Synthesis, phase transformation and mechanical property of SiAlON ceramics from coal gangue

A simple and efficient method for preparation of SiAlON ceramics including β-SiAlON, O'-SiAlON and AlN polytypoid (15R and 12H) using reduction-nitridation of coal gangue and reducing agents at 1800K for 6h was described. The phase transformation of SiAlON at various atmospheres was discussed from thermodynamic and experimental analysis. Thermodynamic calculation revealed that different SiAlON phases could be synthesized at 1800K with the suitable atmosphere parameter Y (Y = lg(PO2 /ρθ)--3 2 lg(PN2 / ρθ)). Low Y value was beneficial to synthesis of β-SiAlON. The experimental result showed that β-SiAlON ceramics with the content of 90% was fabricated at strong reductive atmosphere in flowing nitrogen. O'-SiAlON with the content of 85% can be synthesized in flowing nitrogen atmosphere. In view of AlN polytypoid, the suitable condition to produce 15R was flowing nitrogen and 12H was formed at a weak reductive atmosphere. The mechanical properties of SiAlON ceramics synthesized under optimum conditions, i.e., modules of rupture (MOR) at room temperature, have been reported.