Effect of alumina particle size and distribution on infiltration rate and fracture toughness of alumina–glass composites prepared by melt infiltration

Four commercial alumina powders having different particle sizes (0.44, 2.85, 7.08 and 39.81 μm) were presintered for 2 h at 1120 °C and then lanthanum–aluminosilicate glass was infiltrated for up to 4 h at 1100 °C to prepare the densified alumina–glass composites. Alumina having a bimodal and broader particle size distribution was the most effective to the packing. The penetration rate constant increased with raising the alumina particle size having a parabolic dependence of infiltration distance on time described by the Washburn equation. However, the optimum mechanical properties were observed for the composite containing the 2.85 μm alumina. Although the higher fracture toughness of the composites may be achieved by increasing the alumina particle size probably due to the dispersion toughening, the larger alumina particles reduce the strength.