Synthesis of Porous Silicon Nitride Ceramic with a Compositional Gradient

This paper summarises results of a study on graded surface layer composition in porous silicon nitride ceramics with a nominal Yb-silicate, Yb2SiO5-additive content of 3.2 mol%, corresponding to 10wt%. A compositional gradient of the additive is formed within the sintered part, depending upon the sintering conditions. The thickness and the phase content of the compositional gradient is significantly affected by the nitrogen activity of the sintering atmosphere. When argon gas is used during heating up and replaced by nitrogen upon soaking, the surface of the sintered ceramic is free of Yb2SiO5, whereas in N2-atmosphere a silicate-rich coating is found as surface layer of the porous silicon nitride ceramic. In presence of carbon and nitrogen, the surface is covered by SiC. In particular the Yb-silicate enriched surface layer can be used as base for an Environmental Barrier Coating, EBC, to protect the interior of the ceramic from hot gas corrosion.

[1]  S. Guo,et al.  Improving Heat Resistance of Silicon Nitride Ceramics with Rare-Earth Silicon Oxynitride , 2006 .

[2]  C. Kawai,et al.  Effect of Porosity and Microstructure on the Strength of Si3N4: Designed Microstructure for High Strength, High Thermal Shock Resistance, and Facile Machining , 2005 .

[3]  S. Kanzaki,et al.  Strain Tolerant Porous Silicon Nitride , 2005 .

[4]  S. Kanzaki,et al.  Fracture Energy of an Aligned Porous Silicon Nitride , 2004 .

[5]  Li Jianbao,et al.  Secondary crystalline phases and mechanical properties of heat-treated Si3N4 , 2003 .

[6]  J. Dai,et al.  The phase transformation behavior of Si3N4 with single Re2O3 (Re = Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb) additive , 2003 .

[7]  T. Ohji,et al.  High-temperature mechanical properties of sinter-forged silicon nitride with ytterbia additive , 2003 .

[8]  T. Ohji,et al.  Fabrication and characterisation of porous silicon nitride ceramics using Yb2O3 as sintering additive , 2003 .

[9]  T. Ohji,et al.  Fabrication of porous anisotropic silicon nitride by using partial sinter-forging technique , 2002 .

[10]  T. Nishimura,et al.  The effect of additives on sintering behavior and strength retention in silicon nitride with RE-disilicate , 2002 .

[11]  Jow-Lay Huang,et al.  The effects of ytterbium oxide on the microstructure and R-curve behaviors of silicon nitride , 2002 .

[12]  T. Ohji,et al.  High performance porous silicon nitrides , 2002 .

[13]  K. Niihara,et al.  Microstructural Evolution and Mechanical Properties of Si3N4 with Yb2O3 as a Sintering Additive , 1997 .

[14]  Sylvia M. Johnson,et al.  Strength and Creep Behavior of Rare‐Earth Disilicate–Silicon Nitride Ceramics , 1992 .

[15]  Sylvia M. Johnson,et al.  Fabrication and Secondary‐Phase Crystallization of Rare‐Earth Disilicate–Silicon Nitride Ceramics , 1992 .