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A molecular-scale origin of non-Newtonian behavior of silicate melts revealed by time-resolved X-ray diffraction under tension, compression and shear

Satoshi Okumura1, Kentaro Uesugi2, Akio Goto3, Kazuhisa Matsumoto1, Tatsuya Sakamaki1, Masahiro Yasutake2

  • Affiliations:  1Division of Earth and Planetary Materials Science, Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan; 2SPring-8/Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan; 3Center for Northeast Asian Studies, Tohoku University, Sendai, Miyagi 980-8576, Japan 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 190

  • Programme No: 3.2.13

  • Theme 3 > Session 2

Abstract

Silicate melts exhibit non-Newtonian behavior under high deformation rates. To understand the molecular-scale origin of the non-Newtonian behavior of silicate melts, we have developed the experimental system at the beamline (BL47XU) of SPring-8 (Japan). Using this experimental system, the X-ray diffraction of silicate melts at <~900°C can be obtained every ~100 ms under tension, compression and shear. Our experimental studies revealed that intermediate-range ordering (IRO) of silicate melts changes but short-range ordering (SRO) such as T--O and T--T distances, where T and O represent the T site cations (Si and Al) and oxygen, respectively, show no clear variation under elastic deformation. Both the IRO and SRO indicate no change under the Newtonian regime. The IRO reflects the size of the ring formed by SiO4 tetrahedra; hence, our results imply that the ring size changes during the elastic deformation of silicate melts. Under tension, the ring becomes large anisotropically. Under compression, the small rings form, which are mechanically strong but energetically unstable. Under shear, the rings are anisotropically deformed, that is, the ring structure is compressed and stretched to the directions of macroscopic stress. In all cases of tension, compression and shear, the degree of elastic deformation controls the occurrence of brittle failure; hence, we propose a stress criterion for magma fragmentation.