Galvanic Test Research Articles

Effect of Hyperbaria on the Electrical Exitability of the Vestibular Organ in Rabbits

Abstract This paper presents a study of the effects of hyperbaric conditions on the vestibular organ during sham air exposures in an animal model. The proper functioning of the vestibular organ determines diving safety due to the limited role of the organ of vision underwater, especially in our latitudes. The study was conducted on 16 rabbits by recording the animal’s head movements generated by a ‘galvanic test.’ The tests were performed during compression at positive pressures of 1, 2, 3, 4, 5, and 6 atm and then during decompression at the same overpressures. A decrease in the sensitivity of the vestibular system to stimuli was found as the pressure increased.

Combination of Galvanic Interaction and Acoustic Emission Measurements on Damaged Painted Al Alloys: Towards Instrumented Witness Coupons for Outdoor Corrosion Testing

After real environmental exposures, the presence of corrosion damages on aircraft structures may be detected by means of non-destructive techniques (NDT). However, corrosion initiation and mechanism behind the defect cannot be distinguished by currently used physical methods. Therefore, aircraft industry needs sensors able to detect both corrosion initiation and its propagation.Few years ago, a new test sample design providing accelerated response during atmospheric corrosion tests was reported by G.S. Frankel research group [[1],[2]]. A painted Al alloy panel, uncoated through-hole noble fasteners and scribes, was specially designed to measure the galvanic current between fasteners and scribes during exposure in a salt fog chamber using a zero-resistance ammeter.But galvanic current measurement remains an electrochemical technique which could be difficult to be implemented in environments expected to be encountered in service, even if some attempts were described in literature [[3]]. More robust NDT methods, like acoustic emission was suggested to evaluate corrosion damage on Al alloys [[4]] but their application has not been yet transferred to instrumented witness coupons.Recently a European program [[5]] was launched to validate the application of ultrasonic corrosion sensors for real time detection of early stages of localized corrosion on Al alloys. Following our previous work on laboratory-scale tests based on mass transport control from inhibitors leaching from primer exposed at scribes [[6]], this talk describes the laboratory validation of acoustic emission combined with galvanic corrosion current measurements to evaluate the role of depletion of available corrosion inhibitors in the paint on scratched plates, mimicking riveted aircraft panels, exposed to chloride environments, in various conditions, i.e. immersion and salt spray conditions. [1] C.A. Matzdorf, W.C. Nickerson,B.C. Rincon Troconis,G.S. Frankel, Longfei Li, R.G. Buchheit, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 1—Concept, Corrosion, 69 (2013) 1240-1246. [2] Z.Feng and G.S. Frankel, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction, Corrosion,70 (2014) 95-106. [3] Z. Feng, G.S. Frankel,W.H. Abbott,C.A. Matzdorf, Galvanic attack of coated al alloy panels in laboratory and field exposure, Corrosion, 72 (2016) 342-355. [4] A. Prateepasen, C. Jirarungsatian, Implementation of acoustic emission source recognition for corrosion severity prediction, Corrosion, 67 (2011), 056001/1-056001/11. [5] Early detection and progress monitoring and prediction of corrosion in aeronautic Al alloys through calibrated Ultrasonic-CorROSion Sensor application, EU H2020 Grant agreement ID: 864905, https://cordis.europa.eu/project/id/864905 [6] R. Oltra and F.Peltier, Laboratory-scale testing of the anti-corrosion effectiveness of a primer coating on a bare AA2024 surface, Surface Interface Analysis, 48 (2016) 775–779.

In Vitro Corrosion Assessment of the Essure® Medical Device in Saline, Simulated Inflammatory Solution and Neutral Buffered Formalin

