Localized Pitting Research Articles

Rock cutting performance and wear characteristics of undercutting disc cutter: Based on experiment and DEM

The undercutting disc cutter used to break the hard rock bears a huge load and severe wear during rock fragmentation; however, the wear mechanism and law of the cutter are still unclear. The wear mechanism of the undercutting disc cutter was revealed by comparing and analyzing the three-dimensional topography of the cutter before and after the experiments. Based on the DEM, the numerical model of rock cutting using an undercutting disc cutter was established and the influence of factors such as structural and working parameters on the wear behavior of the cutter was studied. The results indicate that under the large contact force, the hard particles of rock are inset into the cutter tip and the material was spalled, resulting in the local pits; the furrows on the cutter face are not continuous and less deep because of the contact between the cutter face and the bottom rock free-face is discontinuous. The wear of the cutter is positively related to the cutting depth and tip width, and negatively to the cutting angle. The circular tip has better wear resistance than the flat tip, and the effect of the tip angle on the wear of the cutter is not significant. The index of cutter consumption ratio (CCR) is proposed, and combined with the specific energy, the recommended structural and working parameters of the cutter for improving the cutting performance and reducing cutter wear are provided.

ICT-based solution for efficient fecal sludge management: An experience from Bangladesh

In Bangladesh, people primarily depend on on-site sanitation facilities (OSSF) with an immense challenge in achieving safe sanitation due to unplanned infrastructure development, improper management of fecal sludge, and inadequate monitoring. The commitment of attaining Sustainable Development Goals (SDG) 6.2 (ensuring safe sanitation for all) by 2030 requires immediate attention in the management of fecal sludge for low-middle income countries. This paper presented the findings, challenges, and possible ways forward from a study conducted to provide data for Information and Communication Technology (ICT)-based fecal sludge management (FSM) at a municipality in the northwest of Bangladesh. A total of 18,808 households and 407 institutions in Saidpur municipality, a non-sewered town in Nilphamari district, were studied to understand the type of containment structures and on-ground desludging practices. The study showed around 10% of containments were connected to the drains illegally, 95% of the people in Saidpur practiced unsafe disposal, and 7% still practiced open defecation. To identify these malpractices, the study also implemented an ICT-based sustainable solution through a web application that enabled the local administrator to have a global look at the sanitation scenario of the municipality. The dashboard was developed to create a total sanitation monitoring system, identify defaulters, allow target-based safe managed sanitation service strategies, and ensure sustainability in FSM. The study highlighted the accessibility of vacuum truck services projecting through a spatial map and identified methods to empty the septic tanks where Vacutag services are unavailable by engaging local pit emptiers. The innovative approach of fecal sludge management will help not only to improve the existing sanitation practices but also raise community awareness to ensure sustainable sanitation system. Altogether, the web system will work as a medium to manage the faecal sludge for the existing co-compost plant where the faeces is converted into organic soil conditioner, creating prospects for a green business mechanism.

Experimental Research on Pipeline Corrosion Monitoring Technology Based on FSM

The field fingerprint method (FSM), a new online corrosion monitoring method, has a good application prospect. Of all the corrosion defects of pressure pipes, local small corrosion pits are the most commonly seen, and it is also the focus of FSM research. Based on the FSM method, this paper conducts experimental research on the common round and rectangular small corrosion pits of pressure pipes. The results show that the FSM method is sensitive to small volume defects, and the small corrosion pits with the minimum detectable depth of 0.5 mm can accurately reflect the defect growth process, this being of great significance to the safe operation of pipelines.

Localized coupling effects and multiphysics modeling for the laser ablation behavior of composite structure subjected to high-speed airflow

When the composite structure is subjected to high-power laser irradiation and high-speed airflow, its ablation behavior presents significant localized characteristics and strong coupling effect. In this work, a coupled fluid-thermal-ablation model is developed to quantitatively investigate the localized coupling effects. Here a loosely coupled scheme with second order temporal accuracy is utilized to improve the coupling efficiency, and a high-quality mesh reconstruction method combining the Arbitrary Lagrange-Euler (ALE) algorithm and Radial Basis Function (RBF) interpolation algorithm is established to capture the moving boundary of the localized ablation pit with large deformation. The model is validated by simulating the laser ablation behavior of C/SiC composite plate subjected to the hypersonic airflow, and the predicted ablation pit profile shows a good agreement with the available experimental result. Analytical results show that as the evolution of the localized asymmetric ablation pit induces transformation of the flow regime from a closed pit flow to an open pit flow. Moreover, the flow regime transition would remarkably alter the localized flow characteristics, including the local static pressure and dynamic pressure, which in turn significantly affects the sublimation and mechanical erosion rates of C/SiC composite plate, respectively.

