Page 93 - Chalcogenide Glasses for Infrared Optics

CHAPTER 3

Glass Production

3.1 Reactants
After a glass composition has been selected for use, a method of pre-
paring the glass in quantity with high quality must be developed. Of
first importance is identifying a reliable source of the required
elemental reactants in high-purity form. The transport properties,
electrical conductance, of crystalline materials may be dominated by
small concentrations of impurities in their reactants. Chalcogenide
glasses have already been described as poor electronic conductors, so
the metallic impurity effect on conductance is of minor consequence.
However, their optical properties may be adversely affected by small
concentrations of impurities.
Because of the great importance of crystalline semiconductor
materials, tremendous effort has been spent producing important
reactants in high-purity form and developing precise methods to
verify the purity of the product. Reactants used in chalcogenide
glasses have benefited greatly from these efforts. Most of the elements
used to produce what we might call electronic materials are by-products
of primary metals production. The most important are copper, lead,
zinc, silver, and aluminum. A good example is the production of pure
copper at the Asarco Plant in Amarillo, Texas. Plates of 99 percent
copper are electroplated on titanium plates in almost 0.5-mi-long
1
electroplating facility. A photograph of the tank house is shown in
Fig. 3.1. The design goal of the unit is over 400,000 tons /yr of refined
copper. The resulting copper is 99.90 percent pure. A slime of waste,
less than 0.1 percent of the beginning copper, falls to the bottom of the
cell. In that waste are low concentrations of silver, gold, platinum,
palladium, antimony, arsenic, cadmium, indium, selenium, tellurium,
and thallium. These elements are chemically separated and then
purified by chemical means and sold to industry. In similar processes,
germanium is a by-product in the production of zinc and gallium,
used to make the crystalline semiconductor gallium arsenide, which
is a by-product of the production of aluminum.
The costs of reactants used in chalcogenide glasses are not stable
and may vary greatly. The supply of each depends upon the rate of

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