The Effect Of Heat Treatment On The Structural Homogeneity Of Type Ⅳ Silica Glass

Type IV silica glass is one of the important basic materials for the development of optical,inertial navigation,nuclear technology,aerospace and other technical fields.However,with the development of science and technology,the accuracy requirements of the instrument are continuously improved,and its optical homogeneity index needs to be as low as 10^-6order of magnitude to meet the development needs of its application fields.In order to improve the structural homogeneity of type IV silica glass,it is necessary to use heat treatment methods such as groove sinking and annealing to homogenize.In this paper,the influencing factors of optical homogeneity of type IV silica glass were studied by means of infrared reflection spectrum,Raman spectrum and transmission spectrum.Firstly,the influence of groove sinking on the structural homogeneity of silica glass was studied.The experimental results show that the groove sinking can improve the optical homogeneity of type IV silica glass to a certain extent.This improvement is related to the flow of silica glass along the glass radius direction at high temperature.The radial flow of the glass during groove sinking and expanding can lead to an increase in the fictive temperature,an increase in the Si-O bond angle,and an increase in the local density of the glass,resulting in an increase in the refractive index differenceΔn_d.The decrease of the sink pressure makes the main heat transfer mode of glass cooling change from convective heat transfer to radiative heat transfer,the cooling rate is low,and the fictive temperature is reduced.In addition,the downward sinking flow is more obvious with the decrease of pressure,resulting in the inhomogeneous structure of type IV silica glass,which makes the optical homogeneityΔn of low-pressure groove sinking silica glass worse than that of high-pressure groove sinking.Secondly,this paper briefly studies the effect of annealing on the structure of type IV silica glass.The results show that annealing can reduce the fictive temperature of silica glass,make the radial strength of D2 peak tend to be consistent,and improve the structural homogeneity of silica glass.However,the exposure of type IV silica glass to air annealing may lead to an increase in hydroxyl concentration.In addition,the birefringence radial variation of two common stress forms of silica glass is analyzed.The results show that The compressive stress and tensile stress of type IV silica glass with annular stress are alternately distributed along the radius of the glass,which makes the radial stress birefringence fluctuate up and down.Finally,the influence factors of optical homogeneityΔn of type IV silica glass were studied by correlation analysis.The results show that there is a significant correlation between the change of D2 peak and the refractive index differenceΔn_dof the glass,that is,the difference of local density on the surface of the glass is the main factor affecting the optical homogeneityΔn of type IV silica glass.