How similar are amorphous calcium carbonate and calcium phosphate? A comparative study of amorphous phase formation conditions

• Published in: CrystEngComm Vol. 2; no. 1; pp. 35 - 5
• Main Authors: Buljan Mei, I, Kontrec, J, Domazet Jurašin, D, Selmani, A, Njegi D akula, B, Maltar-Strme ki, N, Lyons, D. M, Plodinec, M, eh, M, Gajovi, A, Sikiri, M. Dutour, Kralj, D
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Additives; Amorphous materials; Calcium carbonate; Calcium phosphates; Chemical precipitation; Complexity; Constituents; Materials science; Solid phases; Supersaturation
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/c7ce01693j

Amorphous calcium carbonate (ACC) and calcium phosphate (ACP) increasingly attract attention as initial solid phases in vertebrate and invertebrate hard tissue formation, as well as in materials science as a possible new synthetic route for advanced materials preparation. Although much is known about these two amorphous phases and similarities in the mechanisms of their formation are recognized, no attempt has been made to investigate their formation under defined and comparable initial experimental conditions, viz. supersaturation, the ratio of constituent ions, ionic strength and the presence of relevant inorganic additives. In this paper, the formation of ACC and ACP in three model precipitation systems of increased chemical complexity was investigated: (a) systems containing constituent ions, (b) systems containing additional co-ions, and (c) systems with higher ionic strength and addition of Mg 2+ . The results have shown that ACP is more stable and was formed at lower relative supersaturations in comparison to ACC. The precipitation domain of both phases expanded with increasing complexity of precipitation systems, with the ACP precipitation domains always being larger than those of ACC. In addition to stability, the presence of inorganic ions, especially Mg 2+ , influences the composition of both amorphous phases. The obtained results indicate that general similarity between ACC and ACP exists, but it could also be concluded that the similar chemical environment in which they form not necessarily leads to similar structural properties. Precipitation domains of ACP and ACP increase with the complexity of the system, the ACP one being always larger.