Excessive Diffusion Research Articles

Luminescence Patterns on Multimillimeter Single-Crystal MAPbBr3 Microplatelets via Thermal Ablation Effects.

The single crystal distinguishes itself as the most outstanding representative of excellent optoelectronic performance among perovskite semiconductors due to its exceptional charge carrier properties, extraordinary optophysics, precise structural geometries, and superior material stabilities. However, it exhibits mediocre performance in light emission, which can be attributed to its excessive carrier diffusion lengths and extremely low recombination rates. To address this challenge, this study puts forward a controllable high-temperature annealing treatment strategy concentrating on multimillimeter-scale MAPbBr3 micrometer-thick platelet single crystals (MPSCs). Through the utilization of thermal ablation effects to convert the surface monocrystalline lattices into polycrystalline perovskite nanocrystals (PNCs) with a remarkably increased specific surface area, the fluorescence intensity arising from the rapid recombination of free carriers on the PNC surface is enhanced by 320 times compared to the pristine MPSC surface. These PNCs produced through surface annealing, with the characteristic of loose adhesion to surfaces, can be mechanically wiped away and regenerated in situ via reannealing the residual MAPbBr3 MPSCs, guaranteeing high intensity, durability, and standard geometric fluorescence. Moreover, by regulating the surface distributions of thermal ablation effects and carrying out embossing annealing treatment or laser direct writing, we can design and fabricate relatively complex, high-contrast (255×), and clearly resolved fluorescence patterns on MPSC surfaces.

Effect of Sulfurization Temperature on Properties of Cu2ZnSnS4 Thin Films and Diffusion of Ti Substrate Elements

The addition of flexible Cu2ZnSnS4 (CZTS) thin film solar cells to titanium (Ti) substrates is an attractive way to achieve the low-cost manufacturing of photovoltaics. Prior research has indicated that the appropriate diffusion of Ti elements can enhance the crystalline growth of CZTS films. However, the excessive diffusion of Ti has been shown to adversely affect the photovoltaic performance of CZTS photovoltaic devices. Therefore, it is essential to regulate the diffusion of Ti elements within CZTS thin films to optimize their photovoltaic properties. The tendency for Ti substrate elements to diffuse into CZTS films is also influenced by the activation energy associated with these Ti elements. The sulfurization temperature is posited to be a critical factor in modulating the diffusion and activation energy of Ti elements within CZTS thin films. Consequently, this research investigates the alteration of the sulfurization temperature of CZTS thin films in order to enhance the properties of these thin films and to examine the diffusion behavior of titanium elements. The results reveal that as the sulfurization temperature increases, the diffusion of Ti elements within the CZTS thin films initially increases, then decreases, and subsequently increases again. This pattern suggests that the diffusion of Ti elements is affected not only by the activation energy of the Ti elements but also by the defect hopping distance within the CZTS thin films. Notably, at a sulfurization temperature of 550 °C, the grains at the base of the CZTS thin film demonstrate an increased density, which is associated with a reduced defect hopping distance, thereby hindering the diffusion of Ti elements within the CZTS thin films. Furthermore, at this specific sulfurization temperature, the slope of the current–voltage (I–V) curve for the CZTS/Ti structure reaches its maximum, indicating optimal ohmic contact characteristics.

The grain-scale signature of isotopic diffusion in ice

Abstract. Diffusion limits the survival of climate signals on the water stable isotopes in ice sheets. Diffusive smoothing acts not only on annual signals near the surface, but also on long-timescale signals at depth as they shorten to decimetres or centimetres. Short-circuiting of the slow diffusion in crystal grains by fast diffusion along liquid veins can explain the “excess diffusion” found on some ice-core isotopic records. But experimental evidence is lacking as to whether this mechanism operates as theorised; theories of the short-circuiting also under-explore the role of diffusion along grain boundaries. The non-uniform patterns of isotopic deviation δ across crystal grains induced by short-circuiting offer a testable prediction of these theories. Here, we extend the modelling for grain boundaries (and veins) and calculate these patterns for different grain-boundary diffusivities and thicknesses, temperatures, and vein-water flow velocities. Two isotopic patterns are shown to prevail in ice of millimetre grain size: (i) an axisymmetric “pole” pattern with excursions in δ centred on triple junctions, in the case of thin, low-diffusivity grain boundaries, and (ii) a “spoke” pattern with excursions around triple junctions showing the impression of grain boundaries, when these are thick and highly diffusive. The excursions have widths ∼ 10 %–50 % of the grain radius and variations in δ ∼ 10−2 to 10−1 times the bulk isotopic signal for oxygen and deuterium, which set the minimum measurement capability needed to detect the patterns. We examine how the predicted patterns vary with depth through a signal wavelength to suggest an experimental procedure, based on laser ablation mapping, of testing ice-core samples for these signatures of isotopic short-circuiting. Because our model accounts for veins and grain boundaries, its predicted enhancement factor (quantifying the level of excess diffusion) characterises the bulk-ice isotopic diffusivity more comprehensively than past studies.

