Tokuji Yamamoto

Effect of pressure on radiation-induced color centers in silicate glasses

Abstract Optical absorption spectra of color centers produced in silicate glasses by γ-irradiation were measured before and after application of pressure of 50 kbar to the glass. The two color center peaks, one found at about 400 nm and the other at about 600 nm, shifted toward shorter wavelengths as a result of densification of glass. The local shrinkages around the color centers estimated from the shifts of the peak wavelengths were much larger than the bulk shrinkages of the glasses obtained from the change in density of the glasses due to application of the pressure. Similar shifts of the color center peak wavelengths were observed also when the glass was γ-irradiated after densification. Besides the shift of the peaks, the application of the pressure caused a great increase of broad absorption through the visible region. A tentative explanation was given to this phenomenon on the basis of the formation of unknown defects due to the effect of shear accompanying the application of pressure. The annealing of the various pressure effects was also examined.

Effect of High Pressure on Precipitation of Silver Colloids in Glass

ブリッジマンアンビル型の加圧装置を用いて高圧を加えたガラスの光吸収を測定することにより珪酸塩ガラス中における銀コロイドの生成にたいする高圧の効果を調べた. 室温で65kbまでの高圧を加えておくと, その後250°-500℃の高温で加熱したときにおこる銀コロイドの生成が促進された. 銀コロイドの生成がおこるような高温で圧力を加えてもやはり銀コロイドの析出が促進された. ただし, この場合には, 析出した粒子の寸法はさきの場合にくらべてより小さかった. このように銀コロイドの生成が促進されるのは高圧付加によりガラス中に欠陥が生成し, そのため銀コロイドの結晶核形成が促進されるためと考えられる. なお, ガラスをいったん高温で加熱したのち室温で加圧すると大きい銀コロイドが析出し, そのためガラスは灰色または暗色になることが確かめられた.

Chemicl Durability of Polycrystalline Materials Produced from Glasses

Glasses of the compositions, Li2O⋅1.5SiO2, Li2O⋅2SiO2, Li2O⋅3SiO2, and Li2O⋅3SiO2⋅0.1 MmOn (MmOn=Na2O, K2O, Al2O3 or ZrO2) in mole ratio, each with or without platinum, were prepared in a form of rectangular plate of 20×40×2mm. After polished with 1500-grit Al2O3 powder to make smooth surfaces, these glasses were repeated up to 900°C at the constant rate of 5°C/min. The polycrystalline materials thus obtained were exposed to various solutions, mainly to 5% HCl solution of 90°±2°C for various times. The chemical durability was reported in terms of weight loss per unit surface exposed. Identification of crystalline phases in the specimens by an X-ray diffractometer and electron microscopicobservation of the surface of specimens were made before and after the durability test in order to correlate the durability to the microstructure of the crystallized specimens.The results obtained were summarized as follows:1) Effects of the basic composition.For the two component system, i.e., Li2O⋅1.5SiO2, Li2O⋅2SiO2, and Li2O⋅3SiO2, the durability, in general, increased with the increase in SiO2 content, regardless of the presence of Pt. The durability of the crystallized specimens was much higher than that of their mother glasses. An exception was the Li2O⋅2SiO2 crystallized specimen without Pt, which showed the very poor durability.2) Effects of the addition of Pt.The poor durability of the specimen above described was found to be due to the presence of micro-cracks on the surface of the crystallized specimen. The addition of Pt as a nucleating agent in an appropriate amount (0.005-0.01% in weight) was found effective for suppressing the development of the cracks during reheating, thus improving the durability.3) Effects of addition of the third components.Of the four components, e. g., Na2O, K2O, Al2O3, and ZrO2, Na2O and K2O lowered the durability markedly. This was attributed to the concentration of these components in crystal grain boundaries (matrix glass) of the crystallized specimens, which was confirmed by an electron microscope. The matrix glass was easily attacked by 5% HCl.4) Effects of the kind of test reagent.The durability to various test reagents such as pure water, 5% H2SO4, 5% NaCl, 5% NaOH and 5% Na2CO3, besides 5% HCl, was also measured with the glass of the composition Li2O⋅3SiO2 with 0.01% Pt. In general, the attack of the alkaline solutions was much more severe than that of pure water and the acid solutions.