Effect of Mg Addition and PMMA Coating on the Biodegradation Behaviour of Extruded Zn Material.

Although zinc (Zn) is one of the elements with the greatest potential for biodegradable uses, pure Zn does not have the ideal mechanical or degrading properties for orthopaedic applications. The current research aims at studying the microstructure and corrosion behaviour of pure Zn (used as a reference material) and Zn alloyed with 1.89 wt.% magnesium (Mg), both in their extruded states as well as after being coated with polymethyl methacrylate (PMMA). The grafting-from approach was used to create a PMMA covering. The "grafting-from" method entails three steps: the alkali activation of the alloys, their functionalization with an initiator of polymerization through a phosphonate-attaching group, and the surface-initiated atom transfer radical polymerisation (SI-ATRP) to grow PMMA chains. Electrochemical and immersion corrosion tests were carried out in a simulated body fluid (SBF), and both confirmed the enhanced corrosion behaviour obtained after coating. The electrochemical test revealed a decrease in the degradation rate of the alloy from 0.37 ± 0.14 mm/y to 0.22 ± 0.01 mm/y. The immersion test showed the ability of complete protection for 240 h. After 720 h of immersion, the coated alloy displays minute crevice corrosion with very trivial pitting compared to the severe localized (galvanic and pitting) corrosion type that was detected in the bare alloy.

Text-Mining to Identify Gene Sets Involved in Biocorrosion by Sulfate-Reducing Bacteria: A Semi-Automated Workflow.

A significant amount of literature is available on biocorrosion, which makes manual extraction of crucial information such as genes and proteins a laborious task. Despite the fast growth of biology related corrosion studies, there is a limited number of gene collections relating to the corrosion process (biocorrosion). Text mining offers a potential solution by automatically extracting the essential information from unstructured text. We present a text mining workflow that extracts biocorrosion associated genes/proteins in sulfate-reducing bacteria (SRB) from literature databases (e.g., PubMed and PMC). This semi-automatic workflow is built with the Named Entity Recognition (NER) method and Convolutional Neural Network (CNN) model. With PubMed and PMCID as inputs, the workflow identified 227 genes belonging to several Desulfovibrio species. To validate their functions, Gene Ontology (GO) enrichment and biological network analysis was performed using UniprotKB and STRING-DB, respectively. The GO analysis showed that metal ion binding, sulfur binding, and electron transport were among the principal molecular functions. Furthermore, the biological network analysis generated three interlinked clusters containing genes involved in metal ion binding, cellular respiration, and electron transfer, which suggests the involvement of the extracted gene set in biocorrosion. Finally, the dataset was validated through manual curation, yielding a similar set of genes as our workflow; among these, hysB and hydA, and sat and dsrB were identified as the metal ion binding and sulfur metabolism genes, respectively. The identified genes were mapped with the pangenome of 63 SRB genomes that yielded the distribution of these genes across 63 SRB based on the amino acid sequence similarity and were further categorized as core and accessory gene families. SRB's role in biocorrosion involves the transfer of electrons from the metal surface via a hydrogen medium to the sulfate reduction pathway. Therefore, genes encoding hydrogenases and cytochromes might be participating in removing hydrogen from the metals through electron transfer. Moreover, the production of corrosive sulfide from the sulfur metabolism indirectly contributes to the localized pitting of the metals. After the corroboration of text mining results with SRB biocorrosion mechanisms, we suggest that the text mining framework could be utilized for genes/proteins extraction and significantly reduce the manual curation time.

Using illustrated system analysis for qualitative risk assessment of emptying of pit latrines

Pit latrines as the primary means of sanitation for billions of people. Fecal sludge must be removed regularly when pit latrines fill up, and the workers who empty these latrines are essential service providers. Pit latrine emptying services and approaches are highly variable, ranging from highly trained teams using vacuum trucks with a suite of personal protective equipment to individuals with no protection using simple manual tools like buckets and shovels. While national governments and nonprofits endeavor to make pit latrine emptying safer, the people making day-to-day decisions such as local pit emptying associations, sanitation businesses, utilities, and local governments have limited resources to evaluate how different emptying practices vary in terms of risk. In this paper we describe the development of an open-source Illustrated System Analysis tool for the fecal sludge management community. This tool can be used in conjunction with a simple risk assessment matrix to help decision makers describe, compare, and prioritize risks for mitigation. We demonstrate this process by outlining how a pit emptying team can compare mechanical and manual emptying with respect to ingestion of fecal material and inhalation of fecal bioaerosols. Illustrated System Analysis can be a tool to analyze fecal sludge management systems, and the associated challenges and opportunities so that they could be understood and referenced by the wider public and used to spark innovation. We provide a library of graphics freely under creative commons.

