新種光学ガラスの失透に関する研究

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In order to obtain the glasses of the system B_2O_3-CdO-La_2O_3 Stable against devitrification, the investigations concerning this phenomenon have been carried out. According to Frenkel's nucleation theory, the rate of nucleation depends mainly on the degree of supercooling, the diffusion rate of molecules or ions, and the surface tension between the nucleus and the liquid. The authors, therefore, measured the liquidus temperature, the viscosity, and the surface tension of the ternary system B_2O_3-CdO-La_2O_3,using differential thermal analysis to determine the degree of devitrification, and X-ray diffraction to identfy the crystals. The results obtained are summarized as fo11ows : ( I ) The glass-formation range is limited by the immiscibility in B_2O_3 rich region and by the devitrification In oxide rich region, and it was observed that the crystal appeared was different from those outside of the boundary. ( 2 ) The effect of the addition of the components such as SiO_2,GeO_2,As_2O_3,Sb_2O_5,BeO, Al_2O_3' TiO_2,ZrO2,ThO_2,Ta_2O_5,Nb_2O_5,WO_3,and ZnO on the devitrification was studied. Of these components, the addition of SiO_2,GeO_2,and BeO (<2%) Iowered tbe liquidus temperature and increased the viscosity of the base glass, and Al_2O_3 also lowered the liquidus temperature ; they were effective to reduce the devitrification. TiO_2 and ZrO_2,which reduce the devitrification, act in same different way to the same effect, namely, the former by lowering the liquidus temperature, while the latter by increasing the viscosity. ( 3 ) The more stable glass has had lower liquidus temperature and higher viscosity at the same temperature. On the other hand, the viscosity at the lower limit in the devitrification range was never constant. The more stable the glass, the lower was the viscosity at the lower limit. Thus the viscosity range of the more stable glass was narrower than that of the less stable type. ( 4 ) The differencial thermal analysis curve of the more stable glass showed a lower exothermic peak which moved towared higher temperature where glass had lower viscosity. ( 5 ) The activation energy of the crystal growth rate was not constant when refered to wide temperature range, it varied from 61 .4 to 129 kcal/mol. In the range 660°to 820℃, being about a half of the activation energy of viscous flow at the same temperatures. A similar relatian was found in CdO・B_2O_3 and Li_2O・2 SiO_2 glasses.
社団法人日本セラミックス協会の論文
1962-05-01

新種光学ガラスの失透に関する研究

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