Search results for "Silicate"

Bonding to silicate ceramics : conventional technique compared with a simplified technique

2017

Background Silicate ceramic bonding is carried out by acid-etching with hydrofluoric acid (HF) followed by an application of silane. By replacing HF with ammonium polyfluoride, contained in the same flask as the silane, the number of steps in this clinical procedure, can be reduced, while maintaining bond strength values, and reducing toxicity. A shear bond test was performed to compare the conventional and the simplified surface treatment techniques. Material and methods Twenty ceramic samples were fabricated from IPS emax CAD® ceramic (Ivoclar Vivadent) and divided into two groups (G1 and G2) (n=10). The conventional technique was applied to G1 samples, and the simplified technique to G2 …

A new hydrous Al-bearing pyroxene as a water carrier in subduction zones

2011

Abstract A new Hydrous Al-bearing PYroxene (HAPY) phase has been synthesized at 5.4 GPa, 720 °C in the MgO–Al2O3–SiO2–H2O model system. It has the composition Mg2.1Al0.9(OH)2Al0.9Si1.1O6, a C-centered monoclinic cell with a = 9.8827(2), b = 11.6254(2) c = 5.0828(1) A and β = 111.07(1)°. The calculated density is 3.175 g/cm3 and the water content is 6.9% H2O by weight. Its structure has been solved in space group C2/c by the recently developed automated electron diffraction tomography method and refined by synchrotron X-ray powder diffraction. HAPY is a single chain inosilicate very similar to pyroxenes but with three instead of two cations in the octahedral layer, bonded to four oxygens and…

A New Monte Carlo Method for the Titration of Molecules and Minerals

2007

The charge state of molecules and solid/liquid interfaces is of paramount importance in the understanding of the reactivity and the physico-chemical properties of many systems. In this work, we porpose a new Monte Carlo method in the grand canonical ensemble using the primitive model, which allows us to simulate the titration behavior of macromolecules or solids at constant pH. The method is applied to the charging process of colloidal silica particles dispersed in a sodium salt solution for various concentrations and calcium silicate hydrate nano-particles in a calcium hydroxide solution. An excellent agreement is found between the experimental and simulated results.

Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget-bearing Ca, Al-rich inclusions

2015

Tiny refractory metal nuggets are mainly observed inside Ca, Al-rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI-like liquid at reducing conditions. When quenched, minerals similar to those in…

Nanoparticles and their influence on radionuclide mobility in deep geological formations

2012

International audience; This article gives an overview of the current status of knowledge concerning the role of nanoparticles (inorganic and organic) in deep geological host rocks and the potential influence of these nanoparticles on radionuclide migration in far-field systems. The manuscript is not intended to be a full review paper or overview paper concerning nanoparticles, here the intention is to refer to recent publications but to highlight the progress made in the 6th framework project IP FUNMIG (Fundamental processes of radionuclide migration) and the open literature over the past 5 a concerning the process understanding of nanoparticle related issues in the three host rock formati…

Cosmic-ray exposure ages of pallasites

2015

We analyzed cosmogenic nuclides in metal and/or silicate (primarily olivine) separated from the main-group pallasites Admire, Ahumada, Albin, Brahin, Brenham, Esquel, Finmarken, Glorieta Mountain, Huckitta, Imilac, Krasnojarsk, Marjalahti, Molong, Seymchan, South Bend, Springwater, and Thiel Mountains and from Eagle Station. The metal separates contained an olivine fraction which although small, <1 wt% in most cases, nonetheless contributes significantly to the budgets of some nuclides (e.g., up to 35% for Ne-21 and Al-26). A correction for olivine is therefore essential and was made using model calculations and/or empirical relations for the production rates of cosmogenic nuclides in iron …

Intermediate Range Order in Silicate Melts and Glasses: Computer Simulation Studies

2002

ABSTRACTWe present the results of large scale computer simulations to discuss the structural and dynamic properties of silicate melts with the compositions (Na2O)(2·SiO2), (Na2O)(20·SiO2) and (Al2O3)(2·SiO2). We show that these systems exhibit additional intermediate range order as compared to silica (SiO2) where the characteristic intermediate length scales stem from the tetrahedral network structure. Furthermore we show that the sodium dynamics in the sodium silicate systems exhibits a very peculiar feature: the long–time decay of the incoherent intermediate scattering function can be described by a Kohlrausch law with a constant exponent β for q &gt; qth whereby qth is smaller than the l…

The dynamics of melts containing mobile ions: computer simulations of sodium silicates

2003

We present the results of large-scale computer simulations in order to discuss the structural and dynamic properties of sodium silicate melts with the compositions (Na2O)2(SiO2) (NS2) and (Na2O)20(SiO2) (NS20). We show that, compared to silica (SiO2), these systems exhibit additional intermediate range order on intermediate length scales that stem from the tetrahedral network structure. By means of intermediate-scattering functions, we characterize the dynamics of sodium in the system under consideration. Whereas in NS2 the incoherent scattering functions for Na decay much faster to zero than the coherent ones for Na–Na, in NS20 this different behaviour of the incoherent and coherent functi…

The behaviour of REEs in Thailand's Mae Klong estuary: Suggestions from the Y/Ho ratios and lanthanide tetrad effects

2007

Abstract The concentrations of Rare Earth Elements and yttrium (REY) were measured in dissolved phase, in suspended particulate matter (SPM) and in sediments in seven sampling stations in the Mae Klong estuarine system (Inner Thailand Gulf) in order to study their behaviour and distribution pattern. The analysed samples generally show high Rare Earth Element (REE) content in the dissolved phase, with high Medium Rare Earth Elements (MREEs) and Y enrichments in the shale-normalized pattern (versus PAAS). These chemical features are interpreted in terms of direct influences of weathering processes of REE-rich minerals (e.g., phosphates), which abundantly out-crop in the Mae Klong watershed. T…

2016

Raman spectroscopic data were obtained for (Mg,Fe)2SiO4 samples during compression to 57 GPa. Single crystals of San Carlos olivine compressed hydrostatically above 41 GPa showed appearance of a new “defect” peak in the 820–840 cm−1 region associated with SiOSi linkages appearing between adjacent Embedded Image tetrahedra to result in five- or sixfold-coordinated silicate species. Appearance of this feature is accompanied by a broad amorphous background. The changes occur at lower pressure than metastable crystalline transitions of end-member Mg2SiO4 forsterite (Fo-I) into Fo-II and Fo-III phases described recently. We complemented our experimental study using density functional theory (DFT…