Metallurgical characterization of a failed A106 Gr-B carbon steel welded condensate pipeline in a petroleum refinery

A condensate pipeline made of carbon steel alloy with grade A106-Gr.B, had a leakage in the form of a pinhole at the girth weld after 16 years of operation. Visual examination, optical and scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS), chemical analysis, and hardness measurements were performed on the failed pipeline samples. Visual examination of the inner surface of the circumferential weld line showed many types of welding defects, as well as severe localized corrosion pits in the weld zone at the bottom of the pipe surface. The microscopic analysis shows that the localized corrosion attack is the root cause of the pipe failure. XRD patterns of the inner surface of the failed pipe emphasizes a formation of corrosion products of iron oxyhydroxides such as Lepiodocrocite (Fe + 3O(OH)), and Goethite (FeO(OH)). Additionally, the foreign elements of aluminum, and chlorine, detected by the EDS analytical results promote under-deposit corrosion, particularly in regions with stagnant water, i.e., at 6 O'clock pipe position.

Corrosion Behavior of Cold-Rolled and Solution-Treated Fe36Mn20Ni20Cr16Al5Si3 HEA in Different Acidic Solutions.

New high entropy alloys with good corrosion resistance in severe environment are receiving increasing attention. This work reports upon the microstructure and the corrosion resistance of the non-equiatomic Fe36Mn20Ni20Cr16Al5Si3 alloy in different acidic solutions. This alloy was designed by thermodynamic calculations using CALPHAD SOFTWARE, fabricated through casting, subjected to cold-rolling and solution-treatment, and compared with SS304 stainless steel. The corrosion test was performed through electrochemical behavior in 0.6 M NaCl and 0.6 M NaCl with 0.5 M H2SO4 and 0.6 M NaCl with 1 M H2SO4 solutions. Experimental results indicate that the alloy is composed of FCC phase as the main constituent besides a small amount of other BCC/B2 phases and other intermetallics. The corrosion test measurements revealed that cold-rolled Fe36Mn20Ni20Cr16Al5Si3 alloy is more resistant to corrosion in 0.6 M NaCl, while it is more susceptible to localized pits in H2SO4 to 0.6 M NaCl. Experimental results indicate that the pits are preferentially occurred in the areas of BCC/B2 phase precipitates. The solution-treated Fe36Mn20Ni20Cr16Al5Si3 HEA has the highest corrosion resistance compared to others with the addition of H2SO4 to 0.6 M NaCl. Surface morphologies of the different conditions were studied, and relevant results were reported.

Repassivation Temperature of One-Dimensional Artificial Pits in Stainless Steel

A new framework has been developed in recent works to describe pit growth stability 1-8, based on which many critical scientific issues in localized corrosion were addressed, such as the rate-controlling step in pit growth, the salt film growth and self-regulating mechanism, and the kinetics and the activation energy of metal dissolution in the local pit environment. Although many new insights were generated, there are still some phenomena that are not well understood, such as the pit repassivation temperature (T rp). According to the new framework, T rp is predicted to decrease with the increase of applied potential (E app). However, T rp sometimes exhibits an unexpected dependence on E app that contradicts with the prediction, and the underlying mechanism is not clear.In this study, T rp of one-dimensional artificial pits made from 316L stainless steel was investigated in 3.5 wt.% NaCl by downward temperature scanning. For a given pit depth, T rp exhibits an unexpected “S” dependence on applied potential, which has never been reported previously. Further analysis shows that this relationship is derived from repassivation underneath the salt film, which is different from repassivation that occurs when the pit surface concentration decreases below a critical value. This indicates that there is a reversal of the effect of the salt film on pit growth stability. The systematic study shows that such a reversal depends on temperature, E app, and pit depth. Acknowledgments: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584.References G. S. Frankel, T. Li, and J. R. Scully, Journal of the Electrochemical Society, 164 (4), C180-C181 (2017).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (9), C484-C491 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (11), C762-C770 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (6), C115-C124 (2019).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (11), C3341-C3354 (2019).T. Li, J. Wu, and G. S. Frankel, Corrosion Science, 182 109277 (2021).T. Li, J. Wu, X. Guo, A. M. Panindre, and G. S. Frankel, Corrosion Science, 193 109901 (2021).T. Li, D. E. Perea, D. K. Schreiber, M. G. Wirth, G. J. Orren, and G. S. Frankel, Corrosion Science, 174 108812 (2020).

