Electrochemical noise analysis of cathodically polarised AISI 4140 steel. II. Identification of potential fluctuation sources for unstressed electrodes
“…Hodgson showed that the influence of various electrocatalysts on the departure rate of chlorine bubbles evolving on ruthenium-titanium oxide anodes could be monitored by current noise measurements [11]. Compared to the analysis of the potential or current fluctuations, which depend on several factors (ohmic, activation, concentration of dissolved gas) [3,12], the analysis of the fluctuations of the electrolyte resistance (ER) measured between the reference electrode and the working electrode is easier since only ohmic effects are concerned.…”
In a previous work, the analysis of the electrolyte-resistance (ER) increment due to the presence of an insulating sphere above or in contact with a disk electrode, simulating a spherical particle, drop, or gas bubble close or attached to an electrode has been reported [Bouazaze et al., Electrochim. Acta 55 (2010) 1645]. In the present work, the influence on the ER of the contact angle with the electrode surface, which plays for example a major role in the size of bubbles on gasevolving electrodes, is quantitatively determined. The mathematical collocation method used in the previous work was improved to account for the change in geometry of the electrode-sphere system. The theoretical results show that the ER increment due to the presence of the sphere depends on its size, position, and contact angle. For a given size and position of spheres of aspect ratio less than 0.4, the ER increment due to the contact angle varies roughly between-45% and +35% of the increment due to a perfect sphere, depending on the interplay of the surface and volume competing effects influencing the ER. Despite their low values, the ER increments could be experimentally measured for spheres of different contact angle placed at the electrode centre, owing to a highprecision motorized translation stage and a specific low-noise ER measurement device. An excellent agreement was obtained between the theoretical and experimental results.
“…Hodgson showed that the influence of various electrocatalysts on the departure rate of chlorine bubbles evolving on ruthenium-titanium oxide anodes could be monitored by current noise measurements [11]. Compared to the analysis of the potential or current fluctuations, which depend on several factors (ohmic, activation, concentration of dissolved gas) [3,12], the analysis of the fluctuations of the electrolyte resistance (ER) measured between the reference electrode and the working electrode is easier since only ohmic effects are concerned.…”
In a previous work, the analysis of the electrolyte-resistance (ER) increment due to the presence of an insulating sphere above or in contact with a disk electrode, simulating a spherical particle, drop, or gas bubble close or attached to an electrode has been reported [Bouazaze et al., Electrochim. Acta 55 (2010) 1645]. In the present work, the influence on the ER of the contact angle with the electrode surface, which plays for example a major role in the size of bubbles on gasevolving electrodes, is quantitatively determined. The mathematical collocation method used in the previous work was improved to account for the change in geometry of the electrode-sphere system. The theoretical results show that the ER increment due to the presence of the sphere depends on its size, position, and contact angle. For a given size and position of spheres of aspect ratio less than 0.4, the ER increment due to the contact angle varies roughly between-45% and +35% of the increment due to a perfect sphere, depending on the interplay of the surface and volume competing effects influencing the ER. Despite their low values, the ER increments could be experimentally measured for spheres of different contact angle placed at the electrode centre, owing to a highprecision motorized translation stage and a specific low-noise ER measurement device. An excellent agreement was obtained between the theoretical and experimental results.
“…Poten tiostatic/Galvanostatic mode is usually applied in lab studies, such as SCC monitoring and gas evolution [3,[36][37][38]. In this case, we can only obtain ECN under potentiostatic control or EPN under galvano static control, but we cannot get both of them.…”
The electrochemical noise (EN) experiment and instrumentation aspects are briefly summarized, and the direct current (DC) removal methods before EN analysis are illustrated. The results show that poly nominal trend removal, wavelet analysis and Empirical mode decomposition are effective for DC removal whereas average trend removal and linear trend removal are not suitable for DC removal.
“…(ii) Pit initiation 15 ; metastable pitting [16][17][18] ; stable pitting [19][20][21] ; rust detachment 22 ; (iii) Changes in solution resistance; hydrogen discharge with gas bubble formation and detachment; diffusion of anion into propagating microcracks; discharge on freshly exposed metal at propagating cracks 8,[23][24][25] ; oxygen reduction 26 ; sudden film rupture such as crack propagation involving metal dissolution and water discharge [27][28][29][30][31] ; (iv) Microbial induced corrosion 32,33 ; (v) Crevice corrosion 34,35 ; mechanical impingement and abrasion [36][37][38][39][40] ; (vi) Underfilm corrosion 41 ; intergranular corrosion 42 ; exfoliation 43 ; (vii) Metal at passive state 44,45 ; (viii) High temperature processes 14,46,47 ;…”
Section: Introductionmentioning
confidence: 99%
“…The major sources of EN observed in corrosion systems can be ascribed to macroscopic and microcosmic random (stochastic) phenomena, which have been shown to vary widely. They include the following: Uniform corrosion 13,14 ;Pit initiation 15 ; metastable pitting 16–18 ; stable pitting 19–21 ; rust detachment 22 ;Changes in solution resistance; hydrogen discharge with gas bubble formation and detachment; diffusion of anion into propagating microcracks; discharge on freshly exposed metal at propagating cracks 8,23–25 ; oxygen reduction 26 ; sudden film rupture such as crack propagation involving metal dissolution and water discharge 27–31 ;Microbial induced corrosion 32,33 ;Crevice corrosion 34,35 ; mechanical impingement and abrasion 36–40 ;Underfilm corrosion 41 ; intergranular corrosion 42 ; exfoliation 43 ;Metal at passive state 44,45 ;High temperature processes 14,46,47 ;Electrowinning 48 ; coated metal corrosion. 49–54 1 a schematic diagram of EN applications; b total reported literature related to EN applications in corrosion science from 1997 to 2014 (search conducted at Web of Science database on August 28, 2015) EN measurements can be conducted under corrosion potential or under any constant potential/current depending on the research objectives.…”
Section: Introductionmentioning
confidence: 99%
“…Changes in solution resistance; hydrogen discharge with gas bubble formation and detachment; diffusion of anion into propagating microcracks; discharge on freshly exposed metal at propagating cracks 8,23–25 ; oxygen reduction 26 ; sudden film rupture such as crack propagation involving metal dissolution and water discharge 27–31 ;…”
Electrochemical noise (EN), as one of the most promising in situ electrochemical methods in corrosion and electrochemical science, has been developing rapidly in recent years with the advancements in instrumentation and signal processing methods. One advantage of EN is its application in long-term or early stage corrosion process monitoring because it instantly detects corrosion rate and corrosion forms. Investigators have applied various mathematical methods to extract characteristic parameters from EN. In this paper, identifying corrosion forms using parameters obtained from time domain, frequency domain and time-frequency domain is reviewed, and the correlation between parameters and corrosion forms is discussed. Finally, other in situ techniques are recommended to be employed synchronously with EN measurement in order to obtain reliable analyses.
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