Fabrication of graded porous ceramics using alumina–carbon powder mixtures

Green bodies consisting of mixtures of submicrometric alumina powder and carbon coal were prepared by cold isostatic pressing. Sintering in air atmosphere resulted in alumina ceramics with controlled porous structure and a highly homogenous distribution of pores. Sintering in vacuum (at 1 to 5 Pa) followed by sintering in air for 2 h at 1530°C led to a graded porous structure. These samples exhibited a highly porous core and a dense surface layer. The conditions of thermodynamic equilibrium for the chemical reactions occurring in the studied system during sintering were calculated. These were used to explain the formation of the graded porosity.