Influence of excess alumina on mullite synthesized from pyrophyllite by spark plasma sintering

Abstract

AbstractThe influence of excess Al2O3 on 3:2 mullite produced from α-Al2O3 and pyrophyllite powder was examined. A mixture consisting of 28 wt.% dehydroxylated pyrophyllite and 72 wt.% α-Al2O3 was milled in an attrition mill. The milled powders were sintered by spark plasma sintering (SPS) at 1600°C for 10, 20 and 30 min. Subsequently, the samples were heated at 1350°C for 2 h to determine the influence of the excess Al2O3 on the microstructure. No glassy phase was detected in the sample containing 72 wt.% Al2O3 and sintered at 1600°C for 20 min. The sample with 72 wt.% Al2O3 had greater hardness and fracture toughness compared to 3:2 mullite. The greatest hardness and fracture toughness of 12.43 GPa and 2.71 MPa m–0.5, respectively, were obtained in the sample containing 72 wt.% Al2O3 sintered at 1600°C for 20 min.