The Reinforcement Of Al₂O₃-C Slide Gate Plate By Non-oxide Whiskers

With the development of new steel-making technology, the service life of refractories is put forward to a more and more rigorous condition. The slide gate as a functional refractory with security reliability plays an important role in continuous casting process.This work was to improve the strength of Al₂O₃-C slide gate, by using crystal Si powder, metal Al powder, SiO₂ powder, O'-SiAlON precursor(the milled mixture ofβ-Si3N4 powder,α-Al₂O₃ powder and SiO₂ powder) as additives to formβ-SiC whiskers and O'-SiAlON whiskers by in situ reaction. The influences of different sintering atmosphere and different contents of SiO₂ powder, crystal Si powder and O'-SiAlON precursor on the formation ofβ-SiC whiskers and O'-SiAlON whiskers and the performance of Al₂O₃-C refractories by in situ reaction were studied. The influences of using silicone resin that substitutes for phenol formaldehyde resin as a binder for Al₂O₃-C refractories on its performance were also studied. The phases and microstructure were characterized by means of X-ray diffractometer (XRD), scanning electron microscopy (SEM) attached with an energy dispersive X-ray microanalyzer (EDS). The in situ formation mechanism ofβ-SiC whiskers and O'-SiAlON whiskers and their reaction conditions of thermodynamics and dynamics were discussed. The strengthening mechanism ofβ-SiC whiskers and O'-SiAlON whiskers in Al₂O₃-C refractories was preliminary studied.The results show thatβ-SiC whiskers are originally formed in specimens with Si as additive at 1300℃and mass-produced at 1500℃. Crystal Si is the main formation source ofβ-SiC whiskers. SiO₂ plays an important role of mass transfer in gas phase. The main formation mechanism ofβ-SiC whiskers is gas-solid mechanism. The embedded SiO₂+C powders can effectively restrain the decomposition and volatilization of SiO₂ contained in reaction system during the process of sintering, which can further promote the in situ synthesis of O'-SiAlON whiskers andβ-SiC whiskers. O'-SiAlON whiskers are formed in situ at 1500℃.β-SiC whiskers and O'-SiAlON whiskers formed on the edge of graphite and in the hole of specimens are in the shape of flocculence and needle. These needle-like and flocculent whiskers that interlace in aggregate and matrix can effectively improve the strength of specimens. The strength of specimens withβ-SiC whiskers and O'-SiAlON whiskers synchronously formed is about 3 times higher than blank samples and about 1 times higher than specimens with onlyβ-SiC whiskers or O'-SiAlON whiskers formed.