In the present work, the sol-gel synthesis method was employed as strategy to obtain a magnetic and mesoporous silica-niobia material. The planned synthesis was based on the hetero-condensation of niobium and silicon alkoxide precursors, in the presence of spherical magnetite particles. The resulting material presented interesting characteristics such as magnetism, large mesopores, in the range from 20 to 50 nm, and 68 m2 g-1 of surface area. These features allowed its use as modifier of carbon paste electrode for p-nitrophenol determination, since niobia has never been used in electrochemical sensors for the determination of nitrophenol compounds. By using differential pulse voltammetry technique, the electrode can be applied in a wide range of p-nitrophenol concentration, from 10 to 490 μmol L-1, with a limit of detection of 1.2 µmol L-1 and sensitivity up to 0.60 µA L µmol-1. The proposed electrode presented good sensitivity and selectivity and it was applied in real water samples.

As intensidades de emissão das espécies N2+, H, C, NH, N2, Ar e CN do plasma de carbonitretação (usando os gases Ar+N2+CH4) foram medidas por espectroscopia de emissão óptica (OES) em pressão e temperatura constantes (2mbar e 500 °C) variando o fluxo de CH4. Em seguida, amostras de Ti comercialmente puro (Ti CP) foram carbonitretadas em plasma nas mesmas condições do estudo por OES. O objetivo desse trabalho é avaliar a influência das espécies presentes no plasma, detectadas por seus padrões de emissão, na composição de fases superficiais, nas características topográficas e no perfil de microdureza do revestimento de TiCN. Foi observado que o aumento da concentração de CH4 no plasma gerou as espécies H (dissociado do CH4) N2+, C, NH e CN. A evolução contínua de CN e uma queda progressiva na espécie N2+ influenciaram a composição da superfície e as propriedades aqui avaliadas. A análise de difração de raios X em ângulo rasante revelou a presença de nitreto e carbonitreto de titânio na superfície com composição química correlacionada com as alterações das intensidades de emissão das espécies CN e N2+. As topografias das amostras, avaliadas por microscopia de força atômica, apresentaram aumento nos parâmetros de rugosidade comparados com a amostra padrão. A rugosidade Ra aumentou com o aumento da intensidade de emissão óptica de CN e redução de N2+. Com auxílio da espectroscopia micro-Raman foi encontrado carbono não reagido com o titânio na forma de um filme que se desenvolveu com o aumento da intensidade da linha de emissão do CN. Este filme pode, hipoteticamente, ter sido o responsável pela queda progressiva da dureza superficial do revestimento.

The optical emission intensities of the species N2+, H, C, NH, N2, Ar e CN in a carbonitriding plasma (using Ar+N2+CH4 gases) were studied with optical emission spectroscopy in an atmosphere of constant pressure and temperature, changing the CH4 flow. Afterwards a commercially pure Ti was exposed to a carbonitriding plasma in similar conditions. The objective of this work is to evaluate the influence of the gaseous species on the superficial properties (chemical composition, topography, and microhardness profile) of the TiCN layer. When the CH4 flow was increased, the species H, N2+, C, NH, and CN were observed. The continuous increase of CN and a progressive reduction of N2+were detected. Grazing incidence X-ray diffraction revealed titanium nitride and carbonitride with variable chemical compositions, related to the changes observed in the emission patterns of the species CN and N2+. The topography, evaluated by atomic force microscopy, showed that the roughness increased when CN increased and N2+ decreased. Micro-Raman spectroscopy showed unreacted carbon on the surface that developed with de increase of the CN emission. This carbon film may be responsible for the progressive decrease of surface hardness.

Complex polymetamorphic granulites have been dated in the Santa Catarina granulite complex of southern Brazil through SHRIMP study of zircon. This complex is dominated by intermediate-acid plutonic rocks and contains small volumes of mafic and ultramafic rocks, and minor quartzite and banded iron formation. Porphyroblasts of orthopyroxene, clinopyroxene and plagioclase in mafic and acid rocks are interpreted as magmatic remnants in a volumetrically dominant granoblastic aggregate (M1) of the same minerals and hornblende. Hornblende formed during a later M2 metamorphic event constitutes rims around pyroxene, but the hornblende is also rimmed by granoblastic simplectites of orthopyroxene, clinopyroxene, hornblende and plagioclase in a second granulite facies event (M3). Chlorite and epidote occur in shear zones (M4). This granulite terrain is part of a Neoproterozoic craton, because it was little affected by the Brasiliano Cycle. The two granulite-facies events (M1 and M3) are dated by U/Pb zircon SHRIMP at about 2.68 and 2.17 Ga, while the magmatic protoliths formed at about 2.72 Ga. The amphibolite facies event (M2) probably occurred close to the 2.17 Ga granulitic metamorphism.