L. Baños

University of Quindio, Armenia, Quindío, Colombia

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Publications (30)41.61 Total impact

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    ABSTRACT: Grazing incident X-ray diffraction is used to study oval defects on the surface of silicon doped GaAs layers grown by means of molecular beam epitaxy. The amplitude of the (113) peak from the diffraction data is associated with the defect density obtained from scanning electron microscopy images. These images reveal two different kinds of defects for all samples. It was proven that variations in the silicon effusion cell temperature affect the defect density. By increasing the cell temperature the defect density increases.
    Physica B Condensed Matter 01/2010; 405(9):2185-2188. · 1.28 Impact Factor
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    ABSTRACT: In this paper a complete characterization of lime cycle transitions is described. CaCO3 was collected from a Mexican mine and was processed to obtain Ca�OH�2 through CaO. When the calcium hydroxide interacted with the CO2 in the air forming CaCO3, the lime cycle was completed. Crystal structure and spectroscopy characterization was carried out to get the knowledge of lime cycle CaCO3→CaO→Ca�OH�2→CaCO3 deeply. The changes in the crystalline structures were described using X-ray diffraction by powder to accomplish phase identification. Scanning electron microscopy was done to examine the morphology, topology, crystal structure, and crystalline growth habit. Dynamic light scattering was used to determine the particle-size distribution of Ca�OH�2. Fourier-transform infrared was done to identify molecules and atomic bonds. Finally, inductively coupled plasma-mass spectrometry was done to get quantitative analyses. These results are a contribution to the restoration and construction industry fields, as well as a starting point to new possible applications of lime in current engineering.
    Journal of Materials in Civil Engineering 11/2009; 21(11):625-708. · 0.96 Impact Factor
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    ABSTRACT: Restoration requires the use of appropriate characterization methods and suitable new material preparation processes permit the reproduction of the original material to be as similar as possible in order to be an appropriate application method. The combination of these factors will facilitate a good restoration process. Different stuccos were taken from El Museo del Calendario, a building located in Querétaro, Mexico which was built in the 16th century. All the stucco samples were studied using the characterization process which is proposed in this article. The characterization method consisted of the use of analytical techniques, such as X-ray diffraction, Fourier transform infrared and scanning electron microscopy. This characterization method made reproduction of the original material possible. The new material combined with new application techniques developed in situ will result in a high-quality restoration process.
    Archaeometry 02/2009; 51(5):701 - 714. · 1.29 Impact Factor
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    ABSTRACT: We contrast the production of LaVO3 polycrystalline samples obtained by reduction of m-LaVO4 prepared by sol–gel acrylamide polymerization (SGAP) and solid state reaction (SSR). For SGAP the formation of m-LaVO4 occurs at 400 °C, for SSR at 1400 °C. For m-LaVO4-SGAP we observe a homogeneous morphology with needle-shaped grains of 50 nm average size. The SSR presents a broader size distribution in the micrometer range. Both m-LaVO4 samples were reduced into LaVO3 using a Zr rod at 850 °C in vacuum. LaVO3-SGAP presents a homogeneous grain distribution with an average size of 745 nm. LaVO3-SSR has an average size of 3.45 μm. The stoichiometry of all compounds was confirmed by energy dispersive X-ray spectroscopy. X-ray powder diffraction and transmission electron microscopy give crystal structures in agreement with those reported in the literature.
