Page 111 - Chalcogenide Glasses for Infrared Optics

CHAPTER 4

Characterization of

Glass Properties

glass composition has been selected for development based
on a qualitative evaluation. Now the glass has been prepared
A in quantity and in quality so that quantitative measurements
may be made to fully evaluate the potential usefulness of the glass.
Considerable effort is required. AMI started with one glass and pres-
ently produces seven. AMI thus has gone through this process a
number of times. The AMI established method for preparing a glass
for sale in the marketplace is a major part of the company quality
control plan. Others may develop a different approach while empha-
sizing other properties and other methods.

4.1 Thermal Expansion, Glass Transition Temperature,
and Softening Point
Earlier, it was pointed out that the thermal expansion measurement
defines the difference between a crystalline solid and a glass. Now it is
nice if you are in possession of a sophisticated piece of equipment
capable of carrying out the measurement automatically and then pro-
ducing the data plotted in a nice color slide similar to some reproduced
in this book. But if you are not so fortunate, you may build and use a
simple device such as the AMI system shown in Fig. 4.1. A quartz glass
tube inside a circulating air furnace has a quartz glass rod inside which
rests on a vertical 2-in sample of the chalcogenide glass to be mea-
sured. The glass sample is in a chamber that has two sides open so that
air flows freely through and around the sample. A thermocouple is
placed in the chamber next to the sample, and the temperature is read
from the meter on top of the furnace. Also on top, the rod is pushing
against a linear in length, mildly spring loaded transducer which is
monitored by an indicator. The display is set to show numerical read-
ings in this case ±20,000. Before it is used, the transducer is calibrated
in linear sensitivity to determine the numerical change per 0.001-in
movement. The transducer is calibrated using a good micrometer.

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