Alberto Somoza | Universidad Nacional del Centro de la Provincia de Buenos Aires (original) (raw)

Papers by Alberto Somoza

Materials Science Forum, 2001

ABSTRACT

Materials Science Forum, 1997

ABSTRACT

Scripta Materialia, 2004

A study on the microstructural evolution with the temperature of La 3þ /ZrO 2 cubic solid solutio... more A study on the microstructural evolution with the temperature of La 3þ /ZrO 2 cubic solid solutions obtained by mechanochemical activation of mixtures ZrO 2-La 2 O 3 is presented. The development of crystallinity with thermal treatments in the range 1073-1673 K was followed by means of positron lifetime measurements and X-ray diffraction as main experimental techniques.

materiales-sam.org.ar

... ACERCA DE LA PRECIPITACIÓN EN UNA ALEACION DE AVANZADA BASE ALUMINIO ... cantidades de Ag inf... more ... ACERCA DE LA PRECIPITACIÓN EN UNA ALEACION DE AVANZADA BASE ALUMINIO ... cantidades de Ag influye notablemente sobre el proceso de termoenvejecimiento en aleaciones base aluminio que contienen Mg; además, se encontró que esta micro-adición de ...

Applied Physics A Solids and Surfaces, 1982

A simple model is developed for the trapping of positrons at grain boundaries. It is shown that t... more A simple model is developed for the trapping of positrons at grain boundaries. It is shown that there is a linear relationship between any linear annihilation parameter and the inverse grain size. An effective grain boundary width is defined, which depends on the positron diffusion length and on the strength of the grain boundary for positrons. The effect of detrapping on this effective width is also considered. The model is tested by using the experimental results available in the literature.

En este trabajo se presentan resultados preliminares del estudio con tecnicas positronicas de pas... more En este trabajo se presentan resultados preliminares del estudio con tecnicas positronicas de pasta cementicia elaborada con cemento portland sin adiciones minerales y relaciones agua/cemento en peso de 0.24, 0.40 y 0.60. Las mezclas se estacionaron en condiciones normalizadas hasta las edades de ensayo elegidas: 3, 7, 28 y 365 dias. El relevamiento experimental se efectuo usando espectrometria temporal de aniquilacion de positrones; ensayos mecanicos de compresion y flexion y microscopia electronica de barrido. En los analisis de los espectros temporales se observan cuatro componentes que representan el complejo proceso de aniquilacion de los positrones y de los atomos de positronio que se forman en los poros de la pasta. De la evolucion de la componente mas larga en funcion del tiempo de envejecimiento es posible obtener informacion acerca de la evolucion en los tamanos de los poros, dichos resultados se correlacionan con la informacion obtenida mediante ensayos mecanicos.

Sobre muestras monocristalinas de Cu-Zn-Al en la fase p (derivada de una estructura bcc) se reali... more Sobre muestras monocristalinas de Cu-Zn-Al en la fase p (derivada de una estructura bcc) se realizaron distintos tratamientos termicos de homogeinizacion, templado y recocido isotermico por diferentes lapsos de tiempo, con los cuales se retienen defectos puntuales y se inducen precipitados de la fase gamma. Con espectropia temporal de aniquilacion de positrones se siguio la evolucion posterior de los parametros caracteristicos de la tecnica, a temperatura ambiente. Dada la extrema sensibilidad de los positrones a la presencia de defectos tipo vacancia, es posible seguir con detalle la migracion de estos defectos. Se observa que la presencia de precipitados dentro de la fase matriz modifica los parametros de aniquilacion. Se discuten los resultados n en funcion del modelo standard de atrapamiento de positrones por defecto.

Se presentan resultados del relevamiento de fondo de radiacion gamma de muestras de suelo extraid... more Se presentan resultados del relevamiento de fondo de radiacion gamma de muestras de suelo extraidas en espacios abiertos del centro y entorno de la planta urbana de la Ciudad de Tandil, Provincia de Buenos Aires. La radiacion gamma se midio usando un detector coaxial de Ge-hp de 10% de eficiencia Los resultados obtenidos permitieron identificar picos caracteristicos provenientes de la emision de elementos integrantes de las series radiactivas naturales y de elementos presentes en el ambiente y/o de componentes estructurales proximos al detector. Se discuten los resultados sobre la base de otros reportados en la literatura.

