The approach proposed here is focused on the separation of light fractions (corresponding to fatty acids with molecular chains between 8 to 14 carbons) from the fatty acid methyl esters (FAMES) of the biodiesel obtained by the reaction of transesterification of triacylglycerols in the kernel gueiroba oil (Syagrus oleracea) with methanol. The whole biodiesel was fractionated through atmospheric distillation in a single glass column with thermal insulation. Such a separation produced 59.79% in volume of light biodiesel (LB), which was mixed with the standard mineral Jet-A1 kerosene (cf. ASTM, corresponding to the QAV-1, cf. the Brazilian standard of the ANP) for aviation, in the volumetric ratios LB:Jet-A1 2:98; 5:95; 10:90 and 20:80. The values of density, water content, distillation analysis, flash point, calorific value and freezing point were carefully checked for their compliance with the official recommendations for jet fuel. It was found that the mixtures richest in the Jet-A1 mineral kerosene, that is, those containing no more than 5% LB by volume, well meet the recommended standards and are technologically viable to replace pure Jet-A1 kerosene for the propulsion of turbine aircraft.

The correlation between iron distribution in octahedral or tetrahedral sites in synthetic magnetite and zinc spinel ferrites and their catalytic properties were investigated in this work. The zinc-doped nanomagnetites were prepared by co-precipitation method and annealed at 420 °C. X-ray diffraction, UV-Vis, X-ray absorption and 57Fe Mössbauer spectroscopies were used to identify iron sites. The obtained results showed that ZnII replaces the relatively smaller FeIII cation in the tetrahedral sites, increasing the cubic lattice dimension, and this replacement remarkably enhances the catalytic effectiveness of the Zn-spinel ferrite towards the indigo carmine degradation compared to undoped magnetite. The indigo carmine degradation experiments were carried out using photo-Fenton method in which 50 mL of indigo carmine dye aqueous solutions (20 mg L−1, pH 3.0), 20 mg ZnxFe(3-x)O4, and 2.0 mL H2O2 (aqueous solution at 0.028 mol L−1) were placed under UV light at 25 °C. Under these experimental conditions the degradation rate of indigo carmine was superior to 98%.

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).

Zinc hexacyanoferrate (ZnHCF) is a Prussian Blue analog and can be intercalated by both monovalent and divalent ions. ZnHCF/multi-walled carbon nanotube (MWCNT) film could be used as a cathode for zinc ions battery. Carbon nanotubes improved significantly the electrochemical performance of the electrode. It is described the preparation of ZnHCF/MWCNT films by the interfacial method with cyclohexane/water mixture as solvent. The crystal structure, morphology, and microstructure of the as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, Mossbaüer, Raman spectroscopy, and infrared spectroscopy. Results revealed that the MWCNTs extend the electrochemical properties of the ZnHCF and influence the structure and morphology of the hexacyanoferrate particles. If tested as cathode material for zinc ion batteries, the nanocomposite film exhibits a capacity of 25.81 mA h g-1, which is much higher than those obtained for a ZnHCF single-component film (3.28 mA h g-1). The physical characteristics and properties that allow good reversibility to a high potential difference, achieved with the ZnHCF/MWCNT film, suggest new developments in the manufacture of translucent, flexible and light energy storage devices, which can be used as a lower-cost, safer and environmentally friendly alternative to the currently existing technologies.

A magnetic catalyst (sample MCat) consisting of KI supported on a mixture of silica and maghemite (γ-Fe2O3) was prepared and used in the transesterification reaction for the synthesis of biodiesel. The energy dispersive X-ray spectrum of the catalyst showed signals due to Si, Fe, K, and I. Powder X-ray diffraction data revealed the amorphous nature of the SiO2 and the duly impregnation of the support with KI. 57Fe Mössbauer spectroscopy and magnetization measurements confirmed the ferrimagnetic iron oxide in the catalyst to be maghemite. N2 adsorption-desorption data indicated that the silica is mesoporous with a specific area of 352 m2 g-1, enabling the impregnation of 40 and 11 wt.% of KI and maghemite, respectively, according to the chemical composition obtained by the X-ray fluorescence measurements. The MCat was found to be efficient in the transesterification reaction in the macaúba and soybean oils. The MCat was easily removed from the reaction medium, with a hand magnet, and efficiently reused for more four consecutive reaction cycles. The good catalytic activity along with its magnetic behavior, high chemical stability and recyclability make the MCat a suitable material for the green synthesis of biodiesel.

