San Martín, Argentina
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Zadorozne N.S.,National University of Misiones | Zadorozne N.S.,Instituto Sabato UNSAM CNEA | Giordano M.C.,Instituto Sabato UNSAM CNEA | Ares A.E.,National University of Misiones | And 2 more authors.
Corrosion Science | Year: 2016

The aim of this work is to investigate which alloying element in C-22 is responsible for the cracking susceptibility of the alloy in bicarbonate and two buffer solutions (tungstate and borate). Six nickel based alloys, with different amount of chromium (Cr) and molybdenum (Mo) were tested using electrochemical methods and slow strain rate tests (SSRT) at 90. °C. All Cr containing alloys had transgranular cracking at high anodic potential; however, C-22 containing high Cr and high Mo was the most susceptible alloy to cracking. Bicarbonate was the most aggressive of three tested environments of similar pH. © 2016 Elsevier Ltd.

Perez R.A.,Comision Nacional de la Energia Atomica | Perez R.A.,CONICET | Perez R.A.,Instituto Sabato UNSAM CNEA | Gordillo J.A.,Comision Nacional de la Energia Atomica | Lalla N.D.,CONICET
Philosophical Magazine | Year: 2013

α-spectrometry was used in order to measure the diffusion of U in bulk α-Ti in the temperature range 863-1123 K (540-850 °C). A straight Arrhenius plot was found, giving diffusion parameters Q = 297 kJ/mol and D 0 = 5 × 10-3m2/s, which are similar to the α-Ti self-diffusion ones, when measured in Ti samples with a similar impurity content than presently. This behaviour is compatible with the hypothesis of U diffusing via a vacancy-assisted mechanism in the α-Ti lattice and contrasts with older results in which the activation energy is almost a third the self-diffusion one, even lower than the vacancy formation energy. © 2013 Copyright Taylor and Francis Group, LLC.

Gordillo J.A.,Comision Nacional de la Energia Atomica | Perez R.A.,Comision Nacional de la Energia Atomica | Perez R.A.,CONICET | Perez R.A.,Instituto Sabato UNSAM CNEA | And 3 more authors.
Journal of Nuclear Materials | Year: 2015

U bulk diffusion in α-Zr was measured by mean α-spectrometry in the temperature range 763-1123 K (540-850 °C). A deviation from the Arrhenius law consistent in a downward curvature was observed; such anomaly is similar to the self and hetero substitutional diffusion previously measured in α-Zr matrix. The measurements are compatible with the existences of migrating Fe-vacancy complex that could be competitive with a simplest single vacancy mechanism for substitutional diffusers. The possibility that this could be the reason for the non Arrhenius behaviour is discussed. © 2015 Elsevier B.V.

Sileo N.R.,U. A. Materiales GIDAT | Fuentes N.O.,Programa Nacional de Gestion de Residuos Radiactivos | Fuentes N.O.,Instituto Sabato UNSAM CNEA
Materials Research Society Symposium Proceedings | Year: 2012

Development of numerical tools for performance assessment studies of radioactive waste disposal facilities, must address the management of the wide-ranging uncertainties associated with the long-term behaviour of these complex systems. Different approaches and assumptions are made in order to identify and describe relationships between the disposal system and its environment. They take into account, among other factors, the uncertainties associated with temporal evolution of the system within a proposed scenario; the landscape changes arising from future human actions, climate and geological events and processes; the relationships between components of the disposal system and its immediate environment; the behaviour and characteristics of radionuclides within the system and their role in contributing to radiation exposure. In all cases, the different scenario-based models are typically used to determine the radiological significance of potential future discharges from waste disposal facilities. However, it is important to keep always in mind that in any specific case, the purpose of developing and/or applying a model may vary from a simple calculation (e.g. to support concept development) to detailed site-specific performance assessment in support of a disposal license application. The assumptions and modelling simplifications that are appropriate to one type of calculation may not be so easily justified in different circumstances. In order to develop the capability of modelling different long-term scenarios for a generic disposal site for low and intermediate level radioactive wastes, implementation of models of both the near-field/geosphere and biosphere were performed using general approaches for geosphere-biosphere interface, with sub-models for the whole system. © 2012 Materials Research Society.

