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Title: Magnesite Step Growth Rates as a Function of the Aqueous Magnesium:Carbonate Ratio

Step velocities of monolayer-height steps on the (1014) magnesite surface have been measured as functions of the aqueous magnesium-to-carbonate ratio and saturation index (SI) using a hydrothermal atomic force microscope (HAFM). At SI ≤ 1.9 and 80-90 °C, step velocities were found to be invariant with changes in the magnesium-to-carbonate ratio, an observation in contrast with standard models for growth and dissolution of ionically-bonded, multi-component crystals. However, at high saturation indices (SI = 2.15), step velocities displayed a ratio dependence, maximized at magnesium-to-carbonate ratios slightly greater than 1:1. Traditional affinity-based models were unable to describe growth rates at the higher saturation index. Step velocities also could not be modeled solely through nucleation of kink sites, in contrast to other minerals whose bonding between constituent ions is also dominantly ionic in nature, such as calcite and barite. Instead, they could be described only by a model that incorporates both kink nucleation and propagation. Based on observed step morphological changes at these higher saturation indices, the step velocity maximum at SI = 2.15 is likely due to the rate of attachment to propagating kink sites overcoming the rate of detachment from kink sites as the latter becomes less significant under far frommore » equilibrium conditions.« less
Authors:
 [1] ;  [2] ;  [1]
  1. Wright State Univ. Dayton, OH (United States). Chemistry Department
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
Publication Date:
OSTI Identifier:
1159423
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Crystal Growth and Design
Additional Journal Information:
Journal Volume: 14; Journal Issue: 11; Journal ID: ISSN 1528-7483
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE