1,286 research outputs found
Comportamento eletroquĂmico e susceptibilidade a corrosĂŁo sob tensĂŁo do aço ABNT 1080 utilizado em armaduras de concreto protendido
Estudou-se o comportamento Ă corrosĂŁo e Ă corrosĂŁo-sob-tensĂŁo do aço eutetĂłide empregado em concreto protendido utilizando diversas tĂ©cnicas experimentais, como curvas de polarização, ensaios de tração com velocidades de deformação mĂ©dia, e ensaios fractomecĂąnicos. Utilizou-se como meio, simulando, o que Ă© usualmente encontrado nos poros do concreto, o Ca(OH)2 saturado, contaminado com diversos teores de cloreto e sulfatos. Com fins comparativos, utilizou-se a solução de tiocianato de amĂŽnia padronizada para avaliar a susceptibilidade de aços Ă fragilização por hidrogĂȘnio de aços em concreto. A influĂȘncia de parĂąmetros como potencial, temperatura (entre 0° e 90 ) e temperatura de revenido, entre outros sĂŁo avaliados. O mecanismo de ruptura Ă© avaliado tendo o hidrogĂȘnio uma participação importante neste processo.The corrosion and stress corrosion behaviour of AISI 1080 steel employed in concrete prestressed tendon was studied with different experimental techniques. A simulated solution usually found in concrete with and without contaminants as chlorides and sulphates was used. For comparison purpose the standard ammonium tiocianate solution was employed in some Polarization tests, constant extention rate tests with intermediate velocities and fractomechanic tests. The influence of parameters like potentiall temperature (between 0° and 90°), temper temperature of the steell was studied. The results showed that the fracture mechanism is associated with hydrogen action in the stress corrosion cracking process
2-hydroxyethilammonium oleate protic ionic liquid as corrosion inhibitor for aluminum in neutral medium
Protic ionic liquid (PIL) 2âhydroxyethylammonium oleate (2HEAOl) proved to be a good lubricant for aluminumâforming processes. However, with the aim of keeping the formed component integrity, it is interesting that the same substance employed during forming does not need to be removed and works out as corrosion inhibitor. Then, the aim of this study was to test the performance of 2HEAOl as corrosion inhibitor for aluminum in neutral 0.5 mol/L NaCl medium by electrochemical characterization. Results showed that the concentration of 5 Ă 10â4 mol/L was a suitable concentration to promote corrosion inhibition until 72 h at the high chloride concentration studied. The PIL worked out as mixedâtype organic corrosion inhibitor, as it promoted the diminution of the oxygen reduction reaction rate and, in consequence, the pit initiation by its adsorption on the metal surface
First-principles generation of Stereographic Maps for high-field magnetoresistance in normal metals: an application to Au and Ag
About thirty high-field magnetoresistance Stereographic Maps have been
measured for metals between Fifties and Seventies but no way was known till now
to compare these complex experimental data with first-principles computations.
We present here the method we developed to generate Stereographic Maps directly
from a metal's Fermi Surface, based on the Lifshitz model and the recent
advances by S.P. Novikov and his pupils. As an application, we test the method
with an interesting toy model and then with Au and Ag.Comment: 10 pages, 11 figure
INFLUĂNCIA DO POTENCIAL, E DA PRESENĂA DE Na2S2O3 e Na2S NA FRAGILIZAĂĂO PELO HIDROGĂNIO DO AĂO API 5CT P110 EM ĂGUA DO MAR SINTĂTICA
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Discovery of Nanoscale Electric Field-Induced Phase Transitions in ZrO\u3csub\u3e2\u3c/sub\u3e
The emergence of ferroelectric and antiferroelectric properties in the semiconductor industryâs most prominent high-k dielectrics, HfO2 and ZrO2, is leading to technology developments unanticipated a decade ago. Yet the failure to clearly distinguish ferroelectric from antiferroelectric behavior is impeding progress. Band-excitation piezoresponse force microscopy and molecular dynamics are used to elucidate the nanoscale electric field-induced phase transitions present in ZrO2-based antiferroelectrics. Antiferroelectric ZrO2 is clearly distinguished from a closely resembling pinched La-doped HfO2 ferroelectric. Crystalline grains in the range of 3 â 20 nm are imaged independently undergoing reversible electric field induced phase transitions. The electrically accessible nanoscale phase transitions discovered in this study open up an unprecedented paradigm for the development of new nanoelectronic devices
An amino-based protic ionic liquid as a corrosion inhibitor of mild steel in aqueous chloride solutions