Surface Modification of Silk Fabric by Polysaccharide Derivatives towards High-Quality Printing Performance Using Bio-Based Gardenia Blue Ink.

Ink-jet-printed silk, a premium textile material, was achieved by utilizing a bio-based gardenia blue dye. However, the sharpness of the printing pattern is difficult to control due to the limited water-retention capacity of silk. To address this issue, three polysaccharide derivatives, namely, sodium alginate (SA), low-viscosity hydroxypropyl methyl cellulose (HPMC-I), and high-viscosity hydroxypropyl methyl cellulose (HPMC-II), were employed as thickeners to modify the silk by the dipping-padding method. Firstly, the preparation of the gardenia blue ink and the rheology assessment of the thickener solution were conducted. Furthermore, the impacts of different thickeners on the micro-morphology, element composition, and hydrophilicity of the silk, along with the wetting behavior of the ink on the silk, were analyzed comparatively in order to identify an appropriate thickener for preserving pattern outlines. Lastly, the color features, color fastness, and wearing characteristics of the printed silk were discussed to evaluate the overall printing quality. Research results showed that the optimized ink formulation, comprising 12% gardenia blue, 21% alcohols, and 5.5% surfactant, met the requirements for ink-jet printing (with a viscosity of 4.48 mPa·s, a surface tension of 34.12 mN/m, and a particle size of 153 nm). The HPMC-II solution exhibited prominent shear-thinning behavior, high elasticity, and thixotropy, facilitating the achievement of an even modification effect. The treatment of the silk with HPMC-II resulted in the most notable decrease in hydrophilicity. This can be attributed to the presence of filled gaps and a dense film on the fibers' surface after the HPMC-II treatment, as observed by scanning electron microscopy. Additionally, X-ray photoelectron spectroscopy analysis confirmed that the HPMC-II treatment introduced the highest content of hydrophobic groups on the fiber surface. The reduced hydrophilicity inhibited the excessive diffusion and penetration of gardenia blue ink, contributing to a distinct printing image and enhanced apparent color depth. Moreover, the printed silk demonstrated qualified color fastness to rubbing and soaping (exceeding grade four), a soft handle feeling, an ignorable strength loss (below 5%), and a favorable air/moisture penetrability. In general, the surface modification with the HPMC-II treatment has been proven as an effective strategy for upgrading the image quality of bio-based dye-printed silk.

Effect of NiMo diffusion barrier plating preparation on microstructure and properties of Bi2Te3/Cu joints

Bismuth telluride (Bi2Te3) thermoelectric devices play a significant role in recovering low-grade waste heat. While for Bi2Te3/Cu joints, excessive interfacial reaction and diffusion usually happens, which greatly degrades their properties. In this work, the novel NiMo diffusion barrier plating was prepared on Bi2Te2.7Se0.3 (n-BST) surface prior to the soldering process. The joint interfacial microstructure, shear strength, contact resistance and thermal stability were systematically investigated. The maximum shear strength increased from 7 MPa to 12 MPa with the joint contact resistance decreasing from 11.86 μΩ⋅cm2 to 3.27 μΩ⋅cm2 after NiMo plating preparation. These n-BST/Cu joints were then annealed for different durations to investigate the joint thermal stability. After annealing at 110 °C for 250 h, a thin BiTe + NiTe2 reaction layer formed instead of the initial SnTe reaction layer. The joint shear strength maintained 9 MPa (less than 2 MPa without NiMo plating) and the joint contact resistance was only 12.39 μΩ⋅cm2 (249.89 μΩ⋅cm2 without NiMo plating). This work indicates that NiMo plating is an effective elemental diffusion barrier for n-BST/Cu joints.

