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Title: Reaction of Water with the (100) and (111) Surfaces of Fe3O4

Abstract

We have examined changes in the electronic structure of magnetite (100) and (111) surfaces after reaction with water vapor (p(H2O) ranging from 10-9 to 9 Torr) and liquid water at 298 K using chemical shifts in the O 1a core-level photoelectron spectra obtained with a synchrotron radiation source. The surfaces were prepared in ultra high vacuum from natural magnetite crystals. We found that the vapor pressure, p(H2O), at which first reacts with magnetite is similar for the two surfaces (<10-5 Torr for 3 min. exposures, corresponding to doses of < 1.8 x 103 langmuirs) and is consistent with a small sticking coefficient. This reaction is manifested in the O 1s spectra by the growth of a shoulder at about 1.5 eV lower kinetic energy than the main lattice oxygen feature. We attribute this new feature to hydroxyl groups resulting from dissociative chemisorption of water on the magnetite surfaces, initially on defect sites. The p(H2O) for the onset of an extensive hydroxylatoin reaction is = 10-3 Torr (3 min. dose or = 1.8 x 105 Langmuirs). Magnetite (100) and (111) surfaces exposed to higher p(H2O) react more extensively, with hydroxylation extending several layers (=8 A) deep into the bulk. A comparisonmore » of O KVV Auger K-edge adsorption spectra of water vapor-exposed magnetite (100) and (111) surfaces with the corresponding total yeild spectra of goethite (FeOOH), limonite (FeOOH . nH2O), and hematite (Fe2O3) clearly shows that the reaction product on the magnetite surfaces is not goethite, limonite, or hematite. In addition, similarity of the Fe L3M23M23 Auger yield L-edge absorption spectra before and after exposure of the magnetite (111) surface to liquid water indicates that the oxidation state of iron is unchanged. These annealing experiments indicate that once the magnetite surface is hydroxylated, it is extremely difficult to thermally clean without Ar+ sputtering.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
964245
Report Number(s):
PNNL-SA-33145
Journal ID: ISSN 0039-6028; SUSCAS; KP1301020; TRN: US0904119
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Surface Science, 453(1-3):32-46
Additional Journal Information:
Journal Volume: 453; Journal Issue: 1-3; Journal ID: ISSN 0039-6028
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ABSORPTION SPECTRA; ADSORPTION; ANNEALING; CHEMICAL SHIFT; CHEMISORPTION; DEFECTS; ELECTRONIC STRUCTURE; GOETHITE; HEMATITE; HYDROXYLATION; IRON; KINETIC ENERGY; LIMONITE; MAGNETITE; OXYGEN; SPECTRA; SPUTTERING; SYNCHROTRON RADIATION SOURCES; VAPOR PRESSURE; WATER VAPOR; Magnetite (100) and (111); water vapor p(H2O)

Citation Formats

Kendelewicz, T., Liu, Ping, Doyle, C. S., Brown Jr., G. E., Nelson, Eric J., and Chambers, Scott A. Reaction of Water with the (100) and (111) Surfaces of Fe3O4. United States: N. p., 2000. Web. doi:10.1016/S0039-6028(00)00305-8.
Kendelewicz, T., Liu, Ping, Doyle, C. S., Brown Jr., G. E., Nelson, Eric J., & Chambers, Scott A. Reaction of Water with the (100) and (111) Surfaces of Fe3O4. United States. doi:10.1016/S0039-6028(00)00305-8.
Kendelewicz, T., Liu, Ping, Doyle, C. S., Brown Jr., G. E., Nelson, Eric J., and Chambers, Scott A. Wed . "Reaction of Water with the (100) and (111) Surfaces of Fe3O4". United States. doi:10.1016/S0039-6028(00)00305-8.
@article{osti_964245,
title = {Reaction of Water with the (100) and (111) Surfaces of Fe3O4},
author = {Kendelewicz, T. and Liu, Ping and Doyle, C. S. and Brown Jr., G. E. and Nelson, Eric J. and Chambers, Scott A.},
abstractNote = {We have examined changes in the electronic structure of magnetite (100) and (111) surfaces after reaction with water vapor (p(H2O) ranging from 10-9 to 9 Torr) and liquid water at 298 K using chemical shifts in the O 1a core-level photoelectron spectra obtained with a synchrotron radiation source. The surfaces were prepared in ultra high vacuum from natural magnetite crystals. We found that the vapor pressure, p(H2O), at which first reacts with magnetite is similar for the two surfaces (<10-5 Torr for 3 min. exposures, corresponding to doses of < 1.8 x 103 langmuirs) and is consistent with a small sticking coefficient. This reaction is manifested in the O 1s spectra by the growth of a shoulder at about 1.5 eV lower kinetic energy than the main lattice oxygen feature. We attribute this new feature to hydroxyl groups resulting from dissociative chemisorption of water on the magnetite surfaces, initially on defect sites. The p(H2O) for the onset of an extensive hydroxylatoin reaction is = 10-3 Torr (3 min. dose or = 1.8 x 105 Langmuirs). Magnetite (100) and (111) surfaces exposed to higher p(H2O) react more extensively, with hydroxylation extending several layers (=8 A) deep into the bulk. A comparison of O KVV Auger K-edge adsorption spectra of water vapor-exposed magnetite (100) and (111) surfaces with the corresponding total yeild spectra of goethite (FeOOH), limonite (FeOOH . nH2O), and hematite (Fe2O3) clearly shows that the reaction product on the magnetite surfaces is not goethite, limonite, or hematite. In addition, similarity of the Fe L3M23M23 Auger yield L-edge absorption spectra before and after exposure of the magnetite (111) surface to liquid water indicates that the oxidation state of iron is unchanged. These annealing experiments indicate that once the magnetite surface is hydroxylated, it is extremely difficult to thermally clean without Ar+ sputtering.},
doi = {10.1016/S0039-6028(00)00305-8},
journal = {Surface Science, 453(1-3):32-46},
issn = {0039-6028},
number = 1-3,
volume = 453,
place = {United States},
year = {2000},
month = {5}
}