, e zoneamento dos cristais de quartzo confirmam que essas opalas têm origem hidrotermal. A ruptura do Gondwana teria provocado um vasto magmatismo básico fissural, que por sua vez foi responsável pelo aporte de calor que gerou as primeiras células convectivas de fluidos quentes. A água contida nos arenitos certamente alimentou o sistema e se enriqueceu em sílica através da dissolução parcial ou total dos próprios grãos de quartzo dos arenitos. Este fluido hidrotermal foi posteriormente aprisionado em sistemas de fraturas e nelas se resfriou, precipitando a opala e minerais associados.