Microstructural basis for improved corrosion resistance and mechanical properties of fabricated ultra-fine grained Mg-Akermanite composites

In the present research, a composite with a magnesium alloy (WE43) as the matrix and Akermanite as the bioactive and reinforcing agent was fabricated by friction stir processing (FSP), resulting in a microstructure with uniformly distributed fine grains, second-phase particles and micro-sized Akermanite particles. The effect of an addition of Akermanite to the alloy on the mechanical properties and corrosion resistance of the resulting composite was investigated. The compressive strength and ductility of the composite were found to be significantly higher than those of the monolithic WE43 alloy. The value of yield strength of the WE43 sample increased from 75 MPa up to 119 and 225 MPa for WE43-6P and WE43-A-6P samples, respectively. Also, the value of the ultimate compressive strength of the WE43 sample increased from 210 MPa up to 240 and 362 MPa for WE43-6P and WE43-A-6P samples, respectively. The value of elongation for WE43, WE43-6P, and WE43-A-6P samples were 4.5%, 16%, and 22%, respectively. The EIS test showed that the corrosion mechanism of WE43 sample is a combination of localized pitting and uniform corrosion, which shifted towards more uniform corrosion with higher corrosion resistance by applying FSP and adding Akermanite powder. The potentiodynamic polarization and in vitro immersion tests confirmed this finding, as evidenced by the increase in polarization resistance from 0.192 for the monolithic WE43 alloy up to 0.339 and 0.609 kΩ/cm2 for WE43-6P and WE43-A-6P samples, respectively. The mass loss rate of the WE43 sample decreased from 20.82 to 10.13 mm per year for the WE43-A-6P sample after 312 h immersion in SBF solution. All tests approved that by applying FSP and adding Akermanite to WE43, the corrosion resistance in the SBF solution could be significantly enhanced.

Identification of steel corrosion associated with sulfate‐reducing bacteria by electrochemical noise technique

AbstractDeterioration of steel structures in natural waters can result from microbiologically influenced corrosion (MIC) such as that caused by sulfate‐reducing bacteria (SRB). Corrosion pits associated with MIC have been recently observed in submerged steel bridge piles and there is renewed interest to assess their deterioration. Conventional electrochemical techniques to identify MIC have been complicated due to the effects of the surface films and the mechanism for charge transfer by the bacteria on the steel surface. An electrochemical noise (EN) technique to identify steel corrosion in an aqueous solution has been developed and the method ideally can identify the onset of local pitting, but complications and limitations relating to data acquisition, filtering, and interpretation exist. EN analysis was shown to differentiate SRB and corrosion activity including initial biofilm development, pitting corrosion development, and diminution of SRB activity. Electrochemical behavior, environmental characteristics, SRB activity, and corrosion modality provided consistent correlation to EN and localized corrosion development.

Case Study of PVC Cables Exposed in Accelerated Thermal and Radiation Environment

The objective of the present research is to investigate the degradation phenomenon of Polyvinyl Chloride (PVC) cable jacket exposed under accelerated thermally aged at 100°C for 4 days then irradiated under n’s flux of 1.5x 1011n’s / cm2.sec for 1 hr in PARR-2 reactor at PINSTECH. Thermal, mechanical and chemical etc. properties of degraded cable jacket were studied with respect to fresh sample. It was examined that plasticizer content in PVC matrix started to deplete under the effect of temperature which made the matrix more rigid. In addition, the interaction of radiation with polymeric chains weakens the hydrocarbon bonding. The hydrogen and chlorine ions ejected from PVC molecular chains recombine to form hydrogen chloride (HCl) which induces porosity by creating localized pitting. This phenomenon is known as dehydrochlorination which created scissioning in PVC materials. Hence, due to the synergistic effects of temperature and radiation aging, cracks were observed on the outer surface of cable jacket in 2 years equivalent time. This study concludes that cables having PVC insulation are not suitable for long term exposure (i.e. decades) in thermo-irradiation environment.

