Galvanized Steel Substrates Research Articles

Effect of cerium nitrate concentration on corrosion protection of hybrid organic/inorganic Si/Zr sol-gel coating applied on hot-dip galvanized steel

This present work investigates the corrosion performance of hybrid organic/inorganic Si/Zr sol-gel doped with various cerium nitrate concentrations applied on hot-dip galvanized steel. The Si/Zr sol-gel solution was prepared from tetraethyl orthosilicate (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MAPTMS), and zirconium(IV) propoxide (ZTP). The effect of the addition of cerium nitrate was evaluated by electrochemical impedance spectroscopy (EIS) versus immersion in 0.1 M NaCl solution and salt spray test. The results indicated that cerium nitrate contents affected the protective behavior of sol-gel coating in long term. Additionally, the sol-gel doped with 650 ppm Ce (III) presented the optimal corrosion protection of the sol-gel coating formed on hot-dip galvanized steel substrate.

Reactivity of organogermanes with ZnO substrate

Germanium (Ge)-based thin film through sol-gel coating technology can be a suitable alternative like their silane analogue to develop metal-free and solvent-free corrosion protective coating with additional functional properties for galvanized (GI) steel. In this work, adsorption mechanism and reactivity of functionalized (by functional groups such as epoxy, amine, and mercapto) and non-functionalized - organogermane alkoxides towards GI steel substrate were investigated using density functional theory (DFT), where (ZnO)12 cluster was adopted as model of GI steel and other ZnO substrate. Calculated global reactivity parameters of organogermanes suggested that functionalized organogermanes were more efficient for corrosion protection of ZnO substrate. Adsorption process was exothermic and free energy change (ΔG) in adsorption process lied between 27.4 kcal/mol and 51.9 kcal/mol which confirmed adsorption potentiality of organogermanes. Adsorptions of functionalized organogermanes were much more exothermic (∼50 kcal/mol) than that of non-functionalized one (∼27 kcal/mol) which suggested chemisorption of functional organogermane molecules. Geometry, MOs, and charge analyses of adsorbed structures further supported that all functional organogermanes chemisorbed on the GI steel. Multiple bonds were formed at the interface. Presence of heteroatoms, like O/N/S in organogermane molecules assisted in formations of chemical bonds with Zn atoms of the substrate. Ge center took hypervalency and formed non-classical Ge-O bond with O atom of the substrate in all functional organogermanes. Formation of OH—O hydrogen bonds were also observed at the interface. These Ge-O and OH—O bond formation played key roles in the interface and manifested stronger interaction, making functional organogermane alkoxides suitable for coating applications. Stronger adsorptions of functional organogermanes could be interpreted in terms of higher highest occupied molecular orbital (HOMO) energies and lower HOMO-lowest occupied molecular orbital (LUMO) gap values for functionalized organogermanes which favored the electron donation from the HOMOs of functionalized organogermanes to the LUMOs of (ZnO)12 cluster.

Influence of solution pH on the structure formation and protection properties of ZnAlCe hydrotalcites layers on hot-dip galvanized steel

This study aims at investigating the influence of the solution pH and cerium cations on the formation and the anti-corrosion properties of hydrotalcite (HT) layers grown by the “in-situ” synthesis method on hot-dip galvanized steel substrate (HDG) in the pH range of 11–13. The anti-corrosion properties of all ZnAlCe HT layers were recorded by electrochemical tests and compared to bare HDG substrate during exposure to 0.1 M NaCl. The pH of precursor baths significantly impacted the orientation, chemical composition, microstructure of HT layers, and the intercalation of cerium cations inside HT with significant differences in their anti-corrosion performance. The ZnAlCe HT, prepared at pH 12, showed an obviously enhanced corrosion protection for HDG substrate compared to the other two HT layers. The anti-corrosion mechanism of HT layers as well as the role of cerium inside HT network was investigated and discussed in this research.

Investigation of Superhydrophobic and Anticorrosive Epoxy Films with Al2O3 Nanoparticles on Different Surfaces.

