On the kinetics of phase transformations of dried porous vaterite particles immersed in deionized and tap water

Calcium carbonate exists in three allotropic forms: vaterite, aragonite and calcite. Metastable vaterite can be easily transformed into calcite and/or aragonite via different routes. We report how dry vaterite particles transform into aragonite and calcite when they are immersed into DeIonized water (DI) or tap water without additives at different temperature (22, 40 and 60 degrees C) with and without stirring. We show that the transformation rate of vaterite into more stable crystallographic forms is influenced not only by temperature but also by stirring and water purity. Low temperature, absence of stirring and absence of ions in water significantly slow down the kinetics of transformation of vaterite. Additionally, water purity influences the nature of the allotropic phase obtained after transformation. High temperatures and DI water favor the transformation of vaterite into single crystalline nanowires of aragonite, while tap water yields the transformation of vaterite into calcite. The absence of aragonite in tap water at high temperature can be explained by the presence of sulfate ions, which inhibit the formation of this phase. On the contrary, Mg2+ ions tend to stabilize vaterite. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.