bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Impedance Spectroscopy: Analysis of Formation of Chromate Film
Authors: Hoshi Yoshinao , Endo Yuta , Shitanda Isao , Itagaki Masayuki
Published: February 2020

A chromate conversion coating (CCC) shows the high corrosion resistance and improves the paint adhesion of the base metal[1-4]. It is well known that the scratch or defect in the CCC is protected without further treatment due to the self-healing effect of CCC[2]. We applied a three-dimensional (3D) impedance spectroscopy[5-7] to investigation of the self-healing effect of the chromate film formed on a steel. It is possible to obtain the film resistance with time information because the impedance was plotted on the 3D diagram whose axes are real, imaginary and time. In the present study, the scratched electrodes were used for the 3D impedance measurement in order to investigate the self-hearing effect of the chromate film. The instantaneous impedance was determined at arbitrary time from 3D impedance plot. The film resistance R
df of each electrode was estimated by the curve fitting of the instantaneous impedance with using the equivalent circuit. The increasing rate of R
df until steady state condition was determined precisely.

References:

[1] J.R. Waldrop, M.W. Kendig, J. Electrochem. Soc, 145 (1998) L11-L13.

[2] L. Xia, R.L. McCreery, J. Electrochem. Soc, 145 (1998) 3083-3089.

[3] O. Lunder, J.C. Walmsley, P. Mack, K. Nisancioglu, Corros. Sci., 47 (2005) 1604-1624.

[4] A.S. Hamdy, I. Doench, H. Mohwald, Thin Solid Films, 520 (2011) 1668-1678.

[5] Z. B. Stoynov, B. S. Savova – Stoynov, J. Electroanal. Chem., 183 (1985) 133.

[6] M. Itagaki, N. Kobari, S. Yotsuda, K. Watanabe, S. Kinoshita, M. Ue, J. Power Sources, 135 (2004) 55-261.

[7] M. Itagaki, K. Honda, Y. Hoshi, I. Shitanda, J. Electroanal. Chem. 737 (2015) 78-84.
(Invited) Passivity and Localized Corrosion of Stainless Steels in Energy-Related Applications
Authors: Virtanen Sannakaisa
Published: February 2020

In recent years, new types of environments related to energy technologies can provide new challenges for the passivity of traditional materials. Examples are different types of biofuels (ethanol, ethanol-gasoline blends, biodiesel). For instance, stress-corrosion cracking of steels can take place in ethanolic environments and Al alloys can show very fast degradation in ethanol-containing fuels at higher temperatures.

This presentation will focus on passivity and localized corrosion of stainless steels in such new type of environments. Critical factors of localized corrosion were studied in different ethanol-gasoline blends, in presence of various corrosion-enhancing factors (such as H2O, chloride contamination). The influence of the different factors on occurrence of pitting corrosion and the morphology of growing pits was studied. In addition, XPS measurements were carried out, to explore the effect of the specific environment on the nature of the passive films.

Other examples of the behavior of stainless steels in energy-related applications will be shortly discussed, such as passivity and localized corrosion in molten salts that can be used as heat transfer media in high temperarature applications.
Thin Metal Oxide Coatings for Lightweight Alloys
Authors: Sammelselg Väino , Merisalu Maido , Aarik Lauri
Published: February 2020

A new type of nanocomposite coating and its preparation technology was worked out1 and will be introduced in this presentation. The technology has two main steps – first, the working surface of substrate is anodized and second, the anodized base layer is covered with a thin toplayer, grown by atomic layer deposition method (ALD). Both steps of the coating preparation need special attention. The anodizing of a lightweight substrate, e.g. an aluminum alloy must result in a homogeneous by both thickness and composition anodic layer, and must consist as little as possible cracks and pores. It is well known that the anodic layer consist nanometric pores and at least part of them is reaching the substrate metal part and these are the weakest points of the anodized coating. Thus, the pores must be firmly sealed and even better filled up to the bottom with a corrosion resistant material. This can be achieved with the help of ALD that is a cyclic analogue of chemical vapor deposition method. In the presentation we will demonstrate how the new coating is prepared for Al2024 alloy, which is tending to pitting corrosion due to existing in it Cu-rich and other intermetallic particles, often with micrometer dimensions, part of them laying in near-surface region of the substrate.

In the presentation we will go through the substrate surface pretreatment, anodizing and following ALD growth of nanolaminate of metal oxides as top part of the coating. The process gives micron thick composed coating with filled nanopores, see the scheme, and that coating withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates.

In the presentation will be discussed surface pretreatment, anodizing and following ALD process, which gives micron thick composed coating with filled nanopores, see the scheme, and which withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates.

In the presentation will be discussed surface pretreatment, anodizing and following ALD process, which gives micron thick composed coating with filled nanopores, see the scheme, and which withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates.

L. A. thanks the European Social Funds of Doctoral Studies This work was also supported by the Estonian ME&S by projects IUT2-24, TK117 and TK141.

Reference:

V. Sammelselg, M. Merisalu, L. Aarik, Method of preparing corrosion resistant coatings, WO 2014102758 A1/GB2509335 A, Priority date 31.12.2012 (http://www.google.com/patents/WO2014102758A1?cl=en).

