Dissolution and Passivation of a Silicon-Rich Austenitic Stainless Steel during Active-Passive Cycles in Sulfuric and Nitric Acid

Abstract

The high Si containing X1CrNiSi18-15-4 stainless steel (SS) spontaneously forms a protective oxide film that is mostly composed of mixed chromium and silicon oxides. This film ensures a good durability of the industrial facilities the alloy was designed for, containing very acidic electrolytes such as hot and concentrated nitric acid, HNO 3 , in presence of oxidizing species. In the present work, the chemistry of the oxide formed and the passivation kinetics of the alloy in sulfuric acid, H 2 SO 4 , and for the first time in HNO 3 , were monitored by atomic emission spectroelectrochemistry (AESEC) over successive activation and passivation cycles of the material. X1CrNiSi18-15-4 SS was compared to a low Si containing SS, the X2CrNiN18-10 SS. It was found that a similar quantity and rate of passive film was formed during passivation, and dissolved during activation. Reproducible results were obtained over several active-passive cycles. The excess Cr was correlated with the dissolution rate decay during passivation. The Si/Cr ratio of the passive film was determined by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy (performed using transmission electron microscopy), and AESEC giving similar results within experimental error. The EDX profile suggest that the passive film consists of a Si rich outer and Cr rich inner layer.

Intergranular corrosion in evolving media: Experiment and modeling by cellular automata

“…This is in accordance with the results of Tcharkhtchi et al who showed an increase of the oxide thickness of a 304L SS in nitric acid with the increase of the corrosion potential Ecorr [26]. for these SSs corroded in nitric acid media [26,43,61], the oxide is mainly composed of chromium with a small proportion of iron. Nickel oxide is not observed.…”

Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements

“…Nitric acid is a strong oxidant, and stainless steels spontaneously passivate in concentrated nitric acid solutions and remain passive at open-circuit potential (OCP) conditions. 24 Laurent et al investigated two stainless steels with low and high Si content in nitric acid and concluded that their passive layer was similar at the end of passivation. The naturally formed passive film over the ferrite is different than that of the austenite, giving rise to a typical Volta potential difference of 40-70 mV of numerous DSS's.…”

“…The naturally formed passive film over the ferrite is different than that of the austenite, giving rise to a typical Volta potential difference of 40-70 mV of numerous DSS's. 12,13,19,25 Laurent et al 24 reported a chromium-rich oxide, in the form of chromia, that became further enriched in the passive film upon passivation in nitric acid, with the thickness, however, not been majorly altered. This may explain the reason why the Volta potential of ferrite and austenite of the DSS were similar after immersion in nitric acid.…”

“…26 The passive film of stainless steels is known to be composed of an outer iron-rich oxide, mainly Fe 2 O 3 and Fe(OH) 2 /Fe(OH) 3 , and an inner chromiumrich oxide, often stated as Cr 2 O 3 and Cr(OH) 3 , with also some molybdenum as well as silicon species. [22][23][24]27 The composition and morphology as well as defect contents and semiconductor properties of passive films of stainless steel can largely differ depending on the environment in which they form. In earlier work, it was shown that the native passive film on the studied alloy gets more defective upon anodic polarisation from its passive to transpassive potential regime in 1 M NaCl solution, and becomes thicker and changes its composition and structure.…”

Recent insights in corrosion science from atomic spectroelectrochemistry

“…[ 32 ] The role of Si alloying on the evolution of the passive film was investigated using a similar activation‐passivation cycle, whereby a noticeable release of Si during activation confirmed the contribution of Si to the passive film of austenitic stainless steel. [ 33 ] However, the decay in the dissolution rate during passivation was found to predominantly follow the enrichment of Cr(III) oxides in the film. It indicates that in spite of enrichment in the passive film, the Si(IV) oxide did not contribute much to the passivity of stainless steel.…”