Time-resolved X-ray diffraction of silicate melt and glass under shear

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Silicate melts exhibit non-Newtonian behavior at high deformation rates; however, their molecular-scale origins remain unclear. In this study, we developed a shear deformation apparatus and connected it to the synchrotron radiation X-ray system of SPring-8 (Japan) to collect time-resolved X-ray diffraction of silicate melts and glasses under shear. Using this system, we conducted shear deformation experiments for andesite melts and glasses at temperatures of 700–800 °C and obtained time evolution of the intermediate-range ordering (ring structure) of silicate melts and glasses under shear. Our results exhibited no clear changes in the ring structure at low deformation rates corresponding to viscous deformation, whereas at least two types of deformation of the ring structure were found under the non-Newtonian regime. The deformation of individual rings was observed at high deformation rates, and other types of reversible deformation of the ring structure, such as the formation of a new ring by exchanging bonds between tetrahedra in adjacent rings, may occur at high deformation rates without failure. We infer that the deformed ring structure is energetically and mechanically weak, resulting in enhanced structural relaxation; hence, it reduces the apparent viscosity. The degree of elastic deformation can control shear thinning and the occurrence of brittle failure; hence, we propose a stress criterion for magma fragmentation.