New surfactants N‐alkyl‐N,N‐dimethyl‐N‐(3‐thienylmethylene)ammonium bromides: Preparation and anticorrosion evaluation

A new series of N‐alkyl‐N,N‐dimethyl‐N‐(3‐thienylmethylene)ammonium bromides (designated as NTA‐n, n = 8, 10, 12, 14, and 16) were synthesized. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization showed that NTA‐n could protect availably X70 steel from attack of HCl with an inhibition efficiency of about 95%. And the inhibition ability follows the following sequence: NTA‐8 < NTA‐10 < NTA‐12 < NTA‐14 < NTA‐16, suggesting that prolonging alkyl chain may enhance the inhibition capacity of the molecules. Theoretical investigation backs up well the experiment results. The correlation of theoretical calculation with the experiment results illustrated clearly double logarithmic relations between the corrosion current and the computed quantum chemical parameters such as the highest occupied molecular orbital energy (), energy gap (ΔE), molecular volume ( ν), electronegativity ( χ), the total energy of iron crystal with the adsorbed inhibitor molecule ), the interaction energy of Fe (1 0 0) surface and inhibitor molecules (), while an equation resembling Hammet relation was existed between the corrosion currents and the fraction of electrons transfer (ΔN). These linear correlations suggest the relation of the inhibitor structure with its inhibition activity: long alkyl chain and electron donating groups in NTA‐n will enhance the corrosion efficiency.     

Microstructural investigation of PGM‐based alloy coatings for oxidation protection

It is well known that Pt addition significantly improves the resistance of aluminide coatings to high‐temperature oxidation and hot corrosion, which has led to the widespread application of Pt modified aluminide coatings on the superalloy components of advanced gas turbine engines. Other platinum group metals (PGMs) such as Ir and Ru attract researchers for high temperature applications. In this study, oxidation properties of Pt‐Ir and Pt‐Ru based alloy coatings were investigated. Pt, Ru, and Ir were electroplated on a directionally solidified Ni‐base superalloy DZ125. The cyclic oxidation test revealed that both Pt‐Ir and Pt‐Ru alloys exhibited good oxidation performance. The effect of substrate alloy and coating compositions on microstructural changes during cyclic oxidation tests were discussed.     

Lochkorrosion nichtrostender Stähle und hochlegierte Fe/Ni/Cr/Mo‐Werkstoffe ‐ Entwicklungsstufen und Untersuchungsverfahren

Pitting corrosion of stainless steels and high‐alloyed Fe/Ni/Cr/Mo materials – Stages of development and test methods In relation to the stages of development of pitting the characteristics and factors of influence are explained. After the explanation of distinct pitting potentials different ways of the detection of the stages of pitting are highlighted and their influencing through characteristic featues of the metal, of the chemical composition of the medium, and of the physical conditiones are pointed out. Based upon these facts, loading and methods of analyses and evaluation for the test of pitting resistance are discussed and chemical and electrochemical tests are described which are important to solve technical problems. Furthermore a test for the determination of the pitting resistance of welds directly performed at apparatus and equipments is explained which is still in the development stage.     

Early‐stage oxidation behavior of Co‐rich high‐temperature alloys

The long‐term oxidation performance of an alloy is critically linked to the early‐stage oxidation behavior of high‐temperature alloys. This study investigates early‐stage oxidation behavior in terms of oxidation kinetics, scale evolution, and residual stresses developed within a scale of the commercially available cobalt‐rich alloys: HAYNES® 188, 6B, 25, and HR‐160® and a newly developed nitride‐dispersion strengthened NS‐163® alloy (HAYNES®, HR‐160®, NS‐163® are registered trademarks of Haynes International, Inc). Short‐term isothermal oxidation exposures were conducted in flowing air at 982 °C for durations of 1–50 h. Oxidation kinetics was assessed by weight‐change behavior, which showed that 188 alloy exhibited the lowest weight‐gain, while for similar times HR‐160 alloy underwent weight‐loss. SEM/EDS analysis was performed to characterize oxides formed in these alloys, while stresses developed in the oxides of different alloys were measured using synchrotron X‐ray radiation. The results in this paper clearly demonstrated the effects of alloy composition on the scale evolution and the amount of stresses developed in oxides.     

The inhibitive effect of 5‐amino‐indole on the corrosion of mild steel in acidic media

The inhibitor performance of 5‐aminoindole (5‐AI) on mild steel corrosion in 0.5 M HCl was investigated in relation to the inhibitor concentration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization (LPR) methods. The effect of immersion time on the corrosion behavior of mild steel was also studied. The impedance data obtained were fitted and modeled using an equivalent circuit model. The results show that 5‐AI is an effective inhibitor and has an inhibition efficiency of 90% at 1 × 10^?2 M additive concentration. The adsorption behavior of 5‐AI was also investigated. For this purpose, the adsorption equilibrium constant (K_ads), and the free energy of adsorption (ΔG_ads) were calculated and discussed. It was found that 5‐AI acts as mixed‐type inhibitor and obeys Langmuir adsorption isotherm with a free energy of adsorption of ?27.71 kJ/mol.     

