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Atmospheric corrosion of metals is the most common type of corrosion which has a significant impact on the environment and operational safety in various situations of everyday life. Some of the common examples can be observed in land, water and air transportation systems, electronic circuit boards, urban and offshore infrastructures. The dew drops formed on metal surface due to condensation of atmospheric moisture facilitates corrosion as an electrolyte. The corrosion mechanisms under these droplets are different from classically known bulk electrolyte corrosion. Due to thin and non-uniform geometric thickness of the droplet electrolyte, the atmospheric oxygen requires a shorter diffusion path to reach the metal surface. The corrosion under a droplet is driven by the depletion of oxygen in the center of the droplet compared to the edge, known as differential aeration. In case of a larger droplet, differential aeration leads to preferential cathodic activity at the edge and is controlled by the droplet geometry. Whereas, for a smaller droplet, the oxygen concentration remains uniform and hence cathodic activity is not controlled by droplet geometry. The geometry of condensed droplets varies dynamically with changing environmental parameters, influencing corrosion mechanisms as the droplets evolve in size. In this review, various modelling approaches used to simulate the corrosion under droplet electrolytes are presented. In the efforts of developing a comprehensive model to estimate corrosion rates, it has been noted from this review that the influence of geometric evolution of the droplet due to condensation/evaporation processes on corrosion mechanisms are yet to be modelled. Dynamically varying external factors like environmental temperature, relative humidity, presence of hygroscopic salts and pollutants influence the evolution of droplet electrolyte, making it a complex phenomenon to investigate. Therefore, an overview of available dropwise condensation and evaporation models which describes the formation and the evolution of droplet geometry are also presented from an atmospheric corrosion viewpoint.

A new approach is proposed to numerically predict and study atmospheric corrosion for ranging droplet size distributions and the influence of the droplet geometry. The proposed methodology allows for a corrosion prediction based on observed droplet size distributions and droplet contact angles. A mechanistic finite element model, including oxygen transport and Butler-Volmer kinetics, is solved in order to obtain the current density as a function of the droplet geometry. This is done for a range of both droplet radii and contact angles. The computed corrosion current densities are then used as input for imposed droplet size distributions. This allows for a calculated material loss estimation for different distributions and electrolyte configurations and shows the extent of the impact of the droplet size distribution on atmospheric corrosion.

Corrosion prediction by multiscale modelling aims to achieve the required paradigm shift in the lifetime prediction of metals. Modelling of atmospheric corrosion, for example, based on Finite Element Modelling (FEM) requires an exact description of the boundary region between metal and electrolyte. This requires a radically different research approach for the electrolyte in contact with the metal surface. The critical issue is that most corrosion experiments in fundamental research are performed “in solution” under the assumption that the electrolyte layer is thick enough to approximate it as “infinite”, ignoring significant local effects introduced by dynamic electrolyte dimensions caused by droplets and puddles. In other words, a major part of the research in academia is not relevant to mimic the actual conditions encountered on the metal surface. To create accurate numerical models, we first and foremost needed to abandon this "infinite" and “stationary” approximation and consider dynamic and finite electrolyte dimensions. During atmospheric corrosion of metals, the evolution of the thin-film electrolyte thickness is the primary factor determining the corrosion rate. A full understanding the evolution of the electrolyte thickness and properties as a function of the key environmental parameters is yet to be achieved. A novel methodology has been developed to conduct experiments under a regulated environment to measure the film thickness evolution or individual droplets on an undisturbed metal surface [1]. Experimental results are compared with FEM models predicting both the electrolyte formation as well as the related corrosion. The heat transfer coefficient is noted as a critical parameter influencing both the film characteristics and the resulting corrosion rate. This model was tested in case of cut-edge corrosion of galvanized steel. Combining the in-house MiTReM (Multi ion Transfer Reaction electrochemical model) with the electrolyte film thickness model, we could see that the corrosion rates become very critical in the range of 20 µm [2]. The next step was to go into the dimension of droplets. A thorough literature review [3] was made and published around modelling of droplet formation and corrosion, forming a base for further progress and improvements. The literature study also highlighted that the topic of droplet formation is relatively new within the corrosion research community. A new approach [4] was proposed to numerically predict and study atmospheric corrosion under droplet size distributions. The proposed methodology allows for a corrosion prediction based on observed droplet size distributions and droplet contact angles. A mechanistic finite element model, including oxygen transport and Butler-Volmer kinetics, is solved to obtain the current density for the droplet geometry. This is done for a range of both droplet radii and contact angles. The computed corrosion current densities are then adapted onto imposed droplet distributions for a calculation of overall corrosion current. This allows for a calculated material loss estimation for different distributions and electrolyte configurations and shows the extent of the impact of the droplet distribution on atmospheric corrosion. This model is validated by comparing with experiments introducing droplet-induced corrosion in a lab scale reactor that allows monitoring in parallel droplet geometry and corrosion as function of induced thermal cycles in a controlled atmosphere. Keywords: Atmospheric corrosion, FEM modelling, thin electrolyte films, droplets References: [1] B.G. Koushik , N. Van den Steen, H. Terryn, Y. Van Ingelgem “Investigation of the importance of heat transfer during thin electrolyte formation in atmospheric corrosion using a novel experimental approach” Corrosion Science .vol 189, 2021.109542, https://doi.org/10.1016/j.corsci.2021.109542 [2] M. Saeedikhani, N. Van Den Steen, Nils, S. Wijesinghe, S. Vafakhah, , H. Terryn, D. Blackwood, Daniel “Moving Boundary Simulation of Iron-Zinc Sacrificial Corrosion under Dynamic Electrolyte Thickness Based on Real-Time Monitoring Data” Journal of Electrochemical Society Vol 167,4, 2020,1503. DOI: 10.1149/1945-7111/ab7368 [3] B.G. Koushik, N. Van den Steen, M. Haile Mamme, Y. Van Ingelgem, H. Terryn “Review on modelling of corrosion under droplet electrolyte for predicting atmospheric corrosion rate” Journal of Materials Science & Technology vol 62, 30 January 2021, 254. https://doi.org/10.1016/j.jmst.2020.04.061 [4] N. Van den Steen, Y. Gonzalez-Garcia, J.M.C Mol, H. Terryn, Y. Van Ingelgem “Predicting the effect of droplet geometry and size distribution on atmospheric corrosion” Corrosion Science (2022) https://doi.org/10.1016/j.corsci.2022.110308

Business-to-business transactions include several processes that can be digitized by buyers and suppliers. While prior studies have examined the performance impacts of using digital technologies, they have not investigated the alignment of such digitization between transacting parties. In this paper, we empirically examine the use of different market-based digital technologies by buyers and suppliers for these processes, and analyze the extent to which the digitization of different processes is aligned between transacting buyers and suppliers. Our field study is based on surveys of transacting agents in 174 buyer-supplier dyads about their use of digital technologies. The results indicate that there are misalignments for some processes in both the specific digital technologies buyers and suppliers use, and in the extent to which each of them uses digital technologies. By addressing these misalignments, buyers and suppliers could potentially realize greater benefits from digitized transaction processes.

The Devanathan-Stachurski-cell is the most commonly used electrochemical technique for the investigation of the hydrogen trapping properties of a material. In this set-up, a flux of hydrogen atoms diffuses through a metal membrane under study. The atoms are subjected to the heterogeneities naturally present in the lattice of the metal, acting as traps. This matter influences the diffusion of hydrogen, which is strongly microstructure related. In this paper, we apply a numerical model to different iron-alloys to determine the hydrogen trapping parameters characterizing the materials. We highlight the complexity of the hydrogen trapping mechanism which needs to be further investigated.

Atmospheric corrosion is a complex problem, essentially an electrochemical process under confined thin electrolyte layers. Predictions require better mechanistic models to understand the underlying fundamental subprocesses on a microscopic level. We developed a mechanistic multi-ion transport and reaction model (MITReM) that considers time-dependent accumulation of concentrations in thin (NaCl) confined electrolyte layers. The model predicts local concentration and electrolyte potential distributions, from which corrosion rates are derived. Simulations in the confined dynamic film show that the chloride accumulation causes a deviation from the reverse proportionality of the corrosion current with the film thickness below films of 10 μm . The oxygen distribution and local corrosion current densities demonstrate that the contribution of the edge effect decreases for thinner electrolyte layers. The influence of the electrode geometry on the current density also decreases with decreasing film thickness. These qualitative insights are essential for the development of atmospheric corrosion prediction tools and aid in the design and interpretation of electrochemical techniques for confined thin film electrolytes.

The application of mechanistic electrochemical models is limited to small scale or short term simulations because of the high computational cost. In this work a model is developed to decrease the computational time by applying a dimension reduction based on an averaging theorem. In an example, a two-dimensional problem is reduced to a subsystem of coupled one-dimensional problems. For thin electrolyte films, the deviation between the two models becomes negligible; at an electrolyte thickness of 5% of the electrode width, the underestimation error drops below 10%. We can conclude that the dimension reduction is appropriate when dealing with thin electrolyte layers such as in atmospheric corrosion.

