Mutual Diffusion Research Articles

Study on diffusion barrier layer of gradient Cu doped Be thin films

Beryllium was coated onto the polished Cu mandrel with a diameter of 2 mm by direct current (DC) magnetron sputtering. Cu/Be composite capsules were annealed in the range of 250 °C-550 °C, and their mutual diffusion at the low and medium temperature were measured. In addition, different diffusion barrier materials, such as BeO, Be2C and graphite-like-carbon (GLC) films, have been selected and studied for the diffusion barrier effect of Cu. Under the annealing condition of 425 °C, 26 h and nitrogen atmosphere, the diffusion and migration of Cu atoms were investigated. It is found that both BeO and GLC films can effectively halt the diffusion of Cu atoms, but the thickness of BeO barrier layer is thinner than that of GLC films. After annealing, the stress of Be2C thin film increases due to the change of density, and a large area of Be2C thin film is broken and falls off. Its barrier effect becomes very poor, so it is not suitable to be used as a diffusion barrier layer in gradient Cu doped Be thin films.

Atomic-scale insight into the epitaxial growth mechanism and interfacial coupling of BNT film prepared by hydrothermal synthesis

Revealing the epitaxial growth mechanism and the interfacial coupling effect between oxide films will help to build a “structure-property” bridge for the design of microelectronic devices. Here, the epitaxial growth mechanism and the interfacial coupling in Bi0.5Na0.5TiO3/SrTiO3 (BNT/STO) heterointerfaces are investigated by the aberration-corrected scanning transmission electron microscopy, which is synthesized by a hydrothermal method. The results illustrate that 4 mol/L NaOH leads to not only the epitaxial growth of the BNT film but also the mutual diffusion of elements. The uneven distribution of local elements in BNT films is observed and confirmed to impact the cation displacements of B-site and lattice distortion. However, the overall trend of B-site cation displacement at the BNT/STO heterointerfaces is dominated by the interfacial strain. Additionally, the oxygen octahedral tilt exhibits continuous tilt patterns of a0a0a0 - a−b0c− - a0a0c− - a0b−c− - a−b−c− from the substrate to BNT film due to the constraint of the substrate and presents a strong correlation with cation displacement. These results are helpful to understand the underlying atomic structures and physical properties of BNT epitaxial thin films.

Ion bombardment induced surface microstructural modification of aluminum alloy

Surface microstructural modifications of 2A12 aluminum alloy exposed to 60 keV Ar ion bombardment with the dose of 1 × 1017 ions/cm2 under vacuum were studied in detail. The amorphous layer with the thickness of ∼130 nm accompanied with polycrystalline aluminum was formed at the surface after Ar ion bombardment. Beneath the amorphous layer, Al2CuMg precipitates were observed. Dynamic recrystallization(DRX)and grain growth were observed with the increment of texture intensity. Surface residual compressive stress and strain were enhanced characterized by electron back-scattered diffraction. After ion bombardment, the contact angles of diiodomethane and DI water on aluminum alloy were increased, and a notable decrement of surface energy of aluminum alloy was measured from 32.5 mJ/m2 to 23.4 mJ/m2. The diffusion experiments indicated that the mutual diffusion of Cu and Al was inhibited due to the bombardment-induced amorphous layer at aluminum alloy surface, which is beneficial to its application as a structure material in aerospace field.

Relationship analyses on environmental factors-ablation performance based on ZrC-TaC system: Oxygen partial pressure and gas flow scouring

For better understanding on effects of ablation environmental factors (oxygen partial pressure P(O2) and gas flow scouring), multiple experiments and multiscale simulations based on thermally sprayed ZrC-TaC system were conducted. High P(O2) was found helpful to accelerate Ta2O5/ZrO2 mutual diffusion by variable P(O2) oxidation at 1500 ℃ (5-50 kPa). Effects of gas flow scouring was evaluated by flow filed simulation coupling laser and oxyacetylene ablations, from which its promotion effect on Ta2O5/ZrO2 diffusion efficiency was found. The increased Ta2O5/ZrO2 diffusion efficiency will accelerate the structure instability of Ta doped c-ZrO2 skeletons due to Zr-O bond length extension around Ta atoms.

Role of Mutual Diffusion in the Dissolution Behavior of One Primary Bulk Gas Nanobubble in Liquid: A Molecular Dynamics Study.

