Page 102 - Chalcogenide Glasses for Infrared Optics

80 Cha pte r T h ree

N 2 pressure gage &
manometer system
Mirror

Insulation

Heater control
thermocouple
Heaters

Quartz bourdon
pressure gage

Thermocouple #2

TI 1173 glass
Thermocouple #1

FIGURE 3.8 High-temperature manometer for measuring vapor pressure
above chalcogenide glass melts.

The device constructed for direct measurement of viscosity is
shown in Fig. 3.10. A double quartz chamber is separated by a tube of
known inside diameter and length. An amount of glass is placed in
the chamber; then the chamber is evacuated, sealed, and placed in the
furnace that has a hole at the center such that a HeNe laser beam can
pass through the quartz flow tube. The furnace is mounted so it can
rotate about the center hole. In a vertical position, the glass is melted
in the bottom chamber and the temperature noted. The furnace is
inverted, and the glass flows from the upper chamber through the
tube down to the bottom chamber. The time required is measured by
noting the time from when the laser light is blocked by the glass to