Dilatometric softening point

Linear thermal expansion coefficient (a) and dilatometric softening point (Mg)... 

Figure 10.13 Schematic of a thermomechanical analysis (TMA) thermal expansion curve of an inorganic compound glass (solid curve). The geometrical construction to obtain the dilatometric softening point, A4g, at 10 i =Pas is given. The analogous TMA thermal expansion curve is shown (dotted curve) when a high-fictive-temperature glass sample is heated under load relaxation to a lower-fictive-temperature configurational arrangement can produce an observable contraction as illustrated.

This relation contains three constants (A, B, which can be calculated from three viscosity points. These are usually provided by the sink point, the Littleton softening point and by determined dilatometrically (refer to Section 5.2). By means of these values and of eqn. (9) it is then possible to interpolate satisfactorily and even to extrapolate, within a narrow range, the entire viscosity curve for current types of glasses. The suitability of relationship (9) may easily be checked by plotting the three values measured on the log tj — l/(T— To) diagram the points should lie along a straight line. 

Another viscosity point can be obtained from thermal expansion curves. The dilatometric softening temperature, T, is usually defined as the temperature where the sample reaches a maximum length in... 

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