Shape Of Pits Research Articles

(Invited) 3-D Visualization of Li Metal Plating and Stripping with Operando Video Microscopy

In recent years, there has been an explosion of research into Li metal anodes for high-energy-density batteries. However, despite tremendous progress in the field, the reversible plating and stripping of Li has been hindered by the complex interplay between electrode morphology, surface chemistry, and mechanics. This has led to many empirical observations of improved performance, but our ability to rationally design solutions to solve the challenges of reversibility remain limited by our fundamental understanding of the complex electrodeposition and dissolution processes involved [1]. In an analogous example, Li plating on graphite anodes during fast-charging also plagues the Li-ion community [2], but fundamental studies of the complex nature of Li plating on intercalation electrodes is equally lacking.To address these challenges, in situ/operando analyses are of paramount importance to the community. However, given the dynamic nature of Li plating and stripping, challenges arise with respect to tradeoffs in spatial and temporal resolution. To address these challenges, we have recently integrated our optical visualization cells with a digital microscope capable of focus variation microscopy. This enables 3-D visualization of the electrode morphology with high temporal resolution, allowing for video capture of Li plating and stripping [2-3].In this talk, I will discuss the application of operando 3-D microscopy for visualization of both Li metal anodes and Li plating on graphite surfaces during fast-charging of Li-ion batteries. In the case of Li metal anodes, we observe significant anisotropy in the geometric shape of individual pits during stripping [3]. The nucleation density and anisotropy are shown to be strongly influenced by the surface microstructure and underlying crystallographic texture of the Li metal surface. As a results, pits can exhibit strong faceting, which influences the nature of nucleation at pit edges in subsequent cycles [4]. As a parallel example, we demonstrate 3-D visualization of Li plating on graphite electrodes during fast-charge, which illustrates the coupling between nucleation of Li plating and local heterogeneity in state-of-charge [2]. Overall, these results highlight the importance of both spatial and temporal heterogeneity in the nature of nucleation, growth, dissolution, pitting, and dead Li formationReferences[1] K. N. Wood, M. Noked, N. P. Dasgupta, ACS Energy Lett. 2, 664 (2017).[2] Y. Chen, K.-H. Chen, A. J. Sanchez, E. Kazyak, V. Goel, Y. Gorlin, J. Christensen, K. Thornton, N. P. Dasgupta, J. Mater Chem. A 9, 23522 (2021).[3] A. J. Sanchez, E. Kazyak, Y. Chen, J. Lasso, N. P. Dasgupta, J. Mater Chem. A. 9, 21013 (2021).[4] A. J. Sanchez, E. Kazyak, Y. Chen, K.-H. Chen, E. R. Pattison, N. P. Dasgupta, ACS Energy Lett. 5, 994 (2020).

Etch pit formation on β-Ga2O3 by molten KOH+NaOH and hot H3PO4 and their correlation with dislocations

The chemical etch pitting method is a powerful technique to reveal dislocations in semiconductor materials; however, a reliable etchant has not been established for β-Ga2O3. In this work, we performed a comparative study of two etchants, molten KOH+NaOH and hot H3PO4, to reveal dislocations from the (−201) surface. Using transmission electron microscopy, it was determined that KOH+NaOH could reveal all grown-in dislocations. The dislocation outcrops were located at the pit cores. The pit shape, specifically, its symmetry in the [010] direction, had a close correlation with the line direction of the dislocations but there was no simple correlation with the Burgers vector. On comparing H3PO4 with KOH+NaOH on the same sample, the results indicated that both etchants could reveal dislocations with a large angle to the (−201) surface but H3PO4 could not reveal dislocations nearly parallel to this surface. Surface damage induced by polishing produced etch pits in both etchants with smaller dimensions than those of the grown-in dislocations.

Does the shape of economic recovery matter? An alternative unit root test with new smooth transition model

The subject of economic recovery after the Coronavirus pandemic has received much attention in the media and by academics in recent years. Pandemic experience creates a new transition between the pre-pandemic era trend and the post-pandemic era trend related to the major economic indicators’ time series path. This paper offers a new smooth transition model and a unit root testing procedure to test null of non-stationary against the alternatives of stationary that allow for a pit shape smooth transition from the pre-pandemic trend to post-pandemic trend. The properties of the test statistics are investigated with several simulation studies. Also, the new model and unit root testing procedure are applied to industrial production index, consumer price index and the unemployment rates of Global 8 countries and results state the usefulness of these new tests.

