Mineralogical and geochemical analyses of serpentines from ODP Hole 125-778A

Thirty-five samples from Hole 778A were prepared for X-ray diffraction (XRD) mineralogical analyses and for chemical analyses of major and trace elements. Most of the selected samples were silt- and sand-sized sedimentary serpentinites or microbreccias except for a soft clast of mafic rock, a hard clast of massive serpentinized peridotite, and a pebble of consolidated, undeformed serpentine microbreccia that contained planktonic foraminifers. Both mineralogical and geochemical analyses allow discrimination of three groups among the analyzed samples. These groups correspond to three stratigraphic intervals present along the drilled section. Group A contains the upper samples (lithologic Unit I). These consist of poorly consolidated serpentine muds carrying hard-rock clasts (serpentinized peridotites, metabasalts). They are characterized by the following mineralogical assemblage: serpentine, Fe-oxides and hydroxides, aragonite, and halite. They exhibit variable SiO2, MgO contents, but are characterized by a SiO2/MgO ratio near 1. CaO content is high in relation to development of aragonite. Al2O3 content is low. Relatively high K2O, Na2O, and Sr contents are present, presumably in relation to interactions with seawater. Group B (30-77 mbsf) contains samples exhibiting very homogeneous chemical and mineralogical compositions. They consist of serpentinite microbreccias exhibiting frequent shear structures. Hard-rock clasts are also present (serpentinized peridotites, metabasalts, one possible chert fragment). The mineralogy of the Group B samples is characterized by the presence of serpentine and authigenic minerals: hydroxycarbonates and hydrogrossular. Calcite and chlorite are also present, but all the samples lack aragonite. Their chemical compositions are remarkably similar to compositions of their parent rocks. Group C contains silt- and sand-sized serpentine and serpentine microbreccias, which are locally rich in red clasts, probably strongly altered (oxidized?) mafic fragments. Intervals having clasts of more diverse origin than those higher in the section were recovered. Clast lithology includes serpentinized peridotites, metabasalts, metavolcaniclastite, meta-olivine gabbro, and amphibolite sandstone. Mineralogy and geochemistry reflect these compositions. Serpentine content of the samples is less than in previous groups. Correlatively, sepiolite, palygorskite, and chlorite-smectite are mineral phases present in the analyzed samples. Accessory igneous minerals (amphiboles, pyroxenes, hematite) also were found. The chemical compositions of most of Group C samples differ from that of massive serpentinized peridotites. The main differences are (1) higher SiO2, CaO, TiO2 and Al2O3 contents, (2) a SiO2/MgO ratio greater than 1, and (3) a negative correlation between Al2O3, and MgO, Cr, and Ni. These characteristics suggest new constraints relative to the flow structure of the flank of Conical Seamount.

Geochemistry of the Japan Trench sediments at DSDP Legs 56-57 Holes

The main objective of this investigation was to study distribution of main chemical constituents and several minor elements in sediment sections drilled during DSDP Legs 56 and 57 in the Japan Trench, in order to infer geochemical features of different lithologic types of sediments, and to find out how the geochemistry is associated with major lithologic constituents, such as terrigenous detrital matter, clay, volcanic ash, and biogenic particles. The geochemical data may help to indicate the nature of the sediments and to interpret sedimentation processes. The analyzed samples seem to be representative of most lithologic units, sub-units, and sediment types drilled at all sites on both legs, except for some shallow-water deposits at Sites 438 and 439. We analyzed bulk-sediment composition by X-ray fluorescence (Kuzmina and Turanskaya) and routine wet-chemical methods (Mikhailov); amorphous SiO2, extracted in a boiling sodium carbonate solution (Analythical Laboratory, P. P. Shirshov Institute of Oceanology); Cr, Zn, Cu, Ni, Co, and Al by atomic absorption (Gordeev); and Sn, Pb, Zn, Cu, Ni, Co, Cr, V, B, and Ag by quantitative spectrographic analyses in both bulk samples and granulometric fractions (Mikhailov). In addition, Fe, Ti, Mn, and CaCO3 have been determined in selected samples by routine wet-chemical methods (Analytical Laboratory, P. P. Shirshov Institute of Oceanology). Murdmaa was responsible for interpretation of the results.

