The Nature of the Glass Transition in a Silica-Rich Oxide Melt

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Science  26 Aug 1994:
Vol. 265, Issue 5176, pp. 1206-1209
DOI: 10.1126/science.265.5176.1206


The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K2Si4O9 at temperatures as high as 583°C are presented. Rates of exchange for silicon among silicate species, which involves Si—O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 1010 pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion.