Effect of Water Incorporation on the Diffusion of Sodium in Type I Silica Glass1
Lei Tian and Rüdiger Dieckmann
Department of Materials Science and
Engineering, Cornell University, Bard Hall
Ithaca, NY 14853-1501, U.S.A.
Chung-Yuen Hui and Yu-Yun Lin
Department of Theoretical and Applied
Mechanics, Cornell University, Thurston Hall
Ithaca, NY 14853-1501, U.S.A.
J. Greg Couillard
Corning Incorporated
Corning, NY 14831, U.S.A.
Abstract
The diffusion of sodium ions in
Type I silica glass1 was studied experimentally by
using Na-22 as a radioactive tracer at
temperatures between 400 and 700 ºC. It was
found that the sodium tracer diffusion
coefficient in as-received glass was well described
by an Arrhenius equation. All residual
radioactivity profiles observed after pre-annealing
glass samples in common and wet air at
temperatures between 900 and 1100 ºC and
performing diffusion anneals at 650 ºC cannot
be described by a single diffusion
coefficient. A strong residual radioactivity
decrease occurred near the surface, which was
followed by a much smaller decrease in the bulk
below. This type of profile was attributed
to the generation of a near-surface region with
a reduced sodium mobility during the pre-
annealing. A mathematical model for the
analysis of the observed profiles was developed
and used to determine sodium tracer diffusion
coefficients in the near-surface region and
in the bulk. It was found that the sodium
tracer diffusion coefficient in the near-surface
region was by about two orders of magnitude
smaller than that in the bulk. This
immobilization of Na is believed to de due to a
water-induced structural relaxation in the
near-surface region during pre-annealing.
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1 Heraeus-Amersil Infrasil 302