Carbothermal synthesis, characterization, and mechanical properties of spark plasma sintered β-SiAlON (z = 2) powder prepared from mechanochemically activated precursors

Abstract

Based on technological capabilities, β-SiAlON ceramics are one of the most valuable compounds formed in the Si–Al–O–N system, which can be synthesized from raw materials using different methods. An affordable approach was found in this study for the elaboration of the aluminosilicate precursor necessary for the synthesis of β-Si4Al2O2N6 (z = 2) from Aluminum Chloride hexahydrate, Ammonium Chloride and Sodium Metasilicate nonahydrate used as starting materials. The results obtained by XRD and FTIR revealed that the amorphous precursor prepared by mechanochemical processing originally is crystallized as mullite and silica phases at 1200 °C/2 h. Then, with continuous heating to 1500 °C/2 h, it is progressively converted into high-quality SiAlON powders β-Si4Al2O2N6 and β-Si2Al4O4N4 with a small amount of α-Al2O3 through the reduction and nitridation of mullite and intermediate phases, produced at lower temperatures. After spark plasma sintering (SPS) at 1750 °C, the nanometric particles smaller than 50 nm which are developed and distributed well throughout the microstructure of the sintered sample can be densified to 3.19 gcm−3 (≥98% theoretical density). Evaluation of the mechanical properties reveals that the microhardness of 15.8 GPa and fracture toughness of 4.62 MPa m1/2 are accessible from β-SiAlON powder prepared from the starting materials and the procedure employed in this research.It has been found that the aluminosilicate precursor prepared by mechanochemical processing can be a valuable source for CRN synthesis of SiAlON powders.