Fault feature analysis and detection of progressive localized gear tooth pitting and spalling

Fault feature analysis of gear tooth spalling plays a vital role in gear fault diagnosis. Understanding how fault features evolve as a fault progresses is key to fault severity assessment. Due to the complicated nature of gear meshing, fault features and their development as the fault severity progresses remain mostly unknown. The assessment of fault severity is generally based on the hypothesis that ‘the more severe the fault, the stronger the fault symptom’, an assumption that has not been experimentally validated. This paper provides a comprehensive, experimental analysis of the evolution of fault vibration features of a gear transmission with progressive localized gear tooth spalling. The effects of rotational speed on the vibration features of the gear transmission are analysed. Changes in fault features (e.g. periodic impulses and sideband phenomena) under different fault severity levels and speed conditions are compared. Results indicate that the number, amplitude and distribution of sidebands increase nonlinearly as the fault progresses. Based on feature analysis, a new health indicator of the mean of the nth order peaks is proposed to detect progressive localized tooth spalling. Results indicate that the proposed indicator shows very good performance for tracking the severity of progressive tooth spalling under different speed conditions.

Effect of Si/Ti additions on physico-mechanical and chemical properties of FeNiCrCo high entropy alloys manufactured by powder metallurgy technique

FeNiCrCoSix and FeNiCrCoTix (x=0, 0.3, 0.6, and 0.9 wt.%) high entropy alloys (HEAs) were prepared via the powder metallurgy technique. A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed. The density and hardness of the prepared HEAs are improved by Si and Ti additions, compared to FeNiCrCo HEA. The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.% Si and 0.9 wt.% Ti have the lowest wear rates. X-ray diffraction, SEM, and EDX were used to understand the phases, grain sizes, and microstructures in different investigated HEAs. The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSix and FeNiCrCoTix HEAs were studied by immersion in H2SO4, HNO3, and HCl solutions. Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used. Because of the smaller pit size and the reduced pit density, the FeNiCrCoSi0.3 HEA has an excellent microstructure.

Eddy Current Techniques for Detecting Hidden Subsurface Defects in Multilayer Aircraft Structures

Abstract In-service non-destructive inspection (NDI) is a very important part of the aircraft maintenance program that minimizes aircraft breakdowns due to the fracture of critical components. The eddy current (EC) NDI method is one of the most applicable methods for this purpose, due to its high sensitivity to fatigue cracks and corrosion damage in the main structural materials. In this paper, selective double differential type EC probes characterized by the enhanced possibility of detecting subsurface cracks initiated by fatigue or stress corrosion phenomena are presented. For different applications, a family of double differential type EC probes was developed with different sizes (from 5 to 33 mm) and different spatial resolutions. These types of probes are characterized by different operational frequencies in a wide frequency range (from 0.2 kHz to 1.0 MHz), high penetration depth and unique sensitivity to subsurface defects of different types (like elongated fatigue cracks or local corrosive pitting), and a high level of specific noise suppression concerned with the scanning inspection procedures. The EC probes proposed were investigated as effective tools for characteristic aircraft applications concerned with subsurface defect detection in multilayer structures, such as the detection of cracks in the second layer of a riveted two-layer structure or cracks initiated on the side surface of a multilayer structure with the suppression of the reinforcing hoop influence; the detection of subsurface defects in arc welding with a rough surface; the detection of cracks through repair patches fabricated from aluminum alloy or carbon fiber reinforced plastic, etc. These techniques create remarkable possibilities for the well-timed detection of dangerous damage without disassembling the aircraft structure or removing protective coating.

Diagnosing microbiologically influenced corrosion at a crude oil pipeline facility leak site – A multiple lines of evidence approach

In crude oil transmission pipelines, some parts of the system receive minimal or no fluid flow (‘dead legs’), which can on occasion lead to under deposit corrosion wherein a mixture of sediments, hydrocarbons, water, and microorganisms collectively contribute to an integrity failure. However, the microbial contribution to this phenomenon in crude oil transmission pipelines is poorly characterized. To better understand this process, we used a multiple lines of evidence approach to examine a dead leg failure event using sludge samples collected from at andnear the leak location and from non-corroded areas on the same pipe segment. Chemical analyses revealed elevated levels of acetate, total iron, and FeCO3 at the leak locations compared to non-corroded areas. Electrochemical techniques showed increased evidence for corrosion in leak site samples compared to non-corroded samples, while corrosion coupon analysis revealed many localized pits of up to 20 μm deep in leak location samples compared to fewer pits that were up to 4 μm deep from the non-corroded sample after incubating the samples for 30 days. 16S rRNA gene analysis revealed sulfide-producers, acetogens, and methanogens in all collected samples. The lack of detection of FeS as a corrosion product, no significant differences in sulfate and sulfide concentrations across all samples, and elevated levels of acetate at the leak location suggested that acetogens and/or fermentative bacteria contributed to this pipeline leak. This study highlights the use of a multiple lines of evidence approach that can be used to garner evidence to determine the contribution of MIC to failures in dead leg pipeline segments.

