IG - Instituto de Geociências

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2172

Navegar

Agora exibindo 1 - 20 de 275

Acesso aberto (Open Access)
2-D ZO CRS stack by considering an acquisition line with smooth topography
(2005-03) OLIVA, Pedro Andrés Chira; CRUZ, João Carlos Ribeiro; CALLAPINO, German Garabito; HUBRAL, Peter; TYGEL, Martin
The land seismic data suffers from effects due to the near surface irregularities and the existence of topography. For obtaining a high resolution seismic image, these effects should be corrected by using seismic processing techniques, e.g. field and residual static corrections. The Common-Reflection-Surface (CRS) stack method is a new processing technique to simulate zero-offset (ZO) seismic sections from multi-coverage seismic data. It is based on a second-order hyperbolic paraxial traveltime approximation referred to a central normal ray. By considering a planar measurement surface, the CRS stacking operator is defined by means of three parameters, namely the emergence angle of the normal ray, the curvature of the normal incidence point (NIP) wave, and the curvature of the normal (N) wave. In this paper the 2-D ZO CRS stack method is modified in order to consider effects due to the smooth topography. By means of this new CRS formalism, we obtain a high resolution ZO seismic section, without applying static corrections. As by-products the 2-D ZO CRS stack method we estimate at each point of the ZO seismic section the three relevant parameters associated to the CRS stack process.
Acesso aberto (Open Access)
3D raytracing through homogeneous anisotropic media with smooth interfaces
(2002-12) COSTA, Jessé Carvalho; SCHOENBERG, Michael; URBAN, Jaime Antonio
Two-point raytracing problem is solved for events in a piecewise homogeneous and laterally varying 3D anisotropic media by continuation techniques. In conjunction with the shooting method the algorithm can be used for computation of qP, qS1, and qS2 events. The algorithm has the same performance and robustness as previous implementations of the continuation method for tracing rays in isotropic models. Routines based on our algorithm have several useful applications. First, an efficient forward problem solver for traveltime inversion of elastic parameters in the presence of anisotropy. Second, Newton-Raphson iterations during two-point raytracing produce wavefront attributes, slowness and wavefront curvature. These attributes allows the computation of geometrical spreading and second order approximations for traveltimes. Therefore it can be used to investigate the effects of anisotropy on CRS, in simple velocity models.
Acesso aberto (Open Access)
Ação sonoquímica e influência das condições de tratamento térmico na preparação de cimentos do sistema binário CaO-Al2O3
(2010-03) LOURENÇO, Rafaela Roberta; EXPOSITO, Caio Cesar Dente; ANGÉLICA, Rômulo Simões; RODRIGUES, José de Anchieta
Cements of the CaO-Al2O3, binary system were prepared through a sonochemical process at room temperature followed by heat treatment. The conventional production consists of a reaction in which a stoichiometric mixture of lime and bauxite or alumina is melted or sintered. High temperatures and energy consumption is an inconvenience associated to this type of synthesis. In the sonochemical process, the initial reagents, calcia and alumina, are put in an aqueous suspension under the action an ultrasonic bath during some time. After that, the material is heat treated, after the evaporation of water. Ultrasonic waves can induce changes in the surface morphology of the particles, including size reduction of them. Consequently, the reagent particles become more reactive and this facilitates the final synthesis of the calcium aluminates during the heat treatment. The action of ultrasonic waves and the influence of thermal treatment conditions were studied on two initials molar compositions calcia:alumina of 1:1 and 1:2. Temperatures of 1000, 1200 and 1300 ºC for 1 and 6 h were employed. SEM and X-ray diffraction were used to characterize the obtained materials and the phases were semi-quantified through Rietveld method. In addition, mechanical strength of the products was evaluated through splitting tensile tests. Pastes consisting of cement, alumina and water were prepared using the calcium aluminates prepared through the sonochemical process and commercial cement as reference.
