Detection and a possible mechanism of magnetic field effect on the crystal growth of sedimentary calcium carbonate.
Sedimentary calcium carbonate was grown at a physiological pH6.8 from a mixture of equivolume of 70 mM Ca(NO(3))(2) and 70 mM NaHCO(3) aqueous solution. The kinetics of the crystal growth was monitored by means of turbidity measurement. The apparent absorption is gradually increased with the elapsed time after the mixing and reaches its maximum at t(max). The average t(max) is significantly decreased from <t(max)>=467 s (for n=13 runs) to 408 s (n=13) by application of the static magnetic field (SMF) of H=400 mT to the precipitating solution. The application of SMF at 120 s later the mixing shows the same <t(max)>=396 s (n=9) as that of 408 s. It has been thus detected that the application of SMF is ineffective in the stage of the nucleation or the earlier stage of the crystal growth but effective in the Ostwald ripening stage of the growth nucleus or the later stage of the crystal growth where large numbers of the growing crystalline particles seem greater than a few hundred nanometers. A possible mechanism for the SMF effect is as follows. An ion escaping from the growing crystal surface with a certain 'migration velocity' due to a random walk process has significant probability to drift onto the identical surface or at least the identical crystal by means of Lorentz force, because the translational displacement of the crystal during a cycle of the cyclotron motion of the ion is smaller than the size of the growing crystal. This type of drift results in the suppression of re-dissolution of the ions on the growing surface and in the acceleration of the growth in the later stage of the crystal growth. The undetected SMF effect in the earlier stage of the crystal growth can be partly attributed to the re-dissolution due to the thermodynamic instability of the small nuclei which predominates over the presumable SMF effect. This can be partly ascribed to the large translational displacement of the small particle. The application of this mechanism to an oscillating magnetic field will predict the presence of a window for the frequency of the oscillating magnetic field.
Azuma
N
Department of Chemistry, Faculty of Science, Ehime University, 790-8577, Matsuyama, Japan
Tajima
K
Ishizu
K
Yokoi
I
Mori
A