Microsc. Microanal. Microstruct. 8, 157-165 (1997)
DOI: 10.1051/mmm:1997115

Redrawn Phase-Separated Borosilicate Glasses: A TEM Investigation

Stefano Polizzi¹, Aldo Armigliato², Pietro Riello¹, Nicholas F. Borrelli³ et Giuliano Fagherazzi<sup>1

1</sup>  Dipartimento di Chimica Fisica, Università di Venezia, Dorsoduro 2137, 30123 Venezia, Italy
²  CNR, Instituto LAMEL, via Gobetti 101, 40129 Bologna, Italy
³  Corning Glass Research and Development, Corning, New York 14831, USA

Abstract
Two alkali aluminoborosilicate glasses containing oriented crystalline particles have been investigated by Transmission Electron Microscopy (TEM). Both materials have been thermally treated in order to phase-separate crystalline droplets and have been then redrawn at a temperature above their softening point to elongate and orient them. In one sample the crystalline phase is a Ag(Cl, Br) solid solution, which gives the material birefringence properties, while in the other sample the particles on the surface have been chemically reduced to Ag, giving the material polarizing properties PolarcorTM. Most of the observed needle-like particles are built up by a small number of well grown crystallites often separated by voids. Both the crystallites and the voids occupy the whole width of the particles and can assume very different lengths. Crystallites inside a particle have different orientations.

PACS
6140D - Structure of glasses.
6470K - Solid solid transitions.
8140G - Other heat and thermomechanical treatments.
7820F - Birefringence condensed matter.
6480G - Microstructure.

Key words
alkali metal compounds -- aluminosilicate glasses -- birefringence -- borosilicate glasses -- crystallisation -- crystallites -- drawing mechanical -- glass structure -- heat treatment -- metal clusters -- transmission electron microscopy -- voids solid -- redrawn phase separated borosilicate glasses -- TEM investigation -- alkali aluminoborosilicate glasses -- oriented crystalline particles -- TEM -- crystalline droplets -- crystalline phase -- Ag Cl,Br solid solution -- birefringence -- Ag -- polarizing properties -- needle like particles -- crystallites -- voids -- B sub 2 O sub 3 Al sub 2 O sub 3 SiO sub 2 AgClBr


© EDP Sciences 1997