Fresh Metal Surface Research Articles

Corrosion protection effect of rust and scales: A “metal protects metal” perception by considering the examples of hematite and magnetite

AbstractThe present report proposes a contradictory remark on the idiom “Iron cuts Iron” that could be synonymized as “Metal cuts Metal” using the example of hematite and magnetite. Most metals and alloys are highly reactive, forming rusts and scales primarily consisting of metal oxides. The formation of metal oxide layers is known as passivation. Generally, passivated metallic surfaces provide anticorrosive protection by avoiding the attacks of corrosive species on the fresh metal surface; therefore, “Corrosion is a Necessary Evil (CNE).” Most passive films are protective, but not all, and their actual nature can be determined using the Pilling–Bedworth ratio (PBR). In dry conditions, passivation occurs spontaneously by the oxidation of metal atoms, but in aqueous media, some external additives, called passivators, are added to build the passive films. Herein, by considering examples of hematite and magnetite, the anticorrosive properties of rusts and scales are described in dry and wet (solution and coating) environments.

Investigation of Hafnium Oxide Containing Zirconium in the Scaled Region on the Surface of As-Cast Nickel-Based Single Crystal Superalloy Turbine Blades

Surface scale is usually formed in the aerofoil part of as-cast nickel-based single crystal turbine blades by the strong interaction between the mould wall and the melt, and the subsequent oxidation of the fresh metallic surface of the casting. For better understanding of the scaling, the scaled region was investigated, and an interesting region containing hafnium oxides and a rhenium-rich particle was found. Generally, a continuous aluminium oxide layer was detected on the outer surface of the base material and covered the surface of an unscaled region. In contrast, there was no oxide on the surface of a scaled region, but it was replaced by several tiny particles remaining locally on the outer surface of the base material. SEM-EDX and TEM-EDX point analysis of these particles indicated not only the existence of high amounts of hafnium, but also several particles such as hafnium oxide, aluminium oxide, and even tiny metallic particles. Most of all, STEM-EDX point analysis clearly detected zirconium in the hafnium oxide. Furthermore, a rhenium-rich particle was also detected towards the outer surface of the base material, which suggested that the surface of the scaled region might be exposed to high enough temperatures to allow the diffusion of heavy alloying elements. Based on the observation, the formation mechanism of hafnium oxide containing zirconium and its meaning was discussed.

In situ investigation of aluminum oxide under irradiation by electron beam at atomic-scale

It has yet to be experimentally proven whether the native aluminum oxide layer can still effectively protect pure aluminum from further degradation under an irradiation environment. Here, we directly investigate the microstructure evolution of amorphous Al2O3 in real time by using an electron beam as an irradiation source with in-situ transmission electron microscopy (TEM). At the atomic scale, crystalline Al2O3 grains were found to nucleate and grow along amorphous substrate. With continuous irradiation, both amorphous and newly formed crystalline Al2O3 were removed completely, and then the internal fresh aluminum was exposed. By regulating electrons, new oxides quickly formed on the fresh metal surface and merged with adjacent old oxides, finally leaving a uniform amorphous oxide protection layer. Our work provides experimental evidence for understanding the protection mechanism for the oxide layer on its internal metal under a special service environment.

Investigations of the intrinsic corrosion and hydrogen susceptibility of metals and alloys using density functional theory

Abstract Mechanisms for materials degradation are usually inferred from electrochemical measurements and characterization performed before, during, and after exposure testing and/or failure analysis of service materials. Predicting corrosion and other materials degradation modes, such as hydrogen-assisted cracking, from first-principles has generally been limited to thermodynamic predictions from Pourbaix or Ellingham diagrams and the Galvanic series. Using electronic structure calculations, modern first-principles methods can predict ab initio the key rate-controlling processes for corrosion and hydrogen susceptibility as a function of pH, potential, and solution chemistry, and materials composition and microstructure. Herein we review density functional theory (DFT) approaches for studying the electrochemical reactions occurring on fresh metal and alloy surfaces related to environmentally assisted cracking and localized corrosion/pitting. Predicted changes in surface chemistry as a function of the environment were correlated against experimental crack growth rate data obtained for alloys 718, 725, and pipeline steel under electrochemical control. We also review the application of the method to study the effects of alloying on the chloride susceptibility of stainless steels and Ni–Cr-based corrosion-resistant alloys. Perspectives for improving the model are given, and extending it to future fields of application in corrosion science and engineering.