Mineral and geochemical characterization of a leptic aluandic soil and a thapto aluandic-ferralsol developed on trachytes in Mount Bambouto (Cameroon volcanic line)

Mineral and geochemical investigations were carried out on soil samples and fresh rock (trachytes) from two selected soil profiles (TM profile on leptic aluandic soils and TL profile on thapto aluandic-ferralsols) from Mount Bambouto to better understand geochemical processes and mineral paragenesis involved in the development of soils in this environment. In TM profile, the hydrated halloysites and goethite occur in the weathered saprolite boulders of BC horizon while dehydrated halloysite, gibbsite and goethite dominate the soils matrices of BC and A horizons. In TL profile, the dehydrated halloysites and goethite are the most abundant secondary minerals in the weathered saprolites of C and BC horizons while gibbsite, hematite and kaolinite occur in the soil matrices of BC, B and A horizons. The highest gibbsite content is in the platy nodules of B horizon. In both soil profiles, organo-metal complexes (most likely of AI and Fe) are present in the surface A horizon. Geochemically, between the fresh rock and the weathered saprolites in both soils, SiO2, K2O, CaO, Na2O and MgO contents decrease strongly while Fe2O3 and Al2O3 tend to accumulate. The molar ratio of SiO2/Al2O3 (Ki) and the sum of Ca, Mg, K and Na ions (TRB) also decreases abruptly between fresh rocks and the weathered saprolites, but increases significantly at the soil surface. The TM profile shows intense Al enrichment whereas the TL profile highlights enrichment in both AI and Fe as the weathering progresses upwards. Both soil profiles are enriched in Ni, Cu, Ba and Co and depleted in U, Th, Ta, Hf, Y, Sr, Pb, Zr and Zn relative to fresh rock. They also show a relatively low fractionation of the rare earth elements (REE: La, Nd, Sm, Eu, Tb, Yb and Lu), except for Ce which tends to be enriched in soils compared to CI chondrite. All these results give evidence of intense hydrolysis at soil deep in Mount Bambouto resulting in the formation of halloysite which progressively transforms into gibbsite and/or dehydrated halloysite. At the soil surface, the prominent pedogenetic process refers to andosolization with formation of organo-metal complexes. In TL profile, the presence of kaolinite in soil matrices BC and B horizons is consistent with ferralitization at soil deep. In conclusion, soil forming processes in Mount Bambouto are strongly influenced by local climate: (i) in the upper mountain (>2000 m), the fresh, misty and humid climate favors andosolization; whereas (ii) in the middle lands (1700-2000 m) with a relatively dry climate, both andosolization at the soil surface and ferralitization at soil deep act together. (C) 2009 Elsevier B.V. All rights reserved.

Estudo do aproveitamento do rejeito da mineração de esmeraldas na produção de refratários conformados isolantes

Emerald mining is an important area of the economy in Brazil, country which is in second place among the exporting nations of this gem. Due to the process of extraction, a great amount of reject is generated. Since there is no appropriate destination, the reject is abandoned around the mining industries, contributing to environment degradation. Nowadays, some of the most relevant things to an industry in general are: energy conservation, cost reduction, quality and productivity enhancement. The production of isolating, transformed refractory materials achieves the sustainability dimension when protection of the environment is incorporated to such process. This work investigates the use of emerald mining rejects in the ceramic body of refractory materials, aiming at obtaining a product whose characteristics are compatible with commercial products and, at the same time, allow the use of such rejects to solve the environmental issue caused by its disposal in nature. X-ray fluorescence analysis show that the emerald reject obtained after the flotation to extract molybdenum and mica has 70% of silica and alumina (SiO2+Al2O3) and 21% of a basic oxides and alkaline metals and earthy alkaline mixture (Na2O, K2O, CaO e MgO). Because of the significant amount of silica and alumina present in the reject, four refractory ceramic bodies were prepared. Samples with a rectangular shape and dimensions 100x50x10 mm were pressed in a steel mold at 27,5 MPa and sintered at 1200ºC for 40 min. under environment atmosphere in a resistive oven. The sintered samples were characterized in relation to the chemical composition (FRX), mineralogical composition (DRX), microstructure (MEV) and physical and mechanical properties. The results indicate that the mixture with 45% of reject, 45% of alumina and 10% of kaolin presents a refractory quality of 1420ºC, dimensional linear variation below 2.00%, apparent specific mass of 1,56 g/cm3 and porosity of 46,68%, which demonstrates the potential use of the reject as raw material for the industry of isolating transformed refractory materials

