Abstract It is described for the first time the synthesis and characterization of NiMn2O4 employing the Mn ores from the Amazon Region as starting material, instead of using commercial reagents as normally occurs in its synthesis process. Initially, an Mn ore was transformed into a single product, the octahedral layer (OL) manganese oxide with Ni2+ ions interlayer (Ni-OL-2), which was used as a matrix to obtain NiMn2O4 by thermal decomposition. The following techniques were used for characterization: X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), infrared spectroscopy (FTIR), thermal analysis (TG-DTA), scanning (SEM) and transmission (TEM) electron microscopies. The results revealed that Mn oxide ore composed of nsutite mineral transformed into a well-ordered crystalline Ni-OL-2 phase, after the hydrothermal and cation exchange process. The thermal decomposition of Ni-OL-2 produced the nickel manganite phase at 850 °C with spherical ball morphology and crystal sizes in the range of 200-300 nm.

The present work aims to evaluate the manufacturing processes of free-standing graphene oxide (GO)/reduced graphene oxide(rGO)/carbon nanotube (MWCNT) papers-like and the effect on electrical conductivities after annealing treatment. The pure GO and the hybrid papers were obtained by vacuum filtration and submitted to mild thermal annealing at 400 °C under an argon atmosphere. Analyses comparing the carbon paper-like materials before and after thermal treatment were done by thermogravimetric analysis (TGA), Raman spectroscopy, scanning electron microscopy (SEM), and electrical conductivity measurements. The characterization results show the annealing process effect on the morphology of paper materials. The GO papers and the hybrid (GO/rGO/MWCNT) exhibited good free-standing structure properties. The SEM results suggest the formation of gas void due to the thermal treatment. TGA and Raman results showed the thermal reduction and restoration of the carbon sp2 network of the graphene oxide induced by thermal treatment. The thermal treatment was responsible for changing the almost insulator characteristic of free-standing pure GO paper, achieving an electrical conductivity of 752 S/m, and improving 45% of the free-standing hybrid carbon nanomaterials papers (GO/rGO/MWCNT) electrical conductivity, achieving the value of 1020 S/m.

Resumo O presente trabalho descreve um estudo comparativo das propriedades química e mineralógica de birnessita natural (BIR-AZ) proveniente da mina do Azul (Província Mineral de Carajás, Brasil) e seu análogo sintético obtido pelo método sol-gel (K-OL-SG). As caracterizações foram realizadas por difração de raios X, espectroscopia FT-Raman, análise térmica (TG-DTA), microscopia eletrônica de varredura e análise química. Os resultados confirmam a presença das fases lamelares com sistema monoclínico, grupo espacial C2/m e com os seguintes parâmetros de cela unitária: BIR-AZ, a = 5,148 Å; b=2,843 Å, c=7,175 Å e β = 100,75º; K-OL-SG, a = 5,150 Å; b = 2,846 Å, c = 7,214 Å e β = 101,29º. Birnessita possui estabilidade térmica próxima a 600 ºC, enquanto seu análogo sintético acima de 900 ºC. Bandas obtidas por espectroscopia Raman foram observadas a 635, 570 e 410 cm-1 e atribuídas às deformações Mn-O e K-O na estrutura lamelar. O estudo da morfologia dos produtos revela que birnessita se apresenta como folhas tabulares de 1 a 5 µm, enquanto que o composto sintético possui morfologia em glóbulos (< 1 μm) dispostos aleatoriamente.

Abstract This paper presents a comparative chemical and mineralogical study of birnessite (BIR-AZ) collected from Azul mine (Carajás Province, Brazil) and its synthetic analogous synthesized by sol-gel method. The products were characterized by X-ray diffraction, FT-Raman spectroscopy, thermal analysis (TG-DTA), scanning electron microscopy (SEM) and ICP-MS techniques. The results obtained confirm the presence of well-defined layer structures having monoclinic system, C2/m space group and the unit cell parameters are: BIR-AZ, a = 5.148 Å; b=2.843 Å, c=7.175 Å, and β = 100.75º; K-OL-SG, a = 5.150 Å; b = 2.846 Å, c = 7.214 Å, and β= 101.29º. The birnessite from Azul mine ores shows thermal stability up to 600 ºC, whereas its synthetic analogous, above 900 ºC. FT-Raman bands at 635, 570 and 410 cm-1 were identified and attributed to the Mn-O and K-O bond deformations in the birnessite structure. SEM images reveals that the manganese oxide mineral consist of platy packed particles of about 1 to 5 µm. By contrast, the morphology of the synthetic compound displays randomly arranged globules (<1 µm).

