Sintering of optical wave-guide glasses

Abstract

Sintering kinetics of glasses prepared by external vapour-deposition technique were quantitatively measured at temperatures ranging from 1000 to 1390° C. Sintering kinetics of borosilicates are consistent with the model proposed for the viscous flow sintering mechanism. The magnitude and the activation energy of the viscosity data derived from the sintering data agree reasonably well with the published data in the borosilicate system. From the viscosity data and sintering model, the decrease in sintering temperature per unit change in dopant content is calculated. It is also shown that at a certain compositional range, an increase in the dopant content can actually alleviate the problem of bubble growth while maintaining the same sintering conditions. This study can be used to determine the relative composition-time-temperature relations for sintering borosilicate glasses. Thus, it has direct applicability to the sintering of soot forms prepared by the external vapour-deposition technique. Furthermore, because of the similarity in microstructures of glasses prepared by the external vapour-deposition and the MCVD processes, one can anticipate similar sintering kinetics for MCVD preforms.