Cathodic Depolarization Research Articles

Estudio de la teoría de despolarización catódica con permeación de hidrógeno y la bacteria <i>Desulfovibrio desulfuricans</i>

A Desulfovibrio desulfuricans ssp. desulfuricans (SRB) was used to study the permeation of hydrogen, using a Devanaran and Stachurski cell and a palladium sheet. The aim was to evaluate cathodic depolarization as a Sulfate-Reducing Bacteria action mechanism in Microbiologically Induced Corrosion. The permeation tests were run with and without cathodic polarization, using a sterile deaerated culture medium inoculated with 10 % SRB concentrated at 10 8 cel/ml. The results indicate bacterial growth in the order of 10 9 -10 10 cel/ml after 18 h both in the polarized and non-polarized tests, indicating that SRB developed regardless of the surface polarized as a source of H 0 , generating H 2 S as a product of the anaerobic respiration. It was also determined that, without cathodic polarization, the conditions are not enough to reduce the H + generated by the H 2 S dissociation (Pd is not susceptible to corrosion at this condition). On the other hand, cathodic polarization increased the permeation current, which was associated with the maximum enzymatic activity phase of the bacteria.

In-situ surface potential characterization of a cathodically polarized coating

The relevance of this study pertains to coating material performance in desalination and power plants and particularly during cathodic protection (CP) of coated steel piping network. Organic coatings find various uses in many industries and such coatings are used extensively in conjunction with CP by the petroleum and water industry for corrosion protection. One of the most common technical problems encountered by the inspector or engineers is that of micro-defects (pinholes) in coating and optimization of material selection. The nature of the surface electrochemical reactions associated with defects in these protective coatings and the ability of the Scanning Potential Mapping (SCM) to detect them is the concern of this investigation. The results indicate that this method can monitor the qualitative effectiveness of the cathodic depolarization CP. A demonstration problem is elaborated which gives information on the surface potential distribution on the exterior surface of the coal tar epoxy coated steel substrate with predefined defects. The results demonstrate the evolution with time of the SCM for the coated specimen, which shows initial increase of the surface potential. As the polarization potentials are concerned, the cathodic potential affected mainly their cathodic regions.

Methanogen population in a marine biofilm corrosive to mild steel.

This study was conducted to analyze the methanogen population in a corrosive marine biofilm based on 16S rDNA analysis, using a PCR-cloning-sequencing approach. There were 80 methanogen clones developed from the PCR-amplified DNA extracted from the biofilm on the mild steel surface. All clones were categorized into one of five operational taxonomy units (OTUs). Two OTUs (comprising 57 clones) were affiliated with the acetotrophic Methanosaeta genus; the remaining three OTUs (23 clones) were affiliated with the hydrogenotrophic genera of Methanogenium, Methanoplanus and Methanocalculus. The hydrogenotrophic methanogens could directly cause metal corrosion through cathodic depolarization, whereas the acetotrophic methanogens grew syntrophically with corrosion-causing sulfate-reducing bacteria, as observed by fluorescent in situ hybridization, and thus contribute indirectly to metal corrosion.

Mechanism of a MIC probe

Interaction of bacterial biofilms with stainless steel is expected to alter electrochemical behaviour compared with that obtained under sterile conditions and under non-biological deposits. In principle, electrochemical signals can monitor biofilm formation and microbial activity. In this study, attempts were made to understand the mechanism by which an electrochemical sensor using periodic mutual polarisation of two similar stainless steel electrodes responds to biofilm formation. This probe is believed by others to respond to cathodic depolarisation by the biofilm, but the present study using natural fresh water showed that an increase in the galvanic and applied currents of two similar, coupled AISI Type 304 SS electrodes took place only after biofilms had initiated corrosion on the anodically polarised electrode. Comparison of electrodes with natural biofilms and deposited rust layers showed that both the films showed evidence of crevice action, but with a lower ionic resistance than a conventional crevice, therefore permitting rapid propagation of localized corrosion even in dilute chloride media.