About the occurrence of Elatine macropoda and E. gussonei (Elatinaceae) in Sicily and lectotypification of their names

Morphological and nomenclatural investigations for two critical Mediterranean species of Elatine, i.e., E. macropoda and E. gussonei, as well as their correct distribution in Sicily, are discussed. These two names are lectotypified on herbarium specimens kept, respectively, at NAP and FI. The morphological investigations carried out on both the types, as well as on several living and dried material collected in southern Sicily, Lampedusa, and Malta (loci classici included), allowed to individuate reliable diagnostic characters that can be used for a correct identification of the two species. The most relevant differential features are: ratio petal/sepal, size and shape of the seed testa pits, and their arrangement in row number. According to our results, only E. macropoda occurs in the Hyblaean territory (Sicily), which is the locus classicus, whereas E. gussonei occurs on Lampedusa and Maltese islands only. However, further and in-depth morphological research is necessary to clarify their overall distribution in the Mediterranean area. Finally, an analytic key to the Mediterranean Elatine is provided.

Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers

In this article, the suitability of the etchants NaOH/KOH and Ba(OH)2 for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with a MgO‐assisted “drop method” is compared. Defect selectivity for the new etchant Ba(OH)2 is confirmed by the local TEM analysis. Temperature dependence (420–500 °C) of etch pit sizes of a‐, mixed‐, and c‐type dislocations for both etchants are investigated by statistical evaluation of scanning electron microscopy (SEM) images. Additionally, the etch pit shape is analyzed for samples etched at 460 °C by atomic force microscopy (AFM) measurements. While a‐ and mixed‐type dislocations result in pits of comparable size and shape for both etchants, c‐type dislocations are already strongly etched with NaOH/KOH at low temperatures leading to over‐etching and MgO precipitation. Ba(OH)2, in contrast, generates smaller c‐type etch pits at low and medium etching temperatures and no MgO precipitates and is therefore preferable for drop etching.

Pit Stability Predictions of Additively Manufactured SS316 Surfaces Using Finite Element Analysis

Stainless steels are susceptible to localized forms of corrosion attack, such as pitting. The size and lifetime of a nucleated pit can vary, depending on a critical potential or current density criterion, which determines if the pit repassivates or continues growing. This work uses finite element method (FEM) modeling to compare the critical pit radii predicted by thermodynamic and kinetic repassivation criteria. Experimental electrochemical boundary conditions are used to capture the active pit kinetics. Geometric and environmental parameters, such as the pit shape and size (analogous to additively manufactured lack-of-fusion pores), solution concentration, and water layer thickness were considered to assess their impact on the pit repassivation criterion. The critical pit radius (the transition point from stable growth to repassivation) predicted for a hemispherical pit was larger when using the repassivation potential (Erp) criteria, as opposed to the current density criteria (pit stability product). Including both the pit stability product and Erp into its calculations, the analytical maximum pit model predicted a critical radius two times more conservative than the FEA approach, under the conditions studied herein. The complex pits representing lack-of-fusion pores were shown to have minimal impact on the critical radius in atmospheric conditions.

Assessment of ablation damage on quartz ceramics through experiment and 3D modelling considering a dynamic heat source

The effects of irradiation time (IT), laser power (LP), and spot diameter (SD) on the damage caused to quartz ceramics under continuous-wave laser irradiation were investigated through an orthogonal experiment. The experimental results show that the LP has the dominant effect on the depth of an ablation pit, while the SD has the greatest impact on the diameter of the ablation centre. The diameter and depth of the ablation pit were both positively correlated to the irradiation energy. The bubbles and molten silica transition layer affected the laser beam's reflection and transmission properties, leading to the incident laser beam scattering into the entire ablation pit and forming an elliptical ablation pit. Furthermore, a 3D finite element (FE) model considering a dynamic heat source was developed to simulate the laser damage process. The shape and dimension of the ablation pit predicted by the FE model were consistent with those obtained through the experiment, demonstrating the effectiveness and rationality of the model. The FE analysis results show that the different ablation rates in the radial and depth directions significantly influence the morphology of the ablation pits. The temperature gradient in the transition region increases while the thickness of the transition region decreases as the LP increases. This indicates that a large LP will lead to greater thermal stress in this area and result in more microcracks.