Crack growth behavior of 725 in seawater under cathodic polarization

Hydrogen embrittlement behavior of four heats of alloy 725 (H1, H2, H3, and H4) were characterized by measuring the crack growth rate response over a range of cathodic potentials. Significant grain boundary precipitation in two heats (H1 and H3) may have contributed to higher susceptibility, as evidenced by higher values of crack growth rate. The crack growth rate increased with increasing twin fraction. The crack morphology exhibited evidence of intergranular as well as slip band cracking. The crack growth rate response of the two heats that were less susceptible (H2 and H4) were evaluated in more detail over a range of applied potentials and stress intensity factors. Evidence of nano void formation at the intersection of dislocation slip bands, and grain boundaries suggests that hydrogen stabilized vacancies may play a role in the crack growth mechanism. Crack growth rate exhibited a strong response with applied potential varying by as much as 100 times in the potential range of −1050mV SCE to −850mV SCE. Over the range of K values evaluated, the crack growth rate increased by a factor of 3to 30 with applied K depending on the applied potential. The crack growth rate was related to the water adsorption on fresh metal surfaces of alloy 725 in the anticipated crack tip conditions. A crack tip strain rate based approach was applied to model the measured crack growth response.

Mechanochemical synthesis and spark plasma sintering of hafnium carbonitride ceramics

Submicron powder of non-stoichiometric hafnium carbonitrides (HC0.5N0.2) was fabricated by the mechanochemical synthesis method. It was shown that during the first milling stages, primarily reaction between hafnium and carbon took place. The nitridation occurred later when fresh metal surfaces started to form through defragmentation of the brittle layer of a carbon-solid solution. The synthesized powder was consolidated by spark plasma sintering approach to producing dense bulk hafnium carbonitride ceramics. Hardness and fracture toughness measured on consolidated samples were 20.8 ± 1 GPa и 3.5 ± 0.2 MPa∙m1/2, respectively. The obtained results were compared with previously reported data.

Preparation of Artificial SEI Containing LiNxOy on Lithium Metal Anode By Solid-Gas Interface Reaction for Sulfolane Electrolyte

