In our research group, controlled release systems for the sulfentrazone herbicide has been accomplished by encapsulating this bioactive compound into calcium alginate (Ca-ALG) biodegradable polymer fashion and the release mechanisms were verified by using Korsmeyer-Peppas model (KP). However, the KP model does not allow to evaluate all the phenomena involved in the (Mt/M∞ versus t) curves. Thus, the aim of this work is the development of a new mathematical model to interpret the distinct regions of the controlled release assays of the Sulfentrazone herbicide encapsulated in Ca-ALG microparticles and that can be used for other systems with a similar release profile. The proposed model is based on the herbicide diffusion, dissolution and polymer surface erosion. The results show that the proposed model is closest to the experimental curve when compared to the KP. The new mathematical model allows not just to describe the behavior of the system in terms of Fick’s law, but to know what type of mechanism act in the herbicide release process.

The development and utilization of new energy sources has been extensively studied in the world. Here, we report the development of flexible self-supported metal-free electrodes based on non-oxidized graphene multilayer (MLG) paper containing the lead iodide nanoparticles (PbI2-NPs). The PbI2-NPs was obtained and characterized by X-ray diffraction (XDR) and Raman spectroscopy. Supercapacitor containing the PbI2-NPs in MLG electrodes was fabricated by a simple method and characterized using atomic force microscopy (AFM), cyclic voltammetry (CV) and galvanostatic charge-discharge techniques. The results show a flexible supercapacitor fashion reaching capacitance values of 154 F/g with high prospects in electronic area. Energy and power densities obtained for the pure MLG supercapacitor were 3.40 µWh cm-2 and 0.73 mW cm-2, respectively. Regarding to PbI2-NPs/MLG capacitor the energy and power density obtained were 3.50 Wh kg-1 and 1.10 kW kg-1. The results herein presented open the possibility to new energy storage devices using PbI2-NPs and MLG flexible supercapacitor configuration.

In this paper, we present an alternative method to obtain thin films for coating protection on the surface of the AA2524-T3 Al-alloy by using the Layer-by-Layer (LbL) technique. The LbL films were fabricated by alternated immersion of the Al-alloy into a poly(styrene sulfonate) (PSS) and polyaniline nanoparticles (PAni-NPs) solutions, obtaining a PAni-NPs/PSS bilayer architecture. The LbL films were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), electrochemical and micro-abrasive wear tests. The results show that the number of bilayers promotes shifts to less negative potentials, indicating an optimized system, in which the best performance was observed for a 15-bilayer PAni/PSS LbL film. The pitting potential (Epit) values shifted 130 mV (from -610 mV to -480 mV) in comparing a bare Al-alloy. The predominantly wear mechanism for AA2524-T3 with PAni-NPs/PSS bilayers was scratching whereas for the bare material there was an equivalence between scratching and rolling mechanisms. The results proved that the incorporation of PAni-NPS by the LbL method may be propitious as protective coating against corrosion in AA2524-T3 alloy.

Carbon dots (C-dots) possess the attractive properties of high stability, low toxicity, good water solubility, simple synthetic routes as well as size and excitation-dependent photoluminescence (PL).The aim of this work was to synthesize photoluminescent C-dots by hydrothermal method using acerola fruit (Malpighiaemarginata) as a row material, since this fruit contains large number of organic molecules. Studies about the optimal synthesis conditions were performed, where these organic molecules were converted into C-dots by hydrothermal carbonization at 180 ºC for 18 h. The C-dots exhibited a green emission light at 459 nm when excited under UV-light ( λ ex= 370 nm). These nanomaterials were also successfully used to prepare C-dots/poly (vinyl alcohol) luminescent composites (C-dots/PVA). Both C-dots and C-dots/PVA composite films were investigated by using colorimetric visual sensor for Fe3+ metal ions detection. The results show that the prepared C-dots and C-dots/poly presented strong green emission light. The emission spectra of above materials were quenched in the presence of Fe3+ ions. Thus, highly specific “turn off” fluorescence sensing of Fe3+ was achieved using fluorescent C-dots. Regarding, this work describe that the polymeric films as sensors of metallic ions in aqueous solution appears as a new perspectives to design new composite materials.

