Improved Corrosion Performance Research Articles

Preparation and characterization of linseed oil-filled urea–formaldehyde microcapsules and their effect on mechanical properties of an epoxy-based coating

In this study, urea–formaldehyde based microcapsules containing linseed oil were prepared via in situ polymerization method. Microcapsules with a regular spherical shape, 10–300μm diameter and an oil content of 63–77wt% were synthesized in various core:shell ratios and different mixing speeds. The effect of core:shell ratio and mixing speed on the size and morphology of the microcapsule were studied using optical microscopy, SEM and particle size analysis. Epoxy-based coatings containing various amounts of microcapsules were prepared and the effect of microcapsule size and loading on the mechanical properties and healing performance were evaluated by measuring the tensile properties and corrosion performance of the coatings. The amount of the oil released in the scratched coating was determined both practically and theoretically and the results were compared.The results showed that the addition of microcapsules reduces the tensile properties of the coating, the extent of which depends on the microcapsule size and loading wt%. For instance, sample containing 3wt% of the microcapsules with an average particle size of 53μm showed 8.6% reduction in tensile modulus. Optical microscopy of the scratched sample revealed that with increasing microcapsules’ size and loading, the crack was filled more effectively and this led to an improved corrosion performance. Finally, the optimum combination of self-healing and mechanical properties was found to be for the coating containing 5wt% of microcapsules, with an average particle size of 53μm.

Corrosion behaviors of Mo coating on stainless steel 316 substrates implanted by different nitrogen ion fluences

The molybdenum nitride coating was produced by nitrogen ion implantation of the molybdenum layer deposited on the stainless steel 316 (SS) substrates. At first, molybdenum layers were deposited on the substrates by ion beam sputtering method, then nitrogen ions with an energy of 30 keV and a fluence between 1×10 17 and 12×10 17 N + cm −2 were implanted in Mo/SS system. Crystal structure and topography of the surface are investigated by grazing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM) image respectively. XRD patterns showed the formation of molybdenum nitride phases in all implanted samples. Corrosion tests showed that the corrosion resistance of the samples strongly depends on the nitrogen applied fluences. A considerable improvement of corrosion performance by increasing ions fluences was observed. The lowest corrosion current density with amount of 0.1 μ A/cm 2 was obtained at 12×10 17 ions/cm 2 fluence in our case.

Corrosion of Zinc and Zn-Mg Alloys with Varying Microstructures and Magnesium Contents

This work addresses the effect of the Mg-content on the corrosion performance of Zn-Mg alloys. Since only low Mg-contents are used in modern Zn-Mg-X coatings, the magnesium in the investigated Zn-Mg alloys was varied in the low content range from 0 wt% to 3 wt%. In addition pure, intermetallic MgZn2 was investigated for comparison. Furthermore, for the case of the alloy with 2 wt% magnesium, the effect of different microstructure at same composition was investigated, which was adjusted by applying different cooling rates during solidification from the melt. The alloys can be ranked in order of the fineness of their microstructure. With increasing magnesium content the lamellar eutectic becomes finer and more evenly distributed. The slowly cooled specimen exhibits coarser microstructure than the quenched alloy. The corrosion of the investigated alloys can be described in three stages, i.e. activation, active corrosion and formation of a protective layer. While the development of the corrosion resistance in the first two stages is very similar for all investigated alloys, in the last stage distinct differences were found for the different samples. It was observed that an increase of the fineness of the microstructure leads to an improved corrosion performance.

Multiple Corrosion-Protection Systems for Reinforced-Concrete Bridge Components: Laboratory Tests

Techniques for making epoxy-coated reinforcement more corrosion resistant, including epoxies with increased adhesion to the steel; concrete with a decreased water cement ratio; concrete containing calcium nitrite or one of two organic corrosion inhibitors; bars with a primer coating containing microencapsulated calcium nitrite applied prior to epoxy application; and bars coated with zinc prior to epoxy application are compared based on the chloride content required to initiate corrosion and corrosion losses using the southern exposure and cracked beam tests. The coatings on all bars are penetrated prior to testing to simulate damage in the field. The results indicate that, even when damaged, conventional epoxy coatings result in much higher concrete chloride contents at corrosion initiation and much lower corrosion losses than exhibited by conventional reinforcement. A reduced water-cement ratio, corrosion inhibitors, and the primer coating containing microencapsulated calcium nitrite provide protection in uncracked but less or no protection in cracked concrete. The bars coated with zinc prior to epoxy application exhibit relatively high corrosion rates because of preferential losses to the zinc, and no improvement in corrosion performance is observed for epoxies with increased adhesion.

