Annealing point, glass

To erase information by the transition amorphous — crystalline, the amorphous phase of the selected area must be crystallized by annealing. This is effected by illumination with a low power laser beam (6—15 mW, compared to 15—50 mW for writing/melting), thus crystallizing the area. This crystallization temperature is above the glass-transition point, but below the melting point of the material concerned (Eig. 15, Erase). 

Two other temperatures are important in the working of glass. At the annealing point (p = 10 poise) there is still enough fluidity to relax internal stresses in about... 

Figure 15.8 shows the temperature dependence of several glass compositions. Several temperatures are identified by viscosity the working temperature of a glass by 103 Pa s, the softening point by 4 x 106 Pa s, the anneal point by 2.5 x 1012 Pa s, and the strain point by 4 x 1013 Pa s. Glass objects are usually shaped... 

ASTM C598-88, Standard Test Method for Annealing Point and Strain Point of Glass by Beam Bending , Annual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia, PA. 

Glass Type Thermal Coefficient of Expansion (0-300°C) xlO"7 Acm/cm/°C Strain Pont (=°C) Annealing Point (-°C) Softening Point ( °C) Working Point ( °C) Density (g/cm2) Refractive Index... 

The viscosity parameters for a glass are softening point, 677 °C annealing point, 532 °C strain point, 493 °C. Estimate the activation energy for the viscosity. 

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