    Journal of Alloys and Compounds 01/2009; 479:511-519. · 2.73 Impact Factor
  • Microscopy and Microanalysis 01/2009; 15. · 2.50 Impact Factor
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    ABSTRACT: Often permittivity against T curves do not provide a conclusive characterisation of dielectric features of ferroelectric materials. Particularly, when permittivity is obtained from impedance measurements, where to experimental data is gradually lost at high frequencies when the temperature rises. Here we show how a combination of permittivity measurements and photoacoustic experiments can give a much more complete characterization of the ferro-paraelectric phase transitions and associated phenomena than those obtained from permittivity data alone. Peaked correlation curves, obtained from photoacoustic experiments were interpreted to be a manifestation of large enough microscopic variations of the compressibility as the temperature changed. On one hand, using a classical ferroelectric (BaTiO3) and a well-recognized relaxor (Ba(Ti0.65Zr0.35)O3) the main differences between their photoacoustic response are established. On the other hand, dielectric and photoacoustic results from the compounds Bi2WO6 and Bi2[Ta0.1W0.9]O6 − δ, were combined to characterize the temperature dependence of their dielectric behavior. Results provide evidence of the presence of a diffuse phase transition in Bi2WO6 at 660°C similar to that corresponding to relaxor behavior. Additionally the occurrence of a classical ferro-paraelectric phase transition above 900°C was found. This last phenomenon is detectable only by photoacoustic experiments. In Bi2[Ta0.1W0.9]O6 − δ the presence of a well defined transition was not detected. Dielectric determinations throughout ac measurements were carried out in the frequency interval 5 Hz-13 MHz. A pulsed Nd:YAG laser (10 Hz, 5 ns pulse width) was used to perform the photoacoustic experiments, where the out-coming signal was detected by a piezoelectric transducer. Dielectric and photoacoustic experiments were performed in a temperature interval from 250°C up to 1000°C.
    Ferroelectrics 01/2009; 386(1):50-61. · 0.42 Impact Factor
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    ABSTRACT: The synthesis and characterization of original materials, composed by hydrotalcite and hydroxyapatite, is discussed. All the syntheses were carried out in presence of microwave irradiation during the crystallization step. The interactions between the two compounds depend on the synthesis procedure. If hydroxyapatite is incorporated to hydrotalcite, the first compound is encapsulated by hydrotalcite. Instead, if hydroxyapatite is first prepared, the resulting solid is essentially a hydrotalcite with interlayered hydroxyapatite. When the composite material is synthesized by a simultaneous coprecipitation, the small clusters of hydroxyapatite and hydrotalcite are homogeneously dispersed. Consequently, the specific surface area and the particle size vary.
    Journal of Porous Materials 01/2009; 16(4):401-408. · 1.35 Impact Factor
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    ABSTRACT: KReO4 was synthesized by solid-state reaction and for the first time by sol–gel method via acrylamide polymerization. X-ray diffraction analysis showed that a single phase of KReO4 was obtained by both methods at 500–505 °C having a tetragonal unit cell. The solid-state reaction samples had a grain size of 5 μm and the sol–gel samples had fibrous aspect, agglomerated between 10 and 100 μm. By TEM it was observed nanocrystals of 100 nm, it is suggested that the xerogel fibers are formed by nanocrystals. From the results obtained, we concluded that the morphology is strongly influenced by the method of synthesis used.
    Journal of Sol-Gel Science and Technology 01/2009; 51(2):175-181. · 1.66 Impact Factor
  • Microscopy and Microanalysis 01/2009; 15. · 2.50 Impact Factor
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    ABSTRACT: A complete characterization of Cu–steel impact welded were made using photothermal radiometric (PTR) spectroscopy, scanning electron microscopy (SEM), microhardness, and X-ray diffraction (XRD) in order to study the changes in the structural, metallurgical, and thermal properties of Impact Welding Zone (IWZ) and the Impact Affected Zone (IAZ) after the impact welding. Three samples with different morphological interfaces were prepared for this analysis. According to the SEM analysis in etched samples, it was possible to determine that the IWZ is formed by the collapse of grains of Cu and steel (ferrite and pearlite) into the Cu–steel interface and the IAZ are formed in a region close to the IWZ with low grain damage. Microhardness Vickers test is able to detect the IAZ in all cases, but due to its contact character, it is not possible to obtain continuous hardness information across the Cu–steel interface. According to the XRD patterns after the impact welding process, no new phase was formed. Noncontact PTR amplitude and phase images are able to identify the IAZ and the IWZ.
