光学ガラス表面の酸によるくもり

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The mechanism for producing the white stain on the surface of some optical glasses possessing low chemical durability was investigated. The compositions of the optical glasses used are given in Table 1. All the glasses were ground and polished in the same manner so as to present a similar type of surface. The samples were kept in the humidity cell (Fig. 1) with varying relative humidity from 100, 80.2 to 68.6%, and atmospheres were controlled by adding small content of CO_2, H_2S or other acidic gases. Weathering was once a time stopped after 5hrs, the grade of deterioration of glass surface was measured and then the samples were provided for the repeated exposures under 5hrs, cycle. The surface deterioration was observed by optical microscope, ellipsometer (Figs. 3 and 4), electron diffractometer and electron microprobe X-ray analyzer (EMX). The refractive index and the thickness of anomalous surface film on the glass were measured by means of ellipsometry. The quality and quantity of anomalous surface film were determined by means of electron diffraction and EMX. The relations between the relative humidity and the thickness of anomalous film on the glass SK-16, exposed to the atmosphere containing 50% CO_2 gas at 50℃ during the period of 10 and 20hrs, are shown in Fig. 7. It can be found that the growth of anomalous film increases rapidly with increasing relative humidity and water vapor plays a most important role in these reactions. The changes of film thickness in the case of air atmosphere are shown in Fig. 8. HCI and SO_2 show very violent attack, so the film thickness can not be measured. When acidic gas was added to the atmosphere, the water adsorbed on the surface of glass becomes acidic. Then the exchange reaction takes place between Na^+, Ba^<2+> in glass and H^+ in adsorbed acid solution. In the case of CO_2 gas attacking on the glass SK-16, the growth of stain increases straightly with increasing ionic concentration of H^+ (Fig. 19). In the case of glass BaF-10, the curves are shown in Fig. 20. Clearly the diffusion of Ba^<2+> will carry out the important role in this exchange reaction. The changes of refractive index of the films produced on the glass samples under various conditions are shown in Table 2. It can be found from Table 2 that in the first stage of attacking, the refractive index of anomalous films are 1.45〜1.47 in spite of different glasses and different conditions. But in severe attacking by strong acidic vapor, the values of refractive index become large. From these results, the following model (Fig. 21) may be figured for the mechanism of growth of stain. The Na^+ and Ba^<2+> are diffused out to the surface of glass and these salts are produced to form spotty stain, and SiO_2 rich films are formed underneath (model 1). Corresponding to the increase of anomalous film thickness, the quantity of the salts taking the form of spotty stain increases, and SiO_2 rich films are spread out as shown in model 2. Then the formation of the salts grows large and all of the glass surface will be covered (model 3). The concentrations of Ba and Si in the spot of stain are measured by using EMX. As shown in Fig. 14 the concentration of Ba increases and that of Si decreases in the same place of spot and it may be proved that the present considerations are reasonable. The anomalous films formed on the glass surface are determined by using electron diffraction method and the results are shown in Table 3. It is clear that large parts of crystallites on the glass surface belong to Ba-salts and this also supports the structural pictures figured for reaction mechanism.
社団法人日本セラミックス協会の論文
1972-02-01

光学ガラス表面の酸によるくもり

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