Li-S battery is promising next generation energy storage device, and lithium metal anode is promising electrode due to its low electrochemical potential and high theoretical specific capacity. However, the Li metal anode in Li-S battery has problems such as short circuit by growth of dendrite and low coulombic efficiency by continuous electrolyte decomposition. In past study, it was reported that high concentration sulfolane electrolyte attributed to prevent polysulfide dissolution into electrolyte and suppressed shuttle effect.1) Also, by adding LiNO3 into electrolyte, stable passivation film formed on lithium metal anode, and lithium deposition became rounded shape and dendrite was suppressed, and long life was reported to be achieved.2)3) While LiNO3 does not dissolve much in high concentration sulfolane electrolyte, in this study, in order to achieve the effect of LiNO3 even with high concentration sulfolane electrolyte, artificial SEI including LiNxOy made by solid-gas reaction was examined. Solid-gas reaction is considered to have also the advantage for the mass production.In order to produce artificial SEI containing LiNxOy on Li metal anode, which is LiNO3-derived component, polished Li foil was exposed to NO2 gas for 1 h. For the purpose of reacting fresh Li metal surface with NO2 gas, surface of Li foil was polished until metallic luster appeared.Fig. 1 shows XPS spectra (N1s) of polished Li and NO2 exposed Li. Fig. 1 shows the existence of LiNxOy by an exposure to NO2.Fig. 2 shows charge-discharge curves in Li/Li symmetrical cells. Fig. 2(a) shows charge-discharge curve using the polished Li, and Fig. 2(b) shows the one exposed to NO2. In Fig. 2(a), short circuit was recognized by only 5 cycles of charge and discharge. Contrastingly, analogous voltage profile was obtained for 16 cycles, as shown in Fig. 2(b). In addition, from Fig. 2(b), a larger overvoltage in voltage plateau was confirmed than that in Fig. 2(a). The reason is considered to be that Li electrode surface is covered with artificial SEI composed of inorganic components such as LiNxOy having relatively high ionic resistance. In addition, it was suggested that the artificial SEI improved the morphology of lithium deposition to smoother one from the SEM investigation.With an exposure to NO2 on Li metal anode, it was confirmed that artificial SEI containing LiNxOy was prepared and contributed to a certain improvement in cycle life in Li/Li symmetrical cell. Acknowledgement This work was partly supported by Advanced Low Carbon Technology Research, Development Program Special Priority Research Area “Next-Generation Rechargeable Battery” (ALCA-Spring) from the Japan Science and Technology Agency (JST) (Grant Number JPMJAL1301). Reference 1) Azusa Nakanishi et al, Phys. Chem. C, 2019, 123, 14229-142382) Allen Pei et al, Nano Lett. 2017, 17, 2, 1132-11393) Doron Aurbach et al, J. Electrochem. Soc., 2009, 156, A694 Figure 1

Hydrogen Embrittlement of Low Alloy Steels Under Cathodic Polarization

Hydrogen embrittlement of low alloys steels at three different strength levels (745 Mega Pascals [MPa], 904 MPa, and 1,166 MPa) were evaluated under cathodic polarization. Crack growth rate measurements were performed under constant stress intensity (K) conditions, as a function of applied K values as well as applied potential to characterize the behavior of the three different steels. At −1,050 mVSCE saturated calomel electrode (SCE), the threshold stress intensity (Kth) value increased from 44 MPa√m to 60 MPa√m as the yield strength decreased from 1,166 MPa to 745 MPa. The crack growth rate at 66 MPa√m and −1,050 mVSCE decreased from 3 × 10−5 mm/s to 4 × 10−8 mm/s as the yield strength decreased from 1,166 MPa to 745 MPa. For the 1,166 MPa steel at low values of K, the crack growth rate decreased by two orders of magnitude as the potential decreased from −1,000 mVSCE to −950 mVSCE. At higher values of K, the effect of potential on the crack growth rate was not as significant. The 745 MPa steel in general exhibited slow crack growth rate values (2 to 4 × 10−8 mm/s) over the range of K values and applied potentials in which it was evaluated. Water adsorption on fresh metal surfaces in the estimated crack tip chemistry was modeled using density functional theory. The variation in crack growth rate with applied potential at low and intermediate values of K correlated with the fractional coverage of water adsorption on the fresh metal surface. It is proposed that the water reduction reaction and the subsequent generation of hydrogen are the rate limiting steps in the slow subcritical crack growth rate processes for low alloy steels under the conditions evaluated. For the higher values of K, where the crack growth rate showed a weak dependence on applied potential, water reduction, and generation of hydrogen are likely not the rate limiting steps.

