CHEMICAL-REACTIONS BETWEEN ALUMINUM AND FLY-ASH DURING SYNTHESIS AND REHEATING OF AL-FLY ASH COMPOSITE

Thermodynamic analysis indicates that there is the possibility of chem ical reactions between aluminum melt and cenosphere fly ash particles. These particles contain alumina, silica, and iron oxide, which, durin g solidification processing of aluminum-fly ash composites or during h olding of such composites at temperatures above the melting temperatur e of aluminum, are likely to undergo chemical reduction. These chemica l reactions between the fly ash and molten aluminum have been studied by metallographic examination, differential thermal analysis (DTA), sc anning electron microscopy (SEM), energy-dispersive X-ray analysis (ED X) and X-ray analysis after holding the aluminum-fly ash composites fo r different periods above the liquidus temperature. The experiments in dicate that there is progressive reduction of silica and mullite in th e fly ash, and formation of alumina with holding time of composites at a temperature of 850 degrees C. The walls of the cenosphere fly ash p articles progressively disintegrate into discrete particles as the rea ction progresses. The rate of chemical reaction was high at the start of holding the composite at a temperature of 850 degrees C, and then t he rate significantly decreased with time. The reaction was almost com plete after 10 hours.