Processing of dense nanostructured HAP ceramics by sintering and hot pressing

Abstract

A nanosized HAP powder was sintered and hot pressed, in order to obtain dense HAP ceramics. In a first series of experiments, the powder was isostatically pressed into uniform green compacts and sintered at temperatures ranging from 1000 degrees C to 1200 degrees C in air atmosphere for different times. In a second series, the isostatically pressed green compacts were hot pressed in argon atmosphere at 900 degrees C, 950 degrees C and 1000 degrees C. The SEM micrograph of the sample sintered at 1200 degrees C for 2 h showed a uniform 3 mu m mean grain size dense microstructure. In the case of hot pressed HAP compacts, full dense, translucent nanostructures were obtained having mean grain size below 100 nm and improved mechanical properties. With the grain size decreasing from 3 mu m to 50 nm, the fracture toughness of pure HAP ceramics increased from 0.28 MPa m(1/2) to 1.52 MPa m(1/2).