Application of X‐ray tomography for the verification of corrosion processes in chloride contaminated mortar

Within the scope of examinations at steel specimens embedded in chloride contaminated mortar for the first time X‐ray tomography was used to analyse the areas, damaged by chloride induced corrosion. Damaged areas with dimensions of a few μm could be detected. The results from the X‐ray tomography were verified by inspection of surfaces of the bars after removing the cover mortar.     

X‐ray micro‐computed tomography analysis of accumulated corrosion products in deep‐water shipwrecks

Accumulated corrosion products from two different shipwrecks which had lain on the seabed (2.5 km depth) for 73 years were systematically analysed by three‐dimensional imaging at high resolution using X‐ray micro‐computed tomography. Complementary surface and chemical characterization experiments were conducted to identify the morphological structure of the corrosion products. Goethite was observed as the main corrosion phase found in both the wreck's corrosion products. However, other corrosion products such as silica, lepidocrocite, maghemite, magnetite, benyacarite, jarosite and amorphous materials were noticed using Fourier transform infrared spectroscopy, Raman spectroscopy and X‐ray diffraction. In addition, mineralized microbial structures were also observed as significant constituents of the corrosion products. However, there were significant differences between samples from the two shipwrecks including porosity, distribution and volume percent of the corrosion products components. The mechanism of different corrosion products formation was proposed and discussed in detail.     

Micro‐electrochemical characterization of galvanic corrosion of TA2/316L composite plate

Galvanic corrosion behavior of TA2/316L composite plate was investigated in the solution of 3.5 wt% NaCl by galvanic potential monitoring, scanning localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating micro‐electrode (SVME) techniques. The results demonstrated that the pitting corrosion resistance of 316L for the galvanic combination sample is lower, and the coupled current density is higher than for the single 316L sample. It indicates that the galvanic action works on the corrosion behavior of the TA2 titanium alloy/316L stainless steel galvanic combination in sodium chloride solution. The galvanic effect width was determined as 1500 µm.     

Investigation of the effect of CrO and MoO on carbon steel corrosion using AFM and electrochemical techniques

The effect of chromate ( ) and molybdate ( ) ions on the corrosion of carbon steel in 0.5 M NaCl solution has been studied using electrochemical measurements and atomic force microscopy (AFM) technique. Potentiodynamic polarization data suggest that both and have inhibition effect on carbon steel corrosion, and the inhibition efficiency increases with increase in concentrations of and ; at the same concentration, the inhibition efficiency of is higher than that of . The increase in concentrations of and anions causes a shift of the breakdown potential (E_b) in the positive direction, indicating the inhibitive effect of the added anions on the pitting attack. At the same concentrations, the breakdown potential of is higher than that of . Electrochemical impedance spectroscopy (EIS) tests reveal that the charge transfer resistance and passive film resistance increase with increase in concentrations of or ; at the same concentrations, as for the charge transfer resistance and passive film resistance were bigger than those of . AFM imaging technique shows that local corrosion was inhibited obviously after the addtion of or , and passive film of was much more compact than that of . AFM force–distance curves indicate that the passive film of is much stiffer than that of .     

Monitoring pitting‐crevice corrosion using the WBE‐noise signatures method

An electrochemically integrated multi‐electrode array namely the wire beam electrode (WBE) and noise signatures analysis have been applied in novel combinations to study crevice corrosion behaviour in the presence of pits. Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps, which indicate corrosion rates distributions, corrosion patterns and the degree of pitting and crevice corrosion. Specifically, two characteristic noise patterns were observed: (i) the characteristic noise pattern of quick potential changes towards more negative direction with no recovery (termed noise signature I) was found to correspond with the initiation and stabilization of the anode inside crevice; and (ii) the characteristic noise pattern of the cyclic potential oscillation at a constant frequency (termed noise signature II) was found to correspond with the stable anodic dissolution in the occluded cavity site in WBE current distribution maps. A new parameter namely the localization parameter (LP) has been proposed to describe the degree of localization. The LP for crevice corrosion was found to be low compared to that for pitting corrosion.     