Self-adjustment of calcium phosphate coating on micro-arc oxidized magnesium and its influence on the corrosion behaviour in simulated body fluids

A calcium phosphate (Ca-Ph) coating was prepared on micro-arc oxidized magnesium using deposition method. The microstructure of the Ca-Ph coated sample and corrosion behaviour in simulated body fluid (SBF) were investigated. The results showed that the coating consisted of hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD). Temperature significantly affected the microstructure of the coating. Increased temperature promoted HA formation but inhibited DCPD deposition. The microstructure of the Ca-Ph coating underwent self-adjustment in SBF. Bonelike apatites were formed on the coated sample, which not only increased the thickness of coating, but also improved corrosion performance of the coated sample in SBF.

Effect of nano-ZnO particles on the corrosion resistance of polyurethane-based waterborne coatings immersed in sodium chloride solution via EIS technique

Nano-composite coatings were formed by incorporating 3wt% nano-ZnO in a polyurethane-based waterborne coating. The nano-ZnO based composite coatings were applied on standard phosphated steel panels by cathodic electrodeposition. The electrodeposited nano-composite coatings were then baked for 20min at 165°C. To investigate the corrosion resistance of the coatings, the coated panels were immersed in 3.5wt% NaCl solutions for 2880h (120 days). The improvement in corrosion performance of the composite coatings was evaluated using electrochemical impedance spectroscopy technique. It was found that the films containing nano-sized ZnO particles show a corrosion resistance of 2 orders of magnitude higher than that of the neat films.

The effect of Sn on autoclave corrosion performance and corrosion mechanisms in Zr–Sn–Nb alloys

The desire to improve the corrosion resistance of Zr cladding material for high burn-up has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While commonly accepted, the reason for the improved corrosion performance observed for low-tin zirconium alloys in high-temperature aqueous environments remains unclear. High-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr–Sn–Nb alloys with tin concentration ranging from 0.01 to 0.92wt.%. The alloys studied included the commercial alloy ZIRLO® (ZIRLO® is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited.) and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy was investigated via cross-sectional scanning electron microscopy. Atom probe analysis of ZIRLO demonstrated that the tin present in the alloy passes into the oxide as it forms, with no significant difference in the Sn/Zr ratio between the two. Synchrotron X-ray diffraction measurements on the oxides formed on each alloy revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on the phase and alloy. The amount of tetragonal phase present and, more importantly, the level of tetragonal-to-monoclinic phase transformation both decrease with decreasing tin levels, suggesting that tin is a tetragonal oxide phase stabilizing element. It is proposed that in Zr–Nb–Sn alloys with low Sn, the tetragonal phase is mainly stabilized by very small grain size and therefore remains stable throughout the corrosion process. In contrast, alloys with higher tin levels can in addition grow larger, stress stabilized, tetragonal grains that become unstable as the corrosion front continues to grow further inwards and stresses in the existing oxide relax.

A review of ionic liquid surface film formation on Mg and its alloys for improved corrosion performance

Magnesium and its alloys are prone to corrosion upon exposure to atmosphere thus are usually protected by using a pretreatment before being employed. The use of ionic liquids (ILs) has emerged as a novel chemical in corrosion protection of reactive metals such as lithium and magnesium. This paper reviews the use of ILs in the corrosion protection of magnesium and aluminium with respect to a range of IL chemistries. Emphasis has also been placed on characterisation of the passivating films using various techniques, as well as proposed mechanisms for film formation. This review highlights that there is still much research needed to understand how to generate robust passivating films on reactive metal surfaces in the presence of ILs.

