Diseño e implementación de un laboratorio virtual para el estudio de "Defectos puntuales en cristales iónicos"

El programa: Diseño e implementación de un laboratorio virtual para el estudio de "Defectos puntuales en cristales iónicos" enseña de forma interactiva las reglas de balance necesarias para escribir las ecuaciones de defectos en los cristales iónicos, usando la notación de Kröger-Vink para los defectos puntuales

Cobalt (II) environment characterization in sol-gel thermochromic sensors

Optical absorption and magnetic properties of silica sol-gel monoliths doped with cobalt starting from different precursors and water/1-propanol molar ratios are investigated. Structural characterization of the sol-gel by X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy corroborate, that oxidising state of cobalt is Co^(2+). Furthermore, the Co^(2+) first neighbors are O atoms displaying a temperature transition from octahedral to tetrahedral coordination. The doped monoliths show thermochromic sensor activity ranging from 10 to 50⁰ C, which is related to the environment of Co^(2+) ions. The magnetic susceptibility also varies with Co^(2+) ions environment due to changes in the orbital contribution to the magnetic moment. Thus, we achieve a better understanding about environment of the Co^(2+) ions in the gel matrix and explain their reversible temperature behaviour in spite of the rigid state of the host matrix

Glass and grisailles of the 15th century from the Cartuja de Miraflores (Burgos): characterisation and state of conservation

Producción CientíficaEste trabajo presenta los resultados de la caracterización fisicoquímica y el diagnóstico del estado actual de conservación de una muestra representativa de vidrios y grisallas procedentes de vidrieras flamencas del s. XV del Monasterio de la Cartuja de Miraflores (Burgos). El objetivo principal del estudio consistió en determinar los mecanismos y las causas de los importantes procesos de degradación y alteración observados en las superficies de los vidrios utilizados en estas vidrieras, con el fin de proponer medidas para su conservación preventiva. Las muestras seleccionadas se caracterizaron mediante microscopía óptica (MO), espectroscopía de absorción UV/Vis, fluorescencia de rayos X (FRX), microscopía electrónica de barrido de emisión de campo (MEBEC) y convencional (MEB) y microanálisis de dispersión de energía de rayos X (EDX). La composición química de los vidrios estudiados permite su clasificación como vidrios potásico-cálcicos de transición entre los períodos medieval y renacentista. Los resultados indican que estos vidrios han sufrido una alteración muy severa con una intensa desalcalinización superficial, destrucción de la red estructural vítrea y formación de depósitos insolubles procedentes de los productos de corrosión, que puede atribuirse al efecto sinérgico de los procesos de degradación química y de una actividad biológica.This paper reports the results derived from a combined physicochemical characterisation and state of conservation diagnosis study undertaken on a representative ensamble of 15th century Flemish stained glasses and grisailles from the Cartuja de Miraflores Monastery (Burgos, Spain). The main goal of the research was to determine the mechanisms and causes of the important degradation and alteration processes observed on the surfaces of these glasses, in order to propose preventive conservation steps. Selected samples were charecterised by optical microscopy (OM), UV/Vis spectrophotometry, X-ray fluorescence (XRF), field emission and conventional scanning electron microscopy (FESEM and SEM) and energy dispersive X-ray microanalysis (EDX). The chemical composition of the glasses studied allows their classification as potassium-lime silicate glasses of the Medieval-Renaissance transitional period. Resulting data indicate that these glasses have experienced a very harsh alteration with a strong superficial dealkalinisation, destruction of the glass structural network and formation of insoluble deposits from corrosion by-products, which can be attributed to the synergic effect of chemical degradation processes and biological activity.Madrid Ciencia y Tecnología (Proyecto MAT2002-02549

Hybrid sol-gel coatings doped with non-toxic corrosion inhibitors for corrosion protection on AZ61 magnesium alloy