The aim of this work was to study the corrosion process of new aluminium alloy AA2524-T3 (Solution Heat Treated and Cold Worked), which is a promising substitute of the base line AA2024-T3 for aircrafts fabrication, by global and localised techniques in sodium chloride medium (0.05 mol L-1 NaCl). The open circuit potential results revealed a stochastic evolution of pitting events and to the resulting variations in the ratio of passive/active areas and/or cathode/anode, which may be related to the presence of different types of intermetallics. The cyclicvoltammetry showed that the corrosion potential (Ecorr) and the pit nucleation potential (E pit) values are quite similar (approximately -0.525 V). The results of EIS show that the corrosion rate is quite stable, with no tendency to increase or decrease for longer immersion periods. The results of SVET were in agreement with the results obtained by EIS technique, showing strong anodic activity on the surface with no repassivation along the whole immersion time. Besides, corrosion process led to significant surface degradation after 24h.

A new study about corrosion behavior of CoCrMo alloy used as implant material exposed to the physiological serum and Hank's solution in different temperatures, electrolyte compositions and immersion time were simulated, using open circuit potential (OCP), potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS.) From the results, it can be concluded that CoCrMo biomaterial is influenced by electrolyte composition and temperature, and the passive films were more protective when formed in presence of physiological serum. Comparing the Ecorr for both solutions, it is possible to verify that the Hank's solution presented values more negative for the two studied temperatures (25 and 37 °C), indicating a greater susceptibility to the corrosion process. Regarding the results of potentiodynamic polarization, the ipass, decreased as function of time, indicating a more protective passive film at 25 °C. In regards to the physiological serum, the highest ipass values at 37 ºC evidenced the formation of a less stable passive film. The different behavior of ipass in Hank's solution may be related to the competitiveness between a possible film of D-glucose and oxides of the alloy metals. EIS studies suggest that the film formed in presence of physiological serum is nobler than that with Hank's solution.

A new δ-FeOOH supported nano-Au catalyst was prepared by a facile method using HAuCl4 as the gold source and NaBH4 as the reducing agent. The samples (denoted as AuNPs/FeOOH) were characterized by means of X-ray diffraction (XRD), UV-vis and infrared spectroscopies and scanning electron microscope (SEM). The obtained characterization data confirmed the formation of Au nanoparticles on the δ-FeOOH matrix surface. SEM observations showed that Au nanoparticles have a spherical morphology and good dispersion with a narrow size distribution on the surface of iron (III) oxyhydroxide. The catalyst exhibits significantly high catalytic activity for hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at room temperature. The high performance obtained can be attributed to the specific characteristics of the nanostructure of the catalyst of nano-Au deposited on the external surface of δ-FeOOH, including plenty of oxygen-containing groups of δ-FeOOH for anchoring AuNPs. Moreover, the catalytic activity increased when the AuNPs content in the δ-FeOOH support. The AuNPs-based δ-FeOOH hybrids are interesting catalysts for hydrogenation of nitrophenols to aminophenols.

The development of controlled delivery system formulations has received increasing interest in the agriculture area. Tebuthiuron (TBH) is the most commonly used herbicide for weed control in sugar cane and cotton crops. The TBH and some of its metabolites are detected in surface water by leaching process, evidencing contamination and the need for an efficient process to decrease pesticide residues. The development of a controlled system release appears as a good solution. The present investigation aimed to study the development and evaluation of alginate microparticles as a delivery system for the TBH. The calcium alginate microparticles were prepared from the crosslinking of sodium alginate by Ca++ containing varied amounts of TBH supplied in CaCl2 aqueous solution. The particle size and morphological analysis of microparticles were determined by optical microscopy (OM) and by field emission gun scanning electron microscopy (FEG-SEM). The encapsulation efficiency and release of TBH studies was accessed by UV-vis spectroscopy. The results show that the polymeric microparticles containing TBH can be obtained successfully through a simple method and is suitable as a controlled release carrier system for herbicides and can be effective for controlling weeds.

