Surface Evolution Process Research Articles

Macroscopic perspective on phase transition behavior of natural single-crystal graphite under different pressure environments

Comprehensive understanding of the direct transformation pathway from graphite to diamond under high temperature and high pressure has long been one of the fundamental goals in materials science. Despite considerable experimental and theoretical progress, current experimental studies have mainly focused on the local microstructural characterizations of recovered samples, which has certain limitations for high-temperature and high-pressure products, which often exhibit diversity. Here, we report on the pressure-induced phase transition behavior of natural single-crystal graphite under three distinct pressure-transmitting media from a macroscopic perspective using in situ two-dimensional Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. The surface evolution process of graphite before and after the phase transition is captured, revealing that pressure-induced surface textures can impede the continuity of the phase transition process across the entire single crystal. Our results provide a fresh perspective for studying the phase transition behavior of graphite and greatly deepen our understanding of this behavior, which will be helpful in guiding further high-temperature and high-pressure syntheses of carbon allotropes.

Quantitative Evaluation of the Lunar Seismic Scattering and Comparison Between the Earth, Mars, and the Moon

AbstractThe intense seismic scattering seen in Apollo lunar seismic data is one of the most characteristic features, making the seismic signals much different from those observed on the Earth. The scattering is considered to be attributed to subsurface heterogeneity. While the heterogeneous structure of the Moon reflects the past geological activities and evolution processes from the formation, the detailed description remains an open issue. Here, we present a new model of the subsurface heterogeneity within the upper lunar crust derived through a full 3D seismic wave propagation simulation. Our simulation successfully reproduced the Apollo seismic observations, leading to a significant update of the scattering properties of the Moon. The results showed that the scattering intensity of the Moon is about 10 times higher than that of the heterogeneous region on the Earth. The quantified scattering parameters could give us a constraint on the surface evolution process of the Moon and enable the comparative study for answering a fundamental question of why the seismological features are different on various planetary bodies.

In Situ Monitoring of the Surface Evolution of a Silver Electrode from Polycrystalline to Well-Defined Structures.

Capturing the surface-structural dynamics of metal electrocatalysts under certain electrochemical environments is intriguingly desired for understanding the behavior of various metal-based electrocatalysts. However, in situ monitoring of the evolution of a polycrystalline metal surface at the interface of electrode-electrolyte solutions at negative/positive potentials with high-resolution scanning tunneling microscopy (STM) is seldom. Here, we use electrochemical STM (EC-STM) for in situ monitoring of the surface evolution process of a silver electrode in both an aqueous sodium hydroxide solution and an ionic liquid of 1-methyl-1-octylpyrrolidinium bis(trifluoromethylsulfonyl) amide driven by negative potentials. We found silver underwent a surface change from a polycrystalline structure to a well-defined surface arrangement in both electrolytes. In NaOH aqueous solution, the silver surface transferred in several minutes at a turning-point potential where hydrogen adsorbed and formed mainly (111) and (100) pits. Controversially, the surface evolution in the ionic liquid was much slower than that in the aqueous solution, and cation adsorption was observed in a wide potential range. The surface evolution of silver is proposed to be linked to the surface adsorbates as well as the formation of their complexes with undercoordinated silver atoms. The results also show that cathodic annealing of polycrystalline silver is a cheap, easy, and reliable way to obtain quasi-ordered crystal surfaces.

Visualization of localized deformation of external thermal insulation composite systems during aging

• The deformation at different hygrothermal aging stages is tested. • The localized non-uniformity of displacement and strain field is highly correlated with the initiation and evolution of cracks in the finish layer. • The influence of temperature and rainfall on the crack expansion and contraction and local non-uniform deformation of the finish layer is analyzed. The localized deformation of finish coat materials occurs due to hygrothermal aging under harsh service conditions, which adversely impacts the thermal performance and safety of the external thermal insulation composite systems (ETICS). In this study, digital images of the ETICS finish coat were obtained using an industrial digital camera under artificially generated harsh aging environment. Both local deformation field and strain field as well as the surface crack initiation and evolution process of the ETICS finish coat were assessed by the digital image correlation method. The calculation results revealed that the phenomena associated with the occurrence of a localized non-uniform displacement field and strain field of the ETICS finish coat during aging are very significant especially at the cracks, with obvious regional boundaries. The localization of the strain field is highly correlated with the initiation and evolution of cracks with a significant local distribution band. The maximum horizontal displacement and vertical displacement during the resting phase after being exposed to rain were reduced by 77.14 and 57.69%, respectively compared with those at high temperature. The massive expansion and shrinkage resulted in the cracking of the finish coat. When the cracked finish coat expands at high temperature or shrinks when exposed to rain, the cracks also expand or shrink accordingly, so that the localized non-uniformity level of the displacement field decreases or increases, and the strain on the reference line presents uniform change or sudden change. The non-uniform deformation of the finish coat caused by the cyclic action of aging factors such as high temperature and rainfall eventually becomes more and more significant. The characteristic index for non-uniform deformation was proposed and its evolution laws with the aging time were systematically analyzed. Taken as the next research focus, it can provide a reference for analyzing the deformation and deterioration process of the ETICS and ensuring the operation safety.

