Search results for "Silicate"
showing 10 items of 413 documents
Clinical evaluation of an Er:YAG laser combined with scaling and root planing for non-surgical periodontal treatment
2003
Objectifs: le but de cette etude clinique controlee etait de comparer les traitements de maladie parodontale avancee par une association de laser Er:YAG (KEY II®, KaVo, Germany) et de detartrage et surfacage radiculaire manuels (SRP) avec le laser seul. Materiel & Methodes: 20 patients sains presentant des destructions parodontales moderees a avancees furent traites au hasard en bouche divisee par une association de laser Er:YAG et de detartrage et surfacage radiculaire manuels (SRP) (test) et le laser seul (controle). L'energie utilisee en reglage pour le laser etait de 160 mJ/pulsation a un taux de repetition de 10 Hz. Prealablement au traitement, et 3, 6 etl2 mois apres, les parametres s…
Aqueous solubility diagrams for cementitious waste stabilization systems. 3. Mechanism of zinc immobilizaton by calcium silicate hydrate.
2002
Zinc oxide was added during hydration of alite (C3S) as an analogue for solidification/stabilization by cement of metal-bearing hazardous waste. Curing of samples was stopped at various intervals between 8 h and 100 d, and the reaction products were analyzed by both X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS at Zn, Ca, and Si K-edges). Calcium zincate hydrate (CaZn2(OH)6 x 2H2O) initially formed together with calcium silicate hydrate (CSH) vanishes from X-ray diffractograms after 14 d, and no other crystalline Zn-bearing phase could be detected thereafter. EXAFS Zn K-edge data analysis reveals that Zn(O,OH)4 tetrahedra continue to determine the first shell coordination…
From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling
2015
Abstract It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca 4 H 4 Si 5 O 16 , Ca 2 H 2 Si 2 O 7 and Ca 6 (HSi 2 O 7 ) 2 (OH) 2 , respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups v…
Effect of NiO and/or TiO2 mullite formation and microstructure from gels
1998
Polymeric and colloidal gels with a constant molar ratio of (Al+Ni and/or Ti)/Si=3/1 and various (Al/Ni and/or Ti) ratios (up to 21.42 mol% NiO+TiO2) were prepared and used to study the effect of the precursor chemical homogeneity on mullite formation processes and the resulting microstructure. Both kinds of gel precursors were preheated at 750°C for 3 h in order to obtain appropriate gel-derived glasses for further thermal processing. After annealing for several time periods at temperatures between 750 and 1500°C, differences in crystallization pathways were observed. Polymeric gels crystallized Al–Si and NiAl2O4 spinels from the amorphous form at temperatures in the range between 900 and …
New insights in the formation of silanol defects in silicalite-1 by water intrusion under high pressure.
2010
International audience; The "water-silicalite-1" system is known to act as a molecular spring. The successive intrusion-extrusion cycles of liquid water in small crystallites (6 × 3 × 0.5 μm(3)) of hydrophobic silicalite-1 were studied by volumetric and calorimetric techniques. The experiments displayed a decrease of the intrusion pressure between the first intrusion-extrusion cycle and the consecutive ones, whereas the extrusion pressures remained unchanged. However, neither XRD studies nor SEM observations revealed any structural and morphological modifications of silicalite-1 at the long-range order. Such a shift in the value of the intrusion pressure after the first water intrusion-extr…
The Structure, Stoichiometry and Properties of C-S-H Prepared by C3S Hydration Under Controlled Condition
1998
Hydrations of tricalcium silicate undertaken by keeping constant lime concentration in solution in an open system and in diluted suspensions for different values of [CaO] ranging between 6.5 and 30 mmol/1 show that the lime concentration in solution is the parameter which determines the main characteristics of the reaction and products. The stoichiometry of C3S hydration products vanes with lime concentration in the same way as synthetic C-S-H until C/S c.a. 1.5 corresponding to about [CaO] =20 mmol/1. Beyond this concentration, single phase C-S-H samples were obtained with 1.8<C/S<2. The discontinuity of the variation of stoichiometry with concentration is characteristic of an invariant po…
Selective Antimicrobial Effects of Curcumin@Halloysite Nanoformulation: A Caenorhabditis elegans Study
2019
Alterations in the normal gastrointestinal microbial community caused by unhealthy diet, environmental factors, and antibiotic overuse may severely affect human health and well-being. Novel antimicrobial drug formulations targeting pathogenic microflora while not affecting or even supporting symbiotic microflora are urgently needed. Here we report fabrication of a novel antimicrobial nanocontainer based on halloysite nanotubes loaded with curcumin and protected with a dextrin outer layer (HNTs+Curc/DX) and its effective use to suppress the overgrowth of pathogenic bacteria in Caenorhabditis elegans nematodes. Nanocontainers have been obtained using vacuum-facilitated loading of hydrophobic …
Solubility of Zn(II) in Association with Calcium Silicate Hydrates in Alkaline Solutions
1999
The binding of Zn(II) to the cement mineral calcium silicate hydrate (CSH) was investigated in a well-defined laboratory system. CSH (Ca:Si = 1:1) was synthesized by coprecipitation with varying contents of Zn(II). Zn(II) was added in the proportions 0, 0.1, 1.0, 5.0, and 10% in exchange for Ca. The resulting CSH was characterized by X-ray diffraction. The solid phases were then equilibrated in aqueous suspensions, and the solubilities of Ca, Si, and of Zn(II) were determined as a function of pH and Zn(II) content in the solid phase. The solubility of Ca and Si in equilibrium with the CSH phases was in agreement with that predicted by thermodynamic calculations. Dissolved Zn(II) concentrati…
Triple-Quantum Two-Dimensional 27Al Magic Angle Nuclear Magnetic Resonance Study of the Aluminum Incorporation in Calcium Silicate Hydrates
1998
Triple-quantum two-dimensional 27Al magic angle spinning nuclear magnetic resonance (27Al 3Q-MAS NMR) was used to characterize the substitution of Si4+ by Al3+ into the Te−Oc−Te structure of calcium silicate hydrates (C−S−H). This substitution was studied with C−S−H having an Oc/Te ratio of 1 and in equilibrium with Al(OH)3 in aqueous suspensions. In the absence of NaOH, no substitution into the C−S−H structure occurred. Addition of NaOH in the preparation increased the concentration of Al(OH)4- and favored substitution. The deficit of charge resulting from this substitution was compensated by the accommodation of sodium in the interlayer space of the C−S−H. Increasing levels of substituted…
Expanding the atrane route: Generalized surfactant-free synthesis of mesoporous nanoparticulated xerogels
2008
Abstract A diversity of silica-based and non-silica nanoparticulated mesoporous xerogels have been synthesized from aqueous solution using a surfactant-free strategy, and starting from molecular atrane complexes as precursors. This approach constitutes an extension of the “atrane route” previously described for the surfactant-assisted synthesis of mesoporous materials, and allows us to unify the multiplicity of protocols described for the preparation of conventional xerogels. In fact, we have used exactly the same preparative conditions for obtaining all the compositions reported here. The xerogels synthesized in this way include pure silica (UVM-11), aluminosilicates and titanosilicates (M…