Fluorite castings were produced eventually by freezing purified molten CaF2, contained in chemically clean graphite crucibles, in a vacuum-type contrivance patterned after the atmospheric furnace which had been developed earlier for growing lithium fluoride crystals.
The melt was prepared by heating selected fragments of colorless fluorspar mixed with about 2 percent PbF2 which acted as a scavenger to eliminate certain more or less unavoidable impurities, notably products of hydrolysis, and which escaped before the crystallization. In a few instances it was made from a specially synthesized material although this procedure was not wholly desirable.
The crucibles were made by boring, reaming and turning graphite rods which possessed exceptional strength, homogeneity, and chemical purity. Their wall thickness was approximately 0.03 inch when feasible.
Crystallization occurred preferably in a thermal field characterized by a high, nonlinear temperature gradient which remained nearly constant with time.
Canon:
To meet the demands of customers, we are making company-wide efforts to pursue and guarantee quality by effectively managing all phases from the procurement of materials to production and tests.
We measure the optical properties * of CaF2 that has been grown as crystal material for optical applications. Such CaF2 product has a quality that satisfies the needs of customers when they use it as a crystal material or a material for lenses.
（*）Major optical properties
- Crystal plane orientation
- Transmittance (@ 193 nm)
- Birefringence (@ 633 nm)
- Homogeneity
Reference:
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