DriftScalarDyFoam: An OpenFOAM-Based Multistage Solver for Drifting Snow and Its Distribution Around Buildings

There is a complex coupling relationship between the airflow and snow cover. In a period of hours or even days, the airflow will cause the redistribution of snow, and the redistribution of snow will cause the airflow to change. This study develops a dynamic mesh technology applied in snow drifting simulation through a real-time dynamic mesh update to depict the snow surface evolution process under long-period snow drifting, and a solver application named driftScalarDyFoam based on OpenFOAM is implemented. This solver divides the long-period snow drifting process into several stages, in each of which a snow transport equation is applied to predict the spatial distribution of snow, and finally, the snow surface evolves according to the erosion–deposition model. This method that we have proposed has been validated for several measured cases, including snow distribution on a flat roof and snow distribution around a building.

Surface Reconstruction of Perovskites for Water Oxidation: The Role of Initial Oxides’ Bulk Chemistry

Developing highly active electrocatalysts for oxygen evolution reaction (OER) is crucial for the scalable production of renewable hydrogen fuels by water electrolysis. Perovskite oxides are extensively studied as OER catalysts as they can have high activity and also offer considerable flexibility in composition and structure. Recently, there are increasingly numerous reports regarding dynamic surface reconstruction of perovskite oxides under OER conditions, with claims that the reconstruction‐derived species are the actual catalysts responsible for the measured OER activity. To enable rational design of perovskite oxides as precatalysts to generate actual active components in situ, gaining essential understanding of their reconstruction behaviors is crucial. This perspective discusses the roles of initial bulk chemistry in the surface evolution process of perovskite oxides during OER, including the dependency of surface stability on electronic structure of the precatalyst and the possibility of occurrence of lattice oxygen evolution reaction and cation leaching on the surface of a perovskite oxide precatalyst. It is reasonably argued that tailoring the bulk properties of perovskite precatalysts, such as electronic structure, crystallographic structure, and ion stoichiometry, can influence the occurrence of surface reconstruction and the formation of actual active surface species.

Size of particles ejected from an artificial impact crater on asteroid 162173 Ryugu

A projectile accelerated by the Hayabusa2 Small Carry-on Impactor successfully produced an artificial impact crater with a final apparent diameter of 14.5 ± 0.8 m on the surface of the near-Earth asteroid 162173 Ryugu on April 5, 2019. At the time of cratering, Deployable Camera 3 took clear time-lapse images of the ejecta curtain, an assemblage of ejected particles forming a curtain-like structure emerging from the crater. Focusing on the optical depth of the ejecta curtain and comparing it with a theoretical model, we infer the size of the ejecta particles. As a result, the typical size of the ejecta particles is estimated to be several centimeters to decimeters, although it slightly depends on the assumed size distribution. Since the ejecta particles are expected to come from a depth down to ~1 m, our result suggests that the subsurface layer of Ryugu is composed of relatively small particles compared to the uppermost layer on which we observe many meter-sized boulders. Our result also suggests a deficit of particles of less than ~1 mm in the subsurface layer. These findings will play a key role in revealing the formation and surface evolution process of Ryugu and other small Solar System bodies.

Dynamically Stable Active Sites from Surface Evolution of Perovskite Materials during the Oxygen Evolution Reaction.

Perovskite oxides are an important class of oxygen evolution reaction (OER) catalysts in alkaline media, despite the elusive nature of their active sites. Here, we demonstrate that the origin of the OER activity in a La1-xSrxCoO3 model perovskite arises from a thin surface layer of Co hydr(oxy)oxide (CoOxHy) that interacts with trace-level Fe species present in the electrolyte, creating dynamically stable active sites. Generation of the hydr(oxy)oxide layer is a consequence of a surface evolution process driven by the A-site dissolution and O-vacancy creation. In turn, this imparts a 10-fold improvement in stability against Co dissolution and a 3-fold increase in the activity-stability factor for CoOxHy/LSCO when compared to nanoscale Co-hydr(oxy)oxides clusters. Our results suggest new design rules for active and stable perovskite oxide-based OER materials.

