Insoluble Corrosion Products Research Articles

(Keynote) Leaching of Inhibitor Particles Followed By 4D X-Ray Tomography

Coil-coated zinc-alloy steel is a widely used commodity from white-goods manufacture to architectural claddings. Corrosion protection is generally provided to the substrate, and to any exposed cut edges, by a primer coating using an inhibitive pigme that, conventionally, consists of strontium chromate. However, chromate-free formulations containing phosphate-type pigments are now preferred. A common primer formulation contains strontium aluminium polyphosphate (SAPP) and, in previous work, it has been determined that the solubility of such inhibitors has two conflicting effects. On the one hand, free ions released from the inhibitor migrate to the metal substrate and reduce/inhibit corrosion by formation of a thin precipitated salt film containing zinc, phosphorous and oxygen. On the other hand, the dissolution of the inhibitor results in an increased porosity in the coatings, consequently creating more obvious pathways for aggressive species to reach the metal surface and for the transport of corrosion products. Further, insoluble corrosion products, or precipitated inhibitive salt films, in some cases appear to fill the cavities left by the dissolution of the SAPP inhibitor and, consequently, provide potentially improved barrier protection to the metal substrate. In the present study the leaching behaviour of nano- to micron scale corrosion inhibitor pigment, of strontium aluminium polyphosphate from a polymer coating was followed over 14 days by 4D x-ray nano tomography. It is apparent that SAPP is not a homogeneous material and contains both strontium-rich components, which leach extensively, and aluminium-rich components, which are more resistant to dissolution. Through the investigation of individual pigment particles and their 3D spatial connections in the polymer matrix, the transport routes of the leaching particles in the polymer matrix may be explored. The figure shows the evolution of an organic coating pigmented with SAPP corrosion inhibitor over the course of immersion in sodium chloride solution: (a) before immersion; (b) after immersion for 1 day; (c) after immersion for 7 days; (d) after immersion for 14 days. The oval regions highlight the dissolution of strontium-rich particles while the square region highlight the aluminium-rich components of the SAP. Figure 1

Long-term in vivo corrosion behavior, biocompatibility and bioresorption mechanism of a bioresorbable nitrided iron scaffold.

Pure iron as a potential bioresorbable material has major disadvantages of slow corrosion and bioresorption. However, so far, there are neither quantitative data of long-term in vivo corrosion nor direct experimental evidence for bioresorption of pure iron and its alloys. Only this work systemically investigated long-term in vivo corrosion behavior and biocompatibility of a nitrided iron coronary scaffold up to 53months after implantation and explored its bioresorption mechanism. These are fundamental and vital for developing novel Fe-based alloys overcoming the intrinsic drawbacks of pure iron. Novel testing and section-preparing methods were also provided in this work to facilitate future research and development of novel Fe-based alloy scaffolds.

The Influence of Sodium Molybdate on the Rate of Corrosion of Aluminum in Phosphoric(V) Acid

Corrosion rates of aluminum in phosphoric (V) acid solutions were determined gravimetrically in a presence of sodium molybdate which acts as an inhibitor. Inhibition efficiencies were calculated. The most effective corrosion inhibition was observed for 0.5 M H3PO4 and 100 mM of Na2MoO4. Since insoluble corrosion products precipitated onto specimens and influenced the determined corrosion rates, an analysis of a morphology of the specimens was performed by using a scanning electron microscope. The corrosion products are composed of Mo, P, Al and O. An Mo/P atomic ratio varied between 0.8 and 1.6 depending on the concentrations of phosphoric (V) acid and sodium molybdate. For three concentrations of H3PO4, the concentration ranges of sodium molybdate, where the gravimetric method may be applied were determined.