Phase Field Modeling of Crystallographic Corrosion Pits

The modeling of corrosion to understand and predict corrosion behavior is a topical issue. Here, a 3D phase field model is developed to simulate the pit morphology, primarily focusing on crystallographic pits. A crystallographic function is employed to incorporate different corrosion rates for different crystallographic planes. The model is benchmarked and validated against an analytical solution for a simple case. 3D crystallographic pits in a single crystal are simulated and the effect of substrate orientation on the pit morphology is studied. The crystallographic pit morphology changes significantly with the substrate orientation and these morphologies have a symmetry consistent with the substrate orientation. This first 3D phase field model of crystallographic pits will help in predicting the intricate shapes of pits, thereby, pushing the frontiers of pitting corrosion modeling.

Trachea features and fiber dimensions of fast-growing tree: A case study on wood samples from eastern Indonesia

Fast-growing plant is one of the characteristics of pioneer plants. Commonly, the plants grow in areas that is exposed to sunlight such as open area and forest edges. Fast-growing plants have different anatomical and physical wood characteristics compare with slow-growing plants. Therefore, this study aims to examine the anatomical characteristics of fast-growing plants, especially trees, namely the fiber cells and trachea features. A total of 33 wood samples from 28 species were used in this study. We used wood samples from Eastern Indonesia deposited at Herbarium Bogoriense. Examined wood samples are taken from branches with 1-2 cm of diameter. The anatomical characters observed were focused on two types of cells, namely fiber cells (fiber length, fiber diameter, fiber cell wall thickness, lumen width, identification of septate fibers and fibers pit) and the trachea (perforation type, pit arrangement, and pit form). From the observations of all wood samples showed that the length of fiber cells are classified as short (18 species) and medium (10 species) fiber. There are two groups of fiber cell wall thickness viz. very thin (16 species) and thin to thick (12 species). Septate fibers only found in 7 species especially Chisocheton and Teijsmanniodendron. Fiber’s pit observed in Horsfieldia parviflora, Mallotus peltatus, dan Neuburgia corynocarpa. All species have simple tracheal perforation with alternate or opposite pit arrangement. Moreover, branch wood samples have polygonal pit shape, oval or combination of those two shapes were found in some species, such as Horsfieldia parviflora, Sandoricum koetjape and Teijsmanniodendron bogoreinse.

Influence of corrosion pit geometry on stress distribution within a single artificial pit

ABSTRACT A lower pitting severity produces a shallower corrosion pit shape on a corroded ballast tank. Pit distributions of corroded specimens have a probability model for the non-Gaussian surface. Therefore, the present work focuses on the numerical study of stress distribution within the corrosion pit area, while considering different corrosion pit geometries. Accordingly, 45 dog bone-shaped finite element models with a single corrosion pit are investigated. The geometrical parameters of the corrosion pit are analyzed with quantitative correlations at different sizes, shapes, and different levels of enlargement. Additionally, a corrosion pit alteration scenario is proposed, with a narrow deep, hemispherical, and final shallow wide form. Results show that the stress concentration factor remains relatively constant at the pit edge and increases toward the pit bottom. Furthermore, stress declines on the pit bottom and shallower corrosion pit form, which conforms to the polynomial trendline.

