Search results for " silice"

Sintesi e caratterizzazione di compositi polimetilmetacrilato e nano-SiO2, -TiO2 o -ZrO2

2011

Biomineralization events in Recent volcanic and sedimentary settings: textural features and isotope signatures.

2008

Micromorphological approach to the systematics of Mediterranean Isoëtes species (Isoëtaceae, Lycopodiophyta): analysis of the megaspore surface

2012

Megaspore ornamentation is one of the few morphological characters used in the taxonomy of the genus Isoëtes. In the present work, we test the application of this character for distinguishing some Isoëtes species occurring in the Mediterranean: Isoëtes sicula, which according to some authors should be included as a variety in I. histrix, and the recently described I. todaroana, whose affinity with other taxa is currently unknown. Two additional species (I. duriei, I. velata) were also included in the analysis. The megaspores were studied using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and chemical treatment. In all species, the megaspore surface is cove…

Physico-chemical evolution of low-pH cements : influence of the temperature and the retention mechanisme of alkalins

2010

Because of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50°C or 80…

NANO-EMETTITORI NIR A BASE DI SILICE PER APPLICAZIONI IN-VIVO E RELATIVO PROCESSO DI PRODUZIONE

2010

Realizzazione di nano-sonde paramagnetiche e fosforescenti, ottenibili a partire da particelle nanometriche di silice mediante procedure di sintesi e arricchimento di O2 a seguito di opportuni trattamenti termici in ambiente controllato. Le nano-sonde così ottenute presentano emissioni nel vicino infrarosso (NIR), sono eccitabili nel visibile e nel NIR, e sono caratterizzate da un tempo di vita nell’ordine del secondo. Tali nano-sonde presentano un notevole potenziale scientifico e commerciale nel mercato della spettroscopia confocale per bio-imaging e nel mercato delle applicazioni medico-farmaceutiche di drug-labelling e drug-delivery.

Structural and luminescence properties of amorphous SiO2 nanoparticles

2011

We report an experimental study on the photoluminescence band peaked at 2.7 eV (blue band) induced by thermal treatments in nanometric amorphous SiO 2. In particular the emission dependence on the nanometric particles size as a function of their mean diameter from 7 nm up to 40 nm is investigated. We found that the emission amplitude increases on decreasing the particle diameter, showing a strong correlation between the blue band and the nanometric nature of the particles. By Raman spectroscopy measurements it is evidenced that the SiO2 nanoparticles matrix is significantly affected by the reduction of size. Basing on the shell-like model, these findings are interpreted assuming that the de…

Irradiation Effects in Optical Fibers

2010

Intrinsic and extrinsic optical fiber-based sensors are promising devices to be used in very different and complex environments, by their very nature: capabilities to work under electromagnetic fields; possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass; ability to handle multi-parameter measurements in distributed configuration; possibility to monitor sites far away from the controller. In the case of the optical fibers, the possibility to be incorporated into various types of sensors and actuators, free of additional hazards (i.e. fire, explosion), made them promising candidates to operate in adverse conditions as those required by space appli…

Formation of optically active oxygen deficient centers in Ge-doped SiO2 by γ- and β-ray irradiation

2010

Abstract We report an experimental study on the comparison between the γ- or β-ray induced Ge related point defects in Ge-doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol–gel technique have been irradiated with γ-ray or with β-ray. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E’Ge, GLPC (Germanium lone pair center) and H(II) point defects. No relevant differences between the concentrations of γ- or β-ray induced Ge(1) and E’Ge point defects have been observed and, in addition, it ha…