Dissolution of one primary bulk gas nanobubble in an undersaturated liquid constitutes one of the underlying issues of the exceptional stability of bulk gas nanobubble population. In this paper, the mutual diffusion coefficient at the gas-liquid interface of one primary bulk gas nanobubble is investigated via all-atom molecular dynamics simulation, and the applicability of the Epstein-Plesset theory is verified. The mutual diffusion coefficient, different from the self-diffusion coefficient in bulk gas or bulk liquid, is essentially determined by the chemical potential due to its driving role in the mass transfer across the interface. We could ascribe the low-rate dissolution of one primary bulk gas nanobubble in an undersaturated liquid to the slight attenuation of the mutual diffusion coefficient at the interface. The results show that the dissolution process of one primary bulk gas nanobubble in an undersaturated liquid fundamentally obeys the Epstein-Plesset theory and that the macroscopic dissolution rate is intrinsically determined by the gas mutual diffusion coefficient at the interface rather than the self-diffusion coefficient in the bulk phase. The mass transfer viewpoint from the present study might actively promote subsequent studies on the super-stability of bulk gas nanobubble population in liquid.

Mutual and Thermal Diffusivities in Binary Mixtures of n-Hexane or 1-Hexanol with Krypton, R143a, or Sulfur Hexafluoride by Using Dynamic Light Scattering and Molecular Dynamics Simulations

This work reports Fick diffusion coefficients D11 in the saturated liquid phase(s) of binary mixtures of nonpolar n-hexane (n-C6H14) or polar 1-hexanol (1-C6H14O) with dissolved krypton (Kr), 1,1,1-trifluoroethane (R143a), or sulfur hexafluoride (SF6). Investigations were performed at temperatures T of 303, 323, and 348 K and gas mole fractions up to 0.999. The comparison between Kr and R143a, both having nearly the same molar mass, allows identification of the impact of molecular structure and polarity of the dissolved gas on D11. The investigation of SF6 provides information about the influence of a centrosymmetric molecule with a large molar mass on D11. D11 is experimentally determined by dynamic light scattering (DLS) and predicted by equilibrium molecular dynamics (EMD) simulations by the independent calculation of the Maxwell–Stefan diffusivity and the thermodynamic factor Γ11 in macroscopic thermodynamic equilibrium at or close to saturation conditions. Thermal diffusivity data obtained simultaneously with D11 by DLS are reported as well. The behavior of the experimentally determined D11 as a function of composition and that obtained from EMD simulations show generally good agreement. Distinct structural changes of the saturated liquid phase are reflected by the change of Γ11 which extends for the present study between 0.16 and 1.3. While for mixtures of 1-C6H14O + Kr, D11 as a function of composition is nearly constant at a given T, all other mixtures show a distinct composition-dependent behavior. For mixtures of 1-C6H14O + R143a and 1-C6H14O + SF6, a strong slowing down of D11 was observed and related to approaching a liquid–liquid miscibility gap. For all systems, the behavior of D11 as a function of composition is interpreted with reference to the fluid structure accessible by EMD.

Mutual diffusion coefficients of three alkanes (n-heptane, n-octane and isooctane) in cyclohexane from 288.15 K to 308.15 K

Mutual diffusion coefficients of three alkanes (n-heptane, n-octane and isooctane) in cyclohexane were measured by digital holographic interferometry under atmospheric pressure. The measured temperature points were 288.15 K, 298.15 K and 308.15 K, respectively and the mass fraction of the measured solution range was from 0.05 to 0.95. The extended relative uncertainty of the measurement system was estimated to be less than 2.4%. The dependence of mutual diffusion coefficient on temperature and solution concentration was studied. The mutual diffusion coefficients of these three binary mixtures increase with the increase of temperature and have a nearly linear relationship with the solution concentration. And the image processing process of holographic interference image is introduced in detail. Zhang et al.’s model, Darken model and Vignes model were used to predict the mutual diffusion coefficients of the three binary mixtures, the absolute average of relative deviations (AARDs) are 2.97%, 3.89% and 6.18%, respectively and Zhang et al.’s model is the one with the best agreement among the three models.