In this study, superhydrophobic epoxy coatings were prepared on different surfaces by utilizing hydrophobized aluminum oxide (Al2O3) nanoparticles. The dispersions containing epoxy and inorganic nanoparticles with different contents were coated on glass, galvanized steel, and skin-passed galvanized steel substrates by the dip coating method. The contact angles of the obtained surfaces were measured via a contact angle meter device, and the surface morphologies were analyzed by utilizing scanning electron microscopy (SEM). The corrosion resistance was performed in the corrosion cabinet. The surfaces showed superhydrophobic properties with high contact angles greater than 150° and self-cleaning properties. SEM images indicated that the surface roughness increased as the concentration increased by the incorporation of Al2O3 nanoparticles into epoxy surfaces. The increase in surface roughness was supported by atomic force microscopy analysis on glass surfaces. It was determined that the corrosion resistance of the galvanized and skin-passed galvanized surfaces increased with the increase of Al2O3 nanoparticle concentration. It has been shown that red rust formation on skin-passed galvanized surfaces was reduced, although they have low corrosion resistance due to roughening on their surfaces.

Water-Repellent Galvanized Steel Surfaces Obtained by Sintering of Zinc Nanopowder.

Galvanized steel surfaces are widely used in industry as a solution to prevent corrosion of steel tools that operate in outdoor or corrosive and oxidative environments. These objects are coated with a zinc protective layer deposited by hot dip galvanization. Turning the surface of galvanized steel tools into superhydrophobic may lead to very useful functionalities, although it may be a difficult task, because the preservation of the thin zinc layer is a claim. We propose herein the use of a bottom-up approach based on sandblasting, followed by sintering of zinc nanoparticles on the galvanized steel substrate, which allowed us to produce a zinc-made hierarchical structure required for superhydrophobicity. These samples acquired a double-scale structure that led to superhydrophobicity when they were later hydrophobized with a thin fluoropolymer layer. We found that sandblasting might be useful but not mandatory, unlike the sintering process, which was essential to reach superhydrophobicity. We found that, under certain experimental conditions, the surfaces showed outstanding water-repellent properties. We observed that the sandblasting on galvanized steel caused more damage than the sintering process. Sintering of low-melting-point metal nanoparticles was revealed as a promising strategy to fabricate functional metallic surfaces.

Application of a new strategy for time-efficient laser treatment of galvanized steel substrates to improve the adhesion properties

Laser structuring to improve the adhesion properties of steel substrates in fiber-metal laminates offers many advantages that are highly suitable for modern industrial requirements. Maintenance and energy costs are relatively low, it is easy to automate, and there are no by-products such as chemicals or abrasives to dispose of or recycle. This makes laser structuring a particularly environmentally friendly process, which is nowadays more important than ever. On the other hand, the process time for laser structuring is much higher than for chemical pre-treatment, for example. In past studies, the time and cost efficiency of the laser structuring process has tended to play a minor role. However, there are approaches in which laser structured surfaces are adapted to the shear stress peaks occurring within the adhesive layer, thus requiring only partial structuring of the area to be bonded, potentially saving process time. In this experimental study, electrolytically galvanized steel substrates were partially laser structured to match the shear stress distribution and then bonded to a carbon fiber-reinforced plastic. The adhesion properties achieved were characterized using shear tensile tests and compared with the properties of the fully structured ones. With the partial laser structuring, a saving of 66 % of the conventional process time was achieved while maintaining 95 % of the same shear strength.

Improvement of anti-corrosion performance (surface and near the cut edge) and mechanical properties of epoxy coatings modified with nano, micro and hybrid ZnO particles

Composites were formed by incorporating nano, micro and hybrid-ZnO particles into the epoxy matrix at the same loading levels (3%) and applied at 90 μm thickness on the galvanized steel substrate using a film applicator in this study. The improvement in anti-corrosion performance and mechanical and physical properties of the composite coatings were evaluated using various tests and techniques such as salt-spray, electrochemical impedance spectroscopy, nanohardness, microscratch, cross-cut, bending, Fourier transform infrared spectroscopy, thermogravimetric and Scanning electron microscopy. The corrosion performance of the composite coatings near the cut edge is discussed in detail as well as on the surface of galvanized steel. The results show that the addition of all ZnO particles has a positive effect on the corrosion resistance and mechanical properties of the coatings. The addition of nano, micro and hybrid ZnO particles increased the hardness of the composites by 52, 37 and 56%, respectively, compared to the neat epoxy. Although the cathodic protection performance is weakened near the cut edge due to the loss of Zn after thermal cutting, high barrier protection was provided with composite coatings, especially micro ZnO/Epoxy composite coating.

