"Propiedades estructurales y termicas de la Familia de compuestos AgIn 5 S 8 (VI= S, Se, Te... more "Propiedades estructurales y termicas de la Familia de compuestos AgIn 5 S 8 (VI= S, Se, Te)" Las entalpias de transformacion de fase son parametros importantes para la fabricacion de materiales con aplicacion en la tecnologia de celdas solares. Con respecto a los compuestos del sistema AgIn con VI= S, Se, Te, este parametro no se encuentra reportado hasta la fecha. En este trabajo se realizo el estudio de las propiedades termicas de muestras macizas policristalinas del mencionado sistema. De acuerdo a medidas de difraccion de Rayos X en polvo y de Analisis Termico Diferencial (ATD), el compuesto AgIn 5 S 8 mostro una sola fase a temperatura ambiente, con estructura cubica spinel, y los compuestos AgIn 5 Se 8 y AgIn 5 Te 8 una sola fase tetragonal. Los termogramas mostraron temperaturas de transiciones de fase que coinciden con los respectivos diagramas de fase de los sistemas pseudo-binarios Ag 2 S-In 2 S 3 , Ag 2 Se-In 2 Se 3 y Ag 2 Te-In 2 Te 3 Utilizando las areas de los picos de los termogramas se calcularon y se reportan por primera vez las entalpias de transformacion de fase de los compuestos AgIn 5 S 8 , AgIn 5 Se 8 y AgIn 5 Te 8 , siendo 51,65 Kcal/mol, 15,36 Kcal/mol y 40,26 Kcal/mol, respectivamente.
ABSTRACT Composite aerogels have been prepared by the addition of silica soot (aerosil) in the so... more ABSTRACT Composite aerogels have been prepared by the addition of silica soot (aerosil) in the solution before gelation. The fractal network previously described which results from the aggregation mechanism of the organosiloxane is strongly affected by the influence of the aerosil soot. Ultra small angle X-ray scattering measurements at ESRF show that besides the fractal network built up by the organosiloxane, the silica soot is forming another fractal structure at a higher scale. The fractal dimension characterizing the inorganic network could be interpreted as the signature of the linkage between the polymeric clusters. From a mechanical point of view, for aerosil content lower than 40 wt% , the elastic modulus is not dependent on the aerosil fractal network and the mechanical features are those of the polymeric gel.
Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low den... more Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the aerogels texture can be tailored with meso and/or macroporosity. Fractal geometry has been observed and used to describe silica aerogels at nanoscales in certain conditions. In this review paper, we describe the fractal structure of silica aerogels that can develop depending on the synthesis conditions. X-ray and neutron scattering measurements allow to show that silica aerogels can exhibit a fractal structure over one or even more than two orders of magnitude in length. The fractal dimension does not depend directly on the material density but can vary with the synthesis conditions. It ranges typically between 1.6 and 2.4. The effect of the introduction of silica part...
COVID-19 is a highly infectious disease that emerged in China at the end of 2019. The COVID-19 pa... more COVID-19 is a highly infectious disease that emerged in China at the end of 2019. The COVID-19 pandemic is the first known pandemic caused by a coronavirus, namely, the new and emerging SARS-CoV-2 coronavirus. In the present work, we present simulations of the initial outbreak of this new coronavirus using a modified transmission rate SEIR model that takes into account the impact of government actions and the perception of risk by individuals in reaction to the proportion of fatal cases. The parameters related to these effects were fitted to the number of infected cases in the 33 provinces of China. The data for Hubei Province, the probable site of origin of the current pandemic, were considered as a particular case for the simulation and showed that the theoretical model reproduces the behavior of the data, thus indicating the importance of combining government actions and individual risk perceptions when the proportion of fatal cases is greater than $$4\%$$ 4 % . The results show ...
Research is in progress to incorporate nuclear waste in new matrices with high structural stabili... more Research is in progress to incorporate nuclear waste in new matrices with high structural stability, resistance to thermal shock, and high chemical durability. Interactions with water are important for materials used as a containment matrix for the radio nuclides. It is indispensable to improve their chemical durability to limit the possible release of radioactive chemical species, if the glass structure is attacked by corrosion. By associating high structural stability and high chemical durability, silica glass optimizes the properties of a suitable host matrix. According to an easy sintering stage, nanoporous glasses such as xerogels, aerogels, and composite gels are alternative ways to synthesize silica glass at relatively low temperatures (≈1,000–1,200°C). Nuclear wastes exist as aqueous salt solutions and we propose using the open pore structure of the nanoporous glass to enable migration of the solution throughout the solid volume. The loaded material is then sintered, thereby...
