Haixia Qin

Reaction mechanism for in-situ β-SiAlON formation in Fe 3 Si–Si 3 N 4 –Al 2 O 3 composites

In this work, Fe3Si–Si3N4–Al2O3 composites were prepared at 1300°C in an N2 atmosphere using fused corundum and tabular alumina particles, Al2O3 fine powder, and ferrosilicon nitride (Fe3Si–Si3N4) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe3Si–Si3N4–Al2O3 composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe2C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si5AlON7 indicated that the ferrosilicon alloy accelerated the reactions between Si3N4 and α-Al2O3 fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si3N4 because of its low reactivity.