title: Highly Corrosion Resistant and Sandwich-like Si3N4/Cr-CrNx/Si3N4Coatings Used for Solar Selective Absorbing Applications.
abstract: Highly corrosion resistant, layer-by-layer nanostructured Si3N4/Cr-CrNx/Si3N4coatings were deposited on aluminum substrate by DC/RF magnetron sputtering. Corrosion resistance experiments were performed in 0.5, 1.0, 3.0, and 5.0 wt % NaCl salt spray at 35 °C for 168 h. Properties of the coatings were comprehensively investigated in terms of optical property, surface morphology, microstructure, elemental valence state, element distribution, and potentiodynamic polarization. UV-vis-near-IR spectrophotometer and FTIR measurements show that the change process in optical properties of Si3N4/Cr-CrNx/Si3N4/Al coatings can be divided into three stages: a rapid active degradation stage, a steady passivation stage, and a transpassivation degradation stage. With the increase in the concentration of NaCl salt spray, solar absorptance and thermal emittance experienced a slight degradation. SEM images reveal that there is an increase in surface defects, such as microcracks and holes and -cracks. XRD and TEM measurements indicate that the phase structure changed partially and the content of CrOxand Al2O3has increased. Auger electron spectroscopy shows that the elements of Cr, N, and O have undergone a minor diffusion. Electrochemical polarization curves show that the as-deposited Si3N4/Cr-CrNx/Si3N4/Al coatings have excellent corrosion resistance of 3633.858 kΩ, while after corroding in 5.0 wt % NaCl salt spray for 168 h the corrosion resistance dropped to 13.759 kΩ. However, these coatings still have an outstanding performance of high solar absorptance of 0.924 and low thermal emittance of 0.090 after corroding in 3.0 wt % NaCl salt spray for 120 h. Thus, the Si3N4/Cr-CrNx/Si3N4/Al coating is a good choice for solar absorber coatings applied in the high-saline environment.
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Miao
authors.initials: M
authors.lastname: Du
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Haoa
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Jianping
authors.initials: J
authors.lastname: Meng
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Jining
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Mi
authors.affiliation: Department of Energy Material & Technology, General Research Institute for Nonferrous Metals , No. 2 Xinjiekouwai Street, Xicheng District, Beijing 100088, China.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Liu
keywords: CrNx; Si3N4; electrochemical corrosion; microstructure; solar absorber coatings