Condutividade térmica de rochas: uma aplicação para granitos ornamentais

This dissertation focuses on rock thermal conductivity and its correlations with petrographic, textural, and geochemical aspects, especially in granite rocks. It aims at demonstrating the relations of these variables in an attempt to enlighten the behavior of thermal effect on rocks. Results can be useful for several applications, such as understanding and conferring regional thermal flow results, predicting the behavior of thermal effect on rocks based upon macroscopic evaluation (texture and mineralogy), in the building construction field in order to provide more precise information on data refinement on thermal properties emphasizing a rocky material thermal conductivity, and especially in the dimension stone industry in order to open a discussion on the use of these variables as a new technological parameter directly related to thermal comfort. Thermal conductivity data were obtained by using Anter Corporation s QuicklineTM -30 a thermal property measuring equipment. Measurements were conducted at temperatures ranging between 25 to 38 OC in samples with 2cm in length and an area of at least 6cm of diameter. As to petrography data, results demonstrated good correlations with quartz and mafics. Linear correlation between mineralogy and thermal conductivity revealed a positive relation of a quartz percentage increase in relation to a thermal conductivity increase and its decrease with mafic minerals increase. As to feldspates (K-feldspate and plagioclase) they show dispersion. Quartz relation gets more evident when compared to sample sets with >20% and <20%. Sets with more than 20% quartz (sienogranites, monzogranites, granodiorites, etc.), exhibit to a great extent conductivity values which vary from 2,5 W/mK and the set with less than 20% (sienites, monzonites, gabbros, diorites, etc.) have an average thermal conductivity below 2,5 W/mK. As to textures it has been verified that rocks considered thick/porphyry demonstrated in general better correlations when compared to rocks considered thin/medium. In the case of quartz, thick rocks/porphyry showed greater correlation factors when compared to the thin/medium ones. As to feldspates (K-feldspate and plagioclase) again there was dispersion. As to mafics, both thick/porphyry and thin/medium showed negative correlations with correlation factor smaller than those obtained in relation to the quartz. As to rocks related to the Streckeisen s QAP diagram (1976), they tend to fall from alcali-feldspates granites to tonalites, and from sienites to gabbros, diorites, etc. Thermal conductivity data correlation with geochemistry confirmed to a great extent mineralogy results. It has been seen that correlation is linear if there is any. Such behavior could be seen especially with the SiO2. In this case similar correlation can be observed with the quartz, that is, thermal conductivity increases as SiO2 is incremented. Another aspect observed is that basic to intermediate rocks presented values always below 2,5 W/mK, a similar behavior to that observed in rocks with quartz <20%. Acid rocks presented values above 2,5 W/mK, a similar behavior to that observed in rocks with quartz >20% (granites). For all the other cases, correlation factors are always low and present opposite behavior to Fe2O3, CaO, MgO, and TiO2. As to Al2O3, K2O, and Na2O results are not conclusive and are statistically disperse. Thermal property knowledge especially thermal conductivity and its application in the building construction field appeared to be very satisfactory for it involves both technological and thermal comfort aspects, which favored in all cases fast, cheap, and precise results. The relation between thermal conductivity and linear thermal dilatation have also shown satisfactory results especially when it comes to the quartz role as a common, determining phase between the two variables. Thermal conductivity studies together with rocky material density can function as an additional tool for choosing materials when considering structural calculation aspects and thermal comfort, for in the dimension stone case there is a small density variation in relation to a thermal conductivity considerable variation

