Search results for "physisorption"
showing 10 items of 53 documents
<title>Large-scale computer simulations of metal/oxide interfaces with defects</title>
2003
Ab initio slab simulations have been performed for silver adhesion to the perfect and defective MgO(001) surfaces. For 1/4 Ag monolayer (ML) coverage of perfect substrate, we observe small silver adhesion energies over both O2- and Mg2+ ions on a regular MgO(001) substrate (0.23 and 0.22 eV per Ag atom, respectively), with negligible interfacial charge transfer towards metal atoms. For larger Ag coverages (beginning with 1/2 ML), silver adsorption over regular O2- ions is much more favorable. We demonstrate that point surface defects on a magnesia surface increase markedly the metal adhesion energy and cause a redistribution of the electron density across the interface. The results for elec…
High-resolution physisorption techniques for the characterization of adsorbents and catalysts
1991
Abstract High-resolution physisorption techniques performed in the continuous volumetric mode have been developed to investigate the surface and pore structure properties of porous solids. Physisorption data on well-defined microporous solids (zeolites and aluminophosphates) provide novel information on the mechanism of micropore filling, the behavior of the adsorbed phase and the pore structure of the adsorbent. The combination of physisorption with high-resolution analytical techniques such as calorimetry and neutron diffraction further expands our knowledge and understanding of physisorption processes. The results are not only important for fundamental research but can be applied in the …
The Use of 15N NMR for the Understanding of Nitrogen Physisorption.
1994
Abstract Nitrogen adsorption at liquid nitrogen temperature, 77K, is universally employed to determine pore dimensions. The nature of nitrogen physisorbed within the micropores of ZSM-5 zeolite was studied by in situ15N NMR as it depends on the partial pressure of the nitrogen and the temperature above and below 77K. An increase in the volume of adsorption of nitrogen at 77K occurs at a relative pressure of ~0.18 for this zeolite. The nature of the nitrogen was studied below and above this increase in nitrogen adsorption. We find that two states (phases) of nitrogen are evident. We conclude that two phases can be present but that a solid phase of nitrogen is not evident even as the temperat…
Characterization of porous alumina membranes for efficient, real-time, flow through biosensing
2015
Abstract Nanofluidic sensing devices promise high performance by overcoming issues of mass transport of analyte molecules to the sensing surface, whilst micro-porous membranes promise high sensitivity due to a large surface for their capture. Anodic alumina (AAO) filter membranes allow the flow through of samples, and could be used as a convenient and readily available fluidic platform for the targeted delivering of analytes to bioreceptors immobilized on the pore walls. The relatively small pore dimensions, compared to fluidic diffusion lengths, promise highly efficient capture of analytes from the whole sample volume, enabling relatively fast sensing response times and the use of small sa…
Ellipsometric study of the physisorption of benzene on graphite
1987
The optical thickness of benzene on the (001) surface of a graphite single crystal has been studied by ellipsometry. Ellipsometric adsorption isotherms have been measured in the temperature range from 180 to 290 K. The maximum thickness of the adsorbed benzene film is constant in this temperature range and compares favourably with the value expected for one monolayer of molecules lying flat on the surface.
Watching adsorption and electron beam induced decomposition on the model system Mo(CO)(6)/Cu(111) by X-ray absorption and photoemission spectroscopies
2013
Abstract An in-depth study of the first steps of electron beam assisted growth of Mo from molybdenum hexacarbonyl on Cu(1 1 1) has been carried out exploiting the complementarity of X-ray photoemission and X-ray absorption spectroscopies. Frank van der Merwe (2D) growth mode has been observed for the completion of the two first monolayers of adsorbed molecules through a simple physisorption process. Irradiation of the Mo(CO)6 deposit by 1 keV electron beam induces a modification of molybdenum coordination, the average number of C-neighbors decreasing from 6 to 3. Decomposed molecules remain on the surface after annealing at 520 K and organize themselves, the molybdenum atoms moving in Cu(1 …
Molecular simulation studies of water physisorption in zeolites
2006
We report a series of Grand Canonical Monte Carlo simulations of water adsorption in NaY and NaX faujasite, as well as in silicalite-1. Computed adsorption isotherms and heats of adsorption were in good agreement with the available experiments. The existence of cyclic water hexamers in NaX located in the 12-ring windows, recently disclosed by neutron diffraction experiments (Hunger et al., J. Phys. Chem. B, 2006, 110, 342-353) was reproduced in our simulations. Interestingly enough, such cyclic hexamer clusters were also observed in the case of NaY, in which no stabilizing cation is present in the 12-ring window. We also report cation redistribution upon water adsorption for sodium faujasit…
Ellipsometric thickness and coverage of physisorbed layers of Xe, Kr, Ar and N2 on graphite
1990
Multilayer isotherms of Xe, Kr, Ar and N2 physisorbed on graphite (001) have been studied by ellipsometry. It is shown that the model of Dignam and Fedyk provides an excellent basis for the interpretation of the ellipsometric thickness in terms of the coverage and the polarizability of the admolecules. For N2 conclusions concerning the orientation of the molecule are drawn.
Physicochemical parameters - hydration performance relationship of the new endodontic cement MTA Repair HP
2019
Background To characterize the chemical composition and textural parameters of the MTA Repair HP precursor powder and their influence to hydration performance. Material and methods Un-hydrated precursor material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), laser diffraction (LD), N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated material was analysed by XRD, FT-IR, energy dispersive X-ray (EDX) analysis and FEG-SEM. Results Ca3SiO5 and Ca2SiO4, in addition to CaWO4 as radiopacifier are the main compositional phase…
Adhesion trends and growth mode of ultra-thin copper films on MgO
2004
Ab initio simulations are performed for Cu atoms adsorbed on the perfect MgO(001) substrate, with an ordered metal coverage varied from 1 monolayer (ML), i.e. almost single atoms, up t o1M L. As trong dependence of the adhesion energy and the sub-monolayer film distance from the substrate on the surface coverage and adsorbate positions (Mg 2+ or O 2− )i s discussed. The nature of interfacial bonding at all coverages is physisorption .W hen increasing Cu atomic fraction, a decrease of the substrate-induced polarization of adatoms accompanied by an increase of both in-plane metallic bonding and the interfacial distance has been found. Combining results of ab initio calculations with thermodyn…