Galvanic Corrosion and Electric Field in Lithium Anode Passivation Films: Effects on Self-Discharge

Battery interfaces help govern rate capability, safety/stability, cycle life, and self-discharge, but significant gaps remain in our understanding at atomic length scales that can be exploited to improve interfacial properties. In particular, Li partially plated on copper current collectors, relevant to the anodeless, lithium metal cell which is a holy grail of high density energy battery research, has recently been reported to undergo galvanic corrosion and exhibit short shelf lives. We apply large scale Density Functional Theory (DFT) calculations and X-ray photoelectron spectroscopy to examine the reaction between the electrolyte and Li|Cu junctions coated with thin, uniform electrolyte interphase (SEI) passivating films at two applied voltages. These novel DFT galvanic corrosion simulations show that electrolyte degradation preferentially occurs on Li-plated regions and should lead to thicker SEI films. Our simulations reveal similarities but also fundamental differences between traditional metal localized pitting and Li-corrosion mechanisms. Furthermore, using the recently proposed, highly reactive lithium hydride (LiH) component SEI as example, we distinguish between electrochemical and chemical degradation pathways which are partially responsible for self-discharge, with the chemical pathway found to exhibit slow kinetics. We also predict that electric fields should in general exist across natural SEI components like LiH, and across artificial SEI films like LiI and LiAlO(2) often applied to improve battery cycling. Underlying and unifying these predictions is a framework of DFT voltage/overpotential definitions which we have derived from electrochemistry disciplines like structural metal corrosion studies; our analysis can only be made using the correct electronic voltage definitions.

Study of Size, Shape, and Etch pit formation in InAs/InP Droplet Epitaxy Quantum Dots

We investigated metal-organic vapor phase epitaxy grown droplet epitaxy (DE) and Stranski–Krastanov (SK) InAs/InP quantum dots (QDs) by cross-sectional scanning tunneling microscopy (X-STM). We present an atomic-scale comparison of structural characteristics of QDs grown by both growth methods proving that the DE yields more uniform and shape-symmetric QDs. Both DE and SKQDs are found to be truncated pyramid-shaped with a large and sharp top facet. We report the formation of localized etch pits for the first time in InAs/InP DEQDs with atomic resolution. We discuss the droplet etching mechanism in detail to understand the formation of etch pits underneath the DEQDs. A summary of the effect of etch pit size and position on fine structure splitting (FSS) is provided via the k · p theory. Finite element (FE) simulations are performed to fit the experimental outward relaxation and lattice constant profiles of the cleaved QDs. The composition of QDs is estimated to be pure InAs obtained by combining both FE simulations and X-STM results. The preferential formation of {136} and {122} side facets was observed for the DEQDs. The formation of a DE wetting layer from As-P surface exchange is compared with the standard SKQDs wetting layer. The detailed structural characterization performed in this work provides valuable feedback for further growth optimization to obtain QDs with even lower FSS for applications in quantum technology.

Synergistic effect of O2-Cl− on localized corrosion failure of L245N pipeline in CO2-O2-Cl− environment

To enhance the understanding of the corrosion mechanism on rapid perforation failure, the corrosion behavior of L245N with the synergistic effect of O2-Cl− and different Cl− contents in CO2-O2-Cl− environment were studied by weight-loss test and characterization analysis. It showed that the O2 was the dominant factor inducing localized corrosion and the synergistic effect of O2-Cl− in CO2-O2-Cl− environment mainly accounted for the growth of the corrosion, because porous Fe oxides generated by O2 promoted the mass transfer and catalysis of Cl− and Cl− in turn promoted the expansion of localized corrosion pits. The increase of the Cl− under low content enhanced the synergistic effect with O2, while high content of Cl− (3000–5000 mg/L) could reduce the solubility of CO2/O2 and replace the adsorption of corrosive medium and ions on the substrate surface, inhibiting the cathodic process of corrosion reaction.