Reactive Magnetron Sputtering of Cr-N/Cr-O-N/Si-O Highly Selective, Homogeneous and Stable Coating for Thermal Solar Collectors
Abstract
A state of the art, highly selective, homogeneous, and very stable coating deposited on aluminum foils (1m large) has been developed on an industrial continuous reactive magnetron sputtering system. A high solar absorption (α>95%) and low emittance (ε<6%) were achieved by carefully controlling the transition between the layers of the selective coating. The selective coating was characterized using Visible and Near Infra Red and Fourrier Transformed Infrared Red spectrometers, a thermopile emissiometer at 82.5°C (Devices & Services), and Auger Emission Spectroscopy. After a brief description of the deposition process and system, the architecture of the selective multilayer is presented. The evolution of the reflectance measured between 360 and 2700nm, as well as α and ε values are presented and discussed, according to the deposition parameters of the first chromium based layers. The role of the number and nature of interfaces in the multilayer structure on the emittance of the selective coating is emphasis. The variation of the CIE L*, a*, b* color parameters is also discussed as a function of the deposition parameters. ΔE< 5 was systematically achieved on 1m large samples. In order to study the thermal stability of the selective coating, heat treatments were performed in air at 250°C for various durations. After more than 600h, nearly no change in optical properties or color are observed. Finally task X results (PC=-0.0055 after 600h) are presented.