Dehydration and crystallization of amorphous calcium carbonate in solution and in air.
The mechanisms by which amorphous intermediates transform into crystalline materials are poorly understood. Currently, attracting enormous interest is the crystallization of amorphous calcium carbonate, a key intermediary in synthetic, biological and environmental systems. Here we attempt to unify many contrasting and apparently contradictory studies by investigating this process in detail. We show that amorphous calcium carbonate can dehydrate before crystallizing, both in solution and in air, while thermal analyses and solid-state nuclear magnetic resonance measurements reveal that its water is present in distinct environments. Loss of the final water fraction--comprising less than 15% of the total--then triggers crystallization. The high activation energy of this step suggests that it occurs by partial dissolution/recrystallization, mediated by surface water, and the majority of the particle then crystallizes by a solid-state transformation. Such mechanisms are likely to be widespread in solid-state reactions and their characterization will facilitate greater control over these processes.
School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.
Johannes
J
Ihli
Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge CB2 1EW, UK.
Wai Ching
WC
Wong
School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.
Elizabeth H
EH
Noel
School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.
Yi-Yeoun
YY
Kim
School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.
Alexander N
AN
Kulak
School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK.
Hugo K
HK
Christenson
Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge CB2 1EW, UK.
Melinda J
MJ
Duer
School of Chemistry, University of Leeds, Leeds LS2 9JT, UK.
Fiona C
FC
Meldrum