Measurement of the corrosion rate of aluminium in sodium hydroxide using holographic interferometry

The application of holographic interferometry to the measurement of the corrosion rate of aluminium in sodium hydroxide is investigated. Details of the fabrication of the corrosion cell and the experimental procedure are given. Thickness loss of aluminium was found for different dissolution times and compared with the conventional weight-loss method using a microbalance.

Continuous corrosion rate measurement by noise resistance calculation

A commonly employed method of corrosion rate measurement is to determine the electrochemical impedance of the corroding material. One technique for estimating the impedance is the noise impedance calculation. While it has been shown to yield useful results, there are a number of problems that require attention. This paper identifies some of those problems-specifically, those of detrending and resolution-and provides a solution that allows continuous, time-varying noise resistance and noise impedance calculations to be performed with known time, frequency, and magnitude resolutions. Applications to synthetic and experimental data are included as illustrations

Absolute values of instantaneous corrosion rates by faradaic rectification

Doss and Agarwal 1 discovered the "redoxokinetic effect" which is now familiarly known as faradaic rectification. Subsequently, the theory and applications of faradaic rectification due to a single electrode reaction have been developed by several workers 2-5. The theory and application of faradaic rectification in the case of a corrosion cell sustaining mixed electrode reactions on a corroding metal was reported recently 6"7. This led to the development of a new electrochemical method of corrosion rate determination. It was shown that changes in the instantaneous corrosion rates of a metal are readily evaluated by faradaic rectification measurements at the corrosion potential of the metal in a given medium. The aim of the present work is to show that absolute values of instantaneous corrosion rates may also be obtained by the new method under certain conditions. The practical advantages that arise from this development are pointed out.

Role of Li+ ions in corrosion behaviour of 8090 Al-Li alloy and aluminium in pH 12 aqueous solutions

The influence of Li+ ions on the corrosion behaviour of the Al-Li alloy 8090-T851 and of commercially pure aluminium in aqueous solutions at pH 12 was studied by weight loss and electrochemical polarisation methods. The inhibiting role of Li+ was concentration dependent, corrosion rate decreasing lineally with log[Li+] in the concentration range 10(-4)-10(-1) mol L(-1). A change from general to pitting corrosion was evident from scanning election microscopy studies. Polarisation studies revealed that Li+ primarily acts as an anodic inhibitor (passivator). Passive film formation and stability also become more feasible with increasing Li+ concentration. Fitting potential was dependent on the Cl- ion concentration in the solution. Both materials were affected similarly by the presence of Li+ ions, the corrosion rate of the alloy being slightly lower. This is attributed to the lithium in the alloy acting as a source of lithium for passive film formation. (C) 1995 The Institute of Materials.

Effect of boron addition and processing of Ti-6Al-4V on corrosion behaviour and biocompatibility

Ti-6Al-4V is widely used to prepare biomedical implant for orthopaedic and dental applications, but it is an expensive choice relative to other implant materials such as stainless steels and Co-Cr alloys, in large part due to the high manufacturing cost. Adding boron to refine the as cast microstructure of Ti-6Al-4V can eliminate the need for extensive hot working and thereby reduce processing costs. The effect of 0.1 wt-% boron addition and the choice of processing route (forging or extrusion) was studied in the context of potential biomedical applications. Corrosion tests in simulated body fluid indicated that the presence of boron increased the corrosion rate of Ti-6Al-4V and that the increase was higher for forged alloys than for extruded alloys. Boron addition and processing route were found to have a minimal effect on the viability of osteoblasts on the alloy surfaces. It is concluded that the addition of boron could offer advantages during the processing of Ti-6Al-4V for biomedical applications.

An extended finite-element model coupled with level set method for analysis of growth of corrosion pits in metallic structures

Mass balance between metal and electrolytic solution, separated by a moving interface, in stable pit growth results in a set of governing equations which are solved for concentration field and interface position (pit boundary evolution). The interface experiences a jump discontinuity in metal concentration. The extended finite-element model (XFEM) handles this jump discontinuity by using discontinuous-derivative enrichment formulation, eliminating the requirement of using front conforming mesh and re-meshing after each time step as in the conventional finite-element method. However, prior interface location is required so as to solve the governing equations for concentration field for which a numerical technique, the level set method, is used for tracking the interface explicitly and updating it over time. The level set method is chosen as it is independent of shape and location of the interface. Thus, a combined XFEM and level set method is developed in this paper. Numerical analysis for pitting corrosion of stainless steel 304 is presented. The above proposed model is validated by comparing the numerical results with experimental results, exact solutions and some other approximate solutions. An empirical model for pitting potential is also derived based on the finite-element results. Studies show that pitting profile depends on factors such as ion concentration, solution pH and temperature to a large extent. Studying the individual and combined effects of these factors on pitting potential is worth knowing, as pitting potential directly influences corrosion rate.