Pb-210 and composition data of near-surface sediments and interstitial waters evidencing anthropogenic inputs in Amazon River mouth, Macapa, Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Pb-210-derived chronology in sediment cores evidencing the anthropogenic occupation history at Corumbata River basin, Brazil

Activity profiles of excess Pb-210 combined with chemical data determined in two sediment cores from Corumbatai River basin, São Paulo State, Brazil, provided new insights into the reconstruction of historical inputs of anthropogenic constituents, contributing to improving management strategies of the hydrological resources in the basin since most of the municipalities extensively utilize the waters of Corumbatai River and tributaries for drinking purposes, among other uses. Excellent significant relationships between loss on ignition (LOI) and organic matter were found for sediments of both analyzed profiles. Silica was found to be inversely related to organic matter at both analyzed profiles: its decrease accompanied an increase in the specific surface of the sediments. This relationship was confirmed by a great number of inverse significant correlations among silica and oxides Na2O, K2O, CaO, MgO, Al2O3, P2O5, Fe2O3, MnO, and TiO2. It was possible to identify the role of organic matter on adsorption of several oxides/elements in the core sediments profiles. Apparent sediment mass accumulation rates corresponding to 224 and 802 mg cm(-2) year(-1) were obtained, and are compatible with field evidence, indicating a higher value associated with sand mining activities interfering with the natural/normal sedimentation process, due to modifications of the channel drainage.

Chert petrology and geochemistry at DSDP Leg 62 Holes

Sixty-five chert, porcellanite, and siliceous-chalk samples from Deep Sea Drilling Project Leg 62 were analyzed by petrography, scanning electron microscopy, analysis by energy-dispersive X-rays, X-ray diffraction, X-ray spectroscopy, and semiquantitative emission spectroscopy. Siliceous rocks occur mainly in chalks, but also in pelagic clay and marlstone at Site 464. Overall, chert probably constitutes less than 5% of the sections and occurs in deposits of Eocene to Barremian ages at sub-bottom depths of 10 to 820 meters. Chert nodules and beds are commonly rimmed by quartz porcellanite; opal-CT-rich rocks are minor in Leg 62 sediments 65 to 108 m.y. old and at sub-bottom depths of 65 to 520 meters. Chert ranges from white to black, shades of gray and brown being most common; yellow-brown and red-brown jaspers occur at Site 464. Seventy-eight percent of the studied cherts contain easily recognizable burrow structures. The youngest chert at Site 463 is a quartz cast of a burrow. Burrow silica maturation is always one step ahead of host-rock silicification. Burrows are commonly loci for initial silicification of the host carbonate. Silicification takes place by volume-f or-volume replacement of carbonate sediment, and more-clay-rich sediment at Site 464. Nannofossils are commonly pseudomorphically replaced by quartz near the edges of chert beds and nodules. Other microfossils, mostly radiolarians and foraminifers, whether in chalk or chert, can be either filled with or replaced by calcite, opal-CT, and (or) quartz. Chemical micro-environments ultimately control the removal, transport, and precipitation of calcite and silica. Two cherts from Site 465 contain sulfate minerals replaced by quartz. Site 465 was never subaerially exposed after sedimentation began, and the formation of the sulfate minerals and their subsequent replacement probably occurred in the marine environment. Several other cherts with odd textures are described in this paper, including (1) a chert breccia cemented by colloform opal-CT and chalcedony, (2) a transition zone between white porcellanite containing opal-CT and quartz and a burrowed brown chert, consisting of radial aggregates of opal-CT with hollow centers, and (3) a chert that consists of silica-replaced calcite pseudospherules interspersed with streaks and circular masses of dense quartz. X-ray-diffraction analyses show that when data from all sites are considered there are poorly defined trends indicating that older cherts have better quartz crystallinity than younger ones, and that opal-CT crystallite size increases and opal-CT cf-spacings decrease with depth of occurrence in the sections. In a general way, depth of burial and the presence of calcite promote the ordering in the opal-CT crystal structure which allows its eventual conversion to quartz. Opal-CT in porcellanites converts to quartz after reaching a minimum d-spacing of 4.07 Å. Quartz/opal-CT ratios and quartz crystallinity vary randomly on a fine scale across four chert beds, but quartz crystallinity increases from the edge to the center of a fifth chert bed; this may indicate maturation of the silica. Twenty-four rocks were analyzed for their major- and minor-element compositions. Many elements in cherts are closely related to major mineral components. The carbonate component is distinguished by high values of CaO, MgO, Mn, Ba, Sr, and (for unknown reasons) Zr. Tuffaceous cherts have high values of K and Al, and commonly Zn, Mo, and Cr. Pure cherts are characterized by high SiO2 and B. High B may be a good indicator of formation of chert in an open marine environment, isolated from volcanic and terrigenous materials.