Acesso aberto (Open Access)
Adsorção de fenol e benzeno em montmorilonita modificada com brometo de hexadeciltrimetilamônio
(2014-12) SANTOS, Sheila Silva dos; LEMOS, Vanda Porpino; VILAÇA, A. L. C.; TAVARES, Laís Conceição; QUEIRÓZ, Leandro Santos
This study evaluates the intercalation of the smectite dioctahedric state of Acre, Brazil, with the quaternary ammonium salt bromide, hexadecyltrimethylammonium (HDTMA) at concentrations ranging from 1 to 5 times the value of the original clay CEC and its application in the adsorption of phenol and benzene in the liquid phase. The materials were characterized by microanalysis X-ray diffraction, scanning electron microscopy /energy dispersive spectroscopy and infrared spectroscopy. The adsorption processes were carried out in simple systems and measurements of the concentrations of phenol and benzene were performed by spectrophotometry in the ultraviolet region. The results indicated that the intercalation of smectite with HDTMA provided approximately 78.8 expansion (range d001: 1.47 nm to 1.91 nm) and sharp decrease of the interlayer positions of elements such as Na, Ca, Mg and K, together by delamination/exfoliation of the clay original. In adsorption processes of phenol and benzene at HDTMA-arg 5 the following results were obtained: qmax = 4.44 and 35.8 mg.g-1; KL= 0.076 and 0.115 L.g-1; ΔGº = -16.85 and -18.38 kJ.mol-1, respectively. These data indicated that the adsorption of benzene and phenol in liquid phase in the organophilic HDTMA-arg 5 were favorable, spontaneous and physical interactions.
Acesso aberto (Open Access)
Adsorção de molibdato em minerais de argilas naturais e modificadas com ácido sulfúrico, ácido húmico e uréia
(2013-03) PEREIRA, Patrícia Magalhães; LEMOS, Vanda Porpino; RODRIGUES, E.; FAIAL, Kelson do Carmo Freitas
Clay sediments from the municipalities Assis Brazil (Acre), were leached with solutions of sulfuric acid, humic acid and urea, to evaluate the retention capacity of molybdate in these materials and to investigate the feasibility of the adsorption processes at solid-solution interfaces. The materials were characterized from data of XRD, FTIR spectra, surface charge and chemical composition. The Langmuir isotherm models, Freundlich and Sips were used to fit the experimental data of adsorption. The minerals identified in the clay sediments were smectite, kaolinite, illite, quartz, albite, calcite and microclineo. The chemical modification leads amorphization of the modified sample with sulfuric acid and delamination along the plane 001 of the modified sample with urea. The settings defined by mathematical parameters (KL,Kf) of the adsorption isotherms, evaluation Ce vs. qe, pH vs. Qe, Qmax (sips) and Kd, indicated that the S10H15 sample is more efficient in the adsorption MoO42- ,with com qMax = 6.83 mg. L-1.
Acesso aberto (Open Access)
Águas subterrâneas em Rondônia: análise estatística de dados hidroquímicos, organolépticos e bacteriológicos
(2009-12) ZUFFO, Catia Eliza; ABREU, Francisco de Assis Matos de; CAVALCANTE, Itabaraci Nazareno; NASCIMENTO, Gerson Flôres
In order to improve the ongoing process of managing groundwaters in the State of Rondonia we collected the results of 384 physical-chemical and / or bacteriological analyses of wells on file in the 2nd Socio-Economic and Ecological Zonation of the State of Rondonia, Brazil - ZSEE / RO, submitted by localities. We then treated and reorganized these data according to hydrographic basins using spreadsheets. We sought to characterize the quality of groundwater in major watersheds of the state of Rondonia by considering physical (color, pH and turbidity), chemical (chloride, total iron, sulfate, oxygen consumption, total hardness, calcium hardness, magnesium hardness, total solids, nitrogen as nitrite, nitrogen as nitrate, free carbon dioxide and HCO3 alkalinity) and bacteriological (standard bacterial counts of most probable number of coliform bacteria, most probable number of fecal coliform bacterial, most probable number of colonies - membrane filter method) properties. In order to test the adjustment of the data obtained to a normal distribution, we used the Kolmogorov-Smirnov method, modified by Lilliefors. The study revealed that the groundwater analyzed had good physical-organoleptic properties; the basins of the Madeira and of the Machado rivers showed the greatest changes in pH values, chloride and nitrate, indicative of a loss of quality of groundwater resources depending on population density. The Abunan river basin revealed the highest risk of fecal contamination, with water samples generally showing results that exceeded the bacteriological standards, thus requiring treatment by chlorination or boiling and filtration before human consumption.
