Abstract
Under certain conditions, pptn. of Ba carbonate in alk. SiO2-rich environments affords unusual polycryst. aggregates exhibiting curved shapes and hierarchical structuring, very much reminiscent of biogenic mineral tissues. The formation of these so-called SiO2 biomorphs is thought to rely on a coupling of chem. equil. in soln., which drives concerted co-mineralization and self-assembly of ...
Abstract
Under certain conditions, pptn. of Ba carbonate in alk. SiO2-rich environments affords unusual polycryst. aggregates exhibiting curved shapes and hierarchical structuring, very much reminiscent of biogenic mineral tissues. The formation of these so-called SiO2 biomorphs is thought to rely on a coupling of chem. equil. in soln., which drives concerted co-mineralization and self-assembly of components. We have studied the effect of fluid motion on morphogenesis by conducting syntheses in media stirred at different rates and exposed to an ultrasonic field, resp. The traced growth behavior is discussed on the basis of statistical analyses of the occurring morphologies as well as in terms of expected changes in the supersatn. of the system. The obsd. complex architectures arise as a consequence of an autocatalytic pptn. cycle, during which evolving aggregates synthesize and organize their constituents on their own upon growth. These processes occur only at a local scale within a certain active region that appears to extend over some microns beyond the growth front. The findings provide concrete exptl. evidence supporting the proposed formation mechanism and suggest that growth of SiO2 biomorphs is independent of mass transport from the bulk, unless forced convection becomes strong enough to affect the active region and hence interfere with autocatalysis.
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