Mechanochemical polishing of sintered silicon nitride.

The present paper studies the feasibility of a new method for polishing sintered silicon nitride to make a damage-and scratch-free surface. The method contains development of a polishing disk, on which the workpiece is polished under a dry condition. The polishing disk is a composite consisting of an oxide abrasive and a thermoplastic resin. Various polishing disks and polishing conditions were examined to find the optimum condition. The results may be summarized as follows : (1) Sintered Si3N4 can be polished accurately and efficiently by means of the polishing disk, especially Cr2O3 (chromium oxide) -AN (acrylonitrile) polishing disk. The rate of material removed reaches 22 μm/km·MPa (32 μm/h) and a surface roughness of 4 nmRmax can be easily obtained. (2) Surface analyses of the polished surfaces by ESCA and SIMS indicate that a certain reaction layer is formed on the Si3N4 surface during the polishing process as a result of some mechanochemical reaction between Si3N4 and Cr2O3. The efficiency of the present method is due to the fact that the polishing disk can supply the abrasives which are mechanochemically reactive on the Si3N4, into the polished surface very continuously, efficiently and uniformly.