Internal Surface Quality Enhancement of Selective Laser Melted Inconel 718 by Abrasive Flow Machining

Abstract Additive manufacturing (AM) technology enables a new way for fabricating components with complex internal surfaces. Selective laser melting (SLM), being one of the most common AM techniques, is able to fabricate complex geometries with superior material properties. However, due to the poor surface quality, the fabricated internal surfaces cannot meet the specifications for some real applications. To achieve the required internal surface condition, post-polishing process is essential. As one of the most prominent processes for finishing inaccessible surfaces with a wide range of materials, abrasive flow machining (AFM) shows great potential to polish AM internal surfaces. Hence, this paper presents an analytical and experimental study on the internal surface quality improvement of SLM Inconel 718 by AFM, aiming to verify the feasibility of AFM on internal surface quality improvement. The surface evolution process was modeled, and the effects of process parameters on surface and subsurface quality were evaluated. The results show that good surface roughness was obtained at the medium conditions of high viscosity, large particle size, low extrusion pressure, and low temperature. The surface morphology was greatly affected by the medium particle size which showed consistency with the surface evolution model that small abrasive particles are unable to overcome the width and depth of the valleys, resulting in the formation of craters. The partially melt layer was effectively removed, and no subsurface damage was induced.

XPS study of sulfide minerals surface oxidation under high-voltage nanosecond pulses

Surface modification of natural metal sulfides (pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, and molybdenite) treated by high-power electromagnetic pulses (HPEMPtreatment) has been studied by X-ray photoelectron spectroscopy as a function of HPEMP treatment duration. Two principal common steps and some differences in the surface evolution process were identified. The initial surface modification step was observed at low treatment doses (up to N ~ 103 pulses). Formation or accumulation in the surface layer of metal-deficient sulfide phase, oxides and hydroxides, elemental/polysulfide sulfur and/or metastable sulfur (thiosulfate, sulfite) was observed at this step. The second step (N ≥ 3·103 pulses) is characterized by thermal loss of elemental sulfur.Differences in the modification process, it was found that the chemical transformations of sulfur in the surface layer of pyrite, arsenopyrite, chalcopyrite include accumulation/formation of S0 (Sn2−) at the first transformation stage (up to N ~ 103 pulses) followed by its removal. In the case of sphalerite and galena, the surface sulfur transformation had a different pattern. It included formation/accumulation at the first stage of metastable sulfur species (thiosulfate, sulfite) converted at an increase treatment duration to the initial state (sulfide or disulfide).

Localization of the Anodic Dissolution of Inconel 718 by Using an Electrodeposited Nickel Film

In electrochemical machining (ECM), the machining accuracy is to a great extent affected by the stray corrosion at low current density. In this paper, an electrodeposited nickel film is used to localize the anodic dissolution of Inconel 718 in counter-rotating ECM (CRECM). The anodic dissolution behavior of nickel in NaNO3 solution is investigated by linear sweep voltammetry, cyclic voltammetry, and dissolution efficiency measurement, and the surface evolution process is monitored by using a charge-coupled device. The results indicate that nickel is a favorable material with desired passivation characteristic that can be used for the localization of anodic dissolution of Inconel 718 in CRECM. The cylindrical Inconel 718 workpiece is covered by a thin nickel film, and is tested in the CRECM experiment. The experimental results show that the electrodeposited nickel film on the cylindrical surface can be rapidly dissolved under high current density. In contrast, the nickel film on the low-current-density area can be well reserved, and thereby protect the surface of the convex structure from stray corrosion. As a result, the anodic dissolution of Inconel 718 is located merely in the high-current-density region, and the surface quality and the profile of the convex structure are significantly improved.

Enhanced dye photocatalysis and recycling abilities of semi-wrapped TiO2@carbon nanofibers formed via foaming agent driving

To enhance photocatalysis and recycling abilities of catalyst simultaneously, novel microstructure in which TiO2 nanoparticles were semi-wrapped in carbon nanofibers (CNFs) was proposed and produced successfully. Betaine was employed as a foaming agent to drive the TiO2 nanoparticles to migrate from inner space to the surface of CNFs gradually under the function of calcination. Various characterizations were used to research the surface and crystal evolution process of TiO2 and CNFs, and the semi-wrapped microstructure of TiO2@CNFs was well built up when the composites were carbonized at 800°C. TiO2 was immobilized stably on CNFs while exposed partly to air distinctively. This unique semi-wrapped structure endowed the composites with strong interfacial interaction between TiO2 and CNFs, and the exposed section of TiO2 provided sufficient reaction sites for organic dyes. Notably, photocatalytic degradation ratio of Rhodamine B in the first time reached 98.2% and even remained 95.4% after being recycled for 5 times under the irradiation of ultraviolet light, indicating that the photocatalysis and recycling abilities were obviously strengthened simultaneously compared with other counterparts reported in literature.