The Essure® permanent contraceptive implant, comprised of four alloys (nickel-titanium, 316L stainless steel, platinum-iridium, and tin-silver solder) and Dacron (PET) fibers, has been approved for use in the US for about two decades. However, little has been published on this implant's biomaterials performance, and as this implant gains interest in terms of in vivo performance, methods of implant post-retrieval storage also need to be assessed. This study investigated the electrochemical properties and ion release profile of Essure® during storage in phosphate buffered saline (PBS), 10 mM H2O2/PBS, a simulated inflammatory solution, and 10% neutral buffered formalin (NBF) to investigate the corrosion behavior and metal ion release. First, a galvanic test method was used to measure the galvanic interactions between alloys within the device. Second, an ion-release study over 107 days was performed. Ions were measured using inductively-coupled plasma mass spectrometry and the implants were assessed using digital optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectrometry. The tin-silver (SnAg) solder continuously corroded in PBS and H2O2/PBS. In the presence of H2O2, nickel and titanium ions were released from the nickel-titanium (NiTi) coil, whereas release of these ions was minimal in PBS alone. Overall, corrosion of the SnAg solder, which holds the NiTi and 316L SS together, was significant in both PBS and H2O2/PBS and may result in loss of connection of the NiTi and 316L stainless steel portions of the implant. Storage in NBF exhibited very low corrosion rates for all alloys and low levels of ion release were observed indicating that formalin storage minimally affects the implant's corrosion status. Statement of significanceThe Essure® device is an FDA premarket-approved female permanent sterilization device containing four different metal alloys and poly(ethylene terephthalate) polymer fibers. Significant concerns related to this device have been raised by the FDA since its introduction in 2002. This study is the first published in vitro work to specifically assess the corrosion mechanisms in this multi-alloy device and the role of different solution environments, including formalin storage, inorganic physiological saline and a simulated inflammatory condition. Significant evidence of corrosion of the tin-silver solder is documented, the release of Ni and Ti under simulated inflammatory conditions, and the relative inertness of storage of these implants in neutral buffered saline is presented. The tin-silver corrosion corroborates recent clinical evidence of tin corrosion products in tissues adjacent to these devices in vivo.

Corrosion of Linear-Friction-Welded AZ91 and AZX912 Mg-Al Alloys

The corrosion performance of the AZ91 and AZ91 + 2%Ca (AZX912) magnesium alloys joined using linear friction welding was investigated. For similar and dissimilar metal combinations—namely AZ91/AZ91, AZX912/AZX912, and AZ91/AZX912, the performance was evaluated by mass loss analysis and the scanning vibrating electrode technique in 1 wt% NaCl solution. Galvanic behavior between AZ91 and AZX912 was examined by potentiostatic polarization and galvanic current measurements. Approximately 0.3–0.6 mm thick seamless weld zones were generated in all of the welds, which did not show any appreciable changes in the surface profiles acquired after the corrosion test. The corrosion-induced mass loss rate of the AZ91/AZX912 dissimilar weld was 10% higher than those of the AZ91/AZ91 and AZX912/AZX912 similar welds. The galvanic test indicated that AZ91 and AZX912 were the anodic and cathodic regions, respectively, with a difference in the corrosion potential of 20–30 mV. The corrosion of the AZ91/AZX912 weld was presumed to proceed via a macro-galvanic cell between the base alloys, whereas the weld acted as a bridge and did not influence the corrosion.

