Study of the isothermal oxidation process and phase transformations in B2-(Ni,Pt)Al/RENE-N5 system

Luis Alberto Cáceres Díaz JUAN MANUEL ALVARADO OROZCO Haideé Ruiz Luna JOHN EDISON GARCIA HERRERA ALMA GABRIELA MORA GARCIA LUIS GERARDO TRAPAGA MARTINEZ Raymundo Arroyave Juan Muñoz Saldaña (2016)

Changes in composition, crystal structure and phase transformations of B2-(Ni,Pt)Al coatings upon isothermal oxidation experiments (natural and scale free oxidation) at 1100 °C, as a function of time beyond their martensitic transformation, are reported. Specifically, the analysis of lattice parameter and composition are performed to identify changes in the B2-(Ni,Pt)Al phase upon the chemically-driven L10-(Ni,Pt)Al and L12-(Ni,Pt)3Al transformations. The B2-(Ni,Pt)Al phase was found to disorder and transform the martensite during the heat treatments for both oxidation experiments at approximately 36.3 and 40.9 at. % of Al, 47.7 and 42.9 at. % of Ni, 6.2 and 8.5 at. % of Pt, 4.2 and 2.9 at. % of Cr and 4.4 and 3.8 at. % of Co. The lattice constant and the long-range order parameter of the B2-(Ni,Pt)Al phase decreased linearly as a function of the elemental content irrespective of the nature of the oxidation experiments.

Article

B2-(Ni,Pt)Al bond coatings Oxidation Martensitic transformation Crystal structure INGENIERÍA Y TECNOLOGÍA CIENCIAS TECNOLÓGICAS TECNOLOGÍA MINERA

Slow-­Light in photonic crystals waveguides

GISELA LOPEZ GALMICHE (2012)

We modeled two realistic slow light structures, which are viable to be

fabricated on silicon: Silicon strip waveguide photonic crystal with

periodic SiO2 holes and silicon corrugated waveguide. In order to

modeling these devices we carried out simulations using the Plane Wave

Expansion (PWE) method and the Finite Differences in Time Domain

(FDTD) method. We employed the MIT Photonic Bands (MPB) free

software developed by Massachusetts Institute of Technology and the

FDTD Solutions software developed by Lumerical Solutions Inc.

Also, we analyzed the scattering originated by technological imperfections

in the waveguides, known as extrinsic losses. In this analysis we used a

theoretical model developed by T. Krauss group for described the losses

effect in the photonic crystal waveguides. For this goal, a MPB code

developed by the Krauss group was used.

En este trabajo se muestra el análisis de dos estructuras útiles para la

propagación de luz lenta. El diseño de estas estructuras es realista y son

viables para su fabricación en Silicio, ellas son: un alambre de silicio con

agujeros periódicos de SiO2 y una guía de onda con corrugaciones. Con la

finalidad de modelar estos dispositivos, se llevó a cabo simulaciones

empleando los métodos de expansión de onda plana (PWE) y de

diferencias finitas en el dominio del tiempo (FDTD), para esto se utilizaron

los programas MPB y FDTD Solutions, respectivamente.

Además, se analizó la dispersión originada por las imperfecciones

tecnológicas en las guía de ondas, conocidas como las pérdidas

extrínsecas. Para este análisis se utilizó un modelo teórico desarrollado por

el grupo de T. Krauss, en el cual se describe el efecto de las pérdidas en las

guías de cristal fotónico. Para este objetivo se utilizó el código MIT

Photonic Bands (MPB).

