The crystallographic structural analysis of the magnetite of a steatite rock at 298 K, (saturation magnetization, σ = 95.0 J T-1 kg-1) showed two cubic networks and, below Verwey temperature (TV ca.120 K) a monoclinic structure, basing on their cell dimensions and different transitional behaviors when reducing the temperature. A monoclinic structure was identified from their cell dimensions and different transition behaviors when reducing the temperature. The average chemical formula of this almost stoichiometric magnetite was deduced from the chemical analysis, 298 K-Mössbauer and the structural refinement. The Rietveld fitting of the 298 K X-ray pattern is Fe 3 + Fe 0 . 95 3 + Fe 0 . 88 2 + Cr 0 . 04 3 + Al 0 . 04 3 + Mg 0 . 05 2 + Ni 0 . 02 2 + ⊗ 0 . 02 O 4, where [ ] and { } stand for cations in tetrahedral and octahedral coordination symmetries, respectively. The crystallographic structure below TV in this magnetite was observed from synchrotron X-ray diffraction data (XRD), collected at 15 K. It was identified three structures: two cubic (space group, Fd3m), with significantly different lattice parameters, and one monoclinic (P2/c).

Abstract The performance of commercial explosives is an important subject in rock blast ing modeling and simulation. As a result of its non-ideal behavior, these explosives usu ally react below their ideal detonation velocity. In these cases, the multi-dimensional effects, heterogeneities and confinement conditions become important for properly quantifying the detonation state. In this sense, an engineering approach to model two-dimensional steady non-ideal detonations for cylindrical stick explosives is used to quantify the expected detonation velocity for given reaction rate parameters and con finement conditions. Founded on an ellipsoidal shock shape approach (ESSA), the pro posed model combines the quasi-one-dimensional theory for the axial solution with the unconfined sonic post-flow conditions at the edge of the explosive. A mechanistic confinement approach is coupled with the ESSA model to estimate the effect of the inert confiner on the detonation flow. Finally, the proposed model is used to estimate the expected detonation velocity of two typical commercial explosives in a number of different confinement conditions.

Tendo em vista a necessidade do mercado brasileiro por ligantes que minimizem a prematura falência estrutural dos revestimentos nas vias urbanas, a modificação do cimento asfáltico de petróleo (CAP 50/70) constitui uma excelente opção tecnológica. Nesta pesquisa utilizou-se 2% p/p do copolímero de estireno-butadieno-estireno (SBS) e 2% p/p de fibra natural da casca dos frutos de Couepia edulis (Prance), conhecida como castanha de cutia, material vegetal com característica de reforço e biodisponibilidade na região Amazônica. Os efeitos oxidativos e térmicos, bem como as características físicas dos materiais asfálticos modificados, foram estudados e comparados ao ligante convencional, utilizando-se ensaios estabelecidos pela Agência Nacional de Petróleo, Gás Natural e Biocombustíveis (ANP) e análise térmica - termogravimetria (TG), a fim de determinar as propriedades de degradação e estabilização térmica. Os resultados para os ligantes modificados, confrontados ao ligante tradicional, apresentaram: maior resistência ao envelhecimento, melhorias evidenciadas pelo aumento da consistência, ponto de amolecimento, além da excelente estabilidade térmica em toda faixa de temperatura de utilização (10 ºC a 80 ºC) e aplicação (130 ºC a 170 ºC) dos cimentos asfálticos de petróleo, fornecendo uma opção ao pavimento regional.

There is a need in the Brazilian market for asphalt binders that minimize premature structural failure of the coatings on urban roads, and the modification of asphalt cement oil (CAP 50/70) is an excellent option. In this research we used 2% w/w of the styrene - butadiene-styrene (SBS) copolymer and 2% w/w of natural fiber from Couepia edulis (Prance), known as cutia chesnut, which is a plant from the Amazon region with strengthening properties. The oxidative and thermal effects, as well as the physical characteristics of the asphalt modified materials, were studied and compared to the conventional binder, using the tests set by the National Agency of Petroleum, Natural Gas and Biofuels (ANP) and thermal analysis - thermogravimetry (TG) to determine the properties of thermal degradation and stabilization. In comparison with the traditional binders, the modified ones exhibited increased resistance to aging, evidenced by an increase in consistency, softening point and excellent thermal stability in the whole range of operating (10 ºC to 80 ºC ) and application (130 ºC to 170 ºC) temperatures for the asphalt cement oil, providing an option for regional pavements.