Corrosion resistance of a water-borne resin doped with graphene derivatives applied on galvanized steel

The present work reports the effect of adding Graphene Oxide (GO) and reduced Graphene Oxide (rGO) in the corrosion protection provided by a water-borne resin applied on a galvanized steel substrate. Three concentrations, 0.05, 0.1 and 0.15 (all wt%) were tested. The results were markedly affected not only by the concentration of particles but also by their nature. Although the zeta potential values suggested good dispersibility of the particles in the resin, certain aggregation was observed, mainly in rGO 0.1 wt% and rGO 0.15 wt% formulations. The electrochemical impedance spectroscopy (EIS) technique characterised the free films' transport properties. The results suggested that the aggregation strongly influenced the film morphology. The rGO 0.1 wt% and rGO 0.15 wt% formulations exhibited percolating pores that facilitated the electrolyte uptake through the films. The EIS technique was also used to study the protective performance of the films when applied to the metallic substrate. The results confirmed the harmful effect of the particle's aggregation. The results were interesting for the rGO 0.05 wt% system, which displayed long-lasting protection properties. This performance was explained considering its good barrier properties and the zinc surface passivation by the generation of zincite, ZnO.

Epoxy resin/graphene nanoplatelets composites applied to galvanized steel with outstanding microwave absorber performance

Abstract The necessity of new electromagnetic interference shielding materials has expanded scientific research, especially with regard to microwave frequency range (X-band). In this context, polymer-based composites with nanoparticles – such as graphene – are promising electromagnetic interference shielding materials. In this work, epoxy resin/graphene nanoplatelets (NPG) composites with 0.10, 0.25 and 0.5% w/w were developed and applied to galvanized steel substrates. Dynamic-mechanical tests showed that the addition of NGPs increased the resin rigidity due to molecular restrictions of the organic chains imposed by the NPG. With the increase of the NPG concentration to 0.50%, the impact strength and the adhesion of the composites significantly decreased due to the formation and propagation of large cracks, followed by delamination. The epoxy resin sample containing 0.25% NPG presented the best microwave absorber performance with an increase of 48% in the attenuated energy and 80% in the reflection loss, respectively. Moreover, this sample extended the microwave absorption range to 10 GHz.

Efficiency of Zinc Oxalate Conversion Coating in Protecting Galvanised Steel Substrates Exposed to Alkaline Solutions from Corrosion

Efficiency of Zinc Oxalate Conversion Coating in Protecting Galvanised Steel Substrates Exposed to Alkaline Solutions from Corrosion

Protective Efficiency of ZrO2/Chitosan “Sandwich” Coatings on Galvanized Low-Carbon Steel

Enhanced corrosion efficiency of low-carbon steel was achieved by newly developed hybrid multilayers, composed of low-carbon steel coated with an electrodeposited zinc sublayer (1 µm), a chitosan (CS) middle layer and ZrO2 coating by the sol–gel method (top-layer). The middle chitosan layer was obtained by dipping galvanized steel substrate in 3% tartatic acid water solution of medium molecular-weight chitosan, composed of β-(1–4)-linked D-glucosamine and N-acetyl-D-glucosamine with a deacetylation degree of about 75–85% (CS). The substrates were dipped into CS solution and withdrawn at a rate of 30 mm/min. One part of the samples with the CS layer was dried at room temperature for 2 weeks, and another part at 100 °C for 1 h, respectively. After CS deposition treatment, the substrates were dipped into an isopropanol sol of zirconium butoxide with small quantity of polyethylene glycol (PEG400). The dipping-drying cycles of the ZrO2 coatings were repeated three times. After the third cycle, the final structures were treated at 180 °C. The samples were denoted as T25, which consists of the CS middle layer, and dried at RT and T100 with the CS middle layer treated at 100 °C, respectively. The samples were characterized by means of differential thermal analysis (DTA-TG), XRD analyses, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Hydrophobicity properties were evaluated by measuring the contact angle with a ramé-hart automated goniometer. Two electrochemical tests—potentiodynamic polarization technique (PD) and electrochemical impedance spectroscopy (EIS)—have been used to determine the corrosion resistance and protective ability of the coatings in a 5% NaCl solution. The results obtained by both methods revealed that the applied “sandwich” multilayer systems demonstrate sacrificial character and will hopefully protect the steel substrate in corrosion medium containing chloride ions as corrosion activators. The newly obtained hybrid multilayer coating systems have dense structure and a hydrophobic nature. They demonstrated positive effects on the corrosion behavior at conditions of external polarization independent of their various characteristics: morphology, grain sizes, surface roughness and contact angle. They extend the service life of galvanized steel in a chloride-containing corrosion medium due to their amorphous structure, hydrophobic surface and the combination of the positive features of both the chitosan middle layer and the zirconia top layer.

