ガラス中の銀コロイド析出にたいする高圧の効果 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.

The effect of application of high pressure with an opposed-anvil type apparatus on the formation of silver colloids in silicate glass has been studied mainly by optical absorption measurements, and the following results were obtained.1) Application of pressure at room temperature promotes the formation of silver colloids in glass due to subsequent heating at high temperatures ranging from 250°C to 500°C. This is attributed to the effect of high pressure in enhancing nucleation of silver colloids by producing defect sites in glass.2) Application of pressure at high temperatures where silver colloids form under the pressure also promotes the precipitation of silver colloids. In this case, however, the size of the particles precipitated are smaller than in the case where the glass is compressed at room temperature and subsequently heated, possibly because the application of pressure decreases the ratio of growth to nucleation rate.3) Application of pressure to glass at room temperature after heating at high temperatures, for example, at 500°C, under atmospheric pressure has pronounced effects on the absorption spectra of silver colloids in glass: shift of absorption peaks to longer wavelengths and broadening of absorption bands. These effects are attributed to the size distribution of enlarged silver particles and/or deformed, large silver particles.