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Title: Structure and morphology of hydroxylated amorphous alumina surfaces.

Abstract

The effect of hydroxylation on the surface structure of amorphous alumina is investigated using classical molecular dynamics simulations. It is found that the hydroxylated amorphous alumina surface is terminated by hydroxyl groups singly and doubly coordinated to aluminum. Root-mean-square roughness calculations and density profiles across the film indicate that hydroxylated surfaces are rougher than non-hydroxylated surfaces. The power spectrum identifies different vibrational stretching frequencies for the singly and doubly coordinated surface OH groups. The role of the surface OH groups in surface reactivity is discussed.

Authors:
; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
914953
Report Number(s):
ANL/MSD/JA-58589
TRN: US200817%%32
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Phys. Chem. C; Journal Volume: 111; Journal Issue: 20 ; May 24, 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALUMINIUM OXIDES; HYDROXYLATION; MORPHOLOGY; ROUGHNESS; SURFACE PROPERTIES; MOLECULAR DYNAMICS METHOD

Citation Formats

Adiga, S. P., Zapol, P., and Curtiss, L. A. Structure and morphology of hydroxylated amorphous alumina surfaces.. United States: N. p., 2007. Web. doi:10.1021/jp0701035.
Adiga, S. P., Zapol, P., & Curtiss, L. A. Structure and morphology of hydroxylated amorphous alumina surfaces.. United States. doi:10.1021/jp0701035.
Adiga, S. P., Zapol, P., and Curtiss, L. A. Thu . "Structure and morphology of hydroxylated amorphous alumina surfaces.". United States. doi:10.1021/jp0701035.
@article{osti_914953,
title = {Structure and morphology of hydroxylated amorphous alumina surfaces.},
author = {Adiga, S. P. and Zapol, P. and Curtiss, L. A.},
abstractNote = {The effect of hydroxylation on the surface structure of amorphous alumina is investigated using classical molecular dynamics simulations. It is found that the hydroxylated amorphous alumina surface is terminated by hydroxyl groups singly and doubly coordinated to aluminum. Root-mean-square roughness calculations and density profiles across the film indicate that hydroxylated surfaces are rougher than non-hydroxylated surfaces. The power spectrum identifies different vibrational stretching frequencies for the singly and doubly coordinated surface OH groups. The role of the surface OH groups in surface reactivity is discussed.},
doi = {10.1021/jp0701035},
journal = {J. Phys. Chem. C},
number = 20 ; May 24, 2007,
volume = 111,
place = {United States},
year = {Thu May 24 00:00:00 EDT 2007},
month = {Thu May 24 00:00:00 EDT 2007}
}
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  • Surface energies of silicates influence crack propagation during brittle fracture and decrease with surface relaxation caused by annealing and hydroxylation. Molecular-level simulations are particularly suited for the investigation of surface processes. In this work, classical MD simulations of silica surfaces are performed with two force fields (ClayFF and ReaxFF) to investigate the effect of force field reactivity on surface structure and energy as a function of surface hydroxylation. An unhydroxylated fracture surface energy of 5.1 J/m 2 is calculated with the ClayFF force field, and 2.0 J/m 2 is calculated for the ReaxFF force field. The ClayFF surface energies aremore » consistent with the experimental results from double cantilever beam fracture tests (4.5 J/m 2), whereas ReaxFF underestimated these surface energies. Surface relaxation via annealing and hydroxylation was performed by creating a low-energy equilibrium surface. Annealing condensed neighboring siloxane bonds increased the surface connectivity, and decreased the surface energies by 0.2 J/m 2 for ClayFF and 0.8 J/m 2 for ReaxFF. Posthydroxylation surface energies decreased further to 4.6 J/m 2 with the ClayFF force field and to 0.2 J/m 2 with the ReaxFF force field. Experimental equilibrium surface energies are ~0.35 J/m 2, consistent with the ReaxFF force field. Although neither force field was capable of replicating both the fracture and equilibrium surface energies reported from experiment, each was consistent with one of these conditions. Furthermore, future computational investigations that rely on accurate surface energy values should consider the surface state of the system and select the appropriate force field.« less
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  • Incoherent, inelastic scattering of neutrons by hydrogen in surface hydroxyl groups has been used to probe the dynamics of 60--70-A-diameter spheres of amorphous silica. The high-temperature spectra indicate a pronounced ''small-particle'' enhancement of low-frequency vibrational modes as predicted by theory. At low temperatures, the scattering changes in character and shows evidence of hindered rotational transitons.