| High purity fused glass has excellent properties such as good light transmittance,high temperature resistance,small thermal expansion coefficient,stable chemical properties,etc.,and it was widely used in precise optical equipment and other high-tech fields.The processing quality of fused glass is directly related to its performance and service life,usually,these hightech fields have extremely high requirements for the processing accuracy and surface quality of fused glass.Chemical mechanical polishing(CMP)is usually used as the last surface processing in ultra-precision machining,it can remove the surface material effectively and reduce the processing damage of fused glass greatly through the synergy of chemistry and mechanic.When the machining accuracy reaches the nanometer scale,many traditional processing theories are not fully applicable.However,due to the limitation of experimental equipment and testing equipment,it is difficult to explain the ultra-precision polishing mechanism of fused glass from the micro perspective.Reax FF-MD simulation was applied to the micro study of chemical mechanical polishing of fused glass,it can break through the limitation of experimental condition,and it is an important scientific research method that can clearly and effectively observe the changes of chemical reaction and mechanical action.First,the polishing model of fused glass was constructed and corresponding reactive force field was selected too.Based on these,it is found that the dissociated H protons in water will combine with under-coordinated atoms on the surface of fused glass,and then weaken the bonding strength of Si-O bonds,which makes the structure of the less stable than before.According to the simulation results,when the temperature is increased to 360 K,the weakening effect on the bonding strength of Si-O bonds in sub-surface layer is obviously enhanced.In additions,the effect of temperature is more obvious when the polishing load is low,and increasing the temperature can effectively improve removal rate and reduce scratch force;however,the effect of temperature is greatly weakened under high polishing load,and changing temperature can’t significantly improve the polishing quality.This paper also focuses on the micro influence of hydrogen peroxide concentration on the removal form,removal efficiency and sliding force in the polishing process of fused glass.The simulation results show that hydrogen peroxide can promote the oxidation of fused glass surface,which has double-sided effect on surface removal: on the one hand,it will make it hard to form interfacial Si-O-Si bridge bond between the substrate and abrasive and inhibits atom removal;on the other hand,it can weaken the Si-O bond strength and makes surface structure more unstable and can promote atom removal.In the simulation process,single particle atom removal has occupied a dominant position in 5% concentration,and the best processing quality can be obtained at this time.In the CMP experiment of fused glass,it is found that increasing the mass fraction of abrasive particles or the concentration of hydrogen peroxide can effectively improve the polishing removal rate,but there is no such rule on the polishing quality.When the concentration of hydrogen peroxide is 5%,the surface roughness of polished fused glass is the lowest,about 0.706 nm;and when the mass fraction of abrasive particles in the slurry is low,the surface roughness will decrease with the increase of the mass fraction of abrasive particles.However,when the mass fraction of abrasive particles reaches 15%,the effect of increasing the mass fraction of abrasive particles on improving the surface quality is not obvious.The experimental results are consistent with the simulation results,which not only confirms the accuracy of the research,but also complements each other at the macro and micro levels.In addition,the mechanism explanation proposed in this paper is based on the Si atom and O atom,the relevant conclusions can also provide some theoretical guidance for the exploration of the micromachining mechanism of other silicate glasses. |