Factors that affect the behavior of CoCrMo taper junctions under cyclic loading

Event Abstract Back to Event Factors that affect the behavior of CoCrMo taper junctions under cyclic loading Matthew A. Di Prima1, Oleg Vesnovsky1, L D Timmie Topoleski1, 2 and Paul Kovacs3 1 FDA, CDRH/OSEL, United States 2 UMBC, Mechanical Engineering, United States 3 Consultant, Electrochemistry/Biocompatibility, United States Introduction: Artificial joints are one of the most successful treatments for arthritis; however, artificial joint failure is still a critical issue. For example, wear and corrosion at different modular junctions are thought to be instigators of artificial joint failure[1]. To achieve uniform and predictable contact between the stem and head, it is important to optimize the surface structure and properties, along with the angle mismatch, straightness, and conicity of the taper and trunnion[2],[3]. The purpose of our work was to investigate geometric parameters of four different Co-Cr taper junction designs: A, B, and C with fine-machined tapers and coarse-machined trunnions; and D with ground tapers and trunnions. Design A had a negative taper angle mismatch (taper angle > trunnion angle), while C had a positive one. B and D had no taper angle mismatch. Methods: Cyclic fatigue tests (n=3 for each design) were conducted in PBS solution at 37°C at 10Hz with a loading range from 280 N (minimum) to 2800 N (maximum). Tests were run for 10 million cycles. Displacements between the taper and trunnion were measured at each million cycles with digital extensometers during loading cycles. After 10 million cycles, the force required to separate the head and stem was measured. A head welded to a stem, preventing relative motion, was tested as a control. A composite digital image of each component was created using a Hirox digital microscope and a Bruker optical profilometer[1], through 360o over the trunnion and taper surfaces. Co and Cr ion concentrations in the test fluid were measured by ICP-MS. Results and Discussion: The changes in average surface roughness and visual appearance showed different trends and magnitudes for tapers and trunnions (Fig. 1). Changes in surface roughness should reflect assembly deformation/damage to, and in-use wear on, the machining marks, as well as metal removal by corrosion and material buildup due to corrosion product deposition. At the minimum load, all four designs showed "pistoning" while at the maximum load design A exhibited a much higher level of “rocking” relative motion (Fig. 2). The measured micromotion did not appear to reflect changes in surface roughness. The separation force was lower for design B only (Fig.3), which was the smooth taper – rough trunnion combination without any angle mismatch. The trends in Co ion concentrations and Co/Cr ratios (Fig. 3) suggest that design A exhibited the greatest overall corrosion. The change in the Co/Cr ratio is likely a change in mechanism from wear and fretting corrosion to predominantly crevice corrosion. Conclusions: A combination of experimental techniques can provide a better understanding of taper junction performance. Our results show that the geometry of the taper junction can affect wear and corrosion; however, more study is needed to assess the details of the optimum design parameters. Ideally, taper-trunnion interfaces should neither move relatively to each other while in physical contact nor undergo accelerated corrosion due to the presence of a liquid. It is essential to identify physical contact points, surface roughness changes, types of locking and loosening due to mechanical forces/damage, as well as the source(s) of soluble and insoluble corrosion products.

Degradation of bioabsorbable Mg-based alloys: Assessment of the effects of insoluble corrosion products and joint effects of alloying components on mammalian cells.

This work is focused on the processes occurring at the bioabsorbable metallic biomaterial/cell interfaces that may lead to toxicity. A critical analysis of the results obtained when degradable metal disks (pure Mg and rare earth-containing alloys (ZEK100 alloys)) are in direct contact with cell culture and those obtained with indirect methods such as the use of metal salts and extracts was made. Viability was assessed by Acridine Orange dye, neutral red and clonogenic assays. The effects of concentration of corrosion products and possible joint effects of the binary and ternary combinations of La, Zn and Mg ions, as constituents of ZEK alloys, were evaluated on a mammalian cell culture. In all cases more detrimental effects were found for pure Mg than for the alloys. Experiments with disks showed that gradual alterations in pH and in the amount of corrosion products were better tolerated by cells and resulted in higher viability than abrupt changes. In addition, viability was dependent on the distance from the source of ions. Experiments with extracts showed that the effect of insoluble degradation products was highly detrimental. Indirect tests with Zn ions revealed that harmful effects may be found at concentrations ≥ 150 μM and at ≥ 100 μM in mixtures with Mg. These mixtures lead to more deleterious effects than single ions. Results highlight the need to develop a battery of tests to evaluate the biocompatibility of bioabsorbable biomaterials.