Microcapsule/silica dual-fillers for self-healing, self-reporting and corrosion protection properties of waterborne epoxy coatings

Smart anticorrosive coatings were prepared by adding microcapsules and silica nanoparticles (SNs) in waterborne epoxy matrix and applied on galvanized steel substrates. The microcapsules encapsulated crystal violet lactone (CVL), epoxy monomer and phenyl acetate in methyl methacrylate polymer shell, so that the self-healing and self-reporting functions can be simultaneously realized. SNs can trigger the chromogenic reaction of CVL, while improving the corrosion protection properties of the composite coatings. The comprehensive properties of the coatings were investigated as a function of the weight ratio of CVL/epoxy monomer in microcapsules, the filling content of SNs and microcapsules, as well as the change of pH value. The corrosion current density of the composite coatings decreased with the SNs content and increased with the microcapsule content. Smart coatings with corrosion current density of 2.91 × 10−12 A cm−2 were achieved by adding 15 wt% microcapsules and 15 wt% SNs in epoxy matrix.

Zr-based conversion coating on Zn and Zn-Al-Mg alloy coating: Understanding the accelerating effect of Cu(II) and NO3−

The reactivity of a Zn-Al-Mg galvanized steel substrate was monitored during a two-step conversion coating sequence with an alkaline pretreatment followed by conversion coating with hexafluorozirconic acid (H2ZrF6). The main effect of alkaline pretreatment was to remove initial oxides and to selectively dissolve Al, limiting the dissolution of Al in the zirconate bath. The commercial alkaline cleaner dissolved Mg from the MgZn2 intermetallic phase. The effect of NO3− and Cu(II) on the reactivity of a commercial Zn-Al-Mg alloy coating was investigated in H2ZrF6, simulating a Zr-based conversion coating process. NO3− served as an oxidant which enhanced the production of OH− leading to a more consequent ZrO2 deposition. Cu(II) underwent a displacement reaction with Zn (0) to form Cu(0) which catalyzed the reduction of NO3− and H+. The interplay between activation and passivation was demonstrated by the occurrence of oscillations in the both NO3− and Cu(II) containing electrolyte under certain conditions.

Effect of organic additives in fluoacid-based Ti and Zr-treatments for galvanized steel on the stability of a polymer coated interface

The bonding properties of zirconium- and titanium-based conversion coatings were evaluated using model conversion solutions of H2ZrF6 and H2TiF6 with addition of various organic additives (PAA, PVA, PVP). Macroscopic testing techniques such as contact angle and pull-off adhesion measurements were performed on galvanized steel sheets. Complementary to this, molecular studies were performed on model zinc substrates using ATR-FTIR in the Kretschmann configuration. The macroscopic and molecular approaches showed a good correlation demonstrating ATR-FTIR in the Kretschmann configuration to be a valuable tool to gain fundamental insights in metal oxide-polymer interfacial phenomena. Zirconium-treated galvanized steel substrates were shown to have a higher bonding affinity for the polyester coil coat primer than titanium-treated galvanized steel substrates. The presence of organic additives did not further improve the bonding properties. Yet, organic additives initially improved the interfacial stability of titanium-treated substrates. However, on the long term, organic additives are shown to be detrimental for polyester coil coat adhesion. This adverse effect of organic additives on the long term was assigned to its selective dissolution during immersion and was most pronounced for titanium-treatments. The limited effect of organic additives in case of zirconium-treatments was attributed to the higher portion of chemical interfacial bonds, as well as its tendency for crosslinking reactions causing entanglement of polymeric compounds in the zirconium oxide structure.