Entropy-regulated electrolytes for improving Zn2+ dynamics and Zn anodes reversibility

Entropy-regulated electrolytes exhibit improved performance exceeding traditional liquid systems. Despite their potential merits, the impacts of entropy on thermodynamics and kinetic properties of the electrolyte have remained elusive. A specially designed entropy-regulated Zn-salt electrolyte (ERE) with multiple halogen anions (Cl−, Br−, and I−) is proposed here to discuss the correlation between locally excess entropy and diffusion properties. Owing to the higher pair-correlated entropy of the ERE compared to single-anion systems, it can greatly facilitate the Zn2+ transport and impede the ion aggravation, thus elevating the stability of Zn anodes. The Zn2+ transference number of ERE reaches a high value of 0.822, contributing to much improved cycling life and Coulombic efficiency of plating/stripping processes of Zn anodes. Moreover, the high-entropy identity results in better anti-freezing ability of the electrolyte system, therefore ensuring the ERE stably operating even under a low temperature of −40 °C. This work can provide valuable directions for designing high-performance electrolytes for various batteries by modulating specific excess entropy.

Brazing of high-nitrogen steel to Al0·3CoCrFeNi using a BNi-2 filler: Microstructure, mechanical properties, and corrosion resistance

Studies that focus on brazing high-nitrogen steel (HNS) to high-entropy alloys (HEAs) are currently limited. In this study, the HEA Al0·3CoCrFeNi was successfully brazed to HNS using a commercial BNi-2 filler at 1080–1140 °C. The microstructure and shear strength of the Al0·3CoCrFeNi/HNS brazed joints were observed and evaluated. The typical microstructure of the brazed joint was HNS/infiltration layer/reaction layer/Ni(s,s) (containing NiAl3)/reaction layer/infiltration layer/Al0·3CoCrFeNi. The higher brazing temperature and longer holding time promoted the diffusion of B as a brazing seam with homogeneous Ni(s,s), and more intergranular Cr-rich borides formed in the base materials. The optimized shear strength attained 549.2 MPa after the joint brazed at 1120 °C for 15 min, and ductile fracture occurred in the reaction zone. The insufficient and excessive diffusion of B resulted in residual Cr–B compounds in the brazing seam and excess borides in the HNS, respectively, which negatively affected shear strength. All the joints showed poor corrosion resistance following immersion in a 3.5 wt% NaCl solution because the excess Cr-rich compounds resulted in decreased Cr content in the surrounding matrix. Therefore, Ni-based fillers without B were more suitable for obtaining Al0·3CoCrFeNi/HNS joints with a favorable corrosion resistance.

Laser ablation of thin SiN x layer coated on silicon wafer—evaluation of process performance for PERC solar cell application

In fabricating passivated emitter and rear contact (PERC) solar cells, creating small openings on the SiN x coated silicon substrate to establish metal contacts necessitates using a nanosecond pulsed green laser for ablation. However, the thermal nature of laser ablation poses a challenge. Excessive nitrogen diffusion from SiN x into the silicon substrate can compromise the electrical performance of solar cells. Therefore, this study aims to comprehensively understand how laser parameters impact the electrical properties of such solar cells. PERC solar cell precursors were initially fabricated by ablating the SiN x layer at four laser fluences, each corresponding to different regimes: solid, liquid, vapor, and phase explosion. Subsequently, various optical, chemical, and electrical characterizations were conducted on the solar cell precursors. Complete PERC solar cells were also fabricated to measure quantum efficiency (QE). In the solid regime, SiN x removal is precise, with minimal thermal damage, resulting in a nitrogen concentration of approximately 0.15%. Photoluminescence count and carrier lifetime are notably higher by 21% in the solid regime compared to the explosive regime. The QE measurement at 984 nm quantitatively assesses rear-side recombination losses. Notably, 26% of the area exhibits a 56% QE in the solid state, while this number drops to around 22% in the explosive state. This decline can be attributed to increased thermal damage in the explosive regime, which augments recombination centers and diminishes the solar cell performance. PERC solar cells ablated in the solid regime showcase lower subsurface damage, superior electrical characteristics, and higher performance than those ablated in the explosive regime.

