Abstract
The aim of this work was to study the corrosion behavior of three commercial nanoceramic coatings in comparison to zinc phosphate coatings applied on mild steel (SAE 1010). The coatings were evaluated by scanning electron microscopy (SEM), profilometry and hydrophobicity. The electrochemical behavior was evaluated by dynamic polarization. The results showed that the samples coated with nanoceramics presented contact angles greater than 100º, achieving hydrophobic behavior. Evaluating the electrochemical behavior under dynamic polarization revealed that the nanoceramic coating containing chromium (CHT) exhibited a higher corrosion potential and lower current than the other nanoceramic coatings tested, although its performance in a dilute sodium chloride solution was below that of the zinc phosphate-based coating. Although the nanoceramic coatings exhibited poor electrochemical behavior compared to the zinc-based coatings, they had a higher corrosion resistance when associated with an organic coating.
Highlights
The corrosion of metallic materials causes many industrial problems, decreasing equipment life spans and leading to their maintenance or even replacement and, costing time and money[1].Protective coatings are used on metal materials to inhibit corrosion and to preserve the materials
The scanning electron microscopy (SEM) micrographs (Figure 2) demonstred that the CHT sample (Figure 2b) exhibited a uniform layer covering the surface, with protuberances observed on the surface
According to Banczek et al and Moore et al.[19,20], the morphology observed in the phosphate sample is common due to the formation of hopeite, which consists of hydrated zinc phosphate (Zn3 (PO4)2. 2H2O)[19,20]
Summary
The corrosion of metallic materials causes many industrial problems, decreasing equipment life spans and leading to their maintenance or even replacement and, costing time and money[1]. Protective coatings are used on metal materials to inhibit corrosion and to preserve the materials. The phosphating process is the most widely used metal pretreatment process for ferrous substrates[3], and has been used for various applications in many industrial fields[4]. The most important application of the phosphating process is as a pretreatment for finishing paint, where it increases the film adhesion to the substrate, improving the paint barrier effect, avoiding the subcutaneous corrosion progress. Studies show that the resistence corrosion performance of painted metals is approximately 700 times greater when the metal is phosphatized prior to painting[5]
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