Structure of Borosilicate and Borogermanate Melts at 1300°C; a Viscosity and Density Study

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Abstract
An improved counterbalanced sphere viscometer‐densitometer was used to obtain information at temperatures between 1000° and 1400°C for (a) molten B 2 O 3 , (b) a series of borosilicate melts containing up to 55 mole % SiO 2 , and (c) a series of borogermanate melts containing up to 65 mole % GeO 2 . The dependence on composition of these structure‐sensitive parameters was used to develop a model for the alteration of molten B 2 O 8 by other network‐forming species. The B/Si or B/Ge ratio is shown to be a significant factor in determining melt structure. The silicon (or germanium) atoms appear to be widely separated in the B 2 O 2 solvent for compositions in the 0 to 10‐20 mole % SiO 2 (or GeO 2 ) region. The evidence suggests that a gradual microclustering of SiO 2 (or GeO 2 ) accompanies moderate departures from ideality for B 2 O 3 in the 10‐20 to 60 mole % SiO 2 (or GeO 2 ) region. Extensive micro‐clustering of SiO 2 (or GeO 2 ), approaching network formation, appears to occur in the 60 to 100 mole % SiO 2 (or GeO 2 ) region; some of the boron atoms remain in clusters and/or are forced to adopt a tetrahedral configuration in this region.

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