Mechanical Behavior and Damage of Zinc Coating for Hot Dip Galvanized Steel Sheet DP600

Advanced high strength galvanized steel sheet has been one of the dominant materials of modern automotive panels because of its outstanding mechanical properties and corrosion resistance. The zinc coating thickness of hot dip galvanized steel sheet is only about 10–20 μm, which is a discarded object on the macro level. However, it is obvious to damage and impact on stamping performance. Therefore, this paper takes zinc coating as the research object and builds its mechanical constitutive model based on a nano-indentation test and dimensional analysis theory. We separated the zinc coating from the galvanized steel substrate and constructed a sandwich material model by introducing a cohesive layer to connect the zinc coating and the steel substrate. We obtained the interface binding energy between the zinc coating and the steel substrate through the nano-scratch test. The accuracy of the model is verified by the finite element analysis of hemispherical parts. We used the five-layers element model with 0 thickness cohesive layer to simulate the zinc coating damage of galvanized steel sheet. The hemispherical part drawing experiment is used to verify the feasibility of the finite element analysis results. The results demonstrate that it is more accurate to consider the finite element numerical simulation of the zinc coating, introducing the cohesive element to simulate damage between the coating and the substrate. Drawing depth, stamping force, and the strain of the numerical simulation are closer to the experimental results.

New Triazole and Isoxazole Compounds as Corrosion Inhibitors for Cu-Ni (90/10) Alloy and Galvanized Steel Substrates

Three organic compounds containing azole rings 1-benzyl-4-phenyl-1H-1,2,3-triazole (I1), 5-phenyl-3-propylisoxazole (I2), and 3,5-diphenylisoxazole (I3) were synthesized and characterized as corrosion inhibitors on galvanized steel and copper-nickel (Cu-Ni, 90/10) substrates. The three tested azole inhibitors acted as corrosion inhibitors on galvanized steel in the presence of real cooling water used as electrolyte. Electrochemical performance indicated that the presence of heteroatoms, such as N and O, with free pair electrons, the chain length, and the aromatic ring plays an important role in the capacity to inhibit corrosion of galvanized steel. 3,5-diphenylisoxazole (I3) has the best inhibition activity with jcorr of 2.04 × 10−7 (5 ppm), 7.57 × 10−8 (10 ppm), and 1.73 × 10−8 (20 ppm) A cm−2, followed by compounds I1 and I2. The synthesized compounds are comparable or even higher than the electrochemical performance of commercial inhibitor tolyltriazole (TTA, jcorr = 3.06 × 10−8 A cm−2). Conversely, for Cu-Ni (90/10) substrates, commercial TTA with 20 ppm displayed the lowest corrosion current densities (jcorr = 3.20 × 10−8 A cm−2) through a characteristic anodic pseudo-passivation; however, pits were observed after ~550 mVAg/AgCl. In contrast, the synthesized compounds tended to suppress anodic copper dissolution at positive potentials but, in the best case, displayed greater corrosion rates I3 (1.463 mils per year (MPY)), I2 (1.515 MPY), and I1 (0.677 MPY) in comparison with TTA (0.091 MPY). The low inhibition efficiency (IE) of synthesized compounds is correlated to the weak absorption on the copper surface.

Combinatorial Studies into the Effect of Thermally Inter-Diffused Magnesium on the Kinetics of Organic Coating Cathodic Delamination from Zinc Galvanized Steel

This paper describes a high-throughput study into the role of Mg in preventing corrosion driven coating disbondment of organic coatings from Zn-Mg alloy galvanized steel. A graded Mg wedge is applied to a hot-dip zinc galvanised steel substrate using physical vapour deposition, and subsequently annealed to produce metallic inter-diffusion and formation of Mg2Zn11 intermetallic. An overcoat of electrically insulating polyvinyl butyral (PVB) is applied and corrosion is initiated from a penetrative coating defect using an aqueous electrolyte. The variation in Mg coating weight across the wedge facilitates a systematic investigation of the effect of Mg on Volta potential and the rate of corrosion driven cathodic coating disbondment using scanning Kelvin probe (SKP) potentiometry. The rate of cathodic disbondment is shown to decrease rapidly even at very low Mg coating weight (corresponding to 25 nm thickness before annealing). The results are explained in terms of the galvanic polarity of the corrosion cell formed between Zn exposed at the defect site, and the intact Zn-Mg layer at the metal-organic coating interface.

