Pressure infiltration technique for synthesis of aluminum–fly ash particulate composite

Beds of nickel coated and uncoated cenosphere fly ash can be successfully infiltrated by molten aluminum under very low pressures. The density of the resultant composite is ≈1.4 and 1.2 g cm−3 respectively, compared to 2.68 g cm−3, the density for aluminum. The threshold pressure was found to be between 20.68 and 27.58 kPa for infiltration of molten pure aluminum into uncoated fly ash, and around 6.7 kPa for Ni-coated fly ash. These data were used to back calculate an effective wetting angle between molten pure aluminum and fly ash using Young’s and Washburn equations. The average value of the wetting angle calculated for uncoated fly ash is 111°. The microstructures and chemical composition of the composites made with coated and uncoated fly ash were studied using optical and scanning microscopy; they show good infiltration except for regions between contacting cenospheres. They also show transport of nickel from the bottom to the top of the sample when nickel coated particles were used.