The Validity of Iscan’s Age Estimation Method applied to the Fourth Rib in a Thai Male population

Abstract Iscan’s staging method for age estimation from fourth ribs has been proved to be a potentially useful tool for various populations. However, due to interracial variations, it is necessary to calibrate its’ accuracy in reference to a population of Thai males before it can be applied. This study aimed to evaluate the validity of phasing analyses of sternal ends of fourth ribs developed by Iscan, et al., on a Thai male population. The Iscan’s method was applied to 50 Thai males aged 18 years and above. Staging of sternal ends of the ribs was analyzed based on 3 morphological features: pit depth, pit shape, and rim and wall configurations – designated as components 1, 2, and 3, respectively. The data was analyzed using descriptive statistics, one-way ANOVA, and cross-tabulation with Kendall’s Tau-c correlation. It was found that sternal end stages of fourth ribs in each component, inclusive of composite scores, are positively correlated to the age of the individual (P < 0.001). However, Iscan’s result - which was derived from a population of white males - delivers age-underestimation in a Thai population. Hence, we developed a modified age prediction reference table for application to Thai males. Applying cross-tabulation analysis, stages 1 and 2 were found only in individuals who were less than 40 years old, and stages 4 and 5 were found only in the 40 years and above age-group except for 1 case. Keywords: Age estimation, Fourth rib, Iscan’s method, Thai male

Simulation on coupling effects between surface wear and fatigue in spur gear

A surface wear prediction method is used to determine the wear rate of the tooth surface. This method employs the Archard’s wear model together with the gear contact mechanics model. An equivalent calculation model based on Hertzian contact theory and fracture mechanics is used to investigate crack initiation and crack propagation. The virtual crack extension (VCE) method is employed to analyze the propagation process from the initial crack to occurrences of tooth surface pitting. A life prediction method on the wear-fatigue coupling is developed. The crack propagation process and pit shapes are determined by the iterative analysis. The relationship between service life and the remaining distance from the crack tips to the tooth surface is determined. The damage mechanism of wear-fatigue coupling is explored. The results of the comparative analysis show that the wear of tooth surface affects the cracks propagation characteristics, reduces the service life and even can change the failure mode. The simulated pit shapes and crack propagation process are in good agreement with the results of other literature. The analysis method of wear-fatigue coupling damage can well simulate the damage process and predict service life in spur gear.

Visualization and investigation of the erosion process for natural gas hydrate using water jet through experiments and simulation

Natural Gas Hydrate (NGH) and Hydrate-bearing Sediments (HBS) are emerging as an important potential energy resource. Radial Jet Drilling (RJD) technology, turning sharply in the casing and drilling laterals by using water jet, is a valid approach to solve problems of high cost, low efficiency during the exploitation of NGHs. The performance of water jet drilling remains unclear, and traditional finite element methods cannot accurately depict the water jet drilling ability due to mesh distortion. This paper analyzes the water jet erosion process of NGH and HBS. Experiments on the erosion of reconstituted gas hydrates are conducted and visualized in both submerged and submerged confining pressure conditions. Subsequently, two coupled nozzle–target models are solved by Arbitrary Lagrangian Eulerian (ALE) and Smooth Particle Hydrodynamics (SPH) methods. The flow field, the deformation and erosion of the hydrates induced by water jet are simulated. The experimental results show that there are specific shapes of cylindrical erosion pits for NGH and HBS. The numerical results are consistent with the experiments, which proves the effectiveness of water jet exploring hydrate resources. The submerged condition and the confining pressure condition will hinder the erosion efficiency, and the critical erosion velocities for both HBS and NGH are obtained. ALE method has superior accuracy in modeling the damaged area and erosion pit characteristics; while SPH method, has advantages in showing the motion state of the single particles and unstable and discontinuous flow field. This paper provides a good guidance for understanding the water jet drilling performance and selecting the appropriate simulation method in NGH reservoirs development.

