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Caicedo J.C.,University of Valle | Caicedo J.C.,Autonomous University of Occidente | Cabrera G.,University of Valle | Aperador W.,University Militar Nueva Granada | And 2 more authors.

The erosive-corrosive effect of aqueous NaCl slurries on metals and metals coated with a multilayer system was analyzed. The erosion-corrosion experiments were performed in a test machine in which the impingement velocity, impact angle, concentration of solids and pH of the solution were controlled. Polarization curves were simultaneously obtained to correlate the electrochemical effects to the erosive wear mechanisms. The slurry used consists of silica particles suspended in a mixture of acid solution and 3.5% NaCl, with a pH value of 5.6. Electrochemical results showed the best corrosion resistance for steel coated with CrN/AlN system deposited with 50 bilayer. Additionally, the surface analysis by SEM micrograph revealed formation of cracks in CrN/AlN multilayers coating and plastic deformation in both steel substrates (AISI D3 steel and 304 stainless steel), especially when the mean impact angle is a critical value of 90°. Measurements of critical and passive current densities showed that the behavior of coated materials differed depending on the substrate that is used. Nonetheless, in a general way, by increasing the impact angle and by changing its incidence from normal to grazing, it led to an improved resistance to erosion-corrosion processes. © 2012 Elsevier Ltd. All rights reserved. Source

Aperador W.,University Militar Nueva Granada | Delgado E.,University Militar Nueva Granada | Mejia A.,Escuela Colombiana de Ingenieria Julio Garavito
International Journal of Electrochemical Science

In the present investigation was obtained electro-copper coating on steel AISI SAE 1020, electrolyte was used as an industrial waste obtained from the stripping of copper. The current densities were 2.5 A/dm2, 5 A/dm2 y 7.5 A/dm2 and concentration of 222 g / l of copper sulfate (CuSO4). The corrosion behavior of the substrate and the coatings obtained were studied by electrochemical impedance spectroscopy and potentiodynamic polarization curves. Additionally, we examined the surfaces of the coatings by scanning electron microscopy (SEM). The study shows that these coatings comply with the standards for use as ground poles. © 2013 by ESG. Source

Aperador W.,University Militar Nueva Granada | Mejia A.S.,Escuela Colombiana de Ingenieria Julio Garavito | Caicedo J.,University of Valle
Informacion Tecnologica

Thin films of titanium nitride/zirconium nitride were deposited on AISI 4140 steel by a multi-target magnetron sputtering system with radio frequency. The process was developed under the substrate rotation system which allowed placing the substrate against the titanium and zirconium targets, generating the super-lattice with periods of 1, 50, 100, and 200 bilayers. The multilayers were evaluated against the corrosion-erosion synergy in a solution composed by 3% NaCl and silica. The electrochemical characterization was performed by electrochemical impedance spectroscopy. After the mechanic and electrochemical tests the surface was evaluated using scanning electron microscopy. By performance analysis it was observed that the material with higher synergic effect was the substrate. It is also shown that by increasing the bilayers in the system titanium nitride/zirconium nitride the corrosive phenomenon controls the material deterioration. Source

Romero Rodriguez M.I.,Escuela Colombiana de Ingenieria Julio Garavito | Zhevandrov P.,Universidad Michoacana de San Nicolas de Hidalgo
Journal of Fluid Mechanics

The system describing time-harmonic motions of a two-layer fluid in the linearised shallow-water approximation is considered. It is assumed that the depth is constant, with a cylindrical protrusion (an underwater ridge) of small height. For obliquely incident waves, the system reduces to a pair of coupled ordinary differential equations. The values of frequency for which wave propagation in the unperturbed system is possible are bounded from below by a cutoff, to the left of which no propagating modes exist. Under the perturbation, a trapped mode appears to the left of the cutoff and, if a certain geometric requirement is imposed upon the shape of the perturbation (for example, if the ridge is a rectangular barrier of certain width), a trapped mode appears whose frequency is embedded in the continuous spectrum. When these geometric conditions are not satisfied, the embedded trapped mode transforms into a complex pole of the reflection and transmission coefficients of the corresponding scattering problem, and the phenomenon of almost total reflection is observed when the frequency coincides with the real part of the pole. Exact formulae for the trapped modes are obtained explicitly in the form of infinite series in powers of the small parameter characterising the perturbation. The results provide a theoretical understanding of analogous phenomena observed numerically in the literature for the full problem for the potentials in a two-layer fluid in the presence of submerged cylinders, and furnish explicit formulae for the frequencies at which total reflection occurs and the trapped modes exist. © 2014 Cambridge University Press. Source

Chaves F.,Escuela Colombiana de Ingenieria Julio Garavito | Rocha C.,Escuela Colombiana de Ingenieria Julio Garavito
2015 10th Colombian Computing Conference, 10CCC 2015

The calculational style of E. W. Dijkstra and C. S. Scholten is a semi-formal style for the development, both in terms of verification and derivation, of correct programs. This calculational style heavily relies on the symbolic manipulation of expressions involving, for instance, arithmetic, quantifiers, and collections. This paper presents Calculational, an executable specification language for a broad class of calculational expressions in the style of Dijkstra & Scholten. The Calculational tool offers support for executable specifications, including: (i) quantifier expressions such as summation and universal/existential quantification, and (ii) data types such as lists, sets, and bags (i.e., multisets). The current implementation of Calculational is executable in the Haskell programming language, offering support also for higher order computation and pattern matching. This implementation is available for download as open source code and as a Haskell library too (which can be embedded in other programming languages). The main features of Calculational, some examples of its use-including the formal processing and querying of relational data-, and details of its implementation are included in this paper. © 2015 IEEE. Source

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