Acesso aberto (Open Access)
Albedo da cultura da soja em área de avanço da fronteira agrícola na Amazônia
(2010-01) SOUZA, Paulo Jorge de Oliveira Ponte de; RIBEIRO, Aristides; ROCHA, Edson José Paulino da; LOUREIRO, Renata Silva de; BISPO, Carlos José Capela; SOUSA, Adriano Marlisom Leão de
Soybean expansion in the Amazon has been increasing considerably in recent years, the consequences of which can be serious environmental impacts. In this paper the soybean albedo (Glycine Max (L.) Merryl) was evaluated, which was planted in natural field conditions in Paragominas city (PA), a region representative of agricultural expansion in Amazon. A direct relationship was observed between soybean albedo and its leaf area index (LAI), showing a daily maximum value between 0.24 and 0.25 associated to a LAI of 7.17, when soybean has accumulated 1297.62 degree-days. It was found that the most critical phase of the crop, based on change in surface albedo, is the fruitification phase, when albedo shows a maximum mean value of 0.23 (± 0.0007). Empirical models were fitted to simulate the daily variation of the albedo as a function of LAI and soil humidity during the cycle, and to simulate the diurnal variation of the albedo as a function of solar elevation, for each soybean phase.
Acesso aberto (Open Access)
Ambiente flúvio-deltáico influenciado por maré e tempestade da Formação Rio Maria, leste da Província Carajás (SE) do Cráton Amazônico
(2012-12) NASCIMENTO, Marivaldo dos Santos; OLIVEIRA, Camila Vilar de; ALTHOFF, Fernando Jacques
The Rio Maria Formation is a siliciclastic sedimentary sequence deposited in an eiperic sea formed along of eastern edge of the Carajás Province – the oldest Archean province of the Amazonian Craton – being intruded by rapakivi-type granite (1.88 Ga). Four facies associations have been recognized: prodelta-distal bar, delta-front/shoreface, delta-plain/distributaries and fluvial channels. Large-scale hummocky-swaley cross-stratifications (> 1 m) attest storm waves-influenced in upper shoreface deposits (tempestites). Bipolar cross-beddings with drape and reactivation surfaces reflect tidal-influence. Quartzarenite, sublitharenite and subarkose modal frameworks indicate stable continental block (craton interior) source. Heavy-minerals assemblages (e.g. zircon, tourmaline, staurolite, epidote, etc.) provide evidence of contribution from felsic plutonic igneous and metamorphic rocks. Well-rounded zircon grains can be associated to reworked sediments or metamorphic sources. These litotypes can be related to Rio Maria Block, which includes granitoid and metassedimentary rocks of the Rio Maria granite-greenstone terrain (3.0 – 2,86 Ga).