Технологические особенности ультразвуковой сварки разнородных пластмасс

The paper considers technological features of heterogeneous plastics ultrasonic welding, which specificity is manifested in the volumetric interaction nature. Results of studying the mechanism of a welded joint formation showed that micro-volumes mixing, polymer molecules mutual diffusion in the contacting surfaces and emergence of the new chemical bonds with the block copolymers formation were the simultaneous processes. Their common feature was that all these processes proceeded in the temperature range corresponding to the polymer viscous-flow state. It was experimentally confirmed that one of the criteria for weldability of the heterogeneous plastics was their compatibility in terms of acoustic properties being estimated by the melt density and viscosity. Technological methods were proposed making it possible to compensate for differences in the welded materials acoustic properties, and thereby obtain the high-quality welded joints. Four stages of the welded joints formation mechanism were determined during ultrasonic welding of the heterogeneous plastics. It was established that physical and mechanical properties of the heterogeneous plastics were playing a decisive role in the mechanism of heat generation during the ultrasonic welding. An ultrasonic welding unit for welding the heterogeneous plastics in vacuum was developed.

Facilely prepare high-performance loose nanofiltration membranes through regulation of polymer chain entanglements

The membrane forming process was fundamentally affected by the thermodynamics of polymer solution, the core of which involved the governance of polymer chain entanglements in the solution. In this work, a high-performance loose nanofiltration (LNF) membrane with high water permeance and high separation accuracy was facilely fabricated by the regulation of polymer chain entanglements through only changing CaCO3 nanoparticle (nano-CaCO3) size in the casting solution. The degree of polymer chain entanglements was characterized by the critical entanglement viscosity of the casting solution. The solution viscosity was markedly increased with the decrease of nano-CaCO3 size and then significantly reduced when nano-CaCO3 disappeared. While the mutual diffusion rate between the non-solvent (acidic water) and the solvent was increased to bring about rapid phase inversion with increasing the viscosity of the casting solution. The high solution viscosity and rapid phase inversion, which was a unconventional phenomenon, leaded to the formation of LNF membranes with outstanding performance. The LNF membranes obtained had a pore diameter of 1.4 nm (MWCO = 1625 Da) and a high pure water permeance of 98 L·m−2·h−1·bar−1, accompanying an excellent separation accuracy of small molecule dyes and NaCl mixtures (the rejection is 99.9% for eriochrome black T (EBT, Mw = 461 Da) and 4.5% for NaCl). This work provides general guidance for the structural regulation of high-performance separation membranes.

Interfacial reaction kinetics of (Al63Cu25Fe12) 99Ce1 quasicrystal reinforced 6061 aluminum matrix composites

Due to its superior overall characteristics and effective interface wetting, quasicrystal reinforced aluminum matrix composite is regarded as a type of material with significant development potential. The procedure of hot pressing and sintering was used to create a quasicrystal particle reinforced 6061 aluminum matrix composite made of (Al63Cu25Fe12)99Ce1. Investigated in the composite were the element diffusion and the microstructure of the contact between the reinforcement and matrix. The findings demonstrate that mutual diffusion between reinforcement and matrix leads to the formation of the I-phase, Cu9Al4 phase, Al23CuFe4 phase, and ω-phase. Always present in the reinforcement, which has a strong link to the matrix, is the Al13Ce2Cu13 phase. At the same time, the diffusion kinetics of the transition layer between the quasi-crystalline phase and the matrix during the hot pressing process was revealed, and the most suitable thickness of the transition layer was determined to be 4.85 µm, which plays a great role in the improvement of the composite properties. The study of the microstructure and interfacial dynamics of (Al63Cu25Fe12)99Ce1 quasicrystal-reinforced 6061 aluminum matrix composites has laid the foundation for the creation of long-life, high-strength aluminum alloy materials with excellent properties.

Effect of Annealing Process on Interface Behavior of Al/Zn Laminated Composites

Laminated metal composites have attracted more attention due to their ultra-high strength, fracture toughness and elongation, full considerations of each component, and coordinated deformation effect between interfaces. Herein, Zn and Al were selected as the component materials to prepare Al/Zn laminated composite plates using hot rolling and low temperature annealing, and studied the influence of the thickness of the diffusion layer at the interface to understand the reason for the strengthening and toughening mechanism. The results show that, with an increase in annealing temperature and time, the grain will recover and recrystallize to grow. A diffusion layer with a certain thickness formed at the interface due to the mutual diffusion of Al and Zn atoms at the interface. As annealing time and temperature increase, the yield and tensile strengths first increased and then decreased. The tensile fracture morphology showeds many deep dimples. In the rolling state, the micro-hardness value at the interface was between Al and Zn.

