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Lorentz Center Highlights
Julyan Cartwright and Oliver Steinbock
Universtiy of Granada and Georg-August-University Göttingen
ABSTRACT: The chemical-gardens system is as old as chemistry and has attracted the curiosity of scientists such as Isaac Newton. It involves the formation of hollow tubular solids in aqueous solution under ambient conditions at growth rates of mm/s to mm/day. The diameter of these hollow structures varies from micrometers to millimeters and seemingly involves no length limitation. Conventionally their self-organized synthesis is started from small salt crystals seeded into solutions containing sodium silicate (or other anions such as borates, phosphates, carbonates and sulfides). Tube growth can also be initiated by hydrodynamic injection or the use of pellets and microbeads. The reaction processes involve colloidal intermediates and are driven by the co-precipitation of amorphous silica and metal hydroxides (or oxides, sulfides, etc.) In the classic case of the dissolution of a seed crystal, the precipitates initially form a semipermeable, colloidal all-enveloping membrane which stretches and bursts due to osmotically controlled fluxes. The breach causes further precipitation but now around a buoyant jet of reactant solution, which explains qualitatively the formation of tubes at the system level. These macroscopic structures are self-healing as small damage sites seal themselves rapidly once the interior and exterior solutions begin to mix. Very similar materials form also in setting cement and certain corrosion systems. Furthermore some research groups have proposed precipitation tubes as the birth place of life.