Efficient processing of reaction-sintered silicon carbide by anodically oxidation-assisted polishing

Qunzhang Tu,Xinmin Shen,Jianzhao Zhou,Xiaohui He,Kazuya Yamamura

doi:10.1117/1.oe.54.10.105113

Abstract

Reaction-sintered silicon carbide (RS-SiC) is a promising optical material for the space telescope systems. Anodically oxidation-assisted polishing is a method to machine RS-SiC. The electrolyte used in this study is a mixture of hydrogen peroxide (H2O2) and hydrochloric acid (HCl), and the oxidation potential has two modes: constant potential and high-frequency-square-wave potential. Oxide morphologies are compared by scanning electron microscope/energy dispersive x-ray spectroscopy and scanning white-light interferometer. The results indicate that anodic oxidation under constant potential can not only obtain a relatively smooth surface but also be propitious to obtain high material removal rate. The oxidation depth in anodic oxidation under constant potential is calculated by comparing surface morphologies before and after hydrofluoric acid etching. The theoretical oxidation rate is 5.3 nm/s based on the linear Deal–Grove model. Polishing of the oxidized RS-SiC is conducted to validate the machinability of the oxide layer. The obtained surface roughness root-mean-square is around 4.5 nm. Thus, anodically oxidation-assisted polishing can be considered as an efficient method, which can fill the performance gap between the rough figuring and fine finishing of RS-SiC. It can improve the machining quality of RS-SiC parts and promote the application of RS-SiC products.

Highlights

Reaction-sintered silicon carbide (RS-SiC) is a promising material for making optical mirrors in space telescope systems due to its excellent physical, mechanical, and chemical properties.[1,2,3] With the increasing standard for ultrasmooth surface finishing and the demand for high material removal rate (MRR) in the machining of RS-SiC substrate, methods for processing RS-SiC have become the research focus in the fields of optics and ceramics.[4,5] RS-SiC is a known difficult-to-machine material because of its high hardness and chemical inertness.[3]
The results indicate that the surface quality of the constant potential case is better than that of the HFSW potential case
In order to further investigate the machinability of the oxide layer obtained in anodic oxidation of RS-SiC by the mixture of H2O2 and hydrochloric acid (HCl) under the constant potential, the oxidized sample is polished with the ceria slurry polishing system, as shown in Fig. 9.3 The reason for applying the ceria slurry polishing method is that it is easier to obtain high MRR and ultrasmooth surface simultaneously in the polishing of silica (SiO2) by CeO2 in the chemical mechanical polishing.[16]

Summary

Introduction

Reaction-sintered silicon carbide (RS-SiC) is a promising material for making optical mirrors in space telescope systems due to its excellent physical, mechanical, and chemical properties.[1,2,3] With the increasing standard for ultrasmooth surface finishing and the demand for high material removal rate (MRR) in the machining of RS-SiC substrate, methods for processing RS-SiC have become the research focus in the fields of optics and ceramics.[4,5] RS-SiC is a known difficult-to-machine material because of its high hardness and chemical inertness.[3] These properties make it inefficient to process RS-SiC with traditional mechanical or chemical methods, such as diamond turning[6,7] or plasma chemical vaporization machining (PCVM).[8] the RS-SiC substrate is mainly composed of SiC and Si.[9,10] the differences in physical hardness and chemical activity between the nonuniform SiC grains and Si grains make the homogeneous removal of RS-SiC almost impossible.[11] a novel method for processing RS-SiC is urgently demanded to increase the MRR in the rough figuring process and to improve the surface quality in the fine finishing process. A novel processing method, named anodically oxidation-assisted polishing, is proposed for the. Tu et al.: Efficient processing of reaction-sintered silicon carbide by anodically oxidation-assisted polishing

Experimental Setup

Analysis of Oxide Morphologies

20 KHz Pt

Calculation of Oxidation Rate

Investigation of Polishing Property

Conclusions