Preserving Tracer Correlations in Moment‐Based Atmospheric Transport Models

AbstractA linear non‐diffusive algorithm for advective transport is developed that greatly improves the detail at which aerosols and clouds can be represented in atmospheric models. Linear advection schemes preserve tracer correlations but the most basic linear scheme is rarely used by atmospheric modelers on account of its excessive numerical diffusion. Higher‐order schemes are in widespread use, but these present new problems as nonlinear adjustments are required to avoid occurrences of negative concentrations, spurious oscillations, and other non‐physical effects. Generally successful at reducing numerical diffusion during the advection of individual tracers, for example, particle number or mass, the higher‐order schemes fail to preserve even the simplest of correlations between interrelated tracers. As a result, important attributes of aerosol and cloud populations including radial moments of particle size distributions, molecular precursors related through chemical equilibria, aerosol mixing state, and distribution of cloud phase are poorly represented. We introduce a new transport scheme, minVAR, that is both non‐diffusive and preservative of tracer correlations, thereby combining the best features of the basic and higher‐order schemes while enabling new features such as the tracking of sub‐grid information at arbitrarily fine scales with high computational efficiency.

Effect of Grain Structure of Gold Plating Layer on Environmental Reliability of Sintered Ag-Au Joints.

Gold-plated substrate is widely used in sintering with silver paste because of its high conductivity, stability, and corrosion resistance. However, due to massive interdiffusion between Ag and Au atoms, it is challenging for sintered Ag-Au joints to maintain high reliability. In order to study the effect of grain structure of gold plating layer on the environmental reliability of sintered Ag-Au joints, we prepared four substrates with different gold structures. In addition to the original gold structure (Au substrate), other gold structures were obtained by heat treatment at temperatures of 150 °C (Au-150 substrate), 250 °C (Au-250 substrate), and 350 °C (Au-350 substrate) for 1 h. Compared with the other three gold substrates, the sinter jointed on the Au-350 substrate obtained the highest shear strength. By analyzing the grain structure of the gold plating layer, it is found that the average grain size of the Au-350 substrate is the largest, and the proportion of low-angle grain boundaries is less. Few grain boundaries have a positive impact on inhibiting the excessive diffusion of Ag atoms and improving the bonding performance of the joint. Based on the above study, we further evaluated the environmental reliability of sintered joints. In 150 °C high-thermal storage, the interdiffusion of Ag and Au in the sintered joint on the Au-350 substrate was restricted, retaining stronger bonding until 200 h. In a hygrothermal environment of 85 °C/85% RH, the shear strength of the sintered Ag-Au joint with the Au-350 substrate maintained above 40.2 MPa during 100 h aging. The results indicated that the sintered Ag-Au joint on the Au-350 substrate with the largest grain size has superior high thermal reliability and hygrothermal reliability.

Deep smoothness weighted essentially non-oscillatory method for two-dimensional hyperbolic conservation laws: A deep learning approach for learning smoothness indicators

In this work, we enhance the fifth-order Weighted Essentially Non-Oscillatory (WENO) shock-capturing scheme by integrating deep learning techniques. We improve the established WENO algorithm by training a compact neural network to dynamically adjust the smoothness indicators within the WENO scheme. This modification boosts the accuracy of the numerical results, particularly in proximity to abrupt shocks. Notably, our approach eliminates the need for additional post-processing steps, distinguishing it from previous deep learning-based methods. We substantiate the superiority of our new approach through the examination of multiple examples from the literature concerning the two-dimensional Euler equations of gas dynamics. Through a thorough investigation of these test problems, encompassing various shocks and rarefaction waves, our novel technique consistently outperforms the traditional fifth-order WENO scheme. This superiority is especially evident in cases where numerical solutions exhibit excessive diffusion or overshoot around shocks.