Ramos P.B.,U. A. Materiales GIDAT GAEN CNEA | Fuentes N.O.,Programa Nacional de Gestion de Residuos Radiactivos | Fuentes N.O.,Instituto Sabato UNSAM CNEA | Luca V.,Programa Nacional de Gestion de Residuos Radiactivos
Materials Research Society Symposium Proceedings | Year: 2012

The pyrolysis of ion exchange resin beads that are used for the purification of water in reactor primary- and secondary-cooling circuits can result in stable and leach resistant carbonaceous products. However, free flowing beads are less desirable waste forms for disposal in sub-surface or surface repositories than monolithic masses of low porosity. We have investigated the pyrolysis of polymeric resin - cation exchange resin composites to give mechanically robust and chemically durable monolithic carbonaceous waste forms that are suitable for repository disposition. Also investigated was the dependence of product properties on various processing parameters (temperature ramp and final temperature). As a first approach, epoxy resins were used for the preparation of monoliths since such resins cure at room temperature and result in a relatively high carbon yield. Carbonaceous monolithic products were prepared at 400, 500, 600, 700 and 800°C using a temperature ramp of 2°C/min. The products were maintained at the chosen temperatures for a period of one hour. Mass losses, volume reduction, hardness and compressive strength were measured and mathematical functions are proposed to describe the measured values of these properties. The carbon monoliths were observed to be mechanically robust. © 2012 Materials Research Society.

Raviola L.A.,Instituto Sabato UNSAM CNEA | Rivas A.M.F.,CNEA | Carlo G.G.,CNEA
Physica D: Nonlinear Phenomena | Year: 2011

We have studied two complementary decoherence measures, purity and fidelity, for a generic diffusive noise in two different chaotic systems (the baker map and the cat map). For both quantities, we have found classical structures in quantum mechanicsthe scar functionsthat are specially stable when subjected to environmental perturbations. We show that these quantum states constructed on classical invariants are the most robust significant quantum distributions in generic dissipative maps. © 2011 Elsevier Ltd. All rights reserved.

Mirandou M.I.,Gerencia Materiales GAEN CNEA | Arico S.F.,Gerencia Materiales GAEN CNEA | Arico S.F.,Instituto Sabato UNSAM CNEA | Balart S.N.,Gerencia Materiales GAEN CNEA | Fabro J.O.,Gerencia de Ciclo Del Combustible Nuclear
Journal of Nuclear Materials | Year: 2015

In the frame of U(Mo) dispersion fuel elements qualification, Si additions to Al matrix arose as a promising solution to the unacceptable failures found when pure Al is used. Analysis of as-fabricated fuel plates made with Al-Si matrices demonstrated that good irradiation behavior is correlated with the formation during fabrication of a Si-containing interaction layer around the U(Mo) particles. Thus, the analysis of the influence of fabrication parameters becomes important. Studies on Al-Si dispersion miniplates fabricated in CNEA, Argentina, have been initiated to determine how to obtain the better interaction layer characteristics with the lesser modifications to the fabrication process and the smaller amount of Si in the matrix. In this work results for miniplates made of atomized U-7 wt%Mo particles dispersed in Al-2 wt%Si and Al-4 wt%Si matrices, obtained by mixing pure Al and Si powders, and Al 6061 as cladding are presented. Interaction layer grown during fabrication process (500 °C) consists of Si-containing phases being U(Al, Si)3 its principal component. Its uniformity is not satisfactory due to the formation of an oxide layer. © 2014 Elsevier B.V. All rights reserved.

