Surface tension of melts in the system CaMgSi2O6-CaAl2Si2O8 and its structural significance

The surface tension between silicate melts and air has been measured for melt compositions lying on the diopside-anorthite (Di-An) join from 1300° C to 1580° C. It ranges from 300 dyne/cm to 400 dyne/cm, and decreases with increasing temperature, except for a pure diopside composition. At relatively high temperatures, the surface tension decreases as the anorthite content increases, whereas at lower temperature it is almost constant. These results suggest that diopside melt has a more discrete structure at higher temperatures, whereas, anorthite-bearing melts do not dissociate in the temperature range studied. They also suggest that the structure of both the surface and interior parts of the melt are almost identical at lower temperatures, but at higher temperatures, the surface part has a more polymerized structure with Al₂O₃ enrichment. The surface energy, obtained from the relationship between surface tension and temperature, increases from 294 erg/cm² (Di composition) to 1013 erg/cm² (Di40An60) with increasing anorthite content.