Band 38, Heft 2

The corrosion mechanism of copper and copper alloy is reviewed. A number of scientific papers have been investigated to determine the corrosion mechanism and protection techniques of copper and copper alloy corrosion. Results have shown that copper can be corroded in an acidic or an alkaline environment, and oxide formation is the corrosion initiation process. The use of corrosion inhibitors is one of several ways of controlling metal corrosion. There are inorganic (toxic) and organic (green) corrosion inhibitors invented so far. Nowadays, environmental issue is a concern of several scientists in the world. From the results of recent scientific papers, green corrosion inhibitors can be used for copper corrosion protection and they are both economical and environmentally safe. Furthermore, future researches are needed to determine more efficient, environmentally friendly corrosion inhibitors for copper and copper alloys.

Corrosion products formed on the surface of two silver brazing alloys after the potentiostatic polarization in 3.5% sodium chloride solution were characterized by the standard methods such as, the X-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy with energy-dispersive spectroscopy. This paper presents the results of a laser desorption/ionization mass spectrometry (LDI MS) analysis as a new approach to the characterization of corrosion products. The potential of the anodic polarization was 0.5 V versus saturated calomel electrode, and the process duration was 300 s. The corrosion layers on both investigated alloys were similar in composition with cuprous chloride and silver chloride as the main components and had strong indications of cuprous oxide formation. The major difference between these two layers was the existence of zinc hydroxychloride as the corrosion product of Ag-Cu-Zn alloy. Palladium compounds were not found in the case of Ag-Cu-Pd alloy. The results of different methods have shown a good consistency. Complementarity between the used methods was useful in the interpretation of the results for each used method. This study has demonstrated that LDI MS can be used as an efficient additional method together with the traditional ones.

This paper describes the study of electrodeposition process by cyclic voltammetry for Zn-Ni bimetallic coating on the X52 carbon steel substrate. Prior to the deposition at the bath temperatures of 25°C, 40°C, and 60°C, investigations were carried out to find the optimum potential range for zinc-nickel coatings with respect to the Ag/AgCl reference electrode. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) was used for surface morphology and elemental composition studies. The corrosion rate of the deposits was studied using the linear polarization resistance (LPR) method by immersing the samples (with and without coating) into 3.5% NaCl solution for 24 h. SEM and EDX results showed that the bath temperature has affected the formation of the microstructures and composition of coating. In addition, micro-cracks, nickel content, mobility of ions and compactness of microstructure increased by raising the bath temperature used for electrodeposition. The corrosion rate obtained from the LPR method can be correlated with the SEM/EDX analysis. The coating deposited at the temperature of 60°C including more content of nickel and micro-cracks led to lower corrosion resistance compared to the coating deposited at the bath solution temperatures of 25°C, 40°C, and non-coated X52 steel. Based on the results, the Zn-Ni coating deposited on the X52 steel substrate in the bath solution at 40°C presented the best performance due to more suitable achievements of microstructure compaction, composition, microcracks, and corrosion resistance observations.

The inhibition effect of Thymus zygis subsp. gracilis (TZ) on mild steel corrosion in 1 m hydrochloric acid has been investigated by weight loss measurements, surface analysis [scanning electron microscopy (SEM)-energy-dispersive X-ray (EDX), three-dimensional (3D) profilometry, and Fourier transform infrared analysis], potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Gravimetric results indicate that TZ exhibits good inhibition efficiency of 80.40% attained at 3 g/l. Polarization measurements show that the studied inhibitor is a mixed type. EIS measurements revealed that the charge transfer resistance increases with increasing concentration of TZ, which suggests a Langmuir adsorption isotherm model. Based on SEM-EDX and 3D profilometry, it appears that the surface is remarkably improved in the presence of TZ oil compared to that exposed to the acid medium without TZ oil. From the obtained results, it can be concluded that this oil is a new natural substance that can be used against material corrosion in aggressive medium.

Gel capsules of calcium alginate as a matrix stuffed with a non-ionic surfactant, namely 2-(2-(3,4-bis(2-methoxyethoxy)tetrahydrofuran-2-yl)-2-(2-methoxyethoxy)ethoxy)ethyl stearate, Tween-60, as an inhibitor was prepared by a piercing-solidifying method for corrosion protection of carbon steel tubes from produced water in acidizing oil wells. The Fourier transform infrared and thermal gravimetric analysis techniques were used to study the properties of the capsules. The release of the inhibitor from the solid capsules to the corrosive acidizing produced water was studied gradually using ultraviolet-visible spectroscopy. A heavy additive was used to promote the sinking of the capsules in the oil well downhole tubes. The inhibitive effect of the released inhibitor on carbon steel in the corrosive produced water in acidizing oil wells was investigated using weight loss measurement, potentiodynamic polarization, electrochemical impedance spectroscopy, and morphologically by scanning electron microscopy. It was found that the inhibition efficiency increases with the increase of inhibitor release. The increase in temperature leads to partial desorption of inhibitor molecules at the metal surface, which causes increase in the corrosion rate. The positive sign of the activation enthalpy (Δ H a ) reflects the endothermic nature of the carbon steel dissolution process.

High-temperature oxidation of E110 (Zr-1%Nb) zirconium alloy in steam at Т = 1100°C to various degrees has been carried out. Based on the studies of morphology and microstructure of the oxide film and metal, as well as on review of previously published results, the mechanism of alloy oxidation has been proposed, which includes oxide thickening close to the oxide/metal interface, growth of the thickened areas and their conversion into nodules, growth of the nodules and crowning of the metal surface (white spots), clustering of nodules under the formed oxide, formation of a double (white on the surface) oxide film and delamination of the oxide upper layer.

In order to advance material development for future nuclear systems, an insight into the cracking conditions of T91 ferritic-martensitic steel in heavy liquid metals (HLM) is provided. The paper critically reviews previous experimental data and summarizes them with new results. The new testing of T91 steel was performed in contact with slow flow and static HLM to study crack initiation, especially in liquid PbBi eutectic at 300°–350°C and Pb at 400°C with about 1 × 10 −6 wt.% of oxygen. Pre-stressed coupons were exposed to the liquid metals for up to 2000 h. Constant extension rate tests (CERTs) were performed in the liquid metals to accelerate cracking development. Under static conditions, the testing resulted in oxidation without any crack observation. Under the CERT ones, the T91 steel showed a tendency to crack initiation in PbBi, while in Pb, cracks were not initiated even when the oxide layer was broken. Moreover, the environmentally assisted crack initiated at the maximum load and continued to grow under further loading without unstable failure. Both previous and new data have confirmed that high stress and plastic strain are pre-conditions for the environmentally assisted cracking of T91 in static HLM. It indicates that in the systems utilizing continuous oxygen control of HLM, the LME/EAC of the T91 could develop only in the beyond design load conditions. Further testing is necessary to address the HLM flow speed effect.