The Microbiologically Influenced Corrosion Behavior of C-Mn Ship Structural Steel with Different Manufacturing Processes

The MIC (Microbiologically Influenced Corrosion) of lower deck steel plates in double hull VLCC (Very Large Crude Oil Carrier) cargo tanks has been focused because of severe localized corrosion. Recently, ship companies have reported that TMCP (Thermo-mechanical Control Process) steel plates have been showed more severe localized corrosion than conventional rolled steels. In order to elucidate the MIC resistance of TMCP steels by comparison with conventional rolled steels and normalized steels in environments of double hull VLCC cargo oil tanks, various measurements and corrosion tests were performed such as measurements of polarization curves, immersion tests in bacteria culture medium.All results revealed that three types of steels have almost the same corrosion resistance in bacteria culture medium. Three kinds of steel exhibit almost the same polarization behavior and the corrosion rate. The movement of the open-circuit potential first towards more negative values and later to more positive values is a phenomenon common to all kinds of specimens. This phenomenon resulted from an initial stimulation of the anodes by sulphide ions produced by the bacteria from the reduction of sulphate ions in the medium, followed by the formation of an insoluble partly protective film of ferrous sulphide on the surface of the electrode. The effect of SRB (Sulphate Reducing Bacteria) is clearly showed in the cathodic polarization curve. When the SRB is in a condition of rapid growth, there is a strong cathodic depolarization. However, as the sulphate is depleted and reaction products accumulate, the activity of the bacteria declines and the cathodic polarization curve returns the same form as in the inoculated culture.

Cathodic Depolarization Effect during Cu Electroplating on Patterned Wafers

Electroplated Cu is being used by semiconductor manufacturers as an interconnect material because it offers lower line resistance and better electromigration performance compared to conventional Al metallization. The Cu electrodeposition process yields void and seam free filling of high aspect ratio trenches as a result of accelerated electrodeposition near the trench base, often known as fill. In order to evaluate the mechanism of bottom-up filling, the voltage-time and current-time characteristics of the Cu electroplating process during trench filling were studied. Depolarization (i.e., decrease of cathodic potential at fixed applied current) is observed during Cu electroplating into trenches using baths containing a mixture of current suppressing and accelerating organic additives. This depolarization behavior is explained by accumulation of current accelerating additives in the trenches, and correlates to the bottom-up fill observed during copper electrodeposition from electrolytes containing current accelerating and suppressing additives. A fill mechanism involving accumulation of strongly adsorbing current accelerating additives, which displace initially adsorbed current suppressing additives as surface area decreases within trenches, is consistent with all polarization data collected.

Effects of Tl on the electrocrystallisation of thick Au layers from KAu(CN) 2 solutions

Electrocrystallisation of thick (exceeding a few microns) gold layers from weakly acidic KAu(CN) 2 aqueous solutions is not feasible unless specific addition agents are present in the bath. Tl + salts are empirically known to enhance the growth rate of gold. In this paper we investigate the action of Tl + at the growth interface by electrochemical and spectroelectrochemical techniques and propose a mechanism for its action as a cathodic depolariser. The electrochemical behaviour of Tl + was studied by linear sweep voltammetry, cyclic voltammetry, and differential capacitance measurements. The interactions of Tl + and CN − at the growth interface were studied in-situ during the electrocrystallisation process by Raman and FT-IR spectroscopies. Cyanoaurate baths display a significant cathodic passivation, which is reduced by addition of Tl +. Voltammograms of baths containing Tl + show underpotential deposition features but no stripping peaks. Spectroelectrochemistry shows that the deposition of Tl + is specifically active in cathodically passivated areas. This behaviour is suggestive of an assisted Au electrodeposition mechanism. Tl is oxidatively desorbed by Au(I), giving rise to the growth of thick, pure gold films.

The role of hydrogenases in the anaerobic microbiologically influenced corrosion of steels

The direct electron transfer between 316 L stainless steel and the NAD-dependent hydrogenase from Ralstonia eutropha was studied by spectroelectrochemistry. The presence of hydrogenase and NAD + clearly increased the quantity of electricity, which was consumed during the electrolysis performed at potential lower than −0.70 V/SCE. The involvement of hydrogenase in the cathodic depolarisation theory was discussed in the light of these results.