Magnetic soils forming on tuffite of the region of Alto Paranaíba, Minas Gerais, Brazil, usually contain iron-rich spinels exceptionally rich in magnesium and titanium. In this work, samples of the magnetically separated portion from the sand fraction of a Brunizém (Chernossolo) and from its mother-rock material were analyzed with synchrotron X-ray diffraction and 57Fe-Mössbauer spectroscopy. Magnesioferite (MgFe2O4) and maghemite (its pure non-stoichiometric spinel structure, Fe8/3 ⊕ 1/3 O4, where ⊕ = cation vacancy, corresponds to γFe2O3) were the magnetic iron oxides so identified. Basing on these data, a consistent chemical-mineralogical model is proposed for the main transformation steps involving these iron oxides in the pedosystem, starting on magnesioferrite to finally render hematite (αFe2O3), passing through maghemite as an intermediate specie.

O objetivo deste trabalho foi efetuar a caracterização mineralógica dos óxidos de ferro de horizontes B de três perfis de solos desenvolvidos sobre gnaisse do geodomínio do Complexo Bação, no Quadrilátero Ferrífero, em Minas Gerais. As amostras foram coletadas ao longo dos segmentos de alta, média e baixa vertente. As frações de terra fina (diâmetro médio, fi = 2 mm) foram separadas, em todas as amostras. A composição química dos elementos maiores foi determinada por meio da técnica de fluorescência de raios X; a análise mineralógica foi realizada com difratometria de raios X e espectroscopia Mössbauer. Todas as amostras têm composição mineralógica similar, cuja ocorrência geral corresponde à seqüência quartzo >> gibbsita > caulinita > goethita. Os resultados Mössbauer a 4,2 K confirmam a coexistência de goethita (majoritária) e hematita. Os conteúdos de alumínio isomórfico foram deduzidos dos valores de campos hiperfinos e correspondem às seguintes fórmulas químicas das goethitas: alfaFe0,79Al0,21OOH (alta vertente), alfaFe0,75Al0,25OOH (meia vertente) e alfaFe0,78Al0,22OOH (baixa vertente). A dinâmica de transformação dos óxidos de ferro nos horizontes B ao longo da vertente é um indicador das oscilações paleoclimáticas na área: goethita mais aluminosa é um indicador do paleoambiente úmido, e goethita menos aluminosa revela condições pedogênicas mais secas.

The objective of this work was to characterize iron oxides from B-horizons of three soil profiles developing on gneiss of the Bação Complex geodomain in the Quadrilátero Ferrífero, Minas Gerais, Brazil. Samples were collected from the uppest, middle and lowest segments along the slope. The earth fine fractions (mean diameter, phi = 2 mm) were separated for all samples. The chemical composition of the major elements was determined with the X-ray fluorescence technique; the mineralogical analysis was performed with powder X-ray diffractomer and Mössbauer spectroscopy. All samples have similar mineralogical composition, with a general occurrence corresponding to the sequence quartz >> gibbsite > kaolinite > goethite. From the 4.2 K-Mössbauer results, the coexistence of goethite (major) and hematite is confirmed. The isomorphic aluminum contents, as they were deduced from the hyperfine fields, lead to the following chemical formulas for goethites: alphaFe0.79Al0.21OOH (upslope), alphaFe0.75Al0.25OOH (midslope) and alphaFe0.78Al0.22OOH (downslope). The iron oxides transformation dynamics in B horizons along the slope is a useful indicator of the paleo-climatic oscillations in this area: aluminous goethite is an indicator of humid paleo-environments, whereas aluminous-poorer goethite reveals drier pedogenic conditions.

