ON CHEMOMECHANICAL POLISHING OF SI3N4 WITH CR2O3

Chromium oxide (Cr2O3) is found to be an excellent abrasive for polish ing of silicon nitride (Si3N4) work material. As the hardness of Cr2O3 is nearly the same as that of Si3N4, it appears that the mechanism of material removal would be more chemical action than mechanical abrasi on. However, no evidence of any compound formation of Si3N4 work mater ial with Cr2O3 abrasive has been reported in the literature thus far. Instead, the role of Cr2O3 was considered to be one of a catalyst, in view of the well known role of Cr2O3 as a catalyst, rather than its di rect involvement in the chemical reactions with Si3N4 In this paper, w e report new evidence on the chemomechanical action by examining the w ear debris generated in polishing Si3N4 work material with Cr2O3 abras ive using a scanning electron microscope with an X-ray microanalyser a nd a small-angle X-ray diffraction apparatus. The analysis shows concl usively that Cr2O3 does participate in chemomechanical polishing of Si 3N4 to form chromium nitride and chromium silicate, thus establishing the role of Cr2O3 not as a mere catalyst but as actively taking part i n the chemical reactions during chemomechanical polishing. A new model of the chemomechanical polishing of Si3N4 work material in air and in water environments with Cr2O3 abrasive is presented. This model is ba sed on the formation of such reaction products as chromium silicate an d chromium nitride in addition to the formation of a silica layer on S i3N4 surface as well as gaseous reaction products, such as ammonia (in water) and nitrogen (in air).