Modification of magnetorheological fluid and its compatibility with metal skeleton: Insights from multi-body dissipative particle dynamics simulations and experimental study

Magnetorheological fluid (MRF), as a smart material, plays a pivotal role in sealing equipment. However, the interfacial compatibility between MRF and metal significantly impacts the adhesion of the two phases, which subsequently determines the sealing performance of MRF once it is used as a sealing medium. However, the interface mechanism and dynamical magnetic migration performances between MRF and metals at the microscopic level are not clear. In this study, dissipative particle dynamics (DPD) and multi-body DPD simulations are carried out to examine the settling stability, static wetting characteristics, and magnetic migration ability of MRF droplets incorporating different surfactants. It is revealed that oleic acid stands out as the optimal surfactant for MRF, shedding light on the mechanism of MRF droplet infiltration on metal sheets and unveiling five crucial wetting processes. Furthermore, a thorough comparison among simulation results, experimental findings, and numerical analysis was conducted to verify the reliability of theoretical research on the microscale behavior of MRF. Moreover, investigating the driving characteristics of MRF droplets within a uniform magnetic field confirmed two driving processes: significant deformation and limitation of excessive diffusion. The analysis of the vortical structure within the droplets revealed the presence of diffusion effects caused by magnetic particles. The velocity distribution within the droplets indicated different flow rates, with higher velocities at the core and slower velocities at the edge, suggesting the presence of internal flow patterns.

Pre-plating Cu on the WC–Co surface to inhibit Co-depletion zone and enhance the shear strength of WC–Co/40Cr joints

The Co-depletion zone in WC–Co brazed joints is the main zone of joint failure, so it is crucial to explore novel processes to inhibit the Co-depletion zone and enhance the joint shear strength. In this study, a composite process of pre-plating Cu on the WC–Co surface + brazing was designed. Co-depletion zone reduces from 6 μm to 1 μm due to the Cu plating. Meanwhile, the formation of a plating fusion zone in the filler layer transforms TiCo with a thickness of 2.5 μm into a small number of TiCo particles. Moreover, the high concentration of Cu atoms in the vicinity of the WC particles at the interface changes the Co-segregation layer in the WC into a Cu-rich layer. The concentration of Cu in the filler layer leading to precipitation of TiCu and Ti2Cu particles. Ti2Cu particles encapsulated by ductile Ag–Cu–In ternary eutectic contribute to inhibit the cracks propagation. The shear strength of the joints was enhanced by 51.3 % to 295 MPa. The composite process of pre-plating on the base material surface + brazing has positive significance in inhibiting the excessive diffusion of elements from the base materials to the filler layer.

Clarifying the dominated coercivity enhancement mechanism of grain boundary diffused Nd-Fe-B magnets by Pr-based alloys

Low-melting point Pr-based alloys have been confirmed to be cost-effective grain boundary diffusion sources for enhancing the coercivity of Nd-Fe-B magnets. Various coercivity enhancement mechanisms have been reported for these alloys so far, but the dominated one has not been clarified. Here, the sintered Nd-Fe-B magnet was treated by Pr75Al25 alloy grain boundary diffusion at different temperatures. A detailed investigation on the diffusion kinetics of the elements and the microstructure evaluation have been carried out. After 800 °C diffusion, the intrinsic coercivity of the magnet increased from 1070 kA/m to 1348 kA/m without significant reduction of remanence. The increased rare earth-rich phase continuously distributed along the grain boundaries has great contribution to the magnetic decoupling, leading to high coercivity. In comparison, after 900 °C diffusion, although Pr and Al diffused more sufficiently in the magnet, a drastic lattice diffusion occurred and less grain boundary layer was formed, resulting in insufficient coercivity enhancement. The results thus indicate that, for Pr-Al diffusion, the formation of RE-rich layer is more important than that of (Nd,Pr)2Fe14B shell in order to enhance the coercivity. Therefore, different from that for heavy rare earth diffusion, the diffusion treatment for Pr-based sources should be carefully optimized to form continuous grain boundary phase and suppress the excessive lattice diffusion.

