Zero Resistance Ammeter Research Articles

Thermogalvanic effects on the corrosion of copper in heavy brine LiBr solutions

Thermogalvanic corrosion of copper in heavy brine LiBr solutions has been investigated using a zero-resistance ammeter (ZRA). The temperature gradients between copper electrodes immersed in the same LiBr solution result in the formation of thermogalvanic cells with hot anodes, leading to high and sustained thermogalvanic currents. Copper loss rates, calculated using Faraday’s law, substantially exceed 0.025mmyear−1, a value regarded as the threshold of low corrosion rates. The effects of thermogalvanic coupling on the surface properties of the anode and the cathode have been analysed by means of electrochemical impedance spectroscopy (EIS). The results obtained in this analysis have been related to the process of copper electrodissolution in bromide media.

Influence of Temperature and Reynolds Number on the Galvanic Corrosion of the Copper/AISI 304 Stainless Steel Pair in Lithium Bromide Using a Zero-Resistance Ammeter

The effects of temperature and Reynolds number (Re) on the galvanic corrosion of the copper (UNS C15710)/AISI 304 (UNS S30400) stainless steel pair in a concentrated lithium bromide (LiBr) solution was investigated in a hydraulic circuit using a zero-resistance ammeter. Results show that copper is the anode and that galvanic current density decreases with time because of the formation of a protective film. Initially, galvanic current density increases with Re; however, with time, differences decrease and this tendency is even reversed. As Re increases, greater quantities of corrosion products are initially produced and a thicker film is formed. The galvanic current density increases with temperature, suggesting that the films formed at lower temperatures are less defective and more resistant; however, at the highest flow rate, with time, the galvanic current density is lower at 75°C than at 50°C. This behavior is attributed to the quick and large formation of corrosion products at the highest flow and tem...

Thermogalvanic corrosion and galvanic effects of copper and AISI 316L stainless steel pairs in heavy LiBr brines under hydrodynamic conditions

Thermogalvanic corrosion of the copper/copper and AISI 316L/AISI 316L stainless steel pairs was studied in heavy lithium bromide brines under hydrodynamic conditions. The galvanic coupling effect between copper and stainless steel was also analysed. The cold electrode (25°C) was the stainless steel for the galvanic pair, whereas copper temperature varied (25, 50 and 75°C). A hydrodynamic circuit was designed to study thermogalvanic corrosion by means of the zero resistance ammeter technique. Hot cathodes take place in stainless steel pairs while cold cathodes are present in copper/copper and stainless steel/copper pairs; this agrees with the thermal temperature coefficient of the potential sign. Thermogalvanic corrosion increases corrosion rates, especially working with copper. Weight loss measurements show that there is a combined effect due to the thermogalvanic and the galvanic effects.

The influence of electrode polarization on corrosion beneath paint

A Zn–Fe bi-electrode coated with different clear lacquers was exposed to NaCl solution, so that a well-defined galvanic cell was established with the current directly measured by a zero-resistance ammeter (ZRA). Electrochemical impedance spectroscopy (EIS) was periodically used to monitor the two coated electrodes individually or coupled together. Transient potentiostatic current measurements were also made after applying potential steps of different amplitudes to the individual metals, from which polarization curves were plotted. The ohmic potential drop in the paint was corrected using film resistance values determined by EIS. Evans diagrams were thus plotted from the iR-corrected polarization curves to make the first experimental determination of Evans diagrams as used by Mayne11J.E.O. Mayne, Chem. Ind. (London, UK), 293 (1951). to illustrate his resistance inhibition model.

Correlation between Field Exposure and Laboratory Corrosion Tests for Galvanic Couples between Titanium Diboride and Aluminum Using the Zero-Resistance Ammeter Technique in Humid Environments

not Available.

