Intelligent Coatings for Corrosion Control

Comparative Study on the Corrosion Inhibitive Effect of 2-Mecraptobenzothiazole and Na2HPO4 on Industrial Conveying API 5L X42 Pipeline Steel

“…Furthermore, ordinary structures of lepidocrocite spongy structure (and probably parts of maghemite, a phase that usually adopts the shape of its precursor [54]) and smaller aggregations of magnetite (as more globular, smooth) seem to be present, while a compact continuous inner layer (with cracks from drying process) has been obviously generated, which is indicative of steel surface passivation by phosphates (Figure 4c,d). In addition, large platy crystals of nanocrystalline phases are captured, reassuring the creation of the expected thin adherent passive layer of iron phosphates, maghemite, and lepidocrocite in crystalline and amorphous formations [26,53] (Figure 4e,f). It should be taken into account that the special influence of phosphate anion is participating in various chemical paths.…”

“…It can be seen that characteristic tassel-like structures, mainly consisting of [Fe II -OH] compounds, with substituted hydroxyls by phosphate anions (H 2 PO 4 − , HPO 4 2− , PO 4 3− ) [52], reveal the phosphates incorporation, thus making possible the identification of iron phosphates, appearing in amorphous or crystal phases. The latter are often observed as filamentous agglomerates [53] ( Figure 4a,b). However, phosphorous detection through microscopy techniques of EDS analysis of the surface has been considered harsh, as phosphate anions get incorporated in steel crystal lattice [26].…”

“…Phosphorus consists of a significant alloying element of low-alloyed and carbon steels against atmospheric corrosion [106] and Cl − attack [107], and it is considered to improve machinability, fatigue, and hardenability. Phosphating through immersion baths, as conventionally realized in industry, is considered to be complete after several days, mainly due to recrystallization and solid-state transformation processes and in order to enhance surface coherence with metallic coatings, as zinc phosphating [53] and even with organic protective coatings. There has been a variety of chiefly organic substances proposed as accelerators of phosphating, such as certain imines, pyridines, and other oxidizing substances [108].…”