Experimental Study of 3% Cr Tubing Steel in CO2 and CO2H2S Corrosion Environment

Summary The corrosion behavior of 3% Cr steel is tested by a high-temperature/high-pressure autoclave. The corrosion environment is categorized into CO2-alone and CO2/H2S conditions. At 90°C, with the addition of H2S to the CO2, the surface corrosion condition improved greatly, and the corrosion rates declined compared with the CO2-alone condition. Under CO2/H2S condition, with an increasing CO2/H2S partial-pressure ratio, the corrosion rate reached a peak value at pCO2/pH2S = 100, and then declined. Through the analysis of the corrosion products of the samples in different conditions by scanning electron microscope (SEM), EDS, and X-ray-diffraction (XRD) methods, it was found that the inner film is finer and denser than the outer scale. The partial-pressure ratio of H2S corrosion regime should be between 10 and 100 and is not the previous 200. Introduction Corrosion has wide-ranging implications for the integrity of materials used in the petroleum industry. The implication of CO2 corrosion can be viewed in terms of its effect on capital and operational expenditures and health, safety, and the environment (Kermani and Harrop 1996),which brings huge losses and poses security threats to the development of oil and gas (Minxu et al. 2002; Kinsella et al. 1998). Medium Cr-containing steels showed improved corrosion resistance compared with carbon steel and lower cost than 13% Cr steel (Ueda and Takabe 2002; Muraki et al. 2002; Nose et al. 2001). The effect of medium chromium-additions was attributed to the formation of chromium enriched corrosion products (e.g., observed on 3% Cr steel). Steels alloyed with 3% Cr or more were found to show improved corrosion performance over Cr-free steel by a factor of two or more (Nose et al. 2001). The corrosion becomes complicated when H2S is added into the CO2 corrosion system. The current research should focus on the formation mechanism of the corrosion product film, properties of corrosion product of different structures, and protection to the matrix. The corrosion experiment that has been carried out with 3% Cr tubular steel in pure CO2 and CO2/H2S environments. The results would be to supplement the CO2/H2S corrosion theory of 3% Cr steel and provide theoretical basis for the proper selection of the tubing and casing in oil and gas fields.

Electrodeposition of protective organosilane films from a thin layer of precursor solution

Organosilane films were electrochemically deposited onto aluminium alloy AA 2024-T3 for corrosion protection from a thin electrolyte layer (TEL). Compared with those electrodeposited from a bulk solution, silane films electrodeposited from a TEL compartment exhibit improved corrosion performance and enhanced film formation. These phenomena were explained by the increased OH− ions generation rate under a TEL due to the facilitated oxygen diffusion. Silane films electrodeposited at a “critical electrolyte thickness” (CET) provide the best protection resistance, accompanying with the highest deposition current. The negative effect below the CET was interpreted by the insufficient amount of dissolved oxygen in the TEL.

Electrodeposition of zinc-doped silane films for corrosion protection of mild steels

Organosilane/zinc composite films are prepared by one-step electrodeposition onto cold-rolled steels for corrosion protection. Electrochemical impedance spectroscopy measurement, bulk solution immersion and wet heat tests all show that the composite films have improved corrosion performance. X-ray photoelectron spectroscopy measurement suggests the successful encapsulation of metallic zinc. The embedding of metallic zinc results in negative shift in open-circuit potential of the film-covered electrodes. Such cathodic protection effect given by the metallic zinc provides the improved corrosion resistance of the composite films.

Grain refined and basal textured surface produced by burnishing for improved corrosion performance of AZ31B Mg alloy

Grain refinement and strong basal texture were produced on AZ31B Mg alloy surface concomitantly by a newly developed severe plastic deformation (SPD) process, severe plasticity burnishing (SPB). The remarkably improved corrosion resistance of AZ31 in NaCl solution after SPB was attributed mainly to dramatically reduced grain size and strongly basal-textured grain orientation. The residual stresses introduced by SPB were also found to influence the corrosion resistance to some extent. Compared with other SPD processes, SPB is fast, cost-effective, does not change material bulk properties and requires little changes to the industrial production process.

Improved corrosion performance of electrophoretic coatings by silane addition

Organosilanes are incorporated into a commercial cathodic electrophoretic paint, resulting in significant improvement in the long-term corrosion protective properties of the paint. The addition of organosilanes have strengthened mechanical properties, improved hydrophobicity, lowered water uptake and less decrease in glass transition temperature of the coatings, suggesting the enhancement in bulk structure of the polymeric coatings. In addition, silane-enriched layer preferentially forms at the metal/coating interface during the electrophoresis process, leading to better adhesion between the substrate and the coating. The structural enhancement in both the coating and the metal/coating interface explains the improved corrosion performance of silane-incorporated electrophoretic coatings.

Effect of [Ca2+] and [[formula omitted]] levels on the formation of calcium phosphate conversion coatings on die-cast magnesium alloy AZ91D

The effect of varying [Ca2+]total and [PO43-]total concentrations (nine conditions in total) on the formation of calcium phosphate conversion coatings on magnesium alloy AZ91D was investigated. Corrosion performance was evaluated by measurement of polarisation behaviour and also by salt spray testing. A consistent trend was observed of improved corrosion performance with reduced ionic concentrations. Low [PO43-]total concentration was found to be especially important for the attainment of good corrosion resistance. Both direct measurement using X-ray photoelectron spectroscopy and chemical modelling using MEDUSA software indicated an increase in hydroxyapatite content of the coating accompanying the improved corrosion resistance.

ChemInform Abstract: Laser Surface Modification for Corrosion Protection

AbstractReview: 23 refs.

