Entity

Time filter

Source Type


Lopez-Baez I.,National Polytechnic Institute of Mexico | Martinez-Franco E.,Research Center e Innovacion Tecnologica | Zoz H.,Zoz GmbH | Trapaga-Martinez L.G.,National Polytechnic Institute of Mexico
Revista Mexicana de Fisica | Year: 2011

The ball milling (BM) of blended Ni and Cr elemental powders was carried out in a Simoloyer performing on high-energy scale mode at maximum production to obtain a nanostructured Ni-20Cr alloy. The phase transformations and structural changes occurring during mechanical alloying were investigated by X-ray diffraction (XRD) and optical microscopy (OM). A gradual solid solubility of Cr and the subsequent formation of crystalline metastable solid solutions described in terms of the Avrami-Erofe'ev kinetics model were calculated. The XRD analysis of the structure indicates that cumulative lattice strain contributes to the driving force for solid solution between Ni and Cr during BM. Microstructure evolution has shown, additionally to the lamellar length refinement commonly observed, the folding of lamellae in the final processing stage. OM observations revealed that the lamellar spacing of Ni rich zones reaches a steady value near 500 nm and almost disappears after 30 h of milling. Source


Rojas-Chavez H.,Tlahuac Institute of Technology | Rojas-Chavez H.,Research Center en Ciencia Aplicada y Tecnologia Avanzada | Reyes-Carmona F.,National Autonomous University of Mexico | Garibay-Febles V.,Mexican Institute of Petroleum | Jaramillo-Vigueras D.,Research Center e Innovacion Tecnologica
Journal of Nanoparticle Research | Year: 2013

Transformations from precursors to nanoparticles by high-energy milling are promoted by two major driving forces, namely physical and/or chemical. While the former has been difficult to trace since stress, strain and recovery may occur almost simultaneously during milling, the latter has been sequentially followed as an evolution from precursors to intermediate phases and thereof to high purity nanocrystals. The specific objective of this work is to discern how solid-solid and partially solid-gas reactions manifest themselves correspondingly as a short-range diffusion through an interface or how vapor species, as a subliming phenomenon, grows as a different phase on an active local surface. These series of changes were traced by sub-cooling the as-milled powders extracted during a milling cycle. Through this experimental technique, samples were electron microscopically analyzed and where it was required, selected area electron diffraction images were obtained. High-resolution transmission electron microscopy results, unambiguously, confirm that nanocrystals in the last stage show a cubic morphology which average size distributions are around 17 nm. © 2013 Springer Science+Business Media Dordrecht. Source


Rojas-Chavez H.,Tlahuac Institute of Technology | Rojas-Chavez H.,Research Center en Ciencia Aplicada y Tecnologia Avanzada | Reyes-Carmona F.,National Autonomous University of Mexico | Huerta L.,National Autonomous University of Mexico | Jaramillo-Vigueras D.,Research Center e Innovacion Tecnologica
Materials Research Bulletin | Year: 2013

To elucidate how surface and gaseous phases interact each other to induce chemical reactions, X-ray photoelectron spectroscopy (XPS) analyses were carried out on powders as milling took place. An acute analysis of data acquired by the XPS-technique allowed us to find a series of well-defined chemical transitions from precursors to the stoichiometric PbTe phase. By coupling, theoretical and experimental data a self-consistent model was developed. Initially, the process manifested itself as an oxidation stage and secondly as a reducing process. In agreement with a thermodynamic evaluation of free energy of phases traced during milling, chemical transitions were traced as Te2+ to Te6+ in oxidation reactions. If high oxygen potential prevails in the milling system subsequently Pb2+ evolves to Pb4+. On the other way, high valence oxides like Pb4+ or Te4+ were reduced to Pb 2+ and Te2-. However, the last transition an asymmetric transformations was identified as non-stoichiometric phases. © 2012 Elsevier Ltd. Source


Barron M.A.,Metropolitan Autonomous University | Hilerio I.,Metropolitan Autonomous University | Plascencia G.,Research Center e Innovacion Tecnologica
Advances in Mechanical Engineering | Year: 2012

The emergence of the oscillation death phenomenon in a ring of four coupled self-excited elastic beams is numerically explored in this work. The beams are mathematically represented through partial differential equations which are solved by means of the finite differences method. A coupling scheme based on shared boundary conditions at the roots of the beams is assumed, and as initial conditions, zero velocity of the first beam and three normal vibration modes of a linear elastic beam are employed. The influence of the self-exciting constant on the ring dynamics is analyzed. It is observed that oscillation death arises as result of the singularity of the coupling matrix. Copyright © 2012 Miguel A. Barron et al. Source


Rojas-Chavez H.,Research Center e Innovacion Tecnologica | Rojas-Chavez H.,Research Center en Ciencia Aplicada y Tecnologia Avanzada | Reyes-Carmona F.,National Autonomous University of Mexico | Jaramillo-Vigueras D.,Research Center e Innovacion Tecnologica
Materials Research Bulletin | Year: 2011

Both solid-solid and gas-solid reactions have been traced during high-energy milling of Se and PbO powders under vial (P, T) conditions in order to synthesize the PbSe phase. Chemical and thermodynamic arguments are postulated to discern the high-energy milling mechanism to transform PbO-Se micropowders onto PbSe-nanocrystals. A set of reactions were evaluated at around room temperature. Therefore an experimental campaign was designed to test the nature of reactions in the PbO-Se system during high-energy milling. © 2011 Elsevier Ltd. All rights reserved. Source

Discover hidden collaborations