A novel permselective organo-polysulfides/PVDF gel polymer electrolyte enables stable lithium anode for lithium–sulfur batteries

Lithium–sulfur (Li–S) battery can satisfy the need of the future power battery market because of its high energy density, but the hidden dangers caused by lithium anode have seriously hindered their commercialization. Herein, an innovative gel polymer electrolyte (GPE) composed of polyvinylidene fluoride (PVDF) and organo-polysulfide polymer (PSPEG) is proposed, which could be used in semi-solid-state Li–S batteries for protection of Li anodes. Particularly, organo-polysulfide polymer could chemically/electrochemically generate both inorganic and organic components simultaneously in-situ once contacting fresh Li metal surface and/or during discharging processes. And these inorganic/organic components could participate in the formation of the SEI layer and finally constitute a stable and flexible hybrid SEI layer on the surface of Li metal anode. Moreover, the organic components were permselective to lithium ions against anions. Therefore, PVDF/PSPEG GPE ensures the ideal chemical and electrochemical properties for Li–S batteries. Our work demonstrates an effective solution to solve the problems about Li anodes and contributes to the development of the safe Li metal batteries.

Hydrogen embrittlement of 718 under cathodic polarization

High strength nickel based alloys are extensively used in both O&G and Navy applications. 718 is one of the most commonly used alloys in these applications. Applied cathodic potential had a significant effect on the crack growth rate (CGR) of various grades of 718. Crevice geometry was used to estimate the crack tip pH and potential conditions under cathodic polarization. Density functional theory (DFT) modelling was performed to estimate the water coverage on fresh metal surfaces of 718 under the crack tip conditions. The CGR was related to the estimated water adsorption on fresh metal surfaces in the measured crack tip conditions.

The multiple roles of a chemical tribofilm in hydrogen uptake from lubricated rubbing contacts

A newly developed in-situ technique has been employed to investigate the effect of lubricant additives and water contamination in oil on hydrogen intrusion into the steel. Hydrogen in oil-lubricated contacts is generated as a result of tribochemical reactions. The hydrogen uptake measurement results indicated that tribofilm formation can impede hydrogen ingress, in the substrate, by impeding the formation of fresh metal surfaces. This reduces the generation of hydrogen atoms by preventing the decomposition of hydrocarbon molecules. A uniform tribofilm across the wear track also acts as a physical barrier for hydrogen permeating through the tribo-contact. The water contamination in the oil negatively influenced tribofilm properties and therefore led to higher permeation of hydrogen into the steel.

Surface Modification of Rusted Rebar and Enhanced Passivation/Anticorrosion Performance in Simulated Concrete Pore Solutions with Different Alkalinity

Naturally exposed rusted rebar has been widely used for the production of reinforced concrete. However, rusted rebar is prone to corrosion under chloride ion (Cl−) contamination and/or at a low alkalinity of concrete. This study employed two surface modification methods, sand blasting and wire brushing, to augment the corrosion resistance of naturally exposed rusted rebar. Electrochemical tests revealed that the surface-modified rebar displayed a significant improvement of passivation in the concrete alkaline environment and anticorrosion performance in both the Cl− free and Cl−-containing simulated concrete pore solutions of different alkalinity. The enhanced performance was mainly due to the elimination of the rust layer and the direct exposure of the fresh metallic surface to the alkaline medium. Moreover, the effect of surface nanograins on the intensified passive film led to the best passivation performance of the wire-brushed rebar. The overall findings demonstrate that the two developed methods were conducive to the passivation and anticorrosion performance of the rusted rebar and thereby hold great promise for improving the service life of the reinforced concrete structures.

Liquid-Like, Self-Healing Aluminum Oxide during Deformation at Room Temperature.

Effective protection from environmental degradation relies on the integrity of oxide as diffusion barriers. Ideally, the passivation layer can repair its own breaches quickly under deformation. While studies suggest that the native aluminum oxide may manifest such properties, it has yet to be experimentally proven because direct observations of the air-environmental deformation of aluminum oxide and its initial formation at room temperature are challenging. Here, we report in situ experiments to stretch pure aluminum nanotips under O2 gas environments in a transmission electron microscope (TEM). We discovered that aluminum oxide indeed deforms like liquid and can match the deformation of Al without any cracks/spallation at moderate strain rate. At higher strain rate, we exposed fresh metal surface, and visualized the self-healing process of aluminum oxide at atomic resolution. Unlike traditional thin-film growth or nanoglass consolidation processes, we observe seamless coalescence of new oxide islands without forming any glass-glass interface or surface grooves, indicating greatly accelerated glass kinetics at the surface compared to the bulk.