Acesso aberto (Open Access)
Análise e estimativa dos componentes do balanço de energia em ecossistema de manguezal amazônico
(2013-03) PEREIRA, Priscila Lima; RODRIGUES, Hernani José Brazão
Measurements and estimates of the components of energy balance were made above the canopy of trees in natural mangrove ecosystem, located 30 km from the city of Bragança-PA, between November 2002 and August 2003. The data were used in the analysis of seasonal and hourly variations of the sensible and latent heat flows, as well as the evaluation of the energy partition. Meteorological data were collected by the automatic weather station (AWS) and the energy flows were calculated using the technique of eddy covariance. The Penman-Monteith and Shuttleworth models were used to estimate the sensible and latent heat flow. The objective of this study was to analyze the balance and partitioning of energy in the mangrove and make an assessment of the behavior of empirical models in estimating the energy flows. The net radiation showed higher values in the less rainy season. The Bowen ratio showed generally low value, which indicates that a greater proportion of energy was used in the form of latent heat. The estimates of the energy flows showed satisfactory results. Shuttleworth model is more efficient in estimating sensitive heat flows. For estimating latent heat flow the Penman-Monteith model was more efficient during dry season and the Shuttleworth model during rainy season.
Acesso aberto (Open Access)
Análise faciológica da Formação Alter do Chão (Cretáceo, Bacia do Amazonas), próximo à cidade de Óbidos, Pará, Brasil
(2012-03) MENDES, Anderson Conceição; TRUCKENBRODT, Werner Hermann Walter; NOGUEIRA, Afonso César Rodrigues
Cretaceous deposits of the Alter do Chão Formation, exposed on the banks of the Amazon river, near the town of Óbidos - PA, record a succession of sandstones, conglomerates and mudstones. Seven lithofacies have been recognized which comprise massive conglomerate (Cm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), climbing cross-laminated sandstone (Sl), massive mudstone (Mm), bioturbated mudstone (Mb) and deformed mudstone (Md). These facies are organized in fining-upward cycles, 1 to 6m thick, and have been grouped into two associations: channel fill and overbank deposits belonging to a fluvial meandering system. The channel-fill deposits include lenticular gravel bars composed of facies Cm and St, sandy bedforms with facies St, Sp and Sl, and lateral accretion bar, consisted of facies St, Sp and Mm, but with distinct migration with regard to that of the sandy bed forms. While paleocurrent measurements from facies St and Sp of sandy bedforms indicate a preferred orientation of paleoflow to SW and a subordinate flow to S, the lateral accretion bar migrates to E/ESE. The following overbank elements have been recognized based on their geometric relationships: muddy floodplain deposits including abandoned channel plug, crevasse splay channel filled with facies St and Sp and natural levee deposits composed of facies St, Sl and Mm. While the muddy channel plug overlies sandstones, the crevasse channel fill is in contact with mudstones of the floodplain and also cuts through fine-grained sandstones and mudstones interpreted as natural levee deposits. Adjacent muddy lenses in the same stratigraphic level on sandstone but with smaller width than that of the abandoned channel are attributed to swales, filled during floods, capping lateral accretion bar.
Acesso aberto (Open Access)
Aplicação de Al-PILC na adsorção de Cu2+, Ni2+e Co2+ utilizando modelos físico-químicos de adsorção
(2007) GUERRA, Denis de Jesus Lima; AIROLDI, Claudio; LEMOS, Vanda Porpino; ANGÉLICA, Rômulo Simões; VIANA, Rúbia Ribeiro
Smectite sample from the Serra de Maicuru area (Pará state, northern Brazil, Amazon region) were used for the pillaring process with Al13. Aluminum pillared clay (Al-PILC) was characterized by XRD, SEM and EDS. the textural analysis using nitrogen adsorption-desorption isotherms. The aim of this paper is to study in how Al-PILC adsorb heavy metals. The adsorption of Cu2+, Ni2+, Co2+ ions from aqueous solution in room temperature by Al-PILC have been carried out. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data, with the first model well adjusted with r = 0.999. The one-surface Langmuir equation provided the best fit to the data. The Freundlich equation presented limitations in rises concentrations, but acceptable values of parameters were obtained (Kf and n) with the use of the three models. The parameters were used to calculate the amount adsorbed Nf, a function constant Cs.