Correlation of stress corrosion cracking behaviour with electrical conductivity and open circuit potential in Al‐Li‐Cu‐Mg‐Zr alloys

Studies of stress corrosion cracking (SCC) behaviour by slow strain rate test (SSRT), potentiodynamic electrochemical polarization and measurement of electrical resistivity were carried out on 8090 and 1441 Al‐Li‐Cu‐Mg‐Zr alloys in their peak aged T8, over aged T7 and retrogressed and reaged (RRA) T77 tempers. It has been found that the SCC resistance is maximum in the T7 temper, least in the T8 temper and in the RRA T77 tempers it lies in between to that of the T8 and T7 tempers, indicating that RRA heat treatment given to the T8 temper of both alloys caused an improvement of SCC resistance. Further, studies on the electrical conductivity measurements and electrochemical polarization of all tempers of both alloys showed that T7 temper has maximum electrical conductivity and most negative (anodic) open circuit potential (OCP), T8 has the minimum and the least respectively, whereas, in the T77 tempers these values lie in between to those of the T8 and T7 tempers. Therefore, a definite pattern of variation of these results with RRA treatment draws an attention to correlate SCC behaviour, electrical conductivity and OCP values which are explained on the basis of microstructural features revealed by TEM and XRD studies.     

An in‐situ FT‐IR investigation of the anodic behaviour of WC‐Co hardmetal

An in‐situ FT‐IR spectroelectrochemical and voltammetric study of the corrosion of a WC‐Co hardmetal grade is reported in this communication. A slightly acidic sulphate solution is considered. The potential‐ and time‐dependent anodic formation of CO₂ and Co(OH)₂ can be followed with the variation of the vibrational spectra. The formation of CO₂ occurs at the same potential at which tungsten oxidation starts to be detected and the breakdown of passivity can be observed by electrochemical methods. Our results suggest that a threshold potential exists for the oxidation of WC in WC‐Co, giving rise to the concomitant oxidation of tungsten and carbon at more noble potentials than those typical for the oxidation of the individual elements.     

X‐Ray photoelectron spectroscopic investigations of powder coated steel

Polyester powder coatings are used for corrosion protection of different materials. XPS studies were performed in order to characterize such coatings on steel surfaces as a pre‐treatment for following applications like gluing. Different surface treatments by alkaline cleaner, plasma treatment (Plasma Treat® process), and the use of a silicoater (Pyrosil® process) were investigated. In dependence of such treatments, the resulting surfaces are found to be hydrophilic or hydrophobic. Although this behavior can also be investigated by contact‐angle measurements, the aim of our work is the element‐specific characterization of chemical bonding states (speciation).     

X‐ray micro‐computed tomography analysis of accumulated corrosion products in deep‐water shipwrecks

Accumulated corrosion products from two different shipwrecks which had lain on the seabed (2.5 km depth) for 73 years were systematically analysed by three‐dimensional imaging at high resolution using X‐ray micro‐computed tomography. Complementary surface and chemical characterization experiments were conducted to identify the morphological structure of the corrosion products. Goethite was observed as the main corrosion phase found in both the wreck's corrosion products. However, other corrosion products such as silica, lepidocrocite, maghemite, magnetite, benyacarite, jarosite and amorphous materials were noticed using Fourier transform infrared spectroscopy, Raman spectroscopy and X‐ray diffraction. In addition, mineralized microbial structures were also observed as significant constituents of the corrosion products. However, there were significant differences between samples from the two shipwrecks including porosity, distribution and volume percent of the corrosion products components. The mechanism of different corrosion products formation was proposed and discussed in detail.     

Corrosion characteristics of the wrought Ni‐Cr‐Mo alloys

This paper concerns the wrought, nickel‐chromium‐molybdenum (Ni‐Cr‐Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni‐Cr‐Mo alloys in several key chemicals, using iso‐corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni‐Cr‐Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C‐2000® alloy.     

Sulfate‐reducing bacteria‐assisted hydrogen‐induced stress cracking of 2205 duplex stainless steels

The paper presents the results of a laboratory investigation of the microbiologically assisted hydrogen‐induced stress cracking (HISC) of 2,205 duplex stainless steel (DSS). The testing of susceptibility toward HISC was performed with two different methods. Precharged in sulfate‐reducing bacteria (SRB), inoculated medium samples were subjected to slow strain‐rate testing in artificial seawater. In situ constant load tests were performed directly in SRB‐inoculated medium under hydrogen charging at 70% of the ultimate tensile strength. Samples tested in the biotic (SRB) conditions showed a considerable loss of ductility as compared to those tested in sterile conditions. Quantitative characteristics of fracture surfaces indicated increased susceptibility to HISC of biotic samples, therefore, suggesting a role of SRB in promoting hydrogen damage of DSS.