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The effects of applied stress, ranging from tensile to compressive, on the atmospheric pitting corrosion behavior of 304L stainless steel (SS304L) were analyzed through accelerated atmospheric laboratory exposures and microelectrochemical cell analysis. After exposing the lateral surface of a SS304L four-point bend specimen to artificial seawater at 50°C and 35% relative humidity for 50 d, pitting characteristics were determined using optical profilometry and scanning electron microscopy. The SS304L microstructure was analyzed using electron backscatter diffraction. Additionally, localized electrochemical measurements were performed on a similar, unexposed, SS304L four-point bend bar to determine the effects of applied stress on corrosion susceptibility. Under the applied loads and the environment tested, the observed pitting characteristics showed no correlation with the applied stress (from 250 MPa to −250 MPa). Pitting depth, surface area, roundness, and distribution were found to be independent of location on the sample or applied stress. The lack of correlation between pitting statistics and applied stress was more likely due to the aggressive exposure environment, with a sea salt loading of 4 g/m2 chloride. The pitting characteristics observed were instead governed by the available cathode current and salt distribution, which are a function of sea salt loading, as well as pre-existing underlying microstructure. In microelectrochemical cell experiments performed in Cl− environments comparable to the atmospheric exposure and in environments containing orders of magnitude lower Cl− concentrations, effects of the applied stress on corrosion susceptibility were only apparent in open-circuit potential in low Cl− concentration solutions. Cl− concentration governed the current density and transpassive dissolution potential.

The corrosion of additively manufactured (AM) metallic materials, such as stainless steels (SS), is a critical factor for their qualification and reliable use. This review assesses the emerging knowledgebase of powder-based laser AM SS corrosion and environmentally assisted cracking (EAC). The origins of AM-unique material features and their hierarchal impact on corrosion and EAC are addressed relative to conventionally processed SS. The effects of starting material, heat treatment, and surface finishing are substantively discussed. An assessment of the current status of AM corrosion research, scientific gaps, and research needs with greatest impact for AM SS advancement and qualification is provided.

Understanding the mechanistic relationship between the environment, microstructure, and local kinetics of atmospheric corrosion damage remains a central challenge. To address this challenge, this study used laboratory-based X-ray tomography to directly observe attack in-operando over an extended period, enabling insights into the evolving growth kinetics and morphology of individual pits over months of exposure. Damage progression associated with nine pits in a 99.9% pure aluminum wire exposed to chloride salts in humid air was characterized. Most pits grew at a nominally linear rate up until pit death, which occurred within 12–24 h of nucleation. Exceptions to this were observed, with three pits exhibiting bimodal growth kinetics and growing for 40 or more hours. This was explained by secondary droplets that formed near the pits, increasing the cathode area. A corrosion-driven drying mechanism likely contributed to pit death in both cases. Pits first grew into the material followed by lateral expansion.

The impact of microstructure and processing defects of directed energy deposition (DED) 304L stainless steel on its corrosion behavior was investigated. Materials produced by DED with heat inputs of 0.45 and 0.03 kJ/mm were compared to wrought 304L. Lack of fusion pores in the DED material controlled breakdown potential (Eb) to the first order, reducing it by up to 400 mV versus the base material in 0.6 M NaCl. The hierarchal control of these and other microstructure features, nanoscale oxides and δ-ferrite, and processing features on the Eb of DED 304L is addressed.

Additively manufactured austenitic stainless steels exhibit numerous microstructural and morphological differences compared to their wrought counterparts that will influence the metals corrosion resistance. The characteristic as-printed surface roughness of powder bed fusion (PBF) stainless steel parts is one of these morphological differences that increases the parts susceptibility to localized corrosion. This study experimentally determines the average surface roughness and breakdown potential (Eb) for PBF 316L in 6 surface finished states: as-printed, ground with SiC paper, tumble polished in abrasive media, electro-polished, chemically passivated, and the application of a contour/re-melt scan strategy. In general, a smaller average surface roughness led to a larger Eb. The smoothest surface treatments, ground and electro-polished conditions, led to Eb near the materials limit (~+1.0 VAg/AgCl) while all other surface treatments exhibited significantly lower Eb (~+0.3 VAg/AgCl) The build angle was also shown to impact surface roughness, where surfaces at high angles from the build direction resulted in larger roughness values, hence lower Eb.