Numerical investigation of the submonolayer growth and relaxation of stepped Ag (110) and Au (110) surfaces

The terrace width distribution (TWD) as well as the adatom and island densities for some stepped fcc (110) surfaces with parallel and equidistant steps of equal stiffness are studied by means of kinetic Monte Carlo simulations. Reliable energy barriers for surface diffusion are used. They have been calculated by means of many-body potentials derived within the second moment approximation to the tight-binding model. The effects of the temperature, atom deposition flux and surface diffusion on quantities of interest in the early stage of the surface evolution process have been singled out. In most cases, linear, logarithmic and power-law behaviors are recovered for the evolution of the step width and terrace defects. The TWD is well described by the Gaussian distribution (GD) in the domain of temperature investigated but deviates from the Generalized Wigner Distribution (GWD).

Evolution and equivalent control law of surface roughness in shear-thickening polishing

A comprehensive surface roughness model is established to predict the average surface roughness achieved by shear-thickening polishing (STP) based on calculation of Brinell hardness number (BHN), shear-thickening mechanism and plastic indentation on abrasive wear theory. The model takes the effects of material hardness and plastic wear into account in addition to the calculation of the surface roughness factors concerning the normal pressure, slurry performance, et al. The “size effect” as the ratio of abrasive size to solid colloidal particle size, has also been successfully integrated into the model. STP experiments validate that the maximal difference of surface roughness between theoretical and experimental results is no greater than 12.02%. The surface evolution process can be theoretically and experimentally described with certain feasibility and veracity. An inflection point appears in the trend line of predicted surface roughness when the ratio approaches to 0.5. An equivalent control law of surface roughness in STP exists when the ratio is greater than 0.5 and is revealed by the model and experiments due to the competing effects of kinematics, indentation depth, cutting width, plastic plowing of materials on surface formation. The freedom control for an invariable surface roughness can be achieved by STP according to the equivalent control law. The prediction model for brittle materials shall be revised based on material properties and more removal forms.

Experimental study on magnetically insulated transmission line electrode surface evolution process under MA/cm current density

The design of high-current density magnetically insulated transmission line (MITL) is a difficult problem of current large-scale Z-pinch device. In particular, a thorough understanding of the MITL electrode surface evolution process under high current density is lacking. On the “QiangGuang-I” accelerator, the load area possesses a low inductance short-circuit structure with a diameter of 2.85 mm at the cathode, and three reflux columns with a diameter of 3 mm and uniformly distributed circumference at the anode. The length of the high density MITL area is 20 mm. A laser interferometer is used to assess and analyze the state of the MITL cathode and anode gap, and their evolution process under high current density. Experimental results indicate that evident current loss is not observed in the current density area at pulse leading edge, and peak when the surface current density reaches MA/cm. Analysis on electrode surface working conditions indicates that when the current leading edge is at 71.5% of the peak, the total evaporation of MITL cathode structure can be realized by energy deposition caused by ohmic heating. The electrode state changes, and diffusion conditions are reflected in the laser interferometer image. The MITL cathode area mainly exists in metal vapor form. The metal vapor density in the cathode central region is higher than the upper limit of laser penetration density (∼4 × 1021/cm3), with an expansion velocity of ∼0.96 km/s. The metal vapor density in the electrode outer area may lead to evident distortion of fringes, and its expansion velocity is faster than that in the center area (1.53 km/s).

Improvement of feature-scale profile evolution in a silicon dioxide plasma etching simulator using the level set method

We present a three-dimensional simulator of silicon dioxide etching in a fluorocarbon plasma process. Explicit parametrization of the surface is currently one of the most frequently used methods to evolve the etched surface according to the equipment simulation results. These techniques update the coordinates of the vertices and need to add and/or remove faces to keep an accurate surface representation. These processes can introduce errors and produce unrealistic results, especially in complex structures. In this paper we prove the effectiveness of our level set (LS) implementation to evolve the etched surface according to etching models, resulting in a fully operational plasma etching simulator. The LS implementation is based on a surface reconstruction algorithm from scattered points enabling the simulation of complex topological changes such as coalescing or splitting of contiguous regions. Additionally, our algorithm is based on the sparse field method for reducing computational time of the surface evolution process and it is perfectly suited to be used with the Anetch software package. Finally, several structures are simulated and an experimental result is used to compare and validate the effectiveness of the simulator we have developed.