Galvanic corrosion of aluminum alloy (Al2024) and copper in 1.0M hydrochloric acid solution

The corrosion of an aluminum alloy (Al2024) and copper in 1.0M HCl solution was investigated at 30, 40, 50 and 60 °C using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements. The galvanic corrosion of Al2024 and copper was studied using the zero resistance ammeter (ZRA) method. Galvanic current densities (Ig) and galvanic potential (Eg) were measured at 30 °C in 1.0M HCl solution. Thermodynamic parameters, such as activation energy (Ea), enthalpy of activation (ΔHa) and entropy of activation (ΔSa), were calculated and discussed. The results indicated that the corrosion rates of both Al2024 and copper increased with temperature. The ZRA results demonstrated that Al2024 is a sacrificial anode in 1.0M HCl solution when coupled with copper.

Selection of Electrode Area for Electrochemical Noise Measurements to Monitor Localized CO2 Corrosion

The simultaneous fluctuations of potential noise and current noise between two nominally identical X-65 mild steel electrodes were recorded using a ZRA (Zero Resistance Ammeter) to monitor localized CO2 corrosion in CO2-saturated 1 wt% NaCl solution at 80°C. Electrochemical noise (EN) was obtained from both 11.6 cm2 and 1 cm2 specimens to understand how the surface area affects EN signals. Linear polarization resistance (LPR) measurements were conducted to investigate the general CO2 corrosion behavior. Surface morphologies and pit depths were observed by scanning electron microscopy (SEM) and infinite focus microscopy (IFM) for 3D optical analysis. The results showed that the electrode area significantly influenced the EN signals of localized CO2 corrosion. Transients related to metastable pitting were best observed with 1 cm2 specimens but not clearly obtained for 11.6 cm2 specimens.

Thermogalvanic corrosion of Alloy 31 in different heavy brine LiBr solutions

Thermogalvanic corrosion generated between two electrodes of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), has been investigated imposing different temperature gradients in three deaerated LiBr solutions, under open circuit conditions by using a zero-resistance ammeter (ZRA). Besides EIS spectra were acquired in order to explain the obtained results. On the whole, cold Alloy 31 electrodes were anodic to hot Alloy 31 electrodes, since an increase in temperature favoured the cathodic behaviour of the hot electrode. Thermogalvanic corrosion of Alloy 31 in the LiBr solutions studied was not severe, although it negatively affects the corrosion resistance of the cold anode. The protective properties of the passive film formed on the anode surface were found to improve with thermogalvanic coupling time.

Tribocorrosion of UNS S32750 in chloride medium: Effect of the load level

The tribocorrosion of UNS S32750 sliding against zirconia counterpart in 3.5% NaCl under 2–10 N load range was investigated. The samples were tested in a pin-on-disk tribometer and the main electrochemical techniques employed were potentiodynamic polarization and zero resistance ammeter. The coefficient of friction appeared to be independent of the load level but dependent of the applied potential. Several and complementary electrochemical results could be clearly divided in two distinct groups, below and above ca 7 N. This behavior indicates that the tribocorrosion regime changes as a result of the coupling between mechanical and electrochemical processes, which was interpreted as a change from an adhesive wear regime to an abrasive and corrosion one for higher load levels.

Corrosion Properties of Plasma Electrolytic Oxidation Ceramic Coatings on an A356 Alloy Tested in an Ethanol-Gasoline Fuel (E85) Medium

Ceramic oxide coatings were prepared on an aluminum A356 alloy by a plasma electrolytic oxidation (PEO) technique under unipolar, bipolar and duplex unipolar/bipolar current modes. Cross-sectional morphologies of the coatings were studied using a scanning electron microscope (SEM). The corrosion behavior of the coated and uncoated samples was evaluated in ethanol-gasoline E85 fuels through potentiodynamic polarization and zero resistance ammeter (ZRA) testing methods. The results indicated that all the coatings had a better corrosion resistance compared to the uncoated substrate. The unipolar current mode created the PEO coating with a thicker coating microstructure and thus a better corrosion resistance, compared to a bipolar current mode. The duplex treatments of unipolar/bipolar or bipolar/unipolar current modes produced the best performance of the coatings against galvanic corrosions caused by a steel/Al coupling in the E85 fuel medium.