Microbiological Corrosion: Hydrogen Permeation and Sulfate-Reducing Bacteria

Abstract This study was undertaken to evaluate cathodic depolarization as the action mechanism triggered by sulfate-reducing bacteria (SRB) in microbiologically induced corrosion (MIC), using an inert substrate such as a 1-mm thick Pd foil with and without cathodic polarization, a H0 permeation conventional Devanathan-type cell, and the bacteria Desulfovibrio desulfuricans subsp. desulfuricans ATCC 7757. The permeation tests were run using a deaerated sterile culture medium inoculated or not with 10% D. desulfuricans at 108 cell/mL. Serial dilution was used to evaluate the bacterial growth, and scanning electron microscopy (SEM) was used to analyze the characteristics of the biofilm and products formed on the Pd foil. Results indicated bacterial growth on the order of 4 × 1010 CFU/mL at 24 h in both polarization and nonpolarization tests, and hydrogen permeation tests without cathodic polarization determined that there were no conditions for the reduction of the H+ generated by hydrogen sulfide (H2S) diss...

Research on the mechanisms of anaerobic corrosion

Investigations of anaerobic corrosion of iron over the past years have led to a number of conclusions regarding the mechanisms. In addition several unusual observations related to these corrosion studies were noted. The cathodic depolarization mechanism does not appear too significant. The primary cause appears to be the production of a volatile phosphorous compound by SRB which reacts with iron to form a black precipitate in the medium. The highly reactive phosphorous compound is produced from an organic compound, inositol hexaphosphate, the major source of phosphorous in plants. Other findings include “electrochemical noise”, “hollow whiskers”, and “rusticles”, FeS and Fe 3P in tektites and a most unusual attack on glass.

Enhanced hydrochloric acid leaching of nickel

Dissolution rates of nickel in hydrochloric acid with and without the presence of thiourea have been studied by means of rotating disc methods with solution analysis. In the absence of thiourea an apparent activation energy value of 61.1 ± 12.1 kJ. mol −1 was determined. Such a high value is inconsistent with a diffusion controlled process and this was supported by the lack of dependency of the dissolution rate on rotational speed. A reaction controlled process is indicated. In 8.4 mol. dm −3 hydrochloric acid the thiourea concentration range producing optimum dissolution rates was 10 −3 to 10 −2 mol. dm −3. At 70° C the rate of leaching was enhanced by some 105 %. Tests using radiochemical labelling of the sulphur and of the carbon separately in the thiourea molecule confirmed previous proposals, for cobalt dissolution, that hydrogen sulphide is produced as a by-product of the cathodic depolarisation reaction involving the thiourea and is adsorbed on the metal surface in the molecular state, forming activated anodic sites which enhance anodic dissolution. At the 10 −1 mol. dm −3 thiourea concentration level stimulation of the nickel dissolution process gave way to its partial inhibition with a maximum diminution at 30°C of ∼50 %.

Combined Microbial-Fe(0) Treatment System to Remove Nitrate from Contaminated Groundwater

Experiments were conducted to delineate the applicability and limitations of biologically active Fe(0) barriers to remove nitrate under various geochemical and hydraulic conditions. Microcosm studies showed that, while no Fe(0) treatment was needed to remove nitrate from a high-carbon soil, adding Fe(0) to a low-carbon soil supplemented the electron donor pool and enhanced nitrate removal. Montmorillonite, an acidic aluminosilicate mineral, enhanced Fe(0) corrosion and nitrate removal (from about 1 to 3 mg/L NO3-N per day), and reduced the transient accumulation of nitrite. Combining autotrophic denitrifiers (e.g., Paracoccus denitrificans) with Fe(0) significantly reduced the amount of nitrite eluted from aquifer columns, from up to 7 to less than 1 mg/L NO2∼-N. Bacteria were observed to preferentially colonize the Fe(0) surface, which produces cathodic H2 when corroded by water. The preferential colonization of Fe(0) suggests that hydrogenotrophic consortia are likely to develop around Fe(0) walls to exploit cathodic depolarization as a metabolic niche.

