Fabrication of unusually stable amorphous calcium carbonate in an ethanol medium

Abstract

We report a novel approach to preparing amorphous calcium carbonate (ACC) using ethanolic CaCl2 and ammonium carbonate as the sources of calcium and carbon dioxide, respectively. Other additives or any elaborating pH control are not necessary to form the precursor of ACC, viz., calcium carbonate precipitate (CCP). Ammonia maintains the reaction medium in a neutral or weakly basic condition, and it also retards the crystallization of ACC. On the other hand, ethanol itself inhibits the dissolution of ACC so that the solution mediated phase transition of ACC to vaterite or calcite can barely take place. The freshly prepared CCP contains substantial amount of ammonia and carbon dioxide, and a gentle heating (∼100°C) of the CCP results in ACC, which can further be converted to calcite simply by heating or exposing it to a humid atmosphere. It is thus expected that calcium carbonate crystals of defined morphology are produced by transforming those ACC precursors within a constrained volume.