The possibility of fabricating shrinkage-free sialon ceramics from natural aluminosilicates by simultaneous carbothermal reduction and nitridation (CRN) was explored. X-ray diffraction studies confirmed that the products synthesized contained sialon as the major crystalline phase. The average linear shrinkage of sialon pellets produced by CRN at 1450 oC from bentonite and kaoline was about 9-18%. However, it is interesting to report that the study with kyanite led to an important discovery of the possibility of synthesizing sialon samples by CRN to have zero shrinkage after sintering. This has an important implication as many industrial applications demand close dimensional tolerance of fired ceramic bodies such as honeycomb structures. The volume expansion associated with the transformation of kyanite to mullite around 1350 oC is responsible for compensating the sintering shrinkage which would otherwise occur during CRN. The resulting porosity of sialon pellets was more than 60%.

Keywords: Shrinkage free ceramics, Sialon ceramics, Kyanite, Carbothermal reduction and nitridation, Porous ceramics.