Solos magnéticos derivados de tufito da região do Alto Paranaíba (MG) têm mineralogia bastante variável, mas são relativamente ricos em óxidos de Fe isoestruturais ao espinélio, mais especificamente: (Ti, Mg)-magnetita e (Ti, Mg)-maghemita. No presente trabalho, foram estudados os concentrados magnéticos (magnetização de saturação, 34,4 < sigma/J T-1 kg-1 < 43,7) da fração areia de pedomateriais de um Brunizém (Chernossolo) (amostras AP31CR; AP31B e AP31A) e de um Chernossolo Léptico (AP33CR e AP33A) derivados de tufito, coletados no município de Patos de Minas (MG). Foram identificadas, por difratometria de raios X (método do pó) e espectroscopia Mössbauer do 57Fe, a 298 K e a 110 K, maghemita (gamaFe2O3) e hematita (alfaFe2O3) e uma inédita magnesioferrita (fórmula ideal, MgFe2O4), inédita em solos do Brasil, nas frações minerais desses materiais magnéticos. Observou-se, também, que as proporções ponderais e os tamanhos de partículas dos óxidos de Fe variam progressivamente ao longo dos perfis estudados. Os diâmetros médios estimados dos cristalitos de magnesioferrita variam progressivamente, em cada perfil: 27 nm (concentrado magnético da amostra AP31CR); 25 nm (AP31B); 23 nm (AP31A); 48 nm (AP33CR) e 32 nm (AP33A). A proporção de Al isomorficamente substituinte na hematita aumenta sistematicamente de 5 a 13 mol %, da base para o topo do perfil AP31, e tende a se manter constante, em torno de 9 mol %, no perfil AP33. Propõe-se um modelo geral de transformação envolvendo somente óxidos de Fe, em que magnesioferrita é o precursor pedogenético da maghemita, até hematita, nesses pedossistemas: MgFe2O4 -> gFe2O3 -> aFe2O3.

Tuffite-derived magnetic soils in the Alto Paranaíba region, State of Minas Gerais, Brazil, have a variable mineralogy and are assumed to contain iron oxides that are isoestructural to spinel, more specifically, (Mg,Ti)-rich magnetite and maghemite. In this study, magnetic portions (saturation magnetization, 34.4 < sigma/J T-1 kg-1 < 43.7) were separated from sand fractions of pedomaterials of a Brunizem (Chernosol) (samples labeled AP31CR; AP31B and AP31A) and of a leptic Chernosol (AP33CR e AP33A) developed from tuffite were collected near the city of Patos de Minas, MG. Maghemite (gammaFe2O3), hematite (alphaFe2O3) and a reportedly identified magnesioferrite (ideal formula, MgFe2O4) were found to also occur in these magnetic extracts, as it could be deduced from X ray diffractometry and 298 K and 110 K 57Fe Mössbauer spectroscopy data. It was also observed that the relative proportions and particle sizes of the iron oxides vary progressively in each soil profile. Mean crystallite diameters are 27 nm (magnetic portion of sample AP31CR); 25 nm (AP31B); 23 nm (AP31A); 48 nm (AP33CR) and 32 nm (AP33A). The isomorphical Al contents in hematite also increase systematically from 5 to 13 mol%, from the bottom to the top of the AP31 profile and tend to be constant at about 9 mol% along the AP33 profile. An overall model was proposed including the main transformation pathway involving only iron oxides, in which magnesioferrite is the pedogenetic precursor of maghemite up to hematite in these pedosystems: MgFe2O4 -> gFe2O3 -> aFe2O3.

Sand samples collected from two sampling sites on Guarapari and Iriri beaches, state of Espírito Santo, Brazil, were studied in an attempt to better describe their chemical and mineralogical compositions and radioactive behaviors. The sands were found to contain about 6 (Guarapari) and 2 dag kg-1 (Iriri) of rare earth and thorium that, if allocated to the monazite-(Ce) structure, lead to the averaged formulae Ce3+0,494Gd3+0,012La3+0,209Nd3+0,177Pr3+0,040Sm3+0,024Th4+0,033 (PO4) and Ce3+0,474La3+0,227Nd3+0,190Pr3+0,044Sm3+0,032Th4+0,024 (PO4). From Mössbauer spectroscopy data, the magnetic fractions of these sands were found to contain stoichiometric hematite (47.4 dag kg-1, from Guarapari, and 25.1 dag kg-1, from Iriri) and magnetite (44.1 and 58.8 dag kg-1). The specific alpha and beta radiation activities were also measured for both samples.