The electrolyte film thickness condensation and evaporation is an important parameter for complexity of atmospheric corrosion. Atmospheric corrosion rate of zinc at the west coast of Singapore was measured for one year using an electrical resistance monitoring system. The analysis of the data reveals that significant corrosion rates only occur at specific hours on dry days. The beginning of this period corresponds to falling temperature and rising relative humidity resulting in the formation of a film of moisture on the zinc surface and the end corresponds to a point that this film dries as the temperature increases. This finding allowed the drying rate of the moisture film to be estimated for input into a moving boundary simulation model of the galvanic corrosion in scratched and zinc coating samples. The simulation results showed that the maximum corrosion rate occurs at electrolyte thickness of about 8 μm. Moreover, the simulation suggested that cut-edge is a more harmful defect than scratch, which was confirmed by the appearance of iron corrosion products on atmospheric exposed cut-edge samples whereas scratched samples were not corroded after one week of exposure. Finally, moving boundary simulation allowed to predict the changes to the geometry of the corroding electrodes.

Atmospheric corrosion and accelerated corrosion tests are inherently subjected to dynamic film variations. Modeling and understanding these variations in combination with corrosion processes is therefore of high relevance. From a modeling point of view, accelerated corrosion tests have the advantage of well defined conditions which can be used as an input for the models. From experimental point of view, these models can be of high value because notwithstanding the defined conditions, experimental results of accelerated tests are often difficult to reproduce exactly. This is where models may be able to help in the understanding of the phenomena. In [1] a model to predict the time dependent film thickness was presented, taking into account the relative humidity, temperature, substrate material and the presence of hygroscopic salts. A simple corrosion model was used to calculate a simulated corrosion depth. A simple corrosion model allows to focus on the effect of the film thickness. Based on this work, we present experimental and simulated corrosion depths in accelerated corrosion tests. The corrosion depth is measured using AirCorr loggers. The electrical resistance of a thin metal track is measured and registered over time. As the corrosion processes will decrease the cross-sectional area of the track, the resistance will increase. A reference electrode provides the possibility to compensate for temperature effects. We focus on corrosion depths as measurements on the liquid film thickness itself are not directly available in literature. Several cycles VDA, N-VDA, GMW, etc are simulated and compared with measurements considering a iron substrate. An exact match between the experiments and simulations is not expected, as important phenomena are not (yet) included in the model. For example, run-off effects on the film thickness and the amount of salt on the surface, effects of the corrosion products on the corrosion processes (passivation, blocking) and on the film thickness (hygroscopic effects). What we expect to see similar trends between measurement and simulation, linked with the electrolyte thickness. We study also the effects of different parameters on the results. During the saltspray, a constant film thickness is assumed. In the figure we show the simulated corrosion depths obtained in a partial N-VDA test when different film thicknesses during this spraying phase (50micron, 100micron, 150micron) are assumed. These results are compared with experimental data. Based on the comparison, conclusions are formulated about the accuracy of the model, the applicability, the shortcomings and the points of interest for future work are identified. [1] Van den Steen, N., et al. "An integrated modeling approach for atmospheric corrosion in presence of a varying electrolyte film." Electrochimica Acta 187 (2016): 714-723. Figure 1

Atmospheric corrosion predictions for design and engineering require time-consuming exposure experiments and provide only a rough estimation of the corrosion rate. At the other hand, the multi-scale problem of atmospheric corrosion involves thin film electrolytes, evaporating -highly concentrated- solutions where local variations are controlling the overall process. Conventional (bulk) electrochemistry is therefore inadequate for the quantification or even the understanding of atmospheric corrosion mechanisms. The Multi-Ion Transport and Reaction Model (MITReM) is the link between the underlying electrochemical physics and corrosion rate predictions. With a numerical finite element method we simulate the effect of electrolyte thickness, electrode geometry and NaCl concentrations during evaporation in ultra-thin (sub 50 µm) electrolytes. The zinc corrosion rate in these thin films is function of the calculated local, time-dependent variations in the electrolyte. The two-dimensional simulations demonstrate the geometrical effect on the local current density and its deviation from simple limiting current equations. The time-dependency also describes the evolution of the electrolyte concentrations and the current transients. The simulated formation of corrosion products is compared with experimental measurements of the initial oxidation of zinc in humidified air. The evaporation/condensation dynamics of ultra-thin films in combination with complex electrolyte compositions introduces high computational costs. The application of these models is therefore limited to small or highly simplified geometries. It also implies limits on the time scales that can be simulated. To reduce the computational cost a decoupling method is developed to decrease the number of finite elements and hence the number of unknowns in the system. The transport in the direction of the electrode plane and the perpendicular direction are decoupled. The decrease in computational cost enables numerical simulations of complex electrochemical systems on extended complex geometrical shapes and for longer time scales. The decoupling method has an additional benefit; the complexity of moving triangular meshes is avoided since the electrolyte height geometry is a combination of one-dimensional meshes. The reduced decoupling model is compared with the full-scale simulations of a galvanic couple (zinc-steel). The results show that the decoupled model approaches the full-scale model for thinner electrolyte layers. This observation is supported by the evolution of the edge-effect, illustrated with two-dimensional simulations. In thin layers, the minimal accuracy loss is acceptable in comparison to the gain in computational time. The use of the dimension reduction for the simulation of atmospheric corrosion conditions is therefore justified. The presented work improves the developments of quantification and prediction tools for atmospheric corrosion and electrochemistry in non-conventional (micro-)setups. A better description and prediction of the corrosion process is obtained in ‘dynamic’ thin electrolyte layers.