Assessment of Self-Healing Epoxy-Based Coatings Containing Microcapsules Applied on Hot Dipped Galvanized Steel

This study focuses on the design, development and validation of two coating systems for corrosion protection of hot dip galvanized steel substrates. The coatings consist of epoxy-based resin reinforced with core-shell microcapsules, either cerium oxide or cuprous oxide core and a polymeric shell doped with cerium ions. The effect of the modification of the epoxy resin with a liquid rubber polymer has also been studied. Corrosion studies via electrochemical impedance spectroscopy (EIS) revealed that the coatings have enhanced barrier properties. Moreover, EIS studies on coatings with artificial scribes, demonstrated an autonomous response to damage and a self-healing effect. Heat-induced material re-flow has also been observed after exposure to temperature higher than the Tg of the system, which offered an additional self-healing mechanism, partially inhibiting the underlying corrosion processes when the liquid rubber is present in the system.

Application of Scanning Kelvin Probe in the Study of Protective Paints

Industrial coatings are composed of layers of different polymers (top coats, primers) containing pigments, corrosion inhibitors, and fillers as well as additives. For corrosion protection, it is vitally important to preserve the strong adhesion and long-term stability of the metal-polymer interface in corrosive environments. In recent decades, the performance of painted materials increased, which requires the application of advanced methods for quick assessing, ranking and predicting corrosion stability. Scanning Kelvin probe (SKP) is a highly sensitive and non-invasive technique to analyze in situ the metal-polymer interface of high-performance industrial coatings. SKP is able to monitor the adhesion and corrosion underneath different kinds of paints without the need for long-term corrosion tests. SKP is a localized electrochemical technique with a spatial resolution in the range of 70-100 µm. Hence, it is possible to obtain information about the intact and corroding portions of the interface at defect sites, corrosion blisters, contaminants and intermetallics, quality of pretreatments, and the development of galvanic couples that lead to corrosion de-adhesion of the polymeric coatings. This article reviews the application of SKP to the determination of the mechanisms of corrosion de-adhesion of model paints, thick marine paints, coatings with zinc rich primers, automotive paints and coil coatings applied on galvanized steel substrates.

Developing a Physics-Based Model of the Electrocoating Process: Experimentation and Simulation

The objective of this work is to advance the mechanistic understanding of cathodic electrocoating by improving process performance and enhancing the accuracy of process simulation. Our efforts to do this are focused on the initial processes responsible for deposition, which are examined through direct experimentation and simulation. The principal component of the coating is an epoxy-amine resin dispersed in solution as micelles and stabilized by protonated amines. Electrocoating (e-coating) is a global industrial process providing a corrosive resistant base paint to automobile bodies. Automobile bodies exhibit complex geometries, leading to an inherently non-uniform current distribution during e-coating. Exposed areas such as exterior parts coat first. As the exterior parts coat, the electrically resistive polymer coating shifts deposition to less accessible areas and, eventually, to occluded areas such as rocker panels. Presently, empirical models are used to model coating thickness; these models tend to overpredict deposition in occluded areas. Therefore, an understanding of the mechanisms that control the e-coating process will improve the predictive capabilities of e-coat models, with the goal of enabling accurate digital design. A number of factors that may influence the initial stages of deposition have been identified including: i) regions of locally high current density caused by defects or nonuniformities (e.g., bubbles or partial deposits) on the deposition surface, ii) a concentrated micelle layer in solution near the deposition surface, and iii) changes in the composition of the aqueous phase at the deposition surface (e.g., pH changes). Combinations of these factors are also possible. In this study, we use bulk solution flow under controlled conditions to probe, measure and understand the factors that influence deposition. Anionic exchange membranes are also used to decouple important factors to determine their relative importance. Results show that deposition is possible without a pH increase. Deposits have been shown to initiate at locations on the surface where the current density is locally high. One example of this is ring-shaped deposits that form around bubbles on galvanized steel substrates. Simulations of the current distribution validate the role of the local current density, as does the deposition behavior observed at artificially formed defects. Experiments involving the influence of flow on the initial stages of deposition have yielded unexpected results that have important mechanistic implications. These results provide an increased understanding of fundamental processes responsible for initial deposition, which is the foundation needed for advanced physics-based models of the electrocoating process.