Figure 1
An Investigation into the Stability of Passive Layers on Zinc Under Alkaline Conditions
Authors: Cole Ivan Stuart , Veluchamy Angathevar , Bosco Emmanuel
Published: February 2020

The paper investigates the passivity of zinc as a function of applied potential and chloride concentration. The paper reports primarily on passivation in alkali solution as determined by potentiostatic holds but potentiostatic polarization ( at 1mV/sec) in a borate buffer were carried out to determine appropriate conditions for the holds.  Potentiostatic holds (for 104 sec) at 1.05, 0.8, 0.55, 0.3, 0.05, -0.2, and -0.45Vsce were undertaken in a borate buffer (pH = 9.5) with varying chloride concentration . Two patterns of variation of current with time were observed with the holds, in the first (type1) the current rapidly decreased to low levels , then after some time transients with high current occurred, followed by a return to stable low currents . In the second (type2) once again there was an initial decrease in current but after the transient the current rose to high values. In a further series of tests at a potential (+1.05Vsce) with different chloride ion concentration added at 10000th sec. Again type 1 and type 2 behavior’s where observed with  the addition of low levels of chloride resulted in type1 behavior and the higher in type 2. The relevance of the results to an understanding of the stability of zinc oxide films is discussed.
Nanostructured Iridium Oxide Micro Electrode Array for Neurostimulation Application
Authors: Chung Tsai-Wei , Chen Yi-Cheng , Tso Kuang-Chih , Chen Chien-Chon , Chen Shih-Fan , Wu Pu-Wei , Chen Po-Chun
Published: February 2020

Micro electrode array (MEA) has emerged as one of the most common tools to transmit electrostimulation signals. Innovative nanofabrication process provides high efficiency for implantable bio-devices by creating large surface area. One of the noticeable advantages of such nanostructured micro electrode is to minimize tissue damage and also to provide a suitable platform for neuron attached. Among neurostimulation electrode materials, iridium oxide has received substantial attention in recent years because of its unique ability to inject electric charge and its physical, chemical stability as well as its biocompatibility. On the other hand, anodic aluminum oxide (AAO) can be provide a wide range aspect ratio template for forming iridium oxide nanorods and nanowires on top of the microelectrode. In this study, we combined chemical bath deposition of iridium oxide and AAO templates to fabricate a nanostructured micro electrode array for implantable bio-devices. We also investigated the influence of the aspect ratio of AAO templates on stimulation performances and biocompatibilities of the nanostructured micro electrode array.
Evaluation of Zn Doped Hydroxyapatite Plasma Spray Biocompatible Coatings on Metallic Substrates
Authors: Take Seisho , Kato Masataka , Asami Tomoya , Aihara Yuto , Izawa Satoru , Atsumi Taro
Published: February 2020

In a super-aged society such as Japan, needs for new type implants which has both excellent biocompatibility and high functionality are increasing. Hydroxyapatite (HAp) is known to be very biocompatible since it is the main inorganic content of human tooth and bones.  The development of HAp plasma spray coating on metallic substrate has been engaged by our lab and other researchers. In this study, Zn doped HAp plasma coatings on Ti and SUS316L were prepared by using Zn doped HAp powder obtained by high temperature sintering of the mixture of ZnO and HAp. The credibility, the functionality and the adhesion were investigated by electrochemical impedance measurements, ICP analysis and two types of adhesion tests. After the mixture of ZnO and HAp was sintered at 1150˚C for 10 hours, ZnO X-ray diffraction peaks reduced greatly. Also, the lattice constants of HAp changed with the change of ZnO percentage in the mixture meaning most Zn2+ ions were embedded into the crystal structure of HAp. Long-term credibility evaluation for Zn doped HAp plasma spray coatings in SUS316L was conducted by electrochemical impedance measurements. The results of impedance results showed that corrosion resistance for coatings with post heat treatment kept in a very high value during 12 weeks immersion in Hanks solution, indicating the post heat treatment improved the stability of Zn doped HAp coatings in SUS316L by changing the coating from amorphous structure to a crystalized one. The results from ICP analysis also proved the higher stability achieved by post heat treatment. The dissolution of Zn2+ ions was detected in Hanks solution which implies the possibility of stimulation to the bone growth. The adhesion evaluation was done by three-points bending test and a standard ASTM adhesion test for Zn doped HAp plasma spray coatings on Ti.  Zn doped HAp coatings showed strong adhesion to the metallic substrate. The residual stress in coatings was investigated by x-ray diffraction for understanding the mechanism of strong adhesion.
Electrochemical Behavior of NiTi Alloys during Rapid Straining
Authors: Tsuchiya Hiroaki , Yamamoto Hiroyuki , Fujimoto Shinji
Published: February 2020

Ni-Ti alloy is one of the most investigated alloys as a biomaterial due to its favorable mechanical properties such as superelasticity and shape memory effect. Due to the toxicity of nickel, the dissolution of nickel is one of the most severe problems when Ni-Ti alloy is used in the body. Protective passive films mainly consisting of TiO2 are formed on the alloy, which suppresses the dissolution of nickel. However, the breakdown of the passive films incudes the metal dissolution. Therefore, the metal dissolution from Ni-Ti alloy has been examined using several techniques. In the present work we examine the dissolution and repassivation behavior of NiTi alloys in Hanks’ solution using rapid straining technique.
Crack Initiation of Type 316L Stainless Steel Under Cyclic Deformation in Simulated Body Fluid
Authors: Doi Kotaro , Miyabe Sayaka , Tsuchiya Hiroaki , Fujimoto Shinji
Published: February 2020

The inside of body is a complex environment for metallic biomaterials because of the synergetic effects of biological factors such as a body fluid including Cl-, proteins and cells, and mechanical factors such as strain, bending and friction. These complex factors may lead the corrosion fatigue which is the commonly experienced degradation of metallic biomaterials. However, crack initiation on type 316L stainless steel with cyclic loading in a simulated body fluid including proteins and cells has been little examined. In the present study, a cyclic stress was applied to the tensile specimen of type 316L stainless steel in the simulated body fluid with cell culturing in order to investigate the crack initiation on the metallic biomaterials in the body environment.

A sheet of type 316L stainless steel was shaped into samples for tensile test with a gauge size of 8×4×1 mm3. The samples were mirror-finished, then immersed in a-MEM (Minimum Essential Medium) for 1 day which is a simulated body fluid commonly used for cell culturing (Immersed sample), or immersed in a-MEM+10 vol.% FBS (Fetal Bovine Serum) with cell culturing for 1 week (Sample with cells). During immersion, a-MEM and a-MEM+10 vol.% FBS were kept at 37 °C under an atmosphere of 5 % CO2-20% O2-75 % N2. Initially, Immersed sample and sample with cells were placed in the electrochemical cell filled with a-MEM kept at same condition in immersion, then attached to a corrosion fatigue test machine. A cyclic stress was applied to the sample until 107 cycles. The stress ratio was 0.1 (R=0.1) and the maximum stress was 300 MPa, not exceeding the elastic limit of type 316L stainless steel. The stress frequency was 10 Hz. For comparison, the sample not immersed was also subjected to the test in the air (Sample in the air). After cyclic deformation, cracks initiated on the sample surface were observed using FE-SEM. In addition, crystalline structure of the sample was analyzed using EBSD (Electron Backscatter Diffraction Analysis). From surface observation and EBSD, the relationship of crack initiation and crystalline structure was studied.

Most cracks observed on the sample in the air, immersed sample and sample with cells initiated in the grains with Schmidt factor being from 0.4 to 0.5. This result indicates that the cracks tend to initiate along crystal plane with the largest Schmid factor where slip deformation preferentially occurs. On the other hand, non-negligible amount of cracks were observed on the crystal plane with Schmid factor less than 0.4 for the immersed sample and sample with cells. Such cracks initiated along the slip direction toward inside of the sample. In this case, the newly created surface was exposed to a solution, then corrosion along the slip steps was enhanced. Therefore, in the immersed sample and sample with cells, crack initiation was prompted on the crystal plane with the non-largest Schmid factor.
CMAS Corrosion of Gadolinium and Samarium Zirconate Pyrochlore Thermal Barrier Coating Materials
Authors: Fergus Jeffrey , Wang Honglong , Bakal Ahmet , Deng Wenzhou , Roebbecke Kai
Published: February 2020

The thermal barrier coatings used to increase the operating temperatures of gas turbine engines are susceptible to corrosion by debris that is injected into the engine during operation. The calcium-magnesium-aluminum-silicon oxide (CMAS) deposits can melt and reaction with the oxide coating. To minimize degradation associated with this reaction alternative materials are being developed. Lanthanide zirconates with the pyrochlore structure have been reported to have better resistance to CMAS corrosion as compared to the commonly used yttria-stabilized zirconia coatings. The reaction of pyrochlore lanthanide zirconates with CMAS results in the formation of a two-phase mixture of a cubic fluorite phase with lower lanthanide content and a lanthanide-containing silicate phase. In this paper, results on the corrosion of gadolinium and samarium zirconate in CMAS will be presented and discussed. This materials studied include both sintered ceramics and plasma spray coatings.
Nitridation of a Fecral Alloy in H2+N2 Environment at 900oc: A Microstructural Study
Authors: Mortazavi Nooshin , Geers Christine , Jönsson Bo , Svensson Jan-Erik , Sundell Gustav , Johansson Lars-Gunnar , Halvarsson Mats
Published: February 2020

