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Currently, petroleum-derived plastics are widely used despite the disadvantage of their long degradation time. Natural polymers, however, can be used as alternatives to overcome this obstacle, particularly cornstarch. The tensile properties of cornstarch films can be improved by adding plant-derived nanofibers. Sisal (Agave sisalana), a very common low-cost species in Brazil, can be used to obtain plant nanofibers. The goal of this study was to obtain sisal nanofibers using low concentrations of sulfuric acid to produce thermoplastic starch nanocomposite films. The films were produced by a casting technique using commercial corn starch, glycerol, and sisal nanofibers, accomplished by acid hydrolysis. The effects of glycerol and sisal nanofiber content on the tensile mechanical properties of the nanocomposites were investigated. Transmission electron microscopy findings demonstrated that the lowest concentration of sulfuric acid produced fibers with nanometric dimensions related to the concentrations used. X-ray diffraction revealed that the untreated fibers and fibers subjected to acid hydrolysis exhibited a crystallinity index of 61.06 and 84.44%, respectively. When the glycerol and nanofiber contents were 28 and 1%, respectively, the tensile stress and elongation were 8.02 MPa and 3.4%. In general, nanocomposites reinforced with sisal nanofibers showed lower tensile stress and higher elongation than matrices without nanofibers did. These results were attributed to the inefficient dispersion of the nanofibers in the polymer matrix. Our findings demonstrate the potential of corn starch nanocomposite films in the packaging industry. [ABSTRACT FROM AUTHOR]

A sample of goethite iron ore sinter feed (G_SF) was employed as a raw material in a sintering bed. This sample partially replaced hematite sinter feed (H_SF), which is currently used as raw material in a sintering plant in the state of Minas Gerais, Brazil. This substitution did not adversely affect the chemical and metallurgical proprieties of the sinter mix product, provided that the utilization of G_SF was kept below 30% in weight. Despite the higher proportion of fines in G_SF, the presence of argillaceous minerals in the sample led to an improvement in the granulation index (GI) of the sinter mix product. The GI value increased from 68.4 to 82.7% for the experiments conducted without the presence of goethite ore and with 40% of goethite ore in the sintering mix, respectively. Consequently, the qualities of both the process and the produced sinter product were not compromised. The raw materials and the various sinters produced were characterized through X-ray fluorescence (XRF) and X-ray diffraction (XRD), as well as thermal gravimetric analysis (TGA). The XRD results were used to perform a quantitative assessment of the mineral phase using the Rietveld method (RM). This technique allowed for the determination of goethite content in the studied sample, which was 35.5%. Finally, the incorporation of G_SF in the sintering bed led to a 20% reduction in the cost of raw materials. [ABSTRACT FROM AUTHOR]

In Brazil, a significant amount of tilapia carcass waste is produced every year. The aim of this study is to evaluate the recycling of tilapia carcass waste as an alternative calcium precursor to produce biphasic calcium phosphate (BCP) powder via a wet chemical precipitation method in different HNO3 concentrations. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, average crystallite size, and refinement by the Rietveld method for the quantification of crystalline phases. The experimental results indicated the formation of a BCP bioceramic with different amounts of β-calcium pyrophosphate (β-CPP) and β-tricalcium phosphate (β-TCP), depending on the HNO3 concentration. The new BCP powders showed an average crystallite size between 57.7 and 59.2 nm. Such a result suggests a possibility of friendly recycling of tilapia carcass waste for biomedical applications. [ABSTRACT FROM AUTHOR]

Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more often used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing). Therefore, we performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for the weight percentage ratio of the main phases and mean coherent domain sizes and less similar results for Al substitution rates, thus validating the XRD_rotat approach. No beam damage was observed when increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the previous model for the development of pisolites. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating. [ABSTRACT FROM AUTHOR]

Mixed magnetic composites of manganese ferrite and cristobalite (MnFe 2 O 4 –SiO 2) were produced by the solid-state reaction method, using as starting materials in natura ores found in the state of Rio Grande do Norte – Brazil. Based on the stoichiometric proportions of the precursor ores, various composites in the form of powders and pellets were synthesized at a temperature of 1200 °C/12h under ambient atmosphere. Samples in the form of pellets were made at compression pressures of 370 and 740 MPa to investigate the effect of pressure on the physicochemical, and dielectric properties of the material. Structural, morphological and magnetic analyses were studied for the series of samples. X-ray diffractogram (XRD) results confirmed the formation of the mixed spinel phase MnFe 2 O 4 with cubic symmetry and space group Fd-3m:1, together with peaks corresponding to SiO 2 –cristobalite. The Rietveld refinements identified a predominance of about 90% of the MnFe 2 O 4 phase with crystallite variations of 130–190 nm due to the effect of compaction pressure. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electronic microscopy (TEM) mappings show clusters of triangular crystals in the pellets series. Magnetic hysteresis cycles at room temperature show a fast magnetization saturation (M S) response in a field of ∼4 kOe, with parameters dependent on the size and shape of the crystallites. The magnetically soft ferrites exhibited very low coercive field values. The hysteretic curves measured at 5 K showed a significant gain in the M S of ∼30 emu/g. Analyzes of magnetization as a function of temperature identified a blocked regime with a maximum ∼97 K (powder) and ∼170 K (pellets), and an irreversibility of the ZFC–FC curves up to room temperature. An indication of a spin-glass (SG) like state close to 20 K can also be seen in these results. Dielectric characterization of the pellets was performed from 1.0 to 8.5 GHz, and presented well-defined behavior, where real permittivity can be highly related to Rietveld refinement of XRD, and SEM/EDS results. This research suggests the feasibility of producing manganese ferrite composites directly from minerals, without the use of high-purity chemical reagents, allowing their obtainment on a large scale for commercial use. [ABSTRACT FROM AUTHOR]

