D1 Dilatometry and Characteristic Points

Topic

Dilatometry for this model records how the glass expands or contracts as its temperature changes, utilizing the same linear thermal expansion principles employed for the equivalent metal model. Because the glass expands relatively uniformly while remaining rigid below a certain temperature, the resulting expansion curve exhibits a roughly constant slope in that initial section.

The fact that this slope changes—more or less abruptly—at a specific temperature allows for the determination of the dilatometric glass transition temperature: above this point, the glass ceases to behave as a rigid solid and its expansion coefficient increases, causing the curve to adopt a different slope than in the preceding section. By fitting straight lines to each of these two sections—the one before and the one after the change in slope—the temperature at which the lines intersect is identified precisely as the glass's dilatometric glass transition temperature.

As the temperature continues to rise beyond the glass transition, this same expansion and contraction curve identifies other characteristic points: the deformation point, where the glass begins to deform visibly under its own weight; the annealing point, the reference temperature at which residual stress is relieved; and the softening point, where the glass is soft enough to flow appreciably under its own weight. Since each of these points corresponds to a progressively higher temperature, together they describe the complete sequence of states the glass undergoes as it is heated further. For this reason, the results from this model—initiated using the glass's dilatometry data—feed into two other models within the set: the one describing the glass transition temperature, using the dilatometric glass transition temperature determined by the intersection of slopes; and the one describing standard glass viscosity points, using the deformation, annealing, and softening points identified by that same expansion and contraction curve.

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