Several electrochemical energy technologies (batteries, fuel cells, supercapacitors, …) have been developed. Many have been commercialized, but a large number is still under development. Systems are optimized in terms of life time, performance and cost, and new systems are being designed. The electrode and electrolyte materials must have the required characteristics with respect to ionic and/or electronic transport properties, electrochemical properties, chemical stability, compatibility with other materials, thermal properties, … To be able to tailor the energy materials, characterization of their electrochemical behavior is of prime importance. The electrochemical behavior is influenced by a high number of processes, all occurring at a different rates. Knowing the quantitative mechanism of an electrochemical system is an essential step in the prediction of its behavior. Electrochemical Impedance Spectroscopy (EIS) is the designated experimental technique to that purpose. Yet, identifying and quantifying the characteristic parameters of the reactions governing the system from the experimental EIS results is complex. In our group, we developed a new approach to EIS [1-4]. It consists of an integrated measuring and modelling methodology based on an odd random phase multisine excitation signal (ORP-EIS) and on mathematical modeling via parameter estimation. The mathematical model representing the system is formulated on the relations between the input and output to the system, including the model parameters. These parameters stand for inherent properties of the system; they describe the stability and control the behavior of the system. This methodology is applied in this paper for the investigation of two types of energy materials. The first application concerns Lithium Ion Batteries (LiB’s), used for Hybrid Electrical Vehicles (HEV’s). This study contributes to the quest for electrode materials with high cycling stability. Li4Ti5O12 (LTO) has been proposed as a promising candidate to replace the market-dominating carbon-based anodes (graphite and amorphous carbon). Aged batteries are post-mortem analyzed by EIS to have insight into the origin of the aging phenomena. Reliable impedance modelling is performed to quantitatively address the origin of the rising impedance. The second application is in the field of Solid Oxide Fuel Cells (SOFC’s). Solid electrolytes exhibit electrical conductivity due to ionic conduction through the crystalline structure. For their use in SOFC’s, a sufficient electrical conductivity is achieved at high temperatures. To reduce the application temperature, research is dedicated to increase the conductivity of the ceramic material by heterogeneous doping or reducing the grain size or the film thickness. How the microstructure of the material affects the electrical conduction is still a matter of debate in literature. A good understanding of the relationship between microstructure and ion conductivity would open the possibility to engineer advanced materials for SOFCs. Oxides with fluorite structure are measured by EIS at low to high temperatures, varying the oxygen flow. Thin film and bulk electrolytes of doped ceria with different grain size and dopants are investigated. [1] Y. Van Ingelgem, E. Tourwé, O. Blajiev, R. Pintelon, A. Hubin, Electroanalysis 21(6) (2009) 730 [2] T. Breugelmans, J. Lataire, T. Muselle, E. Tourwé., R. Pintelon, A. Hubin, Electrochimica Acta 76 (2012) 375 [3] L. Fernández Macía, M. Petrova, T. Hauffman, T. Muselle, T. Doneux, A. Hubin, Electrochimica Acta, 140 (2014) 266 [4] L. Fernández Macía, M. Petrova, A. Hubin, Journal of Electroanalytical Chemistry, 737 (2015) 46

Lithium-ion battery (LIB) technology further enabled the information revolution by powering smartphones and tablets, allowing these devices an unprecedented performance against reasonable cost. Currently, this battery technology is on the verge of carrying the revolution in road transport and energy storage of renewable energy. However, to fully succeed in the latter, a number of hurdles still need to be taken. Battery performance and lifetime constitute a bottleneck for electric vehicles as well as stationary electric energy storage systems to penetrate the market. Electrochemical battery models are one of the engineering tools which could be used to enhance their performance. These models can help us optimize the cell design and the battery management system. In this study, we evaluate the ability of the Porous Electrode Theory (PET) to predict the effect of changing positive electrode density in the overall performance of Li-ion battery cells. It can be concluded that Porous Electrode Theory (PET) is capable of predicting the difference in cell performance due to a changing positive electrode density.