This work aims to investigate the waterline corrosion of pure copper in 4 M NaCl solution. Three distinct regions are identified. Corrosion products formed at the waterline are characterized by micro-Raman spectroscopy, complemented by SEM/EDS, as a function of immersion time. The co-existence of four copper species is explained by thermodynamic equilibrium consideration. The composition of spreading region is determined and compared with the oxide film formation in different pH NaOH solutions. The anodic dissolution of copper exposed to the bulk electrolyte is investigated by electrochemical methods. The pH and potential profiles across three regions are proposed.

This study describes the evolving state of electrolyte and corrosion processes associated with sodium chloride on copper at the initial stage of corrosion and the critical implications of this behavior on controlling kinetics and damage distributions. Sodium chloride droplets were placed on copper in humid conditions and the resulting electrolyte properties, corrosion products and damage were characterized over time using time-lapse imaging, micro Raman spectroscopy, TOF-SIMS and optical profilometry. Within minutes of NaCl droplet placement, NaOH-rich films resultant from oxygen reduction advanced stepwise from the droplets, leaving behind concentric trenching attack patterns suggestive of moving anode-cathode pairs at the alkaline film front. Corrosion attack under these spreading alkaline films was up to 10x greater than under the original NaCl drops. Furthermore, solid Cu2Cl(OH)3 shells formed over the surface of the NaCl drops within hours of exposure. Thermodynamic modeling along with immersed electrochemical experiments in simulated droplet and films electrolytes were used to rationalize this behavior and build a description of the rapidly evolving corroding system.

During typical atmospheric conditions, cathodic reduction reactions produce hydroxyl ions increasing the pH in the cathodic region. Therefore, cathodic reduction reactions are investigated on platinum and stainless steel 304 L (SS304L) in NaOH solutions ranging in pH from 13.6 to 16.5. It was found that in solution pHs less than 16.5 the cathodic reduction reaction on Pt and SS304L was ORR with an electron transfer number less than two due to superoxide formation as an intermediate. Increasing pH decreased the number of electrons transferred. At a pH of 16.5, the cathodic reduction reaction on SS304L is no longer ORR and the cathodic current on the surface of the alloy is due to oxide reduction occurring on the surface as indicated by the creation of multi-component Pourbaix diagrams. The results of this study have important implications for predicting corrosion in atmospheric environments.

The natural convection boundary layer ( δ n c ) and its influence on cathodic current in a galvanic couple under varying electrolytes as a function of concentration (1 − 5.3 M NaCl) and temperature (25 °C−45 °C) were understood. Polarization scans were obtained under quiescent conditions and at defined boundary layer thicknesses using a rotating disk electrode on platinum and stainless steel 304L (SS304L); these were combined to determine δ n c . With increasing chloride concentration and temperature, δ n c decreased. Increased mass transport (Sherwood number) results in a decrease in δ n c , providing a means to predict this important boundary. Using Finite Element Modeling, the cathodic current was calculated for an aluminum alloy/SS304L galvanic couple as a function of water layer (WL) thickness and cathode length. Electrolyte domains were delineated, describing (i) dominance of ohmic resistance over mass transport under thin WL, (ii) the transition from thin film to bulk conditions at δ n c , and (iii) dominance of mass transport under thick WL. With increasing chloride concentration, cathodic current decreased due to decreases in mass transport. With increasing temperature, increased cathodic current was related to increases in mass transport and solution conductivity. This study has implications for sample sizing and corrosion prediction under changing environments.

The corrosion susceptibility of a laser powder bed fusion (LPBF) additively manufactured alloy, UNS S17400 (17-4 PH), was explored compared to conventional wrought material. Microstructural charact...

During routine pharmaceutical development and scale-up work, severe corrosion of a Hastelloy Alloy C-22 (Alloy 22) filter dryer was observed after single, short (several hour) contact with the product slurry at room temperature. Initial investigations showed that the presence of both 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and HCl was sufficient in an acetonitrile solution to cause rapid corrosion of Alloy 22. More detailed mass loss studies showed initial corrosion rates exceeding 25 mm/y that then decreased over several hours to steady state rates of 3 mm/y to 5 mm/y. The corrosion was highly uniform. Electrochemical measurements demonstrated that although Alloy 22 is spontaneously passive in acetonitrile solution, the presence of HCl leads to the development of a transpassive region. DDQ is a sufficiently strong oxidizer, particularly in acidic solutions, to polarize the Alloy 22 well into the transpassive region, leading to the observed high-corrosion rates.

Ground 304 stainless steel (SS) samples were exposed to sea salt particles at 35 °C and two relative humidity (RH) levels for durations ranging from 1 week to 2 years. For all exposure times, pit number density and total pit volume at 40% RH were observed to be considerably greater than those at 76% RH. Statistical analysis of distributions of pit populations for both RH conditions showed that pit number density and total pit volume increased rapidly at first but slowed as exposure time increased. Cross-hatched features were observed in the 40% RH pits while ellipsoidal, faceted pits were observed at 76% RH. Optical profilometry indicated that most pits were not hemispherical. X-ray tomography provided evidence of undercutting and fissures. Piecewise curve fitting modeled the 40% RH data closely, predicting that corrosion damage would eventually plateau. However, a similar treatment of the 76% RH data suggested that corrosion damage would continuously increase, which implied that the piecewise power-law fit was limited in its ability to model atmospheric corrosion generally. Based on these observations, the operative mechanisms determining long-term corrosion behavior were hypothesized to be different depending on the RH of exposure.

Maximum pit sizes were predicted for dilute and concentrated NaCl and MgCl2 solutions as well as sea-salt brine solutions corresponding to 40% relative humidity (RH) (MgCl2-rich) and 76% RH (NaCl-rich) at 25 °C. A quantitative method was developed to capture the effects of various cathode evolution phenomena including precipitation and dehydration reactions. Additionally, the sensitivity of the model to input parameters was explored. Despite one's intuition, the highest chloride concentration (roughly 10.3 M Cl−) did not produce the largest predicted pit size as the ohmic drop was more severe in concentrated MgCl2 solutions. Therefore, the largest predicted pits were calculated for saturated NaCl (roughly 5 M Cl−). Next, it was determined that pit size predictions are most sensitive to model input parameters for concentrated brines. However, when the effects of cathodic reactions on brine chemistry are considered, the sensitivity to input parameters is decreased. Although there was not one main input parameter that influenced pit size predictions, two main categories were identified. Under similar chloride concentrations (similar RH), the water layer thickness (WL), and pit stability product, ( i · x ) s f , are the most influential factors. When varying chloride concentrations (RH), changes in WL, the brine specific cathodic kinetics on the external surface (captured in the equivalent current density ( i e q )), and conductivity ( κ o ) are the most influential parameters. Finally, it was noted that dehydration reactions coupled with precipitation in the cathode will have the largest effect on predicted pit size, and cause the most significant inhibition of corrosion damage.

Cathodic kinetics in magnesium chloride (MgCl2) solutions were investigated on platinum (Pt) and stainless steel 304 L (SS304 L). Density, viscosity, and dissolved oxygen concentration for MgCl2 solutions were also measured. A 2-electron transfer for oxygen reduction reaction (ORR) on Pt was determined using a rotating disk electrode. SS304 L displayed non-Levich behavior for ORR and, due to ORR suppression and buffering of near surface pH by Mg-species precipitation, the primary cathodic reaction was the hydrogen evolution reaction (HER) in saturated MgCl2. Furthermore, non-carbonate precipitates were found to be kinetically favored. Implications of HER are discussed through atmospheric corrosion and stress corrosion cracking.

Predicting the kinetics and morphology of localized damage produced during corrosion of passive alloys is a foundational challenge in the development of robust damage models. This is especially the case for atmospheric corrosion, wherein the complex mechanistic interrelationships between environment, material microstructure, and the electrochemical processes driving corrosion are still little understood. This work shows the first results of long-term, in-situ characterization of atmospheric corrosion pits in commercially pure aluminum using x-ray microtomography to address the following questions: 1) how fast do individual pits in this material grow and what controls this growth rate? 2) how does the morphology of pits in this material evolve over time? 3) what is the relationship between pit morphology, the evolving electrolyte on the metal surface, and the microstructure? The mechanism involving the stifling of pit growth will also be discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

The effects of applied stress, ranging from tensile to compressive, on atmospheric pitting corrosion of stainless steel 304L (SS304L) were analyzed through laboratory exposure and localized corrosion experiments. Pitting characteristics, analyzed through optical profilometry, scanning electron microscopy, and electron backscatter diffraction, were obtained after exposure for 50 days of an SS304L four-point bend bar to simulated seawater conditions at 50°C and 35% RH. Additionally, localized electrochemical measurements were carried out on an unexposed SS304L four-point bend bar to analyze the effects of applied stress on the corrosion susceptibility in analogous chloride solutions. In the tested, simulated seawater environment, the applied stress showed no effect on the pitting characteristics due to the aggressivity of the 4g/m2 loading of simulated seawater. Pitting depth, surface area, roundness, and distribution were found to be largely stochastic and rely on the available cathodic area and preexisting microstructure. However, through localized corrosion experiments in more benign environments, containing lower Cl- concentrations, the effects of stress on corrosion susceptibility start to become noticeable from the open circuit potential (OCP) measurements. A measurable decrease in the OCP indicated increased susceptibility to corrosion in the region of applied tensile stress as compared to the compressively stressed region. These findings indicate that stress may be less of a contribution to corrosion susceptibility than Cl- concentration under the exposure conditions examined. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-4490 A

Ultrathin nanocomposite films fabricated by layer-by-layer (LbL) assembly are an emerging class of coatings with remarkable barrier performance. Here, we examine LBL polymer-clay nanocomposite (PCN) coatings that afford anti-corrosion properties comparable to those exhibited by more traditional films that are orders of magnitude thicker. PCN barrier thin films comprised of up to 40 bilayers of polyethyleneimine (PEI) and exfoliated laponite (LAP), montmorillonite (MMT), or vermiculite (VMT) clay platelets were coated onto steel plates using a scalable LBL dip-coating process. A combination of electrochemical impedance spectroscopy and ex-situ electron and vibrational spectroscopy were used to evaluate coating performance during exposure in 0.6 M NaCl for up to 7 days. A PEI/VMT crosslinked coating of only 250 nm thick slowed the corrosion rate of mild steel by three orders of magnitude (Rct = 106 vs. 103 Ω-cm2) after seven days in 0.6 M NaCl. This performance exceeded the reported performance of other LBL coatings along with much thicker multilayer composite coatings and several conventional pretreatments on mild steel under similar test conditions. The exceptional performance is attributed to the effective barrier properties imparted by a high loading (>80 wt%) of orientated, high aspect ratio (2000:1) platelet layers in a nanobrick wall morphology. Substitution of VMT with lower aspect ratio clay platelets of either MMT (400:1) or LAP (30:1) showed that coated steel corrosion rates and apparent coating permeability scales with platelet size following LAP > MMT >> VMT. Thus, this study has for the first time shown that platelet aspect ratio is a primary means of improving the performance LbL nanocomposite coatings which is in line with the expected behavior of conventional nanocomposites. Given film debonding from the substrate was observed as a common failure mode during exposure for all coating types, replacement of the PEI polymer component with a more debonding-resistant polymer may be an additional pathway to further improve LbL PCN anticorrosion performance.

