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Atrazhev V.V.,Russian Academy of Sciences | Burlatsky S.F.,UTRC - United Technologies Research Center | Dmitriev D.V.,Russian Academy of Sciences | Sultanov V.I.,Science for Technology LLC
Journal of Statistical Mechanics: Theory and Experiment

The microscopic model of semi-crystalline polymer in a high-elastic state is proposed. The model is based on the assumption that, below the melting temperature, the semi-crystalline polymer comprises crystal nuclei connected by stretched chain segments (SCS) with a random configuration of monomers. The key factor that stalls the phase transition below the melting temperature is the tension of the SCS. External stress applied to the polymer also shifts the equilibrium and causes unfolding of the nuclei, which enables large reversible deformation of the polymer without loss of integrity. The simple 1D model predicts a plateau in the stress-strain curve of the high-elastic polymer above the yield stress, which agrees with experimental observations. The model prediction for the temperature dependence of polytetrafluoroethylene (PTFE) yield stress in the high-elastic state is in satisfactory agreement with experiment. © 2013 IOP Publishing Ltd and SISSA Medialab srl. Source

Lomaev I.L.,RAS Institute of Metal Physics | Novikov D.L.,UTRC - United Technologies Research Center | Okatov S.V.,Science for Technology LLC | Gornostyrev Y.N.,RAS Institute of Metal Physics | Burlatsky S.F.,UTRC - United Technologies Research Center
Journal of Materials Science

Diffusion of the 4d transition elements in Ni has been investigated within the five-frequency model framework using migration energy barriers calculated from the first principles. Agreement with counterintuitive experimental/ calculated data is observed; atoms in the middle of 4d row have the smallest atomic radii while exhibiting the lowest diffusivity as compared to larger atoms at the beginning and the end of 4d row. We show that 4d solute diffusion is controlled mainly by the size misfit. The larger atoms have higher solute-vacancy binding energies and lower migration barriers. Both were shown to correlate with a displacement of the equilibrium solute position toward the adjacent vacancy. The difference in mechanisms controlling sp- and transition elements diffusion rates in Ni is discussed. © 2014 Springer Science+Business Media New York. Source

Pandy A.,UTC Power | Yang Z.,UTRC - United Technologies Research Center | Gummalla M.,UTRC - United Technologies Research Center | Atrazhev V.V.,Russian Academy of Sciences | And 3 more authors.
Journal of the Electrochemical Society

A carbon corrosion model is developed based on the formation of surface oxides on carbon and platinum of the polymer electrolyte membrane fuel cell electrode. The model predicts the rate of carbon corrosion under potential hold and potential cycling conditions. The model includes the interaction of carbon surface oxides with transient species like OH radicals to explain observed carbon corrosion trends under normal PEM fuel cell operating conditions. The model prediction agrees qualitatively with the experimental data supporting the hypothesis that the interplay of surface oxide formation on carbon and platinum is the primary driver of carbon corrosion. © 2013 The Electrochemical Society. All rights reserved. Source

Sultanov V.I.,Science for Technology LLC | Atrazhev V.V.,Russian Academy of Sciences | Dmitriev D.V.,Russian Academy of Sciences | Burlatsky S.F.,UTRC - United Technologies Research Center
JETP Letters

The mobility of polymer chains in perfect polyethylene crystal was calculated as a function of temperature and chain length through Molecular dynamics in united atom approximation. The results demonstrate that the chain mobility drastically increases in the vicinity of the phase transition from the orthorhombic to quasi-hexagonal phase. In the quasi-hexagonal phase, the chain mobility is almost independent on temperature and inversely proportional to the chain length. © 2013 Pleiades Publishing, Inc. Source

Lomaev I.L.,Science for Technology LLC | Novikov D.L.,UTRC - United Technologies Research Center | Okatov S.V.,Science for Technology LLC | Gornostyrev Yu.N.,Science for Technology LLC | And 4 more authors.
Acta Materialia

The origin of abnormally fast diffusion of sulfur in face-centered cubic (fcc) nickel was investigated within an ab initio band structure calculation approach. A vacancy-mediated model of substitutional impurity diffusion with first-principles calculated parameters was used to determine the diffusion coefficients of S and Al impurities in fcc Ni. The sulfur diffusion coefficient was found to be two orders of magnitude higher than that of aluminum, in good agreement with experimental data. We demonstrate that ultrafast diffusivity of sulfur arises from its chemical interaction with the Ni matrix. The valence electron transfer from Ni3d-Ni3d bonds to sulfur softens the Ni-Ni bonding. That increases the sulfur-vacancy exchange rate, the sulfur-vacancy binding energy and the rotation rate of vacancy around sulfur. The latter is shown to be the key factor that governs S diffusion. We also discuss the impact of Ni-Ni bond softening on the mechanical properties of Ni. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

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