ENERGETICS OF NANOPHASE CALCITE

Nanophase calcite is an intermediate in the transformation of both biogenic and synthetic amorphous calcium carbonate to well crystallized bulk calcite. The surface energy of calcite is an important parameter in understanding this transformation and also in understanding polymorphism, crystal growth and dissolution in the calcium carbonate system. Despite such importance, we know of no previous direct measurement of surface energy in any carbonate system. Here we report the first such direct measurement of the surface energy of calcite based on acid solution calorimetry of samples with different surface areas to obtain a surface energy of 1.4 ± 0.4 J/m².

Several studies modeling the surface energy of calcite show a range of values depending on the modeled face and the surface terminating groups. De Leeuw et al, 1998 has reported values from 0.59 J/m² for the {1014} face to 1.39 J/m² for the {1120} face for dehydrated surfaces. Hydrated surfaces were lower, ranging from 0.16 to 0.81 J/m². Titilovye et al, 1998 also reported a similar range in surface energies for calcite. Therefore, the surface energies determined here are within the range for the modeled values. The measured values for calcite are similar to surface energies of a number of oxide minerals.