When exposed to O2 and/or H2O at high temperature, iron-chromium-aluminum (FeCrAl) alloys form an adherent a-Al2O3 scale that grows very slowly. Because of the excellent protective properties of this scale, the FeCrAls resist high temperature corrosion and oxidation very well and they are used in a wide range of high temperature applications up to 1300oC. However, when exposed to nitrogen-containing environments with low oxygen activity, e.g. H2+N2 mixtures, the FeCrAls become sensitive to nitridation. Such environments are often used in heat treating and sintering operations. This paper investigates the nitridation behavior of the FeCrAl alloy Kanthal APMT at 900°C. In order to provoke nitridation, the material was exposed to a N2+H2 mixture with very low water vapour content. Microstructural analyses after 24h exposure revealed that a continuous Al2O3 scale covered almost all of the alloy surface. However, the oxide scale contained a distribution of Cr2O3 patches with diameters of 10-40 mm. Cross-sectional studies using Focused Ion Beam (FIB) milling showed internal nitridation of the alloy, displaying a variety of precipitates below the Cr2O3 patches, including needle shaped AlN, equiaxed Cr2N and CrN particles. In contrast, the alloy beneath the Al2O3 scale was not nitrided. To investigate possible reasons for the formation of chromia patches we kept track of specific regions before and after exposure. Hence, several analytical techniques were employed to fully characterize the alloy microstructure prior to the exposures, using Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Energy Dispersive X-ray (EDX) analysis. Some markers were used to enable identification of specific areas during post-exposure analysis and to enable correlation of chromia formation and internal nitridation with the alloy microstructure.
Mitigation of Chromium Assisted Degradation of LSM Cathode in SOFC
Authors: Liang Chiying , Hu Boxun , Aphale Ashish , Rodriguez Weyshla , Uddin Md. Aman , Singh Prabhakar
Published: February 2020

Chromium evaporation, from chromia forming ferritic alloys used in interconnect (IC) and the low cost iron and nickel base alloys used in balance of plant (BOP) during exposure to ambient air, and subsequent interactions of gaseous chromium species with the cathode is considered as one of the leading causes for the long term irreversible performance degradation in SOFC power generation systems. Although, surface coatings and alloy modifications have proved helpful in providing near term solution for the mitigation of chromium poisoning, the aforesaid remain susceptible to structural degradation in long term. A novel approach for mitigating cathode degradation by capturing gas phase chromium vapor from the air stream has been developed. Results from transpiration and symmetric electrochemical tests, conducted under simulated SOFC systems operating conditions, will be presented. Underlying thermodynamic and electrochemical processes associated with chromium evaporation and subsequent interactions with getters will be presented.
Investigation of Passive Layers Formed on Alloy 600 in Zinc Containing High Temperature Primary Water
Authors: Jiang Yifan , Devine Thomas
Published: February 2020

Nickel-based Cr-Fe alloys have been found to show very low corrosion rates in extreme environments and thus have been extensively used in industries, such as in nuclear power plants. One of the reasons that Ni-Cr-Fe alloys show good corrosion resistance is that there are oxides that prevent the bare metal from general corrosion. However, Pressurized Water Reactors (PWRs) have experienced stress corrosion cracking (SCC) on the primary side of the Alloy 600 (Ni-15Cr-9Fe) steam generator tubing. It is believed that passive layer formed on Alloy 600 is crucial for SCC initiation. Zn ions are added to primary water in industry in order to reduce SCC initiation. However, the mechanism of SCC suppression with Zn is not yet fully understood. The Zn incorporation process is of great importance in the way that it can help understand the mechanism of SCC initiation. Our research aims to understand the influence of surface oxides of Alloy 600 on SCC in primary water of PWR, focusing on the effect of Zn ions during short period of time (less than 100 hours) at different potentials.

The present research examined the effect of Zn ions on the passive layer using in-situ electrochemical method as well as ex-situ characterization method. We constructed a system simulating the high temperature primary water with 100ppb Zn addition and operated the system at 320 C and 1800psi. The sample was oxidized in the autoclave for up to 48 hours at different potentials. During the oxidation period, electrochemical impedance spectroscopy (EIS) was applied at different oxide forming potentials in order to get information of how the alloy performs at different potentials. Ex-situscanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron dispersive spectroscopy (EDS) were also performed on the samples to determine the morphology and chemical profiles of the passive layer.

Our EIS study indicated that there was likely a change in oxide property on Alloy 600, likely related to the incorporation of Zn ion, at different potentials for short time oxidation. It was found from the ex-situ experiments that with potential changes, both the thickness and the morphology of the passive layer changes, which agreed with the changes in the impedance results. Figure 1 shows the changes on surface morphology on Alloy 600 samples polarized at different potentials for up to 40 hours. It is indicated that both the distribution and the size of oxide particles changes with polarizing potentials. Zn was found to incorporate into the passive layer of the oxide, substituting some of the Ni content in the passive layer. As potential increased, the content of Zn incorporation changed.

Figure 1
High Temperature Corrosion in Molten Salts in Solar Power Concentration Plants: Dynamic and Static Corrosion Test
Authors: Perez Trujillo Francisco Javier , Lasanta Maria Isabel , Garcia Martin Gustavo , de Miguel Maria Teresa , Encinas Sánchez Víctor
Published: February 2020

The solar power concentration plants (CSP) are at the present time operating in the heat storage and transfer fluids with binary molten nitrates mixtures.Those mixtres at hgh temperature are dealing with hot corrosion processes in the metallic materials that compose those technologies. In order to determine the corrosion processes in storage tanks and piping, the corrosion test have to be perfomed under static and dynamic conditions. In order to determine the dynamic conditions a new molten salts dynamic loop have been develop and patented (PCT) by the UCM research team. Comparison between dynamic and static results will be provided and a comprehensive mechanism in both conditions will be provided.

The high temperature corrosion test in molten salts will be performed in different steels, in oder to analyze the salt effect,and also the influence of impurities in the salt content.

