In this work, the nanoflake model is utilized here to
provide a structural explanation for the anomalies of the density-temperature
relation of silica glass. Silica glass is the most essential glass-forming
material with several technologically important properties. The structure, formation
and properties of silica glass have been studied for many decades. The creation
of medium-range ordering structure during the glass transition process explains
the abnormal density-temperature connection of vitreous silica with low
hydroxyl content. The two layers of SiO4 tetrahedra in the organized
medium-range structure, which resembles a "nanoflake," are joined by
O atoms in the center of the formation. The nanoflakes use van der Waals bonds
in addition to covalent chemical connections to interact with the surrounding
structures. In the formation of the van der Waals bonds, the orientation of
SiO4 tetrahedra can change, which results in an increase of distance between
the nanoflakes and their surrounding structures. Thus, there is a slight volume
enlargement associated with the formation of nanoflakes. Since the nanoflakes’
formation starts at a temperature near 1480°C, and the population of the
nanoflakes grows continuously as temperature decreases until about 950°C, the
bulk volume of silica glass increases in the temperature range from about
1480°C to 950°C. The density anomaly of silica glass can be explained as a
byproduct of the formation of medium-range ordering structure in the glass
transition and provides additional support for the new structural model.
Author(s) Details:
Shangcong Cheng,
Molecular Foundry of Lawrence Berkeley National Laboratory,
Berkeley, CA 94720, USA.
Please see the link here: https://stm.bookpi.org/CICMS-V8/article/view/14102
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