Corrosion behaviour of creep-resistant AE42 magnesium alloy-based hybrid composites developed for powertrain applications

The corrosion behaviour of AE42 magnesium alloy and its composites reinforced with Saffil short fibres and SiC particles in various combinations was investigated. The corrosion rate of the unreinforced alloy was the lowest. The composite reinforced with Saffil short fibre alone exhibited slightly lower corrosion rate than the hybrid composites containing both Saffil short fibres and SiC particles. However, there was no specific trend observed in the corrosion rate of the hybrid composites with respect to the SiC particle content. The degradation of corrosion resistance of the composites was mainly attributed to the irregular and loose surface films.

Surface modification of mild steel by a self-assembled cetyl-trimethyl ammonium bromide (CTAB) monolayer: Evaluation of its corrosion protection property

The surface of mild steel was modified by generating cetyl-trimethyl ammonium bromide (CTAB) self-assembled monolayer (SAM) to enhance the corrosion resistance property. The experimental parameters (pH and time) for SAM generation were optimized. The modified surface was characterized by infrared reflection absorption spectroscopy (IRRAS) and contact angle measurements. The SAM generated in 1 mM solution of CTAB at pH 2.5 for 2 h showed a regimented monolayer. Polarization and electrochemical impedance spectroscopic (EIS) studies demonstrated a significant enhancement in the corrosion resistance property of the SAM protected steel in both 1 M HCl and 3.5% NaCl solution. The CTAB SAM surface substantially reduced the corrosion rate by approximately 4 times in 1 M HCl and 1.5 times in 3.5% NaCl media as compared to bare steel. Scanning electron microscopy images confirmed the formation of lesser amounts of corrosion products on the SAM protected surface. (C) 2015 Elsevier B.V. All rights reserved.

Effect of sulphide on corrosion of copper in seawater

The corrosion of ETP copper in natural seawater and putrid seawater has been studied. The corrosion rates and the sulphide content were monitored at regular intervals. In the absence of oxygen in the putrid media, the presence of sulphide favoured a reduction in the corrosion rate.

Corrosion behaviour of steel in beach soil along Bohai Bay

Research on corrosion of steel structures in various marine environments is essential to assure the safety of structures and can effectively prolong their service life. In order to provide data for anticorrosion design of oil exploitation structures in the Bohai Bay, the corrosion behaviour and properties of steel in beach soil, using typical steel samples (Q235A carbon steel and API 5Lx52 pipeline steel) buried 0.5, 1.0 and 1.5 m deep under typical beach soils in Tanggu, Yangjiaogou, Xingcheng, Yingkou and Chengdao for 1-2 years were studied. The carbon steel and pipeline steel were both corroded severely in the beach soil, with the form of corrosion being mainly uniform with some localised attack (pitting corrosion). The corrosion rate of the carbon steel was up to 0.16 mm/year with a maximum penetration depth of 0.76 mm and that of the pipeline steel was up to 0.14 mm/year, with a maximum penetration depth of 0.53 mm. Compared with carbon steel, the pipeline steel generally had better corrosion resistance in most test beach soils. The corrosion rates and the maximum corrosion depths of carbon steel and pipeline steel were in the order: Tanggu>Xingcheng>Chengdao>Yingkou>Yangjiaogou with corrosion altering with depth of burial. The corrosion of steel in the beach soil involves a mixed mechanism with different degrees of soil aeration and microbial activity present. It is concluded that long term in situ plate laying experiments must be carried out to obtain data on steel corrosion in this beach soil environment so that the effective protection measures can be implemented.

Prediction of marine sediment corrosion by fuzzy clustering analysis

Along with the development of marine industries, especially marine petroleum exploitation, more and more pipelines are buried in the marine sediment. It is necessary and useful to know the corrosion environment and corrosiveness of marine sediment. In this paper, field corrosion environmental factors were investigated in Liaodong Bay marine sediment containing sulfate-reducing bacteria (SRB) and corrosion rate of steel in the partly sediment specimens were determined by the transplanting burying method. Based on the data, the fuzzy clustering analysis (FCA) was applied to evaluate and predict the corrosiveness of marine sediment. On that basis, the influence factors of corrosion damage were discussed.