A homemade Josephson junction was successfully obtained using a superconductor thin film of the BSCCO system. The film was deposited on a lanthanum aluminate, produced from a commercial powder with a nominal composition Bi1.8Pb0.4Sr2CaCu2Ox, was thermally treated by a domestic microwave oven. The XRD analysis of the film indicated the coexistence of Bi-2212 and Bi-2223 phases and SEM images revealed that a typical superconductor plate-like morphology was formed. From the electrical characterization, performed using DC four probes technique, it was observed an onset superconducting transition temperature measured around 81K. At the current-voltage characteristics curve, a step of electric current at zero-voltage could be observed, an indicative that the tunneling Josephson occurred.

The aim of this study was to evaluate and compare the effect of low temperature and saline environment on the fatigue crack growth behavior of the AA7050-T7451 Al alloy and the recently developed AA2050-T Al-Cu-Li alloy. Fatigue at room and low temperature and corrosion-fatigue tests were carried out using an applied stress ratio (R) of 0.1, 15 Hz frequency (air at RT and –54 °C) and 1 Hz frequency (seawater fog) using a sinusoidal wave form. In the near-threshold region, in air and at RT it was found a ΔKth = 2.9 MPa.m1/2 for AA2050-T84, in saline environment this value increased to ΔKth = 4.9 MPa.m1/2, due to closure effect through wedge effect by the corrosion products. At the beginning of the Paris-Erdogan region, the crack closure effect was not present for the AA7050-T7451, but persisted for the AA2050 Al-li alloy. It was observed that both alloys were equally affected by temperature reduction. When the saline environment is considered it was observed that the AA7050-T7451 presents lower m value (2.6) than the one for AA2050-T84 (3.4), meaning a lower FCG rate variation with ΔK, however it presented the highest C value, as a consequence the worst FCG behavior.

The friction and wear properties of AISI 1045 steel, nylon 6.6 composites with different types and percentages of reinforcement and a nitrile rubber, Alpha 66, were submitted to sliding wear tests. The five types of nylon 6.6 composites tested generated matching, low values for the coefficient of friction. This may be due to the greater influence of the nylon 6.6 matrix on the coefficient of friction. However, the wear in nylon composites showed wide variation, determined by the type of reinforcement added to the composite. The other two materials tested, nitrile rubber and 1045 steel, showed behavior different from that of the composites. The NBR (signifying a norm established by the Brazilian Association of Technical Norms) rubber showed a superior coefficient of friction and greater wear. On the other hand, the steel showed a high coefficient of friction and low wear, suggesting that the coefficient of friction has no direct connection to the wear resistance of the materials studied here.

Ensaios de tração a quente e fluência foram realizados na liga Kanthal A1 na faixa de temperatura de 600º a 800ºC. Cada um desses conjuntos de dados foram analisados separadamente de acordo com suas próprias metodologias, mas, neste trabalho, uma tentativa foi realizada para se estabelecer uma correlação entre os mesmos. Um novo critério proposto para converter dados de tração para fluência torna possível a análise conjunta desses dois grupos de resultados de acordo com relações usuais de fluência como: Norton, Monkman-Grant, Larson-Miller e outros. A notável compatibilidade entre os dois conjuntos por esse procedimento sugere que dados de tração a quente podem ser convertidos para dados de fluência para a liga Kanthal A1, como verificado anteriormente para outros materiais metálicos.

Hot tensile and creep tests were carried out on Kanthal A1 alloy in the temperature range from 600 to 800ºC. Each of these sets of data were analyzed separately according to their own methodologies, but an attempt was made to find a correlation between them. A new criterion proposed for converting hot tensile data to creep data, makes possible the analysis of the two kinds of results according to usual creep relations like: Norton, Monkman-Grant, Larson-Miller and others. The remarkable compatibility verified between both sets of data by this procedure strongly suggests that hot tensile data can be converted to creep data and vice-versa for Kanthal A1 alloy, as verified previously for other metallic materials.