Synthesis of pure rod-like α-Si ₃N ₄ powder with in situ C/SBA-15 composite

Well crystallized pure rod-like α-Si ₃N ₄ powder (PRSN) without β-Si ₃N ₄ was successfully synthesized by carbothermal reduction-nitridation (CRN). In situ carbon/mesoporous silica composite (C/SBA-15) was used as a new kind of raw material. Due to in situ composited carbon, the CRN temperature was decreased and the phase transition from α to β-Si ₃N ₄ was hindered. The sintering temperature was lowered to 1380 °C and the soaking time of the optimal synthesis condition was reduced to 6 h. Moreover, the as-synthesized rod-like α-Si ₃N ₄, which is induced by SBA-15, was used to enhance the fracture toughness (K _Ic) of α-Si ₃N ₄ based ceramics, which was sintered by spark plasma sintering (SPS). Compared with the undoped ceramics (2.9 MPa m ^1/2), α-Si ₃N ₄ ceramics doped with 10 vol% PRSN exhibited a higher K _Ic value (4.9 MPa m ^1/2), and lower dielectric loss in MHz frequency range. The results demonstrated that the PRSN powder would be promising for toughening α-Si ₃N ₄ based ceramics.