 |
| Titel |
In situ and time resolved quantification of the kinetics and mechanisms of CaCO3 nucleation and growth |
| VerfasserIn |
J. D. Rodriguez-Blanco, S. Shaw, L. G. Benning |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021005
|
|
|
|
|
|
| Zusammenfassung |
| The crystal chemistry, occurrence and relevance of amorphous CaCO3 and its crystalline
polymorphs in inorganic and organic environments have been studied for decades and are
nowadays relatively well known [1]. However, due to the fast kinetics of the reactions that
take place in solution [2], there is virtually no quantitative data available about the kinetics
and mechanisms of the nucleation, growth and transformation of these phases in aqueous
solutions.
In this study we demonstrate that in situ and time resolved synchrotron-based Energy
Dispersive X-Ray Diffraction combined with the corresponding solution chemistry and
imaging can be successfully applied to evaluate quantitatively kinetic rates and mechanisms
of the crystallization and transformation of CaCO3 phases in solution. The precipitation of
amorphous calcium carbonate (ACC) and its crystallization to vaterite and calcite was
followed in closed thermostated reactors at temperatures between 7.5 and 40Ë C with the
time-resolved data collected every 15 secs. The growth/decay of vaterite and calcite
diffraction peaks was fitted using a Johnson-Mehl-Avrami-Kolmogorov model [3] to evaluate
the kinetics and mechanisms of crystallization [4]. The results show that vaterite grows fast
via a 3D growth process following a first order reaction and the subsequent transformation to
calcite takes place slower, being controlled by the dissolution of the vaterite precursor.
From the temperature dependent data apparent activation energies of nucleation
and crystallization for both crystalline CaCO3 polymorphs have been calculated.
In addition, wet chemical data and imaging also confirm these findings. Finally,
this approach was applied also to other carbonate systems (i.e., dolomite , Ca/Mg
carbonates).
[1] Reeder R. (1983) Rev. Mineral, 11.
[2] Ogino et al. (1987) Geochim. Cosmochim. Acta 51, 2757-2767.
[3] Johnson, P.F. and Mehl, R.F. (1939) Reaction kinetics in processes of nucleation and
growth. American Institute of Mining Engineering, Technical Publication, 1089,
1-27.
[4] Hulbert, S.F. (1969) J. Br. Ceram. Soc., 6, 11-20. |
|
|
|
|
|
|