Here, we present preliminary results of impedance and light scattering investigations of CaCO₃ crystallization under a sounding rocket experiment. In addition, we discuss phase transition of crystalline and amorphous states of calcium carbonates after homogeneous nucleation by ground-based Macro-Raman spectroscopical measurements.

   Compared to ground-based data obtained, rapid crystallization (around 2 sec induction) occurs at a relatively high concentration of 5 mM solution of the rocket experiment, which might be due to a presence of a bubble within the solution at high G conditions. Other cells (at medium or low concentrations) show relatively long induction time such as: 3 mM-132 sec, 3.8 mM-49 sec, 4 mM-23 sec and 4.5 mM-14 sec.

   In the medium spectral range, there are two typical carbonate-related Raman bands, which centered at around 1085 cm^-1 (CO₃-bending in calcite) (Urmos et al., 1991) and 1650 cm^-1 (H₂O-bending).  H₂O-related antisymmetric and symmetric stretching vibrational modes at 3250 and 3450 cm^-1 are dominant (Tlili et al., 2001). An additional peak appears at around 540 cm^-1 (in most cases at 544 cm^-1) at 2, 3.6, 4.5 and 50 mM, however, this peak is an absent one from 4 and 5 mM solutions, which may be related to the lattice H₂O libration or translation in the hexahydrate carbonate (CaCO₃xH₂O) (Gauldie et al., 1997).

   Consequently, high concentrations show rapid crystallization under the microgravity conditions, whereas medium or low concentrations represent relatively slow processes as same as under the gravity. Macro-Raman spectral investigations were not conclusive in terms of the phase determination, however, further systematic analyses must be done.

References

Gauldie, W.R., Sharma, K.S. and Volk, E. (1997) Comp.Biochem.Physiol. 118A, 753-757

Tlili, M.M., Ben Amor, M., Gabrielli, C., Joiret, S., Maurin, G. and Rousseau, P. (2001) J. Raman Spectroscopy 33, 10-16. 

Urmos, J., Sharma, S.K., Mackenzie, F.T. (1991) American Mineralogist 76, 641-646.

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