Two-Dimensional Small-Angle X-ray Scattering Investigation of Stretched Borosilicate Glasses

A two-dimensional fit of a suitable model for interpreting small-angle X-ray scattering (SAXS) has been shown to be a valuable tool in obtaining quantitative microstructural information. The model is based on the hypothesis that dilute ellipsoidal particles are arranged parallel to each other. The method has been applied to two glasses containing oriented particles. The investigated materials are both alkali aluminoborosilicate glasses, thermally treated and redrawn at a temperature above their softening point. The Ag(Cl, Br) crystalline droplets, formed during the preliminary thermal treatment, assume, after drawing, a cigar-like shape, oriented in the stretching direction, and give the material birefringence properties. The volumetric particle distribution has an average of 22 × 70 nm and is skewed up to length values of about 1200 nm. The composition of the solid solution, determined by X-ray diffraction (XRD), is Ag(Cl_0.35, Br_0.65). When the Ag(Cl, Br) particles on the surface are chemically reduced to Ag, a material with polarizing properties is obtained (Polarcor^TM). For this sample, two distributions of particles have been found: one with an average of 18 x 230 nm and skewed up to 600 nm, and one, very sharp, of much shorter particles (14 × 30 nm).