Search results for "fluoride"
showing 10 items of 314 documents
Atomic Layer Deposition of LiF Thin Films from Lithd, Mg(thd)2, and TiF4 Precursors
2013
Lithium fluoride is an interesting material because of its low refractive index and large band gap. Previously LiF thin films have been deposited mostly by physical methods. In this study a new way of depositing thin films of LiF using atomic layer deposition (ALD) is presented. Mg(thd)2, TiF4 and Lithd were used as precursors, and they produced crystalline LiF at a temperature range of 300–350 °C. The films were studied by UV–vis spectrometry, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM), time-of-flight elastic recoil detection analysis (ToF-ERDA), and energy dispersive X-ray spectroscopy (EDX). In addition, film adhesion was t…
A Combined Experimental and Theoretical Study of the Ammonium Bifluoride Catalyzed Regioselective Synthesis of Quinoxalines and Pyrido[2,3-b]pyrazines
2015
International audience; Ammonium bifluoride was efficiently used (at a 0.5 mol % loading) to catalyze the cyclocondensation between 1,2-arylenediamines and 1,2-dicarbonyl compounds at room temperature in methanol-water, affording quinoxalines and pyrido[2,3-b]pyrazines in excellent yields. Importantly, 2,8-disubstituted quinoxalines and 3-substituted pyrido[2,3-b]pyrazines were regioselectively formed by reacting aryl glyoxals with 3-methyl-1,2-phenylenediamine and 2,3-diaminopyridine, respectively. Analysis of the DFT reactivity indices allowed to explain the catalytic role of ammonium bifluoride.
Vinyl Fluorides: Competent Olefinic Counterparts in the Intramolecular Pauson–Khand Reaction
2019
Despite the great advances achieved in the Pauson-Khand reaction and the ever-increasing demand for fluorinated compounds, the use of vinyl fluorides as olefinic counterparts in the above-mentioned transformation had been completely overlooked. Herein, we describe, for the first time, the intramolecular Pauson-Khand reaction of enynes containing a vinyl fluoride moiety.
A metal-free and regioselective approach to (Z)-β-fluorovinyl sulfones and their chemoselective hydrogenation to β-fluoroalkyl sulfones
2018
Abstract A highly regioselective, metal-free hydrofluorination reaction of alkynyl sulfones was developed using TBAF—one of the cheapest and most commonly available fluoride sources. In addition, the reactivity of the resulting β-fluorovinyl sulfones was studied, focusing on their selective hydrogenation reaction. Both β-fluorovinyl sulfones and their hydrogenation products β-fluoroalkyl sulfones may find applications in medicinal and agrochemical sciences.
High-resolution spectroscopy and analysis of the nu3/2nu4 dyad of CF4
2011
International audience; CF4 is a strong greenhouse gas of both anthropogenic and natural origin [D.R. Worton et al., Environ. Sci. Technol. 41, 2184 (2007)]. However, high-resolution infrared spectroscopy of this molecule has received only a limited interest up to now. Until very recently, the public databases only contained cross-sections for this species, but no detailed line list. We reinvestigate here the strongly absorbing ν3 region around 7.8 μm. New Fourier transform infrared (FTIR) spectra up to a maximal resolution of 0.0025 cm−1 have been recorded: (i) room-temperature spectra in a static cell and (ii) a supersonic expansion jet spectrum at a 23 K estimated temperature. Following …
The high overtone and combination levels of SF6 revisited at Doppler-limited resolution: A global effective rovibrational model for highly excited vi…
2017
Abstract Sulfur hexafluoride is an important prototypal molecule for modeling highly excited vibrational energy flow and multi quanta absorption processes in hexafluoride molecules of technological importance. It is also a strong greenhouse gas of anthropogenic origin. This heavy species, however, features many hot bands at room temperature (at which only 30% of the molecules lie in the ground vibrational state), especially those originating from the lowest, v 6 =1 vibrational state. Using a cryogenic long path cell with variable optical path length and temperatures regulated between 120 and 163 K, coupled to Synchrotron Radiation and a high resolution interferometer, Doppler-limited spectr…
Nitrogen broadening of SF6 transitions in the nu3 band
2001
Abstract Nitrogen induced pressure-broadened halfwidths of a number of ν3 transitions of SF6 are calculated using the complex Robert–Bonamy (CRB) formalism. The calculations are made at 200, 250, 296 and 350 K and the temperature dependence of the halfwidths are determined. The intermolecular potential is taken as a sum of the leading electrostatic and Lennard-Jones [6] , [7] , [8] , [9] , [10] , [11] , [12] atom–atom components. The dynamics of the collision process are correct to second order in time. The calculated halfwidths are used to simulate the ν3 spectrum, which is compared to a simulation made using the HITRAN96 halfwidths and measurements made at the Universite Pierre et Marie C…
High-resolution spectroscopy and analysis of the V2 + V3 combination band of SF6 in a supersonic jet expansion
2013
International audience; Sulphur hexafluoride is a very strong greenhouse gas whose concentration is increasing in the atmosphere. It is detected through infrared absorption spectroscopy in the strong ν3 fundamental region. Due to the existence of low-lying vibrational states of this molecule, however, many hot bands arise at room temperature and those are still not known. We present here a contribution to the elucidation of this hot band structure, by analysing the ν2 + ν3 combination band. We use a supersonic jet expansion high-resolution spectrum at a rotational temperature of ca. 25 K that was recorded thanks to the Jet-AILES setup at the Source Optimisée de Lumière d'Energie Intermédiai…
Effectiveness of sodium bicarbonate combined with hydrogen peroxide and CPP-ACPF in whitening and microhardness of enamel
2017
Background: This study investigated the effects of sodium bicarbonate (NaHCO3) combined with 1.5 hydrogen peroxide (H2O2) and casein phosphopeptide amorphous calcium phosphate fluoride (CPP-ACPF) on color and microhardness of enamel. Material and Methods: Seventy-five bovine incisors were immersed in a tea solution for 7.5 days. The specimens were randomly divided into five groups according to the whitening agent applied: 1) 94 NaHCO3, 2) a blend of 94 NaHCO3 and CPP-ACPF, 3) a blend of 94 NaHCO3 and 1.5 H2O2, 4) a blend of 94 NaHCO3, 1.5 H2O2 and CPP-ACPF, 5) control. The whitening procedure was performed for 10 times over 10 days. At each day, the buccal surfaces were covered with whiteni…
Comments on "Dental lessons from past to present: Ultrastructure and composition of teeth from plesiosaurs, dinosaurs, extinct and recent sharks" by …
2016
The paper mentioned in the title suggests that several groups of extinct vertebrates used fluoroapatite as a tooth mineral in dentine and enamel when alive; its authors posit that this tooth mineralization drastically changed in all these lineages at some point during their evolution, leading to the use of hydroxyapatite as an alternative primary tooth mineral, because of hitherto unconsidered environmental changes. These conclusions are based on their finding high fluoride levels (i.e. fluoroapatite) in the dentine of fossilised shark teeth as well as in both the dentine and enamel of plesiosaurs, mosasaurs, and dinosaurs, which is in sharp contrast to recent teeth (which contain almost no…