The Structure and Properties of Graphite Monofluoride Using the Three-Dimensional Cyclic Cluster Approach

In this paper, we present the theoretical study of the crystal and electron structure of an intercalated compound of graphite —the graphite monofluoride {CF}n. The latter is widely used as a lubricant under extremely high temperatures and high vacuum, and as a successful cathodic depolarizer in batteries with high energy density. The layered structure of the graphite monofluoride has been confirmed, but statistical distributions of the individual layers are possible. This fact helps in understanding the problems linked to an experimental determination of the structure of this material. Small interlayer dissociation energies show that the bonding between the individual layers is mainly due to the weak interlayer electrostatic forces, which explains the excellent lubricant properties of this material. Band structure calculations reveal that, whereas some layer arrangements of the bulk material lead to insulating properties, others have a conductive character. This fact explains the weak overall conductive properties of synthetic graphite monofluoride.

Enhanced hydrochloric acid leaching of cobalt

Dissolution rates of cobalt in hydrochloric acid with and without the presence of thiourea have been studied by means of weight loss and rotating disc (with solution analysis) methods. In the absence of thiourea an apparent activation energy value of 67.7 ± 3.4 kJ. mol −1 was determined from weight loss measurements and 70.3 ± 7.5 kJ. mol −1 using rotating disc techniques. These high values are inconsistent with a diffusion controlled process and this was supported by the lack of dependency of the dissolution rate on the rotational speed. A reaction controlled process is indicated. In 8.4 mol. dm −3 hydrochloric acid the thiourea concentration producing optimum dissolution rates was found to be ∼ 1 × 10 −3 mol. dm −3. Above 60°C rates of leaching were enhanced by some 700–800%. Tests using radiochemical labelling of the sulphur and carbon in the thiourea molecule confirmed previous proposals that H 2S is produced as a by-product of the cathodic depolarisation reaction involving the thiourea and is adsorbed on the cobalt surface in the molecular state forming activated anodic sites which enhanced anodic dissolution.

Evidence for Surface Changes During Ennoblement of Type 316L Stainless Steel: Dissolved Oxidant and Capacitance Measurements

Abstract Ennobled open-circuit potential (Ecorr) for type 316L stainless steel (SS [UNS S31603]) exposed to fresh river water was investigated using microelectrodes to measure dissolved oxygen (DO), hydrogen peroxide (H2O2), and local Ecorr within biofouling deposits. Galvanostatic techniques were used to measure capacitance (C) and to titrate reducible surface material. Results indicated deposits were uniformly aerobic and did not contain elevated levels of cathodic depolarizers. Development of ennobled potential was related to Ecorr near the beginning of exposure and occurred on surfaces with as little as 3% to 5% biofouling coverage. Galvanostatic measurements revealed a strong correlation between C and Ecorr as Ecorr increased during biofouling. Galvanostatic reduction measurements indicated increased abundance of reducible surface-bound material during the same period. Results suggested an ennoblement mechanism involving modifications of the metal oxide surface.

Electrokinetic Remediation. I: Pilot-Scale Tests with Lead-Spiked Kaolinite

The feasibility and efficiency of transporting lead under electric fields are investigated at pilot scale in three 1 t Georgia kaolinite specimens spiked with lead nitrate solution and at an electrode spacing of 72 cm. Enhancement methods such as cathode depolarization and/or catholyte neutralization techniques are not used in processing. A constant direct current density of 133 μmA/cm 2 is applied. Two of the tests are conducted on specimens spiked with lead at concentrations of 856 mg/kg and 1,533 mg/kg. The third test is conducted on a 1:1 mixture of compacted kaolinite/sand spiked with lead at a concentration of 5,322 mg/kg. Lead was transported toward the cathode and precipitated at its hydroxide solubility value within the basic zone in direct contact with the cathode compartment. Subsequent to 2,950 h of processing and an energy expenditure of 700 kWh/m 3, 55% of the lead removed across the soil was found precipitated within the last 2 cm close to the cathode, 15% was left in the soil before reaching this zone, 20% was found precipitated on the fabric separating the soil from the cathode compartment, and 10% was unaccounted. Heavy metals and species that are solubilized in the anodic acid front can be efficiently transported by electromigration under an electrical field applied across electrodes placed in soils.