Master thesis

Losses Crystal structure Modeling CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA

NMR analysis and crystal structure of hydroxyclerodanes from Mexican Salvia species

Alfredo Ortega NAYTZE DALIA ORTIZ PASTRANA BRENDA YUDITH BEDOLLA GARCIA Rubén A. Toscano FRANCISCO ELIHU BAUTISTA REDONDA (2017)

"NMR and single crystal X-ray diffraction analysis of seven clerodanes from Mexican Salvia species was performed. We focused on clerodanes with tertiary hydroxyl group at C-4, C-8, and C-10, in which the establishment of absolute configuration around these chiral centers is nontrivial and the 13C NMR signals can be misassigned. In addition, the analysis by 1H NMR in aprotic solvent allowed us to establish a common pattern that correlates the chemical shift with the position of the hydroxyl groups, which constitute a good methodology for future structural elucidation of these kinds of compounds. The obtained data allowed us to establish the absolute configuration of five of these diterpenes and the structural revision of salvimicrophyllin D (7)."

Article

Clerodane diterpenes Hydroxyclerodanes Salvia species NMR analysis X-ray diffraction Crystal structure BIOLOGÍA Y QUÍMICA QUÍMICA QUÍMICA

Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound

Pablo Álvarez Alonso Pedro Gorria JOSE LUIS SANCHEZ LLAMAZARES Maria J. Perez Victorino Franco Reiffers Marian Jozef Kovac Inés Puente Orench Jesús Angel Blanco Rodríguez (2011)

"We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray and neutron powder diffraction show that the crystal structure is rhombohedral with space group (Th2Zn17-type). The investigated compound exhibits a broad isothermal magnetic entropy change ?SM(T) associated with the ferro-to-paramagnetic phase transition (TC ? 290 K). The |?SM| (?2.3 J kg?1 K?1) and the relative cooling power (?100 J kg?1) have been calculated for applied magnetic field changes up to 1.5 T. A single master curve for ?SM under different values of the magnetic field change can be obtained by a rescaling of the temperature axis. The results are compared and discussed in terms of the magneto-caloric effect in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys."

Article

Intermetallic compounds Magnetic materials Crystal structure Thermomagnetic effects CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA FÍSICA

Structure formation in polyaniline-based polymer blends

RICARDO HERBE CRUZ ESTRADA CARLOS VIDAL CUPUL MANZANO (2005)

This paper provides evidences on the feasibility of using an in-situ deformation process to produce elongated structures of a polyaniline complex (PANI CX), embedded in the bulk of filament-like polymer composites, and longitudinally oriented along the composites' main axial direction. The polyaniline complex was thermally blended with polystyrene- polybutadiene- polystyrene (SBS) at different weight compositions, and the resultant blends were capillary extruded into filaments. The extrudates' microstructure was analysed by scanning electron microscopy (SEM). The results of the analysis revealed a phase- separated morphology in the extrudates, which consisted of elongated domains of PANI CX embedded in the bulk of the SBS. The elongated structures displayed a considerable degree of uniformity and continuity, and were preferentially oriented in the extrusion direction. The formation of these structures was ascribed to a combination of factors, the main ones including elongational and shearing flows occurring in the molten/softened blends during the processing, and the stresses transferred from the highly viscous matrix to the particles of the PANI complex filler. 

Article

COMPOSITE MATERIALS CRYSTAL STRUCTURE MORPHOLOGY INGENIERÍA Y TECNOLOGÍA

Mechanochemical synthesis and crystal structure of the lidocaine-phloroglucinol hydrate 1:1:1 complex

NANCY EVELYN MAGAÑA VERGARA PORFIRIO DE LA CRUZ CRUZ ANA LILIA PERAZA CAMPOS FRANCISCO JAVIER MARTINEZ MARTINEZ JUAN SAULO GONZALEZ GONZALEZ (2018)

Molecular complexation is a strategy used to modify the physicochemical or biopharmaceutical properties of an active pharmaceutical ingredient. Solvent assisted grinding is a common method used to obtain solid complexes in the form of cocrystals. Lidocaine is a drug used as an anesthetic and for the treatment of chronic pain, which bears in its chemical structure an amide functional group able to form hydrogen bonds. Polyphenols are used as cocrystal coformers due to their ability to form O–H···X (X = O, N) hydrogen bond interactions. The objective of this study was to exploit the ability of phloroglucinol to form molecular complexes with lidocaine by liquid assisted grinding. The formation of the complex was confirmed by the shift of the O–H and C=O stretching bands in the IR spectra of the polycrystalline ground powders, suggesting the formation of O–H···O=C hydrogen bonds. Hydration of the complexes also was confirmed by IR spectroscopy and by powder X-ray diffraction. The molecular structure was determined by single crystal X-ray diffraction.

