On the degradation mechanism of corrosion protective poly(ether imide) coatings on magnesium AZ31 alloy

Biofunctional composite coating architectures based on polycaprolactone and nanohydroxyapatite for controlled corrosion activity and enhanced biocompatibility of magnesium AZ31 alloy

“…The total impedance of the sample increases from values around 100 kΩ·cm 2 to values slightly above 1 MΩ·cm 2 during the first day of immersion. This increase may result of ongoing reactions between the imide groups in the polymer (PEI) and magnesium hydroxy-fluoride [26,34,35] formed during etching in HF solutions [36,37]. These reactions are slow and can improve adhesion of PEI to the metal, improving the protective effect [38].…”

“…These reactions are slow and can improve adhesion of PEI to the metal, improving the protective effect [38]. Conceicao et al [35] suggested a reaction between magnesium hydroxide and PEI with formation of magnesium polyamate. The final product helps to build a protective interfacial layer at the polymer-metal interface.…”

Corrosion resistance of a composite polymeric coating applied on biodegradable AZ31 magnesium alloy

“…This modifier can covalently bond with the PEI, filling the micropores in the coating and therefore improving its barrier properties. The result is a protective coating with enhanced adhesion to the substrate [25] and, according to Da Conceicao [24], with a self-healing effect. The thickness of this coating is $4 lm and there are no relevant features, such as pores or other defects in the coating, as can be observed in Fig.…”

“…This reaction is frequently promoted using bases such as NaOH, KOH and NR 4 OH, resulting in an improved metal/PEI adhesion [20][21][22]. In this reaction, the imide ring is opened and an amide and a carboxylate salt are formed [23,24]. In general, the electrophilic imide group of polyimides (PIs) reacts with a nucleophilic agent.…”

Effect of phosphate surface pretreatment on corrosion resistance and adhesion of PI coating on Mg-5 wt.% Sn alloy

“…[7,11] For environmental protection reasons, many surface treatments have been found to take the place of chromate containing surface treatment processes, such as cold spray coating, [12,13] electrodeposition of aluminum in ionic liquid, [14,15] PVD (physical vapor deposition) coating, [16] phosphate conversion coating [17,18], or polymer/ organic coatings. [11,19,20] Polymer/organic coatings, which are also called organic finishing's, are considered to be the most cost-effective treatments among the abovementioned techniques [20] and are commonly used in the final stage of a coating treatment on every kind of substrate. [21,22] The most important issue of organic coating is to find an adequate surface pretreatment process which is the decisive factor in the adhesion strength between an organic film and an inorganic substrate, and the time of failure of the protection during the immersion test.…”