Fabrication of high density cordierite ceramics using a coal fly ash

Abstract

The aim of this study is to obtain highly densified cordierite ceramics using a coal fly ash as one of the starting raw materials. In the previous studies, however, only porous cordierite ceramics were obtained since the utilized coal fly ashes were not finely pulverized. It was because fly ash was generally so hard to be finely pulverized. In addition, no detailed information for the properties of the obtained cordierite ceramics was available. We succeeded in pulverizing the fly ash by improving pulverizing procedure. Namely, its original grain size of 12 μm could be decreased to 1.2 μm. The pulverized fly ash was mixed with magnesia and alumina sources in a wet ball mill. X-ray diffraction revealed the presence of cordierite phase only for the sample heat-treated at 1150°C. The density of the sintered powder reached 97% theoretical, which was beyond the value required for HIP treatment = 95%. The sintered samples using the pulverized powder revealed sufficiently high thermo-mechanical and electrical properties compared with those of the sintered samples using the unpulverized powder. For instance, flexural strength of 132 MPa, fracture toughness of 3.0 MPa·m1/2 , thermal expansion coefficient of 2.1 × 10-6/K and dielectric constant of 6.5 were obtained for the sample using the pulverized powder. HIP treatment enhanced flexural strength of the treated samples and suppressed bubble formation in them.