On the Bimodal Effects of Silicic Acids on Calcite Growth

Abstract

The effects of silicic acids on calcite growth are a model for the effects of partially polymerized additives on crystal growth. At alkaline pH, silicic acid polymers coexist with small mono-and oligomers. Atomic force microscopy (AFM) showed that large polymers promote two-dimensional nucleation, while mono-and oligomers have a bimodal promoter/inhibitor effect on step propagation. This bimodality can be interpreted as the result of attachment of mono-and oligomers along the steps along with a modification of the kinetics of kink generation and/or propagation. The bimodal step kinematic effect is accompanied by a single morphologic effect: growth islands transform from a rhombus into an ellipse. This effect has been reported for other additives, indicating that many additives generate few morphologies. Such a convergence limits the versatility of chemical control on biomorphogenesis. Contrarily, the strong kinetic effect of silicic acids may make them very efficient controllers of biomorphogenesis, if coupled with a physical shape control, for example, by templates. Thus, silicic acids show a unique bimodality as a controller of calcite biomineralisation and as an abundant biomineral.

Polymorphic Crystallization and Diversified Growth of CaCO3 in HPAM‐HABS‐Na2SiO3 Hybrid Solutions

“…Different thicknesses of SiO 2 coating have been found in Figure b, 2d and 2 f, as varying the content of calcite (Figure , A and B). A previous report demonstrated that amorphous silica can deposit on the surface and the basement of composite grains, potentially hindering the energetically favoured transformation to calcite ,. In the control experiment, CaCO 3 precipitation occurs in several minutes, and cubic grains of calcite with diameters ≥10 μm are generated with smooth surfaces (Figure S2).…”

“…Since there are sufficient silica to be pinned to the kink or step on the lattice plane edge, the behaviour of CaCO 3 growth is blocked, and the circular arc is formed as polycrystals during stage two or three (Figure , B, c and d). Meanwhile, ≡Si‐OH (or ≡Si‐O − ) of the silica‐coating is further solidified, and peanut‐like CaCO 3 nuclei are coalesced by silica bridges . In Figure , C, e and f, a calcite@SiO 2 core‐shell structure and particles with irregular shapes are buried in the silica networks layers, which are obtained in Na 2 SiO 3 solution (9 mmol L −1 ) …”

“…Silica, an effective coating molecule, can cover the calcium carbonate precursor, and impedes the process of chemical exchange within a micro‐region medium and then stabilizes the phase of CaCO 3 in a metastable state. [9,10] The growth orientation of kinks (or steps) can be adjusted as long as silica attached to the surface of CaCO 3 ,. These findings provide strong evidence that silica plays a role as an inhibitor during the crystallization of CaCO 3 .…”

On the effect of carbonate on barite growth at elevated temperatures

“…Whereas, for example, silicic acids (Pina et al 2009) or polyaspartate (Elhadj et al 2006) show an opposing effect on calcite growth depending on additive concentration, the opposing effect of carbonate on barite growth depends on the specific location of the growth layer. The so called "template effect" (e.g.,…”

Simple solution routes for targeted carbonate phases and intricate carbonate and silicate morphologies

“…Various aspects of the effect of the presence of silicate species on carbonate precipitation have been reviewed by Pina et al [54]. Ours is a cursory attempt to extend the findings of Series 1 by including soluble silicate species; in particular we use as reference sample S 2 , for which we employed gelatin and obtained vaterite globules (spherulites), and explore the effect of using a limited range of calcium nitrate/sodium silicate ratios.…”