BK7光学玻璃化学机械抛光机理研究OA

BK7 optical glass is an excellent material in the optical industry due to its low dispersion and high transmittance.However,its surface polishing still remains a serious challenge.BK7 optical glass is a typical hard-brittle material with high hardness,high brittleness,low fracture toughness,and good chemical stability.Traditional mechanical processing methods are difficult to meet the technical requirements of modern industry.CMP(Chemical Mechanical Polishing)can achieve an extremely low roughness on the surface of BK7 glass while causing minimal surface and subsurface damage.The work aims to explore the effect of various factors during the chemical mechanical polishing(CMP)process on the removal rate(MRR)and surface roughness(Ra)of BK7 optical glass materials,to reveal the chemical mechanical polishing mechanism of BK7 optical glass in a polishing liquid containing nano-scale cerium dioxide(CeO2)abrasive particles,and improve the efficiency and achieve low-damage surface polishing of BK7 optical glass. By the single-factor experimental method,CMP experiments were conducted on BK7 optical glass to compare the polishing effects under different polishing time,platen speed,CeO2 contents,slurry pH values,and citric acid contents,to analyze the effect of these conditions on the polishing performance of BK7 optical glass,and the optimal parameter combination was determined through orthogonal experiments.The variations in the concentration of Ce3+on the surface of CeO2 abrasive particles were investigated through energy dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),and scanning electron microscopy(SEM),as well as the aggregation and adsorption behavior of CeO2 under different conditions. Through orthogonal experimental design,the optimal combination of polishing parameters was determined:the polishing time of 50 min,the polishing disc speed of 60 r/min,the slurry pH value of 6,the CeO2 abrasive concentration of 0.5%,and the citric acid concentration of 2%.Under these conditions,the best MRR of 139.6 µm/h and a Ra of 2 nm were achieved,with a 99.6%reduction in surface roughness.No obvious abrasive residues were observed on the polished surface of the BK7 optical glass.Based on the characterization results obtained from X-ray photoelectron spectroscopy(XPS),energy dispersive spectroscopy(EDS),and nanoindentation testing,the material removal mechanism of BK7 optical glass during CMP was proposed.Citric acid acted as a reducing agent,reduced Ce4+ions on the surface of CeO2 abrasive particles to Ce3+.This reduction process increased the surface concentration of Ce3+on the CeO2 particles,forming oxygen vacancies.With the increase in Ce3+concentration,the chemical adsorption between CeO2 abrasive particles and silicate ions increased,forming Ce—O—Si bonds.Meanwhile,free electrons in Ce3+migrated to the surface of SiO2,which promoted the breaking of Si—O bonds.This facilitated the mechanical removal of the softened layer on the polished surface of BK7 optical glass by CeO2 abrasives,thereby improving the polishing efficiency. Compared with the chemical mechanical polishing method that prepares complex CeO2 core-shell structures and adds low-valent metal ions to CeO2 abrasive particles,this study employs the addition of citric acid to enhance the surface concentration of Ce3+on CeO2 abrasive particles.This method accelerates the reaction rate between CeO2 abrasives and the polished surface of BK7 optical glass,thereby facilitating the cleavage of Si—O bonds and significantly improving the polishing efficiency of BK7 optical glass surfaces.It can also be applied to ultra-precision machining with high accuracy,which provides guidance for optimizing polishing process parameters and elucidating the material removal mechanism to achieve high-quality surfaces on BK7 optical glass.