THE BARROW OF THE EARLY IRON AGE NEAR MOTRONYN HILLFORT

In 2019, the Scythian Right-bank expedition organized by the Institute of Archaeology of the National Academy of Sciences of Ukraine and the National Historical and Cultural Reserve «Chyhyryn» excavated the barrows on the Motronyn hillfort suburb, located near Melnyky village, Chyhyryn district, Cherkasy Region, in the south of the Forest-Steppe of Dnieper Right-bank area.
 The barrows were erected in pre-Scythian Age and the barrow 97 also contained the inlet Scythian burial. This mound was 0.65 m high, the diameter was 8.8—9.8 m. A pre-Scythian burial-memorial complex was discovered under the mound, destroyed by a later burial. Finds from it are represented by fragments of ceramic ware: pots, large earthenware pots, bowls, ladles. Some fragments are decorated with geometric patterns. Ceramic spindle whorls, iron knives, bronze arrowheads, plaques, and animal bones were also found.
 During the Middle Scythian period another deceased was buried in the center of the mound. The tomb had the shape of a rectangular pit, oriented along the west — east line. Its length was 1.89—2.16 m, width — 0.7—0.82 m, depth from the surface of the mound — 1.45 m. The skeleton laid supine, with its head to the west. The left leg was lying on a stone slab. A quiver with arrows was placed next to it. An iron sword and a knife with a bone handle were found near the belt. This burial was also accompanied with the laying of wares in the mound borders. A pot was buried in the north, and handmade and wheel-made bowls in the east.
 Pre-Scythian finds from the mound have analogies in different regions of the Ukrainian Forest-Steppe where antiquities of the Late Chornoliska and Zhabotyn cultures are widespread, in particular on the Middle Dniester and in the Southern Bug River region, on the Right-bank of the Dnieper and in the Vorskla River region. A set of pottery and an arrowhead of the Novocherkassk type allows us to date the mentioned assemblage by the second half of the 8th century BC.
 Funeral rite and grave goods of the Scythian Age burial also have parallels in the sites of that time, including the south of the Right-bank of Middle Dnieper. According to the pot type and arrowheads, this burial can be dated to the second half of the 6th century BC.

Using Multi-Physics Models to Capture the Influence of Microstructure on Pitting Corrosion Morphologies and Stress Concentrations

Pitting corrosion is of particular concern to the navy because while significant progress has been made in preventing uniform and general corrosion, the possibility of corrosion pits transitioning to crack initiation sites remains a persistent threat with potentially catastrophic consequences. Beyond considerations for the magnitude and mode of mechanical loading, the transition from pit to crack may be influenced by the prevailing electrochemical environment and the microstructural composition of the corroding material. Additionally, both the microstructure and evolving pit morphologies will directly affect local stress concentrations, potentially leading to crack initiation. Until recently, most studies of pitting corrosion, with or without the application of mechanical load, have dealt with the phenomenon from an electrochemical and compositional perspective at the macroscale and have not considered the microstructure nor changes in the evolving pit shape over time. This work presents an investigation of how underlying microstructures can influence the pitting corrosion process, and the resulting stress distributions around pits, through a multi-physics computational modeling framework that incorporates crystallographic orientation dependencies into both the corrosion potential and mechanical response. This is accomplished by importing a microstructure’s orientation data, i.e., the Euler angle information, directly into the computational modeling domain in order to provide crystallographic information.Based on this modeling paradigm, computational simulations are conducted using both experimental and synthetic microstructures for conventionally and additively manufactured stainless steel alloys. Experimental microstructures are provided from electron backscatter diffraction data, while the synthetic microstructures are generated using DREAM3D software. The computational modeling framework utilizes phase field methods to resolve the moving pit boundary while the underlying concentration and displacement gradients are solved over a finite element mesh. Over the course of the simulations, the orientation dependence of the corrosion potentials, and ensuing corrosion current densities, lead to non-uniform growth and propagation of the pit throughout the model domain as it evolves over time, producing irregular pit morphologies. Further, the microstructural influence on mechanical response is measured through differences in peak stresses and stress concentrations along the pit boundary, as well as stress intensity factors. This work highlights the significant local impact microstructure has on the pitting corrosion process and contrasts these impacts over different manufacturing processes (conventional vs. additive) for the same alloy system.

Time-lapse observation of pitting corrosion in ferritic stainless steel under bipolar electrochemistry control

A bipolar electrochemistry approach has been applied to characterise pit nucleation and growth kinetics in 13% Cr ferritic stainless steel. In-situ time-lapse imaging, supported by laser confocal microscopy measurements, were applied to obtain pit nucleation frequencies and associated pit growth characteristics. The development of champion pits is observed, and the effect of pit shape and aspect ratio on pit nucleation and growth are discussed. Pits preferentially nucleated and grew with depth to width aspect ratios of 0.4–0.6. The observed pit growth kinetics are independent of pit volume and the acting potentials.