Influence of Ge doping on the magnetic properties and microstructure of Fe-Si-B-P-Cu alloys prepared with industrial raw materials

With the increasing demand for energy efficiency and miniaturization, there is a growing need for magnetic materials with high saturation magnetic flux density (Bs) and low coercivity (Hc). Here, Fe82.3Si4B9P4-xCu0.7Gex (x = 0, 1, 2) nanocrystalline ribbons were prepared using industrial raw materials (IRMs). We found that appropriate Ge doping can optimize Bs by enhancing the crystallization volume fraction of α-Fe phase, and refine grain size by increasing the energy barriers for the growth of α-Fe and Fe(B, P) phases, which ultimately reduces Hc. However, Ge doping can also induce surface crystallization of the ribbons due to the enrichment of Cu elements. Excessive diffusion of Cu into the crystalline layer is not favorable for grain refinement, which deteriorates the soft magnetic properties of the ribbons.

Driven transport of active particles through arrays of symmetric obstacles.

We numerically examine the driven transport of an overdamped self-propelled particle through a two-dimensional array of circular obstacles. A detailed analysis of transport quantifiers (mobility and diffusivity) has been performed for two types of channels, channel I and channel II, that respectively correspond to the parallel and diagonal drives with respect to the array axis. Our simulation results show that the signatures of pinning actions and depinning processes in the array of obstacles are manifested through excess diffusion peaks or sudden drops in diffusivity, and abrupt jumps in mobility with varying amplitude of the drive. The underlying depinning mechanisms and the associated threshold driving strength largely depend on the persistent length of self-propulsion. For low driving strength, both diffusivity and mobility are noticeably suppressed by the array of obstacles, irrespective of the self-propulsion parameters and direction of the drive. When self-propulsion length is larger than a channel compartment size, transport quantifiers are insensitive to the rotational relaxation time. Transport with diagonal drives features self-propulsion-dependent negative differential mobility. The amplitude of the negative differential mobility of an active particle is much larger than that of a passive one. The present analysis aims at understanding the driven transport of active species like, bacteria, virus, Janus particle etc. in porous medium.

A production term study of delayed detached eddy simulation for turbulent near wake based on proper orthogonal decomposition

In this study, we investigate the distribution of turbulent kinetic energy (TKE) in the near wake of a circular cylinder in a turbulent flow. Numerical calculations were performed using the delayed detached eddy simulation method, incorporating two different production terms for TKE: one in its original form and the other with the Kato–Launder correction term. Our results demonstrate that the turbulence model utilizing the Kato–Launder correction term exhibits a strong correlation between TKE and the vorticity field, which is related to the calculations of mean velocity, velocity fluctuation, and other parameters that are in closer agreement with direct numerical simulation and experimental values. By employing the proper orthogonal decomposition technique, we extract and reconstruct three significant modes within the flow: the shear layer mode, vortex shedding mode, and near-wake bubble mode. The findings reveal that the Kato–Launder correction term offers a more detailed portrayal closer to the real flow physics. Conversely, the original form of the TKE production term exhibits an uneven energy distribution among the three modes and affects the role of the diffusion term within the flow. This leads to a less accurate representation of the vortex shedding mode and an excessive diffusion effect in the near-wake bubble mode. Finally, possible modifications of the turbulence model in this problem are given to enhance the portrayal of these characteristics. This work presents an analytical framework that enables a comprehensive analysis of turbulence models, providing valuable physical insights and guidance for improvement.

Coupled fluid flow, solute transport and dissolution processes in discrete fracture networks: An advanced Discontinuous Galerkin model

Modeling dissolution processes in discrete fracture networks (DFNs) is a challenging task. Challenges are related to the highly nonlinear coupling between flow, mass transport, and reactive processes associated with fracture aperture evolution by dissolution. Further, advection-dominated transport due to fast fluid flow in fractures renders the problem more complex from a computational point of view, as traditional numerical methods may introduce unphysical oscillations or excessive numerical diffusion. The Discontinuous Galerkin (DG) method is known to be suitable for the simulation of advection-dominated transport. In this work, an advanced DG model is developed to model transport with dissolution in DFNs. We propose an upwind formulation to deal with the upstream concentration at the intersection of several fractures. The upstream concentration at an intersection node is calculated based on the average nodal concentrations of all the fractures having an inflow at that node, weighted by the volumetric fluxes of these fractures. The dispersion term is discretized with the Mixed Finite Element (MFE) method, which ensures the continuity of the dispersive flux at the intersection of fractures with different apertures. The obtained nonlinear coupled flow-transport-dissolution equations are discretized in time with a high-order scheme via the method of lines (MOL). Numerical examples and comparisons with standard finite element (FE) and finite volume (FV) solutions are performed to investigate the correctness and efficiency of the developed model. Results show that the new DG-DFN model avoids unphysical oscillations encountered with the standard FE method and strongly reduces the numerical diffusion observed with the upwind FV scheme. The DG-DFN model is then used to investigate the effect of the dissolution rate on the flow, transport, and aperture evolution processes for a single fracture and for a DFN. A quasi-linear evolution of the fracture aperture is observed for low dissolution rates. For high dissolution rates, a funnel-shaped enlargement is observed with a significant widening for the fractures near the inlet and minor effects for those away from the injection location.

