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Dissolution Kinetics of Hot Compressed Oxide Glasses
The
chemical durability of oxide glasses is an important property
for a wide range of applications and can in some cases be tuned through
composition optimization. However, these possibilities are relatively
limited because around 3/5 of the atoms in most oxide glasses are
oxygens. An alternative approach involves post-treatment of the glass.
In this work, we focus on the effect of hot compression on dissolution
kinetics because it is known to improve, for example, elastic moduli
and hardness, whereas its effect on chemical durability is poorly
understood. Specifically, we study the bulk glass dissolution rate
of phosphate, silicophosphate, borophosphate, borosilicate, and aluminoborosilicate
glasses, which have been compressed at 0.5, 1.0, and 2.0 GPa at the
glass transition temperature (<i>T</i><sub>g</sub>). We
perform weight loss and supplementary modifier leaching measurements
of bulk samples immersed in acid (pH 2) and neutral (pH 7) solutions.
Compression generally improves the chemical durability as measured
from weight loss, but the effect is highly composition- and pressure-dependent.
As such, we show that the dissolution mechanisms depend on the topological
changes induced by permanent densification, which in turn are a function
of the changes in the number of nonbridging oxygens and the network
cross-linking. We also demonstrate a direct relationship between the
chemical durability and the number of chemical topological constraints
per atom (<i>n</i><sub>c</sub>) acting within the molecular
network