Preparation of machinable cordierite/mica composite by low-temperature sintering

In order to fabricate machinable cordierite/mica composite at low temperatures, the mica-composition glass powder was mixed with the conventional magnesia, alumina and silica powders which are raw materials of cordierite, compacted and fired in a sealed platinum container. By the addition of the 40 mass% mica-composition glass powder, machinable cordierite/mica composite was obtained. The machinability was caused by the interlocking microstructure of mica developed in the composite. In the firing process, mica crystallized at about 730NBDGC, cordierite was suddenly formed at 1050-1100NBDGC and the densification progressed markedly at 1000-1100NBDGC. The formation and sintering of cordierite were strongly promoted by a small amount of gaseous fluorine and/or fluorides. It was considered that fluorine and fluorides such as AlF3 evaporated from the mica-composition glass at > 800NBDGC and gaseous HF was formed in the sealed platinum container by the reaction of fluorine with water evaporated from the glass.