A complete review of the state of the art will be provided.
Si/SiGe Heterointerfaces in One-, Two-, and Three-Dimensional Nanostructures: Their Effect on SiGe Light Emission
Authors: Lockwood David J , Wu Xiaohua , Baribeau Jean-Marc , Mala Selina A. , Wang Xiaolu , Tsybeskov Leonid
Published: February 2020

The development of a light emitter compatible with Si based complementary metal-oxide- semiconductor (CMOS) circuit technology and fast optical interconnects is important for the new generations of microprocessors and computers. Self-assembled Si/Si1-xGex nanostructures (NSs) with light emission in the important optical communication wavelength range of 1.3 – 1.55 μm are compatible with conventional CMOS processes. However, the predicted and experimentally confirmed long carrier radiative lifetimes in Si and Si/Si1-xGex NSs impede the demonstration of efficient light-emitting devices and lasers. Thus, engineering of Si/Si1-xGex heterostructures with controlled composition and interface abruptness is critical in producing the desired fast and efficient photoluminescence (PL) peaked at around 0.8-0.9 eV. In this paper we assess how the nature of the interfaces between SiGe NSs and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in one dimension (corresponding to the case of quantum wells), two dimensions (quantum wires), and three dimensions (quantum dots). The interface sharpness is influenced by many factors such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for NS confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/Ge NW diameter in the range 50 – 120 nm produce a clear PL signal associated with band-to-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1-xGex NSs incorporated into a Si0.6Ge0.4 wavy structure exhibit an intense PL signal with a characteristic decay time as much as 1000 times shorter than that observed in conventional Si/SiGe NSs. The experimentally observed non-exponential PL decay in Si/SiGe NSs is explained as being due to variations of the distances separating electrons and holes at the Si/SiGe heterointerface. The results demonstrate that an abrupt Si/SiGe heterointerface reduces the carrier radiative recombination lifetime and increases the PL quantum efficiency making these SiGe NSs promising candidates for applications in CMOS compatible light-emitting devices.
Self-Organized TiO2 Nanotube Arrays: Latest Features and Applications
Authors: Schmuki Patrik
Published: February 2020

TiO2 nanomaterials have over the last 30 years attracted tremendous scientific and technological interest. Main research direction using TiO2 in functional applications are still the use in photocatalysis e.g. for the direct splitting of water into H2 and O2 to generate the potential fuel of the future, hydrogen, or the use in Grätzel type solar cells. In order to achieve a maximum turn-over rate (by creating a high surface area), usually nanoparticles are used either suspended or compacted to a photoelectrode. Over the past decades various 1D and highly defined TiO2 morphologies were explored for the replacement of nanoparticle networks and were found in many cases superior to nanoparticles. Nanotubes or wires can be grown by hydrothermal or template methods, or even more elegantly, by self-organizing anodic oxidation. The latter is not limited to TiO2 but to a full range of other functional oxide structures on various metals and alloys can be formed. These advanced and doped morphologies can be grown on conductive substrates as ordered layers and therefore can be directly used as functional electrodes (e.g. photo-anodes). The presentation will focus on these highly ordered nanotube arrays of TiO2 and discuss most recent progress in synthesis, modification and applications.

Literature: (review):

1. P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904

2. K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385
(Invited) Stress-Assisted Formation of Self-Organized Porous Anodic Oxides
Authors: Hebert Kurt , Mishra Pratyush , Capraz Omer , Shrotriya Pranav
Published: February 2020

Porous anodic oxide (PAO) films are grown by electrochemical polarization of Al, Ti, and other metals in baths that dissolve the oxide. Procedures to grow films with highly ordered and controllable arrangements of nanoscale pores have led to the extensive use of PAO films in nanofunctional devices.  Experiments and calculations show that transport in the oxide occurs by electrical migration coupled with plastic flow driven by mechanical stress in the oxide, and suggest that flow may play a role in formation of self-ordered PAO (1-3). Pores initiate by a morphological instability at the oxide-solution interface when the initially formed barrier oxide reaches a critical thickness (4).

Herein is reported a combined experimental and modeling investigation of the formation and self-ordering of PAO. Experiments were carried out to identify stress generation mechanisms during galvanostatic formation of Al barrier films in 0.4 M H3PO­4. Stress distributions in these films were measured by monitoring stress-induced sample curvature changes during oxide formation followed by open circuit dissolution of the films (5). Elevated compressive stress reaching several GPa was found to build up within a few nanometers of the oxide-solution interface, coinciding with high phosphorus contamination in the same layer revealed by GDOES (6). The compressive surface stress is likely due to electric field-induced phosphate incorporation.   

The experimentally characterized surface stress was incorporated in our anodizing model based on transport by coupled viscous flow and electrical migration (2). Morphological stability analysis of the model reveals pattern formation consistent with the well-established characteristic pore spacing to voltage relationship of PAO (7). Pore formation is governed by competition between stabilizing oxide formation at the solution interface and destabilizing flow driven by gradients of anion incorporation-induced surface stress. The model successfully predicts the critical threshold electric field and the narrow ranges of anodizing efficiency characterizing PAO formation on many metals (3,4). A compelling analogy exists between the mechanisms of PAO ordering and formation of hexagonally-ordered Marangoni patterns in thin liquid films.

