Synthesis and Formation Mechanism of Amorphous CaCO₃ in Anhydrous Ethylene Glycol

Pure and stable amorphous calcium carbonate (ACC) was synthesized by using alcohol-calcium method in anhydrous ethylene glycol, i.e. the reaction between CaCl₂ and K₂CO₃ ethylene glycol solutions. The effect of solution concentration, aging temperature and time on polymorphs and morphologies of CaCO₃ was studied. XRD results indicate that ACC is formed upon the mixing of the two solutions. At the reaction temperatures of 0 ℃ and 20 ℃, the product maintains amorphous even prolonging aging time to 4 months. ACC is the only polymorph in product obtained from different solution concentrations at 20 ℃. IR spectra, TEM images and SAED patterns verify the formation of ACC. SEM images reveal that the shorter aging time, the lower reaction temperature and the more diluted solution, the more readily for the formation of porous loose ACC. With prolonging aging time to 4 months, porous loose ACC becomes irregular particle at 0 ℃ and relative regular ellipsoidal or near-spherical particle at 20 ℃. The formation mechanism of ACC was discussed from the viewpoint of the ionization of CaCl₂ and K₂CO₃ in ethylene glycol. This research extends the route to prepare stable pure ACC and provides new insights into its controllable synthesis.