Electrochemical and morphological characterisation of polyphenazine films on copper

The morphology of films of the phenazine polymers poly(neutral red) (PNR), poly(brilliant cresyl blue) (PBCB), poly(Nile blue A) (PNB) and poly(safranine T) (PST), formed by potential cycling electropolymerisation on copper electrodes, in order to reduce the corrosion rate of copper, has been examined by scanning electron microscopy (SEM). The copper surface was initially partially passivated in sodium oxalate, hydrogen carbonate or salicylate solution, in order to inhibit copper dissolution at potentials where phenazine monomer oxidation occurs, and to induce better polymer film adhesion. SEM images were also taken of partially passivated copper in order to throw light on the different morphology and anti-corrosive behaviour of the polyphenazine films. Analysis of the morphology of the polymer-coated copper with best anti-corrosive behaviour after 72h immersion in 0.1M KCl, Cu/hydrogen carbonate/PNB, showed that the surface is completely covered by closely packed crystals. By contrast, images of PST films on copper partially passivated in oxalate solution, that had the least protective behaviour, showed large amounts of insoluble corrosion products after only 4h immersion in 0.1M KCl.

Beneficial effects of CeO2 addition on microstructure and corrosion behavior of electrodeposited Ni nanocrystalline coatings

This paper presents an experimental study of the effects of CeO2 addition on the microstructure and corrosion behavior of nanocrystalline Ni coatings. A novel method of ultrasound-assisted pulsed electrodeposition was used to prepare the coatings from a modified Watts-nickel electrolyte. Surface morphologies and micro-structural evolution of the coatings before and after aging treatments were characterized using E-SEM and TEM observations. Furthermore, electrochemical techniques attached with the XRD and XPS analysis were applied to study their corrosion behavior in a 5wt.% HCl aqueous solution. The underlying mechanisms of corrosion inhibition resulted from the Ce-rich passive layer were discussed in detail. Experimental results indicated that the existence of well-distributed CeO2 phase in the coatings promoted dispersion strengthening through a proper aging treatment at 650°C for 4h, thereby achieving an effective bonding link between interfacial boundaries for denser microstructure. According to the measured results from polarization curves and the AC-impedance measurements, it exhibited superior corrosion resistance of the Ni-CeO2 coatings as compared to pure nickel. During the long-term static immersion tests in an acid 5wt.% HCl aqueous solution, a small amount of Ce3+/4+ ions was released from the dissolution–precipitation of a Ce-rich phase and served as the corrosion inhibitors. Furthermore, some insoluble corrosion products resulted from the process of electrochemical reactions were favorable for precluding the corroded surface from the corrosive attack and diffusion behavior by Cl− ions.

Degradation mechanisms occurring in precious metallic artefacts

Since ancient times, precious metallic artefacts have gained a remarkable interest from a historical, artistic and economical point of view. They were used as jewels or artistic items but also for currency, medium of exchange and form of saving, and in many cases were manufactured with a high level of technological competence. Several Roman and Phoenician–Punic gold, silver and copper‐based, gold and silver‐plated artefacts characterised by a wide compositional range and different metallurgical nature have been studied to identify the microchemical surface structure and the metallurgical features. Four case studies are reported. The investigation was carried out by means of the combined use of surface and microanalytical techniques, such as XPS, X‐ray diffraction and SEM equipped with an energy dispersive X‐ray spectrometer. The results revealed that the artefacts surface is characterised by a thin layer of insoluble corrosion products like AgCl, Ag2S or AgCuS, CuS, Cu2O, Pb or Cu‐carbonates mixed to form a complex composite structure. The presence and the concentrations of these corrosion compounds is strongly related to the archaeological context. The overall experimental findings confirm that the nearly pure gold artefacts and the gold‐based artefacts are more stable with respect to the silver ones where the ubiquitous presence of chlorides is often found. The microchemical and micromorphological characterization allows to identify the plating and manufacturing techniques. Several methods were used by the craftsmen, including fire gilding, a highly complex and sophisticated method based on the use of mercury. Finally, the proposed approach may help, when feasible, to preserve, restore and protect the artefacts without causing further damaged. Copyright © 2011 John Wiley & Sons, Ltd.

