Moisture Protective Coatings for Alkali Halide IR Optics

The objective of this program is to develop plasma-polymerized films that are transparent, moisture-protective coatings to increase the lifetime and durability of press-forged KBr IR optical elements. Reaction conditions have been established that yield uniform films of plasma-polymerized ethane (PP...

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Bibliographic Details
Main Authors: Yamagishi, Frederick G, Miller, Leroy J
Format: Report
Language:English
Subjects:
ALKAL HALIDE OPTICS
ALKALI METAL COMPOUNDS
Coatings, Colorants and Finishes
FORWARD LOOKING INFRARED SYSTEMS
HALIDES
INFRARED WINDOWS
MOISTURE
OPTICAL MATERIALS
OPTICS
PLASMA POLYMERIZATION
PLASMAS(PHYSICS)
Plastics
POLYMERIC MATERIALS
POLYMERS
PROTECTIVE COATINGS
SURFACE CHEMISTRY
TRANSMITTANCE
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Summary:The objective of this program is to develop plasma-polymerized films that are transparent, moisture-protective coatings to increase the lifetime and durability of press-forged KBr IR optical elements. Reaction conditions have been established that yield uniform films of plasma-polymerized ethane (PPE) on polished and etched single-crystal KBr flats. On polishing, polycrystalline KBr formed localized grains that could not be removed by chemical etching with HBr. Surface passivation could be achieved with a plasma of CF3Br or CF2C12. An air leak in the reactor caused extensive corrosion problems with CF3Br. Repairing the leak eliminated the corrosion problem. On a concurrent IR&D program, we are developing a new surface passivation method for NaCl using a non-IR-absorbing surfactant. PPE deposited on this treated surface afforded protection from damage by 98% relative humidity for 11 days. It is important to eliminate trapped free radicals in the film to reduce the chance of forming a more polar material caused by the reaction of the radicals with atmospheric oxygen. Treating the film briefly with a hydrogen plasma quenched the radicals, but the method was no more effective than the present method of storing under an ethylene atmosphere. The use of DEHA, a two hydrogen atom donor, is being studied in an IR&D program as a radical quencher and may be applied to this program if it proves successful.