Application of bipolar electrochemistry to assess the ambient temperature corrosion resistance of solution annealed type 2205 duplex stainless steel

The corrosion resistance of solution annealing heat-treated type 2205 duplex stainless steel microstructures was assessed with a bipolar electrochemistry technique. Chemical element partitioning in both crystallographic phases was correlated to simulations of critical pitting temperatures. The as-received microstructure had the highest pit nucleation resistance, with high-temperature solution annealing treatment revealing reduced pit growth rates. Pit nucleation occurred either within the ferrite phase or at ferrite-austenite interfaces, with the resulting pit shape affected by the microstructure characteristics. The results of this study are discussed in the framework of microstructure design for enhanced corrosion resistance in duplex stainless steels.

On the effect of pit shape on pitted plates, Part I: Tensile behavior due to artificial corrosion pits

Pitting corrosion threatens the safety of steel structures by degrading material properties. In this paper, the effect of pitting damage on tensile behavior of Q345 and Q235 steels is studied experimentally and numerically. Material tensile tests were carried out on small steel specimens with artificially introduced corrosion pits of a cylindrical, semi-ellipsoidal, or conical shape, and used to validate their numerical models. Numerous numerical analyses were carried out to study the tensile properties and behavior of different steels due to varying pitting features in the pit shape and degree of volume loss (DOV) of corroded material. Results showed that pit shape influences the tensile properties of corroded steel significantly, depending on the ratio of pit diameter to pit depth. In the worst case, variation of pit shape could result in a difference of 7.58% in strength deterioration, and it could become worse if combined with the random nature of pit size, pit depth, and pitting distribution. An equivalent material model was proposed to correlate the reduction ratios of tensile properties with the DOV and pit shape. The ultimate strength of pitted plates can be predicted properly, using the equivalent material model instead of modelling the detailed corrosion pits.

Study on corrosion models of structural steel exposed in urban industrial atmospheric and laboratory simulated environments based on the 3D profile

The time-dependent safety assessment and reliability analysis of a structure depends primarily on the corrosion model that directly affects the calculation accuracy. The three-dimensional non-contact surface topography instrument was used to study the corrosion morphology under urban industrial atmospheric exposure conditions and the dry/wet cycle accelerated corrosion test. The evaluation indices of the proposed corrosion model were study, including pit shape, pit depth, pit diameter–depth ratio, etch pit distribution, and thickness. Time-dependent mathematical models between these parameters and the corrosion degree are discussed. The pit depth distribution follows the normal distribution and a probability distribution model related to the rust ratio is established. There is a certain relationship between the thickness loss and etch pit depth. A corrosion model suitable for the common Q235 steel used in civil engineering in an acid rain corrosion environment is proposed. The applicability of the corrosion model is verified through the machine-simulated corrosion on the same batch of structural steel.

Stochastic Modeling of Corroded Surface Features of Structural Steel Under Sulfate Attack

Steel structures exposed to the sulfate corrosive environment for a long time will inevitably suffer random corrosion damage, which will lead to uncertain degradation in the mechanical properties of materials and structures. The safety and reliability assessments of corroded steel structures largely depend on the quantification of corrosion characteristics. In order to investigate the corrosion features of structural steel under sulfate attack, six batches of accelerated corrosion experiments were conducted on 18 steel specimens. The surface morphologies of all corroded coupons were first measured by a 3D surface profilometer, and then the surface parameters were calculated/extracted and analyzed by a self-written analysis algorithm to clarify the distribution characteristics and evolution laws of corrosion depth, pit depth, and pit shape. The results revealed that the corrosion form of structural steel under sulfate attack was a rather uneven general corrosion, which exhibited the intersection of general corrosion and pits. The corrosion depth obeyed a normal distribution, and its average value, standard deviation, and the power spectrum peak increased as the corrosion age increased. The depth and aspect ratio of corrosion pits were both in accord with the lognormal distribution and showed the increasing and decreasing trend with the corrosion time going on, respectively. Additionally, the probabilities of different pit shapes in different depth ranges were obtained, in which cone pits accounted for the largest proportion, and the pits gradually changed from cylindrical and hemispherical to conical with the increase of pit depth. In the end, the random models for corrosion depth and pits were established based on the statistical results, which realized the reconstruction and random modeling of corrosion characteristics of structural steel under sulfate attack.