Acesso aberto (Open Access)
Aplicação de dados multisensor (SAR e ETM+) no reconhecimento de padrões de uso e ocupação do solo em costas tropicais: Costa Amazônica, Amapá, Brasil
(2009) SANTOS, Valdenira Ferreira dos; POLIDORI, Laurent; SILVEIRA, Odete Fátima Machado da; FIGUEIREDO JÚNIOR, Alberto Garcia de
Environmental studies require information on land use and land cover. This paper presents the applicability of multi-sensor satellite data (optical and radar) for land use and land cover on the Amapá coastal plain for mapping and recognition of natural and anthropogenic dynamics. This area is influenced by the Amazon River, by tides (tidal bore) and by the Intertropical Convergence Zone (ITCZ). Anthropogenic processes are associated with water buffalo ranching. The environmental information was acquired from previous data and field observation and was correlated with remote sensing data (JERS-1, RADARSAT-1, image from ETM+ sensor from Landsat 7 and DEM SRTM), digitally processed for multi-sensor, multi-scale and multi-date approach. Eight patterns of land use and land cover were identified (mangrove, "várzea" forest, arbustive vegetation area, freshwater marsh, anthropic field, intertidal plain, estuarine channel and lakes) as well with indication of natural and anthropogenic geomorphic features. The results from the evaluation of remote sensing data and the techniques applied demonstrated the potential of the remote sensing tool for studying environments in highly dynamic tropical coastal areas of difficult access. However, these tools may present some limitations once applied to application to the Amazon coast, which is a region under strong dynamic natural and anthropogenic processes.
Acesso aberto (Open Access)
Aplicação de Zr/Ti-PILC no processo de adsorção de Cu(II), Co(II) e Ni(II) utilizando modelos físico-químicos de adsorção e termodinâmica do processo
(2008) GUERRA, Denis de Jesus Lima; AIROLDI, Claudio; LEMOS, Vanda Porpino; ANGÉLICA, Rômulo Simões; VIANA, Rúbia Ribeiro
The aim of this investigation is to study how Zr/Ti-PILC adsorbs metals. The physico-chemical proprieties of Zr/Ti-PILC have been optimized with pillarization processes and Cu(II), Ni(II) and Co(II) adsorption from aqueous solution has been carried out, with maximum adsorption values of 8.85, 8.30 and 7.78 x10-1 mmol g-1, respectively. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data with a linear regression process. The energetic effect caused by metal interaction was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.
Acesso aberto (Open Access)
Aplicações de GNSS meteorologia: estudos de caso de eventos extremos de precipitação no Rio de Janeiro e Belém
(Universidade Federal do Pará, 2024-06-18) MOTA, Galdino Viana
Extreme rainfall events, concurrently triggered with floods, waterlogging and landslides, are temporally related to variations in zenith total delay (ZTD) and integrated water vapor (IWV) from the Global Navigation Satellite System (GNSS) meteorology. The relationship between ZTD/IWV variations and precipitation was investigated in this work, using means, time series, and case studies of extreme events in Rio de Janeiro between 2015 and 2018, and in Belém between 2010 and 2022. The GNSS data are from the International GNSS Monitoring and Assessment System (iGMAS) and the Brazilian Continuous Monitoring Network (RBMC), while the precipitation data come from the Rio de Janeiro City Hall Alert System (Alerta Rio), the National Institute of Meteorology (INMET), and the Vale Technology Institute (ITV). In the composition of the ZTD/IWV and precipitation time series in Rio de Janeiro, quasi-linear ramps followed by nonlinear ramps were identified, with the highest rates of change and ZTD/IWV peaks occurring, respectively, 1–2 hours and 0.5 hours before the precipitation maxima, predominantly between 18:00 and 00:00 local time (LT). Case studies of extreme precipitation events during the rainy season revealed configurations in ZTD/IWV curves in the shape of: (i) oscillations named ‘asymmetric semisinusoid’ lasting 3–5 hours, formed by rapid vespertine growth in non-linear ramps, with an average rate of change at the inflection point of +11 (1.4) mm [15min]–1; (ii) a jump with an average rate of change of +17.3 (+2.66) mm [15min]–1 and a maximum of +21.3 (+3.33) mm [15min]–1; (iii) elongated ramps and oscillations named ‘bumps’ that were sequentially staggered on the ascending ramps lasting 1–2 hours; and (iv) ‘bumps’ or ascending ramps in