UNDERSTANDING STRENGTH AND MICROSTRUCTURE OF SGA USING NANOINDENTATION AND ULTRASOUND TESTING

Wijayaratne, H. , Perander, L., Hyland, M., Metson, J., Framil Carpeño, D.

The strength of agglomerated particles of Smelter Grade Alumina (SGA) is a very important property as it indirectly impacts on how the material behaves during handling, transportation, storage and ultimately feeding to aluminium reduction cells. Poor strength contributes to the generation of fines as a result of particle breakdown. The level of fines in alumina impacts on the working environment through the formation of dust as well as on the cell operation. Eventually this leads to poor pot line performance and increased emissions.

Determination of an industrially relevant measurement of alumina strength is a considerable challenge. The Forsyth-Hertwig method, which is well established in the industry, has many limitations. One of the main limitations is the fact that it is an aggressive test and evaluates only the <45 μm fraction which easily leads to a perceived attrition strength that is inaccurate. Thus the development of a measurement of true particle strength is of value for the industry as well as for fundamental understanding of alumina microstructure and particle strength. This paper reports on experimental investigations of industrial SGAs and laboratory prepared samples to explore alumina particle strength using nanoindentation as well as ultrasound mediated particle breakage tests. These techniques demonstrate the influence of alumina microstructure on its apparent strength and provide insights into the evolution of strength within alumina particles in the calcination process.