Conference paper

The Mechanism of Precipitation of Biological Minerals. The Phosphates, Oxalates and Carbonates of Calcium

George H. Nancollas ; Chemistry Department, State University of New York at Buffalo, Buffalo, New York, 14214, USA

Abstract

The precipitation of the phosphates, oxalates, and carbonates
of calcium is complicated by the possible formation of different
precursor phases involving polymorphs, hydrates, and acid salts.
In order to elucidate the mechanisms of the reactions, it is necessary
to study the kinetics under conditions of controlled supersaturation
calculated from the activities of free ionic species. In
general, the rates of formation of the salts are proportional to the
(supersaturation)", where n = 1.25-2.0 suggesting a surface controlled
process. However, in the case of the calcium phosphate
phases, the precipitation of the thermodynamically most stable
hydroxyapatite is often complicated by the formation of precursor
phases which form and subsequently dissolve during the overall
reactions. The sensitivity of the various solid phases to the presence
of crystal growth inhibitors is markedly different. Thus in
the case of calcium carbonate, it is possible to selectively inhibit
calcite and aragonite by adding traces of phosphonate inhibitor,
thereby encouraging the formation of vaterite, the most thermodynamically
unstable phase. Such selective inhibition may explain
the existence of thermodynamically unstable phases in biological
systems.

Keywords

Hrčak ID:

194194

URI

https://hrcak.srce.hr/194194

Publication date:

9.11.1983.

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