Abstract
We have produced hollow copper-containing precipitate tubes using a flow-injection technique, and characterized their linear and volume growth. It is shown that the ratio of the volume increase rate to that of pumping is constant independent of the chemical composition. It is also found that osmosis significantly contributes to the tube growth, since the inward flux of chemical species dominates during the precipitate pattern formation. The asymmetric hydrodynamic field coupled with the inherent concentration and pH gradients results in different particle morphology on the two sides of the precipitate membrane. While the tubes have a smooth outer surface, the inner walls are covered with nanoflowers for copper phosphate and with nanoballs for copper silicate.
Highlights
Delicate structures in nature arise from elementary reactions in an imposing way
The surface increase rate rA will be inversely proportional to the tube radius as rA,Si/rA,P = RP/RSi = 1.29 Æ 0.08. Both phosphate and silicate tubes form semi-permeable membrane walls at their tips that allow osmosis to contribute to the sufficiently slow flow. These relations suggest that the walls of the formed copper phosphate tubes are more porous than those of copper silicate, since the same amount of outer liquid is enclosed in the hollow precipitate structure yet their surface area is smaller
We have characterized and compared hollow 3D precipitate patterns evolved in the flow-driven copper–phosphate and copper–silicate systems
Summary
Delicate structures in nature arise from elementary reactions in an imposing way. In a simple system where transition metal salt crystals are placed in sodium silicate solution, complex precipitate structures in the form of colourful plant-like objects grow.[1]. Presence of barium ions.[17] It was shown that either polymorph or crystallite type selection may be achieved by applying a simple flow-injection technique even without the usage of any additives, which draws the attention of materials science.[18,19,20] the selection of appropriate conditions (type of reactants, concentration, flow rate, etc.) can result in selfsustainable precipitate tubes that are stable against time even after drying. This gives the opportunity for producing composite tubes with ingredients being, e.g., catalytically relevant. The microstructure of the synthesized copper phosphate is characterized and compared to that of copper silicate produced under similar conditions
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