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Search Results: 1 - 10 of 252474 matches for " José G. Carriazo "
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Laboratory projects using inquiry-based learning: an application to a practical inorganic course
Carriazo, José G.;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000600029
Abstract: this paper reports how laboratory projects (lp) coupled to inquiry-based learning (ibl) were implemented in a practical inorganic chemistry course. several coordination compounds have been successfully synthesised by students according to the proposed topics by the lp-ibl junction, and the chemistry of a number of metals has been studied. qualitative data were collected from written reports, oral presentations, lab-notebook reviews and personal discussions with the students through an experimental course with undergraduate second-year students at the universidad nacional de colombia during the last 5 years. positive skills production was observed by combining lp and ibl. conceptual, practical, interpretational, constructional (questions, explanations, hypotheses), communicational, environmental and application abilities were revealed by the students throughout the experimental course.
Thermal and structural study of guava (Psidium guajava L) powders obtained by two dehydration methods
Osorio, Coralia;Carriazo, José G.;Barbosa, Helber;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000400016
Abstract: two food products (powders) were obtained by hot-air drying or lyophilisation methods on the whole guava fruits. the powders were characterised by sensory and thermal analyses (tga-dsc), infrared spectroscopy (ir), x-ray diffraction (xrd) and scanning electron microscopy (sem). thermal, morphological and structural characterisations showed a similar behaviour for the two solids. tga-dsc and ir showed the presence of pectin as the main constituent of solids. a semi-crystalline profile was evidenced by xrd, and lamellar/spherical morphologies were observed by sem. sensory analyses revealed an aroma highly related to guava. these value-added food products are an alternative to process guava and avoid loss during postharvest handling.
Actitudes hacia la química de estudiantes de diferentes carreras universitarias en Colombia
Molina, Manuel F;Carriazo, José G;Farías, Diana M;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000900032
Abstract: this work reports a study on the attitudes of colombian students towards chemistry in different undergraduate programs. the research was performed on 769 students belonging to several chemistry courses, by applying an adaptation of salta and tzougraki's test and using likert's scale. the results revealed that chemistry is being considered as difficult and little useful, but very interesting. thus, the difficulty to learn chemistry may be associated with its language and abstract conceptual nature. in addition, more attention should be given to the class contents and methodologies provided to the students, in order to engage them with those interest aspects and meaningful topics of each program
Impregnación de platino y dimensión fractal en dos tipos de sólidos microporosos
Carriazo,José G.; Barrera-Vargas,Mario; Molina,Manuel F.;
Revista Ingenierías Universidad de Medellín , 2010,
Abstract: this research shows the modification of a zeolite y and a pillared clay (saponite) by impregnation with different platinum quantities (synthesis of pt catalysts). the solids were characterized about the chemical composition and texture. the textural characterization reveals important changes in the solids, showing that in the zeolitic catalysts microporosity is formed, whereas in the pillared clay the microporous structures are partially blocked. fractal dimension (by avnir-jaroniec method) indicates that the topographic features of the pillared clay surface are significantly affected due to the modification with platinum, probably as a consequence of platinum clusters formation.
Impregnación de platino y dimensión fractal en dos tipos de sólidos microporosos Platinum impregnation and fractal dimension on two types of micro-porous solids
José G. Carriazo,Mario Barrera-Vargas,Manuel F. Molina
Revista Ingenierías Universidad de Medellín , 2010,
Abstract: El presente trabajo muestra la modificación de una zeolita-Y y una arcilla pilarizada (tipo saponita) mediante impregnación con diferentes cargas de Pt (catalizadores a base de Pt). Los sólidos se caracterizaron en cuanto a su composición química y su textura. La caracterización textural revela cambios importantes en los sólidos, mostrando que se genera microporosidad en la serie de catalizadores zeolíticos y se bloquean las estructuras microporosas en la serie de catalizadores obtenidos a partir de la arcilla pilarizada. La determinación de la dimensión fractal (mediante el método de Avnir-Jaroniec) indica que la modificación con Pt afecta significativamente las características topográficas de la superficie de la arcilla pilarizada como consecuencia de la posible formación de agregados de Pt. This research shows the modification of a zeolite Y and a pillared clay (saponite) by impregnation with different platinum quantities (synthesis of Pt catalysts). The solids were characterized about the chemical composition and texture. The textural characterization reveals important changes in the solids, showing that in the zeolitic catalysts microporosity is formed, whereas in the pillared clay the microporous structures are partially blocked. Fractal dimension (by Avnir-Jaroniec method) indicates that the topographic features of the pillared clay surface are significantly affected due to the modification with platinum, probably as a consequence of platinum clusters formation.
Energías de Interacción y Geometrías de Equilibrio para Aglomeraciones de 1,2-propanodiol con 3, 4, 5 y 6 Moléculas de Agua
Ensuncho,Adolfo E; López,Jesús M; Carriazo,José G;
Información tecnológica , 2011, DOI: 10.4067/S0718-07642011000600010
Abstract: the equilibrium geometries and interaction energies in clusters of 1,2-propanediol with 3,4,5 and 6 water molecules were evaluated. this was done to better comprehend the predominant interactions existing at molecular level in aliphatic diols with water. the clusters were stochastically generated and selected by using a modified metropolis acceptance test implemented in the s imulated a nnealing program with quantum e nergy software. the geometry of these systems was optimized by b3lyp/6-31g(d) calculations. the different generated configurations were characterized by the preferential formation of cyclic geometries. in these geometries, the primary hydrogen bonds have a fundamental role on the stability and probability of existence of these molecular aggregates.
