Internal friction analysis of structural relaxation in Si–C–O glass

Abstract Forced torsional oscillations has been recorded in Si–C–O glass up to elevated temperatures (≈1900 K). An attempt is shown to extend the measurements into the transformation range where internal friction merely arises from a viscosity-related mechanism and is represented by a background curve, or network contribution (i.e., that component of the internal friction curve which remains after a peak caused by stress-induced anelastic phenomena has been subtracted). Below 2000 K, the internal friction background curve is affected by delayed elasticity. On the other hand, using an approximate expression which relates the tangent of the loss angle to the glass viscosity, it is shown that the frequency dependence of the background internal friction above 2000 K can be simply explained in terms of a Maxwell model. In other words, viscous flow simply represents the high-temperature limiting behavior for the silicon oxycarbide glass, but it is overlapped by an anelastic phenomenon which hampers the full stabilization of its network structure. Some details of the viscoplastic behavior of the material could be obtained by examining internal friction data collected upon cooling.