Liquid alumina reveals its secrets
6 Jun 2001
The structure of liquid alumina has been determined for the very first time by scientists at the University of Wales, Aberystwyth (UWA).
Alumina, a white crystalline powder used in the production of glasses, ceramics, abrasives and aluminium, melts at 2054 degrees centigrade making it difficult to study at an atomic level.
Until now, the use of a container within a conventional furnace was precluded by the high reactivity of the alumina with the vessel containing it.
The discovery by Professor Neville Greaves and colleagues within the Department of Physics at UWA was achieved using an aerodynamic levitator furnace to heat the alumina and to levitate it in a neutron beam.
Use of a computer simulation procedure that directly predicts the experimental results then enabled Professor Greaves and his colleagues to undertake the first neutron diffraction study of molten alumina in contactless conditions and to obtain the first reliable structural model of liquid alumina.
Their studies have shown that, in liquid alumina, each aluminium atom has four neighbouring oxygens and each oxygen just 3 aluminiums.
This is reported to be different from the structure of crystalline alumina that furnaces are made from. Moreover, the precise distribution of the different atomic configurations in the liquid state may explain the 30% drop in density (from 3.8 g/cm 3 to 2.8 g/cm 3) when alumina melts.
The change in structure and the resultant change in density between the liquid and crystalline solid is said to help explain the shrinkage seen when alumina ceramics are fabricated.
The discovery of the structure of alumina in its molten state will enable materials scientists to begin to understand the properties of this and other high temperature materials and to incorporate that knowledge in the development of ceramics and glasses for the future.
