materials Article Effect of Zinc Phosphate on the Corrosion Behavior of Waterborne Acrylic Coating/Metal Interface Hongxia Wan 1, Dongdong Song 1,2,*, Xiaogang Li 1,3,*, Dawei Zhang 1, Jin Gao 1 and Cuiwei Du 1 1 Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China; [email protected] (H.W.); [email protected] (D.Z.); [email protected] (J.G.); [email protected] (C.D.) 2 Aerospace Research Institute of Materials and Processing Technology, Beijing 100076, China 3 Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China * Correspondence: [email protected] (D.S.); [email protected] (X.L.); Tel.: +86-010-68383576 (D.S.); +86-010-62333931 (X.L.) Academic Editor: Yong-Cheng Lin Received: 22 April 2017; Accepted: 30 May 2017; Published: 14 June 2017 Abstract: Waterborne coating has recently been paid much attention. However, it cannot be used widely due to its performance limitations. Under the specified conditions of the selected resin, selecting the function pigment is key to improving the anticorrosive properties of the coating. Zinc phosphate is an environmentally protective and efficient anticorrosion pigment. In this work, zinc phosphate was used in modifying waterborne acrylic coatings. Moreover, the disbonding resistance of the coating was studied. Results showed that adding zinc phosphate can effectively inhibit the anode process of metal corrosion and enhance the wet adhesion of the coating, and consequently prevent the horizontal diffusion of the corrosive medium into the coating/metal interface and slow down the disbonding of the coating. Keywords: waterborne acrylic coating; zinc phosphate; LEIS 1. Introduction Serious environment problems have directed attention toward water-based coatings because of their low volatile organic compounds VOC advantages [1–3]. However, waterborne coatings have performance limitations; moreover, they have been extensively used indoors, where the corrosion environment is below the C3 level [4]. Thus, waterborne coatings need to have improved performance for long-term applications [5–8]. Acrylic coatings have good barrier properties and ageing resistance, which has attracted much attention [9,10]. Disbonding is the first sign of coating/metal interface corrosion [11–14], which is the most common form of failure that limits coatings, especially for long-term applications of waterborne coatings [15]. Hence, the ability to resist disbonding characterizes the coating service life, which is the main purpose for developing long-lasting water-based coatings suited for harsh environments [16]. Traditional coatings would exhibit significant cathodic disbonding under different environments that would affect the coating service life. Adding an electrochemically active antirust pigment is a common method for improving the antirust capacity of the coating [17,18]. Therefore, the effect of an electrochemically active antirust pigment on the cathodic disbonding process when added into a waterborne acrylic coating is significant. Much attention has been given to phosphate antirust pigments for their relative environmental protection [19–23]. Phosphate pigments mainly contain aluminum tripolyphosphate [24] and zinc phosphate [25]. The antirust function and mechanism of zinc phosphate have been previously studied. Bethencourt et al. [26] studied the failure process of a waterborne acrylic zinc phosphate coating using Materials 2017, 10, 654; doi:10.3390/ma10060654 www.mdpi.com/journal/materials Materials 2017, 10, 654 2 of 13 electrochemical impedance spectroscopy (EIS). The corrosive failure of composite coatings in 3.5% NaCl solution were divided into three stages: the first stage is the water diffusion stage, wherein Materials 2017, 10, 654 2 of 13 the coating impedance decreases; the second stage involves the zinc phosphate coming in contact withcoatings water, whereinin 3.5% NaCl a passivation solution were rust divided resistance into effectthree stages: reaches the a first certain stage concentration is the water diffusion after water absorption;stage, wherein and the the third coating stage isimpedance the start ofdecreases; the shielding the second decline stage after involves the zinc the phosphate zinc phosphate is exhausted. 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Furthermore, we studied the effects of active pigments on coating/metal interface corrosion and disbonding processes in waterborne 2. Results2. Resultsacrylic coatings. 2. Results 2.1. The2.1. CoatingThe Coating Adhesion Adhesion Test Test FigureFigure2.1.1 showsThe 1 Coating shows the Adhesion the adhesion adhesion Test values values of of 0% 0% and and 8%8% zinc phosphate phosphate coatings. coatings. The The adhesion adhesion values values werewere the samethe sameFigure in the in 1 showsthe 0% 0% and the and adhesion 8% 8% zinc zinc values phosphate phosphate of 0% and coatings.co 8%atings. zinc phosphateAdding Adding zinc coatings. zinc phosphate phosphate The adhesion did didnot values affect not affect the the initialinitial coatingwere coating mechanicalthe same mechanical in the performance. 0% performance.and