Design and fabrication of porous Si3N4-Si2N2O in situ composite ceramics with improved toughness. (15th November 2016)

• Record Type: Journal Article
• Authors: Yang, Xuejin; Li, Bin; Zhang, Changrui; Wang, Siqing; Liu, Kun; Zou, Chunrong
• Is Part Of: Materials & design. Volume 110(2016)
• Page Start: 375
• Page End: 381
• Publication Date: 2016-11-15
• Subjects: Ceramic matrix composites -- Oxidation -- Gel-casting -- Mechanical properties -- Dielectric properties; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2016.08.023
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: In order to improve the fracture toughness and ease the machining process of porous silicon nitride (Si3 N4 ), pre-oxidation combining with gel-casting near-net forming method was adopted to prepare a kind of porous silicon nitride-silicon oxynitride (Si3 N4 -Si2 N2 O) in situ composite ceramics. The oxidation of Si3 N4 powders and its influence on the rheological properties of Si3 N4 slurries were carefully studied, and the microstructure, composition, mechanical and dielectric properties of the sintered composite ceramics were also investigated. It is interesting that the existence of the SiO2 coating improved the maximal absolute Zeta potential of Si3 N4 powders, which could in turn increase the stability and decrease the viscosity of ceramic slurries. Si2 N2 O phase was synthesized by the reaction between SiO2 and Si3 N4 at 1750 °C, and it was unstable at temperatures over 1850 °C. Appropriate introduction of Si2 N2 O could optimize the toughness of porous Si3 N4, but it was always at the expense of the flexural strength. In addition, the dielectric constant of the composite ceramics increased with the decrease of theoretical porosities, while the loss tangent reversed and remained at a relatively low level. Graphical abstract: Highlights: Porous Si3 N4 -Si2 N2 O with improved toughness were fabricated by pre-oxidation, gel-casting and pressureless sintering. The existence of the SiO2 coating was beneficial to the rheological performance of Si3 N4 slurries. Si2 N2 O phase was formed by the reaction between Si3 N4 and SiO2 at 1750 °C, and it was unstable at 1850 °C. Proper amount of Si2 N2 O optimized the toughness of porous Si3 N4, but it was always detrimental to the flexural strength. The dielectric constant of porous Si3 N4 -Si2 N2 O increased with the decreasing porosity, but the loss tangent reversed.