Determining the Evolution of Galvanic Corrosion in a Complex Geometry

In aerospace structures, the balance between strength and weight is vital to maintain. Dissimilar alloys are often employed to build individual components which, when put together, create a structure achieving the optimized properties. In particular, aluminum alloys have a very high strength-to-weight ratio which makes them ideal for structural components, while stainless steel is often used for hardware, such as fasteners and washers, which holds the aluminum components together [1]. On their own, both aluminum and stainless steels form a passive oxide film which increases their resistance to corrosion. However, when in the presence of an electrolyte, such as a light rain or morning dew, a possibility of galvanic corrosion between the dissimilar metals is present. In the scenario above, stainless steel would act as the cathode, consuming electrons, and the aluminum alloy would act as the anode, releasing electrons and dissolved metal ions.The surface of the aluminum alloy is generally painted with a pretreatment, primer, and topcoat to limit exposure of the bare metal to the environment, thereby decreasing the probability of corrosion. However, the layers of surface coating are often scratched off from mechanical or external damage, leaving the aluminum alloy susceptible to galvanic corrosion. Surface scratches can provide a pathway for an electrolyte into the fastener hole, if no sealant was used in installing the fasteners. Furthermore, an occluded cell is formed between the fastener and panel, which can lead to a build-up of aggressive species and further exacerbate the galvanic corrosion. Previous work has determined how severe corrosion within this occluded region can be, with intergranular corrosion sites up to 2mm in length seen after exposure of 504 hours in an accelerated salt spray environment [2].From a structural perspective, corrosion damage within the fastener hole has much larger implications for cracking than corrosion damage occurring on the surface of the panel. The geometry of the fastener hole is a stress concentrator, which localized corrosion can promote by acting as a nucleation site for cracks [3]–[5]. Conversely, the surface of the panel has no stress concentrators, and the exposed surface makes early detection of corrosion damage feasible.Determining when the fastener hole is most susceptible to corrosion damage is of upmost importance, from a practical standpoint. In this work, finite element modeling is used to determine under what scenarios will the majority of predicted damage be within the fastener hole (worst-case) or on the surface of the panel (best-case). External factors, such as the scribe dimensions, and environmental factors, such as the water layer thickness, will be investigated. In particular, the impact of water layer thicknesses beyond the natural convection boundary layer thickness are considered. Time-dependent studies shed light on a potential transition time between damage concentrating on the surface vs. concentrating within the fastener hole. The time-dependent model will include pH-dependent boundary conditions to simulate the crevice environment. The calculated pH profile along the complex geometry will be compared with experimental results via pH probes in a crevice.[1] C. A. Matzdorf, W. C. Nickerson, B. C. Rincon Tronconis, G. S. Frankel, L. Li, and R. G. Buchheit, “Galvanic test panels for accelerated corrosion testing of coated al alloys: Part 1 - Concept,” Corrosion, vol. 69, no. 12, pp. 1240–1246, 2013.[2] R. S. Marshall, R. Kelly, A. Goff, and C. Sprinkle, “Galvanic Corrosion Between Coated Al Alloy Plate and Stainless Steel Fasteners, Part 1: FEM Model Development and Validation,” Corrosion, vol. 75, no. 12, pp. 1461–1473, 2019.[3] M. D. Mcmurtrey, D. Bae, and J. T. Burns, “Fracture mechanics modelling of constant and variable amplitude fatigue behaviour of field corroded 7075-T6511 aluminium,” Fatigue Fract. Eng. Mater. Struct., 2016.[4] J. T. Burns, J. M. Larsen, and R. P. Gangloff, “Effect of initiation feature on microstructure-scale fatigue crack propagation in Al-Zn-Mg-Cu,” Int. J. Fatigue, vol. 42, pp. 104–121, 2012.[5] J. T. Burns, J. M. Larsen, and R. P. Gangloff, “Driving forces for localized corrosion‐to‐fatigue crack transition in Al–Zn–Mg–Cu,” Fatigue Fract. Eng. Mater. Struct., vol. 34, no. 10, pp. 745–773, 2011.

Effect of Bi content on microstructure and corrosion behaviour of Zn–8Al–(Bi) alloys

ABSTRACT Electrochemical techniques such as Polarisation and Galvanic tests as well as immersion test were used to analyse both the effects of different Bi contents and the length scale of dendritic spacings on Zn–8 wt-%Al–(1.5, 2.3 and 3 wt-%Bi) alloys on their corrosion behaviour. The results revealed that no significant differences in the corrosion kinetics were observed with the scale of the dendritic and lamellar spacings. Conversely, the corrosion behaviour was shown to be dependent on the alloy Bi content. Despite the cathodic character of Bi, its addition to the Zn–8%Al alloy was shown to reduce the corrosion rate as compared with that of the binary alloy.