The effect of Al content on the galvanic corrosion behaviour of coupled Ni/graphite and Ni–Al coatings

In this study, the corrosion behaviour of 75Ni/25graphite abradable coating and Ni–Al bonding coatings with different Al content were investigated with open circuit potential and polarization tests. The galvanic corrosion of the coupled Ni/graphite and Ni–Al coatings was studied by using a zero-resistance ammeter in 5 wt% NaCl solution. The experimental results showed that the corrosion resistance of the Ni–Al coatings decreased with increasing Al contents. In the galvanic corrosion test, the Ni–Al coatings with high Al contents (80Ni–20Al, 85Ni–15Al, and 90Ni–10Al) were the anodic element of the couples, while, the 95Ni–5Al acted as the cathode element in the couple.

Corrosion behaviour of micro-plasma arc welded stainless steels in H 3PO 4 under flowing conditions at different temperatures

This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25–60 °C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i G values at 60 °C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H 3PO 4 media from a corrosion point of view for all the temperatures analysed.

Improving the corrosion behaviour of powder metallurgical 316L alloy by prepassivation in 20% nitric acid

The electrochemical improvement of PM 316L stainless steels by pre-alloyed powder prepassivation in 20% nitric acid in comparison with as-received specimens has been studied in this work. For comparison purposes a simultaneous study was carried out on similar composition wrought AISI 316L steels. Corrosion resistance was studied using evolution of the corrosion potential vs. time, anodic polarisations curves and Zero Resistance Ammeter technique. Reductions of the corrosion rate ( i corr) were observed in prepassivated specimens in neutral chloride media. Crevice resistance was higher for prepassivated specimens and for higher densities and annealing as post-heat treatments.

Investigation of Electrochemical Reactions beneath Paint Using a Combination of Methods

A Fe-Zn bi-electrode coated with paint was exposed to NaCl solution, so that a well-defined galvanic cell was established with the current directly measured by a zero-resistance ammeter (ZRA). Electrochemical impedance spectroscopy (EIS) was periodically used to monitor coating behaviour for the two electrodes separately or coupled together. Potentiostatic current measurements were also made on each metal at different overpotentials to plot polarization curves. The ohmic potential drop in the paint was corrected using film resistance values determined by EIS. Evans diagrams were thus plotted from the corrected polarization curves to make a quantitative assessment of Mayne's resistance inhibition model.

Effect of Temperature on Galvanic Corrosion of Non-Welded/Welded AISI 316L Stainless Steel in H3PO4

Galvanic corrosion of non-welded/welded AISI 316L SS at different temperatures (25 ºC to 60 ºC) at a Reynolds number of 1456 in phosphoric acid has been studied using polarization curves (by the mixed potential theory) and zero resistance ammeter (ZRA) measurements. Imposed potential measurements provide more active predicted coupled potentials and higher galvanic current densities than those obtained using ZRA measurements. Polarization curves show that the anode of the pair is the non-welded AISI 316L. Galvanic current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60 ºC; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluate the Galvanic phenomenon importance. Both techniques present the most positive potentials at the highest temperature.

Propagation and Arrest of Localized Attacks in Carbon Dioxide Corrosion of Carbon Steel in the Presence of Acetic Acid

Abstract The presence of acetic acid (HAc) has been identified as one factor that may contribute to enhance localized top-of-the-line corrosion attacks in gas condensate pipelines. The role of free HAc on the growth of localized attacks in carbon dioxide (CO2) corrosion of carbon steel pipelines therefore was studied by means of a preinitiated localized attack electrode assembly (“artificial pit electrode”). The current flowing between the localized attack and the outer surface was measured with a zero-resistance ammeter. It is shown that the corrosion potential increases with increasing free HAc concentration. Depletion of free HAc inside the attack imposed a potential difference that triggered the propagation of the attack at room temperature. The pit growth was self-sustained in CO2 and HAc environments only to a certain depth, beyond which the dissolution current at the bottom of the attack vanished. This is in good agreement with field observations in the case of top-of-the-line corrosion phenomena.