 References

1. S. J. Garcia-Vergara,  et al., Electrochim. Acta.
52, 681 (2006).

2. J. E. Houser and K. R. Hebert, Nature Mater.
8, 415 (2009).

3. J. Oh and C. V. Thompson, Electrochim. Acta,
56, 4044 (2011).

4. K. R. Hebert et al., Nature Mater.
11, 162 (2012).

5. Ö. Ö. Çapraz, P. Shrotriya, and K. R. Hebert, J. Electrochem. Soc
161, D256 (2014).

6. Ö. Ö. Çapraz, et al., Electrochim. Acta
167, 404-411 (2015).

7. A. P. Li et al., J. Appl. Phys.,
84, 6023 (1998).
Oil-Impregnated Aluminum Anodic Oxide Layer with Bottle-Shaped Pores for Enhanced Anti-Corrosion and Self-Healing Properties
Authors: Lee Junghoon , Choi Chang-Hwan
Published: February 2020

An oil-impregnated porous surface has been considered as a promising candidate to solve various surface-related problems, such as corrosion, icing, and organic/inorganic contamination on the surface. The performance and durability of the oil-impregnated porous surface depends on the porous structure retaining the oil. In particular, in the case of anti-corrosion application, not only the oil on the surface but also the oil inside porous structure serve an important function to prevent the penetration of corrosive media into the porous structure. We designed an anodizing procedure for aluminum to fabricate aluminum anodic oxide (AAO) layer with bottle-shaped pores that feature a smaller pore diameter at the upper layer than at the lower layer. The anti-corrosion performance of the oil-impregnated AAO layer with the bottle-shaped pore was compared with AAO layers with typical cylindrical pores as well as pillar structures. It was demonstrated that the bottle-shaped pore stably immobilized the oil in the nanostructure, showing robust corrosion resistance for chloride-containing liquid. In addition, the larger volume of oil in the bottle-shaped pore allowed to cover the underlying metallic aluminum surface exposed by cracks more effectively, indicating the damage (e.g., crack) tolerance for corrosion with the unique self-healing capability.
Pitting Corrosion of Copper Tubes for Drinking Water Applications Due to Silicate Films
Authors: Feser Ralf , Schewe Sven
Published: February 2020

Water installations are often constructed from copper tubes. Copper is a well-established material for water transport. Sometimes pitting corrosion could appear.  In the last few years some serious failures in cold water tubes in one special region in Germany have been observed. Some influencing factors are well known (sulfates, chlorides and hydrogen carbonate), in detail some knowledge about the mechanism is missing.  Beginning with a detailed failure analysis some possible factors have been identified. Especially the appearance of silicate films at the metal surface has been detected. Laboratory investigations have been performed in an electrolyte which simulates a drinking water. The experiments have been performed  to study the mechanism of pitting corrosion. Measurements with the Scanning Kelvin Probe and Scanning Vibrating Electrode do show the existence of local anodes under artificially prepared silicate films on copper. At the phase boundary between the silicate film and the untreated copper surface, the free corrosion potential shows the most negative value. Interestingly this anode is surrounded by the cathode formed by the free copper surface and also by a cathodic area represented by the complete silicate covered copper surface.  Polarization curves do show that the cathodic oxygen reduction is increased by the appearance of silicate films. Polarization curves and galvanostatic investigations do show that the mechanism of copper dissolution is changed. The formation of Cu2+ -ions is hindered, only Cu+ ions can be formed under thick silicate films. Moreover the existence of the silicate film hinders the copper to form a protective oxide film. The copper dissolution is higher than without a silicate film. Without a silicate film at the surface, the copper dissolution decreases with exposition time. This is the first time that the mechanism of pitting corrosion of copper in cold water due to the formation of silicate films has been proofed.

Therefore the mechanism of pitting corrosion of copper in drinking water with a sufficient amount of silicate is quite clear. First a silicate film is formed at the fresh copper surface. A local anode is established under the silicate film. A passivation of copper is hindered due to the existing silicate film. The local cathode surrounds the anode. The electrochemical reactions are increased due to the hindered oxidation of the copper surface by silicate layers. 

Results of the experiments will be presented as well as the explanation of the model.
Microelectrode Test Configurations for Measurement of Galvanic Current Under Saline Drops in Simulated Atmospheric Conditions
Authors: Hangarter Carlos , Policastro Steven
Published: February 2020

Atmospheric corrosion is characterized by thin film and discontinuous electrolytes that behave in fundamentally different ways than bulk electrolytes. These differences arise due to their finite volumes that limit availability of ionic species and permit the accumulation of corrosion products that can then impact reaction kinetics. To explore these differences between bulk and droplet electrolytes, two different cells were conceived, tested, and used to study galvanic couples in atmospheric environments. The first examined galvanic kinetics of droplets with two discrete half cells. This configuration, shown in Figure 1, allows the time resolved galvanic current and potential of the zero-resistance-ammeter (ZRA) connected anode and cathode to be examined during humidity cycling in the absence of reaction product cross-talk. The galvanic corrosion current and potential were examined during humidity cycling between 95% and 20%. This test configuration was shown to be sensitive to the deliquescence/efflorescence points.

