Experimental evidence for the existence of an ordered structure in a silicate liquid above its liquidus temperature

The strategy of this study is to repeatedly thermally scan a basaltic glass sample up and down at a rate of 20 K/min in a differential scanning calorimeter (DSC) from 60 to 1250degreesC (T-liq + 70degreesC), and to 1300degreesC (T-liq + 120degreesC), where T-liq is the liquidus temperature, so as to observe the structural development of both crystals and the liquid above T-liq. A gradual transformation from a polycrystalline to a mono-crystalline phase occurs during down scans, indicating that the degree of the structural ordering of the liquid at T > T-liq increases, when the up- and -down scans are repeated. The liquid remembers the structure of its previous crystalline state. The ordered structure of the liquid favors the structure of one stable, mono-crystalline phase. The degree of the structural ordering of the liquid decreases as the maximum up scanning temperature (above T-liq) is raised. Furthermore, the present paper discusses several aspects of the industrial significance of the new experimental approach and the findings about the ordered structure in the system above its T-liq. (C) 2004 Elsevier B.V. All rights reserved.