A Study on the Location of the Cathode in Galvanic-Induced Crevice Corrosion

Fastener-in-panel systems are commonly used in aerospace construction. The geometries are very complicated, especially in the context of corrosion. Generally, fasteners are made of more noble materials, such as stainless steels, due to their good mechanical properties. Panels can represent the structural components of an aircraft, which are generally built with aluminum alloys, due to their high strength-to-weight ratio. The combination of these two metals when in electrolytic contact, as could occur from a light rain or morning dew, makes the system susceptible to galvanic corrosion. The fastener also forms an occluded region within the panel, adding in the possibility of crevice corrosion. Furthermore, aircraft are often exposed to cyclic wet and dry environments, leading to an atmospheric water layer which can exacerbate corrosion.The complicated and interacting mechanisms involved in the fastener/panel design have been investigated through finite element modeling (FEM) in this work. FEM has been advancing in recent years, and specifically has become a useful tool in studying galvanic corrosion [1]. The complexities surrounding a fastener-in-panel system are difficult to isolate individually experimentally. Modeling allows deconvolution of the specific parameters, efficiently assessing the effects and isolating changes in parameters in a way that is not possible experimentally.Previous work has compared experimental analysis with FEM in a large-scale fastener geometry [2]. This paper describes a similar investigation, with a more prominent focus on the fastener hole. Specifically, galvanic-induced crevice corrosion was studied in order to determine which location on the cathode was producing the main driving force. Therefore, the geometry was representative of a cross-section of one fastener installed in a panel, in order to negate the interaction of multiple fasteners. Knowledge of the location driving the cathodic reactions would aid in finding mitigation strategies for crevice corrosion, such as whether coating the head of the fastener or the shaft of the fastener is more important.Different locations of the active cathode were tested systematically, such as variations between an inert fastener shaft (that is, the crevice former) or an active shaft coupled with an inert or active fastener head. The transport of aluminum ions was tracked within the model as well. Both steady-state and time-dependent models are described, in order to determine if the cathode inside of the fastener hole acts as a driving force before being stifled through the production of hydroxyl.SS316 and AA7075 are the materials of focus for the fastener and panel, respectively. SS316 has been shown to form a severe galvanic couple with AA7075 [3], leading to the formation of intergranular corrosion fissures of 2mm in length inside of the fastener hole [2]. A sol-gel coated SS316 fastener was also investigated, to determine the level of mitigation achieved. Boundary conditions for these materials were generated experimentally, through potentiodynamic scans.[1] C. Liu and R. G. Kelly, “A Review of the Application of Finite Element Method (FEM) to Localized Corrosion Modeling,” CORROSION, 2019.[2] R. S. Marshall, R. Kelly, A. Goff, and C. Sprinkle, “Galvanic Corrosion Between Coated Al Alloy Plate and Stainless Steel Fasteners, Part 1: FEM Model Development and Validation,” Corrosion, vol. 75, no. 12, pp. 1461–1473, 2019.[3] C. A. Matzdorf, W. C. Nickerson, B. C. Rincon Tronconis, G. S. Frankel, L. Li, and R. G. Buchheit, “Galvanic test panels for accelerated corrosion testing of coated al alloys: Part 1 - Concept,” Corrosion, vol. 69, no. 12, pp. 1240–1246, 2013.

An eHealth System for Monitoring the Relapse of Salmonella Typhi in Outpatients.

Typhoid fever remains a major health problem in developing countries: According to the World Health Organisation, there are 21 Million cases worldwide and 222,000 typhoid-related deaths occurring annually [1]. Mobile monitoring systems have been proposed for observing patient's physiological signals; these hardware and software solutions are broadly categorised as Healthcare Sensor Networks (HSNs). Since no two patients are alike with regards to biometric parameters and access to healthcare professionals can be difficult because of geography or scarcity of resources, monitoring must be observed in situ. Various serological and culture diagnostic tests for enteric fever exist, including the Widal test [44], TUBEX [45], ELISA [46] and the Gold Standard Blood Culture test [32]. The limitations of these existing conventional tests include lack of speed, sensitivity, and specificity, ambiguity in the classification of symptoms, diagnosis by inexperienced healthcare workers and the fact that they are predominantly clinic-based tests. Critical to typhoid care is outpatient support after the completion of courses of antibiotics, and the two to three-week reoccurrence period is crucial in aftercare. Our research is designed for patients during this period. In this paper, we propose a mobile-based monitoring methodology, which uses vital signs monitoring apparatus, which is configured to recognise the characteristics of typhoid recurrence. Key to our design is the implementation of sensors for body temperature monitoring and physiological testing through galvanic skin response (GSR), electrocardiographic testing (ECG) and electromyography (EMG). The paper introduces an invaluable tool for (i) software programmers and algorithm designers working with biometric HSNs and (ii) practitioners working in public health monitoring and disease prevention.

Corrosion of coated aluminium alloy 7075-T6 galvanic test assemblies, part II: impact of fastener through-hole condition

ABSTRACT The influence of the condition of through-holes on the corrosion of galvanic test assemblies was studied. Holes in coated aluminium alloy 7075-T6 were tested as received, in a worst-case bare condition and with extra protection. Regions away from fastener holes were also tested. Corrosion performance was assessed by electrochemical impedance spectroscopy in immersed conditions. Defects in the coatings at through-holes of as-received panels resulted in degraded corrosion performance, which could be mitigated by the application of additional protection. The presence of a fastener in the hole affected the corrosion performance for all three conditions even without galvanic coupling interactions. Galvanic interactions were studied on panels exposed to ASTM B117 salt fog conditions, where the through-hole condition also had a large effect.

