Estudo da emissão por fluorescência de ultravioleta na quantificação de um inibidor de corrosão do tipo sal de amônio quaternário em água

Quaternary ammonium salts are the corrosion inhibitors most frequently used by the oil industry. In this study, the ultraviolet fluorescence technique was evaluated for the analysis of a quaternary ammonium salt in water as a corrosion inhibitor. The comparison with standard salt showed that an alkyl aryl quaternary ammonium salt is the main fluorophore, with emission maxima at 306 and 593 nm. The best instrumental parameters were: width of excitation and emission slits of 10 and 15 nm, respectively, and scan rate of 10 nm min-1. The presence of aromatic compounds and biocides affects the analysis of corrosion inhibitors.

Coeficientes de difusão de metais em materiais não convencionais (agarose e acetato de celulose) usados na técnica de difusão em filmes finos por gradientes de concentração

The DGT technique allows one to measure quantitatively free and labile metal species in aquatic systems. Nevertheless, for this approach, knowledge is required of the diffusion coefficients of the analytes in a diffusive layer. In this study, the diffusion coefficients of Hg(II), As(III), Mn(II), Mg(II), Cu(II), Cd(II) were determined in agarose gel and those of Ba(II), Cd(II), Cu(II), Mg(II), Mn(II) e Zn(II) in cellulose acetate membranes. These materials presented good performance and the reported results can be used as a data base for further DGT studies.

Desenvolvimento e uso do compósito de Nb2O5|Cu como revestimento aplicado por aspersão térmica sobre o aço AISI 1020 para proteção contra a corrosão pelo solo em estruturas enterradas

An Nb2O|Cu corrosion-resistant coating was developed and applied onto AISI 1020 steel substrate by Powder Flame Spray. A galvanostatic electrochemical technique was employed, with and without ohmic drop, in four different soils (two corrosively aggressive and two less aggressive). Behavior of coatings in different soils was compared using a cathodic hydrogen reduction reaction (equilibrium potential, overvoltage and exchange current density) focusing on the effect of ohmic drop. Results allow recommendation of Nb2O5|Cu composite for use in buried structure protection.

Nanotubos de TiO2 dopados com nitrogênio: comparação das atividades fotocatalíticas de materiais obtidos através de diferentes técnicas

TiO2 nanotubes were synthesized by hydrothermal method and doped with three nitrogen compounds to enhance photocatalytic activity under visible light. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and specific surface area and pore volume determined by BET and BJH methods, respectively. Photocatalytic activity was evaluated by photodegradation of rhodamine B under visible and UV radiations. Results showed doped-nanotubes were more efficient under visible light. The best photocatalytic activity was for sample NTT-7-600/NH3I, being 30% higher than the non-doped sample.

Uso de materiais recicláveis na determinação gravimétrica de CO2 no ar ambiente e tratamento dos resíduos de laboratório gerados

An alternative system was tested for the determination of CO2 in air using recyclable materials. The results indicate that the proposed system allows for reliable, accurate, robust and efficient collection, comparable to the standard gravimetric method. Laboratory wastes are easily treated using a filtrate that can be discharged into the sewer and solids that can be reused. The proposed system is a simple and low-cost tool that encompasses important aspects of environmental education, which should be part of the education in chemistry of undergraduate students and technicians.

Ácidos orgânicos de baixa massa molar em solos e materiais orgânicos

Determination of organic acids in soils and organic materials is important due to the important role they play in improving the soil's physical, chemical and microbiological conditions. This study identified and quantified low molecular weight organic acids (LMWOA) in soils (dystroferric Red Latosol, dystrophic Red-Yellow Latosol and Quartzarenic Neosol) and organic materials (cow, pig, chicken, quail and horse manures, sawdust, coconut fiber, pine bark, coffee husks, biochar, organic substrate, sewage sludges 1 and 2, garbage compost, pig slurry compost). The following acids were identified: acetic, citric, D-malic, formic, fumaric, maleic, malonic, oxalic, quinic, shikimic, succinic and tartaric.

Síntese de poliuretanos modificados por óleo de mamona empregados em materiais energéticos

The aim of this work was to synthesize a polyurethane polymer matrix using castor oil as a polymer chain modifier, whose characteristics can be adjusted for use as a binder in the manufacture of energetic materials such as propellant and pyrotechnics for aerospace use. We attempted the partial substitution of hydroxyl-terminated polybutadiene (HTPB), a pre-polymer commonly used as a starting polyol in obtaining energetic matrix composites. Thermoanalytical techniques were employed to characterize the material based on castor oil and the unmodified HTPB. The results showed similar behaviors, confirming the possibility of their use as polymer matrix composites through the proposed adaptations.