Behaviors and effects of Zn coating on welding-brazing process of Al-Steel and Mg-steel dissimilar metals

The behaviors and effects of Zn-coating on the welding-brazing processes of steel with aluminum and magnesium were investigated by Cold Metal Transfer (CMT) arc. The behaviors of Zn-coating at the very beginning of burning and during the spreading of the liquid aluminum and liquid magnesium droplet over the steel plate were observed respectively. The effects of Zn-coating on the wetting process of liquid droplets and on the fracture of welding-brazing joints were analyzed. The effects of Zn-coating on joining mechanisms and tensile load of Al-steel joints and Mg-steel joint were compared and analyzed. For Al-steel, Mg-steel, some common behaviors can be found, the main effect of Zn is its evaporation which decreases the temperature at the interface to prevent steel from melting and makes the steel to expose the fresh metallic surface which is much easier to be spread by a liquid droplet than an oxidized surface. Zn-coating improves the wettability of liquid Al or liquid Mg over the steel surface. However, some effects of zinc coating on wetting behavior, joining mechanisms and tensile load of Al-steel joints and Mg-steel joint are still different. For Al-steel arc, Zn-rich triangle zone is not formed by driving the liquid Zn from inside and accumulated at the toe, rather it is formed by the diffusion of the liquid Zn from outside Zn-enriched periphery into the droplet. In the case of Mg-steel arc, the Zn-rich zone forms partly due to the accumulation of Zn driven from the center during the Zn evaporation. For Al-steel joint, Zinc coating has not reacted to form the interface layer between Al weld metal and steel, however, zinc coating reacted to form the interface layer between Mg weld metal and steel. Zinc coating improved the strength of Al-steel joints, but, it is not beneficial to the strength of Mg-steel joint.

Anodic Dissolution Behavior of the Crack Tip of X70 Pipeline Steel in Near-Neutral pH Environment

In this work, the anodic dissolution behavior of the fresh metal surface at crack tip of X70 steel in near-neutral pH environment was investigated using galvanic corrosion simulation method. The solution environment, strain, strain rate, hydrogen enrichment, and fresh metal surface at the crack tip were considered. Corrosion current of the specimen during fast stretching increased linearly with plastic strain. The increment and increase rate of the corrosion current during plastic deformation stage were dependent on the strain rate. Combining Faraday’s law and crack tip strain rate equation, the crack growth rate (CGR) induced by the anodic dissolution of the fresh metal surface was calculated. Results show that CGR caused by anodic dissolution was roughly one order lower than that measured on the compact tensile specimen under cyclic load. This finding indicated that hydrogen embrittlement may play a dominate role in stress corrosion crack propagation of pipeline steels in near-neutral pH environment.

An insight on amine air-cooled heat exchanger tubes’ corrosion in the bulk CO2 removal plant

The corrosion behavior of activated MDEA solution was investigated in the background of CO2 bulk removal in ammonia plant, Kermanshah, Iran. The visual inspection reports demonstrated a consistent pattern of damage at the tubes’ entrance of lean amine air-cooled heat exchanger, made from carbon steel. To provide information on the corrosion in tubes, a series of experiments was carried out at 85°C, with different combinations of CO2 loading (0.02, 0.25 and 0.6mol/mol) using electrochemical techniques, weight loss coupons, chemical analysis, and surface analytical techniques. Results showed that the dominant process was the effect of erosion corrosion. It seems that impinging particles remove the semi-protective layer of FeCO3 on the carbon steel surface, resulting in continuous exposure of fresh metal surface to the corrosive environment, and a higher corrosion rate.

