Instituto Sabato

San Martín, Argentina

Instituto Sabato

San Martín, Argentina
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Pasianot R.C.,Gcia. Materiales | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Philosophical Magazine Letters | Year: 2016

By solving the problem of a periodic distribution of point defects in general anisotropic media, we give an alternative, more direct proof, of the relatively recent procedure that extracts dipole tensors from the stress acting on the cell of atomistic simulations performed under periodic boundary conditions. Moreover, we show that naive superposition of individual defect fields is not a solution of the problem, though correction terms can be identified; as a byproduct, analysis of the latter allows us to reveal a spurious contribution to the elastic interaction energy as calculated in current literature procedures, that therefore must be subtracted in order to obtain correct results. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Perez Rodolfo A.,Comision Nacional de la Energia Atomica | Perez Rodolfo A.,CONICET | Perez Rodolfo A.,Instituto Sabato
Defect and Diffusion Forum | Year: 2017

Diffusion at infinite dilution of U in metals, with particular emphasis in those used in nuclear facilities, is revisited. Early works present some particularities such as activation enthalpies lower than the vacancy formation enthalpy in the matrix, large differences with self-diffusion in the base material, up to four orders of magnitude differences between measurements performed by different authors in similar temperature ranges, etc. In particular U self-diffusion was qualified as abnormal when compared with other metals. Recent studies by means of á-spectrometry reveal a normal behaviour: Activation enthalpies and pre-exponential factors similar to the self-diffusion one and diffusion coefficient values in the same order of magnitude than self-diffusion. The possible influence of short circuits, impurities and/or uncertainties in the techniques used in the early works is discussed in order to explain the differences obtained. © 2017 Trans Tech Publications, Switzerland.

Brites C.D.S.,University of Aveiro | Fuertes M.C.,CONICET | Fuertes M.C.,Instituto Sabato | Angelome P.C.,CONICET | And 4 more authors.
Nano Letters | Year: 2017

The past decade has seen significant progresses in the ability to fabricate new mesoporous thin films with highly controlled pore systems and emerging applications in sensing, electrical and thermal isolation, microfluidics, solar cells engineering, energy storage, and catalysis. Heat management at the micro- and nanoscale is a key issue in most of these applications, requiring a complete thermal characterization of the films that is commonly performed using electrical methods. Here, plasmonic-induced heating (through Au NPs) is combined with Tb3+/Eu3+ luminescence thermometry to measure the thermal conductivity of silica and titania mesoporous nanolayers. This innovative method yields values in accord with those measured by the evasive and destructive conventional 3ω-electrical method, simultaneously overcoming their main limitations, for example, a mandatory deposition of additional isolating and metal layers over the films and the previous knowledge of the thermal contact resistance between the heating and the mesoporous layers. © 2017 American Chemical Society.

Chalfoun D.,Instituto Sabato | Chocron M.,Comision Nacional de la Energia Atomica | Kappes M.A.,CONICET | Rebak R.B.,General Electric
NACE - International Corrosion Conference Series | Year: 2017

UNS A95052(AA 5052) results very attractive for desalination applications due to its good corrosion resistance in seawater at temperatures up to 125°C, low cost, good thermal conductivity, and non-toxic corrosion products. The pitting potential, Epit, and the pit repassivation potential, Er, pit, of AA 5052 were measured in deaerated 65,000 ppm sodium chloride solutions at 30, 60 and 85°C. Pitting potential decreased with temperature, in accord with literature results. Er, pit was a function of anodic charge passed during pit growth stage. A complete evaluation of suitability of this alloy from a corrosion perspective requires also studies of crevice corrosion at different temperatures, considering that the metal plates for desalinators are usually in contact with rubber gaskets and seals. Different techniques were used to estimate crevice repassivation potential at 30, 60 and 85°C, in samples with an attached rubber O-ring as a crevice former. Some samples were exposed at the corrosion potential in deaerated 65,000 ppm sodium chloride (normal operation) and in aerated 65,000 ppm sodium chloride solution with 5 ppm Cu++ ions (possible contaminants in feed water), in order to predict corrosion performance of the alloy. © 2017 by NACE International.

Massani M.B.,INTI Plasticos | Vignolo G.M.,CONICET | Eisenberg P.,INTI Plasticos | Morando P.J.,CONICET | And 2 more authors.
LWT - Food Science and Technology | Year: 2013

Adsorption of bacteriocins produced by Lactobacillus curvatus CRL705, lactocin 705 (whose activity depends upon complementation of two peptides, lac705α and lac705β) and bacteriocin/s with strong anti-Listeria activity, on a multilayer film was investigated. Lactocin 705 adsorption equilibrium at 30 °C was reached from 1 h of film contact. This bacteriocin exhibited a Langmuir-type adsorption, showing a mass adsorption maximum of 0.72 ± 0.05 μg cm-2 and a minimum inhibition concentration of 1 μg ml-1. The influence of impurities, generated from bacteriocinogenic strains growth, on bacteriocins adsorption to the film was investigated by inhibition area evaluation in semisolid agar. Impurities from LAB growth strongly influenced adsorption and lactocin 705 antimicrobial activity on the film, while antilisterial bacteriocin/s adsorption remained unaffected. To explain these results, a lack of lac705β and lac705α peptides complementation necessary for antimicrobial activity, while no interactions among impurities and antilisterial bacteriocin/s during adsorption was suggested. Antilisterial bacteriocin/s activity on the film was not influenced by lactocin 705 adsorption; conformational reorganization of adsorbed antilisterial bacteriocin/s in the presence of lactocin 705 could allow the adsorption of both bacteriocins while maintaining antilisterial antimicrobial activity. This study highlights the technological importance of adsorption optimization to obtain effective antimicrobial food packaging systems. © 2013 Elsevier Ltd.

