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This content will become publicly available on December 12, 2016

Title: Growth kinetics of step edges on celestite (0 0 1) surfaces as a function of temperature, saturation state, ionic strength, and aqueous strontium:sulface ratio: An in-situ atomic force microscopy study

Step velocities on the celestite (0 0 1) surface have been measured as a function of temperature (23–45 °C), saturation state (S = 1.1–2.2), ionic strength (I = 0.01, 0.06, and 0.1 M), and aqueous strontium:sulfate ratio (r = 0.01–100) using atomic force microscopy (AFM). Celestite growth hillocks were flanked by [0 1 0]-aligned step edges, which are polar, and step edges vicinal to <1 2 0>, which are non-polar. [0 1 0] step velocities increased with temperature and saturation state, however step velocities did not vary significantly with ionic strength. Step velocities were non-linear with saturation state, suggesting a change in mechanism at high S as compared with low S. At constant S, the step velocities were maximized at r = 1 and decreased significantly at extreme r, demonstrating the governing role of solute stoichiometry. We successfully fit the step velocity data as a function of r using the Stack and Grantham (2010) nucleation and propagation model. Based on the results as a function of ionic strength and r, the mechanism at low S is likely ion-by-ion attachment to the step with an activation energy of 75 (±10) kJ mol–1. In conclusion, at high S the mechanism is amore » combination of the one at low S and possibly attachment of a neutral species such as an ion pair with an activation energy of 43 (±9) kJ mol–1.« less
 [1] ;  [2] ;  [1]
  1. Wright State Univ., Dayton, OH (United States)
  2. Wright State Univ., Dayton, OH (United States); Hogeschool Utrecht, Utrecht (Netherlands)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 175; Journal ID: ISSN 0016-7037
The Geochemical Society; The Meteoritical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States