Triple-layered, thick glassy grain boundaries in porous cordierite ceramics

Mechanical tests and microstructural investigations were performed on porous cordierite ceramics. Four-point bending tests were carried out both in air and in water. It was shown that the mechanical strength was strongly influenced by the experimental conditions. Triple-layered, thick amorphous grain boundaries were observed by high-resolution transmission electron microscopy. The composition of each layer as measured by energy dispersive X-ray spectroscopy was shown to be different. It is concluded that applying an external stress causes water-induced stress corrosion cracking preferentially occurring at the amorphous grain boundaries and at the triple grain junctions. This may have caused the dramatic decrease in the mechanical strength in water compared with that in air.