Article

BIOLOGÍA Y QUÍMICA Lidocaine Phloroglucinol Crystal structure Hydrogen bonding Hydration Molecular complex

Synthesis of protonated titanate nanotubes tailored by the washing step: Effect upon acid properties and photocatalytic activity

ROBERTO CAMPOSECO SOLIS ISIDRO MEJIA CENTENO VICENTE RODRIGUEZ GONZALEZ (2017)

"In this work, the acid and photocatalytic properties of titanate nanotubes (NTs) were surveyed. The surface acidity of the NTs was characterized by FTIR with lutidine and pyridine. The photocatalytic degradation of phenol in aqueous suspension was performed to test the photocatalytic properties of the NTs. The results were compared with those obtained from commercial TiO2. NTs were prepared by hydrothermal treatment of TiO2 nanoparticles in a NaOH aqueous solution. During the washing step, three different acid agents (HCl, H2SO4, and HNO3) were used. TiO2 nanoparticles were synthesized previously by the sol-gel method. The photocatalytic materials were characterized by FTIR, XRD, XPS, SBET, UV–vis, and HRTEM. It was found that the used acid agent significantly affected the amount and type of acid sites. Brönsted acid sites were favored by the use of HNO3. Lewis acid sites were promoted when HCl was employed during the washing step, which is in contrast with the results obtained using the other acids chosen in this work. Besides, the use of HCl promoted the H2Ti3O7 phase. The acid phase H2Ti4O9·H2O was favored when HNO3 was used and H2SO4 formed the H2Ti2O4·(OH)2 acid phase. The presence of Cl, S, and N species on the NTs was not found. Furthermore, Na+ ions were completely removed from the surface of the NTs, which were exchanged by H+ ions. It was found, in general, that the three catalysts presented a relatively high photocatalytic activity to remove phenol. However, NTs washed with HNO3 (NT-HNO3) displayed the best photocatalytic activity compared to the other NTs. After 200 min, NT-HNO3 reached a phenol degradation yield close to 100%. Commercial TiO2 presented a phenol degradation yield close to 60%. It could be concluded that the acid phase (H2Ti4O9·H2O) and concentration of Brønsted acid sites promoted the photocatalytic activity of NT-HNO3."

Article

Nanostructures Heat treatment Crystal structure FTIR Rietveld analysis XPS BIOLOGÍA Y QUÍMICA QUÍMICA QUÍMICA

Modifications in the rhombohedral degree of distortion and magnetic properties of Ba-doped BiFeO3 as a function of synthesis methodology

LUIS EDMUNDO FUENTES COBAS ARMANDO REYES ROJAS GABRIEL ROJAS GEORGE (2014)

We present an analysis of crystallographic symmetry and the origin of the pseudo-cubic character of doped BiFeO3. Specifically, barium-doped bismuth ferrite, Bi1−xBaxFeO3 (x = 0.05, 0.075, 0.1, 0.125), perovskite-type nanoparticles have been synthesized by implementing five modifications to the sol–gel technique (citric acid-assisted sol–gel method, ethylene glycol method, tartaric acid-assisted sol–gel method, polyvinyl alcohol–ethylene glycol method, and EDTA complexing sol–gel method) and their final pseudo-cubic character is discussed. The effect of the carboxylic groups and hydroxyl groups during synthesis is critical to obtain single phase BBFO. Fourier transform infrared spectroscopy and thermogravimetric analysis is used to study the decomposition and thermal behavior of the precursors and their relation to the final nanoparticle characteristics. X-ray diffraction analysis shows a single phase with symmetry changes for four of the five synthesis methodologies employed. Only the EDTA complexing sol–gel method, where EDTA is used as dissolver and chelating agent, is not satisfactory in all concentration ranges. Rietveld results suggest that the degree of distortion of the rhombohedral symmetry in the crystallized BiFeO3 powders decreases 12% as a result of progressive substitution of Bi3+ by Ba2+ and that there is no shift from rhombohedral to tetragonal symmetry. Magnetization properties of samples with a low-distortion rhombohedral structure show higher magnetic saturation and remanent magnetization than samples with high-distortion rhombohedral structure.