Se midieron espectros de la radiacion retrodispersada en hierro, para distintos espesores y dimen... more Se midieron espectros de la radiacion retrodispersada en hierro, para distintos espesores y dimensiones laterales, como una funcion del angulo e entre la normal a la superficie del dispersor y el eje del detector. Se presentan resultados del relevamiento del numero diferencial de albedo en fw1cion de e. del numero total de albedo en funcion de las dimensiones de las placas dispersoras y las distribuciones energeticas de la radiacion retrodispersada para las fuentes utilizadas. Se propone una expresion para estimar el valor del numero total de albedo en funcion de la geometria del dispersor.

Mediante espectroscopia temporal positronica se estudia la influencia de la densidad de entrecruz... more Mediante espectroscopia temporal positronica se estudia la influencia de la densidad de entrecruzamientos (crosslink) sobre el volumen libre en el caucho butadieno de estireno (SBR) vulcanizado con diferentes estructuras de red, evaluando la variacion de volumen libre en el elastomero en funcion de la temperatura. Las diferentes estructuras de red se obtienen usando como sistema de curado sulfenoamida N-t-butil-2benzotiazol (TBBS) y diversos contenidos de azufre (entre 0.9 y 5.4 phr). Las muestras se curan a 433 K hasta alcanzar la maxima densidad de entrecruzamientos, que se determina a partir de ensayos tension-deformacion uniaxial a temperatura ambiente analizados en el marco del modelo de tubo.

Rubber Chemistry and Technology, 2021

ABSTRACT

European Polymer Journal, 2017

A study on the effect of the composition and chemical aging in tung oil-styrene networks prepared... more A study on the effect of the composition and chemical aging in tung oil-styrene networks prepared by cationic polymerization is presented. To this aim, the experimental techniques positron annihilation lifetime spectroscopy and dynamicmechanical analysis were used. The representative experimental parameters were the nanohole free volume, the glass transition temperature and the dynamic mechanical properties, storage and loss moduli and tan . The results obtained were discussed in terms of the structure of the formed network, in particular to the packing of the molecular segments and the presence of dangling chains derived from the tung oil. In the case of aged samples the results were interpreted in terms of the oxidative polymerization and degradative processes in the copolymers studied. Highlights  Tung oil-styrene networks prepared by cationic polymerization present chemical aging.  Positron annihilation lifetime spectroscopy and dynamic-mechanical analysis were used.  Higher styrene content, lower nanohole free volumes and higher Tg.  Tung oil partially inhibits the positronium formation.  The aging process enhances the efficiency of the positronium inhibition effect.

Los procesos de formacion de zonas de Guinier Preston y de precipitacion en aleaciones terrnoenve... more Los procesos de formacion de zonas de Guinier Preston y de precipitacion en aleaciones terrnoenvejecibles comerciales base Al-Zn-Mg (serie 7000), inducidos por tratamientos termicos en dos etapas, han sido estudiados con espectrometria temporal positronica y microdureza Vickers. En especial, se ha estudiado el comportamiento del tiempo de vida y la dureza para los primeros minutos de la segunda etapa de envejecimiento (envejecimiento artificial a 150°C) en donde se observa un ablandamiento inicial de las aleaciones, el cual se correlaciona con una fuerte caida en el tiempo de vida. Los parametros que caracterizan los cambios microestructurales recuperan su valor inicial como consecuencia de un posterior tratamiento de envejecimiento a temperaturas inferiores (temperatura ambiente o 70°C). Utilizando la selectividad de la tecnica positronica, se discute la cinetica de estos procesos en terminos de la reconstruccion de zonas GP, obteniendo, tambien, valores para las energias de activacion de tales procesos.

