Effects of oil shale addition and sintering cycle on the microstructure and mechanical properties of porous cordierite-ceramic

Porous cordierite ceramics were produced from stevensite-rich clay and andalusite mixture using oil shale (OS) as a natural pore-forming agent. The pressed pellets of powdered samples were sintered at 1300 °C for 2 h using both conventional sintering (CS) and three-step sintering (TSS) cycle. The mechanical properties were evaluated by three-point bending test, Brazilian test and ultrasonic measurements. The microstructure and mechanical properties are strongly influenced by the sintering conditions and the amount of (OS) added (0-20 wt%). The (CS) cycle and the maximum addition of (OS) resulted in an increase in pore size and open porosity from 17.7% to 52.8%. The samples sintered using (TSS) exhibited a higher flexural and tensile strengths (25.4 and 16.8 MPa, respectively) than those of samples sintered via (CS) cycle (11.2 and 7.54 MPa, respectively). However, the gradual increase in (OS) addition revealed a strong decrease in mechanical properties such as flexural strength (44.6-17.8 MPa), tensile strength (19.2-13.3 MPa) and Young׳s modulus (70.5-46.8 GPa). The formation mechanism of the porous structures by adding (OS) are also reported and discussed.