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How does the cooling schedule of molten glass affect the structure of solid glass?

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The cooling schedule of molten glass is fundamental to determining its final atomic structure and physical properties. When a liquid is cooled rapidly—a process known as quenching—it bypasses the freezing point, preventing crystallization and resulting in an amorphous solid where atoms lack long-range order but maintain short-range order.12

The rate of cooling significantly influences the glass transition temperature ( $T_{g}$ ); slower cooling rates shift $T_{g}$ downward because they allow more time for molecular rearrangement before the atomic configuration becomes "frozen" into fixed positions.1

Cooling schedules also dictate the distribution of internal stresses:
* Annealing: By cooling glass slowly through the glass-transition range, internal stresses caused by uneven cooling rates in different regions of the material are reduced, ensuring dimensional stability.3
* Thermal Tempering: Rapidly quenching glass from above the transition range causes the outer layers to shrink and solidify faster than the interior. This creates a state of permanent compression on the surface and tension in the interior, which significantly strengthens the material but can lead to spontaneous fracture if the internal tension is too high.4