Search results for "engineering.material"
showing 10 items of 2352 documents
The Messinian salinity crisis in the Mediterranean basin: A reassessment of the data and an integrated scenario
2006
Abstract After a long period of controversial debate about the interpretation of the Messinian salinity crisis (MSC), a near consensus existed since the ODP Leg 42A for a model keeping the major lines of the deep basin-shallow water model initially proposed by Hsu et al. (1973) . The knowledge of the crisis was improved since the 1995s by the availability of a very accurate astronomically calibrated timescale. The debate about its interpretation was then reactivated by several new scenarios that questioned most the major aspects of the previous classical models. The updated re-examination of the most salient features along with consideration of the hydrological requirements for evaporite de…
Synthetic and natural chromium bearing spinels: an optical spectroscopy study
2014
Four samples of synthetic chromium-bearing spinels of (Mg, Fe2+)(Cr, Fe3+)2O4 composition and four samples of natural spinels of predominantly (Mg, Fe2+)(Al, Cr)2O4 composition were studied at ambient conditions by means of optical absorption spectroscopy. Synthetic end-member MgCr2O4 spinel was also studied at pressures up to ca. 10 GPa. In both synthetic and natural samples, chromium is present predominantly as octahedral Cr3+ seen in the spectra as two broad intense absorption bands in the visible range caused by the electronic spin-allowed 4A2g → 4T2g and 4A2g → 4T1g transitions (U- and Y-band, respectively). A distinct doublet structure of the Y-band in both synthetic and natural spine…
Thermal and structural properties of a hemp–lime biocomposite
2013
Abstract The need to reduce greenhouse gases emission produced by the building sector leads to the research of renewable and less impacting materials that can replace traditional ones. This subject has encouraged new researches on biocomposite concretes with the aim to exploit renewable resources like vegetal fibres intended as materials whose production processes are generally characterized by low costs and energy demand. This biocomposite is obviously much lighter than concrete and, therefore, can be suitably used in such cases where a structure cannot be overloaded, for instance in the realization of a green covering on top of a preexistent building. In this work, a first analysis of the…
The genesis of actively growing siliceous stromatolites: Evidence from Lake Specchio di Venere, Pantelleria Island, Italy
2010
This study documents the attributes of siliceous stromatolites growing in the Lake Specchio di Venere, on the volcanic island of Pantelleria, Italy, in a setting characterized by very shallow cold waters and pools and by scattered hydrothermal activity, which exhales mainly CO2, at emission point temperatures of 34 to 58 °C. The saturation indexes indicate that the lake waters are saturated with respect to tridymite, cristobalite, chalcedony and quartz, and slightly undersaturated with respect to amorphous silica. Common roughly laminated and poorly lithified stromatolites show scanning electron microscope (SEM) evidence for silicified microbial mat structures, including biofilms, filamento…
Advanced fragmentation stage of oxide coating on polymer substrate under biaxial tension
2005
Crack patterns of 100-nm-thick silicon oxide coating on polypropylene film subjected to equibiaxial stress loading are studied experimentally. The loading is achieved by means of a bulging cell mounted under an optical microscope with stepwise pressurization of film specimens. The evolution of the coating fragment area distribution at relatively high strains is modeled using Weibull statistics to describe the coating strength. The fragment area distribution at an advanced fragmentation stage is shown to scale with the average fragment area, the latter being a power function of the applied biaxial strain.
Control of the pore wall thickness and thermal stability in low-cost bimodal porous silicas
2019
Abstract A new hierarchical bimodal mesoporous silica, labelled as UVM-12 (acronym of University of Valencia Materials), has been prepared by using a solution of sodium silicate as low-cost silicon source. The final self-assembling between cationic micelles of CTAB and anionic inorganic Si-based oligomers occurs in a homogeneous aqueous medium. The reaction is carried out from low-sized building blocks through a bottom-up approach. The UVM-12 solids combine two mesopore systems according to N2 adsorption–desorption isotherms, what is corroborated by TEM micrographs and XRD patterns. This material has been inorganically modified by incorporation of Al or Ti (M-UVM-12, M = Al, Ti) without alt…
Reactivity of commercial silicon and silicides towards copper(I) chloride. Effect of aluminium, calcium and iron on the formation of copper silicide
1998
Abstract The reaction of CuCl with silicon, containing Al, Fe and Ca as impurities, or with silicides (Si2Ca, Si2Fe, Si2Al2Ca, Si8Al6Fe4Ca) has been investigated in the temperature range 200–300°C. For the reaction between CuCl and commercial Si, it was found that, at 282°C, aluminium promotes the reaction between Cu3Si and CuCl while the rate of consumption of Cu3Si is greatly reduced by the presence of iron. The combined action of these two impurities leads to the formation of more copper–silicon alloy. In the presence of mixed silicides, the reaction with CuCl also leads to the formation of Cu3Si. For the quaternary Al–Ca silicide containing iron the rate of formation of Cu3Si is not inc…
On-line tools for microscopic and macroscopic monitoring of microwave processing
2007
International audience; Direct monitoring of temperature, chemistry and microstructure is required to understand microwave heating in more detail, in order to fully exploit the unique features this non-equilibrium processing method can offer. In this paper, we show first that microwave radiometry can be used to follow volumetrically the thermal trajectory of microwave-heated aluminium powder. In-situ Raman spectroscopy is then shown to evidence thermal gradients between diamond and silicon grains in a binary powder mixture. Finally, perspectives and preliminary results of microstructural analysis obtained from X-ray microtomography are presented.
Separation of Nanoparticles by Gel Electrophoresis According to Size and Shape
2007
We demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer. The separation is monitored optically using the size- and shape-dependent plasmon resonance of noble metal particles and confirmed by transmission electron microscopy (TEM). Electrophoretic mobilities are quantitatively explained by a model based on the Henry formula, providing a theoretical framework for predicting gel mobilities of polymer coated nanoparticles.
Effect of surface treatment with sandblasting and Er,Cr:YSGG laser on bonding of stainless steel orthodontic brackets to silver amalgam
2011
Objectives: Satisfactory bonding of orthodontic attachments to amalgam is a challenge for orthodontists. The aim of this in vitro study was to compare the shear bond strength of stainless steel orthodontic brackets to silver amalgam treated with sandblasting and Er,Cr:YSGG laser. Study Design: Fifty-four amalgam discs were prepared, polished and divided into three groups: In group 1 (the control group) the premolar brackets were bonded using Panavia F resin cement without any surface treatment; in groups 2 and 3, the specimens were subjected to sandblasting and Er,Cr:YSGG laser respectively, before bracket bonding. After immersing in distilled water at 37°C for 24 hours, all the specimens w…