Catalytic nitridation preparation of high-performance Si_3N_(4(w))-SiC composite using Fe_2O_3 nano-particle catalyst: Experimental and DFT studies

摘要

The complete conversion from Si into Si_3N_4 was achieved after 2 h nitridation at 1400°C by using in-situ formed Fe_2O_3 nano-particles (NPs) as a catalyst. Such a synthesis condition was remarkably milder than that (>1450°Cfor many hours) required by the conventional Si nitridation method. Density functional theory (DFT) calculations suggest that Fe_2O_3 catalyst accelerates the Si nitridation via weakening the bond strength of absorbed N_2 molecule. Furthermore, Si_3N_(4(w))-SiC composites prepared by the present catalytic nitridation method showed excellent high-temperature properties including modulus of rupture (MOR of 29.9 MPa at 1400°C), thermal shock resistance (residual MOR percentage of 50% at ΔT= 1300 C), as well as good oxidation resistance and cryolite corrosion resistance against molten cryolite. It can be concluded that, Fe_2O_3 NPs not only greatly accelerated the Si nitridation and Si_3N_4 formation, but also facilitated the epitaxial growth of reinforcement phase of Si_3N_4 whisker in the Si_3N_(4(w))-SiC composites.