Crespo E.A.,National University of Comahue | Claramonte S.,Instituto Sabato | Ruda M.,Bariloche Atomic Center | Ruda M.,National University of Comahue | De Debiaggi S.R.,CONICET
International Journal of Hydrogen Energy | Year: 2010

From the atomistic simulation of pressure-composition isotherms of hydrogen absorption of Pd nanoparticles we calculated thermodynamic properties and evaluated them as a function of particle size. In the particle range studied both ΔH and ΔS decreased with particle size towards the corresponding bulk values. H atoms were segregated to the subsurface of the particles forming a shell structure that may explain an initial plateau shown in the particles isotherms that is not present in bulk simulations. We used potentials of the embedded-atom type (EAM) to describe the interaction between atoms and we performed Monte Carlo simulations to calculate the isotherms. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Bonny G.,Belgian Institute for Nuclear Sciences | Pasianot R.C.,CAC CNEA | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Philosophical Magazine Letters | Year: 2010

Many-body interatomic potentials play an important role in atomistic modelling of materials. For pure elements it is known that there exist gauge transformations that can change the form of the potential functions without modifying its properties. These same transformations, however, fail when applied to alloys. Even though different research groups may use the same potentials to describe pure elements, the gauges employed for fitting alloys will generally be different. In this scenario, it is a priori impossible to merge them into one potential describing the combined system, and thus no advantage is taken from state-of-the-art developments in the literature. Here, we generalise the gauge transformations applied to pure species in order to leave the properties of alloys invariant. Based on these transformations, a strategy to merge potentials developed within different gauges is presented, aiming at the description of the combined system. Advantage of existing state-of-the-art potentials is so taken, thus focusing the efforts on fitting only the missing interactions. Such a procedure constitutes a helpful tool for the development of potentials targeted to alloys of increased complexity, while maintaining the description quality of their constituents. © 2010 Taylor and Francis.

Fernandez J.R.,Dep. Materiales | Fernandez J.R.,Instituto Sabato | Fernandez J.R.,CONICET | Pascuet M.I.,CONICET
Modelling and Simulation in Materials Science and Engineering | Year: 2014

A new interatomic potential in the framework of the modified embedded atom method (MEAM) to model U metal is presented. The potential acceptably reproduces the lattice parameters and cohesive energy of the orthorhombic αU. The relative stability of the experimentally observed phase at low temperatures with respect to several other structures (bct, bcc, simple cubic, tetragonal β Np, fcc and hcp) is also taken into account. Intrinsic point defect properties compare reasonably well with data from the literature. To determine the quality of the interaction, the potential is used to study a number of properties for the pure metal at finite temperatures and the results are compared with the available data. The obtained allotropic αU↔γU transformation and melting temperatures are in good agreement with experimental values. Based on the simulations, a new αU↔γU transformation mechanism is proposed. © 2014 IOP Publishing Ltd.

Mieza J.I.,Centro Atomico Constituyentes | Mieza J.I.,Instituto Sabato | Vigna G.L.,Centro Atomico Constituyentes | Domizzi G.,Centro Atomico Constituyentes
Journal of Nuclear Materials | Year: 2011

Delayed Hydride Cracking (DHC) is a failure mechanism that may occur in zirconium alloys used in nuclear reactor core components. The knowledge of the direct effects of the variables affecting the cracking velocity could be used to minimize the risk of crack propagation. In practice, most of these variables - as for example the alloy yield stress and hydrogen diffusion coefficient - are coupled and vary during reactor operation, leading to a complex variable dependence of the cracking mechanism. In order to get an insight into the relative effect of these variables, experimental data and a theoretical approach using a generally accepted DHC model were used in this work. A series of DHC velocity measurements were made in Zr-2.5Nb tube with different heat treatments. The yield stress, the Nb concentration in β phase, and hydrogen solvus of the alloy were measured for different heat treatments. Niobium concentration in β phase gave an indirect indication of β-phase continuity and, with a proper correlation, of the hydrogen diffusion coefficient. The obtained values were used as inputs in a theoretical calculation of cracking velocity. Good agreement between experimental data and predicted values was obtained, showing that hydrogen diffusion coefficient was the most relevant variable affecting DHC velocity cracking. Furthermore, this approach has been demonstrated to be useful in estimating DHC velocity in irradiated materials. © 2011 Elsevier B.V. All rights reserved.

Pasianot R.C.,Gerencia Materiales | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Journal of Nuclear Materials | Year: 2016

We study the structure of several standard and non-standard self-interstitial configurations in a series of hcp metals, by using Density Functional Theory as embodied in the computer codes SIESTA and WIEN2k. The considered metals include Be, Mg, Ti, Zr, Co, Zn, and Cd, thus spanning the whole range of experimental c/a ratios, different kinds of bonding, and even magnetism (Co). The results show the importance of low symmetry configurations, closely related to the non-basal crowdion, in order to rationalize the experimental data on self-interstitial structure and migration. © 2016 Elsevier B.V.

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