Composites based on nanosized particles of magnetite and natural microsized zeolite were prepared and their efficiency to adsorb arsenate from aqueous systems was evaluated through kinetic data and adsorption isotherms, considering the proportion of magnetic iron oxide, composite:solution ratio and zeolite particle size. A well-crystallized nanomagnetite with an averaged particle size of 50 nm when supported on zeolite was obtained; the nanomagnetite enhances the arsenate adsorption of zeolite. The composite prepared with a nanomagnetite:zeolite mass ratio of 0.43:1 and 0.30:1 presented on zeolite milled 20 and 120 min, respectively, showed a similar adsorption capacity as that observed for pure magnetite. Supported nanomagnetite prevents risks of the nanoparticles contamination. The smaller the mean particle size of zeolite the lower the mass proportion of nanomagnetite in the composite required to reach the maximum adsorptive efficiency. Acidic conditions improve arsenate remotion, in agreement with the development of positive surface charge in the composite.

A review of most of the reported studies on the use of iron oxides as catalyst in specific processes, namely Haber-Bosch reaction, Fischer-Tropsch synthesis, Fenton oxidation and photolytic molecular splitting of water to produce gaseous hydrogen, was carried out. An essential overview is thus presented, intending to address the fundamental meaning, as well as the corresponding chemical mechanisms, and perspectives on new technological potentialities of natural and synthetic iron oxides, more specifically hematite (α-Fe2O3), goethite (α-FeOOH), magnetite (Fe3O4) and maghemite (γ-Fe2O3), in heterogeneous catalysis.

This work aimed at putting in evidence the influence of the pH on the chemical nature and properties of the synthesized magnetic nanocomposites. Saturation magnetization measurements evidenced a marked difference of the magnetic behavior of samples, depending on the final pH of the solution after reaction. Magnetite and maghemite in different proportions were the main magnetic iron oxides actually identified. Synthesis with final pH between 9.7-10.6 produced nearly pure magnetite with little or no other associated iron oxide. Under other synthetic conditions, goethite also appears in proportions that depended upon the pH of the synthesis medium.

Frações magnéticas de duas amostras coletadas a 5 m e 52 m de profundidade, a partir do topo de um manto de intemperismo desenvolvido sobre periodito, da área de mineração de níquel em Cerro Matoso (7° 54' 31" N 75° 33' 23" O), Departamento de Córdoba, Colômbia, contêm minerais magnéticos e não magnéticos, intimamente associados. Frações magnéticas, posteriormente concentradas por tratamentos químicos seletivos com NaOH 5 mol L-1, para remover silicatos, e com uma mistura citrato - bicarbonato - ditionito (CBD), para remover óxidos de ferro não magnéticos, foram analisadas por difratometria de raios X, espectroscopia Mössbauer à temperatura do ambiente, magnetização de saturação, microscopias ótica e eletrônica por varredura e espectroscopia de energia dispersa, para se obter uma descrição detalhada das fases magnéticas presentes. Os tratamentos químicos foram efetivos na concentração dos óxidos de ferro, de tal sorte a permitir melhores resultados da análise mineralógica do minério de níquel. Os resultados Mössbauer revelaram que o tratamento com NaOH removeu silicatos e cromita e que a mistura CBD solubilizou seletivamente hematita, goethita e magnetita não estequiométrica, parcialmente oxidada.

Two magnetic samples, collected at 5 m and 52 m from the top of a weathering mantle developing on peridotite, from the Cerro Matoso (7° 54' 31" N 75° 33' 23" W) mining area for nickel, Department of Cordoba, Colombia, were submitted to magnetic separation with a hand magnet in the laboratory. The so concentrated samples were found to contain intimately associated magnetic and non-magnetic minerals. The magnetic phases were further concentrated by selective chemical treatments with 5 mol L-1 NaOH to remove silicates, and with a mixture citrate - bicarbonate - dithionite, to remove non-magnetic iron oxides. Powder X-ray diffractometry, RT Mössbauer spectroscopy, saturation magnetization measurements, scanning electron microscopy, energy dispersive spectroscopy and optical microscopy analyses were used to give a mineralogical description of the magnetic phases. The chemical treatments were effective on concentrating iron oxides so to improve the mineralogical analysis of this nickel ore. Mössbauer analysis revealed that NaOH selectively removed silicates and chromite from samples, whereas CBD dissolved hematite, goethite, and partially oxidized non-stoichiometric magnetite.

The classical interpretations of Nicolas Léonard Sadi Carnot on some physical principles involved in the operation of heat engines were fundamental to the development and formulation of the Second Law of Thermodynamics. Moreover, an accurate historical survey clearly reveals that Carnot was, by that time, also well aware about some new concepts, which were further worked out by other scientists to lead to what was, some time later, known as the mechanical equivalent of heat and the conservation of energy. Benoit Paul Émile Clapeyron recognized these original concepts in the first of Carnot´s monographs, published in 1824, but no explicit citation is found in any post-Carnot classical texts dealing with the First Law of Thermodynamics, including those by Julius Robert Mayer, James Prescott Joule and Hermann Ludwig Ferdinand von Helmholtz. The main objective of the present work is to point out some historical evidences of the pioneering contribution of Carnot to the modern concept of the First Law of Thermodynamics.