Crystallization of monohydrocalcite in a silica-rich alkaline solution

Abstract

Monohydrocalcite was crystallized in a silica-rich alkaline solution at room temperature using the counter diffusion method (CDM) in the absence of magnesium, by the reaction of calcium chloride and sodium carbonate. Field emission scanning electron microscopy observations showed monohydrocalcite crystals that were hundreds of micrometers in size exhibiting a unique multi-layered structure. X-ray diffraction and Raman microspectroscopy characterizations demonstrated that monohydrocalcite remained in a stable phase for a number of months. After monitoring the crystallization process by in situ Raman microspectroscopy, it was found that monohydrocalcite was the initial phase, with no phase transformation occurring during the crystal growth. This work demonstrates that silica plays a key role in the formation and stabilization of the monohydrocalcite phase.