A selective absorber formed by catalytic deposition of pyrolytic carbon on a silver infrared reflecting layer

Abstract

A carbonaceous selective absorber of rather high solar absorptance and quite low thermal emittance has been studied to determine the optimum conditions for its formation. A large number of variables are involved in the formation of this selective absorber, making the determination of these conditions rather time consuming. This absorber is formed by chemically depositing silver on glass, electroplating a thin nickel catalyst layer on the silver, and exposing this surface to hot acetylene at temperatures usually in the range of 475 to 535°C. Under proper conditions a selective absorber is formed which has an air-mass-two normal solar absorptance near or above 0.90, a 100°C hemispherical thermal emittance near or below 0.03, and which appears to be stable in vacuum at temperatures near 500°C. The carbonaceous coating formed is rather hard and adhesive, such that it can withstand the “scotch tape test”. This absorber has the advantage that its formation is entirely at atmospheric pressure using inexpensive materials, and thus can be produced more cheaply than many other high temperature absorbers.