Geochemistry at DSDP Leg 70 Holes

The hydrothermal mounds on the southern flank of the Galapagos Spreading Center are characterized by the following main features: 1) They are located over a young basement (0.5 to 0.85 m.y. of age) in a region known for its high sedimentation rate (about 5 cm/10**3 y.) because it is part of the equatorial high biological productivity zone. 2) They are located in a region with generally high heat flow (8 to 10 HFU). The highest heat-flow measurements (up to 10**3 HFU) correspond to mound peaks (Williams et al., 1979), where temperatures up to 15°C were measured during a dive of the submersible Alvin (Corliss et al., 1978). 3) They are often located on small vertical faults which displace the basement by a few meters (Lonsdale, 1977) and affect the 25- to 50-meter-thick sediment cover. Most of these characteristics have also been observed in the other three known cases of hydrothermal deposits with mineral parageneses similar to that of the Galapagos mounds. However, the case of the hydrothermal mounds south of the Galapagos Spreading Center is unique because of the unusual thickness of the hydrothermal deposits present. The mounds are composed of several, up to 4.5-meter-thick, layers of green clays which, in one case (Hole 509B), are overlain by about 1.4 meters of Mn-oxide crust. We suspect that such a large accumulation of hydrothermal products results from the "funnelling" of the hydrothermal solutions exiting from a highly permeable basement along the faults. This chapter reports a preliminary study of those green clays collected by hydraulic piston coring of the Galapagos mounds during Deep Sea Drilling Project (DSDP) Leg 70 of the D/V Glomar Challenger. Green clays have also been reported from three presently or recently active hydrothermal areas in or close to spreading centers.

Geochemistry at DSDP Leg 73 Holes

In the South Atlantic, at Sites 519 to 523, the dissolution of calcareous oozes ended in the formation of red clays rich in iron and manganese. The early authigenesis of manganese oxides and clays is described in Miocene marly calcareous oozes. The mineralogical and geochemical influences of basaltic basement weathering are shown by the occurrence of palagonite, authigenic clays, and oxides in the basal sediments. The development of red clay facies can be inhibited by local topographic and paleoceanographic changes, as at Site 520.

