Highly Corrosion Resistant and Sandwich-like Si3N4/Cr-CrNx/Si3N4 Coatings Used for Solar Selective Absorbing Applications

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• 作者：Ke Zhang ; Miao Du ; Lei Haoa ; Jianping Meng ; Jining Wang ; Jing Mi ; Xiaopeng Liu
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：December 14, 2016
• 年：2016
• 卷：8
• 期：49
• 页码：34008-34018
• 全文大小：737K
• ISSN：1944-8252

文摘

Highly corrosion resistant, layer-by-layer nanostructured Si₃N₄/Cr-CrN_x/Si₃N₄ coatings 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-CrN_x/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 CrO_x and Al₂O₃ has 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-CrN_x/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-CrN_x/Si₃N₄/Al coating is a good choice for solar absorber coatings applied in the high-saline environment.