Hydrogen-induced formation of colloids of arsenic, antimony, and bismuth in oxide glasses

Abstract

Glasses containing arsenic, antimony, or bismuth gradually darken during exposure to hydrogen at temperatures within the glass transformation region. The coloring process is a complex function of the glass composition, the identity and concentration of the dopant (As, Sb, or Bi) present, and treatment temperature. Coloration occurs via the formation of a dark layer at the surface of the glass. This surface layer increases in thickness with treatment time. Combined X-ray diffraction and electron microscopy studies demonstrate that the color changes are due to the formation of metallic colloids, which may be either crystalline (Sb and Bi) or amorphous (As). It is suggested that the overall coloring process is controlled by the initial reduction of the ion to the atomic state and by the subsequent diffusion of the atoms to a growing nuclei to form colloids which increase in size with time.