Chemo-mechanical interactions in optical polishing

A large number of interactive chemical and mechanical factors significantly influence optical glass polishing processes. Uncertainty regarding in-process evolution makes characterization of the chemo-mechanical interactions difficult, effectively precluding deterministic polishing. This research has systematically investigated the influence of process chemistry and mechanics on glass removal rate and surface quality for a variety of silicate glass types, metal-oxide polishing agents and aqueous fluids. Experimental work has been performed at two levels, recognizing the importance of friction and glass corrosion in polishing. At the microscopic level, an atomic force microscope (AFM) has been used to measure the near-surface forces between individual polishing agent particles and planar glass surfaces immersed in aqueous fluids of carefully controlled chemistry. At the macroscopic level, experiments have been conducted on a continuous polishing machine (CPM), seeking process chemistry which optimizes the glass removal rate and surface quality.; Evolution of the slurry particle size distribution during polishing has been found to be the most significant manifestation of surface charge effects. An effective polishing agent has surface charge which is the same sign as that of the glass work, thereby inhibiting any tendency to agglomerate with silica species in the slurry. This enables the fabrication of very smooth surfaces.; The removal rates obtained for the six glass types are highly dependent on the fluid pH and the choice of polishing agent. Monoclinic ZrO{dollar}sb2{dollar} has been found to exhibit an extremely wide process latitude relative to the other oxides. Nanocrystalline Al{dollar}sb2{dollar}O{dollar}sb3{dollar} has been found to polish fused silica, BK7 and SF6 very effectively, but only at pH 10. These observations have demonstrated the deficiencies of an existing polishing process model and have clearly shown the need for further study of glass corrosion and surface chemistry before a deterministic polishing model can be constructed.