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

Crystals are known to affect bubble behavior in natural and industrial melts. In volcanology, high crystal contents (ϕ_c > 30 vol.%) may drastically increase the suspension viscosity, altering bubble dynamics severely enough to modify eruptive style. During industrial glass production, crystals can affect the process and the final product. In this work, we investigate how a small crystallinity of nano-sized RuO₂ (ϕ_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.