A comparison of Rietveld refinement results for a bauxite-bearing regolith and its clayey cover in the Amazon region was made with stoichiometric calculations from chemical analysis and partly from thermogravimetric results. For this investigation a profile in the bauxite-bearing regolith occurrence in the ALCOA bauxite mine at Juruti, Brazil was studied. The different minerals, their compositions and their low crystallinity in the different horizons were investigated and the contents determined. It is evident that some minerals show several generations and some chemical composition changes that must be included in the Rietveld refinement. Al-rich hematites and goethites are common along the bauxite profile. Amorphous contents were determined with rutile added as an internal standard and shown to have gibbsite- or kaolinite-like composition. The minerals could be quantified in the different horizons and the difficulties were mainly related to variable crystalline aspects of the phases. Rietveld refinement can be a powerful tool in bauxite prospecting, quality control and during mining and beneficiation of ore minerals using the adapted refinement strategies. [ABSTRACT FROM AUTHOR]

Mössbauer spectra and X-ray diffraction data show a chalcopyrite from the Cristalino Cu(Au) deposit in the Carajás Mineral Province in northern Brazil to consist of a single, tetragonal phase. This is in stark contrast to a previously described chalcopyrite from the Camaquã copper mine in southern Brazil, obviously reflecting differences in mineral (and thus ore deposit) genesis. [ABSTRACT FROM AUTHOR]

Atenolol is the most used drug in Brazil to hypertension treatment. Two crystal structures are known for this molecule: a racemic form (R,S)-atenolol and a pure form S-atenolol. The racemic form is found in commercial tablets. X-ray powder diffraction (XRD) is an adequate tool to study crystalline structures including drugs. Using the Rietveld Method with XRD data it is possible to quantify the crystalline structures existing in the raw material. Other methods like Le Bail and Pawley can be used to the profile fit and phases identification. For this work we analyzed three tablets of atenolol, two generics and the reference (materials were purchased from a drugstore at the city of Araraquara). These tablets were analyzed by Rietveld, Le Bail and Pawley methods. All tablets exhibited the racemic mixture API (R,S)-atenolol. Some crystalline excipients could be characterized: magnesium carbonate hydrate, lactose monohydrate and talc. The conclusion is that the three methods can be efficiently used to characterize the three atenolol tablets. [ABSTRACT FROM PUBLISHER]

A new occurrence of rankamaite is here described at the Urubu pegmatite, Itinga municipality, Minas Gerais, Brazil. The mineral forms cream-white botryoidal aggregates of acicular to fibrous crystals, intimately associated with simpsonite, thoreaulite, cassiterite, quartz, elbaite, albite, and muscovite. The average of six chemical analyses obtained by electron microprobe is (range in parentheses, wt%): Na2O 2.08 (1.95-2.13), K2O 2.61 (2.52-2.74), Al2O3 1.96 (1.89-2.00), Fe2O3 0.01 (0.00-0.03), TiO2 0.02 (0.00-0.06), Ta2O5 81.04 (79.12-85.18), Nb2O5 9.49 (8.58-9.86), total 97.21 (95.95-101.50). The chemical formula derived from this analysis is (Na1.55K1.28)σ2.83(Ta8.45Nb1.64Al0.89Fe0.013+Ti0.01)σ11.00[O25.02(OH)5.98]σ31.00. Rankamaite is an orthorhombic "tungsten bronze" (OTB), crystallizing in the space group Cmmm. Its unit-cell parameters refined from X-ray diffraction powder data are: a = 17.224(3), b = 17.687(3), c = 3.9361(7) Å, V = 1199.1(3) ų, Z = 2. Rietveld refinement of the powder data was undertaken using the structure of LaTa5O14 as a starting model for the rankamaite structure. The structural formula obtained with the Rietveld analyses is: (Na2.21K1.26)σ3.37(Ta9.12Nb1.30 Al0.59)σ11.00[O26.29(OH)4.71]σ31.00. The tantalum atoms are coordinated by six and seven oxygen atoms in the form of distorted TaO6 octahedra and TaO7 pentagonal bipyramids, respectively. Every pentagonal bipyramid shares edges with four octahedra, thus forming Ta5O14 units. The potassium atom is in an 11-fold coordination, whereas one sodium atom is in a 10-fold and the other is in a 12-fold coordination. Raman and infrared spectroscopy were used to investigate the room-temperature spectra of rankamaite. [ABSTRACT FROM AUTHOR]