Geochemistry of Neogene sediments of ODP Hole 115-711A

Pelagic sedimentation in the northwest Indian Ocean has been studied using sediments from Hole 711A (the section from 0 to 70.5 mbsf, 0-22 Ma), a deep site (4428 m) drilled during Ocean Drilling Program Leg 115. The clay fraction of the sediments represents poorly developed pelagic deposits with considerably lower contents of Mn, Ba, Cu, Ni, Cr, and Zn than is typical for well-oxidized pelagic sediments formed far from the continents (e.g., in the central Indian or Pacific oceans). Geochemical provenance models, representing conservative mixing models with terrigenous, exhalative-volcanic, and biogenous matter as the only inputs, explain most of the compositional variations in the sediments. The models show that terrigenous matter accounts for about 96%-100% of all SiO2, Al2O3, TiO2, and Zr; about 73%-85% of all Fe2O3, V, and Ni; and about 40%-60% of the Cu and Zn abundances. Exhalative-volcanic matter delivers a large fra tion of Mn (78%-85%), some Fe (15%-219/o), and possibly some Cu (38%-51%). Biogenous deposition is generally of restricted significance; at most 6%-35% of all Cu and Zn may derive from biogenic matter. The exhalative-volcanic matter is slightly more abundant in the oldest deposits, reflecting a plate tectonic drift away from the volcanic Carlsberg Ridge. The Al/Ti ratio reveals that silicic crustal matter plays a somewhat larger role in the upper and lower part of the section studied, whereas the basaltic input is slightly higher in the intermediate levels (age 5-15 m.y.). The sediment abundances of Ba generally exceed those predicted by the models, an anomalous behavior also observed in equatorial Pacific sediments. This is possibly caused by poor knowledge of the input components. Several changes in accumulation rates seem to correlate with climatic changes (onset of monsoon-driven upwellings and sea-level regressions of about 50-100 m at 10, 15-16, and 20-21 Ma). A number of constituents show higher accumulation rates at or shortly after these regressions, suggesting an accelerated removal of fines from shallow oceanic areas. Furthermore, the SiO2/Al2O3 ratio shows a small increase in sediments younger than 10 Ma, implying an increase in biological productivity, particularly after the onset of monsoon-driven upwelling in the northwest Indian Ocean. This trend is paralleled by a general increase in the accumulation rates of Ba and CaCO3. However, these accumulation rates are generally significantly lower than under the biological high-productivity zone in the equatorial Pacific. The onset of these upwelling systems about 10 Ma is probably related to the closing of the gap between India and the main Asiatic continent, preventing free circulation around the Indian subcontinent.

Geoquímica de elementos maiores e traços de granitoides neoproterozoicos da província Borborema e sua correlação com propriedades físicas de rochas

This paper discusses the correlation of thermal conductivity, density and magnetic susceptibility with composition of major and trace elements of Neoproterozoic igneous bodies from Borborema Province, Northeastern Brazil. These properties were used as potential markers among the studied magmatic suites. For the correlation between petrophysical and geochemical properties it was considered a set of 195 chemical analyzes of granitoid rocks, separated by the degree of acidity in basic, intermediate and acidic. Major (SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O and TiO2) and some trace elements (Rb, Sr, Ba, Zr, Th and U) that are usually linked to the formation of the most common minerals of igneous rocks were used. The results show that SiO2 has the best positive correlation with the thermal conductivity, while Al2O3, CaO, Fe2O3, MgO and TiO2 exhibit negative correlation for the same property. The correlation with density is opposite to that one for these oxides with the thermal conductivity. The magnetic susceptibility did not correlate with the elements studied. The results for thermal conductivity and density indicate a tendency of SiO2 and oxides with higher affinity with mafic minerals (Al2O3, CaO, Fe2O3, TiO2 and MgO) in controlling these petrophysical parameters. The set of samples was divided into five different magmatic suites based on their lithogeochemical aspects into: i) peralkaline / alkaline; ii) alkaline; iii) calc-alkaline; iv) high potassium calcium alkaline; and v) shoshonitic. Data analysis showed that the thermal conductivity and density presented good results in the individualization of these suites, notably between peralkaline / alkaline, alkaline suites, calc-alkaline and shoshonitic. However, the high-K calc-alkaline suite overlapped with the other. In contrast, the magnetic susceptibility did not show effective results for separating the five chemical suites.

Metamorphism on Chromite Ores from the Dobromirtsi ultramafic massif, Rhodope Mountains (SE Bulgaria)