Corrosion of coated aluminium alloy 7075-T6 galvanic test assemblies, part I: unscribed panels

ABSTRACTGalvanic corrosion of samples consisting of coated aluminium alloy 7075-T6 panels connected to stainless steel 316 fasteners was examined. Two coating systems were evaluated, one containing chromate pretreatment and primer along with a topcoat, and the other a chromate free system. No intentional defects such as scribes were imparted to investigate the attack associated with intrinsic defects in the coatings. The galvanic current between the fasteners and panel was greater for the assembly with chromate-free coatings than for the one with chromated coatings, and for the exposure to a salt spray chamber than for immersion. The attack was much deeper for the chromated system and more localised. The galvanic current increased with time and then was equal to that measured for a sample with an intentional scribe.

Investigations of the Effects of Electrochemical, Environmental and Geometric Parameters on Galvanic Coupling through Finite Element Modeling

Experimental studying of the galvanic coupling between different alloys can quickly become a difficult task, because of the many parameters to consider. Many of these parameters are dependent on each other, forcing researchers to create a web of test matrices in order to isolate one parameter at a time. Both electrochemical and geometric parameters must be considered, along with a constant environmental storage of samples before and after tests to guarantee that there has been no change in the system. This complexity makes experimental testing slow, however it can produce thorough results. Finite element modeling (FEM) has become a useful tool in studying galvanic corrosion[1] mainly because of its ability to both efficiently assess the effects of specific parameters and to isolate changes in parameters in a way that may not be possible experimentally. A computational study using FEM can allow a vast portion of parameter space to be assessed, guiding experimental tests to regions of interest. This approach narrows the daunting sea of parameters which experimentalists swim in, especially in the field of galvanic corrosion. In real applications, these parameters can be changed in a variety of ways. For example, different coatings can affect the electrochemical kinetics of the alloys, humidity changes can affect the concentration of the electrolyte solution, and atmospheric pressure or environmental changes can affect the temperature of the solution. The focus of this research therefore was to study the effects of different parameters on the galvanic coupling of AA7075 and SS316. These two materials are both common in aerospace applications, particularly with AA7075 as the structural material and SS316 as the fastener holding the assembly together. SS316 has been shown to severely couple with AA7075[2], leading to the formation of intergranular corrosion fissures of 2mm in length inside of the fastener hole[3]. Knowing which parameters create a large impact on this galvanic corrosion, and which do not, is valuable information when trying to maintain the safety of structures. A detailed computational matrix was run in the model, analyzing the effects of cathodic and anodic kinetics, conductivity, and temperature on the overall current distributions. These effects were quantified to determine which parameter made the largest contribution to the galvanic current, and which were negligible. A study of the interactions between these parameters was also conducted, in order to determine which parameter would be easily isolated by experimental technique. The computations were first run on a simple geometry in the model with one cathode surface and one anode surface, to get a generalized idea of the importance of the parameters. Afterwards, an occluded cell geometry was utilized in the model, to determine how the geometric change effects the contributions of the different parameters on the current distributions. A comprehensive analysis of these parameters will be presented, along with ideas of how to use this analysis for practical applications. [1] C. Liu, V. N. Rafla, J. R. Scully, and R. G. Kelly, “Mathematical modeling of potential and current distributions for atmospheric corrosion of galvanic coupling in airframe components,” Corros. 2015, no. May 2016, 2015. [2] C. A. Matzdorf, W. C. Nickerson, B. C. Rincon Tronconis, G. S. Frankel, L. Li, and R. G. Buchheit, “Galvanic test panels for accelerated corrosion testing of coated al alloys: Part 1 - Concept,” Corrosion, vol. 69, no. 12, pp. 1240–1246, 2013. [3] R. J. Skelton and R. G. Kelly, “Investigation of Galvanic Coupling on AA7075-T6 Navair Plate inside Fastener Hole,” in ECS Meeting s, 2018.