GeO 2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique an... more GeO 2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO 2 laser. The effects of CO 2 laser processing on the optical and structural properties of the waveguides were evaluated by different techniques including m-line, micro-Raman spectroscopy, atomic force microscopy, and positron annihilation spectroscopy. After laser annealing, an increase of the refractive index of approximately 0.04 at 1.5 µm and a decrease of the attenuation coefficient from 0.9 to 0.5 db/cm at 1.5 µm was observed. Raman spectroscopy and microscopy results put in evidence that the system embeds GeO 2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 µm thickness. In addition, a density value of the amorphous GeO 2 samples was evaluated.

Philosophical Magazine, 2009

The skin is the physical barrier between the fruit and the environment in which it develops. Envi... more The skin is the physical barrier between the fruit and the environment in which it develops. Environmental conditions during fruit development have a large influence on fruit quality, both at the time of harvest and during subsequent storage. It is hypothesised that some features of the skin and sub-epidermal tissues could provide information about the past growing conditions to which the fruit was exposed and therefore be of predictive value for storage quality. In this study, five commercial kiwifruit cultivars ('Hayward', 'Hort16A', 'G3', 'G9' and 'G14') were studied, and 'Hayward' fruit were manipulated during growth with different cultural practices. After harvest at horticultural maturity, X-ray micro computed tomography (CT) was used to investigate features of the skin and the immediate parenchyma tissue. Despite orchard management practices (crop load and girdling) being observed to effect macro fruit quality parameters (mass, firmness, SSC, and DM), differences in microstructure (e.g. porosity) caused by these practices were not observed. However, porosity and pore size were found to be highly variable between cultivars. The thickness of dense sub-epidermal tissue could be readily measured and the 3-D distribution of raphide bundles was visible as high density particles distributed within the parenchyma. Overall, CT was found to be a powerful technique to explore fruit epidermal and sub-epidermal structures in three dimensions at a micro level. However, the length of time required for data capture and analysis and the large number of samples required to overcome natural variation within horticultural products need to be considered. Future work may define the impact of differences in porosity or sub-epidermal anatomy on kiwifruit physiology (e.g. firmness change or sensitivity to low oxygen storage atmospheres). With this information, CT could be used as a screening tool during plant breeding, or to determine the response to agronomic treatments, without conducting lengthy storage trials.

Materials Science Forum, 2001

ABSTRACT

Materials Science Forum, 1997

ABSTRACT

Scripta Materialia, 2004

A study on the microstructural evolution with the temperature of La 3þ /ZrO 2 cubic solid solutio... more A study on the microstructural evolution with the temperature of La 3þ /ZrO 2 cubic solid solutions obtained by mechanochemical activation of mixtures ZrO 2-La 2 O 3 is presented. The development of crystallinity with thermal treatments in the range 1073-1673 K was followed by means of positron lifetime measurements and X-ray diffraction as main experimental techniques.

materiales-sam.org.ar

... ACERCA DE LA PRECIPITACIÓN EN UNA ALEACION DE AVANZADA BASE ALUMINIO ... cantidades de Ag inf... more ... ACERCA DE LA PRECIPITACIÓN EN UNA ALEACION DE AVANZADA BASE ALUMINIO ... cantidades de Ag influye notablemente sobre el proceso de termoenvejecimiento en aleaciones base aluminio que contienen Mg; además, se encontró que esta micro-adición de ...

Applied Physics A Solids and Surfaces, 1982

A simple model is developed for the trapping of positrons at grain boundaries. It is shown that t... more A simple model is developed for the trapping of positrons at grain boundaries. It is shown that there is a linear relationship between any linear annihilation parameter and the inverse grain size. An effective grain boundary width is defined, which depends on the positron diffusion length and on the strength of the grain boundary for positrons. The effect of detrapping on this effective width is also considered. The model is tested by using the experimental results available in the literature.