Minerais de óxidos de Mn com estrutura em túnel, hollandita (Apuí, Amazonas, Brasil, zona em prospecção) e criptomelana (Urucum, Mato Grosso do Sul, Brasil) foram isolados e caracterizados quanto à composição química, mineralógica, estabilidade térmica e morfologia. As seguintes técnicas foram utilizadas para caracterização: microscopia eletrônica de varredura-EDS, análise térmica (TG-DTA) e difração de raios X estático e com aquecimento contínuo entre 100-900 ºC. As seguintes fórmulas empíricas, calculadas com base em 16 átomos de oxigênios foram obtidas: (Ba0,18K0,12Ca0,02Pb0,04)0,76(Mn6,34Al0,61Si0,25Fe0,24Ti0,08)7,54O(16)0,4H2O para hollandita e (K0,9Na0,04Ca0,03Sr0,04)1,04(Mn7,38Fe0,28Al0,27Si0,08)8O16 para criptomelana. Mediante o uso de microscopia eletrônica de varredura foi possível diferenciar a morfologia da hollandita e da criptomelana. Os resultados de DRX e TG-DTA mostraram que os minerais apresentaram estabilidade térmica acima de 900 ºC.

The tunnel-structure manganese oxide minerals, hollandite (Apuí, Amazonas state, Brazil, area in prospection) and cryptomelane (Urucum, Mato do Sul Grosso state, Brazil) were isolated and characterized chemical, mineralogical, thermal and morphologically. The following techniques were employed: scanning electron microscopy-EDS, thermal analysis (DTA-TG), X-ray diffraction with continuous-heating. The empirical formula, were calculated on the basis 16 oxygen gave as (Ba0.18K0.12Ca0.02Pb0.04)0.76(Mn6.34Al0.61Si0.25Fe0.24Ti0.08)7.54O(16)0.4H2O for hollandite and (K0.9Na0.04Ca0.03Sr0.04)1.04(Mn7.38Fe0.28Al0.27Si0.08)8O16 for cryptomelane. The SEM investigations allowed the differentiation of the morphologies for hollandite and cryptomelane. The minerals were thermally treated among 100-900 ºC and X-ray diffraction patterns in situ were collected. The analysis of X-ray diffractions experiments showed that a hollandite-crytomelane mineral has a thermal stability up to 900 ºC.

This article presents a finite element simulation of Carreau flows through an abrupt contraction. The employed mechanical model consists in using the Carreau viscosity equation to characterize the shear-thinning fluid behavior, giving rise to a generalization of Navier-Stokes equation containing a non-linear diffusion term. A Galerkin-Least Squares methodology approximates the mechanical model circumventing the Babuška-Brezzi condition, which consists of adding to the classical Galerkin method mesh-dependent residuals, resulting from least squares of the Euler-Lagrange equations. Numerical results for both velocity and pressure fields accounting for shear-thinning and fluid inertia effects have been obtained for an axisymmetric 4:1 sudden contraction with Carreau number ranging from 0 to 100, power-law exponent from 0.2 to 1.0 and Reynolds number from 2 to 100. These results have shown good agreement with the literature.

This article studies the heat transport in a flow through a saturated rigid porous medium. The mechanical model is based on the Continuum Theory of Mixtures which considers the fluid and the porous matrix as overlapping continuous constituents of a binary mixture. A Petrov-Galerkin formulation is employed to approximate the resulting system of partial differential equations, overcoming the classical Galerkin method limitation in dealing with advective-dominated flows. The employed method is built in order to remain stable and accurate even for very high advective-dominated flows. Taking advantage of an appropriated upwind strategy, the applied finite element method proved to generate accurate approximations even for very high Péclet regime. Some two-dimensional simulations of the advective-diffusive heat transfer in a flow through a porous flat channel employing lagrangean bilinear and serendipity biquadratic elements have been performed attesting the reliability of the employed Petrov-Galerkin formulation as well as the poor performance of Galerkin one even when mesh refining is considered.

As amostras de esmectita do estado do Pará, Amazônia, Brasil foram caracterizados utilizando XRD, FTIR e análise textural por curvas isotérmicas adsorpition-desorption nitrogênio. Na produção das argilas pilarizadas foi usado o íon Al13 (o íon de keggin), este íon foi obtido pela reação das soluções AlC(l3)6H2O / NaOH, com razão molar OH/Al=2, com intercalação em temperatura ambiente, durante as 3 horas e calcinada em 450ºC (temperatura adequada da calcinação). O material foi preparado utilizando soluções produzidas na faixa de temperatura de 25, 45, 65, 85, 105ºC, o Resultado mostrou que o processo de pilarização aumenta o espaçamento basal da argila natural de 14,02 para 19,74 Å e a área superficial de 44,30 para 198,03m²/g. a estabilidade térmica da argila natural foi melhorada pelo procedimento de pilarização.

Clays pillared with Keggin ions (AL-PILC) have been synthesized at OH/Al=2 molar ratio and various pretreatment temperatures (ambient temperature to 105ºC) in order to determine the optimum preparation conditions of the pillaring agent (Al13). The evolution of basal spacing, FTIR spectra, TG-curves, surface area and pillars number in function of temperatures of Al13 formation were studied. It was observed an increase number pillars and surface area at low temperatures.

The two-dimensional spin-1 Baxter-Wu model is studied by using Monte Carlo simulations. The standard single-spin-flip Metropolis algorithm is used to generate the configurations from which the order parameter, specific heat and magnetic susceptibility are measured. The finite-size scaling procedure is employed in order to get the critical behavior. Extensive simulations show that the critical exponents are different from those of the spin-1/2 model suggesting that the spin-1 model is in a different universality class.