Galvanic coupling and mechanical properties of low Ni orthodontic brackets with representative types of orthodontic wires

Abstract Aim To characterise the mechanical properties and galvanic coupling of Ni-free orthodontic brackets with stainless steel (SS) and Nickel-Titanium (NiTi) orthodontic wires. Methods Three Ni-free bracket types (Topic [TOP], Equilibrium [EQU] and Orthos [ORT] made of Ni-free alloys), one conventional (Mini 2000 [MIN]) made of SS alloy and an SS and a NiTi wire were examined in the present study. All brackets and wires were embedded in epoxy resin and, after metallographic grinding and polishing, the Martens hardness (HM), the indentation modulus (EIT), and the elastic index (ηIT) were recorded, employing Instrumented Indentation Testing (IIT) by monitoring force over indentation depth curves during a loading-unloading cycle. The galvanic coupling of all bracket-wire combinations was tested in 0.1M NaCl-0.1M lactic acid and 0.3% (wt.) NaF solutions by noting the potential differences over 48 hours. The mechanical properties were statistically analysed by one-way ANOVA and Tukey multiple comparison tests at alpha = 0.05. Results Significant differences were identified in the mechanical properties of the materials tested. The TOP (2372 ± 182 N/ mm2), ORT (wing) (2418 ± 164) and SS wire (2302 ± 85) showed significantly higher HM compared with all other materials tested. The MIN (base) (1115 ± 81) and ORT (base) (1237 ± 101) showed the lowest HM while MIN (wing) (1520 ± 138), EQU (1620 ± 139) and NiTi wire (1526 ± 42) demonstrated intermediate HM values. The ORT (wing) (101 ± 6 GPa) displayed the highest EIT while NiTi wire (24 ± 5) showed the lowest. The latter had the highest elastic index (59 ± 5%) with MIN (base)(15 ± 3) possessing the lowest. The potential difference for all bracket wire combinations was found below the threshold for the initiation of galvanic corrosion (200 mV) apart from MIN coupled with NiTi wire in the NaF solution. Conclusions The mechanical properties of Ni-free brackets are significantly different compared with the SS bracket assessed. Galvanic testing revealed that conventional and Ni-free brackets are compatible with both SS and NiTi wires in media containing chloride and fluoride ions.

Investigation of Galvanic Coupling on AA7075-T6 Navair Plate inside Fastener Hole

AA7075-T6 is widely used in aerospace structures, and often SS316L fasteners are extensively used, especially for repairs because they are relatively cheap and easy to acquire. Separately, these materials are very efficient at performing their functions. However, when placed in intimate contact (such as in a fastener/hole configuration) and exposed to marine atmospheres, a galvanic couple forms which exacerbates the localized corrosion of the AA7075-T6. In service, the AA7075-T6 is coated with a primer and organic topcoat. Thus any defects in the coating serve as anodes in the galvanic couple with an extremely unfavorable cathode:anode area ratio. In addition, the interior of the hole is often poorly coated or suffers mechanical damage during operations. The overall goal of this research is to evaluate the efficiency of the mitigation strategy of coating the cathodic material with a sol-gel coating, thereby effectively ionically isolating the stainless steel fasteners from the AA7075-T6. Titanium fasteners are also under study, as they are expected to have very limited galvanic coupling with the AA7075-T6. This characteristic made them a positive baseline to which we continually compared the stainless steel corrosion. Experimentally the interactions between the SS316 and Ti-6Al-4V bolts, washers, and nuts and the coated AA7075-T6 were assessed using a configuration designed by NAVAIR [1]. It consists of a plate with eight holes and eight fasteners. Details can be found elsewhere [1]. In the present work, the fasteners were spray coated with low quality sol-gel coating to serve as a baseline of damage accumulation. Around four of the holes for the fasteners, two scribes were made through the coating in order to assess the effects of coating defects on the corrosion morphology. These NAVAIR plates underwent ASTM B117 [2] testing for 1,344 hours. Once the plates were taken out of the testing environment, they were stripped of the primer, coating, and the fasteners were removed. The plates were then cut into sections dividing the hemispheres of the holes. The exposed holes were polished down to a 1 micron mirror finish, and Keller’s Etchant was used to highlight the grains. Cross-sectional images of the holes were acquired using the Hirox RH 8800 optical microscope. The primary focus was assessment of damage within the holes as these are the locations of highest stress. Corrosion damage is known to serve as an initiation site for fatigue cracks [3]. After the samples were taken out at 1,344 hours, it was observed that the corrosion damage in the hole in which the stainless steel fastener had been was far more severe than that in the hole in which the titanium fastener had been (see Figure 1). The most intense pitting on all of the holes occurred near the head of the fastener, indicating that the head of the fastener is throwing cathodic current not only to the surface of the plate, but also inside the hole. In the case of the stainless steel fastener, the damage was primarily long intergranular fissures, whereas the Ti-6Al-4V caused more pitting with a smaller amount of intergranular attack. Using polarization curves generated in relevant simulants of the different localized sites as boundary conditions, FEM modeling results will be presented that rationalize the type, location, and extent of the damage observed for the different noble metal fasteners as well as the expected reduction in that damage if a high-quality sol-gel coating were applied to them. References Feng, Z., & Frankel, G. S. “Galvanic test panels for accelerated corrosion testing of coated al alloys: Part 1 – Concept” Corrosion 2014; 70(1), 95–106. https://doi.org/10.5006/0907ASTM B117, “Standard Practice for Operating Salt Spray (Fog) Apparatus” (West Conshohocken, PA: ASTM International, 1994)Burns JT, Larsen JM, Gangloff RP. “Driving forces for localized corrosion-to-fatigue crack transition in Al-Zn-Mg-Cu” Fatigue Fracture Engineering Material Structures 2011; 34:745–73. doi:10.1111/j.1460-2695.2011.x Figure 1