    Materials and Manufacturing Processes 10/2008; 23(8):823-828. · 1.30 Impact Factor
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    ABSTRACT: Well crystallized silicalite-1 has been obtained from three sources of amorphous silica, namely, rice hull ashes, commercial Davisil, and a fume silica from Aldrich. The silicas were first dissolved in glycerol according to a recently described reaction. This reaction transforms rapidly and efficiently large surface area silicates into poly-alkoxide gels. It can be schematized as an etherification of an alcohol function of glycerol by the weakly acid surface silanol groups. The facile hydrolysis of the alkoxide permits the preparation of relatively pure and reactive silica, keeping the mesoporous character of the parent starting material. We insist on the mesoporous character of the solids obtained upon hydrolyzing the organo-silicic gel because we believe the gel plays a role of template in the secondary synthesis of mesoporous structures. The hydrolysis is carried out in presence of a structure directing agent, namely tetra-propylammonium hydroxide, TPAOH. After aging, the residue is dried and calcined. The first advantage of using the organo-silicic gel is probably related to the high degree of depolymerization of silica, witness by the C/Si ratio. The second one, more subtle to define, is to provide an intermediate silica with hydrophilic a hydrophobic regions, interfering differently with the surfactant. After calcination at 500 degrees C, well crystallized silicalite-1 is obtained. The texture of the starting silica influences the textural characteristics of the final silicalite-1.
    Journal of Colloid and Interface Science 08/2008; 323(2):359-64. · 3.17 Impact Factor
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    ABSTRACT: The formation of the YVO3 compound obtained by sol–gel acrylamide polymerization is reported. This synthesis method is contrasted with solid state reaction. Differential thermal analysis (DTA) results show the formation of YVO3 at 805 °C compared with 1312 °C for solid state reaction. Thermogravimetric analysis (TG) results show that between 400 and 600 °C the denaturalization of the organic part, ethylenediamine, and the decomposition of nitrates occur. The evolution of YVO4 into YVO3 was also studied by X-ray powder diffraction (XRD). The refinement results obtained for both YVO3 samples show an orthorhombic phase with Pbnm (62) space group and lattice parameters: a = 5.283 Å, b = 5.605 Å and c = 7.580 Å. Grain size and morphology evolution for different heat treatments were studied with scanning electron microscopy (SEM). The use of sol–gel acrylamide synthesis allows us to start with a homogeneous grain distribution with a mean size of 5.03 ± 0.65 nm growing up to 4.11 ± 0.87 μm in YVO4. After reduction to YVO3 the final grain size was 2.87 ± 0.10 μm also with grain size homogeneity. This is in contrast with samples prepared by solid state reaction for which the grain size starts (YVO4) between 1 and 7.0 μm and ends (YVO3) with a size distribution centered at 90.32 ± 74.46 μm. Transmission electron microscopy (TEM) results corroborate XRD results. Energy dispersive X-ray (EDX) results are in agreement with theoretical values.
    Journal of Sol-Gel Science and Technology 01/2008; 46(1):1-10. · 1.66 Impact Factor
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    ABSTRACT: The aim of this work was to investigate the effect of the carbides precipitated on the hardness and structure in the heat-affected zone of a Hadfield steel that has been used as broke stone tool during ten months and that have to be repaired by the welding process. The steel presents significant structural changes for the presence of the discontinuities in the heat-affected zone, that affect the hardness and the structure in comparison to the homogenized sample. The investigation is carried out with X-ray diffraction (XRD), microhardness Vickers, and Scanning Electron Microscopy (SEM) system. According to the XRD patters, the presence of Manganese carbides was identified. The identification of the types of carbides present in the steel structure allows us to say that it belongs to the Mn23C6 and Mn7C3 type.
    Materials and Manufacturing Processes 01/2008; 23(1):14-20. · 1.30 Impact Factor
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    ABSTRACT: This work presents the study of the structural changes of the endo-sperm of Quality Protein Maize (QPM H-368C), modified by alkaline cooking at two different temperatures (72 and 92°C) and steeping time of 0–7 hr. Structural changes in the outermost 10% layers, the subsequent 10%, and the remaining 80% of the endosperm as a function of the steeping time were studied using scanning electron microscopy (SEM), X-ray diffraction, and differential scanning calorimetry (DSC) tech-niques. SEM images revealed that soft and hard endosperm have different shapes and packing factors. The X-ray diffraction patterns of the hard and soft endosperm from raw corn suggest that the hard endosperm consists mainly of amylopectin and has a bigger relative crystallinity quality than the soft endosperm. Samples cooked at 72 and 92°C with and without the Ca(OH) 2 and steeped for 0, 3, and 7 hr, showed structural changes, X-ray diffraction patterns from the outermost 10% layers and subsequent 10% of the endosperm were completely amorphous. This fact is related to the total or partial gelatinization of the starch. The crystallinity in the internal layers of endosperm (remaining 80%) did not have significant changes after the treatments and exhibited the characteristic patterns of crystalline amylose and amylopectin. DSC measurements in the outermost layers of the endosperm did not exhibit the characteristic endothermic peak of starch (from 64 to 81°C) compared with the raw sample, while the endotherm peak for 80% of the endosperm internal layers appears in all cases (72 and 92°C). According to these results, a new definition of the nixtamalization process can be developed as follows. During the nixta-malization process there is a total gelatinization of the starch granules from the most external layers, and a partial gelatinization of the innermost internal layers of the endosperm.
