Development of the microstructure of the silicon nitride based ceramics

Abstract

Basic regularities of silicon nitride based materials microstructure formation and development in interrelation with processing conditions, type of sintering additives, and starting powders properties are discussed. Models of abnormal or exaggerated grain growth are critically reassessed. Results of several model experiments conducted in order to determine the most important factors directing the microstructure formation processes in RE-fluxed Si3N4 ceramics are reviewed. Existing data on the mechanisms governing the microstructure development of Si3N4-based ceramics are analyzed and several principles of microstructure tailoring are formulated.

Dense and near-net-shape fabrication of Si3N4 ceramics

“…Undoubtedly, last this causes exaggerated grain growth due to solution of ␣-as well as small ␤-Si 3 N 4 particles and reprecipitation onto larger ␤-Si 3 N 4 grains. In addition, the effect of abnormal grain growth is enhanced by high sintering temperatures and long sintering times [223,224]. It is very important to control the abnormal grain growth to obtain Si 3 N 4 ceramics with high fracture toughness accompanied by high strength.…”

Low-temperature synthesis and sintering of γ-Y2Si2O7

“…The reason for these differences has not been identified at present. In the sintering of Si 3 N 4 with Y 2 O 3 /Y 2 O 3 + SiO 2 as additives, 27 one of the major factors for micrographic differences was the viscosity of the liquid phase formed during sintering. A liquid phase with higher viscosity would lead to elongated grains with a higher aspect ratio.…”

Characterization of High-Temperature Hierarchical Porous Mullite Washcoat Synthesized Using Aluminum Dross and Coal Fly Ash

“…This is because the SiO 2 that originated from CFA was excessive and associated with impurities such as K 2 O, Fe 2 O 3 , TiO 2 , P 2 O 5 , CaO and CuO. The presence of these impurities has lowered the melting point of the SiO 2 and also decreased the viscosity of the molten liquid phase [13]. At the same time, Al 2 O 3 from the AD has begun to diffuse into the SiO 2 -rich molten liquid phase and formed an aluminosilicate molten liquid phase.…”