Corrosion inhibition of mild steel in sodium chloride solution by some zinc complexes

The corrosion inhibitive effect of zinc acetate, zinc acetylacetonate and zinc gluconate on the mild steel immersed in 3.5% NaCl solution was evaluated by electrochemical impedance spectroscopy (EIS). The results revealed superiority of zinc gluconate whilst zinc acetate showed inferior corrosion inhibition. The surface of the samples exposed to the inhibited solutions was analyzed using XRD and SEM techniques. The pH measurement of the test solutions before and after corrosion, also before and after addition of Fe +2 and Fe +3 revealed that the superior inhibition of zinc gluconate is related to formation of insoluble corrosion products on the mild steel surface.

The protection of galvanised steel using a chromate‐free organic inhibitor

PurposeThe purpose of this paper is to investigate corrosion protection provided by a water‐soluble corrosion inhibitor as a non‐toxic alternative to the chromate and phosphate conversion coatings on galvanised steel.Design/methodology/approachUntreated galvanised steel samples were assessed simultaneously with galvanised steel samples treated with the chromate‐free organic inhibitor, a conventional chromate conversion coating or a zinc phosphate modified with nickel, by means of immersion – weigh loss and electrochemical tests, using a naturally aerated 0.5 M NaCl aqueous solution as corrosive medium. In addition, selected superficial conditions of galvanised steel were submitted to a salt fog test. The electrochemical tests used were: open circuit corrosion potential logging, linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy. Corrosion products formed on samples withdrawn from the solution at different intervals were characterized using X‐ray diffraction.FindingsAll tests gave concordant results, indicating that the chromate‐free inhibitor showed moderate protective properties in this electrolyte. Among the considered superficial conditions, the phosphate coating showed the most deficient performance. In all cases, it was observed that after moderately intense initial attack, the corrosion rate diminishes due to the formation and growth of insoluble corrosion product layers, which exhibit a passivating action.Research limitations/implicationsThe chromate‐free organic corrosion inhibitor protected galvanised steel in this environment but the degree of protection was less than that provided by the chromate conversion coating.Originality/valueThe paper presents an alternative to the toxic treatments with chromates, since the inhibitor works as an additional coating, sealing pores and other discontinuities found in the zinc coating.

Peculiarities of long-term effect of hydrosulfide-enriched seawater on a copper alloy

Copper specimens (coins) found at the bottom of Taman bay, which lied in water for about 1600 years, manifested a very high corrosion resistance. The uniqueness of the phenomenon is attributed to the heightened concentration of hydrogen sulfide caused by the activity of mud volcano in this region. Under the layer of insoluble corrosion products, namely copper sulfides and disulfides, the items preserved the original surface relief.

In situ soft X-ray dynamic microscopy of electrochemical processes

We report a pilot study in in situ electrochemical X-ray dynamic microscopy, based on a model system: the anodic and cathodic behaviour of Ag in neutral NaCl and (NH 4) 2SO 4 aqueous solutions. In situ X-ray imaging highlighted mesoscopic features related to corrosion processes, yielding soluble (NH 4 + solution) and insoluble (Cl − solution) corrosion products, as well as cathodic growth morphologies. X-ray absorption and phase contrast images were collected, confirming the feasibility of soft X-ray microscopic measurements with lateral resolution down to a few tens of nm in electrochemical cells for operation in a high vacuum environment in presence of liquid electrolytes.

Single pit on iron generated by SECM: An electrochemical impedance spectroscopy investigation

The analysis of a single pit behavior on iron in various media (sulfuric acid, borate buffer, and potassium hydroxide solutions) is reported. The use of SECM technique to generate a single pit has allowed usual electrochemical techniques to be applied. Electrochemical impedance spectroscopy was used to characterize the pit propagation. In acidic solution, the pit returned to its passive state quickly whereas for the same amount for chloride ions generated locally, the pits remained active for long time in KOH solution. An intermediate behavior was evidenced in borate buffer for which a slow repassivation ascribed to the accumulation of insoluble corrosion products inside the pit was observed. The Raman analysis also evidenced the strong influence of the thin-layer-cell configuration on the nature of corrosion products in borate buffer.