    Cereal Chemistry 04/2007; 84(4):304-312. · 1.25 Impact Factor
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    ABSTRACT: This contribution deals with the synthesis of a silicon-rich ZSM-5 obtained from an amorphous organo-alumino-silicic gel. The gel was formed by reacting a mechanical mixture of RHA (rice hull ash), silica’s source, and of natural clinoptilolite, source of alumina, with glycerol during 2 h at 200 °C. After a maturation period of one day at 60 °C, the reaction product was hydrolyzed by a tetra-propyl-ammonium (TPA) solution and then aged for two days at 135 °C in a stainless steel autoclave. After washing and drying, the X-ray pattern showed a well crystallized ZSM-5. The textural analysis of the slowly calcined solid at 500 °C for 4 h, and the SEM micrographies evidence that the zeolite was supported on mesoporous silica. The proportion of both components depends on the tunable hydrolysis conditions.
    Microporous and Mesoporous Materials 01/2007; 100:70-76. · 3.37 Impact Factor
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    ABSTRACT: This article discusses the use of various measurement techniques for physico-chemical and mineralogical analyze of lime for its safe use as a food additive. Two types of samples were taken from a mine in Queretaro, Mexico, and measurements were made to determine Pb (CaO—0.0012mg/kg, Ca(OH)2—0.0527mg/kg), As (CaO—0.0290mg/kg, Ca(OH)2—0.0849mg/kg), F (under the quantification limit), and V (CaO—1.9068mg/kg, Ca(OH)2—4.3403mg/kg). The samples were within the safety limits for human consumption. It is suggested that similar analysis be carried out on commercially marketed lime products.
    Sensing and Instrumentation for Food Quality and Safety 01/2007; 1(4):169-175.
  • Microscopy and Microanalysis. 01/2007; 13(S02):676-677.
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    ABSTRACT: An as-cast Al–Li(2%)–Hf(1%) alloy was structurally and mechanically characterized; X-ray diffraction made it possible to detect the presence of Li and Hf and to determine their effect on aluminum lattice parameter and formation of intermetallic precipitates. The crystalline quality of the Al matrix was influenced by the Li distribution into the Al lattice. The full-width-at-half-maximum was used to determine the crystalline quality of each part of the ingot. The solution of Li in the α-Al matrix decreased the Al lattice parameter and the Hf was found to be present as an intermetallic precipitate, which improve the hardness of the as-cast alloy.
    Materials and Manufacturing Processes - MATER MANUF PROCESS. 01/2007; 22(2):247-250.
  • Microscopy and Microanalysis. 01/2006; 12(S02):736-737.
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    ABSTRACT: In this paper we present a study of the optical properties of CdZnTe single crystal for low Zn concentrations at room temperature using photoacoustic spectroscopy and photoreflectance (PR) measurements. The photoreflectance measurements were carried out in order to determine the Eg value at room temperature of the CdTe sample to validate the criterion for the photoacoustic absorption measurements. The closed photoacoustic cell configuration (CPC) was used for the absorption measurements and, we use the knee method in the spectra for the energy band gap determination of CdZnTe as a function of the Zn concentration. The samples under study are commercial samples grown by the Bridgmann technique. X-ray diffraction was carried out in order to determine the Zn concentration of the samples and the FWHM of the diffraction peaks. The correlation between FWHM of the diffractograms and the photoacoustic absorption slopes shows that the absorption slopes could be associated with the crystalline quality of samples.
    Journal of Crystal Growth 01/2006; · 1.55 Impact Factor