Influences of urea and sodium nitrite on surface coating of plasma electrolytic oxidation

Electron-Donor and -Acceptor Agents Responsible for Surface Modification Optimizing Electrochemical Performance

“…Second, the wider pores and higher porosity in the samples that used urea, hydrazine, and urea-hydrazine mixture could thus be attributed to the decomposition and reactions of these compounds in solution, which creates fewer long-lived sparks. Our results were thus in good agreement with previous studies. , On the other hand, reactions – below indicated that Al 2 O 3 was first produced during the high-temperature PEO process, and then reacted with MgO to form MgAl 2 O 4 …”

“…Thus, the precipitate affected the layer thickness, which incompletely protected of the surface of those samples after 15 min in baths A–D. Evidently, a portion of the plasma energy could be diverted into urea decomposition or reactions between urea and magnesium or into precipitate activation, leading to weakening microarc intensity. , …”

“…revealed, on the basis of plasma electrolysis of magnesium alloy in the silicate-phosphate electrolyte with (CH 2 ) 6 N 4 working as electron donor, that the formation of the microdefects in the oxide film was inhibited sufficiently to enhance the anticorrosion properties through surface modification mechanism which would allow donor of (CH 2 ) 6 N 4 to provide a number of electrons to the electrolyte, transforming O 2 gases into particular water molecules during electrochemical process . In addition, some recent studies have reported that nitrogen might contribute to the growth behavior of the oxide layer by adding donor–acceptor agents, such as H 2 NCONH 2 , NaNO 2 , NaNO 3 , or NH 4 NO 3 , to the aqueous electrolytes. − Shang et al suggested that the addition of sodium nitrite to the sodium-aluminate electrolyte would result in the increase of the layer thickness as well as the decrease of the porosity . The effect of NaNO 2 was attributed to oxidation enhancement, not to nitridation …”

“…In addition, some recent studies have reported that nitrogen might contribute to the growth behavior of the oxide layer by adding donor–acceptor agents, such as H 2 NCONH 2 , NaNO 2 , NaNO 3 , or NH 4 NO 3 , to the aqueous electrolytes. − Shang et al suggested that the addition of sodium nitrite to the sodium-aluminate electrolyte would result in the increase of the layer thickness as well as the decrease of the porosity . The effect of NaNO 2 was attributed to oxidation enhancement, not to nitridation …”

Corrosion behavior and adhesion strength of PEO/Epoxy duplex coating applied on aluminum alloy

“…Based on the mentioned description and as can be seen in Figure 1, the sample formed in more urea and higher current density (EPU4) has more compressed and uniform structure. Therefore, more delicate structure and high porosity in the PEO structure containing more urea in higher current density are developed (Yeh et al, 2015). As shown, the PEO coating has the wave-shaped interface with the substrate (Figures 2 and 3).…”