Effect of impurities MgO, CaO, Al2O3, AlN and Al on α/β ratio in combustion synthesis of α-Si3N4

• Published in: Journal of alloys and compounds Vol. 688; pp. 1002 - 1007
• Main Authors: Ge, Yi-Yao, Gao, Wenchao, Sun, Si-Yuan, Tian, Zhao-Bo, Zou, Yi-Feng, Xie, Zhi-Peng, Agathopoulos, Simeon, Chen, Ke-Xin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.2016
• Subjects: Combustion synthesis; Impurity; Liquid phase; Seeding; Silicon nitride; Combustion synthesis; Liquid phase; Impurity; Seeding; Silicon nitride
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2016.07.170

The effect of common impurities, specifically MgO, Al2O3, CaO, Al, and AlN, which are usually incorporated in the raw materials in the combustion synthesis (CS) of α-Si3N4 powders, was thoroughly investigated. The experimental results showed that these impurities seriously jeopardize the production of powders with a high content in α-Si3N4 via CS. Two main mechanisms are seemingly involved in this phenomenon. First, these impurities react with SiO2 to form eutectic compounds and with the NH4Cl additives to form liquid chlorides of the metals of the impurities. This liquid phase favors the formation of β-Si3N4. In the samples with Al-containing impurities, in addition to the formation of liquid phase, nuclei of β′-SiAlON act as seeds to produce β-Si3N4 crystals. •The strong effect of MgO, CaO, Al2O3, AlN and Al in CS of α-Si3N4 has been studied.•Above impurities inevitably existed in CS system were confirm to reduce α/β ratio.•We proposed two influencing mechanisms of these impurities on reducing α/β ratio.•The seeding effect of β′-SiAlON exclusive to the system with Al doped was presented.•EPMA analysis was applied to directly demonstrate the seeding effect of β′-SiAlON.