Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Nonresinous material only
Patent
1994-04-22
1996-11-19
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Nonresinous material only
264 123, 264 65, 264 66, 264 85, 264125, 4235661, B29D 1100
Patent
active
055759599
ABSTRACT:
Low cost broadband infrared windows are fabricated using a near net shape process which greatly reduces the cost of machining and grinding window materials. The fabrication of zinc sulfide (ZnS) IR windows uses ceramic powder processing to avoid the expensive prior art chemical vapor deposition method. Further, the invention involves a means of hardening and strengthening ZnS as part of the powder process, with IR transmission performance comparable to undoped CVD-prepared ZnS. The compositional modification used in the practice of the invention involves the introduction of gallium sulfide (Ga.sub.2 S.sub.3) as a second phase which acts to toughen and harden the ZnS. The process of the present invention achieves a hardening effect without degrading the IR transmission properties also by means of controlling the polycrystalline microstructure grains to a very small size. At the same time, porosity, which strongly degrades IR transmission, is minimized by full densification. The gallium is introduced into the ZnS by a coprecipitation process to both lower the raw material cost and obtain a suitable submicrometer precursor for the subsequent ceramic processing. The Ga-doped ZnS is then densified into an IR window and a second phase, zinc thiogallate (ZnGa.sub.2 S.sub.4), is precipitated out as a hardening phase by heat treatment. Alternatively, Ga metal is evaporated onto densified ZnS and subjected to heat treatment to form the zinc thiogallate phase.
REFERENCES:
patent: 3131238 (1964-04-01), Carnall, Jr. et al.
J. A. Savage, "Infrared Optical Materials and Their Antireflection Coatings", Adam Hilger Ltd., Bristol and Boston (1985), pp. 95-111.
J. Zhang et al., "Solid-State Phase Equilibria in the ZnS--Ga.sub.2 S.sub.3 System", Journal of the American Ceramic Society, vol. 73, No. [6], pp. 1544-1547 (1990).
W. W. Chen et al, "Experimental and Theoretical Studies of Second-Phase Scattering in IR Transmitting ZnS-Based Windows", Proceedings of SPIE, San Diego, (1991).
Dougherty Thomas K.
Harris Norman H.
Denson-Low W. K.
Fiorilla Christopher A.
Hughes Aircraft Company
Lachman M. E.
Sales M. W.
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