Uso de elementos Terras Raras na agricultura

The Rare Earth Elements (REEs) is a group of 17 chemical elements, where 15 belong to the group of lanthanides, and the other two are scandium and yttrium. The largest mineral deposits of REEs are in China, which dominates over 95% of the world market. Research on crops with the use of compounds based on REEs – performed mostly in China – showed an increase in productivity, plant growth, disease control and other beneficial effects, usually when they are applied in low concentrations. The reasons for these effects are not sufficiently understood, but recently, physiological interactions with calcium, effects on the structure and function   of  the  cytoplasmic  membranes,  changes  in  photosynthesis,  hormone  metabolism, enzyme activity, and increased efficiency on water use have been proposed as possible mechanisms affected by REEs. The positive results of the use of these elements in agriculture, combined with the few researches realized outside of China, are strong indicators of the need for further studies on these substances. Thus, in the present review are shown some of the resulting effects from the use of REEs on crops, emphasizing the used concentrations, and the physiological interactions with plants, among other mechanisms. Still, it contribute to disseminate knowledge involving these substances and also highlight the potential which they assume on the agricultural scenario in the world and, consequently, in increasing food production.O grupo da tabela periódica denominado Terras Raras é formado por 17 elementos químicos, onde 15 pertencem ao grupo dos lantanídeos, e os outros dois são o escândio e o ítrio. Os maiores depósitos minerais de Elementos Terra Raras (ETRs) se encontram na China, que domina mais de 95% do mercado mundial. Pesquisas em culturas agrícolas com o uso de compostos baseados em ETRs, realizadas majoritariamente na China, mostraram um incremento da produtividade e do crescimento das plantas, controle de doenças, além de outros efeitos benéficos, geralmente quando estes são aplicados em baixas concentrações. As razões para a ocorrência destes efeitos não são suficientemente compreendidas, mas, recentemente, interações fisiológicas com o cálcio, efeitos sobre a estrutura e a função das membranas citoplasmáticas, alterações na fotossíntese, no metabolismo dos hormônios, na atividade enzimática, e o aumento da eficiência no uso da água têm sido propostos como possíveis mecanismos de atuação dos ETRs. Os resultados positivos do uso destes elementos na agricultura, aliado às poucas pesquisas realizadas fora da China, são fortes indicativos da necessidade de maiores estudos com estas substâncias. Deste modo, na presente revisão são mostrados alguns dos efeitos advindos do uso dos ETRs nas culturas agrícolas, enfatizando as concentrações utilizadas e as interações fisiológicas com as plantas, entre outros mecanismos. Busca-se, ainda, contribuir para a disseminação do conhecimento envolvendo estas substâncias e evidenciar o potencial que estes podem assumir no cenário agrícola mundial e, consequentemente, no aumento da produção de alimentos

Structural and Magnetic Characterization of Nanostructured Iron Acetate

Iron(II) acetate anhydrous, (i) as received (FeAc) and (ii) processed by freeze-drying (FeAc-FD), were characterized structural, magnetic and morphologically by thermal analysis, scanning electron microscopy, thermogravimetry, differential scanning calorimetry and X-ray diffraction.  As a result of these analyzes, it was found that the FeAc- FD type leaves showed a morphology with a thickness in the nanometer scale. The activation energy (Ea) for the exothermic events related to the decomposition of the above acetate was estimated in the range of 275-328 °C. Values for Ea ​​equal to 100,225 and 127,824 kJ / mol were obtained for the FeAc and FeAc-FD, respectively. Mössbauer spectra showed as isomer shift (IS) characteristic of a Fe+3 to the FeAc-FD, and Fe+3 and Fe+2 to the FeAc. The results indicate that freeze-drying of FeAc could be used as a precursor to further processing method of decreasing the synthesis temperature. DOI: http://dx.doi.org/10.17807/orbital.v9i4.1006</p

SYNTHESIS, FREEZE-DRYING AND CHARACTERIZATION OF 57

Iron(III) acetate was synthesized by the reflux method using iron enriched in the 57Fe isotope and the compound processed by freeze-drying. The as-synthesized and freeze-dried acetates were characterized regarding their structural, thermal, vibrational and hyperfine properties. Similar diffractometric and spectroscopic results were found for both materials and also for an industrial acetate made with natural iron. However, the microstructures differed: the as-synthesized compound showed flake morphology with micrometric dimensions, whereas the freeze-dried showed flake morphology with sub-micrometric dimensions. The activation energies for thermal decomposition, calculated from the exothermic events occurring in differential scanning calorimetry measurements, were 100.9 kJ/mol (as-synthesized) and 114.7 kJ/mol (freeze-dried)

Structural and magnetic characterization of the Nd2Fe14B + 10%wt.Fe system subjected to high-energy milling

International audienc

Synthesis, structural characterization and Mössbauer study of LnV 0.5Fe 0.5O 3 perovskites (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er)

Perovskites LnV 0.5Fe 0.5O 3 (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) were synthesized by rapid solidification from arc-melted samples and characterized by the study of their crystal structure and hyperfine properties. These metastable solid solutions crystallized in the Pbnm symmetry, with the iron and vanadium cations randomly distributed in the transition metal octahedral sites. Depending on the lanthanide present at the A site of the perovskite, iron is present with two valences (i.e., Fe 3+ and Fe 2+). The volume of the unit cell for these perovskites increases linearly with the lanthanide ionic radius, as the perovskite approaches its ideal structure. At room temperature, the quadrupolar splitting of the trivalent paramagnetic Mössbauer component works as an indirect measurement for the Goldshmidt tolerance factor. Close to or below 100 K, these perovskites undergo a crystallographic phase transformation, probably due to orbital ordering of the V 3+ cations, originating two different magnetic iron sites. © 2012 Elsevier Ltd.Fil: Ivashita, Flávio F.. Universidade Estadual de Maringá; BrasilFil: Biondo, Valdecir. Universidade Estadual de Maringá; BrasilFil: Bellini, Jusmar V.. Universidade Estadual de Maringá; BrasilFil: Paesano Jr., Andrea. Universidade Estadual de Maringá; BrasilFil: Blanco, Marìa Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Fuertes, Valeria Cintia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Pannunzio Miner, Elisa Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Carbonio, Raul Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin