High performance Al–N cermet solar coatings deposited by a cylindrical direct current magnetron sputter coater

Abstract

High efficiency Al–N cermet solar selective coatings have been designed using a numerical computer model and deposited experimentally. In numerical modeling calculations, Bruggeman approximations of dielectric function for composite materials were employed. Aluminum is used as a metallic component and AlON as a ceramic component in cermet. Numerical calculation results show that the double cermet layer film structure has the highest photothermal conversion efficiency for the Al–AlON cermet solar selective coatings. The optimized film has a solar absorptance of 0.958 and a hemispherical emittance of 0.035 at 80 °C. The optimized film yields two cermet layers with metal volume fractions of 0.143 and 0.275, and with layer thicknesses of 43 and 80 nm, going from the antireflection coating to the infrared reflector layer. In the optimized double cermet layer film the solar radiation is efficiently absorbed internally and by phase interference. Thermal loss is also efficiently reduced by using thin cermet layers with such low metal volume fractions, which are substantially transparent in the main wavelength region of blackbody radiation within the temperature range of interest, 50–200 °C. The predicted film structure has been used as a guide for the experimental deposition. The Al–N cermet solar selective coatings with double cermet layer film structure have been deposited onto batches of solar collector tubes using a commercial-scale cylindrical dc magnetron sputter coater. Two Al–N cermet solar absorber layers are deposited by dc reactive sputtering in a gas mixture of argon and nitrogen. The different metal volume fractions in the cermet layers are achieved by changing the reactive nitrogen gas flow rate, while the sputtering current is fixed. A solar absorption of 0.96 and a normal emittance of 0.08 at 80 °C have been achieved for deposited Al–N cermet solar coatings. The baking process, for 1 h at 400 °C in vacuum, hardly affects solar absorptance, however the emittance reduces about 0.01 at 80 °C. These high-performance low-cost Al–N cermet solar collector tubes may be a less-polluting replacement for black chromium solar collectors produced by electrochemical methods.

Rugometric and Microtopographic Inspection of Cr–Cr2O3Cermet Solar Absorbers

“…The light levels absorption is good enough for our weather but surface emittance is not [1][2][3]. Spectrally selective surface coatings for absorbers in high performance solar collectors and electrochromic devices for modulation solar transmittance in "smart buildings" can be produced with increasing success by different processes [1][2][3][4][5][6][7][8] from many years. Magnetron sputtering is such a technique widely used in thin film production [3][4][5][8][9][10][11].…”

“…Spectrally selective surface coatings for absorbers in high performance solar collectors and electrochromic devices for modulation solar transmittance in "smart buildings" can be produced with increasing success by different processes [1][2][3][4][5][6][7][8] from many years. Magnetron sputtering is such a technique widely used in thin film production [3][4][5][8][9][10][11]. This physical vapour deposition process is a cleaner process compared to conventional techniques to produce black paintings (chemical processes) or selective surfaces such as black chrome (by electrodeposition), with pollutant solvents, dangerous solutions, and environmental impact of the solid waste and water residuals.…”

“…The influence of preparation conditions on the microstructure and on the solar selective properties of these oxides and layered coatings is investigated [1,3]. A large array of characterisation techniques of surface and interface analysis using advanced surface analysis systems (including XPS, AES, XRD, SEM; TEM, AFM, STM, UPS) is employed [1,4,9,10,12]. Further, we introduce the issue of roughness measurement and microtopographic evaluation of coatings's final materials as a quality nondestructive evaluation [1].…”

A study of the DC discharge in a cylindrical magnetron comparison of experiment and a pic model

“…Cylindrical magnetrons are nowadays used for deposition of thin films with special optical properties and for high-temperature superconducting thin films [1,2,3,4]. Moreover, as a relatively simple system, the DC discharge in cylindrical magnetron offers a possibility to create a numerical model and compare its results with experiment.…”

A novel system for studies of dc discharge in cylindrical magnetron

“…Cylindrical magnetrons are nowadays used for deposition of thin films with special optical properties and for high-temperature superconducting thin films [1,2,3,4]. Moreover, as a relatively simple system, the DC discharge in a cylindrical magnetron offers a possibility to create a numerical model and compare its results with experiment.…”