En este trabajo se presentan resultados preliminares del estudio con tecnicas positronicas de pas... more En este trabajo se presentan resultados preliminares del estudio con tecnicas positronicas de pasta cementicia elaborada con cemento portland sin adiciones minerales y relaciones agua/cemento en peso de 0.24, 0.40 y 0.60. Las mezclas se estacionaron en condiciones normalizadas hasta las edades de ensayo elegidas: 3, 7, 28 y 365 dias. El relevamiento experimental se efectuo usando espectrometria temporal de aniquilacion de positrones; ensayos mecanicos de compresion y flexion y microscopia electronica de barrido. En los analisis de los espectros temporales se observan cuatro componentes que representan el complejo proceso de aniquilacion de los positrones y de los atomos de positronio que se forman en los poros de la pasta. De la evolucion de la componente mas larga en funcion del tiempo de envejecimiento es posible obtener informacion acerca de la evolucion en los tamanos de los poros, dichos resultados se correlacionan con la informacion obtenida mediante ensayos mecanicos.

Sobre muestras monocristalinas de Cu-Zn-Al en la fase p (derivada de una estructura bcc) se reali... more Sobre muestras monocristalinas de Cu-Zn-Al en la fase p (derivada de una estructura bcc) se realizaron distintos tratamientos termicos de homogeinizacion, templado y recocido isotermico por diferentes lapsos de tiempo, con los cuales se retienen defectos puntuales y se inducen precipitados de la fase gamma. Con espectropia temporal de aniquilacion de positrones se siguio la evolucion posterior de los parametros caracteristicos de la tecnica, a temperatura ambiente. Dada la extrema sensibilidad de los positrones a la presencia de defectos tipo vacancia, es posible seguir con detalle la migracion de estos defectos. Se observa que la presencia de precipitados dentro de la fase matriz modifica los parametros de aniquilacion. Se discuten los resultados n en funcion del modelo standard de atrapamiento de positrones por defecto.

Se presentan resultados del relevamiento de fondo de radiacion gamma de muestras de suelo extraid... more Se presentan resultados del relevamiento de fondo de radiacion gamma de muestras de suelo extraidas en espacios abiertos del centro y entorno de la planta urbana de la Ciudad de Tandil, Provincia de Buenos Aires. La radiacion gamma se midio usando un detector coaxial de Ge-hp de 10% de eficiencia Los resultados obtenidos permitieron identificar picos caracteristicos provenientes de la emision de elementos integrantes de las series radiactivas naturales y de elementos presentes en el ambiente y/o de componentes estructurales proximos al detector. Se discuten los resultados sobre la base de otros reportados en la literatura.

Se midieron espectros de la radiacion retrodispersada en hierro, para distintos espesores y dimen... more Se midieron espectros de la radiacion retrodispersada en hierro, para distintos espesores y dimensiones laterales, como una funcion del angulo e entre la normal a la superficie del dispersor y el eje del detector. Se presentan resultados del relevamiento del numero diferencial de albedo en fw1cion de e. del numero total de albedo en funcion de las dimensiones de las placas dispersoras y las distribuciones energeticas de la radiacion retrodispersada para las fuentes utilizadas. Se propone una expresion para estimar el valor del numero total de albedo en funcion de la geometria del dispersor.

Mediante espectroscopia temporal positronica se estudia la influencia de la densidad de entrecruz... more Mediante espectroscopia temporal positronica se estudia la influencia de la densidad de entrecruzamientos (crosslink) sobre el volumen libre en el caucho butadieno de estireno (SBR) vulcanizado con diferentes estructuras de red, evaluando la variacion de volumen libre en el elastomero en funcion de la temperatura. Las diferentes estructuras de red se obtienen usando como sistema de curado sulfenoamida N-t-butil-2benzotiazol (TBBS) y diversos contenidos de azufre (entre 0.9 y 5.4 phr). Las muestras se curan a 433 K hasta alcanzar la maxima densidad de entrecruzamientos, que se determina a partir de ensayos tension-deformacion uniaxial a temperatura ambiente analizados en el marco del modelo de tubo.

