The effect of bicarbonate additive on corrosion resistance and microstructure characteristics of the zirconium-based con
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The effect of bicarbonate additive on corrosion resistance and microstructure characteristics of the zirconium-based conversion coating on carbon steel Linqing Niu, Ruiguang Guo, Qingmin Si, Hongyan Guan
American Coatings Association 2020 Abstract Zirconium-based conversion coating (ZrCC) with modification has been studied for improving the corrosion resistance of carbon steel in this paper. Ammonium bicarbonate (NH4HCO3) and sodium bicarbonate (NaHCO3) were used as additives to investigate their roles on the conversion coating properties. The surface of the modified coating was characterized by scanning electron microscope, X-ray photoelectron spectroscopy, and electron probe microanalyzer. In addition, the corrosion resistance was studied by Tafel polarization, electrochemical impedance spectroscopy, and the neutral salt spray test (NSST). The results indicated that both NH4HCO3 and NaHCO3 as additives could promote the precipitation of ZrO2, ZrF4, K2ZrF6, Fe2O3, and FeOOH on carbon steel and NaHCO3 as the additive could make the surface thicker and more uniform. According to the electrochemical and NSST results, NH4HCO3- and NaHCO3-modified zirconium-based conversion coating (ZrCC–NH4, ZrCC–Na) exhibited more effective corrosion protection property compared with ZrCC, among which ZrCC–Na sample showed the highest corrosion resistance. Keywords Carbon steel, Corrosion, Zirconium-based conversion coating, Bicarbonate
L. Niu, Q. Si, H. Guan Zhengzhou University of Aeronautics, Zhengzhou 450046, People’s Republic of China R. Guo (&) Key Lab of Water, Environment and Ecology in North China, Ministry of Education, Xi’an University of Architecture and Technology, Xi’an 710055, People’s Republic of China e-mail: [email protected]
Introduction Owing to good mechanical properties and low costs, carbon steel has been widely applied as a key material in construction, machinery, transportation, chemical, and other fields. However, its application in production is limited due to its poor corrosion resistance accompanied by unsatisfying economic and safety benefits. In view of this, many attempts have been made and different coatings and surface treatment methods have been adopted to improve the corrosion resistance of carbon steel. Specifically, the chemical conversion treatment formed by precipitation of conversion solution onto metal substrate has a wide range of applications with an economic advantage as well as a promised protection result.1 Traditional chromium and phosphate conversion coatings suffer serious restrictions for facing the pressure of environmental protection, health, low carbon, and other aspects. As representatives of environmentally friendly coating materials, rare-earth elements (cerium, lanthanum, etc.2–5) and friendly transition metals (zirconium, titanium, etc.6–9) are currently the focus of research. In the early 1990s, protective coatings were prepared by using acidic aqueous solution containing zirconium ions.10 Several properties, such as the precipitation mode similar to the chromium
