Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90142-R· OSTI ID:6139972

Stipp, S L; Hochella, Jr, M F ^[1]

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1. Stanford Univ., CA (United States)

The pure calcite surface was examined using techniques sensitive to the near-surface (XPS and LEED) immediately after fracture in ultra-high vacuum (10{sup {minus}10} mbar) and then following exposure to various atmospheres and aqueous solutions that were free of trace metals. These spectroscopic techniques allow molecular-level observations that offer the possibility of gaining more insight into geochemical processes elucidated from macroscopic solution studies. Several absolute electron binding energies for the atoms in calcite were redetermined with XPS using the gold dot method. Surface hydration is also supported, independently, by the XPS peak intensity ratios and is consistent with adsorption theory derived from macroscopic solution studies. The modified oxygen Auger parameter, {alpha}{prime}, (using O{sub 1s} and O(KVV)), was found to be 1043.9 eV for all samples of calcite tested, whether powder or cleaved from iceland Spar, clean or contaminated by adventitious carbon, freshly fractured, or exposed briefly to water, or in the process of dissolution or precipitation. LEED patterns of the {l brace}101{r brace} cleavage surface of samples that were freshly fractured in air and that were exposed to dissolving or precipitating solutions showed that the top few atomic layers exhibit long range order. Lattice spacings at the surface are statistically identical to those of bulk calcite, though some surface CO{sub 3} groups may be rotated relative to the bulk structure. This work provides direct, molecular-level evidence for the processes of reconfiguration and hydration at the calcite surface. These results provide a basis for future spectroscopic studies of trace metal adsorption on calcite and subsequent solid-solution formation.

• OSTI ID: 6139972
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:6; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BINDING ENERGY
CALCITE
CARBONATE MINERALS
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMISTRY
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
ELECTRON DIFFRACTION
ENERGY
GEOCHEMISTRY
HYDRATION
KINETICS
MINERALS
MOLECULAR STRUCTURE
REACTION KINETICS
SCATTERING
SOLVATION
SORPTIVE PROPERTIES
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
SURFACE PROPERTIES
X-RAY SPECTROSCOPY