Page 113 - Chalcogenide Glasses for Infrared Optics
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Characterization of Glass Pr operties 91
9.0
8.0
7.0
6.0 T g
Expansion mils (0.001 in) 5.0
4.0
3.0
2.0
1.0
0
50 100 150 200 250 300
Temperature (°C)
FIGURE 4.2 AMI dilatometer measurement performed on Amtir 3 glass.
2
Earlier, it was mentioned that Robert Patterson in the TI Air Force
Development Program developed the Ge-Sb-Se glass designated as
TI 1173. Patterson decided to develop a device for use with chalco-
genide glasses that would measure the softening point, strain point,
and glass transition temperature in the absolute terms of viscosity. A
diagram of this device is shown in Fig. 4.3. The device used a pointed
spring-loaded (70-g) quartz rod against polished glass samples of
standard size and thickness placed in a heated enclosure. Sample
temperature was measured by a thermocouple placed underneath.
When the penetration depth in the heated sample reached 0.05 mm,
the temperature was recorded as the softening point by method A.
Method B, with identical procedures, was performed except the pen-
etration depth was increased to 0.45 mm. Softening by method B was
recorded. A third ASTM softening point method sometimes used involves
