Effects of silica sol on the preparation and high-temperature mechanical properties of silicon oxynitride bonded SiC castables

Abstract

Abstract Silicon oxynitride bonded SiC castables (SS castables) were prepared via in-situ nitridation at 1420 °C for 6 h in flowing N 2 , using black SiC, SiO 2 fume and Si powder as starting materials, and silica sol as a binder. Phase compositions and microstructures of as-prepared SS castables were characterized, and the effects of silica sol's type and amount on their cold and hot moduli of rupture (CMOR and HMOR) and thermal shock resistance examined and discussed. The results indicated that using silica sol containing well-dispersed spherical SiO 2 nanoparticles as a binder not only resulted in improved workability of fresh castables and packing density of green samples, but also promoted the in-situ formation of Si 2 N 2 O bonding phase on nitridation. HMOR at 1400 °C of nitrided SS castables using 7 wt% silica sol was as high as 51 MPa, and their residual strength after one thermal shock cycle (1100 °C-room temperature) remained significantly higher than their CMOR value before the thermal shock. It is believed that the in-situ formed Si 2 N 2 O in the castables was responsible for the much improved cold/hot strength and thermal shock resistance.