Siloxane-poly(methyl methacrylate) (PMMA) organic-inorganic hybrid coatings were deposited on galvanized steel by the dip-coating sol-gel technique. Anticorrosion properties, as well as the morphological, surface and structural features were studied. Hybrid coatings were synthesized from tetraethoxy-silane (TEOS) and methyl methacrylate (MMA) as inorganic and organic phases, respectively, linked by 3-metacriloxypropyl-trimethoxysilane (TMSM) as a coupling agent. The MMA/TMSM ratio was kept constant, whereas the four TEOS/TMSM ratios were varied. The characterization of coatings was assessed using several techniques such as Scanning Electronic Microscopy (SEM), Contact Angle, Fourier Transform Infrared (FT-IR), Open Circuit Polarization (OCP), Atomic Force Microscopy (AFM) and Electrochemical Impedance Spectroscopy measurements (EIS). The EIS results, which were obtained for the hybrid coatings, were discussed based on an electrical equivalent circuit used to adjust the experimental data. The results showed that the increasing the TEOS content caused increase in coating thickness, increased in the surface roughness and increased in the surface hydrophobicity. The film with the highest TEOS content presented the best electrochemical performance, more effective in protecting against corrosion.

Recent studies evidenced that the Zamak 5 corrosion is associated to solidification defects arising from the injection process that occur mainly in areas where the solidification rate is faster. Given this factor, the aim of this research was to evaluate the influence of Zamak 5 casting temperature. For this study, Zamak 5 was casted at different temperatures (430 °C, 450 °C, 500 °C, 550 °C) with respective solidification curves. Zamak 5 was analyzed for chemical composition and microstructure. Moreover, complementary tests of microhardness and electrochemical analyses of open circuit potential and polarization were performed. From these analyses it was observed that the highest casting temperature of Zamak 5 originates larger grains and higher microhardness value, due to the lower solidification rate. In none of the leaking temperatures porosity defects were observed on the samples, which is coherent with previous researches, being originated from the injection process.

During anodizing, the chemical attack of hydrofluoric acid (HF) electrolytes on niobium can promote the formation of oxides with porous structures. However, this chemical attack can also cause an intense dissolution of the oxide during its formation. This effect can be minimized by varying the HF concentration of the anodizing electrolyte, thereby controlling the growth of the porous oxide. Studies have alternative electrolytes that do not use HF to obtain porous oxides. Thus, organic electrolytes, such as acetic acid, may be a viable alternative. In this context, the objective of this study is to obtain and evaluate the anodization of niobium in acetic acid at different current densities (10, 20 and 50 mA/cm 2 ) and to study the influence of the addition of HF to the electrolyte. The results showed that the anodized anodic in acetic acid, under conditions of 100 V and 10 mA/cm 2 , presented porous oxide with less defects. Therefore, this result indicates that it is possible to produce porous niobium oxides by anodizing in HF-free electrolyte. Keywords: Niobium; Anodizing; Acetic acid. OBTENÇÃO DE ÓXIDOS DE NIÓBIO EM ÁCIDO ACÉTICO COM ADIÇÃO DE HF ResumoDurante a anodização, o ataque químico de eletrólitos de ácido fluorídrico (HF) sobre o nióbio pode promover a formação de óxidos com estruturas porosas. Contudo, este ataque químico pode causar uma intensa dissolução do óxido durante sua formação. Esse efeito pode ser minimizado variando-se a concentração de HF do eletrólito de anodização, controlando assim o crescimento do óxido poroso. Estudos têm buscado por eletrólitos alternativos que não utilizam HF na obtenção de óxidos porosos. Logo, eletrólitos orgânicos, como o ácido acético, podem ser uma alternativa viável. Neste contexto, o objetivo deste estudo é obter e avaliar a anodização de nióbio em ácido acético em diferentes densidades de correntes (10, 20 e 50 mA/cm2 ) e estudar a influencia da adição de HF ao eletrólito. Os resultados mostraram que a amostra de nióbio anodizada em ácido acético, nas condições de 100 V e 10 mA/cm 2 , apresentou óxido proroso com menor quantidade de defeitos. Portanto, este resultado indica que é possível a formação de óxidos de nióbio porosos por anodização em eletrólito livre de HF. Palavras-chave: Nióbio; Anodização; Ácido acético.

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The present study aimed to characterize the structure of nanocomposites obtained from the incorporation of three different polyhedral oligomeric silsesquioxane (POSS) in an epoxy resin. glycidylisobutyl-POSS, triglycidylisobutyl-POSS and glycidyl-POSS were added (5% by weight) in an epoxy matrix, diglycidyl ether of bisphenol-A (DGEBA), through a sonication process. The nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and dynamic mechanical analysis (DMA). The XRD analysis presented a characteristic peak of POSS. The incorporation of glycidylisobutyl-POSS showed a significant increase in the value of glass transition temperature (Tg), being also the most effective in terms of dispersion. It should also be noted that glycidyl-POSS presented a greater influence on the thermal stability.

For the polyhedral oligomeric silsesquioxane (POSS) nanocomposites with epoxy resins, the POSS functionality is an important issue since these compounds will be diluted in the resin that will later undergo a chemical reticulation process. In this study, mono, tri and octa‐functional POSS containing glycidyl groups were dispersed in an epoxy resin by applying ultrasound. Based on the results obtained from the transmission electron microscopy, POSS tended to form an ordered phase to minimize the interfacial tension; however, this form was influenced by its functionality. The use of mono‐functional POSS shows finer dispersion and promotes an increase in the resin glass transition temperature. However, the octa‐functional POSS leads to improvement in thermal stability as seen in the degradation analysis. These results showed that the equilibrium of the dispersed nanoparticle is more evident for lower functionalized particles since higher functionalized ones hinder diffusion movements which ultimately form an ordered and dispersed phase in the resin during reticulation. POLYM. COMPOS., 38:E229–E236, 2017. © 2016 Society of Plastics Engineers

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