In this work, the inhibition effect of nitrate on the pitting corrosion of 17-4PH stainless steel was investigated in the chloride solution. Potentiodynamic and potentiostatic techniques were used to measure the pitting potential and induction time in various concentrations of chloride and nitrate ions. According to the results, the equation of E pit = 259.1 − 147.4 log½Cl − + 52.1 log½NO − 3 was developed to show the relationship between the pitting potential and the concentrations of nitrate and chloride ions at room temperature. Moreover, it has been shown when the ratio of ½NO − 3 =½Cl − 1.02 is greater than a threshold value of 0.35, the alloy remains passive in whole potentials during the potentiodynamic experiments. In addition, the results indicated that pitting is rarely observed in the potentials above the 400 mV SCE in the chloride solutions containing nitrate.
The protectiveness of coatings based on 3-mercaptopropyl-trimethoxysilane (PropS-SH) applied on bronze artworks was enhanced by investigating and tuning a variety of factors. In particular, the coating performances were optimized by proper additive choice among oxide nanoparticles (CeO2, La2O3, TiO2) and microparticles (fly ash (FA)), and by varying the aging time of the nanoparticle suspensions before coating application and the RT curing time of the coatings. Moreover, the possibility of conservation of the silane solution under refrigerated conditions was assessed. The aggressive environment was a tenfold concentrated synthetic acid rain (AR × 10). The techniques adopted comprised electrochemical tests (polarization curve recording and EIS tests) and SEM-Energy Dispersion Spectroscopy (EDS) observations. In the case of FA microparticles, never used before as additives in silane coatings, further tests were performed in FA suspensions in AR × 10 to clarify the contribution of these particles to PropS-SH coating protectiveness. The tests included pH measurements, elemental chemical analyses, and electrochemical tests on bare bronze. Improved performances of PropS-SH coatings were achieved by La2O3, CeO2, and FA addition, with La2O3 affording the best results during 20 days of immersion. The positive influence of FA was connected to its alkaline character and to the release of soluble silicates.
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