The microstructure of borosilicate glasses containing elongated and oriented phase-separated crystalline particles

The microstructure of phase-separated and stretched silver halide particles, embedded in an aluminoborosilicate glass, is studied by small angle X-ray scattering. The data are quantitatively analysed, using a model of prolate ellipsoids of revolution generated by the elongation of a distribution of spheres. The average particle is 22 +/- 3 x 160 +/- 20 nm(2), but the distribution is very much skewed so that a fraction of much longer particles is also present. Chemical reduction in hydrogen causes the formation of metal particles inside the rigid glass cavities formed during drawing. Two thirds of the volume of these cavities remains empty, due to the loss of the halide atoms and to the higher density of the silver crystals. The longer particles are lost, each one giving rise to two or three smaller ones. These data are compared with transmission electron microscopy (TEM) results.