Al 2O 3-containing droplets (“model cords”) were placed on an Al 2O 3-free matrix glass of the system Na 2OCaOSiO 2 and were allowed to sink-in and react with the glass melt. From a comparison using Al 2O 3-free substances it could be shown that the Al 2O 3-containing droplets achieved characteristic rotationally-symmetric contours, which can be explained only by assuming an acting interfacial energy in the contact zone between the two glass melts. From the droplet contours an effective interfacial tension between 0.4 and 1.1 mN m −1 could be calculated. The interdiffusion profiles in the contact zone showed that although Al 2O 3 and SiO 2 equilibrated slowly by diffusion, both Na 2O and CaO withstand equilibration by up-hill diffusion. In conclusion, both the effective interfacial energy and the uphill diffusion prevent a rapid dissolution of Al 2O 3-containing cords.
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