[en] Mn_1-xFe_xIn₂S₄ spinel compounds (x=0.3, 0.8) were grown by the chemical vapor transport method. The analysis of the X-ray diffraction data suggest that both the compounds crystallize in a cubic structure under the space group Fd3m. The magnetic study done between 300 and 2 K showed a paramagnetic behavior for the intermediate concentration sample x=0.3. A good fitting to the Curie-Weiss law allows us to calculate the paramagnetic Curie temperature. They are negative indicating predominant antiferromagnetic interactions. However, in sample with high Fe concentration, x=0.8, it was possible to observe a peak at around T_sg congruent with 10 K. From ac magnetic susceptibility data at different driving frequencies f, it is found that the peak at T_sg shifts to lower temperatures with decreasing frequency suggesting an spin-glass behavior

[en] The alkanes are a kind of the principal compounds of petroleum. when the n-alkanes are solid, also called paraffins, are spilled into the field, they form a dense layer in the surface that hinders the oxygen and nutrients transport, affecting the quality and functionality of the soil. (Author)

[en] AA 2024 aluminum alloys have broad applications in the aeronautics industry, since they have an excellent mechanical resistance: weight ratio. The increased mechanical resistance of aluminum is achieved by alloying copper with other metals, as well as by submitting the material to thermal treatments. However, its heterogeneous composition and metallurgical history fosters the generation of galvanic piles that cause localized pitting and intergranular corrosion on the metallic surface in aggressive environments. Given the catastrophic corrosion of aluminum alloys used in aeronautics, the traditional methods of protection include multi-stage processes that involve anodizing, the incorporation of additives in case of water permeability and painting of the metallic piece. This is an efficient process in terms of protection but highly toxic and contaminating due to the handling of elevated concentrations of Cr⁶⁺. Among alternative methodologies the most outstanding are protective coatings obtained with the sol-gel technique. This type of coating, however, has drawbacks, mostly associated with its low adherence and limited mechanical properties. Considering the above, this work studied the effect of adding AI₂0₃ to zirconium polymeric matrices, for their application as anticorrosive coatings in the protection of AA 2024 surfaces. The evaluation of the doped coatings with nanoparticles compared to those without doping was carried out using potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscopy. The results show that the zirconium coatings doped with a low concentration of nanoparticulated additive and submitted to a consolidation treatment at reduced pressure display a significant drop in the population of fractures, responding directly to an increase in their corrosion protection

[en] A model is presented of the movement of nutrients and artificial radionuclides in the soil-plant system. The model has a hierarchical structure and is composed of modular elements (submodels) that integrate themselves additively at different levels, with each sub-model containing the submodels of the previous levels. This integration is achieved using the state and flow variables of each submodel as auxiliary variables of the higher level submodels. This hierarchical scheme is an operative solution that simplifies the construction of complex models with different and strongly related dynamic processes. The levels of the model are represented by the following processes: level I: plant biomass dynamics; level II: nutrient movement between the soil and the plant; and level III: deposition of radionuclides and movement between the soil and the plant. Each submodel is structured in different compartments an has its own boundaries. Definition of the compartments of a given submodel is not only dependent on the process that it represents but is also determined by its subsequent integration at higher levels. The plant biomass dynamics submodel is composed of four compartments: root + shoots, young leaves, old leaves and litter. The boundaries of this submodel are defined by the plants themselves. The nutrient dynamics submodel adds two new compartments representing the soil system and uses the differentiation between young and old leaves, established at the previous level according to the changes that take place in their chemical composition. The boundaries of this submodel are defined by the above ground parts of the plants and by the depth of the roots underground. The radionuclide dynamics submodel integrates the two previous submodels and incorporates some additional compartments for the surface of the leaves and the above ground parts of the root + shoots fraction. This submodel has the same boundaries as the previous one. (author). 14 refs, 4 figs

[en] The anticorrosive protection of metal alloys, like stainless steel, is usually carried out with chrome-based coatings, but the toxic wastes associated with the process minimizes its applicability. The above has motivated the search for alternative protection methodologies, among which are the inorganic polymers prepared by the sol-gel method, which are a viable protection alternative because of their outstanding chemical and physical properties in aggressive environments. Despite the method's benefits, the application of sol-gel coatings to metals exposed to highly corrosive materials is restricted due to the substantial porosity of the films. Recent studies report that this limiting factor can be diminished by adding inorganic nanoparticles to the polymeric matrices, significantly improving the anticorrosive properties of the coatings. Considering the above, this work evaluated the inclusion of iron oxide nanoparticles (III) in zirconium polymeric matrices for the protection of 316 and 316L stainless steel. Electrochemical techniques, such as polarization curves and electrochemical impedance spectroscopy and morphological analysis with atomic force microscopy were used for this purpose. The responses obtained showed improvements in the anticorrosive properties of the zirconium films when doped with nanoparticles, and the best protective response was obtained with the minimum amount of the nanomaterial, aided by a significant increase in the metallic material's passivity. A critical content of nanoparticles was also identified in the polymeric matrix, above which the coating suffers serious deterioration, caused by the apparent formation of percolation channels leading to the oversaturation of the polymeric matrix

[en] Measurements of X-ray diffraction, differential thermal analysis (DTA) and of magnetic susceptibility χ, in the temperature range from 2 to 300 K, were carried out on polycrystalline samples of the Zn_1-zMn_zIn₂Te₄ alloy system. The X-ray diffraction patterns were used to check the equilibrium conditions and to estimate crystalline parameter values. The DTA transition temperature values were plotted as a function of alloy composition z. The 1/χ vs T curves indicated that samples in the α₁I4-bar range (0< z<0.4) were antiferromagnetic showing ideal Curie-Weiss behavior, but for all samples in the γI4-bar 2m range (0.4< z<1) the behavior was spin-glass. The values of the Curie-Weiss temperature θ determined from all of the 1/χ vs T curves were used to give the type ordering and the degree of order of the Mn atoms in the several solid fields which occur in the present T(z) diagram.