LOW-CARBON STEELS CORROSION IN WATER-CONTAMINATED ORGANIC MIXTURES OF ADIPIC ACID AND METHANOL

The corrosion resistance of three types of low-carbon steels in water-contaminated mixtures of adipic acid and methanol was investigated. The concentration of water in the organic mixture was progressively raised from 1% to 5%, while the carbon concentration in the steel samples varied from 2% to 4%. Infrared spectroscopy (IR) and X-ray diffraction (XRD) were used to investigate the insoluble corrosion products. Based on the weight losses measurements, on the polarization curves and on the scanning electron microscopy (SEM) analysis, a corrosion mechanism was assigned for each type of steel. The kinetics parameters of corrosion: Ecor (corrosion potential), Est (steady potential) and Icor (corrosion current density) were determined from experimental polarization curves. The highest corrosion resistance was exhibited by the steel sample containing 4% of carbon.

Corrosion behaviour of hafnium diboride in aqueous solutions

Abstract A dense HfB 2 ceramic material was prepared by hot pressing in the presence of 2.5 wt.% Si 3 N 4 , as a sintering aid. The microstructure consisted of a fine HfB 2 matrix with refractory secondary phases (BN, HfO 2 , Hf(C,N,O)) and Si, mainly located at the triple points. The material corrosion behaviour in acid and alkaline solutions of chlorides and sulphates was investigated by means of several experimental techniques, that is potentiodynamic polarization curve recording and potentiostatic tests coupled to solution chemical analysis, scanning electron microscope (SEM) observations and X-ray photoelectron spectroscopy (XPS) surface chemical characterization. Sintered HfB 2 undergoes an electrochemical corrosion attack of the HfB 2 phase and a chemical corrosion attack, mainly localized on the secondary phases. In acid sulphate solution a strong corrosion attack on the diboride phase occurs which leaves a secondary phase skeleton. In acid chloride solution and in alkaline chloride and sulphate solutions, the rate of secondary phase dissolution is quicker than the dissolution rate of the primary diboride phase and an intergranular corrosion attack morphology occurs. The Si phase dissolves relatively fast only in alkaline solutions. In analogy with the corrosion behaviour of ZrB 2 , corrosion of HfB 2 phase is thought to produce both soluble and insoluble (hafnium and boron oxides) corrosion products. In acid sulphate solution the soluble corrosion products are mainly boric acid and a sulphate complex of Hf(IV). In the other solutions they are mainly constituted by boric acid (or borates, depending on the solution pH). The high corrosion rates detected in acid sulphate solution are due to the marked stability of the soluble sulphate complex of Hf(IV).

Corrosion study of electrodeposited Zn and Zn-Co coatings in chloride medium

The corrosion behavior of electrodeposited Zn and Zn-Co coatings in 0.1 mol dm-3 NaCl aqueous solutions was investigated using scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), galvanostatic electrochemical stripping (GES), electrochemical impedance spectroscopy (EIS) techniques and open circuit measurements (Eoc). All coatings were electrodeposited on mild steel. Using GES it was possible to identify Zn-Co intermetallic phases in the coatings with Co content higher than 1 at.%. The GES, SEM and EDX results revealed that the corrosion mechanism of the Zn-Co layers with high Co content is related to the appearance of cracks due to the dissolution of the gamma Zn-rich phases, while the corrosion of the Zn and Zn-1Co layers was characterized by dissolution of the coatings. The Zn and Zn-Co coatings were found to contain the same insoluble corrosion products, which act as a corrosion barrier that delays but does not prevent corrosion. The better corrosion resistance of the Zn-Co coatings obtained in the bath without additive, in comparison with Zn-1Co obtained in the bath containing additive is due to the high Co content which leads to an ennoblement of the coating. All Zn-Co electrodeposits showed greater corrosion resistance than the Zn electrodeposits. The Zn-18Co layer showed the best corrosion resistance, with a lifetime about three times longer than that of the Zn layer.

