DENSITY-MEASUREMENTS OF XK(2)S+(1-X)B2S3 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.75) GLASSES - CORRELATION WITH SHORT-RANGE ORDER

Densities of potassium thioborate glasses, xK(2)S + (1 - x)B2S3, are reported over the range, 0 less than or equal to x less than or equal to 0.75. The variation of the density with x is quite strong and is characterized by a maximum at x similar or equal to 0.3. The density increases from 1.7 g/ml for pure B2S3 to 1.92 g/ml at x = 0.35 and decreases thereafter. The increase in density in the 0 less than or equal to x less than or equal to 0.35 range is attributed to the increasing fraction of the tetrahedral boron group, K+BS4-, which has heavier mass but only slightly larger volume. The density decrease in the 0.40 less than or equal to x less than or equal to 0.75 range is associated with the decreasing fraction of these groups with the concomitant increase in the fraction of trigonal boron groups with increasing numbers of non-bridging (terminal) sulfurs. Using estimates of the fractions of short-range order groups in the alkali thioborates, the molar volumes of these groups were determined by a best fit of the density data. The calculated densities were found to agree with the experimental values. The molar volumes of the structural units present in the potassium thioborate glasses were found to be larger than those in the corresponding sodium thioborate glasses. The infrared spectrum analysis of the polycrystalline pyrothioborate phase, 2K(2)S:B2S3, shows strong evidence that this phase does not form in this system.