Low-pressure chemical vapor deposition of emissivity modification coatings on complex shapes

Abstract

Modifying the emissivity of non-planar surfaces and objects with complex geometries has proven to be a difficult task. Optical interference coatings have been successfully used to change the spectral emissivity of a surface. However, typical deposition processes for these coatings, such as evaporation, are line-of-sight processes that require complex masking and/or rotation systems in order to coat non-planar surfaces. Objects with very complex geometries cannot be coated at all by line-of-sight processes. In addition, evaporative processes often do not provide films with good resistance to thermal cycling to high temperatures. Low Pressure Chemical Vapor Deposition (LPCVD) is a non-line-of-sight process that unifonnly coats all exposed surfaces of objects with complex shapes. DSI has developed an LPCVD process that is capable of the routine manufacture of optical interference coatings. We have used this process to deposit high quality, uniform, conformal coatings for the modification of the emissivity of a variety of materials including ceramics and metals. Coatings of these substrates in very complex, non-planar forms have been demonstrated. The coatings show excellent durability and withstand repeated cycling to high temperatures. In this paper we will briefly describe the coating process, show examples of some of the substrate forms, and describe the spectral and environmental performance of these emittance control coatings.