"Propiedades estructurales y termicas de la Familia de compuestos AgIn 5 S 8 (VI= S, Se, Te... more "Propiedades estructurales y termicas de la Familia de compuestos AgIn 5 S 8 (VI= S, Se, Te)" Las entalpias de transformacion de fase son parametros importantes para la fabricacion de materiales con aplicacion en la tecnologia de celdas solares. Con respecto a los compuestos del sistema AgIn con VI= S, Se, Te, este parametro no se encuentra reportado hasta la fecha. En este trabajo se realizo el estudio de las propiedades termicas de muestras macizas policristalinas del mencionado sistema. De acuerdo a medidas de difraccion de Rayos X en polvo y de Analisis Termico Diferencial (ATD), el compuesto AgIn 5 S 8 mostro una sola fase a temperatura ambiente, con estructura cubica spinel, y los compuestos AgIn 5 Se 8 y AgIn 5 Te 8 una sola fase tetragonal. Los termogramas mostraron temperaturas de transiciones de fase que coinciden con los respectivos diagramas de fase de los sistemas pseudo-binarios Ag 2 S-In 2 S 3 , Ag 2 Se-In 2 Se 3 y Ag 2 Te-In 2 Te 3 Utilizando las areas de los picos de los termogramas se calcularon y se reportan por primera vez las entalpias de transformacion de fase de los compuestos AgIn 5 S 8 , AgIn 5 Se 8 y AgIn 5 Te 8 , siendo 51,65 Kcal/mol, 15,36 Kcal/mol y 40,26 Kcal/mol, respectivamente.
ABSTRACT Composite aerogels have been prepared by the addition of silica soot (aerosil) in the so... more ABSTRACT Composite aerogels have been prepared by the addition of silica soot (aerosil) in the solution before gelation. The fractal network previously described which results from the aggregation mechanism of the organosiloxane is strongly affected by the influence of the aerosil soot. Ultra small angle X-ray scattering measurements at ESRF show that besides the fractal network built up by the organosiloxane, the silica soot is forming another fractal structure at a higher scale. The fractal dimension characterizing the inorganic network could be interpreted as the signature of the linkage between the polymeric clusters. From a mechanical point of view, for aerosil content lower than 40 wt% , the elastic modulus is not dependent on the aerosil fractal network and the mechanical features are those of the polymeric gel.
Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low den... more Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the aerogels texture can be tailored with meso and/or macroporosity. Fractal geometry has been observed and used to describe silica aerogels at nanoscales in certain conditions. In this review paper, we describe the fractal structure of silica aerogels that can develop depending on the synthesis conditions. X-ray and neutron scattering measurements allow to show that silica aerogels can exhibit a fractal structure over one or even more than two orders of magnitude in length. The fractal dimension does not depend directly on the material density but can vary with the synthesis conditions. It ranges typically between 1.6 and 2.4. The effect of the introduction of silica part...
COVID-19 is a highly infectious disease that emerged in China at the end of 2019. The COVID-19 pa... more COVID-19 is a highly infectious disease that emerged in China at the end of 2019. The COVID-19 pandemic is the first known pandemic caused by a coronavirus, namely, the new and emerging SARS-CoV-2 coronavirus. In the present work, we present simulations of the initial outbreak of this new coronavirus using a modified transmission rate SEIR model that takes into account the impact of government actions and the perception of risk by individuals in reaction to the proportion of fatal cases. The parameters related to these effects were fitted to the number of infected cases in the 33 provinces of China. The data for Hubei Province, the probable site of origin of the current pandemic, were considered as a particular case for the simulation and showed that the theoretical model reproduces the behavior of the data, thus indicating the importance of combining government actions and individual risk perceptions when the proportion of fatal cases is greater than $$4\%$$ 4 % . The results show ...
Research is in progress to incorporate nuclear waste in new matrices with high structural stabili... more Research is in progress to incorporate nuclear waste in new matrices with high structural stability, resistance to thermal shock, and high chemical durability. Interactions with water are important for materials used as a containment matrix for the radio nuclides. It is indispensable to improve their chemical durability to limit the possible release of radioactive chemical species, if the glass structure is attacked by corrosion. By associating high structural stability and high chemical durability, silica glass optimizes the properties of a suitable host matrix. According to an easy sintering stage, nanoporous glasses such as xerogels, aerogels, and composite gels are alternative ways to synthesize silica glass at relatively low temperatures (≈1,000–1,200°C). Nuclear wastes exist as aqueous salt solutions and we propose using the open pore structure of the nanoporous glass to enable migration of the solution throughout the solid volume. The loaded material is then sintered, thereby...
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Papers by Juan Primera