In this work we have synthesized and characterized new hybrid nanoplatforms for luminescent biolabeling based on the concept of Eu3+complexes encapsulation in mesoporous silica nanoparticles (≈100 nm). Eu complexes have been selected on the basis of their capability to be excited at 365 nm which is a currently available wavelength, on routine epifluorescence microscope. For Eu complexes encapsulation, two different routes have been used: the first route consists in grafting the transition metal complex into the silica wall surface. The second way deals with impregnation of the mesoporous silica NPs with the Eu complex. Using the second route, a silica shell coating is realized, to prevent any dye release, and the best result has been obtained using Eu-BHHCT complex. However, the best solution appears to be the grafting of Eu(TTA)3-Phen-Si to mesoporous silica NPs. For this hybrid, mSiO2-Eu(TTA)3(Phen-Si) full characterization of the nanoplatforms is also presented.
The mineral constituents of a typical clay from Campos dos Goytacazes, Brazil, were investigated in terms of their nature and morphology by analytical methods including transmission electron microscopy and energy dispersive spectroscopy. The clay was found to have a large amount of finer, < 2 μm, aluminumsilicate particles of kaolinite and, in smaller proportion, halloysite, which is also an aluminumsilicate. At 1050oC the clay shows a consolidated structure with continuous glassy matrix in which Ti, Fe and Si oxides as well as mullite crystals are thoroughly embedded.
The Cu-Co system has been investigated as a precipitation-hardening alloy for several years using various experimental techniques, especially TEM [1]. These alloys can develop microstructures which promote new interesting magnetic properties such as giant magneto resistance effect (GMR). It has been reported that there are two different precipitation mechanisms occurring in the decomposition of these alloys: homogeneous and heterogeneous precipitation [1].The alloy composition we are currently investigating ranges from 1 to 4 at% Co, with the balance being Cu. The samples were homogenized about 30 minutes in the single phase region, quenched and then cold rolled (70%) and reanelled in order to promote recrystallization and generated a fine grain size. Isothermal aging treatments were then conducted at temperatures of 500 to 700 0 C. Thin specimens for TEM analysis were prepared using the double jet technique in a solution composed, in volume, of 30% nitric acid and 70% methanol, kept at -20 0 C.In the homogeneous mode of decomposition, it is observed in all studied conditions, the presence of Co precipitates which are spherical and coherent with the matrix. These precipitates of about 20 nm in size show a typical strain field contrast due to elastic distortions of the matrix around the particles, Fig. 1. Hardening is due to the precipitation of these coherent spherical particles. The coexistence of nano-scale coherent precipitates together with micro-scale incoherent precipitates was observed to occur at higher temperatures; the latter forming well developed faceted Co crystals, incoherent with the matrix and ranging from 0.1 to 0.6 in size as shown in Fig. 2.Discontinuous precipitation (DP) occurred at some grain boundaries under conditions of aging at significant undercooling below the solubility limit and for short times. The samples presenting DP show rod-like particles with regular inter-rod spacing. In general, the rods are not perfect, having a break down along its length. The rare presence of true rods is due to shape instability, especially at high temperatures, where volume diffusion dominates the process [2]. An interesting feature of DP product observed in this system is related to a coagulation process, in which a rod transforms into a columnar array of spherical coherent particles. These spheres are thought to be formed as a consequence of Rayleigh instability [2]. Also, the mobility of the grain boundary is low and attributed to the presence of general coherent particles which form ahead of the reaction front. Analytical TEM has been applied to detect the nature of these particles. EDS line profiles across a particle, stopping the probe at 6 nm intervals, corroborate that are Co-rich metastable precipitates, as shown in Fig. 3. Typical nanostructural configuration of this system results from a combination of DP of rods driven by migration boundaries together with conventional heterogeneous precipitation at the same boundary when this has seased to migrate, leaving behind an alignment of rods (when ...
Over the past few decades, considerable effort has been directed towards the study of Al-Li base alloys. This has been largely motivated by the appreciable improvement in the specific properties the presence of Li brings about. However, the use of Cu, Mg and Zr as additional alloying elements has been a common practice with the objective of promoting the formation of more uniformly distributed second phase precipitates, thus considerably improving both the monotonic and cyclic mechanical behaviors over those of binary Al-Li alloys. [1,2] The material used for the present work was an 8090 T3 Al-Li base alloy supplied by Pechiney Recherche in the form of a 3.3 mm thick plate, having the following chemical composition (in weight %): 2.4 Li; 1.2 Cu; 0.6 Mg; 0.12 Zr; balance Al. 608
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