The Mössbauer analysis along with the structural Rietveld refinement based on powder X-ray data for the magnetic fraction (saturation magnetization, sigma = 19 J T-1 kg-1) separated from a tuffite material from Alto Paranaíba, state of Minas Gerais, Brazil, reveal that a (Ti, Mg)-rich maghemite (deduced sigma = 17 J T-1 kg-1) and, for the first time observed in this lithodomain, magnesioferrite (characteristic sigma = 21 J T-1 kg-1) respond for the magnetization of the rock material. Consistent models for the ionic distribution in these iron-rich spinel structures are proposed.

O presente trabalho descreve, basicamente a caracterização dos constituintes da fração argila, principalmente da caulinita e sua permutabilidade com alguns cátions metálicos, em solo Amazônico. Para tanto, amostras de Latossolo Amarelo foram coletadas em um perfil de estrada da Usina Hidrelétrica Balbina, Km 12, próximo ao município de Presidente Figueiredo (AM). Estas foram secadas ao ar (TFSA), desagregadas e separadas granulometricamente nas frações areia, silte e argila. As amostras da fração argila foram tratadas com H2O2/HC1 para eliminar a matéria orgânica e óxido de ferro. As amostras da fração argila sem tratamento e tratada foram caracterizadas por difração de raios X de pó e espectroscopia no infravermelho. Os constituintes químicos da fração argila tratada foram determinados por espectrometria de absorção atômica, volumetria e gravimetria. Os resultados obtidos mostraram que as amostras da fração argila sem tratamento apresentaram a seguinte constituição: gibsita goethita, quartzo, matéria orgânica e caulinita. A fração argila tratada apresentou basicamente quartzo c caulinita, sendo a caulinita membro final da série caulinítica, com pouca distribuição de cargas negativas. Nas amostras tratadas foram efetuados também experimentos de permutabilidade com Na+, K+ e Fe3+ e os teores determinados por espectrofotometria na região do ultravioleta-visível e fotometria de chama. Os resultados mostram que a fração argila tratada possui capacidade de retenção de 2,21% de água de absorção, no caso de cátions monovalentes: 1,3 e 2,7 meq/100 g de amostra, para o K+ e Na+, respectivamente. No entanto, essa fração retêm cerca de 21,7 meq/100 g de amostra para o Fe3+. Esse valor elevado para a retenção de Fe3+ é provavelmente atribuído ao fenômeno de permutabilidade entre o Fe3+ e a caulinita acompanhado dc redução no valor de pH para 2,2, seguida de substituição de Fe3+ por Al3+, no sítio octaédrico, revelada pela espectroscopia no infravermelho.

The present work, basically of the fraction clay characterization, mainly of the kaolinite and its exchange with some metallic cation (Na+, K+ e Fe3+), in Amazon soil. The samples of Latosoil Yellow were collected from a pedon located in the vivinity of the Presidente Figueiredo city. State of Amazon, Brazil. The particles were fractionated on the basis of particle size, and sand, silt in clay fractions were obtained. The samples of the clay fraction were treated with H2O2/HC1 to eliminate the organic matter and oxide of free iron and submitted the analyses using the following techniques: X-ray diffraction, infrared spectroscopy, ultraviolet-visible spectroscopy, atomic absorption spectroscopy, as well as, volumetric, gravimetric and flame photometric analyses. The obtained results showed that the clay fraction presents to the following constitution: gibsite, goethite, quartz, organic material and kaolinite. Being the kaolinite the final member of the series, with little distribuition of negative. For this study, it was possible to also propose that the fraction treated clay possesses capacity of retention of 2.21% of adsortion water, in the case of cations monovalence: 1.3 and 2.7 meq/100g of sample, for K+ and Na+, respectively. However, that fraction retains about 21.7 meq/100g of sample for the Fe3+. That value elevated for the retention of Fe3+ is probably attributed to the several species hydrolyzed of Fe3+ in that caused the reduction in the pH value for 2,2 and it can also facilitate, the substituition of Fe3+ for Al3+, by in the octahedral site.