Photovoltaic (PV) power plants and their constituent components, by virtue of their application, are exposed to some of the harshest outdoor terrestrial environments. Most equipment is subject directly to the environment and myriad stresses (micro and macro environment). Other aspects including local site conditions, construction variability and quality, and maintenance practices also influence the likelihood of such hazards. Many discrete components, including PV modules, wires, connectors, wire management devices, combiner boxes, protection devices, inverters, and transformers, make up the PV generation system. While there are abundant data that illustrate PV modules and PV inverters to be the major contributors of PV system failures, the mentioned data illustrate the importance of minimizing failures in the often ignored components such as PV connectors, PV wires (both above and below ground), wire splices, fuses, fuse holders, fuse holder enclosures, and wire management devices. With the exception of PV fuses, these components predominantly use polymeric materials. Therefore, it is crucial to understand the typical materials used in components, degradation processes and mechanisms leading to component failure, and their impact on system performance or failure. It further provides some practical considerations, approaches, and methods in addressing the problems with practical solutions in the design to assure the performance of the PV plant over the intended design lifetime.

Aluminum and aluminum alloys are widely used in many outdoor applications due to their inherent corrosion resistance attributed to the formation of a protective oxide layer. While corrosion rates are generally considered low for aluminum in many atmospheric environments, understanding of the corrosion performance over time is necessary to predict the cost, safety, and esthetics of these materials. The vast majority of the knowledgebase of atmospheric aluminum corrosion is built on environment–response relationships; often based on statistical correlation of corrosion rate data with atmospheric environmental conditions. However, there is still a limited mechanistic understanding of corrosion processes associated with this linkage. This lack in knowledge prevents interpretation and limits the extrapolation of these statistical datasets for prediction purposes. Here, the mechanistic dependence of aluminum corrosion rate on salt loading is explored through complimentary experimental and theoretical analysis relating corrosion rate to electrolyte chemistry, volume and corrosion products. From these results a reaction pathway is proposed for the atmospheric corrosion of aluminum that accounts for the governing effects of CO2 and salt loading on corrosion rate. This reaction pathway provides a new perspective that highlights the importance of the formation and growth of dawsonite (NaAlCO3(OH)2), and the subsequent gettering of sodium from the electrolyte leading to the stifling of corrosion kinetics. This study highlights the importance of accounting for the dynamic physical and chemical state of the electrolyte during corrosion in process models and measurement techniques to better understand and predict atmospheric corrosion behavior. Corrosion of aluminium in a saline atmosphere hinges so much on carbon dioxide and sodium that it can become stifled after corrosion products build up. A team led by Eric Schindelholz at the Sandia National Laboratories in New Mexico, USA, took time-resolved gravimetric measurements of commercial aluminium loaded with sodium chloride and characterized the corrosion product weight and volume with time. The aluminium corroded by forming sodium aluminium carbonate - dawsonite—which trapped the sodium on the surface, leading to the salt water drying. This caused a decrease and, in some cases, stifled corrosion at the aluminium surface. While dawsonite has usually been ignored in aluminium corrosion, research into lesser-known corrosion reaction pathways may help us better understand and predict atmospheric and environmental corrosion.

Exposure testing was performed on CoCrFeMnNi equiatomic high entropy alloy (HEA) produced via directed energy deposition additive manufacturing in NaNO3-KNO3 (60–40 wt%) molten salt at 500 °C for 50 h to evaluate the corrosion performance and oxide film chemistry of the HEA. Potentiodynamic electrochemical corrosion testing, scanning electron microscopy, focused ion beam milling coupled with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy were used to analyze the corrosion behavior and chemistry of the HEA/nitrate molten salt system. The CoCrFeMnNi HEA exhibited a higher passive current density during potentiodynamic polarization testing than steel alloys SS316L and 4130 and the high-Ni alloy 800 H in identical conditions. The oxide film was primarily composed of a (Mn,Co,Ni)Fe2O4 spinel with a vertical plate-like morphology at the surface. Cr and Ni were found to be totally depleted at the outer surface of the oxide and dissolved in high concentrations in the molten salt. While Cr was expected to dissolve into the molten salt, the high concentration of dissolved Ni has not been observed with traditional alloys, suggesting that Ni is less stable in the spinel when Mn and Co are present.

This study investigates the mechanical and corrosion properties of as-built and annealed equiatomic CoCrFeMnNi alloy produced by laser-based directed energy deposition (DED) Additive Manufacturing (AM). The high cooling rates of DED produced a single-phase, cellular microstructure with cells on the order of 4 μm in diameter and inter-cellular regions that were enriched in Mn and Ni. Annealing created a chemically homogeneous recrystallized microstructure with a high density of annealing twins. The average yield strength of the as-built condition was 424 MPa and exceeded the annealed condition (232 MPa), however; the strain hardening rate was lower for the as-built material stemming from higher dislocation density associated with DED parts and the fine cell size. In general, the yield strength, ultimate tensile strength, and elongation-to-failure for the as-built material exceeded values from previous studies that explored other AM techniques to produce the CoCrFeMnNi alloy. Ductile fracture occurred for all specimens with dimple initiation associated with nanoscale oxide inclusions. The breakdown potential (onset of pitting corrosion) was similar for the as-built and annealed conditions at 0.40 VAg/AgCl when immersed in 0.6 M NaCl. Pit morphology/propagation for the as-built condition exhibited preferential corrosion of inter-cellular Ni/Mn regions leading to a tortuous pit bottom and cover, while the annealed conditions pits resembled lacy pits similar to 304 L steel. A passive oxide film depleted in Cr cations with substantial incorporation of Mn cations is proposed as the primary mechanism for local corrosion susceptibility of the CoCrFeMnNi alloy.

In this research, a novel methodology was developed to study corrosion under aqueous electrolyte drops ranging in diameter from 20-1000 mm, the most common drop sizes found in coastal marine environments. The objective of this work was to examine the relationship between drop size and corrosion attack of bare low carbon steel under simulated atmospheric marine conditions. A drop-on-demand inkjet printer was custom built by coupling a commercial jetting device with a programmable two-axis stage. Singular droplets of sodium chloride (6.2 M NaCl in H2O and 8.7 mM in ethanol) were deposited on polished 1010 steel coupons and then exposed to a 75% relative humidity environment for 24 hours. It was found that, in general, the volume loss increased with drop diameter according to a power law. Corrosion always occurred under drops greater than 150 μm in diameter, but was not consistently observed under drops in the 20-100 mm range. The fraction of drops that showed no corrosion increased with decreasing drop size below 100 μm. However, drops smaller than 100 μm that caused corrosion were found to have the greatest volume loss compared to their salt loading density. Therefore, the manner and geometry in which salt is deposited onto a low carbon steel surface, along with the mode of attack, will significantly affect corrosion loss. From a technical standpoint, these results suggest that service life prediction approaches, including accelerated testing, will more accurately simulate natural atmospheres if electrolyte geometry is taken into account for these materials.

This research focused on the development and use of a novel methodology to study corrosion under aqueous electrolyte drops ranging in diameter from 20–1000 μm, the most common deposited aerosol size range found in coastal marine environments. A drop-on-demand inkjet printer was custom built by coupling a commercial jetting device with a programmable two-axis stage. Singular droplets of sodium chloride solution were deposited onto steel and pure iron substrates with various surface finishes, followed by an isohumidity exposure for 24 hours. The volume loss increased with drop diameter according to a power law with an exponent of approximately 2 for highly polished steel and iron, increasing to 3 for iron with higher surface roughness. Attack was primarily filiform-like for the smallest drops, whereas deep, separate pits formed under the largest drops. Corrosion was not consistently observed under all drop sizes. The fraction of drops that showed no corrosion increased with decreasing drop size for all substrates. This behavior appears to have a strong dependency on the microstructure and surface finish. Corrosion initiation on 1010 steel was dominated by manganese sulphide inclusions when a mirror surface finish was maintained. For high purity iron, initiation was dominated by surface roughness. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.1171412jes] All rights reserved.

