Search results for "CORROSION"
showing 10 items of 456 documents
Macroscopic and local electrochemical studies of austempered ductile iron in perchlorate solutions.
2006
The corrosion behavior of austempered ductile iron (ADI) in alkaline environment has been investigated at the microscale by means of the electrochemical microcell technique, surface analysis methods, and at the macroscale using classical electrochemical techniques. Local electrochemical investigations have revealed that the matrix (ausferrite), far from spheres, undergoes passivation in 1 M NaClO 4 , pH 10 solution within a wide potential range, from the corrosion potential (of about -280 mV/SCE) until 800 mV/SCE. Surface observations combined with local electrochemical analysis have shown that corrosion of ADI first occurs in the close vicinity of some graphite spheres and then around oxid…
Passivation-Induced Physicochemical Alterations of the Native Surface Oxide Film on 316L Austenitic Stainless Steel
2019
Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis were combined to characterize the physicochemical alterations induced by electrochemical passivation of the surface oxide film providing corrosion resistance to 316L stainless steel. The as-prepared surface is covered by a ~2 nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is concentrated, mostly as Mo(VI), in the outer layer. Nickel is only present at trace level. These inner and outer layers have band gap values of 3.0 and 2.6-2.7 eV, respe…
Investigation of the kinetics of growth of anodic oxide films on niobium by galvanostatic and tensiodynamic experiments
1990
Abstract The kinetics of growth of anodic oxide films on niobium has been investigated by interferometric methods. Tensiodynamic experiments allow the growth of the films at constant rate. Photoeffects during the growth of the films under absorbed light give additional information on the growth process.
Repassivation of the damage generated by cavitation on UNS N08031 in a LiBr solution by means of electrochemical techniques and Confocal Laser Scanni…
2010
Abstract The objective of this work is to study the influence of cavitation on the corrosion behaviour of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), in a LiBr heavy brine solution (992 g/L) at 25 °C. The presence of cavitation shifted the OCP value towards the active direction by 708 mVAg/AgCl, increased anodic current densities and passivation current density, ip, and reduced the pitting potential, Ep. Repassivation behaviour of Alloy 31 has been investigated by using potentiostatic tests at different potentials. The current density transient obtained after interrupting cavitation was used to obtain the repassivation index, n, provided by the slope of the log i(t) …
Investigation of pitting resistance of titanium based on a modified point defect model
2011
Abstract The pitting resistance of titanium was studied under potential control in solutions containing chloride ions. The results evidenced that Cl − concentration had an effect on the metastable pitting intensity, but no significant influence on the uniform corrosion. XPS characterization revealed that some Cl − ions were present in the outer hydroxide layer, but few in the inner oxide layer, indicating that the inner oxide layer was impervious to Cl − ions. A cation–anion-vacancy condensation mechanism was considered for pit initiation based on the point defect model (PDM). The experimental results analyzed by the charge integration technique were in agreement with the derived relations.
Evaluation of metastable pitting on titanium by charge integration of current transients
2010
Abstract The metastable pitting of titanium has been studied under potentiostatic control in solutions containing chloride ions. An approach based on the charge integration of current transients was proposed for a quantitative determination of metastable pitting. A pit density (dmpit) was defined as the number of metastable pits per unit area per unit time (cm−2 h−1) with a typical size, instead of a size distribution. The calculated dmpit of titanium at 0.5 VSCE in 0.6 M NaCl was about 1.0 × 103 cm−2 h−1 with a typical radius of 0.12 μm. An exponential potential dependence of dmpit was obtained through the integration approach.
Electrochemical impedance spectroscopy for studying passive layers on steel rebars immersed in alkaline solutions simulating concrete pores
2007
Present paper deals with the use of the electrochemical impedance spectroscopy to identify different processes in the passive layer growth over steel rebar surface immersed in an alkaline media simulating the concrete pore solution. Two cases have been considered: a passive layer spontaneously grown in a high alkaline media and a passive layer assisted by the application of an anodic potential in the same media. The application of electric equivalent circuits allows distinguishing between the different mechanisms occurring in this passive layer when grows in different conditions. An electric equivalent circuit with two RC loops connected in parallel is often used for fitting the EIS diagram…
Electrochemically-induced TiO2 incorporation for enhancing corrosion and tribocorrosion resistance of PEO coating on 7075 Al alloy
2018
Abstract 7075 Al alloy was PEO-treated in a silicate based electrolyte containing 3 g l-1 potassium titanyl oxalate using unipolar and bipolar pulsed current waveforms. The coating formed by the bipolar waveform with the wider cathodic pulses showed volcano-like surface morphology with no evidence of large pores at the metal/coating interface. It revealed the highest corrosion performance due to the synergistic effect of TiO2 incorporation and structural/morphological features along with a better passivation behavior indicating no pitting susceptibility. For this coating, the tribocorrosion tests showed no potential drop during sliding under 1 N with the lowest volume loss of 0.022 mm3.
Influence of an elastic stress on the conductivity of passive films
2001
Abstract The electrochemical impedance was measured over a large range of frequency and under straining condition in sodium chloride solution. The Mott-Schottky analysis, performed at high frequency, appears as very useful method to study the effect of an elastic stress on the capacitance values. The results obtained indicate that the semi-conductive properties of passive films formed on a type 316 L stainless steel (SS) are not markedly modified by an elastic stress when applied after ageing. In contrast, passive films formed in the presence of elastic stress have a higher donor and acceptor concentration than those formed in a stress-free state, suggesting that the passive film conductivi…
Passive Behavior and Passivity Breakdown of AISI 304 in LiBr Solutions through Scanning Electrochemical Microscopy
2014
The passive behavior and passivity breakdown of AISI 304 stainless steel in LiBr solutions has been investigated by means of scanning electrochemical microscopy (SECM). The sample generation - tip collection (SG-TC) mode was used to operate the SECM and the tip potential was biased to detect the electroactive species. The evolution of the current at the ultramicroelectrode tip with the applied potential within the passive range was followed at different LiBr concentrations. Results show that the absolute value of the current at the tip increases with the applied potential. Additionally, SECM was also used to detect stable pits formed on the stainless steel surface in a 0.2 M LiBr solution. …