Tube Formation in Reverse Silica Gardens

The flow injection of sodium silicate solution into a large reservoir of lighter cupric sulfate solution creates single, downward growing precipitation tubes. These hollow structures have diameters in the range of 0.8−2.4 mm and can grow several centimeters in length. Four distinct growth regimes are observed, and their stability in terms of flow rate and cupric sulfate concentration is investigated. Three of these growth regimes resemble behavior reported earlier for the injection of cupric sulfate into silicate solution. However the “reverse” conditions studied here reveal one distinctly different regime in which tube growth is limited by repetitive fracturing. The lengths of the broken-off tube segments and the times between subsequent break-off events can be described by log−normal distributions.