DSpace Collection:
http://repositoriodigital.ipn.mx/handle/123456789/3215
2024-03-29T06:51:32Z
2024-03-29T06:51:32Z
Calcium content and speciation in alkaline-cooked corn studied bysynchrotron Ca K-edge X-ray absorption spectroscopy.
Caballero Briones, Felipe
http://repositoriodigital.ipn.mx/handle/123456789/21699
2019-10-02T18:19:48Z
2015-10-07T00:00:00Z
Title: Calcium content and speciation in alkaline-cooked corn studied bysynchrotron Ca K-edge X-ray absorption spectroscopy.
Authors: Caballero Briones, Felipe
Abstract: Using Ca K-edge X-ray absorption spectroscopy the calcium uptake and species in alkaline corn have been studied and compared with corn starch and crystalline cellulose as main compounds in corn endosperm and pericarp. XANES data showed that calcium binds preferably to hemicelluloses in the pericarp. The main calcium species found by EXAFS in cellulose and starch is calcium carbonate although some protein-calcium species could be formed within the starch granules. From X-ray diffraction and microscopy techniques, pericarp dissolution, mainly at the amorphous hemicellulose fraction was inferred. The hemicellulose dissolution during steeping increases the apparent pericarp crystallinity, while the relative calcium content determined by XANES absorption edges reduces. XANES and EXAFS spectroscopies showed to be a valuable tool in order to determine the calcium species and to make a semiquantitative determination of calcium in the different nixtamalized corn fractions. © 2014 Elsevier Ltd.
2015-10-07T00:00:00Z
Mg-doped CdS films prepared by chemical bath deposition. Optical and electrical properties
CABALLERO BRIONES, FELIPE
CALZADILLA, O.
CHALÉ LARA, FABIO FELIPE
REJON, V.
PEÑA, J.L.
http://repositoriodigital.ipn.mx/handle/123456789/21620
2019-10-02T18:19:17Z
2015-07-29T00:00:00Z
Title: Mg-doped CdS films prepared by chemical bath deposition. Optical and electrical properties
Authors: CABALLERO BRIONES, FELIPE; CALZADILLA, O.; CHALÉ LARA, FABIO FELIPE; REJON, V.; PEÑA, J.L.
Abstract: Mg-doped CdS thin films were prepared onto glass substrates by the chemical bath deposition method increasing Mg2+ contents in the chemical bath. Film composition was studied by X-ray photoelectron spectroscopy. The physical properties of the films such as the lattice parameter, crystallite size and crystal structure were studied by X-ray diffraction and the film morphology was examined by atomic force microscopy. XPS results indicate an incorporation of up to 0.27 at. %. X-ray diffraction showed that films occur primarily in the hexagonal phase. The band gap increased with the Mg2+ added to the bath. The film resistance reduced with the Mg doping and an increased photocurrent response was observed under illumination. Using photocurrent sensing atomic force microscopy (PCAFM) in selected samples, an increasing photocurrent response was measured in the grain boundaries. I-V curves in PCAFM indicate n-type doping character. © 2015, National Institute R and D of Materials Physics. All rights reserved.
2015-07-29T00:00:00Z
Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass-ceramics
NARRO GARCÍA, ROBERTO
DESIRENA, H.
LÓPEZ LUKE, T.
GUERRERO CONTRERAS, J.
JAYASANKAR, C.K.
QUINTERO TORRES, R.
DE LA ROSA, E.
http://repositoriodigital.ipn.mx/handle/123456789/21619
2019-10-02T18:21:23Z
2015-07-29T00:00:00Z
Title: Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass-ceramics
Authors: NARRO GARCÍA, ROBERTO; DESIRENA, H.; LÓPEZ LUKE, T.; GUERRERO CONTRERAS, J.; JAYASANKAR, C.K.; QUINTERO TORRES, R.; DE LA ROSA, E.
