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[June 2001]
Structure of Liquid Alumina Determined for the First Time
According to the University of Wales (UWA), the structure of liquid alumina has been determined for the very first time by scientists at UWA's Aberystwyth (Ceredigion, Wales) site. At over two thousand degrees, this is the hottest liquid to reveal where its atoms are to be found (Physical Review Letters, Volume 86, Number 21, May 2001).
The extremely high temperature at which alumina melts - 2054°C - has meant that the understanding of the properties of alumina while in its liquid form relies heavily on the ability to study it at such temperatures. 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.
This discovery by Professor Neville Greaves and materials scientists within the Department of Physics at UWA has therefore been achieved by using an aerodynamic levitator furnace to heat the alumina and to levitate it in a neutron beam. Use of a special 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 just 4 neighbouring oxygens and each oxygen just 3 aluminiums. This is totally different from the structure of crystalline alumina from which furnaces are made. Moreover, the precise distribution of the different atomic configurations in the liquid state may explain the enormous (30%) drop in density - from 3.8g/cm3 down to 2.8g/cm3 - when alumina melts.
The change in structure and the resultant change in density between the liquid and crystalline solid helps to explain the shrinkage seen when alumina ceramics are fabricated.
For more information, e-mail Professor Greaves at: gng@aber.ac.uk
ENDS