An Experimental Study of Galvanic Corrosion on an Underwater Weld Joint

Kong, X.F.; Lv, J.; Gao, N.; Peng, X., and Zhang, J., 2018. An experimental study of galvanic corrosion on an underwater weld joint. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 63–68. Coconut Creek (Florida), ISSN 0749-0208.This study aimed to explore the galvanic corrosion behavior of an underwater weld joint using the polarization curve, galvanic current test, and microcurrent distribution test. The results revealed that galvanic corrosion evidently occurred in the area of the underwater weld joint, accelerating the corrosion process. The weld metal acted as the cathode, whereas the base metal (BM) and heat-affected zone (HAZ) acted as anodes. The maximum value of the cathode current in the weld region reached 3.5 μA. Corrosion current density was mainly decided by the diffusion process of dissolved oxygen (DO) in the seawater. As the immersion time increased, the oxygen diffusion process was hindered by the biofilm and sedimentary cover on the surface of the weld region, whereas the oxygen reduction reaction was suppressed. Therefore, the galvanic corrosion between the weld region and BM was further weakened.

Galvanic Attack of Coated Al Alloy Panels in Laboratory and Field Exposure

A galvanic test panel design incorporating a painted and scribed Al alloy panel and uncoated through-hole noble fasteners has recently been utilized to compare effects of different surface pretreat...

Early Stage Galvanic Corrosion of 5383 Al Alloy Coupled with 907 Steel and Aluminum Bronze in 3.5%NaCl Solution

Galvanic corrosion performance of 5383 Al alloy coupled with 907 steel and aluminum bronze respectively in the early stage was studied by galvanic current test and scanning electron microscopy(SEM). The results showed that the 5383 Al alloy acted as anodes for the two galvanic couples, while 907 steel and aluminum bronze were cathode. The corrosion morphology of 5383 Al alloy could be metastable pitting, irregular stable pitting and filiform- like corrosion. The galvanic current density Igof two couples varied similarly with immersion time, they decreased at the beginning and then became stable. The galvanic current density decreased with the increase of distance from the couple joint, and it became uniform in the far end. Compared with the couple 5383 Al alloy/aluminum bronze, the galvanic corrosion for couple 5383 Al alloy/907 steel was less severe,but it was more concentrated with in an area of 2 mm nearby the joint line.