Podiform chromitite bodies occur in highly serpentinized peridotites at Dobromirtsi Ultramafic Massif (Rhodope Mountains, southeastern Bulgaria). The ultramafic body is believed to represent a fragment of Palaeozoic ophiolite mantle. The ophiolite sequence is associated with greenschist - lower-temperature amphibolite facies metamorphosed rocks (biotitic gneisses hosting amphibolite). This association suggests that peridotites, chromitites and metamorphic rocks underwent a common metamorphic evolution. Chromitites at Dobromirtsi have been strongly altered. Their degree of alteration depends on the chromite/silicate ratio and to a lesser extent, on the size of chromitite bodies. Alteration is recorded in individual chromite grains in the form of optical and chemical zoning. Core to rim chemical trends are expressed by MgO- and Al2O3- impoverishment, mainly compensated by FeO and/or Fe2O3 increases. Such chemical variations correspond with three main alteration events. The first one was associated with ocean-floor metamorphism and was characterized by a lizardite replacement of olivine and the absence of chromite alteration. The second event took place during greenchist facies metamorphism. During this event, MgO- and SiO2-rich fluids (derived from low temperature serpentinization of olivine and pyroxenes) reacted with chromite to form chlorite; as a consequence, chromite became altered to a FeO- and Cr2O3-rich, Al2O3-poor chromite. The third event, mainly developed during lower temperature amphibolite facies metamorphism, caused the replacement of the primary and previously altered chromite by Fe2O3-rich chromite (ferritchromite).

Controle da porosidade em fases vítreas formadas pela ação de fundentes em cerâmicas gresificadas

O presente trabalho teve como objetivo investigar os fenômenos que controlam a porosidade em corpos cerâmicos com fases vítreas, formadas pela ação de fundentes, e associá-los com sua microestrutura final. Foram selecionados os fundentes albita, feldspato alcalino, wollastonita e espodumênio, representativos daqueles comercializados no setor cerâmico, a partir de critérios como teor e tipo de álcali, e teor em SiO2 e Al2O3 na composição química. Estes fundentes foram formulados com cada uma das seguintes matérias-primas e combinações destas: quartzo, caulim e talco. As composições foram formuladas com o objetivo de obter-se uma gama de diferentes microestruturas, variando porosidade, e a presença de fases vítreas ou cristalinas. Os corpos cerâmicos foram obtidos em fornos elétricos, tipo mufla, variando-se a temperatura entre 1140 e 1260°C, conforme a formulação investigada. Foram determinadas as propriedades dos corpos cerâmicos, como porosidade aparente, absorção de água e retração linear. Os resultados obtidos foram associados com sua microestrutura e formulação. Para tanto, fez-se uso de microscopia eletrônica de varredura e difratometria de raios-X. Em especial, a porosidade foi avaliada quanto sua distribuição, morfologia e tamanho, e sua influência na definição da microestrutura final, e relação com propriedades dos corpos cerâmicos investigados. Os resultados obtidos indicaram que o comportamento dos fundentes em massas cerâmicas define decisivamente a formação da porosidade em função da composição química do fundente e da combinação desta com a dos outros constituintes da massa cerâmica. O espodumênio forma fase vítrea reagindo basicamente com o quartzo em baixas temperaturas, retendo a porosidade principalmente junto às trincas de contração do mesmo. A albita propicia na expansão da porosidade e interconexão da mesma. O feldspato alcalino forma um líquido de maior viscosidade mantendo a menor porosidade e de maneira mais isolada. A wollastonita reage de modo diferenciado dos demais no que diz respeito à sílica presente, reagindo melhor na presença do alumínio e do magnésio.

Catalisadores de vanádio (V) contendo ligante tris(pirazolil)borato : rotas de imobilização e avaliação em polimerização de etileno