Dalibon E.L.,University of Concepción del Uruguay | Dalibon E.L.,Instituto Sabato UNSAM CNEA | Trava-Airoldi V.,National Institute for Space Research | Pereira L.A.,National Institute for Space Research | And 2 more authors.
Surface and Coatings Technology | Year: 2014

Precipitation hardening stainless steels are extensively used as a material for plastic injection dies because of their dimensional stability during hardening, impact strength and wear and corrosion resistance. Plasma surface engineering can enhance even more the working life of these components preserving them from wear and corrosion damage by means of surface modification or coatings. In this work PH stainless steel Corrax® was ion nitrided and coated with DLC in a modified PACVD duplex process. DLC films are known not only for their hardness but also for their low friction coefficient, features that improve the wear resistance of steel components. Adhesion tests were performed; wear resistance was tested in a pin on disk machine with different counterparts and in the abrasion ASTM G65 test. Nitrided samples were compared in all tests with DLC only coated samples and the duplex ones (nitriding. +. coating). The thickness of the nitrided layer was of 14. μm, and the coating, 1.8. μm. The duplex samples had the best abrasive wear resistance; their mass loss was almost negligible and within the error of the instrument. The only coated samples had a very low mass loss compared with the only aged steel, but the coating was detached.The coated samples presented a low friction coefficient, about 0.03 against alumina and the no wear loss was detected. On the other hand, only the duplex samples presented an acceptable adhesion in the Rockwell C indentation test with 600. N and the critical load was 28. N in the scratch test. © 2013 Elsevier B.V.

Dalibon E.L.,Technological University of Pereira | Dalibon E.L.,Instituto Sabato UNSAM CNEA | Charadia R.,Technological University of Pereira | Cabo A.,IONAR S.A. | And 2 more authors.
Surface and Coatings Technology | Year: 2013

DLC films have a high hardness, extremely low friction coefficient, and they are chemically inert. Plasma nitriding can serve as a pre-treatment to increase adhesion and improve tribological performance of the DLC coating.In this work, the mechanical and tribological behaviour of a DLC film deposited on martensitic stainless steel is studied. Two different surface finishing techniques were accomplished before the nitriding process: paper grinding and polishing with diamond powder. Plasma nitriding was carried out in a DC pulsed discharge, and the DLC film was deposited by Plasma Assisted CVD. The nitrided layer and film were observed with an optical microscope and SEM. The tribological behaviour was analysed in sliding wear tests and adhesion was tested. The coating was 3. μm thick, and the nitrided layers were about 11. μm in the polished samples and only 8. μm in the grounded ones. The coated samples yielded a better wear resistance than the pre-nitrided samples but only on the polished nitrided samples did the film present an acceptable adhesion. © 2013 Elsevier B.V.

Dalibon E.L.,Technological University of Pereira | Dalibon E.L.,Instituto Sabato UNSAM CNEA | Bozzano P.B.,Instituto Sabato UNSAM CNEA | Bozzano P.B.,Gerencia Materiales Centro Atomico Constituyentes | Bruhl S.P.,Technological University of Pereira
Acta Microscopica | Year: 2013

Austenitic stainless steels are widely used in many industrial fields, mainly due to their good corrosion resistance; however, their low hardness and poor wear resistance limit their applications. Among different methods of surface hardening, the plasma or ion nitriding technique has also proven to be effective in preserving their corrosion resistance. When austenitic stainless steels such as AISI 316L are nitrided at low temperature, i.e. below 420 °C, an expanded austenite phase free of nitrides is formed, called "S" phase. This phase is a diffusion layer, it is wear and corrosion resistant but there is still a great discussion about its nature. In this work, the structure of the modified layers in AISI 316L nitrided in a pulsed DC discharge were characterized by SEM, SIMS, normal incidence and grazing angle XRD with a Synchrotron source and TEM, for which the sample was prepared with FIB. The nitrogen expanded austenite layer was 4,5 μm thick with a nitrogen content of 27 at% and the calculated expansion of the lattice was about 6,5 %. A second carbon expanded austenite layer, could be observed below the nitrogen expanded phase. With GI XRD, no Cr or Fe nitrides were detected, only the S-phase with broader peaks than the original of the base material and shifted to lower angles, showing not only a lattice expansion but also a stressed layer with defects. In fact, the layer presented a large plastic deformation, since twins were observed in the dark field of the TEM image. Chromium nitrides reflections were also detected.

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