In the process of milling α-Si₃N₄ raw powder with sintering additives using balls and mill made of β-Si₃N₄, the increment of the specific surface area of the powder and the wear of the balls and mill were measured.
The wear rate to the increment of the specific surface area depended on the filling ratio of balls, powder and liquid into the mill. Under the condtion that the volume of slurry was the same as that between balls, which is recognized as the effctive milling condition, the specific surface area increased from 6.1 to 22.4 m²/g after milling for 72h. The amount of Si₃N₄ contaminated from the balls and mill under the above milling condition, was accounted for 5.8 wt% of the raw powder.