Sand, K.K., Cooke, David J., Hassenkam, T., Yang, M., Makovicky, E., Bechgaard, K. and Stipp, S.L.S. (2009) The influence of ethanol adsorption on the {10¯14} calcite surface. Geochimica et Cosmochimica Acta, 73 (13, Su). A1152. ISSN 0046-564X
Abstract

Previous studies have demonstrated that water is ordered
by the calcite surface and that OH is bonded to Ca.
Theoretical work on polysaccharides shows sorption through
OH. To increase understanding about the fundamental
controls on biomineralisation, we investigated the interaction
between calcite and the OH of ethanol, and bonding strength
relative to that of water. Ethanol is known to stabilize vaterite and may stabilize calcite but the mechanism is not
known. Molecular simulations show that ethanol orders itself
on the {10¯14} calcite surface with the OH group near Ca and
the CH3 group oriented away from the surface. The next layer
is semi-ordered so the OH end faces solution. Ethanol
attachment to calcite is stronger than that of water, meaning
that once ethanol is adsorbed, energy is needed for water to
detach it.

We used atomic force microscopy (AFM) to watch calcite
surface behaviour during exposure to air after cleavage under
ethanol or water. Behaviour was considerably different.
Ostward ripening was much slower and the pattern and
placement of the recrystallised areas were controlled by
terrace edges on the ethanol-exposed sample. Modelling
combined with imaging under a variety of conditions suggests
that growth is controlled by differences between water and
ethanol bonding at step edges.

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