Volume 33, Issue 3-4

In recent years, magnesium (Mg) alloys have attracted great attention due to superior biocompatibility, biodegradability, and other characteristics important for use in biodegradable implants. However, the development of Mg alloys for clinical application continues to be hindered by high corrosion rates and localized corrosion modes, both of which are detrimental to the mechanical integrity of a load-bearing temporary implant. To overcome these challenges, technologies have been developed to improve the corrosion resistance of Mg alloys, among which surface treatment is the most common way to enhance not only the corrosion resistance, but also the bioactivity of biodegradable Mg alloys. Nevertheless, surface treatments are unable to fundamentally solve the problems of fast corrosion rate and localized corrosion. Therefore, it is of great importance to alter and improve the intrinsic corrosion behavior of Mg alloys for biomedical applications. To show the significance of the intrinsic corrosion resistance of biodegradable Mg alloys and attract much attention on this issue, this article presents a review of the improvements made to enhance intrinsic corrosion resistance of Mg alloys in recent years through the design and preparation of the Mg alloys, including purifying, alloying, grain refinement, and heat treatment techniques. The influence of long-period stacking-ordered structure on corrosion behavior of the biodegradable Mg alloys is also discussed.

This paper reviews the current corrosion fatigue strength issues of light metals, which include the corrosion fatigue cracking behaviors, such as the prior-corrosion pit deformation mechanism, the synergistic interaction between prior-corrosion pits and local stress/strain, the coupling damage behavior under mechanical fatigue loading, and the surrounding environmental factors such as a high humidity and a current 3.5 wt.% or 5.0 wt.% NaCl aqueous solution. The characterization of corrosion fatigue crack growth rate based on simple and measurable parameters (crack propagation length and applied stress amplitude or stress intensity factor) is also of great concern in engineering application. In addition, an empirical model to predict S-N curves of aluminum alloys at the environmental conditions was proposed in this paper. One of the main aims was to outline the corrosion fatigue cracking mechanism, which favors the corrosion fatigue residual life prediction of aluminum alloys subjected to the different environmental media that are often encountered in engineering services. Subsequently, this paper explores recently various surface modification technologies to enhance corrosion fatigue resistance and to improve fatigue strength. For example, the fatigue strength of 2024-T4 aluminum alloy has been modified using plasma electrolytic oxidation coating with the impregnation of epoxy resin modification method to compare with other oxide coating or uncoated substrate alloy.

Sm 2 (Co,Cu,Fe,Zr) 17 are the best high-temperature permanent magnets because of their high Curie temperature (800°C–850°C). However, irreversible and unacceptable coercivity losses retard their use in applications at temperatures over 550°C. The coercivity loss has been correlated with poor oxidation resistance at high temperatures. The current research progress on the effect of oxidation and its prevention, for 2:17-type magnets, is reviewed. Oxidation in air at 500°C–700°C causes the magnets to form three regions: (1) an external oxide scale mainly consisting of (Co x Fe 1-x ) 3 O 4 , (2) a thicker internal oxidation zone where the typical cellular precipitation (2:17R cell and 1:5H cell boundary) structure has been completely collapsed due to the Sm oxidation into Sm 2 O 3 , and (3) an oxidation-free zone where the cellular precipitates remain unchanged in lattice structure. No unacceptable coercivity loss is seen in the oxidation-free zone. Its thickness can be impressively increased within the magnets at high temperature, when they are covered with surface diffusion barriers for oxygen from the atmosphere, such as thin films of Cr 2 O 3 , Al 2 O 3 , and the metals with the ability to thermally grow these oxides.

Carbon dioxide (CO 2 ) corrosion at low partial pressure has been widely recognized, but research on supercritical CO 2 (SC CO 2 ) corrosion is very limited. By far, investigations on steel corrosion under SC CO 2 conditions have mainly focused on the corrosion rate, structure, morphology, and composition of the corrosion scales as well as the electrochemical behaviors. It was found in aqueous SC CO 2 environment, that the corrosion rate of carbon steel was very high, and even stainless steels (13Cr and high-alloy CrNi steels) were subjected to some corrosion. Inhibitor could reduce the corrosion rate of carbon steels and stainless steels, but none of the tested inhibitors could reduce the corrosion rate of carbon steel to an acceptable value. Impurities such as O 2 , SO 2 , and NO 2 and their mixtures in SC CO 2 increased the corrosion rate of carbon steel. However, the existing studies so far were very limited on the corrosion mechanism of steels in SC CO 2 conditions. Thus, this paper first reviews the finding on the corrosion behaviors of steels under SC CO 2 conditions, points out the shortcomings in the present investigations and finally looks forward to the research prospects on SC CO 2 corrosion.

Corrosion is a crucial worldwide problem that strongly affects the oil and gas industry. Natural gas (NG) is a source of energy used in industrial, residential, commercial, and electric applications. The abundance of NG in many countries augurs a profitable situation for the vast energy industry. NG is considered friendlier to the environment and has lesser greenhouse gas emissions compared with other fossil fuels. In the last years, shale gas is increasingly exploited in the USA and in Europe, using a hydraulic fracturing (fracking) technique for releasing gas from the bedrock by injection of saline water, acidic chemicals, and sand to the wells. Various critical sectors of the NG industry infrastructure suffer from several types of corrosion: steel casings of production wells and their drilling equipment, gas-conveying pipelines including pumps and valves, plants for regasification of liquefied NG, and municipal networks of NG distribution to the consumers. Practical technologies that minimize or prevent corrosion include selection of corrosion-resistant engineering materials, cathodic protection, use of corrosion inhibitors, and application of external and internal paints, coatings, and linings. Typical cases of corrosion management in the NG industry are presented based on the authors’ experience and knowledge.

Electrochemical noise measurement and analysis enable one to obtain information on corroding systems without applying any potential or current perturbation to the corroding surface, and they are thereby nondestructive techniques, suitable for corrosion monitoring. The measurement process requires converting the analog potential or current signal in a digital dataset that can be used to perform mathematical operations with a variety of approaches. The analog-to-digital conversion is a critical step since, after the conversion has been performed, it is impossible to correct for artefacts that occurred during the conversion. Additionally, the electrochemical noise generated during corrosion is generally overlapped to the instrumental noise and to the electrical interference that are present in the environment where the measurement is performed. In this work, the process of analog-to-digital conversion of electrochemical noise signals is analyzed in detail by simulating the conversion of a representative simulated noise signal. With this approach, the possible issues arising from the analog-to-digital conversion process are highlighted and the key features arising from instrumental noise, aliasing, and electrical interference are identified.

There has been a considerable surge of experimental inquiry in recent years into understanding the factors responsible for the corrosion inhibition efficiency of chalcones; however, the question of what actually determines the efficiency still remains a topic of debate. In this study, the dependence of the inhibition effect of such two compounds, namely, 3-(3-oxo-3-phenyl-propenyl)-1 H -quinolin-2-one and 3-(3-oxo-3-phenyl-propenyl)-1 H -benzoquinolin-2-one, on their molecular and electronic structure is analyzed using density functional theory calculations. In agreement with experiments, this study found strong evidence to link corrosion inhibition property of the compounds to their actual molecular structures in acidic media.