Alternative to Nitric Acid Passivation of 15-5 and 17-4PH Stainless Steel Using Electrochemical Techniques

Abstract

Increasingly stringent environmental regulations in different sectors of industry, especially the aeronautical sector, suggest the need for more investigations regarding the effect of environmentally friendly corrosion protective processes. Passivation is a finishing process that makes stainless steels more rust resistant, removing free iron from the steel surface resulting from machining operations. This results in the formation of a protective oxide layer that is less likely to react with the environment and cause corrosion. The most commonly used passivating agent is nitric acid. However, it is know that high levels of toxicity can be generated by using this agent. In this work, a study has been carried out into the electrochemical behavior of 15-5PH (precipitation hardening) and 17-4PH stainless steels passivated with (a) citric and (b) nitric acid solutions for 60 and 90 min at 49 °C, and subsequently exposed to an environment with chlorides. Two electrochemical techniques were used: electrochemical noise (EN) and potentiodynamic polarization curves (PPC) according to ASTM G199-09 and ASTM G5-13, respectively. The results obtained indicated that, for both types of steel, the passive layer formed in citric acid as passivating solution had very similar characteristics to that formed with nitric acid. Furthermore, after exposure to the chloride-containing solution and according with the localization index (LI) values obtained, the stainless steels passivated in citric acid showed a mixed type of corrosion, whereas the steels passivated in nitric acid showed localized corrosion. Overall, the results of the R n values derived show very low and similar corrosion rates for the stainless steels passivated with both citric and nitric acid solutions.

Frequency Analysis of Transients in Electrochemical Noise of Superalloys Waspaloy and Ultimet

“…This behavior is present in other research with different materials [24,55], denoting that Rn and Ψ 0 can be considered counterpart parameters to determine corrosion resistance. However, to analyze the type of corrosion, slope parameters divergent from statistical parameters, they cannot be considered mechanistic [84,85]. For this type of alloy, slope parameters should be employed with discretion.…”

Electrochemical Behavior of Ti6Al4V Alloy Used in Dental Implants Immersed in Streptococcus gordonii and Fusobacterium nucleatum Solutions

“…A change in the electrolyte composition (for example, pH and bacteria life) can reduce the corrosion rate in the implant as mentioned by Bhola, et al [ 4 ]. The Ti6Al4V alloy at 48 and 96 h presents stable behavior of the passive film, demonstrating that the electrochemical reactions on the surface of the alloy are in balance [ 44 , 45 ]. This is consistent with Grosgogeat et al [ 46 ], who studied the electrochemical behavior of titanium in near-real clinical conditions and concluded that it is essential to have oxidated layers that are characteristic of a pseudo-stationary state.…”

Special Issue: Advanced Coatings for Corrosion Protection

“…The most commonly used passivating agent to develop such an oxide layer is nitric acid. Lara-Banda et al investigated an environmentally friendly alternative for the passivation of 15-5 and 17-5PH stainless steels based on citric acid [ 1 ]. It could be shown that, for both types of steel, the passive layer formed in citric acid as passivating solution had very similar characteristics to that formed with nitric acid.…”