Characterization by X ray diffraction of mechanically alloyed tripotassium sodium sulfate

Nanocrystalline powder of tripotassium sodium sulfate (K3Na(SO4)2 - KNS) was successfully obtained by mechanical alloying a mixture of potassium sulfate (K2SO4) and sodium sulfate (Na2SO4) with a proportion of 3:1 in a planetary mill. X ray powder diffraction (XRPD) was used to characterize this material. Powders produced with high milling times: 15, 30, 45 and 60 hours, have shown a single phase. For 60 hours of milling time, the powder was formed with very small grains (60 nm in average). We also prepared several samples with low milling times: 30, 60, 120, 150 and 180 minutes. The results for this series show that 120 minutes of milling is enough to produce a single crystalline phase of KNS. Therefore, we showed that a nanocrystalline powder of tripotassium sodium sulfate is easily obtained by mechanical alloying and that the grain size can be controlled by the amount of milling time

A self-assembly of graphene oxide@Fe3O4/metallo-phthalocyanine nanohybrid materials: synthesis, characterization, dielectric and thermal properties

In this work, we report the synthesis of novel inorganic–organic hybrid nanomaterials (GO@Fe3O4/CuPc) and GO@Fe3O4/ZnPc) consisting of sheets of graphene oxide (GO) decorated by iron oxide nanoparticles (Fe3O4), the whole heterostructure functionalized with metallo-phthalocyanines (MPc, M:Cu or Zn). First the synthesis of nanomaterial (GO@Fe3O4) was prepared by hydrothermal self-assembly process through the mixture of graphene oxide and Fe?2/Fe?3 salt solution. The metallo-phthalocyanines anchorage on the surface of nanosystem was lately performed by facile and effective ultrasonication method. The structure, composition and morphology of nanohybrids and intermediates were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, UV–visible spectroscopy, scanning and transmission electron microscopy and impedance spectroscopy. All the results suggested that iron-based nanoparticles were successfully deposited onto graphene oxide sheet networks in the form of Fe3O4, forming nanospheres, decreasing in lattice defects of the GO sheets and dramatically increasing the dielectric properties of nanosystems. Nanomaterials presented saturation magnetization in the 52–58 emu/g and superparamagnetic behavior. It was observed that the values of dielectric constant decreased as a function of the amount of phthalocyanines in the nanomaterials. Therefore, because of their versatile magnetic and dielectric performances, the novel superparamagnetic hybrid nanomaterials, herein described, can be considered as potential for microwave devices

Um estudo inter-comparativo de previsão sazonal estatística-dinâmica de precipitação no nordeste do Brasil A study inter-comparative of statistical-dynamical seasonal forecast precipitation in nordeste´s Brazil

Apesar dos avanços da modelagem dinâmica da atmosfera nas últimas duas décadas do século 20 as aplicações com modelagem empírica ainda têm sido muito utilizadas em função do seu fácil uso e pouca dependência de recursos computacionais. Neste estudo é mostrada uma comparação dos resultados de simulação de precipitação para o Nordeste do Brasil (NEB) - 1971-2000 obtido por modelagem dinâmica de grande escala e regional (downscaling) e a previsão de um método de modelagem empírica K´neigbhors. Foram usados o modelo de circulação geral da atmosfera ECHAM4.5, e dois modelos regionais, o Modelo Regional Espectral (MRE/97) do National Centers for Atmospheric Prediction- NCEP e o Regional Atmospheric Model System (RAMS) desenvolvido na Universidade do Colorado. Os modelos regionais foram aninhados aos dados simulados pelo ECHAM4.5 tendo como condição de contorno a Temperatura da Superfície do Mar observada no período de fevereiro a maio. Os resultados mostraram que o modelo empírico apresentou menor erro absoluto nos períodos fevereiro a abril (FMA) e março a maio (MAM) que os modelos dinâmicos em áreas do no norte do Maranhão e Piauí, oeste e sul do Ceará, centro-sul do Piauí e oeste e nordeste da Bahia. Quanto ao bias, o ECHAM4.5 e o MRE/97 mostraram um bias úmido em grande parte do NEB, porém com um valor médio para o setor norte do NEB (2ºS-12ºS e 45ºW-37ºW) mais próximo do observado. Para o RAMS e o método análogo houve um predomínio de um bias seco sobre o NEB, com valores em magnitudes mais distantes do observado. A previsibilidade (Heidke Skill) em três categorias Seca (S), Normal (N), Chuvosa (C), mostrou que o método análogo tem baixo Skill, entre 0,1 e 0,3 em todas as categorias, enquanto os modelos dinâmicos apresentaram Skill superiores, com valores maiores para as categorias S e C (da ordem de 0,4 a 0,5), até superiores a 0,6 em algumas áreas do setor norte do NEB para a categoria C como visto nos resultados dos modelos ECHAM4.5 e MRE/97.Despite significant advances of the dynamic atmosphere models over the last decades of the 20th century, the empirical atmospheric models have been widely used due mostly to both its general applicability and its little dependence on the computational resources. This study is show comparison of precipitation simulation to Northeast Brazil (NEB) - 1971-2000 from large scale dynamical modeling and regional model (downscaling) and the forecast of empirical modeling (K-nearest-neighbor (k-NN). Were user the general circulation model ECHAM4.5 together two regional models, the Regional Spectral Model (RSM/97) from the National Centers for Atmospheric Prediction-NCEP and the Regional Atmospheric Model System (RAMS) developed at Colorado State University. The regional models were nested in ECHAM4.5, forced with the observed Sea Surface Temperature as a boundary condition, for the period from February to May. The results show that the empirical model presented a smaller absolute error than the dynamic models for the periods February to April (FMA) and March to May (MAM) in isolated areas of the north of Maranhão and Piauí states, west and south of Ceará, center-south of Piauí and west and northeast of Bahia state. Regarding model biases, ECHAM4.5 and the RSM/97 produced, to a large extent, a humid bias over large areas of NEB, however with an average precipitation for the northern sector of NEB (2ºS-12ºS and 45ºW-37ºW) close to the observations. RAMS and the analog method had a dominance of a dry bias over NEB, with precipitation totals below the observed values. The model skills (using the Heidke score) were evaluated for three categories Dry (S), Normal (N), Rainy (C), showed that the analogous method has low skills, between 0,1 and 0,3 in all categories, while dynamic models presented superior skills, with larger values for categories S and C (of the order of 0,4 the 0,5), exceeding 0,6 in some areas of the northern sector of NEB for category C as seen in the models ECHAM4.5 and RSM/97 models