Energías de Interacción y Geometrías de Equilibrio para Aglomeraciones de 1,2-propanodiol con 3, 4, 5 y 6 Moléculas de Agua Interaction Energies and Equilibrium Geometries for Clusters 1,2-propanediol with 3, 4, 5 and 6 Water Molecules
Adolfo E Ensuncho,Jesús M López,José G Carriazo
Información Tecnológica , 2011,
Abstract: Se reportan las geometrías de equilibrio y energías de interacción de aglomeraciones (clusters) formadas por los sistemas 1,2-propanodiol con 3, 4, 5 y 6 moléculas de agua. Esto con el fin de avanzar en la comprensión de las interacciones que predominan a nivel molecular en compuestos tipo dioles alifáticos con agua. Las aglomeraciones fueron generadas estocásticamente, seleccion adas mediante una prueba de aceptación metrópolis modificado implementado en el programa Recocido Simulado (Simulated Annealing) con Energía Cuántica y optimizados con el nivel de teoría B3LYP/6-31G(d). Las diferentes configuraciones generadas se caracterizaron por la formación preferencial de geometrías cíclicas. En estas geometrías, los enlaces de hidrógeno primario jugaron un rol fundamental en la estabilidad y probabilidad de existencia de estos agregados moleculares. The equilibrium geometries and interaction energies in clusters of 1,2-propanediol with 3,4,5 and 6 water molecules were evaluated. This was done to better comprehend the predominant interactions existing at molecular level in aliphatic diols with water. The clusters were stochastically generated and selected by using a modified metropolis acceptance test implemented in the S imulated A nnealing program with Quantum E nergy software. The geometry of these systems was optimized by B3LYP/6-31G(d) calculations. The different generated configurations were characterized by the preferential formation of cyclic geometries. In these geometries, the primary hydrogen bonds have a fundamental role on the stability and probability of existence of these molecular aggregates.
CARACTERIZACIóN ESTRUCTURAL Y TEXTURAL DE UNA BENTONITA COLOMBIANA
Carriazo,José; Molina,Rafael; Moreno,Sonia;
Revista Colombiana de Química , 2007,
Abstract: in the present work a colombian bentonite (from valle del cauca) was characterized by x-ray diffraction, spectroscopic techniques (ir, nmr and epr) and textural analysis. the results indicate that dioctahedral (aluminian) smectite is the principal component in the natural material. in addition, both 29si nmr and 27al nmr analysis reveal the isomorphous substitution of al3+ by si4+ in the tetrahedral sheet. the epr study shows iron (iii) in octahedral sheet positions of the clay mineral besides ?nanoclusters? probably in oxides or oxyhydroxides form. the textural analysis indicates that the bentonite is predominantly a mesoporous material.
EVALUACIóN DEL EFECTO DE LA IMPREGNACIóN DE PLATINO SOBRE LAS CARACTERíSTICAS SUPERFICIALES Y ESTRUCTURALES DE UNA ZEOLITA Y
Carriazo,José; Barrera,Mario; Almanza,Ovidio;
Revista Colombiana de Química , 2007,
Abstract: the present paper shows the evaluation of texture, surface and structure changes on a zeolite y employed in the synthesis of solids based on supported platinum. the structure features were analyzed by x-ray diffraction (xrd) whereas the texture and morphologic properties were studied from nitrogen adsorption isotherms (77k) and scanning electron microscopy (sem). in addition, fractal dimension and adsorption potential distribution were determinedall solids. the results show that the synthesis process induces the microporosity formation, maintaining the zeolite structure and without important topographic or energetic alterations on the surface.
CARACTERIZACIóN TéRMICA Y ESPECTROSCóPICA DE ARCILLAS PILARIZADAS CON SOLUCIONES POLIHIDROXOCATIóNICAS DE Al, Ce, Fe
Carriazo,José; Molina,Rafael; Moreno,Sonia;
Revista Colombiana de Química , 2008,
Abstract: this work shows the characterization by ir spectroscopy, thermogravimetric analysis (tga), differential thermal analysis (dta) and nuclear magnetic resonance spectroscopy (29sinmrand 27al nmr) of a set of pillared clays synthesized with al, al-fe, al-ce or al-ce-fe polyhydroxocationic solutions. tgadta analyses indicate a favorable thermal effect (higher thermal stability) when ce, fe or ce-fe are added. ir and 29si nmr results reveal a probable formation of a bond between the alumina pillar and the clay (sio4)-tetrahedral sheet, whereas the 27al nmr does not evidence any isomorphous substitution of iron or cerium in the alumina pillars. moreover, by ir spectroscopy was not observed any structural difference between solids pillared with al and those pillared with al-ce, showing that cerium is possibly incorporated in an independent way to the alumina pillar.
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