This paper is the second of two that examines between the hygroscopic behavior of sea salt aerosol proxies and the atmospheric corrosion of mild steel contaminated with them. In this work, artificial seawater (ASW) and MgCl2 were examined. The wetting and drying behavior of ASW was characterized by impedance measurements across an interdigitated electrode sensor. Steel coupons loaded with ASW and MgCl2 microparticles were subjected to isohumidity exposures for up to 30 days. The resulting damage was quantified by optical profilometry. The corrosion chemistry that developed was identified using EDS and Raman spectroscopy. Together, the results bring into question whether sea salt-contaminated surfaces ever dry in ambient outdoor environments. Sustained corrosion was detectable down to 11% RH for MgCl2 and 23% RH for ASW, with significant admittance of ASW deposits at

Three balance of systems (BOS) connector designs common to industry were investigated as a means of assessing reliability from the perspective of arc fault risk. These connectors were aged in field and laboratory environments and performance data captured for future development of a reliability model. Comparison of connector resistance measured during damp heat, mixed flowing gas and field exposure in a light industrial environment indicated disparities in performance across the three designs. Performance was, in part, linked to materials of construction. A procedure was developed to evaluate new and aged connectors for arc fault risk and tested for one of the designs. Those connectors exposed to mixed flowing gas corrosion exhibited considerable Joule heating that may enhance arcing behavior, suggesting temperature monitoring as a potential method for arc fault prognostics. These findings, together with further characterization of connector aging, can provide operators of photovoltaic installations the information necessary to develop a data-driven approach to BOS connector maintenance as well as opportunities for arc fault prognostics.

The hygroscopic behavior of soluble salts bears importance in many research fields including atmospheric sciences, corrosion, porous building materials, and pharmaceuticals. Several methods have been used to study deliquescence (solid to liquid) and efflorescence (liquid to solid) phase transitions of these salts. In this study, we measured the deliquescence and efflorescence RH values of single salt microparticles deposited on an interdigitated microelectrode sensor via electrical impedance. The salts examined were NaCl, LiCl, NaBr, KCl, and MgCl2. Measured values were in agreement with in situ optical microscopic observations and, with the exception of MgCl2, literature values. In the case of MgCl2, deliquescence occurred at 33% RH and 12-15% RH, with the latter range being previously unreported. The depressed deliquescence RH was hypothesized to be a result of the formation of a metastable MgCl2 hydrate. Incomplete efflorescence of MgCl2 was also observed after exposure to1.5% RH for up to 22 h due to formation of solid shells which trapped fluid. The phenomena elucidated by these results provide an explanation for the anomalous water retention and uptake behavior of MgCl2 below 33% RH reported elsewhere in the literature. The results presented in this study validate the use of this method as an alternative or complementary method for study of bulk-phase transitions of substrate-deposited particles across a broad RH range. These findings also demonstrate the utility of this method for detection of fluid trapping which cannot be directly ascertained by gravimetric and line-of-sight techniques commonly used in the study of hygroscopic particles.

This work is in support of a pilot program for the Corrosion Policy and Oversight Office within the Office of the Undersecretary for Acquisition, Technology and Logistics, Corrosion Policy and Oversight. The research and technological investigations within have several objectives. One is to support graduate student research and education in the field of corrosion. This objective is met by the training of graduate students in the Materials Science and Engineering discipline to conduct the research listed and the subsequent placement of a high portion of them in US DoD, national laboratory, governments and industry professional positions. A second objective is the conduct of research studies that will support the implementation of other Corrosion Policy and Oversight Office projects that have been completed or are in progress. A third objective is to plan and conduct targeted studies that within about a 2 year period have a significant probability of delivering products to DoD interested end users that could begin along a path to implementation.