Stabilization of amorphous calcium carbonate in inorganic silica-rich environments.
In biomineralization, living organisms carefully control the crystallization of calcium carbonate to create functional materials and thereby often take advantage of polymorphism by stabilizing a specific phase that is most suitable for a given demand. In particular, the lifetime of usually transient amorphous calcium carbonate (ACC) seems to be thoroughly regulated by the organic matrix, so as to use it either as an intermediate storage depot or directly as a structural element in a permanently stable state. In the present study, we show that the temporal stability of ACC can be influenced in a deliberate manner also in much simpler purely abiotic systems. To illustrate this, we have monitored the progress of calcium carbonate precipitation at high pH from solutions containing different amounts of sodium silicate. It was found that growing ACC particles provoke spontaneous polymerization of silica in their vicinity, which is proposed to result from a local decrease of pH nearby the surface. This leads to the deposition of hydrated amorphous silica layers on the ACC grains, which arrest growth and alter the size of the particles. Depending on the silica concentration, these skins have different thicknesses and exhibit distinct degrees of porosity, therefore impeding to varying extents the dissolution of ACC and energetically favored transformation to calcite. Under the given conditions, crystallization of calcium carbonate was slowed down over tunable periods or completely prevented on time scales of years, even when ACC coexisted side by side with calcite in solution.
Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstrasse 31, D-93040 Regensburg, Germany.
Matthias
M
Kellermeier
Emilio
E
Melero-García
Fabian
F
Glaab
Regina
R
Klein
Markus
M
Drechsler
Reinhard
R
Rachel
Juan Manuel
JM
García-Ruiz
Werner
W
Kunz
D002119:Calcium Carbonate / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053758:Nanoparticles / Q000737:chemistry; D010316:Particle Size; D011208:Powders; D012822:Silicon Dioxide / Q000737:chemistry* / Q000494:pharmacology; D014867:Water / Q000737:chemistry
D011208:Powders; D014867:Water; D012822:Silicon Dioxide; D002119:Calcium Carbonate