Rubber Chemistry and Technology, 2021

ABSTRACT

European Polymer Journal, 2017

A study on the effect of the composition and chemical aging in tung oil-styrene networks prepared... more A study on the effect of the composition and chemical aging in tung oil-styrene networks prepared by cationic polymerization is presented. To this aim, the experimental techniques positron annihilation lifetime spectroscopy and dynamicmechanical analysis were used. The representative experimental parameters were the nanohole free volume, the glass transition temperature and the dynamic mechanical properties, storage and loss moduli and tan . The results obtained were discussed in terms of the structure of the formed network, in particular to the packing of the molecular segments and the presence of dangling chains derived from the tung oil. In the case of aged samples the results were interpreted in terms of the oxidative polymerization and degradative processes in the copolymers studied. Highlights  Tung oil-styrene networks prepared by cationic polymerization present chemical aging.  Positron annihilation lifetime spectroscopy and dynamic-mechanical analysis were used.  Higher styrene content, lower nanohole free volumes and higher Tg.  Tung oil partially inhibits the positronium formation.  The aging process enhances the efficiency of the positronium inhibition effect.

Los procesos de formacion de zonas de Guinier Preston y de precipitacion en aleaciones terrnoenve... more Los procesos de formacion de zonas de Guinier Preston y de precipitacion en aleaciones terrnoenvejecibles comerciales base Al-Zn-Mg (serie 7000), inducidos por tratamientos termicos en dos etapas, han sido estudiados con espectrometria temporal positronica y microdureza Vickers. En especial, se ha estudiado el comportamiento del tiempo de vida y la dureza para los primeros minutos de la segunda etapa de envejecimiento (envejecimiento artificial a 150°C) en donde se observa un ablandamiento inicial de las aleaciones, el cual se correlaciona con una fuerte caida en el tiempo de vida. Los parametros que caracterizan los cambios microestructurales recuperan su valor inicial como consecuencia de un posterior tratamiento de envejecimiento a temperaturas inferiores (temperatura ambiente o 70°C). Utilizando la selectividad de la tecnica positronica, se discute la cinetica de estos procesos en terminos de la reconstruccion de zonas GP, obteniendo, tambien, valores para las energias de activacion de tales procesos.

GeO 2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique an... more GeO 2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO 2 laser. The effects of CO 2 laser processing on the optical and structural properties of the waveguides were evaluated by different techniques including m-line, micro-Raman spectroscopy, atomic force microscopy, and positron annihilation spectroscopy. After laser annealing, an increase of the refractive index of approximately 0.04 at 1.5 µm and a decrease of the attenuation coefficient from 0.9 to 0.5 db/cm at 1.5 µm was observed. Raman spectroscopy and microscopy results put in evidence that the system embeds GeO 2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 µm thickness. In addition, a density value of the amorphous GeO 2 samples was evaluated.

Philosophical Magazine, 2009

The skin is the physical barrier between the fruit and the environment in which it develops. Envi... more The skin is the physical barrier between the fruit and the environment in which it develops. Environmental conditions during fruit development have a large influence on fruit quality, both at the time of harvest and during subsequent storage. It is hypothesised that some features of the skin and sub-epidermal tissues could provide information about the past growing conditions to which the fruit was exposed and therefore be of predictive value for storage quality. In this study, five commercial kiwifruit cultivars ('Hayward', 'Hort16A', 'G3', 'G9' and 'G14') were studied, and 'Hayward' fruit were manipulated during growth with different cultural practices. After harvest at horticultural maturity, X-ray micro computed tomography (CT) was used to investigate features of the skin and the immediate parenchyma tissue. Despite orchard management practices (crop load and girdling) being observed to effect macro fruit quality parameters (mass, firmness, SSC, and DM), differences in microstructure (e.g. porosity) caused by these practices were not observed. However, porosity and pore size were found to be highly variable between cultivars. The thickness of dense sub-epidermal tissue could be readily measured and the 3-D distribution of raphide bundles was visible as high density particles distributed within the parenchyma. Overall, CT was found to be a powerful technique to explore fruit epidermal and sub-epidermal structures in three dimensions at a micro level. However, the length of time required for data capture and analysis and the large number of samples required to overcome natural variation within horticultural products need to be considered. Future work may define the impact of differences in porosity or sub-epidermal anatomy on kiwifruit physiology (e.g. firmness change or sensitivity to low oxygen storage atmospheres). With this information, CT could be used as a screening tool during plant breeding, or to determine the response to agronomic treatments, without conducting lengthy storage trials.