Thin-film Deposition of Silicon Nitrides and Oxides from Trihydridosilanes

Trihydridosilanes can provide a route for generating self-assembled monolayers on metal substrates. Under mild conditions, these precursors interact with a variety of clean, hydrogenated and fresh metal and metalloid surfaces, including titanium, silicon and gold. All classes of hydridosilanes have minimal interaction with anhydrous oxide surfaces. After initial deposition, SAMs formed from 2-chloroethyltrihydridosilanes may be converted to silicon nitride by pulsing with ammonia or silicon dioxide by pulsing water or oxygen. A proposed mechanism for the initial steps of deposition involves the dissociative adsorption of the silanes with the formation of hydrogen, followed by topmost atom layer insertion and concomitant surface reconstruction

Thin-film Deposition of Silicon Nitrides and Oxides from Trihydridosilanes

MOCVD of trihydridosilanes provides a route for generating self-assembled monolayers on metal substrates. Under mild conditions, trihydridosilanes interact with a variety of clean, hydrogenated and fresh metal and metalloid surfaces, including titanium, silicon and gold.1 In contrast, monohydridosilanes appear to have minimal interaction. All classes of hydridosilanes have minimal interaction with anhydrous oxide surfaces. A proposed mechanism for the initial steps of deposition involves the dissociative adsorption of the silanes with the formation of hydrogen, followed by topmost atom layer insertion and concomitant surface reconstruction. New alpha, omega bis(trihydrido)silane precursors are also described which offer the ability for dipodal substrate interaction. Alpha, omega trihydridosilane terminated oligopermethylsilanes with the potential to form molecular wires are presented.2 1 B. Arkles, Y.Pan, Y. Kim, E. Eisenbraun, C. Miller, A. Kaloyeros, J. Adhesion Science and Technology, 2014, 2012, 41. 2 B. Arkles, Y. Pan, G. Larson, US Pat. 8,575,381, 2013.

Changes in valence, coordination and reactivity that occur upon oxidation of fresh metal surfaces

To promote a greater understanding of the process and nature of metal passivation, we have performed a first-principles analysis of partially oxidized Ni(111) and Ni(311) surface and ultra-thin film NiO layers on Ni(111). We have adopted a bimodal theoretical strategy that considers the oxidation process using either a fixed generalized gradient approximation (GGA) functional for the description of all atoms in the system, or a perturbation approach, that perturbs the electronic structure of various Ni atoms in contact with oxygen by application of the GGA+U technique. This strategy allows us to assess the relative merits of the two approaches, and whether or not the two approaches are at variance with one another as concerns the process of metal passivation. We consider oxygen binding in the cases of isolated atomic adsorption, the development of an oxygen monolayer, and epitaxial NiO(111) monolayers and bilayers with various terminations. Selective application of GGA+U drives structural and charge-transfer processes at the interface, in particular, the octopolar reconstruction of high oxygen coverage pre-passive systems, which, in fact, template an epitaxial NiO(111)-oriented film. These outputs are observable through the development of cationic states in the nickel atoms at the interface, the emergence of a band gap in the projected density of states and in oxygen binding energies that approach the energy of oxide formation.

Deformation characteristic of aluminum sheet/powders/aluminum sheet sandwich rolling process

The aluminum sheet/powders/aluminum sheet sandwich rolling process which was applied to manufacturing precursor of foam aluminum sandwich panel was put forward. The purpose of sandwich rolling was to obtain high densification precursor and bonding of metal face-sheet/powders interface. Compared with mold-compacting, powder densification process and deformation characteristic of interface were studied for the first time in the process of aluminum sheet/powders/aluminum sheet sandwich rolling. The experimental results show powder deformation is a continuous deformation process. Elastic deformation and plastic deformation were produced in powders, thus powders became lamellar structure under rolling pressure. Powders were compacted bonded and atomic force formed among the powders. Metal aluminum sheet exposed fresh metal surface under tensile rolling force. Powders near the interface filled the fresh surface of the metal face sheet and bonded each other.