Fig. 1 shows the XRD patterns of the combustion-synthesized
powders with various durations of ball milling. β-SiAlON was
the dominant phase, except for a little un-reacted Si before ball
milling that was less than 5 mass% according to the intensity
ratio of the corresponding XRD peaks. No new phase was
detected after the long ball milling time. Broader diffraction
peaks were observed because the grain size was reduced along
with the increasing ball milling time.