Improvement of corrosion performance of HVOF MMC coatings by laser surface treatment

In order to improve corrosion performance of T800 (Co–Mo–Cr–Si) and T800 based WC HVOF sprayed coatings, laser surface modification was carried out using a high power diode laser to eliminate/reduce the microstructral defects of the coatings by precise control of treatment depth with or without melting. Characterisation of the laser modified surfaces was conducted, in terms of microstructural morphology and phase analysis. Corrosion behaviours of the coatings before and after laser treatment were evaluated using electrochemical impedance spectroscopy and immersion tests. The results indicated that the corrosion resistance of the HVOF coatings can be improved as a result of laser densification of the coatings by elimination of discrete splat structure and porosity. However, the improvement of resistance to microgalvanic corrosion between the WC and Co matrix after laser treatment can be limited depending on the extent of melting occurred to the WC within the coatings.

Influence of cerium molybdate containers on the corrosion performance of epoxy coated aluminium alloys 2024-T3

Cerium molybdate containers loaded with 2-mercaptobenzothiazole were incorporated into epoxy coatings onto aluminium alloys 2024-T3 and investigated with respect to the corrosion protection of the metallic surfaces. The coatings were deposited via the dip-coating process. The morphology of the coatings was examined by Scanning Electron Microscopy. Their composition and structure were investigated by Fourier Transform Infrared Spectroscopy and Energy Dispersive X-ray Analysis. The corrosion resistance of these coatings was investigated by using electrochemical impedance spectroscopy and open circuit potential. After exposure to 0.05 M NaCl solution for 28 days, the coatings with the loaded containers exhibit improved corrosion performance.

Corrosion performance of laser-remelted Al–Si coating on magnesium alloy AZ91D

Laser remelting was applied to plasma-sprayed Al–Si coating on magnesium alloy AZ91D to improve corrosion performance. Both salt spray testing and potentiodynamic polarization measurement in 3.5% NaCl solution indicated that laser-remelted Al–Si coating acquired better corrosion resistance than AZ91D and plasma-sprayed Al–Si coating. The decreasing order of the corrosion rates are AZ91D base metal, sprayed Al–Si coating and laser-remelted Al–Si coating. The fine Al–Si eutectic matrix in the laser-remelted microstructure contributed to the improved corrosion performance relative to the AZ91D and the plasma-sprayed coating. The predominant corrosion mechanisms in AZ91D, plasma-sprayed coating and laser-remelted coating are intra-granular corrosion, crevice corrosion and the combined pitting and galvanic corrosion, respectively.

The effect of calcination on the corrosion performance of TiO2 sol–gel coatings doped with benzotriazole on steel CK45

AbstractSol–gel method under dip coating process and tetra‐n‐butyle orthotitanate as precursor were used to produce titanium oxide coating on steel CK45. The effect of calcination at 400 °C, after drying at 120 °C, on the morphology and corrosion performance of the coatings was investigated. Benzotriazole (BTA) as an inhibitor was doped on titanium oxide coatings to improve corrosion performance of the coatings as well as its self‐healing properties. The morphology and structure of the coatings were studied by X‐ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X‐ray spectroscopy (EDS) techniques. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of the coatings. The results revealed that after calcination the dominant crystalline phase was anatase. The results obtained from potentiodynamic polarization curves and electrochemical impedance spectra showed that the calcinated and doped with BTA coatings possessed higher corrosion resistance than non‐calcinated although doped with BTA coatings.

Laser-induced microstructural modification for corrosion protection

Laser surface modification of materials by melting and annealing has been the subject of considerable interest as a means of enhancing the corrosion performance of metallic alloys. Microstructural modification without changing surface chemical composition, in terms of homogenization/refinement of microstructures, dissolution/re-distribution of intermetallic particles, and extended solid solubility, resulting from rapid rates of cooling, provides the basis for property enhancement. This paper reviews authors’ work on laser surface melting (LSM) and laser annealing (LA) for the purpose of improved corrosion performance. Microstructural evolution and corrosion performance in a range of metallic alloys, followed by different treatments with different types of lasers, are presented. For LSM of aerospace aluminium alloys, the corrosion mechanisms of the laser-melted alloys have been discussed in the consideration of electrochemical characteristics of intermetallic particles with respect to the aluminium matrix and cooling rates leading to different degrees of refinement/removal of intermetallic particles. For LA of amorphous electroless Ni-W-P plating, porosity formation and grain growth and microstrain/residual stress resulting from laser-induced nanocrystallization are the major concerns, affecting corrosion performance. In addition, potential applications of LSM as pre-treatment method prior to conventional anodizing or post-treatment of thermal sprayed coatings have been demonstrated.