Abstract: This paper reports the fabrication and characterization of Eu3+/Nd3+ co-doped phosphate (PNE) glasses and glass-ceramics as a function of Eu3+ concentration. The precursor glasses were prepared by the conventional melt quenching technique and the opaque glass-ceramics were obtained by heating the precursor glasses at 450 °C for 30 h. The structural and optical properties of the glass and glass-ceramics were analyzed by means of X-ray diffraction, Raman spectroscopy, UV-VIS-IR absorption spectroscopy, photoluminescence spectra and lifetimes. The amorphous and crystalline structures of the precursor glass and opaque glass-ceramic were confirmed by X-ray diffraction respectively. The Raman spectra showed that the maximum phonon energy decreased from 1317 cm-1 to 1277 cm-1 with the thermal treatment. The luminescence spectra of the glass and glass-ceramic samples were studied under 396 nm and 806 nm excitation. The emission intensity of the bands observed in opaque glass-ceramic is stronger than that of the precursor glass. The luminescence spectra show strong dependence on the Eu3+ ion concentration in the Nd3+ ion photoluminescence (PL) intensity, which suggest the presence of energy transfer (ET) and cross-relaxation (CR) processes. The lifetimes of the 4F3/2 state of Nd3+ ion in Eu3+/Nd3+ co-doped phosphate glasses and glass-ceramics under 806 nm excitation were measured. It was observed that the lifetimes of the 4F3/2 level of Nd3+ of both glasses and glass-ceramics decrease with the increasing Eu3+ concentration. However in the case of opaque glass-ceramics the lifetimes decrease only 16%. © 2015 Elsevier B.V. All rights reserved.
2015-07-29T00:00:00Z
Role of Preparation Method on the Microstructure and Mechanical Properties of PPy/Ni Organic–Inorganic Hybrid Bilayer Coatings on Carbon Steel
TORRES HUERTA, AIDE MINERVA
DOMINGUEZ CRESPO, MIGUEL ANTONIO
ALANIS VALDELAMAR, A.
ONOFRE BUSTAMANTE, EDGAR
ESCUDERO, M.L.
GARCÍA ALONSO, M. C.
LOIS CORREA, J.A.
http://repositoriodigital.ipn.mx/handle/123456789/21618
2019-10-02T18:21:21Z
2015-07-29T00:00:00Z
Title: Role of Preparation Method on the Microstructure and Mechanical Properties of PPy/Ni Organic–Inorganic Hybrid Bilayer Coatings on Carbon Steel
Authors: TORRES HUERTA, AIDE MINERVA; DOMINGUEZ CRESPO, MIGUEL ANTONIO; ALANIS VALDELAMAR, A.; ONOFRE BUSTAMANTE, EDGAR; ESCUDERO, M.L.; GARCÍA ALONSO, M. C.; LOIS CORREA, J.A.
Abstract: The efficacy of the conducting polymers as coating on a metallic substrate is strongly dependent on the manner how they are applied. Polypyrrole (PPy)/Ni organic–inorganic hybrid coatings were electropolymerized on commercial carbon steel (AISI 1018) by combining potentiostatic and potentiodynamic techniques. In first instance, it was analyzed the electrodeposition of PPy using a constant potential regime and cyclic voltammetry techniques evaluating different synthesis parameters such as deposition time, applied potential, and potential cycles, respectively. Thereafter, it was used a potentiostatic method to obtain PPy/Ni bilayer films. The morphological, mechanical, and adhesion properties of these films depend on the synthesis parameters. The results revealed that polypyrrole films formed by both methods provide a globular-type structure, although coatings produced by cyclic voltammetry are denser and slightly thicker than those produced potentiostatically. Ni (oxide/hydroxide) particles are capable of sealing the pores of globular PPy coatings, thus increasing the hardness of the carbon steel (CS)/PPy/Ni system. As a result of the study, we have seen that PPy/Ni bilayer films are more uniform, compact and enhanced the hardness when the PPy is obtained by cyclic voltammetry than that observed for potentiostatic approach. Specifically, when four potential cycles are used to electropolymerized pyrrole, the more convenience properties in the CS/PPy/Ni arrangement are obtained. © 2015, The Minerals, Metals & Materials Society and ASM International.
2015-07-29T00:00:00Z