Selection of Electrode Area for Electrochemical Noise Measurements for CO2 Corrosion in Different NaCl Solutions

Electrochemical investigation of localized CO2 corrosion of X-65 mild steel in 0.1, 1.0, 10 and 20 wt% NaCl solutions at 80oC has been conducted using linear polarization resistance (LPR) and electrochemical noise (EN) techniques. EN measurements were carried out only on 11.6 cm2 electrodes in 0.1, 10 and 20 wt % NaCl solution. EN was obtained from both 11.6 cm2 and 1 cm2 electrodes in 1 wt % NaCl solution to learn how the surface area affects EN measurements. Current noise and potential noise between two nominally identical electrodes were simultaneously recorded using a ZRA (Zero Resistance Ammeter). Chemical dissolution of corrosion product layer was accomplished by adjusting pH and saturation values with respect to FeCO3. Surface morphologies and pit depths were observed by scanning electron microscopy (SEM) and infinite focus microscopy (IFM) for 3D optical analysis. The results showed that electrode size influenced the EN signal. Transients related to metastable pitting were best observed with 1 cm2 coupons in 1 wt % NaCl solutions, but such transients were not clearly obtained for 11.6 cm2 coupons in the 0.1, 1, 10, 20 wt % NaCl solution. Both general corrosion rate and localized corrosion rate did not significantly change with increasing NaCl concentrations.

Pit growth and stifling on carbon steel in CO 2-containing media in the presence of HAc

CO 2 corrosion of carbon steel pipelines in the presence of acetic acid was studied using artificial pit electrode assembly. The potential difference and the coupling current between the small attack and the outer large surface were monitored by means of a zero resistance ammeter (ZRA). The results give strong and complementary evidence about the major role of acetic acid in the growth mechanism of localized attacks in CO 2 corrosion. Pits seem to propagate and stifle mainly according to counteracting depletion effects of respectively acetic acid and CO 2. It is also shown that the purely ohmic drop is not the only factor contributing to the stifling of localized corrosion attacks in systems like those of top of line corrosion. On the basis of the obtained results, a complete scenario was therefore proposed for the morphological trend of localized attacks, which is in good agreement with field observations.

Evaluation of the short and long-term efficiencies of electro-chemical chloride extraction

The short and long-term effects of electro-chemical chloride extraction (ECE) treatment on corrosion rate of corroded reinforcement have been studied. The factors controlling ECE treatment were identified, and the alterations which occurred in the chloride profile of the cover zone due to ECE process were followed. Contaminated reinforced OPC and SRC mortar specimens made with 1 or 2% NaCl, by mass of cement, were prepared, cured and then subjected to 3 or 5% NaCl for one year. These specimens were finally treated with ECE using various impressed current densities (1 and 2 A/m 2) and electrolytes (water and calcium hydroxide) for 2, 4 and 8 weeks. The state of corrosion was monitored regularly every 2 weeks from halting ECE process up to 52 weeks using zero-resistance ammeter device for measuring the corrosion current density of reinforcement. Selected samples from the cover zone of the untreated and treated specimens were finally taken to assess their chloride profiles.

P‐61: A Study on the Galvanic Reaction between Cu and Mo as Well as MoW for TFT‐LCDs by Using a Zero‐Resistance Ammeter

AbstractRecently, copper metallization has been widely developed in TFT‐LCD industry, because of its lowest electrical resistivity compared to aluminum and its alloys. In addition, the copper metallization becomes a more significant issue in a high frequency driving technology for large sized TFT‐LCD panel. Since copper has a low adhesion force against the glass substrate, copper is inevitably used with an aid of an adhesive metal layer such as Ti, Ta and Mo. When dissimilar metals like copper and molybdenum are exposed together in a wet etchant, a typical galvanic reaction occurs and this results in an undercutting of copper line or partial stains on the metal surface after drying. The suitable taper angle of Cu line is difficult to obtain especially coupled with pure molybdenum. Such failures often lead to a bad performance of thin film transistor and the display quality. There are many literatures related to the copper metallization for TFT. However, a systematic approach on the galvanic reaction occurred in copper multilayered system has not been made. In this work, we investigated a feasibility of molybdenum alloy film (MoW) for copper metallization on the basis of the thin film analysis and the advanced electrochemical techniques such as Zero Resistance Ammeter (ZRA) method.