Coarse-to-fine surface reconstruction from silhouettes and range data using mesh deformation

We present a coarse-to-fine surface reconstruction method based on mesh deformation to build watertight surface models of complex objects from their silhouettes and range data. The deformable mesh, which initially represents the object visual hull, is iteratively displaced towards the triangulated range surface using the line-of-sight information. Each iteration of the deformation algorithm involves smoothing and restructuring operations to regularize the surface evolution process. We define a non-shrinking and easy-to-compute smoothing operator that fairs the surface separately along its tangential and normal directions. The mesh restructuring operator, which is based on edge split, collapse and flip operations, enables the deformable mesh to adapt its shape to the object geometry without suffering from any geometrical distortions. By imposing appropriate minimum and maximum edge length constraints, the deformable mesh, hence the object surface, can be represented at increasing levels of detail. This coarse-to-fine strategy, that allows high resolution reconstructions even with deficient and irregularly sampled range data, not only provides robustness, but also significantly improves the computational efficiency of the deformation process. We demonstrate the performance of the proposed method on several real objects.

Heat transfer in nucleate pool boiling of aqueous SDS and triton X-100 solutions

Variation in degree of surface wettability is presented through the application of Cooper’s correlative approach (h ∝ M−0.5qw″0.67) for computing enhancement (ϕ) in nucleate pool boiling of aqueous solutions of SDS and Triton X-100 and its presentation with Marangoni parameter (χ) that represents the dynamic convection effects due to surface tension gradients. Dynamic spreading coefficient defined as σdynNa, which relates spreading and wetting characteristics with the active nucleation site density on the heated surface and bubble evolution process, represents cavity filling and activation process and eliminates the concentration dependence of nucleate pool boiling heat transfer in boiling of aqueous surfactant solutions. Using the dynamic spreading coefficient (σdynNa = 0.09qw″0.71), correlation predictions within ±15% for both SDS and Triton X-100 solutions for low heat flux boiling condition (qw″ ≤ 100 kW/m2) characterised primarily by isolated bubble regime are presented.

Morphological instability of spherical soft particles induced by surface charges

We here demonstrate that surface charges on a spherical soft particle may induce its morphology instability. It is found that various patterns can be obtained by varying the surface charge density. The critical condition for the occurrence of surface instability and the wavelength of the induced surface patterns are derived analytically and, thereby, the morphological phase diagram of soft particles can be provided easily. Besides the electric stress, surface tension also plays a significant role in the surface evolution process. In addition, the morphological evolution behavior of a soft particle is demonstrated to exhibit distinct dependence on its size.

Surface Morphology of Electroless Copper Deposits Using Different Reducing Agents

Electroless copper plating has been used in the printed circuit industry for plating from bare laminate and plating through hole. Common commercial plating solutions consist of formaldehyde as the reducing agent. However, due to its hazardous nature, many alternatives were brought out to reduce the potential risk in electroless copper plating process, among which glyoxylic acid is highly competitive. The aim of this research is to examine the surface evolution process and the surface morphology of the electroless copper deposits plated under different conditions with either formaldehyde or glyoxylic acid as the reducing agent. Electroless copper deposits were plated on the epoxy board in solutions with either formaldehyde or glyoxylic acid as the reducing agent with different chemical concentrations at 60°C or 45°C. Four substrates were used for each plating, each of which was taken out of the plating solution after being plated for 5, 15, 60 and 120 minutes, respectively. The surface morphology of all the samples was characterized using scanning electron microscopy (SEM). The SEM image of the epoxy substrate before plating shows an eroded‐like rough surface where many dimples can be observed. The images of the plating sequence indicate that copper was plated almost evenly on both inside and outside of the dimples in the formaldehyde solutions and the final surface tended to be still rough or even hollow, while in the glyoxylic acid solutions, copper was plated more on the inside of the dimples and the final surface tended to be smoother. Lowering temperature resulted in much smoother surfaces from both formaldehyde and glyoxylic acid solutions. The research reveals that glyoxylic acid has promising prospect as an alternative to formaldehyde in electroless copper plating. Under certain conditions, glyoxylic acid can be very effective for smooth plating on rough surfaces.