A feedback mechanism between crystals and bubbles in a RuO2-bearing melt

Crystals are known to affect bubble behavior in natural and industrial oxide glass melts.[1] In volcanology, high crystal contents (c > 30 vol.%) may drastically increase the suspension viscosity, altering bubble dynamics severely enough to modify the eruptive style.[2] During industrial glass production, crystals may affect the process and the final product, if formed in an uncontrolled way. In this work, we investigate in laboratory-scale how a small crystallinity of nano-sized RuO2 (c  2 vol.%) modifies bubble behavior in a melt, generating a cyclic gas-release phenomenon.We conduct a series of experiments on a three-phase system composed of a borosilicate melt, bubbles, and RuO2 crystals. Optical microscopic investigation is performed on the products of thermal treatment at 1000 °C for different durations. Based on viscosity measurements, contact angle measurements, and numerical simulations, we propose a mechanism of entrainment of bubbles carrying crystals to the upper surface accompanied by crystal aggregation, and followed by an increase in viscosity to explain the observed phenomenon