Protic ionic liquids (PILs) have shown to be promising substances as corrosion inhibitors (CIs). In line with this, the aim of this study is to study the performance and propose the corrosion inhibition mechanism of Nâmethylâ2â hydroxyethylamine (Mâ2HEAOL) and bisâ2âhidroxyethylamine (BâHEAOL) oleate, for mild steel, in a neutral chloride solution. Electrochemical characterization was conducted under static and hydrodynamic conditions, and it was revealed that Mâ2HEAOL and BâHEAOL worked as mixedâtype CIs with more interference on the anodic reaction. Inhibition efficiency depended on the concentration reaching 97% of inhibition efficiency in 5 mmol/L concentration. Scanning electron microscopy, optical interferometry, Raman spectroscopy, and Fourierâtransform infrared spectroscopy are used to elicit the chemical composition of the surface film and corrosion morphology of steel in the presence of CIs, the adsorption processes of which involved physical and chemical adsorption between metal and different parts of ionic liquids. The results allowed the proposition of a corrosion inhibition mechanism
N-methyl-2-hydroxyethylammonium oleate ionic liquid performance as corrosion inhibitor for mild steel in hydrochloric acid medium
The aim of the present study is to evaluate the performance of Nâmethylâ2â hydroxyethylammonium oleate ([mâ2HEA][Ol]) as a corrosion inhibitor for mild steel in a 0.1âmol/L hydrochloric acid solution and also investigate the role of chloride in the inhibition mechanism. This protic ionic liquid (PIL) has formerly shown a high efficiency as a corrosion inhibitor in a neutral chloride medium. Electrochemical and weight loss measurements, surface contact angle determination, scanning electron microscopy, and Raman spectroscopy were used to understand the factors that influence the response of the studied inhibitor. Results revealed that [mâ2HEA][Ol] behaves as a mixedâtype adsorption inhibitor, by blocking cathodic sites and by modifying the activation energy of the anodic reaction, and it can reach up to 94â97% of inhibition efficiency. PIL adsorption was enhanced by the excess of positive charge of the mild steel. The effect of inhibitor molecule has been discussed to propose a mechanism that explains the inhibitory action of the corrosion inhibitor, pointing out the role of chloride in the inhibition mechanism
Controlling the generation of bilayer and Q1 multilayer vesicles in block copolymer/epoxy blends by a slow photopolymerization process
Vesicles are a highly attractive morphology to achieve in micellar dispersions of block copolymers (BCP) in epoxy thermosets due to the fact that small amounts can affect a large volume fraction of the matrix, a fact that is important for toughening purposes. However, generating vesicles in epoxy matrices requires operating in a narrow range of formulations and processing conditions. In this report, we show that block-copolymer vesicles dispersed in an epoxy matrix could be obtained through a sphere-tocylinder-to-vesicle micellar transition induced by visible-light photopolymerization at room temperature. A 10 wt% colloidal solution of poly(ethylene-co-butene)-block-poly(ethylene oxide) (PEB-b-PEO) block copolymer (BCP) in an epoxy monomer (DGEBA) self-assembled into spherical micelles as shown by small-angle X-ray scattering (SAXS). During a slow photopolymerization of the epoxy monomer carried out at room temperature, a sphere-to-cylinder-to-vesicle transition took place as revealed by in situ SAXS and TEM images. This was driven by the tendency of the system to reduce the local interfacial curvature as a response to a decrease in the miscibility of PEO blocks in the polymerizing epoxy matrix. When the BCP concentration was increased from 10 to 20 and 40 wt%, the final structure evolved from bilayer vesicles to multilayer vesicles and to lamellae, respectively. In particular, for 20 wt% PEB-b-PEO, transient structures such as partially fused multilayered vesicles were observed by TEM, giving insight into the growth mechanism of multilayer vesicles. On the contrary, when a relatively fast thermal polymerization was performed at 80 1C, the final morphology consisted of kinetically trapped spherical micelles. Hopefully, this study will lead to new protocols for the preparation of vesicles dispersed in epoxy matrices in a controlled way.Facultad de Ciencias ExactasInstituto de Investigaciones FisicoquĂmicas TeĂłricas y Aplicada
MĂ©todo de prevenção da fragilização por hidrogĂȘnio de componentes a partir de revestimentos por aspersĂŁo tĂ©rmica
Universidade Federal do Rio Grande do SulEngenhariaDepositad
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