Thermochemistry of the Amorphous System SiO 2 -GeO 2 : Comparision of Flame Hydrolysis Materials to High Temperature Fus
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THERMOCHEMISTRY OF THE AMORPHOUS SYSTEM SiO 2-GeO2 : COMPARISION OF FLAME HYDROLYSIS MATERIALS TO HIGH TEMPERATURE FUSED GLASSES 2 1 P.D. MANIAR 1, A.NAVROTSKY , AND C.W. DRAPER
1. Dept. of Geological and Geophysical Sciences, Princeton University, Princeton, NJ 08544. 2. AT&T, Engineering Research Center, Princeton, NJ 08540.
ABSTRACT Energetics and structure of germania doped silica prepared from high temperature melts and by flame hydrolysis were investigated using transposed temperature drop and solution calorimetry. Heat contents (H973 -H298 ) are similar for first and second drops for the flame hydrolysis preforms reflecting the effect of temperature of deposition (1073 K) increating a relaxed structure which is not easily rearranged. Heats of solution, at 973 Kin molten lead borate, of fused glasses along the Si0 2 -GeO 2 binary show ideal heats of mixing between the endmembers. This'indicates that fused glasses behave ina simple manner, with ideal substitution of Ge for Si inthe tetrahedral framework. Flame hydrolysis samples (preform and annealed glasses) also show ideal heats of mixing. This suggests that the flame hydrolysis materials are energetically very similar to their bulk-melted counterparts. This insensitivity of energetics to preparation conditions is consistent with our previous studies on silica prepared at various temperatures [1].
INTRODUCTION Si0 2 -GeO 2 glass is primarily used to manufacture low attenuation optical waveguides. The need for ultra pure products has promoted the use of the flame hydrolysis technique inproducing amorphous preforms which can be sintered to glass without melting. Previously studied vapor deposited, amorphous Si0 2 and Si0 2 -P2 0 5 materials show decreasing metastability, relative to fused glass, with increasing temperature of preparation [1,4]. Amorphous solid solutions inthe system Si0 2 -GeO 2 prepared by high temperature fusion and flame hydrolysis is, therefore, of interest to further understand the inter-relation of structure and energetics to preparation conditions. Linear behavior of density and refractive Index and non-linear behavior of viscosity and thermal expansion of glasses along the Si0 2 -GeO2 binary have been reported [2,3]. In this paper we investigated the energetics of the flame hydrolysis preforms by transposed temperature drop calorimetry and heats of mixing by high temperature solution calorimetry, of fused glasses and annealed glasses prepared by sintering the preforms. Heats of mixing of the binary Si0 2 -GeO 2 reported previously [4] were reinvestigated due to the possibility of trace crystallinity inthose glasses.
Mat. Res. Soc. Symp. Proc. Vol. 172. ©1990 Materials Research Society
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EXPERIMENTAL
Sample Preparation Fused glasses were prepared by thoroughly mixing pure, powdered silica and germania glasses (prepared from pure oxides) inrequired stoichiometry. Mixtures (several grams) were placed in a platinum crucibles and suspended ina furnace at 1923 K for 12 to 24 hours. Melts were quenched to a glass inliquid nitrogen. T
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