Zusammenfassung
Under certain conditions, mineralization of barium carbonate in silica-contg. media at high pH results in the formation of complex crystal aggregates called "silica biomorphs". These self-assembled, purely inorg. materials exhibit hierarchical structure and curved morphologies much reminiscent of certain living forms, thus constituting an interesting model system for the study of the ...
Zusammenfassung
Under certain conditions, mineralization of barium carbonate in silica-contg. media at high pH results in the formation of complex crystal aggregates called "silica biomorphs". These self-assembled, purely inorg. materials exhibit hierarchical structure and curved morphologies much reminiscent of certain living forms, thus constituting an interesting model system for the study of the biomineralization processes. In this paper, we report on the influence of the bulk pH on the morphogenesis of silica biomorphs in alk. solns. To that end, crystn. expts. were carried out at initial pH values between about 9.8 and 11.9, using atm. CO2 as a carbonate source. Formed aggregates were characterized quant. by statistical analyses of their morphol., no. and size. Corresponding data evidence that well-developed polycryst. architectures with elaborate shapes occur only when the starting pH is adjusted to values within a rather narrow corridor, ranging roughly from 10.2 to 11.1. Otherwise, merely ill-defined, globular or dumbbell-shaped particles were obtained. In addn., the pH of the mother solns. was monitored continuously during growth and correlated with time-dependent Ba2+ concn. profiles detd. by in-situ X-ray fluorescence spectroscopy. By combining the collected data, temporal progressions of the bulk supersatn. were estd. for different conditions and used to re-evaluate the role of pH in the formation of silica biomorphs, particularly with regard to the recently proposed model of the growth mechanism. It is shown that a suitable starting pH is required not only to allow for dynamically coupled co-pptn. of the components, but also to maintain continuous CO2 uptake and hence adequate levels of supersatn. over extended periods of time during growth. Our expts. rationalize previous observations concerning the effect of pH on the formation of silica biomorphs, and disclose fundamental differences between growth in solns. and gels.
Altmetric