Morphological evolution of porous silicon nitride ceramics at initial stage when exposed to water vapor

The reaction behavior of porous silicon nitride (Si₃N₄) ceramics at initial stage when exposed to water vapor ranging from 5 to 20 vol% at 1200 °C was investigated using online thermogravimetric (TG) method. The effect of water vapor on the surface morphology and corrosion interface of porous Si₃N₄ ceramics was characterized using scanning electron microscopy (SEM). The results show that water vapor can aggravate the reaction and the reaction rate accelerates with the water vapor content increasing. As for the morphological evolution, water vapor promotes the formation of interconnected pores, which is possibly caused by the breakage of amorphous SiO₂ by inner massive gas product and gas releasing through crystalline SiO₂. Based on these, a gas-solid model is adopted to describe the effect of different water vapor partial pressure on the reaction kinetics and obtains a good agreement. - Highlights: • The effect of water vapor on the morphology of porous Si₃N₄ is studied at 1200 °C. • Higher water vapor content can aggravate the reaction of porous Si₃N₄ ceramics. • Mechanism of pores formation and aggravated reaction process are discussed. • A gas-solid model is used to describe the effect of water vapor on reaction kinetics.