The second galvanic atmospheric corrosion cell is that depicted in Figure 2. In this configuration the anode and cathode are brought into intimate contact with a single microliter droplet, in which the droplet is placed on the cathode and the anode is polished to a fine tip. The anode is then translated to pierce the droplet surface with a three axis micromanipulator and the aid of a microscope camera. This configuration differentiates itself from Figure 3 in that a fixed quantity of electrolyte utilized in this system and reaction products from both electrodes are free to interact with one another and either electrode.

The galvanic corrosion test cell from Figure 2 displayed a precipitous decay in corrosion current that was found to be dependent upon electrolyte composition. ZRA measurements were compared with SEM and EDS mapping of corrosion products and electrolyte residue to understand the conditions that diminish the galvanic current. These results support significant anion consumption; Cl-, in this case; with a clear dependence on pH that suggests ambient CO2 plays a role as well. This talk will also discuss how the two test configurations compare with one another and use polarization curves to understand the information they provide in a broader context and how they should be applied.

Figure 1
Electrochemical Evaluation of Degradation of Zn-Coated Steel Exposed to Cyclic Wet-Dry Condition
Authors: Nishikata Atsushi , Okazaki Takafumi , Tada Eiji
Published: February 2020

The corrosion process of Zn-coated steel is divided into four stages: τ1; Zn-coating corrosion, τ2; sacrificial protection by zinc, τ3; protection by zinc corrosion products, τ4; substrate steel corrosion. To understand the degradation process, it is very important to quantitatively evaluate the corrosion behavior in each stage. In this study, the corrosion behavior of Zn-coated steel has been investigated under cyclic wet-dry condition.

 An Electro-galvanized steel plate (EG, 5μm coating thickness) was used as the test sample. The surface area exposed was 10 mm in diameter and the rest was masked with tape. Solution of NaCl was placed on the surface. The mount of chloride ion placed on the sample was 3.0 g/m2. The attached salt was washed away by distilled water every week and the same amount of the fresh salt was newly placed on the surface. The six samples each metallic coating were exposed to alternate conditions of drying at 40 %RH for 2h and wetting at 95 %RH for 2h in a chamber at 25 oC. One sample was removed from the chamber every week and corrosion potential E
corr and EIS were measured using a conventional three-electrode set-up. The corrosion surface was observed with optical microscope. The remaining coating thickness was measured by an anode stripping method. All electrochemical measurements were carried out in 10 mM NaCl solution.

 Optical microscopic observation showed a trace amount of red rust appeared at 1 week and increased with the cycle number. The E
corr did change so much until 3 weeks, afterward, changed drastically. The anodic stripping showed the coating layer disappeared at an early period at three weeks. From the results described above, the τ2 stage would start from the 2nd week and τ3 from the 3rd week. Zn-coated steel sample at each stage (τ1 ~ τ4) indicated characteristic EIS. It seemed that the oxide film resistance R
oxide in the high frequency region and charge transfer resistance R
ct in the low frequency would appear. The degradation stages of τ1 ~τ4 can be distinguished by the changes of both E
corr and EIS.
The NaCl-Induced Atmospheric Corrosion Performance of Magnesium-Based Metal Matrix Composites
Authors: Esmaily Mohsen , Svensson Jan-Erik , Johansson Lars-Gunnar
Published: February 2020

Magnesium alloys-based metal matrix composites (Mg alloys-based MMCs) are emerging as light structural materials for variety of new applications. They exhibit superior properties such as low specific weight, improved tensile strength and high wear resistance. However, composite technology is a difficult application for these class of metallic materials due to the fact that Mg is the least noble engineering metal. Hence, Mg alloys-based MMCs are very prone to environmental degradation. In this research, the occurrence of micro-galvanic corrosion cells in cast Mg alloys-based MMCs are evaluated. The relationships between the microstructure and atmospheric corrosion performance of SiC (10 vol.%)-reinforced Mg alloy AZ91D-based composites are studied. Microstructural studies are performed using various types of analytical techniques including electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) revealed the formation Al carbides, Mg-hydride (MgH2), and MgO at the a-Mg/SiC interfaces. The corrosion rates of the MMCs are compared with those of the monolithic alloys. The higher corrosion rate of the AZ91D-based MMCs than the alloy AZ91D is shown to be linked to a less degree of the connectivity of the β phase (Mg17Al12 intermetallic particles) and also higher fraction of casting pores in the MMCs as compared to the monolithic alloys. We show that the corrosion resistance of MMCs can be significantly enhanced by controlling the casting process. The current advances and challenges in the field of Mg-based composites are also discussed.

Figure 1
Corrosion Resistant and UV Durable PVDF-Co-HFP /Al2O3 Superhydrophobic Nanocomposite Coating for Aluminum
Authors: Bahgat Ahmed , Abdullah Aboubakr Moustafa , Mohamed Adel M , Almaadeed Mariam
Published: February 2020

The interest in superhydrophobic surfaces, which demonstrate high water-repellency, have recently increased dramatically because of their wide range of applications in many fields. The two major needed conditions to get a nanostructured superhydrophobic surfaces are the optimum surface roughness and low surface energy.

