Tribochemical polishing of silicon nitride

Tribochemical polishing (TCP) is a new technique for polishing materials that is based on the friction-stimulated dissolution of material in a liquid. It differs from chemomechanical or mechanochemical polishing in that it does not use abrasives. Tribochemical polishing of silicon nitride was explored as a function of the mechanical parameters and the nature of chemical solutions and their concentrations. Over 30 chemical solutions such as acids, bases, salts, and inorganic and organic oxidizers were studied for material removal, polishing rate, and surface quality. Optical, scanning electron, and atomic force microscopy have been used to explore the polishing rate and the surface morphology Distilled water produces purely tribochemical material removal and very smooth surfaces at low contact pressures. In hydrogen peroxide, the polishing rates are higher and increase with concentration; 3 vol % hydrogen peroxide gives a high polishing rate and smooth surfaces by pure tribochemical reaction. Chromium (VI) oxide (CrO3) in all concentrations less than the solubility limit shows the best, purely tribochemical polishing results and the smoothest surface. Combinations of chromium oxide and hydrogen peroxide, and many of the chromates (VI) show excellent efficiencies. Some chemical solutions containing excess oxygen also present high performance of tribochemical polishing. Some strong organic oxidants which have excess oxygen and some inorganic chemical solutions show 10-250 times lower polishing rates than water. These low material removal rates suggest their use as antiwear agents in aqueous lubricants.