PEMFC Subzero Cold Start in a Quasi-Adiabatic Single Cell Fixture

Polymer electrolyte membrane fuel cells (PEMFC) are a global contender to replace the internal combustion engines in automobiles. One key element for making PEMFCs viable for automotive applications is to improve their cold-start performance and survivability from sub-zero temperatures. The main factor limiting cold-start performance is the inherent presence of water—both residual and product water. Water within a fuel cell under subzero conditions has the potential to cause mechanical damage from ice lens formation and limit the diffusion of reactant gases during cold-starts. The DOE has set several automotive targets for 2010 regarding PEMFC freeze, identical to those for the internal combustion engine: survivability from -40¢ªC and cold-start capability from -30¢ªC. The 2010 cold-start performance target from -20¢ªC, requires the fuel cell to attain 50% rated power in the first 30 seconds after start-up. Additionally, the maximum shut down energy expenditure is limited to 5 MJ, for functions—such as, drainage and dry out. Common single cell testing methodologies of testing PEMFCs’ materials for subzero cold start applications include freeze/thaw cycling for durability and isothermal water fill tests for cold start approximation. These testing protocols are limited because of the massive thermal sink of the fixtures endplates. In a stack of 350 or more repeat cells there is exothermic heating from adjacent cells. An adiabatic single cell fuel cell fixture was developed in 2004 at United Technologies Research Center.[1] The goal of the proposed work presented herein is to further refine the design and testing methodologies. A quasi-adiabatic single-cell fuel cell fixture was designed, built, and validated to emulate cold starts at the stack level, see Figure 1. This cell meets or exceeds internal requirements for pressure distribution at the MEA/GDL interface based on both modeling and mechanical testing. Balsa wood (vs synthetic alternatives) was used as a rigid insulation material. With the current fixture geometry (16cm2 active area), stresses do not exceed the ultimate stress of the weakest piece of balsa. To examine thermal distribution, the cell was frozen to a uniform temperature and heated using embedded heating pads as guard-heaters with a constant heat flux. This temperature data was then input into a finite element model in COMSOL. It was found that a large degree of insulative and guard-heat ability was obtained noted by the zero heat flux condition of the model results within the graphite flow field. Galvanic and potentiostatic cold starts were performed with the fuel cell fixture and show limitations in the MEA and the fuel cell test station. The galvanic tests set to 600 mA cm-2 were dominated by sufficiently high membrane resistances such that the fuel cell test station could not apply a constant current condition forcing the cell to be ramped up from a voltage minimum of less than<0.1V. Potentiostatic cold starts were set to 0.1V till the current attained a value of 600 mA cm-2. 1. Rice-York, C., J. Needham, N. Gupta, and P.L. Hagans, 'Platform for Rapid Prototyping of PEM Fuel Cell Designs with Enhanced Cold-Start Performance and Durability', ECS Transactions, 2006, 1, 383. Figure 1

Light-weight cementitious conductive anode for impressed current cathodic protection of steel reinforced concrete application

This paper presents the results of a study of the effectiveness of lightweight conductive cementitious mortar as an anode material for impressed current cathodic protection of concrete structures. The anode is made up of pumice aggregate (fine), carbon fibres and cement with MMO-Ti as a primary anode. Accelerated galvanic test, conductivity measurement, dry density and compressive strength were carried out and compared with the cement mortar without fibres. Results have shown that the mortar at 20–30% replacement level of pumice aggregate with 1.1% carbon fibre content is a percolation threshold at which highest conductivity of 0.2S/cm is achieved. The weight of the anode was found to have reduced to half of the weight of the conventional anodes. Polarisation and impedance studies confirmed the possible use of this material as an anode in cathodic protection of reinforced concrete structures.

Elucidating Corrosion Performance of Weld in CO&lt;sub&gt;2&lt;/sub&gt; Corrosion Environment

Weld corrosion is suspected to contribute to localized corrosion failure of pipelines in CO2 environment. Some studies on the mitigation of the weld corrosion had been focused on weld metal micro-alloying producing cathodic weld metal but with mixed success result. The inconsistent result is due to lack of understanding on the mechanism of weld corrosion in this corrosive CO2 environment. This paper presents the study of the possibility of weld corrosion from the galvanic and self-corrosion effects of welded low carbon steel ASTM 106 B pipeline in pH 5-CO2 saturated environment at 25 °C and 60 °C under stagnant condition. The weld region samples were prepared by metallography method to identify the parent metal (PM), heat affected zone (HAZ) and weld metal (WM) microstructures. Galvanic current was measured for each weld region by zero resistance ammeters (ZRA) and self-corrosion rate was measured by electrochemical impedance spectroscopy (EIS). The total corrosion rate was determined from the summation of galvanic corrosion and self-corrosion for all weld regions. From the galvanic current test result, weld metal was found to be anodic for both 25 °C and 60 °C. Weld metal also experienced the highest self-corrosion rate in the range of 40-98% as compared to parent metal and HAZ region for both 25 °C and 60°C. The total corrosion rate was mainly contributed by the self-corrosion rates and the contribution from galvanic corrosion was considered insignificant. Possible preferential weld corrosion can occur on weld metal region due to differential self-corrosion rates of each weld regions.

Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction

A test sample incorporating a painted Al alloy panel, uncoated through-hole fasteners, and scribes has recently been shown to provide an accelerated response during atmospheric corrosion testing in...