As sínteses, caracterizações e estudos referentes a polimerização do etileno de uma série de complexos {TpMs*}V(NtBu)Cl2 (1), {TpMs*}V(O)Cl2 (2), {TpMePh]V(NtBu)Cl2 (3) e {Tp*}V(O)Cl2 (4) são descritas. A reação destes complexos com MAO geram espécies catalíticas ativas para a polimerização do etileno. Para as reações de polimerização realizadas em tolueno a 30°C, as atividades variaram entre 71 e 1.126 kg de PE/mol[V]·h·atm. A atividade mais alta foi obtida usando o precursor catalítico 1. As curvas de DSC mostraram a formação de polietileno de alta densidade com temperaturas de fusão entre 134 e 141ºC. Visando a obtenção de catalisadores suportados, o complexo 1 foi imobilizado através do método direto sobre os seguintes suportes inorgânicos: SiO2, SiO2 modificada com MAO, SiO2-Al2O3, MCM-41, MgO e MgCl2. O teor de metal imobilizado, determinado por XRF, permaneceu entre 0,22 e 0,50 % g V/g suporte (p/p %).Os maiores teores de metal foram encontrados para os suportes com maiores áreas superficiais (SiO2–Al2O3 e MCM-41). Todos os sistemas mostraram-se ativos na polimerização do etileno na presença de MAO ou TiBA/MAO (1:1) (Al/V = 1000). A atividade catalítica mostrou-se dependente da natureza do suporte, ficando esta entre 8 e 89 kg de PE/mol[V]·h·atm. Os melhores resultados foram obtidos para sílica. Suportes ácidos ou básicos forneceram sistemas catalíticos menos ativos. Os polietilenos apresentaram pesos moleculares médios (Mw) superiores a 2.000.000 g/mol, sugerindo a produção de polímeros com ultra-alto peso molecular. Baseado nos resultados referentes a imobilização de 1, o complexo 2 foi imobilizado sobre SiO2 e SiO2 modificada com MAO. As reações de polimerização deste catalisador suportado foram realizadas em tolueno a 30ºC, utilizando MAO ou TiBA/MAO (1:1) (Al/V = 1000). Os resultados de atividade variaram entre 7 e 236 kg de PE/mol[V]·h·atm, sendo a maior atividade encontrada para o sistema suportado 2/SiO2/MAO(4,0 % Al/SiO2) na presença da mistura de cocatalisadores TiBA/MAO (1:1). Os complexos 1 e 2 foram imobilizados “in situ” utilizando SiO2 e SiO2/MAO (4,0 % em peso de Al/SiO2) como suportes, empregando 0,02 % em peso de V/g suporte. Todos os sistemas estudados foram ativos nas reações de polimerização do etileno. Para o complexo 1, a maior atividade (1.903 kg de PE/mol[V]·h·atm) foi obtida utilizando o sistema 1/SiO2/MAO (4,0 % em peso de Al/SiO2) na presença do MAO. Cabe ressaltar que, para este sistema catalítico, o uso de TMA ao invés de MAO proporciona a formação de um sistema catalítico altamente ativo (1.342 kg de PE/mol[V]·h·atm). A maior atividade (1.882 kg de PE/mol[V]·h·atm) para o complexo 2 foi encontrada quando o mesmo foi suportado “in situ” sobre SiO2, utilizando MAO como cocatalisador. O catalisador de vanádio preparado “in situ” sobre o suporte na presença do MAO apresentou uma atividade catalítica de 22 kg de PE/mol[V]·h·atm) sendo a mesma inferior àquela obtida utilizando o sistema via imobilização do catalisador “in situ”. Várias rotas sintéticas (hidrolíticas e não-hidrolíticas) objetivando a preparação “in situ” do catalisador sobre sílicas-híbridas foram empregadas, entretanto todas as tentativas falharam devido à alta reatividade do grupo NCO com alguns reagentes empregados no processo de preparação das mesmas. Uma série de catalisadores híbridos foram preparados pela combinação e imobilização seqüencial de {TpMs*}V(NtBu)Cl2 (1) e [LFeCl2] (8) (L = 2,6-bis(imino)piridila) sobre SiO2/MAO (4,0% em peso de Al/SiO2) em diferentes proporções (1:1) e (1:3). Todos os sistemas foram ativos na polimerização do etileno na presença de MAO como cocatalisador. A atividade mostrou-se dependente da natureza do complexo e da ordem de imobilização. A maior atividade foi obtida para o sistema V/Fe/SMAO-4 (1:1) (117 kg de PE/mol[M]·h·atm). Baseado nas curvas de DSC, diferentes tipos de PE podem ser obtidos dependendo da natureza do complexo imobilizado e da ordem da adição dos catalisadores no suporte. Para os sistemas híbridos, a presença do Fe determina a formação de PE com dois picos de fusão.