Compression creep and dynamic viscoelastic studies of binary sodium and lithium silicate glasses around deformation temperature
Journal of the Ceramic Society of Japan
Uniaxial-compression creep test and dynamic viscoelastic measurement were performed on binary sodium-and lithium-silicate glasses at around their deformation temperature. The derived creep function was converted into a relaxation modulus using the Laplace transformation and its inversion. Shear relaxation modulus G(t) was expressed by a 1-term Maxwell model for both glass systems. In the sodium system, the viscous term in the model decreased with increasing modifying oxide. In contrast, the
... ium system showed a higher value in the elastic term and a lower value in the viscous term than the sodium system. The storage elastic modulus E¤(½) observed in the dynamic measurement started to decrease at the glass transition temperatures, and complicated fluctuation of the modulus was observed at around the deformation temperatures for frequencies larger than a few Hz. The decrease in the modulus at the transition temperature has been suggested to originate from slipping between silicate clusters which were separated by non-bridging oxygen with the modifying cations similar to polymer materials. The master curve of the loss elastic modulus E¤¤(½) showed unique frequency dependence in all sodium-silicate glasses, while the data at high frequencies at around the deformation temperature deviated from the curve. This suggested that slipping between silicate clusters is the main process of structural relaxation, and anomalies in the dynamic modulus at around the deformation temperature could be related to other relaxation. The E¤(½) of the lithium-silicate glass showed similar temperature dependence and the master curve of E¤¤(½) had a narrower frequency distribution. The contribution to E¤¤(½) below 10 ¹2 Hz was smaller than in the sodium system. This lack of slow relaxation was well consistent with the comparably lower viscous term of G(t) in the Maxwell model. Injection testing into a narrow pore showed a faster saturation of the injected volume for the lithium-silicate glass.