already elevated values of ZTD/IWV due to the influence of meteorological systems such as the Humidity Convergence Zone (in Portuguese Zona de Convergência de Umidade, ZCOU) or the South Atlantic Convergence Zone (SACZ) (in Portuguese Zona de Convergência do Atlântico Sul, ZCAS). Events with large volumes of rainfall were identified, resulting in the elevation of river, igarapé, and canal levels, causing flooding in various locations in Belém. Three events occurred during the less rainy season with very heavy rainfall from Mesoscale Convective Systems (MCSs), and others during the rainy season under the main influence of the Intertropical Convergence Zone (ITCZ). The ZTD curves showed non-linear variations before and after significant rainfall events, with quasi-linear ascending ramps and peaks followed by descending ramps. As the events approached, the curves exhibited a ‘ZTD jumps’ configuration, with sudden increases preceding heavy rainfall or occurring in multiple jumps during intense rain events over several hours. However, some ZTD/IWV curves showed semisinusoid, bump, or jump configurations without resulting in precipitation, highlighting the existence of false alarms. Installing meteorological stations alongside GNSS stations to measure at least precipitation, pressure, temperature, and relative humidity with a 5-minute resolution is essential for monitoring extreme weather events. It is recommended to expand the analyses to longer periods, identify significant configurations in ZTD and IWV time series, define critical thresholds, and use advanced and more complex techniques such as neural networks, wavelet analysis for ZTD/IWV time series, or tropospheric tomography. These approaches are essential to improve the prediction of severe precipitation events, prevent and mitigate the impacts of adverse meteorological phenomena, ensure safety, and provide adequate infrastructure in affected areas.
Acesso aberto (Open Access)
Application of bauxite waste from amazon region in the heavy clay industry
(2013-12) HILDEBRANDO, Edemarino Araujo; SOUZA, José Antônio da Silva; ANGÉLICA, Rômulo Simões; NEVES, Roberto de Freitas
In this work, a method was developed for the application of red mud, an alkaline leaching waste, from a bauxite processing plant located in northern Brazil (Amazon region) as starting material for heavy clay products. Samples were prepared by pressing blends of red mud and clay, which were then fired at temperatures from 900 ºC to 1190 ºC. Characterization was carried out by chemical analysis, differential thermal analysis (DTA) and X-ray diffraction (XRD), and the following ceramic properties were evaluated: water absorption, linear shrinkage and flexural strength. In order to evaluate the Na+ stability in the dense ceramic, leaching tests were also carried out on the specimens after sintering process. Results indicated that samples with 50 and 70 wt% of red mud are proper for being used in the production of ceramic bodies, due to its excellent properties, mainly high mechanical resistance and low water absorption, showing thus, an option to minimizing the environmental impacts caused by the aluminum industry.
Acesso aberto (Open Access)
Araçatuba formation: palustrine deposits from the initial sedimentation phase of the Bauru Basin
(2003-06) FERNANDES, Luiz Alberto; GIANNINI, Paulo César Fonseca; GÓES, Ana Maria
The Bauru Basin (Upper Cretaceous) accumulated an essentially sandy continental sedimentary sequence. In a first desertic phase the basaltic substratum was covered by a widespread and homogeneous aeolian sand unit with minor loess intercalations. The substratum relief favored the formation of an endorheic drainage system under semi-arid climate, a process that started the development of the Araçatuba Paleoswamp. The palustrine deposits (Araçatuba Formation) comprise siltstone and tipically greenish gray narrow tabular strata of sandstone cemented by carbonate. Moulds and gypsite and dolomite pseudomorphs were identified. The moulds seem to be genetically associated with desiccation cracks, root marks and climbing ripple lamination levels, that, on the whole, indicate calm shallow saline waters undergoing phases of subaerial exposition. At the boundaries of the study area, sand units may exhibit sigmoidal features and convolute bedding structure, which is characteristic of marginal deltaic deposits. TheAraçatuba Formation is enclosed in and later overlaid by the aeolian deposits of the Vale do Rio do Peixe Formation.
