Zn 2/ strongly inhibits the transformation of aragonite to The effects of Ag / , Al 3/ , and Cr 3/ ions on calcium carbonate calcite, but the presence of Cu 2/ does not (12). polymorphs were investigated using a double diffusion technique.
Recently, we investigated the formation of CaCO 3 when
The experimental results, analyzed by the equivalency rule, were Sr 2/ , Pb 2/ , and Ba 2/ , which form aragonite-type carbonate, as follows: (i) Ag / , Al 3/ , and Cr 3/ ions promoted the formation were added, and found that Sr 2/ and Pb 2/ favored aragonite of aragonite; (ii) in the presence of Ag / ions, Ag 2 CO 3 crystals precipitation, while Ba 2/ promoted vaterite precipitation acted as a nucleus for the epitaxial growth of aragonite; (iii) Al 3/ (10). We have also studied the formation of CaCO 3 in the and Cr 3/ ions reduced the growth rate of the metastable phase presence of Fe 2/ , Mg 2/ , Ni 2/ , Co 2/ , Zn 2/ , Cu 2/ , and (aragonite), which was formed at the initial stage of CaCO 3 crys-Cd 2/ , which form calcite-type carbonate, and pointed out tallization. Due to their adsorption onto growth sites, the supersaturation remained at a high level in this system. Aragonite was that the cations forming calcite-type carbonate favored the therefore able to be the dominant phase. ᭧ 1998 Academic Press formation of aragonite, except Cd 2/ (11). We demonstrated Key Words: calcium carbonate; impurity effect; double diffusion that the following process and mechanism took place when technique; epitaxial growth; transformation.
the cations (Sr 2/ , Pb 2/ ) forming aragonite-type carbonate were added. At a large impurity concentration, the solid solution of aragonite containing SrCO 3 or PbCO 3 compotion time of the precipitation (15).