Influence Of Lepidocrocite (γ-FeOOH) on Escherichia Coli Cultivability in Drinking Water

A washed suspension of the bacteria Escherichia coli, pre-grown on a complex culture medium, was stored in sterilized drinking water for 21 days at 25°C in glass flasks in order to assess the effect of iron corrosion products on the persistence of the bacteria in drinking water. Four conditions were tested: aerobic with 50 mM lepidocrocite (γ-FeOOH, an insoluble iron corrosion product), anaerobic with 50 mM lepidocrocite, aerobic without lepidocrocite and anaerobic without lepidocrocite. The survival of E. coli was monitored by their cultivability and their membrane integrity (propidium iodide staining). When the samples were not supplemented with the iron oxide, the cultivability and cell integrity of the bacteria were dramatically altered: from the 107 initially added, only 10 CFU ml-1 remained after 21 days; 90% of the cells exhibited membrane alteration after 2 weeks of storage. In contrast, bacteria with lepidocrocite preserved their cultivability and integrity over the 21 days of storage. In the presence of di-oxygen and without iron oxide, the alteration of cell cultivability was more pronounced than that in anaerobic conditions, suggesting that oxidative stress was part of the phenomenon. When the cells were pre-grown in a growth medium supplemented by a large excess of an easily available form of iron (ferric-citrate), the cells stored a higher amount of iron and persisted one week longer in the iron-free drinking water than cells pre-grown in the standard growth medium. Therefore, in an oligotrophic environment like drinking water, E. coli cells can find the ability to survive a long time through the presence of iron corrosion products. The necessity of controlling the corrosiveness of drinking water for sanitary reasons is therefore emphasized by this study.

EIS study of corrosion behaviour of organic coating/Dacromet composite systems

Three organic coating/Dacromet composite systems, namely two solvent-borne coatings, polyurethane, alkyd primers and a water-borne coating, styrene-acrylate emulsion, were prepared on Dacrometed carbon steel. Electrochemical impedance spectroscopy (EIS) was employed to study their corrosion behaviour in 3.5% NaCl medium. Characteristic EIS plots with two undistinguishable loops were observed for the styrene-acrylate emulsion/Dacromet system and of which the second one was greatly flatter with immersion time. The stable evolution of R p, C p, C d, and a higher value of R c illustrated an original fact that the water-borne styrene-acrylate emulsion/Dacromet system exhibited the best protective performance among the three systems. According to the investigation of thin organic film/Dacromet composite systems, a synergetic effect of multiple interface factors including the passivation, the seal and barrier function of insoluble corrosion product of Dacromet, especially the interpenetration of organic micropolymer particle with corrosion product in styrene-acrylate emulsion/Dacromet system was proposed to explain the corrosion behaviour of the composite systems.

Development of a Magnetic Filter System Using Permanent Magnets for Separating Radioactive Corrosion Products from Nuclear Power Plants

Radioactive corrosion products generated through the neutron activation of general corrosion products at nuclear power plants are the major source of occupational radiation exposure. Generally, radioactive corrosion products exit in soluble and insoluble forms, and are removed by ion exchangers and purification filters. Most of the insoluble radioactive corrosion products have the characteristic of showing strong ferrimagnetism. With the development and production of permanent magnets (rare earth magnets) capable of generating a much stronger magnetic field than conventional permanent magnets, a new type of magnetic filter that can efficiently separate radioactive corrosion products and eventually reduce radiation exposure to personnel at nuclear power plants is proposed and developed. Magnetic separation by using permanent magnets has certain advantages, such as high flow purification, high pressure and temperature operation, and energy saving. The magnetic separator consists of an inner magnet assembly and an outer magnet assembly, a coolant channel, and a container surrounding the outer magnet assembly. The rotation of the inner and outer permanent magnet assemblies by a driving motor system produces moving and alternating magnetic fields in the coolant channel, which is located between the two magnet assemblies. The particulate in the radioactive corrosion products is separated from the coolant by the alternating magnetic fields as a result of the shifting arrangement of the permanent magnets. This study describes the preliminary experimental results of using different particle sizes and various materials at the different flow rates and rotation velocities of the magnet assemblies. This new magnetic filter performs well in filtering magnetite, cobalt ferrite, and nickel ferrite from aqueous coolant simulation.

Electrochemical Behavior of ZrB2 in Aqueous Solutions.

AbstractFor Abstract see ChemInform Abstract in Full Text.