Carbothermal reduction and nitridation of powder pyrophyllite raw material

The influence of nitrogen flow rate, temperature, time and α-Al2O3 addition on the carbothermal reduction and nitridation of powder pyrophyllite raw material with particle size below 60 μm has been investigated with the aim to prepare a precursor for subsequent synthesis of β-SiAlON. A fast conversion of pyrophyllite raw material to the major phase β-Si3N4 and two minor phases, α-Si3N4 and AlN, was observed at 1510 °C. The addition of fine α-Al2O3 to increase the amount of AlN (higher value of z) led to the considerable lengthening of the conversion time. Depending on the amount of added α-Al2O3, two kinds of β-SiAlON based material, containing as minor phases either SiAl4O2N4 and α-Al2O3 or alone α-Al2O3 were prepared by hot-pressing. The same value of z=3.8 was determined for all the prepared β-SiAlONs.