Search results for "Pressure"
showing 10 items of 4493 documents
The synthesis of zeolites from dry powders
1995
Summary ZSM-5 was synthesized by different methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO 2 * Al 2 O 3 gels at 650°C were transformed into zeolites in the presence of dried NH 4 F and TPABr. The reaction products were characterized by XRD, REM, TG/DTA, MAS NMR and Electron Micropobe. Pure ZSM-5 or Silicalite-1 was obtained in all cases. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure at the given reaction conditions. To explain the formation of…
Internal ion impact ionization for Fourier-transform ion cyclotron resonance
1994
A general scheme for ionization and fragmentation of ions in Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICRMS) is introduced. The technique is based upon excitation of high-frequency (i.e. lowmass) primary ions (e.g. N, Al+, H2O+·) which may be generated by standard ionization methods (e.g. electron ionization or laser desorption) inside the trap. Generation of the primary ions is followed by excitation of their cyclotron motion to high translational energy to serve as projectile ions. The projectiles serve two functions: to ionize neutral gas atoms and/or molecules (secondary ions) within the trap internal ion impact ionization (IIII), and to collisionally activate the…
Determination of bisphenol diglycidyl ether residues in canned foods by pressurized liquid extraction and liquid chromatography–tandem mass spectrome…
2005
Abstract A new confirmatory method for simultaneous determination of bisphenol diglycidyl ether residues (BADGE, BADGE·H2O, BADGE·2H2O, BADGE·H2O·HCl, BADGE·HCl, BADGE·2HCl, BFDGE and BFDGE·2HCl) from canned food has been developed. The proposed method includes extraction by pressurized liquid extraction (PLE) followed by liquid–liquid partition and purification by solid phase extraction (SPE). Several solvent systems and different operating conditions (time, temperature) have been investigated for PLE optimization. A reversed-phase high-performance liquid chromatography (RP-HPLC) coupled to atmospheric pressure chemical ionisation tandem mass spectrometry (APCI-MS–MS) method was developed …
Determination of a three-step excitation and ionization scheme for resonance ionization and ultratrace analysis of Np-237
2011
Abstract The long-lived radio isotope 237 Np is generated within the nuclear fuel cycle and represents a major hazard in the final disposal of nuclear waste. Related geochemical research requires sensitive methods for the detection of ultratrace amounts of neptunium in environmental samples. Resonance ionization mass spectrometry (RIMS) has proven to be one of the most sensitive methods for the detection of plutonium. A precondition for the application of RIMS to ultratrace analysis of neptunium is the knowledge of an efficient and selective scheme for optical excitation and ionization. Therefore, a multitude of medium to high-lying atomic levels in neptunium was located by applying in-sour…
The influence of water and of alkali promotor on the carbon number distribution of fischer-tropsch products formed over iron catalysts
1987
The carbon number distribution of Fischer-Tropsch products formed over an alkalized precipitated iron catalyst has been studied as a function of the water vapor pressure of the synthesis gas. The carbon number distribution of formed hydrocarbons is characterized by a bimodal Schulz-Flory distribution of growth probabilities P1 ≈ 0.6 and P2 ≈ 0.87 attributed to unpromoted and promoted (alkalized) sites on the catalyst surface. Promoted sites are more stable with respect to oxidation (deactivation) by water than unpromoted sites. The growth probability of unpromoted sites decreases with increasing ratio P/P — Studies using Mossbauer spectroscopy have shown that iron foils treated with water c…
Modelling the Reverse ElectroDialysis process with seawater and concentrated brines
2012
Technologies for the exploitation of renewable energies have been dramatically increasing in number, complexity and type of source adopted. Among the others, the use of saline gradient power is one of the latest emerging possibilities, related to the use of the osmotic/chemical potential energy of concentrated saline solutions. Nowadays, the fate of this renewable energy source is intrinsically linked to the development of the pressure retarded osmosis and reverse electrodialysis technologies. In the latter, the different concentrations of two saline solutions is used as a driving force for the direct production of electricity within a stack very similar to the conventional electrodialysis …
Vibronic Relaxation Pathways in Molecular Spin Qubit Na9[Ho(W5O18)2]·35H2O under Pressure
2023
In order to explore how spectral sparsity and vibronic decoherence pathways can be controlled in a model qubit system with atomic clock transitions, we combined diamond anvil cell techniques with synchrotron-based far infrared spectroscopy and first-principles calculations to reveal the vibrational response of Na9[Ho(W5O18)2]·35H2O under compression. Because the hole in the phonon density of states acts to reduce the overlap between the phonons and f manifold excitations in this system, we postulated that pressure might move the HoO4 rocking, bending, and asymmetric stretching modes that couple with the MJ = ±5, ±2, and ±7 levels out of resonance, reducing their …
The lithium isotope response to the variable weathering of soils in Iceland
2021
Abstract This study has analysed Li isotopes ratios from well-studied soil and pore water profiles from Iceland that have the same parent material but have experienced different degrees of chemical weathering. Thus, from least to most weathered, we have analysed vitrosols (V), gleyic andosols (GA), brown andosols (BA), Histosols (H) and Histic Andosols (HA). Although the most weathered H and HA soils have the highest content in clay-sized material, they have the least fractionated δ7Lipore water values. In contrast, the least weathered GA and BA pore waters are most fractionated for Li isotopes. Given that Li isotope ratios are fractionated by clay mineral formation, this appears counter-in…
Supramolecular assembly using helical peptides
1997
Abstract We investigated supramolecular assemblies of various hydrophobic helical peptides. The assemblies were formed at the air/water interface or in aqueous medium. The hexadecapeptide, Boc-(Ala-Aib)8-OMe (BA16M), was reported to take α-helical structure by X-ray analysis. Several derivatives were prepared, which have the repeating sequence of Ala-Aib, Lys(Z)-Aib or Leu-Aib, or have the terminal chemically modified. CD spectra of the peptides indicated helical conformation in ethanol solution. The surface pressure-area isotherms of the peptide monolayers showed an inflection at the surface area corresponding to the cross section along the helix axis, and the monolayers were collapsed by …
Water vapour adsorption onto Ca2+ Camp–Berteau montmorillonite and comparison with properties of Na+ sample
2004
Abstract In this paper, we present an analysis of the adsorbed amounts and adsorption heats of water vapour of Ca2+ Camp–Berteau montmorillonite. Measurements were obtained at 298 K using thermogravimetry and calorimetry as a function of relative pressure and the study was completed by the adsorption of nitrogen at 77 K. Experimental data were analysed with BET and t-method theories and compared with those of the Na+ sample. A correlation was shown between models and two domains observed on the calorimetric curves. These domains have been attributed to a multilayer equivalent adsorption. However, the determination of the surface area of clays remains a difficulty. So, the areas of interlaye…