Hadjittofis Eftychios, Vargas Silvia M, Litster James D, Campbell Kyra L Sedransk
Department of Chemical and Biological Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
UCB Pharma SA, 1420 Braine l'Alleud, Belgium.
Proc Math Phys Eng Sci. 2022 Feb;478(2258):20210601. doi: 10.1098/rspa.2021.0601. Epub 2022 Feb 9.
The crystallization of calcium carbonate is shown to be dictated by the Ostwald rule of stages (ORS), for high relative initial supersaturations ( ), under sweet (carbon dioxide saturated) and anoxic (oxygen depleted) solution conditions. Rhombohedral calcite crystals emerge after the sequential crystallization and dissolution of the metastable polymorphs: vaterite (snowflake-shaped) and aragonite (needle-shaped). However, the presence of certain cations, which can form trigonal carbonates (e.g. Fe and Ni), in concentrations as low as 1.5 mM, triggers the emergence of calcite crystals, with a star-shaped crystal habit, first. These star-shaped crystals dissolve to yield needle-shaped aragonite crystals, which in turn dissolve to give the rhombohedral calcite crystals. The star-shaped crystals, formed at high S , possess higher surface free energy (therefore higher apparent solubility) than their rhombohedral counterparts. This sequence of dissolution and recrystallization demonstrates that the ORS does not only drive the crystal towards its thermodynamically most stable polymorph but also towards its most stable crystal habit.
研究表明，在甜水（二氧化碳饱和）和缺氧（贫氧）溶液条件下，对于高相对初始过饱和度（ ），碳酸钙的结晶受奥斯特瓦尔德阶段规则（ORS）支配。在亚稳多晶型物（球霰石（雪花状）和文石（针状））依次结晶和溶解之后，菱面体方解石晶体出现。然而，某些能够形成三角碳酸盐的阳离子（例如铁和镍），其浓度低至1.5 mM时，首先会触发具有星形晶习的方解石晶体的出现。这些星形晶体溶解产生针状文石晶体，而针状文石晶体又溶解生成菱面体方解石晶体。在高过饱和度（S）下形成的星形晶体比其菱面体对应物具有更高的表面自由能（因此具有更高的表观溶解度）。这种溶解和重结晶序列表明，ORS不仅将晶体驱动至其热力学上最稳定的多晶型物，而且还驱动至其最稳定的晶习。