The Synergistic Effect of Hydrogen Sulfide and Nitrogen Dioxide on the Atmospheric Corrosion of Zinc

A laboratory study of the effect of sub‐ppm levels of and on the atmospheric corrosion of zinc in humid air is reported. Each sample was exposed individually to a synthetic atmosphere with careful control of pollutant concentrations, relative humidity, and flow conditions. Corrosion products were analyzed by grazing angle x‐ray diffraction and x‐ray photoelectron spectroscopy. Ion chromatography was employed to identify water soluble anions. The interaction of the pollutants with zinc metal was studied using trace gas analysis in real time. A strong synergism was observed. The main solid product was zinc blende (ZnS), accompanied by small amounts of sulfate. The optically smooth zinc sulfide film was shown to grow by solid‐state diffusion of ions, the rate controlling step being the deprotonation of adsorbed on the ZnS surface. acts as a cathodic depolarizer, forming , resulting in a strongly increased rate of zinc sulfidation.

Study of effect of pollutant additions on corrosion behaviour of Al-brass in sea water

AbstractThe corrosion behaviour of Al-brass was studied in stagnant and flowing sea water in the absence and presence of 5 ppm Mn and 4 ppm Cl. The addition of Mn or Cl to stagnant sea water had little effect on the free corrosion potential. In flowing sea water, Mn caused a shift in the corrosion potential to more noble values at a flowrate of 0·1 m s−1 and to more active values at 2·2 m S−1. Addition of Cl caused an electropositive shift at both flow velocities. Under all testing conditions, the linear polarisation resistance decreased in the presence of Mn and increased in the presence of Cl. Potentiodynamic polarisation tests indicated that the presence of either pollutant in stagnant sea water causes cathodic depolarisation, electropositive shift in corrosion potential, and elimination of active-passive transition. Microscopic examination revealed that the film formed in the presence of Mn was thicker and more porous than that formed in clean sea water. In the presence of Cl, the film was smooth and ...

Microbially sustained pitting corrosion of 304 stainless steel in anaerobic seawater

A system has been developed in which a small anode and large cathode can be induced in a concentric stainless steel electrode. A current of approximately 11 μA cm −2 was applied for 72 h while bacteria were allowed to colonize the electrode in a closed system, in artificial seawater under anaerobic conditions. Once the applied current was removed, the resultant galvanic current was monitored and a flow of nutrients resumed to an open system. Only a co-culture of SRB and Vibrio sp. maintained a current of approximately 3 μA cm −2 for >200 h. No current was maintained with pure axenic cultures or in sterile controls. Bacterial counts revealed that the resultant current was dependent on the number and type of bacteria on both the anode and cathode. It would appear that SRB are necessary on the cathode, leading to high charge transfer resistance above 100 kΩ cm 2, while a mixed consortium is necessary on the anode giving low charge transfer resistance below 1 kΩ cm 2. These results would appear to give further evidence for the previously proposed cathodic depolarization theory as a mechanism for MIC and for another anodic reaction involving a mixed consortium.

Reductive dechlorination of carbon tetrachloride with elemental iron

Carbon tetrachloride (CCl 4) was abiotically dechlorinated to chloroform (CHCl 3) and methylene chloride (CH 2Cl 2) by zero valent iron (Fe 0). Dechlorination of CCl 4 was rapid, and approximately followed first-order kinetics in the range of concentrations tested (CCl 4: 1.5–5.5 μ M; Fe 0 powder: 1–10 g per 265 ml distilled water). Initial dechlorination rate coefficients for anoxic batch reactors (0.290 ± 0.009 h −1 for 1 g Fe 0; 1.723 ± 0.078 h −1 for 10 g Fe 0) increased with iron surface area (initially 2.4 ± 0.2 m 2/g). Rate coefficients also increased with time, probably because of an increase in reactive surface area due to cathodic depolarization and pitting of the iron surface. Dechlorination also occurred under oxic conditions, although the rates were significantly slower (e.g., 0.085 ± 0.041 h −1 for 1 g Fe 0 and initial dissolved oxygen 7.4 mg/l). A rapid pH increase was synchronous to dissolved oxygen consumption, and the pH remained constant after the oxygen was depleted. This was attributed to the proton and oxygen consuming aerobic corrosion of the Fe 0 surface. The potential for developing remediation technology with Fe 0 is discussed.