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Vargas-Caamal A.,Research Center Estudios Avanzados | Cabellos J.L.,Research Center Estudios Avanzados | Ortiz-Chi F.,Campeche Institute of Technology | Rzepa H.S.,Imperial College London | And 2 more authors.
Chemistry - A European Journal

The potential energy surfaces of the HCl(H2O)n (n is the number of water molecules) clusters are systematically explored using density functional theory and high-level ab initio computations. On the basis of electronic energies, the number of water molecules needed for HCl dissociation is four as reported by some experimental groups. However, this number is five owing to the inclusion of entropic factors. Wiberg bond indices are calculated and analyzed, and the results provide a quadratic correlation and classification of clusters according to the nondissociated, partially dissociated, and fully dissociated character of the H-Cl bond. Our computations show that if temperature is not controlled during the experiment, the values obtained for the dipole moment (or for any measurable property) are susceptible to change, providing a different picture of the number of water molecules needed for HCl dissociation in a nanoscopic droplet. Acid dissociation: High-level ab initio and DFT computations show that four water molecules are needed for HCl dissociation, but this number increases to five if entropic factors are considered (see figure). The temperature affects the dipole moments obtained, giving a different picture of the number of water molecules needed for HCl dissociation in a nanoscopic droplet. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Sosa M.,Autonomous University of Campeche | Perez-Lopez T.,Autonomous University of Campeche | Reyes J.,Autonomous University of Campeche | Corvo F.,Autonomous University of Campeche | And 3 more authors.
International Journal of Electrochemical Science

Chloride ion, present in marine breeze and seawater is considered the main external agent to damage reinforced concrete in marine environments. It affects the passivity of steel film and provokes the initiation of corrosion. This study analyzes the changes in concrete contour and interface steel-concrete on samples exposed to continuous immersed seawater, alternated wet in seawater/dry at atmosphere and continuous weathering at atmosphere. The next elements: chloride, calcium, iron, oxygen and magnesium were determinate by using SEM/EDX analysis. Immersed concrete specimens show high amount of chloride at the steel-concrete interface, followed by those exposes to alternated wet-dry cycles, while atmospheric samples practically do not present this ion. Similar sequence of chloride concentration was obtained for the contour of specimens. The noticeable presence of high quantity of magnesium at contour evidence the formation of particular compounds such as brucite and dolomite in those samples exposed to total immersion and alternated wet-dry alternated cycles. Monitoring of electrochemical impedance spectroscopy, shows passivity for steel embedded bars for concrete samples exposed to atmosphere, activity to immersed specimens and transition passive-active for wet-dry cycles. The effect of the exposure conditions on concrete degradation in marine environment is presented. © 2011 by ESG. Source

Perez-Pacheco E.,Campeche Institute of Technology | Cauich-Cupul J.I.,Research Center Cientifica Of Yucatan | Valadez-Gonzalez A.,Research Center Cientifica Of Yucatan | Herrera-Franco P.J.,Research Center Cientifica Of Yucatan
Journal of Materials Science

A carbon fiber/epoxy unidirectional laminated composite was exposed to a humid environment and the effect of moisture absorption on the mechanical properties and failure modes was investigated. The composites were exposed to three humidity conditions, namely, 25, 55, and 95 % at a constant temperature of 25 C. The carbon fiber-epoxy laminated composites for two different carbon fiber surface treatments were used. The results showed that the mechanical properties differ considerably for each fiber surface treatment. The application of a coupling agent enhanced the fiber-matrix adhesion and reduced dependence of the properties on humidity. The damage mechanism observed at micromechanical level was correlated to acoustic emission signals from both laminated composites. The untreated carbon fiber failure mode was attributed to fiber-matrix interfacial failure and for the silane-treated carbon fiber reinforced epoxy laminate attributed to matrix yielding followed by fiber failure with no signs of fiber-matrix interface failure for moisture contents up to 1.89 %. © 2012 Springer Science+Business Media New York. Source

Perez-Pacheco E.,Campeche Institute of Technology | Moo-Huchin V.M.,Campeche Institute of Technology | Estrada-Leon R.J.,Campeche Institute of Technology | Ortiz-Fernandez A.,Campeche Institute of Technology | And 3 more authors.
Carbohydrate Polymers

In this paper, the Ramon starch was isolated and its chemical composition and physical and microscopic characteristics were determined. Corn starch was used as reference. In general, the proximal composition was similar between starches studied. Ramon starch granules were oval-spherical and rounded with sizes between 6.5 and 15 μm. Starch purity was high (92.57%) with amylose content of 25.36%. The gelatinization temperature was 83.05 C and transition enthalpy was 21.423 J/g. At 90 C, solubility was 20.42%, swelling power 17.64 g water/g starch and water absorption capacity was 13 g water/g starch. The pH, clarity and color (Hue angle) of Ramon starch were higher to those reported for corn starch. The results achieved suggest that Ramon starch has potential for application in food systems requiring high processing temperatures and it is also a promising option for use in the manufacture of biodegradable materials. © 2013 Elsevier Ltd. All rights reserved. Source

Rios-Soberanis C.R.,Research Center Cientifica Of Yucatan | Wakayama S.,Tokyo Metroplitan University | Sakai T.,Tokyo Metroplitan University | Rodriguez-Laviada J.D.L.A.,Research Center Cientifica Of Yucatan | Perez-Pacheco E.,Campeche Institute of Technology
International Journal of Polymer Science

This research work focuses on the processability and mechanical characterization of blends of polylactic acid (PLA) and tire (elastomeric part). Wasted tires used as filler in the PLA matrix were reduced by two different processes (thermal shock and pyrolysis) in order to acquire the solid residuals in powder to be characterized and compared. Elastomeric solids obtained from scraped tires were used as filler in the PLA matrix and mixed in a Brabender 60 cc mixer at different concentrations ranging from 0% to 60% of filler volume fraction. The blend was laminated, and then samples were obtained in order to undertake mechanical properties at tension and Izod impact tests. A fully detailed analysis on the solid powders by Differential Scanning Calorimeter (DSC), thermogravimetric analysis (TGA), infrared analysis (IR), and scanning electron microscopy analysis (SEM) identified them as a rich source of carbon. Blends were characterized thermally and mechanically showing a direct effect due to the tire nature (thermoset rubber) and concentration. Fracture mechanisms were also identified. © 2013 Carlos Rolando Rios-Soberanis et al. Source

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