Physiological human fluid is a natural corrosive environment and can lead to serious corrosion and mechanical damages to light Mg-Al alloys used in prosthetics for biomedical applications. In this work, organic-inorganic hybrid coatings doped with various environmentally friendly and non-toxic corrosion inhibitors have been prepared by the sol-gel process for the corrosion protection of AZ61 magnesium alloys. Effectiveness has been evaluated by pH measurements, optical microscopy, and SEM during a standard corrosion test in a Hanks' Balanced Salt Solution. The results showed that the addition of an inhibitor to the sol-gel coating can improve significantly the corrosion performance, being an excellent barrier for the L-cysteine-doped hybrid sol-gel films. The incorporation of TiO2 nanoparticles, 2-Aminopyridine and quinine organic molecules slowed down the corrosion rate of the Mg-Al alloy. Graphene oxide seemed to have the same response to corrosion as the hybrid sol-gel coating without inhibitors

Correction: A feasible pathway to stabilize monoclinic and tetragonal phase coexistence in barium titanate-based ceramics

Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

A feasible pathway to stabilize monoclinic and tetragonal phase coexistence in barium titanate-based ceramics

Multiphase coexistence has attracted significant interest in recent years because its control has entailed a significant breakthrough for the piezoelectric activity enhancement of lead-free piezoelectric oxides. However, the comprehension of phase coexistence still has many controversies including an adequate synthesis process and/or the role played by crystalline phases in functional properties. In this study, functional barium titanate [BaTiO_(3), (BTO)]-based materials with tunable functional properties were obtained by compositional modification via Bismuth (Bi) doping. Towards this aim, we systematically synthesized BTO-based materials by a sol-gel method, focusing on the control of Bi substitution in the BaTiO_(3) structure. In particular, we found that the substitution of Bi^(+3) leads to the stabilization of a monoclinic-tetragonal (M-T) phase boundary close to room temperature, which facilities the polarization process of the system. As a surprising result, we believe that the simple and cost-effective strategy and design principles described in this work open up the possibility of obtaining BTO-based lead-free ceramics with enhanced properties induced by the stabilization of the phase coexistence, expanding their application range

Self-assembly of iron oxide precursor micelles driven by magnetic stirring time in sol-gel coatings

The purpose of this work is to fabricate self-assembled microstructures by the sol-gel method and study the morphological, structural and compositional dependence of epsilon-Fe_2O_3 nanoparticles embedded in silica when glycerol (GLY) and cetyl-trimethylammonium bromide (CTAB) are added as steric agents simultaneously. The combined action of a polyalcohol and a surfactant significantly modifies the morphology of the sample giving rise to a different microstructure in each of the studied cases (1, 3 and 7 days of magnetic stirring time). This is due to the fact that the addition of these two compounds leads to a considerable increase in gelation time as GLY can interact with the alkoxide group on the surface of the iron oxide precursor micelle and/or be incorporated into the hydrophilic chains of CTAB. This last effect causes the iron oxide precursor micelles to be interconnected forming aggregates whose size and structure depend on the magnetic stirring time of the sol-gel synthetic route. In this paper, crystalline structure, composition, purity and morphology of the sol-gel coatings densified at 960 degrees C are examined. Emphasis is placed on the nominal percentage of the different iron oxides found in the samples and on the morphological and structural differences. This work implies the possibility of patterning epsilon-Fe_2O_3 nanoparticles in coatings and controlling their purity by an easy one-pot sol-gel method

Miniaturized Devices For Au Nanorods Detection

We present here some miniaturised devices designed for the detection of nanorods in water and blood media. The devices use light emitting diodes as monochromatic light sources and Si photodiodes for detection. Devices working on transmission mode are able to detect nanorods concentration below micrograms/litre. Sensitivity is reduced is one or of magnitude for nanorods in blood. We show detection of low nanorods concentration with devices working in reflection mode, opening the possibility to perform direct imaging of nanorods in vivo. The optima condition for detection and resolution limits are also discussed

Evidence of intrinsic magnetism in capped ZnO nanoparticles

We present here direct experimental evidence of the magnetic polarization of Zn atoms in ZnO nanoparticles capped with different materials by means of x-ray magnetic circular dichroism (XMCD). Our results demonstrate that the magnetism in this material is intrinsic and relays in the ZnO conduction band. The analysis of both x-ray absorption spectroscopy and XMCD signals points out the formation of a well-defined interface between ZnO and the capping molecule in which the exotic magnetism arises at the hybridized band formed among Zn and the bonding atom of the molecule. The magnetic properties of these systems should critically depend on the details of this interface which may offer a new insight into the different observations for seemingly identical materials