In our present work, the fabrication process of a porous superhydrophobic coating on aluminum surfaces was achieved using a one-step electrospinning technique. The wettability properties of the prepared coating was inspected by measuring the water contact (WCA) and sliding angle (WCAH) before the addition of Al2O3 nanoparticles (150±2.9 and 6.25±1) while the measured WCA and WCAH after addition of nanoparticles was found to be 152±0.59 and 5±2.5, respectively. The wettability of the prepared coatings was inspected also after being irradiated with strong ultraviolet (UV) radiation of 1.5 W/m2 at a high temperature of 70 °C for 64 h. In fact no big difference was noticed after the UV test with respect to the wettability properties. The morphology of the superhydrophobic coating was studied using scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX). It shows the formation of a beaded fiber structure. Furthermore, Fourier transform infrared (FTIR) spectroscopy was used to check the nanocomposite coating before and after irradiation with UV. The surface roughness of the composite materials were measured using atomic force microscope (AFM). The corrosion behavior of the superhydrophobic nanocomposite coating was evaluated by the electrochemical impedance spectroscopy (EIS) and the potentiodynamic polarization in 3.5% NaCl. The results have shown that new nanocomposite coating exhibits a very high corrosion resistance.
An Svet Study of the Throwing Power of Smart-Release Corrosion Inhibitor Pigments in Organic Coatings
Authors: Glover Carol Frances , Williams Geraint , Ansell Phil , Dodds Patrick Charles
Published: February 2020

An SVET study of the throwing power of smart-release corrosion inhibitor pigments in organic coatings

Ion-exchanged anti-corrosion pigments phenylphosphonic acid, benzotriazole and 5-methylbenzotriazole exchanged in hydrotalcite (HT) are studied in terms of ‘throwing power’ when dispersed in a model polyvinyl-butyral (PVB) primer coating adherent to a hot dip galvanised steel substrate. The Scanning vibrating electrode technique (SVET) is used in a novel study to determine the inhibitory effects of the primer coatings when fully immersed in 5% w/v NaCl electrolyte. Samples are prepared as shown in Figure 1 where a coated sample is insulated such that only the edges of the protective coating and a defined area of bare metal are exposed to electrolyte. Current density mapping of the exposed area is carried out over a 24 h period.   HT has been shown previously to reduce cathodic delamination, by moderation of under coating pH, reduce chloride activity and also release ionic inhibitors[1].  In the presence of a penetrating electrolyte, effective inhibition is achieved through the leaching of anions creating an insoluble blocking layer[2]
[3]. The current study enables the isolation of the leaching mechanism. By systematically altering distance x, the extent to which inhibitors are able to leach into the bulk electrolyte and stifle corrosion can be mapped, allowing a threshold to be determined.

Figure 1. Sample set-up showing coated hot dip galvanised steel surface with exposed scan area.

References

[1]      T. T. X. Hang, N. T. Duong, T. A. Truc, T. Hoang, D. T. M. Thanh, S. Daopiset, A. Boonplean, J. Coatings Technol. Res.
2015, 12, 375.

[2]      C. F. Glover, R. Subramanian, G. Williams, J. Electrochem. Soc.
2015, 162, C433.

[3]      M. Finsgar, I. Milosev, Corros. Sci.
2010, 52, 2737.

Figure 1
Enhancement of Corrosion Resistance in Carbon Steels Using Fe-Based Amorphous Metallic Coatings Under High-Temperature Flowing Water
Authors: Kim Seunghyun , Kim Jeong Won , Kim Ji Hyun
Published: February 2020

Carbon steels are the backbone material of modern industry applications owing to excellent forming, machining, and welding properties.   However high-temperature flowing water condition induces complex corrosion phenomena involving destructive electrochemical reactions and mechanical wear for carbon steels thus a cost-effective countermeasure for the corrosion of carbon steels is highly required.   In this study, to enhance the corrosion resistance in carbon steels under high-temperature flowing water, Fe-based amorphous metallic coatings (AMC) are deposited on carbon steels using high-velocity oxygen fuel (HVOF) technique.   The Fe-based AMC gathers tremendous interests as they exhibit excellent corrosion and wear resistance thus it is expected that it provides effective corrosion protection ability for carbon steels even in severe environments including nuclear power plants.   To examine the corrosion resistance of the Fe-based AMC, rotating cage corrosion (RCC) test was designed with a magnedrive-installed autoclave and recirculation loop system. The temperature for each test was 125, 150, 175, and 200 oC, respectively. To simulate power plant water chemistry, pH 9.3 ETA solution was continuously supplied.   The weight loss of each specimen was measured after 2 weeks of elapsed time and the result shows that the Fe-based AMC exhibits excellent RCC resistance at all temperature and most effective at 150 oC as shown in Fig. 1.   Further, while microstructure evolution of carbon steels displays the formation of porous Fe3O4 at the surface, the Fe-based AMC displays the formation of thin Cr2O3 layers meaning passivity as shown in Fig. 2.. At 200 oC, the formation of FeCr2O4 was also observable (Fig. 3)   The early conjecture is that the Fe-based AMC is able to protect carbon steels by forming passive oxide layer at its surface. Previous research argued that Cr and its passive layer is the most effective RCC barrier in high-temperature. Thus, further investigation using transmission electron microscopy and X-ray photoelectron spectroscopy will be carried out to figure out their stoichiometry and detailed microstructure evolution.

Figure 1