Acesso aberto (Open Access)
Aspectos texturais do magmatismo e tramas da tectônica impostas ao Granito Chaval na Zona de Cisalhamento Santa Rosa, extremo Noroeste da Província Borborema
(2014-12) GORAYEB, Paulo Sérgio de Sousa; LIMA, Aline Maria Meiguins de
The Northwestern region of Borborema Province features a wide variety of granitic bodies with diverse nature and tectonic evolution, since the Paleoproterozoic to Early Paleozoic, presenting higher incidence related to Neoproterozoic emplaced at different stages of Brasiliano (Panafrican) orogeny. One of these examples is the Chaval Granite representing a batholith body intruded in orthogneisses of Granja Complex and supracrustal rocks of Martinópole Group, outcropped near the Ceará and Piauí Atlantic coasts, Northeastern Brazil. The batholith is partly covered by Cenozoic coastal deposits and sedimentary rocks of the Paleozoic Parnaíba Basin. The Chaval Granite has a striking textural feature, which is represented by porphyritic highlighting microcline megacrysts in syenogranites and monzogranites, and many others textural/structural features of magmatic origin. They allowed interpreting the plutonic evolution at relatively shallow crustal level emplacement acting processes of fractional crystallization, magma mixing with intense magmatic flow, and gravitational force due to density difference of magma that lead to fluctuation of megacrysts of microcline and plagioclase in the residual magma, and accommodation of small bodies of leucogranite and pegmatites in the final stages of plutonic magmatic evolution of such plutonism. On the other hand, across the Eastern half of the pluton, there is a rich collection of shear structures related to the tectonic construction of the Santa Rosa Transcurrent Shear Zone, which led to tectono-metamorphic transformations superimposed on magmatic features that reached peak metamorphic conditions in the low amphibolite facies. Cartographically, three homogeneous structural domains were individualized, and each of them presents a variety of petrographic-structural features of the Chaval of igneous or tectonic nature. The plutonic rocks were deformed and progressively modified Eastward, in which the rocks change to darker gray, and comminution and dynamic recrystallization processes are reduced, as well as the coarse-grained granites are progressively, as well as the size of the phenocrysts to thinner dimensions, keeping their porphyroid characteristics, being accentuated the mylonitic features to achieve the main portion of Santa Rosa Transcurrent Shear Zone. As main structural features, there is the ondulatory extinction, cleavage and twining bending, twinning deformation, anastomosing foliation, badinage, S-C foliation, mineral stretching lineation, rotated and segmented crystals, lenticular, almondy or fish forms of porphyroclasts, pressure shadow, and ribbon quartz. The products of this shear deformation result in the formation of protomylonites, mylonites, and ultramylonites. These mylonite zones represent areas with the highest concentration of deformation that can gradually follow their textural and mineralogical changes, setting up a classic sequence of progressive heterogeneous deformation by simple shear in brittle-ductile and ductile conditions. The emplacement of Chaval Granite happened at the end of the Cryogenian (approximately 630 Ma) and can be interpreted as syn-tardi tectonic magmatism regarding the Brasiliano event. The process that generated the Santa Rosa Shear Zone resulted from lateral extravasation crustal masses in ductile flow took place in the final increments of deformation of a continental collision on an oblique thrust system, which built the Northwest Ceará Shear Belt, and happened at the end of Brasiliano (Panafrican) orogeny in Northwest Borborema Province.