A comparative study of the corrosion stability of dental amalgams with electrochemical impedance measurements

The corrosion susceptibility of a selection of amalgams used in dentistry has been examined with the electrochemical impedance method. The results are compared with data derived from cyclic voltammetry performed with these materials before. Most examined materials including a conventional amalgam show similar corrosion resistance; however, only one product shows a significantly higher corrosion resistance.     

Identification of steel corrosion in alkaline sulfate solution by electrochemical noise

Research on the effects of sulfate ions on steel corrosion has been conducted in response to the observations of premature localized corrosion of steel strands in cementitious grouts in posttensioned bridge construction. Electrochemical noise (EN) was shown to be an effective technique to assess the development of localized corrosion of steel in the alkaline sulfate solution. General statistics of the EN potential and current time signatures revealed the negative effect of elevated sulfate concentrations and the development of pitting events. Spectral analysis indicated an increase in the characteristic charge and decrease in characteristic frequency with sulfate ion concentration, whereas an increase in the overall corrosion rate was observed, indicating the development of pitting corrosion. Pitting events could be sustained in solutions above 10 g Na₂SO₄/L H₂O and more extensive localized corrosion developed above 20 g Na₂SO₄/L H₂O.     

A double‐mode cell to measure pitting and crevice corrosion

Pitting corrosion and crevice corrosion of passivated steels were measured by using a double‐mode syringe electrolyte cell built on an environment chamber. The setup, when set in noncontact mode, could measure pitting potentials and critical temperatures, and crevice corrosion potentials if in contact mode. It could be employed to distinguish the pitting and crevice corrosion damage of reinforcing steel in concrete.     

Morphology of corrosion products of steel in concrete under macro‐cell and self‐corrosion conditions

In this paper investigations into the formation of specific corrosion products during the process of chloride induced corrosion of steel in concrete are presented. The extension of corrosion products within concrete was established by means of X‐ray tomography analyses. Then a detailed analysis of the nature of corrosion products has been conducted by means of Raman micro‐spectroscopy and energy dispersive spectroscopy. Results emphasize two different corrosion patterns. The first one is composed of shallow cavities, where mostly magnetite and goethite were identified, traducing aerated to moderate aerated conditions in these media. The second pattern was identified as deep, needle‐like pits, where chlorinated‐iron‐oxides phases were present associated with more or less important chloride enrichments. The presence of these particular species is indicating low redox and low pH conditions within these pits.     

SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO₃) solutions at 50°C using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS‐4 solution, chloride (Cl^?) and/or sulfate ( ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I_corr, was maximum in 0.01 M NaHCO₃ and with additions of ions. Higher or lower solution concentrations or additions of Cl^? alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO₃. Higher or lower solution concentrations of additions of Cl^? or decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO₃ solution, but it was minimum with the addition of Cl^? or ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO₃ solutions seems to be hydrogen‐assisted anodic dissolution.     

Effect of Sn addition on the corrosion behavior of Ti‐Ta alloy

In the present paper, the effect of Sn addition on phase constitution and corrosion behavior of Ti₆₅Ta_(35?x)Sn_x (x = 0, 1, 3, 5 at%) alloys has been investigated using X‐ray diffraction and electrochemical measurements. The results show that the β phase is stabilized when quenching after the addition of Sn into Ti₆₅Ta₃₅ alloy, with Ti₆₅Ta₃₀Sn₅ alloy consisting of single β phase at room temperature. The corrosion resistance is enhanced with increase in the Sn content. When the Sn content increases up to 5%, the addition of Sn results in a decrease of corrosion current density from 0.690 µA/cm² of the Ti₆₅Ta₃₅ alloy to 0.098 µA/cm², and corresponding passive current density decreased from 37.7 µA/cm² of the Ti₆₅Ta₃₅ alloy to 9.30 µA/cm².     

Identification of steel corrosion associated with sulfate-reducing bacteria by electrochemical noise technique

Deterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate-reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.     

Study on the corrosion behavior of NdFeB permanent magnets in nitric acid and oxalic acid solutions with electrochemical techniques

Corrosion behavior of sintered NdFeB magnets in nitric acid and oxalic acid was investigated. The experiment results indicated that NdFeB is strongly corroded in nitric acid solution, and is passivated in oxalic acid solution. Based on the corrosion behavior, the possible corrosion mechanisms are discussed.