Fabrication of graded porous ceramics using alumina-carbon powder mixtures

Green bodies consisting of mixtures of submicrometric alumina powder and ca rbon coal were prepared by cold isostatic pressing. Sintering in air atmosp here resulted in alumina ceramics with controlled porous structure and a hi ghly homogenous distribution of pores. Sintering in vacuum (at 1 to 5 Pa) f ollowed by sintering in air for 2 h at 1530 degreesC led to a graded porous structure. These samples exhibited a highly porous core and a dense surfac e layer. The conditions of thermodynamic equilibrium for the chemical react ions occurring in the studied system during sintering were calculated. Thes e were used to explain the formation of the graded porosity. (C) 2001 Elsev ier Science Ltd and Techna S.r.l. All rights reserved.