Effect of process parameters on surface quality and bonding quality of brass cladding copper stranded wire prepared by continuous pouring process for clad

Brass cladding copper stranded wire with an outer diameter of 10 mm and core material of d2.12mm × 7 strand was prepared by solid-liquid composite method with continuous pouring process for clad. Compared with the cladding welding method which requires multiple drawings to make the composite welding wire achieve metallurgical bonding, it saves a lot of manpower and material resources and shortens the production cycle. The bonding mechanism of brass and copper was analyzed by experiments, meanwhile, the effects of brass melt temperature and casting speed on the surface quality and interface bonding quality of the composite wire were investigated. The results show that, on the one hand, increasing the melt temperature of brass and reducing the casting speed can inhibit the surface defects of the composite. On the other hand, reducing the temperature of the brass melt and increasing the casting speed can inhibit the excessive element diffusion at the bonding interface, thereby reducing the degree of surface erosion of the copper strand. The final reasonable process parameters are as follows: the brass melt temperature is 970 °C–990 °C, the traction speed is 40 mm/min∼80 mm/min, and the cooling water volume of the crystallizer is 450L/h. The prepared brass cladding copper stranded wire has good quality, Vickers hardness is between 80 - 85HV, and tensile strength is between 265 - 297 MPa. Elongation after fracture is 40.3%∼43.9%, conductivity is 53.8–62.1% IACS.

Isotopic diffusion in ice enhanced by vein-water flow

Abstract. Diffusive smoothing of signals on the water stable isotopes (18O and D) in ice sheets fundamentally limits the climatic information retrievable from these ice-core proxies. Past theories explained how, in polycrystalline ice below the firn, fast diffusion in the network of intergranular water veins “short-circuits” the slow diffusion within crystal grains to cause “excess diffusion”, enhancing the rate of signal smoothing above that implied by self-diffusion in ice monocrystals. But the controls of excess diffusion are far from fully understood. Here, modelling shows that water flow in the veins amplifies excess diffusion by altering the three-dimensional field of isotope concentration and isotope transfer between veins and crystals. The rate of signal smoothing depends not only on temperature, the vein and grain sizes, and signal wavelength, but also on vein-water flow velocity, which can increase the rate by 1 to 2 orders of magnitude. This modulation can significantly impact signal smoothing at ice-core sites in Greenland and Antarctica, as shown by simulations for the GRIP (Greenland Ice Core Project) and EPICA (European Project for Ice Coring in Antarctica) Dome C sites, which reveal sensitive modulation of their diffusion-length profiles when vein-flow velocities reach ∼ 101–102 m yr−1. Velocities of this magnitude also produce the levels of excess diffusion inferred by previous studies for Holocene ice at GRIP and ice of Marine Isotope Stage 19 at EPICA Dome C. Thus, vein-flow-mediated excess diffusion may help explain the mismatch between modelled and spectrally derived diffusion lengths in other ice cores. We also show that excess diffusion biases the spectral estimation of diffusion lengths from isotopic signals (by making them dependent on signal wavelength) and the reconstruction of surface temperature from diffusion-length profiles (by increasing the ice contribution to diffusion length below the firn). Our findings caution against using the monocrystal isotopic diffusivity to represent the bulk-ice diffusivity. The need to predict the pattern of excess diffusion in ice cores calls for systematic study of isotope records for its occurrence and improved understanding of vein-scale hydrology in ice sheets.