Polishing Mechanism of Optical Glass

Abstract

The purpose of this work is to show the polishing mechanism of the cerium oxide and water slurry polishing process, most commonly used.We observed:Using the polishing of 18 different kinds of optical glasses, the relationship between microvickers hardness, softening point and chemical durability of the glass, and the rate of polishing; and the relationship between the change of surface roughness and that of the weight before and after polishing. The glass surface was observed with an electron microscope. In order to compare the water polishing with the oil polishing or the dry polishing, each type of glass was polished three ways: with cericm oxide and water slurry, with cerium oxide and kerosene slurry, and with cerium oxide alone.Our observations follows:1) There is no relationship between the rate of polishing glass and microvickers hardness and softening point.2) The rate of polishing for each type of glass is dependent upon the chemical durability of the glass. In other words, the rate of polishing using cerium oxide and water slurry is mainly dependent upon the rate at which hydrated layers formed as a result of the chemical reaction between the polishing solution and the glass surface. The rate of polishing also depends upon the hardness of the hydrated layers.3) Many scratches are observed on the polished surface. The progressive polishing is accompanied by a nearly proportional weight loss through the polishing process. These observations are conclusive evidence that the cerium oxide granules in the polisher physically remove outside layer of glass.4) Using the cerium oxide and water slurry the polishing rate is much faster than either the cerium oxide and kerosene slurry or the dry cerium oxide. Because the polishing is accelerated by hydration, which makes the surface of the glass softer than the bulk glass.Our observations conclude that optical glass polishing is both chemical and physical processes, i.e. chemical, in that hydration is a chemical reaction to the cerium oxide and water slurry, and mechanical, in that the cerium oxide granules physically remove the rough surface from the glass layers softend by hydration. The heat generated in the process of polishing does no more than accelerated hydration in the cerium oxide and water slurry polishing process.