Desenvolvimento de um sistema de análise por injeção em fluxo utilizando materiais alternativos de baixo custo para fins didáticos

This work describes a simple and inexpensive flow injection analysis system in which gravity force provides fluid propulsion while needles for insulin administration or metallic wires act as electrodes for amperometric detection. The proposed system was able to demonstrate the influence of several operational parameters on the transient signals. Moreover, this system was successfully used to evaluate both the stoichiometry of Cu2+-EDTA complex and the effect of pH on the kinetics of the reaction between ferricyanide and ascorbic acid. Therefore, the proposed system can be regarded as an efficient and accessible didactic tool for the teaching of FIA principles.

CORROSÃO DO AÇO-CARBONO: UMA ABORDAGEM DO COTIDIANO NO ENSINO DE QUÍMICA

In this paper, two simple ways of evaluating carbon steel sheet corrosion in a hydrochloric acid solution were presented as an experimental proposal for corrosion teaching. The first method is based on direct measurements of mass before and after corrosion tests. The second approach follows the principle of visual colorimetry by which soluble corrosion products are transformed into red complexes allowing monitoring of the products’ concentration according to increases in solution color intensity. Both methods proved able to determine the corrosion rate.

DESENVOLVIMENTO DE MATERIAIS HÍBRIDOS MICRO-MESOPOROSOS DO TIPO ZSM-12/MCM-41

Micro-mesoporous hybrid materials of ZSM-12/MCM-41 type with different micro- and mesoporosity contributions were prepared by a procedure that uses the desilication of the zeolite in an alkaline medium, followed by recrystallization onto the mesostructure, where the zeolite is used as the silica source in the formation of mesoporous phase. The materials were characterized by X-ray diffraction, nitrogen adsorption-desorption at 77 K, scanning electron microscopy and thermal analysis. The results showed that the methodology utilized is efficient for obtaining hybrid materials of ZSM-12/MCM-41 type with optimized micro-and mesoporosity.

DISPOSITIVOS DGT MODIFICADOS COM MATERIAIS ALTERNATIVOS PARA USO NA ESPECIAÇÃO DE ELEMENTOS TRAÇO

The use of MT-K10 Montmorillonite immobilized onto agarose was investigated in this work as an alternative binding phase in Diffusive Gradient in Thin Film (DGT) devices for the determination of metallic labile species. In addition, agarose itself was also used as the diffusive phase. The percentage of sorption of Zn2+, Cu2+, Cr3+, Mn2+, Cd2+, Pb2+, and Ni2+ onto the binding phase was higher than 80% and the desorption process for all elements was also greater than 75%. Elution factors were determined experimentally, ranging from 0.74 for Zn2+ and 0.90 for Cr3+ and Pb2+. The accumulation of all species was linear with time, in agreement with the Fick's 1st law of diffusion. The deployment of the alternative devices in natural waters was compared to commercial devices. Labile concentrations determined by the alternative devices were slightly superior compared to results obtained with the deployment of original DGT devices due to the less restrictive pores of agarose.

MATERIAIS VÍTREOS E LUZ: PARTE 1

2015 is the Year of Light, according to UNESCO. Chemistry has a close relationship with light and one of the materials that allows such synergy is glass. Depending on the chemical composition of the glass, it is possible to achieve technological applications for the whole range of wavelengths extending from the region of the microwave to gamma rays. This diversity of applications opens a large range of research where chemistry, as a central science, overlaps the fields of physics, engineering, medicine, etc., generating a huge amount of knowledge and technological products used for humanity. This review article aimed at discussing some families of glasses, illustrating some applications. Due to the extension of the theme, and all points raised, we thought it would be good to divide the article into two parts. In the first part we focus on the properties of heavy metal oxide glasses, fluoride glasses and chalcogenide glasses. In the second part we emphasize the properties of glassy thin films prepared by sol-gel methodology and some applications, of both glasses as the films in photonics, and more attention was given to the nonlinear properties and uses of photonic fibers.

MATERIAIS VÍTREOS E LUZ: PARTE 2

In this second part it will be discussed some photonic applications of glassy and glass ceramic thin films which can be used as planar waveguides. Some photonic applications require certain specifications of glass, which can be quantified by studying the nonlinear optical properties of the materials. Therefore, a brief introduction of these phenomena is discussed, as well as the use of femtosecond lasers to manipulate the composition or for the preparation of waveguides into glasses. Finally, the article will address a brief introduction on microstructured optical fibers and commercial application prospects for these devices.

Seleção de genótipos de soja resistentes a duas estirpes de Soybean mosaic virus

Soybean mosaic virus (SMV) is the most prevalent virus on soybeans (Glycine max) throughout the world. It causes mottling on seeds and has been associated with yield reduction. Recently, a new strain (SMV 95-1) was found infecting resistant cultivars, causing dwarfing and systemic necrosis. In a screening test carried out with the strains SMV 95-1 and SMV 95-2 on the germplasm collection, several resistant cvs. Embrapa 60, Embrapa 61, Embrapa 62, Embrapa 66 , Embrapa 133, Embrapa 134, Embrapa 135, and Embrapa 136 were identified as resistant to both strains. The resistant genotypes may serve in future soybean breeding programs in Brazil.