Compositional analysis of copper–silica precipitation tubes

Abstract

Silica gardens consist of hollow tubular structures that form from salt crystals seeded into silicate solution. We investigate the structure and elemental composition of these tubes in the context of a recently developed experimental model that allows quantitative analyses based on predetermined reactant concentrations and flow rates. In these experiments, cupric sulfate solution is injected into large volumes of waterglass. The walls of the resulting tubular structures have a typical width of 10 microm and are gradient materials. Micro-Raman spectroscopy along with energy dispersive X-ray fluorescence data identify amorphous silica and copper(ii) hydroxide as the main compounds within the inner and outer tube surfaces, respectively. Upon heating the blueish precipitates to approximately 150 degrees C, the material turns black as copper(ii) hydroxide decomposes to copper(ii) oxide. Moreover, we present high resolution transmission electron micrographs that reveal polycrystalline morphologies.

Tube Formation in Reverse Silica Gardens

“…Pagano et al reports that tube walls formed by cupric sulfate injection are non-homogeneous materials showing high silica content on the outside and high copper hydroxide content on the inside of the tube. 45 This layering reflects the geometrical arrangement of the initial reactants, which suggests that tubes grown under reverse conditions should consist predominantly } of amorphous and/or colloidal silica on the inside and copper hydroxide on the outside. Reverse reaction conditions also give rise to a growth regime that we coined "fracturing".…”

“…To eliminate these problems, ThouvenelRomans et al developed a method which allows the collection of quantitative data based on flow-controlled injection. [42][43][44][45] This method replaces the seed particle with a "seed solution" which is injected into a large volume of waterglass at constant flow rates of several milliliters per hour. This approach yields long, solitary tubes that grow in upward direction and has allowed the identification of three distinct growth regimes coined jetting, popping, and budding.…”

Filament dynamics in confined chemical gardens and in filiform corrosion

“…Chemical similarities include the product composition, basically a metal oxyhydroxide, that in the case of silicate chemical gardens typically also includes an outer layer of amorphous silica. 30,31 Earlier studies have analysed the detailed composition of the brown rust trail which typically contains a mixture of iron(II) and iron(III) hydroxides and oxides. 19,32 They both form filamentary reaction products at macroscopic length-scales and belong to the large class of self-organizing far-from-equilibrium systems.…”

The Fuel Cell Model of Abiogenesis: A New Approach to Origin-of-Life Simulations

“…In a fuel cell concept of prebiotic alkaline hydrothermal vents, the anode and cathode would be the interior and exterior chimney mineral surfaces, respectively. The exterior and interior of a chimney could have different mineral compositions, since chemical garden-like structures tend to exhibit compositional variations across the membrane reflecting the chemical gradients in which they precipitate (Russell and Hall 2006;Pagano et al 2006;Cartwright et al 2011;Barge et al 2012). Though a hydrothermal chimney would likely also contain components such as silica gel or carbonate, the ability of the "electrodes" to drive redox reactions would probably be dependent on the presence of electrocatalytic minerals such as metal sulfides and oxyhydroxides (cf.…”