Article

Chemical synthesis; Magnetic materials; Crystal structure; Nanostructures BIOLOGÍA Y QUÍMICA QUÍMICA

Upper critical fields in a FeSeO.5TeO.5 superconducting single crystal

DIEGO VELASCO SOTO (2013)

A single crystal with a nominal composition FeSe0.5Te0.5 was obtained by the Bridgman method. A

quartz ampulla with the sample inside was vacuum-sealed and maintained at 1050 !C for 37 h to

homogenize the sample. Subsequently, the quartz ampulla with the sample was moved with a

speed of 2.2 mm/h to a furnace which was at 450 !C. X-ray diffraction confirmed the tetragonal

structure of the grown single crystal with the cleavage plane corresponding to the ab plane.

Resistance measurements were carried out with magnetic fields from 0 to 9 T, applied parallel to

the c axis and ab plane, respectively. A zero-field critical temperature Tc¼14K was determined.

The upper critical field vs. temperature phase diagram was built for temperatures where the

resistance drops to 90%, 50%, and 10% of the normal state resistance. The linear extrapolation to

T¼0K gave upper critical fields of 57.2, 51.8, and 46.0 T for Hjjc axis and 109.6, 95.5, and 80.9 T

for Hjjab. Applying the Werthamer–Helfand–Hohenberg (WHH) theory, upper critical fields of

39.6, 35.9, and 31.8 T and coherence lengths of 28.8, 30.3, and 32.1A ° were obtained for Hjjc;

while for Hjjab, upper critical fields of 51.3, 40.7, and 37.5 T and coherence lengths of 22.3, 26.7,

and 31.5A ° were obtained. The value of l0Hc2/kBTc calculated by the WHH theory exceeds the

Pauli limit (1.84 T/K) indicating the unconventional nature of superconductivity. The activation

energy U0 has two different rates of change with the applied magnetic field probably due to two

different thermal activation mechanisms; the origin of which requires further investigation. A

similar behavior is observed in the irreversibility lines.

Article

Crystal CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA OTRAS ESPECIALIDADES FÍSICAS OTRAS

El protocolo familiar: Herramienta para la transferencia generacional de las empresas familiares

LIBNAZARET BETANCOURT RODRIGUEZ ANNISEL DIAZ MONTES THANAIRI DE FATIMA MEZO UC ANDRES MIGUEL PEREYRA CHAN RAYMA IRERI MALDONADO ASTUDILLO (2020)

En México, más del 90 % de las empresas son de tipo familiar. A pesar de su relevancia en la economía nacional, diversos autores concuerdan que son quienes más sufren las altas tasas de mortalidad, primordialmente a raíz del traspaso de una generación a otra. Esta problemática de continuidad, entre otras causas, está asociada a la falta de un protocolo familiar a razón de la inadecuada planeación de la sucesión.

In Mexico, more than 90 % of the companies are family owned. Despite its relevance in the national economy, several authors agree that they suffer the most from high mortality rates, primarily as a result of the transfer from one generation to another. This problem of continuity, among other causes, is associated with the lack of a family protocol due to the inadequate planning of succession.

Article

Empresa familiar Protocolo familiar Continuidad Sucesión Estructura Contenido Family Business Family protocol Succession Continuity Structure Content CIENCIAS SOCIALES SOCIOLOGÍA COMUNICACIONES SOCIALES