Acesso aberto (Open Access)
Atividade pozolânica de arenito zeolítico da região Nordeste do Brasil
(2012-06) PICANÇO, Marcelo de Souza; ANGÉLICA, Rômulo Simões; BARATA, Márcio Santos
In northeastern Brazil, sedimentary zeolites occur associated with sandstones of the Corda Formation (Parnaiba Paleozoic Basin), discovered in the 2000s. These sandstones are composed of quartz, natural zeolites (estilbite) and clay minerals (smectite). Preliminary studies have shown that this sandstone can be used as a pozzolanic material in Portland-cement-based systems after the material has been sieved to remove the quartz and after thermal activation because the estilbite has low pozzolanic activity. The main objective of this study was to determine the best particle size distribution that yields the highest smectite and zeolite concentration, besides the best temperature for higher pozzolanic activity. The experimental program employed the zeolitic sandstone passing through a #200 and #325 mesh sieve and calcination at the following temperatures: 150°C, 300°C and 500°C. Chemical analysis of the sieved samples was carried out by X-ray fluorescence spectroscopy and X-ray diffractometry, while mineralogical characterization was done by X-ray and thermogravimetric analysis and thermogravimetry..To assess reactivity, calorimetry driving and mechanical tests for pozzolanic activity in hydrated lime and cement Porltand were performed. The results showed that the sample sieved through at #200 mesh was the most suitable because it had a higher concentration of estilbite and a higher percentage of material seived compared to the sample sieved at #325 mesh, 15% and 2% respectively. The 500°C calcination temperature was accompanied by increased pozzolanic activity due to changes in estilbite and smectite cristalinity; the more moderate temperatures of 150°C and 300°C were not sufficient to achieve similar results. The mortars with sandstone sieved at #200 mesh and calcinated at 500°C reached the minimum limits required for a material to be considered as pozzolanic, i.e, 6 MPa for hydrated lime mortars and 75% for the pozzolanic index activity (PAI).
Acesso aberto (Open Access)
Atividade pozolânica dos resíduos cauliníticos das indústrias de mineração de caulim da Amazônia
(2011) BARATA, Márcio Santos; ANGÉLICA, Rômulo Simões
The Capim and Jari regions, northern Brazil, are the main Kaolin mining areas in the Amazon region. They encompass the biggest high-grade (high whiteness) kaolin reserves for the paper coating industry. During the beneficiation of this kaolin, different kinds of processed and non-processed wastes are generated. The main objective of this work was to evaluate the reactivity of pozolans produced after calcinations and milling of such residues, by the comparison of the mineralogical composition and the type of kaolinite from the two regions (different kinds of structural order/disorder). The heating temperature to produce the pozolans was evaluated in order to obtain the better reactivity with lower energy consumption. The results showed that the pozolans obtained from both residues exhibited high reactivity, also better than those commercially available. Those obtained from kaolinites with high structural defects needed lower temperatures in comparison with low-defects kaolinites. The use of the former kaolinites reduces the production costs to obtain pozolans without losing quality in terms of reactivity.
Acesso aberto (Open Access)
Avaliação da resistência ao desgaste de aluminas nanométricas produzidas a partir da decomposição térmica de acetato de alumínio liofilizado
(2007-12) FAGURY NETO, Elias; KIMINAMI, Ruth Herta Goldschmidt Aliaga
Wear resistance tests, using the pin-on-disk test method with sliding pairs, were carried out on pins produced from alumina powders prepared by thermal decomposition of lyophilized aluminum acetate. Alumina powders of a-Al2O3 and g-Al2O3 phases, with and without sintering additives (MgO and La2O3), were used to produce wear pins. In addition, pins made of commercial alumina (A1000 SG) were tested and the results compared. The tests, carried out according to the ASTM standard, indicated that the pins made with a-Al2O3 powder showed high wear resistance, a finding corroborated by mass loss tests and scanning electron microscopy. The g-Al2O3 pins showed an intermediary performance while the A1000 SG pins showed less interesting results.