STUDY OF WEAR OF THE BUILDING-UP ZONE OF MARTENSITE-AUSTENITIC AND SECONDARY HARDENING STEELS OF THE Cr-Mn-Ti SYSTEM

The work deals with wear of the building-up zone of martensite-austenitic and secondary hardening steels of the Cr-Mn-Ti system (partially alloyed with Mo, B, and V). Additional alloying of the studied steels with titanium in the amount of 2…5% supported avoiding cleavages along the building-up zone. It was determined that there is a 7…15 µm wide parent metal zone next to the weld line. The influence of temperature on the weld toughness of the building-up zone was assessed according to the criterion of Malkin and Tetelman. The microhardness of the surface layers of built-up layers and the range of its dispersion are close to the results of laboratory tests, where ТСт ~ 823 K. This approves the formation of structure of metal of contact volumes with the collective effect of heating, plastic deformation and diffusion. It was experimentally approved that the change of microhardness in the sub-surface layers at the wear stage is justified simultaneously with the processes of mutual diffusion of friction pair materials, selective oxidation and thermodiffusion redistribution of the hardening phase under the influence of temperatures and deformations. The diffusion coefficient in the deformed sub-surface layer, which is up to some dozen micrometers thick, is one of the values providing the kinetics of growing of nuclear cracks and development of destruction cracks. The received results provide an opportunity to use martensite-austenitic and secondary hardening steels of the Cr-Mn-Ti system with built-up surface for the hot forming tools.

On the measurement of the mutual diffusivity of binary gas mixtures with FTIR Spectroscopy

The diffusion of carbon dioxide and either methane, ethane or propane is investigated in situ with FTIR Spectroscopy in the transmission mode. The apparatus is a closed measuring system divided into two parts separated by a shut-off valve. The concentration evolution during the diffusion process is monitored with IR gas signals calibrated according to the Beer-Lambert law. The mutual diffusivity is determined by modelling the diffusion process as in a two-bulb system using Fick’s law for binary diffusion. The geometry of the theoretical setup is calibrated by analysing the diffusion kinetics of C3H8 in CO2. Then, the mutual diffusivity of the binary systems CO2–CH4, CO2–C2H6 and of CO2 in C3H8 are evaluated. The results are in agreement with those reported in the literature and deviate by 9% from the values predicted with the Chapman–Enskog theory when the molecular interactions are modelled with the Lennard-Jones potential.

Microstructural evolution of a nickel-based single-crystal superalloy embrittled by molten Zn

The embrittlement treatment of Ni-based single-crystal superalloys in a Zn atmosphere causes the superalloys to break easily. This considerably increases the contact area in the dissolution process. Hence, this treatment has the potential for conveniently recovering rare precious metals from Ni-based superalloys. This study systematically examines the microstructures of Ni-based single-crystal superalloys after Zn embrittlement. Microstructural changes in the superalloy after reaction with Zn at 700, 900, 1100, and 1200 °C for 8 h were investigated and analyzed in detail via X-ray diffractometry, scanning electron microscopy, and electron probe microanalysis, using the phase and element composition as the evaluation indices. Results showed that the formation of the Ni5Zn21 intermetallic compound in the superalloys was the main reason. The formation of Ni5Zn21 disturbed the distribution balance and promoted the recombination of metallic elements, resulting in the embrittlement of the superalloys. The embrittlement mechanism involved a mutual diffusion reaction of Zn and Ni, but the degree of Zn diffusion was higher.

Structure and Properties of Graphite-Molybdenum Brazed Joints

The paper presents the results of X-ray microspectral studies of dissimilar brazed joints of molybdenum with graphite. It is shown that during active brazing of graphite with molybdenum, mutual diffusion processes occur, and the adhesion-active brazing filler metals penetrates into graphite, and interacts with it, which leads to the formation of carbide phases. When using the Ti-Cr-V and Cu-Ti-Ni systems brazing filler metals, titanium carbides are formed. The zirconium carbides are formed, when using the brazing filler metals based on the Zr-Pd(Mo) systems and the CxMey(Mo, Cr) carbides are formed using the brazing filler metals of the Pd-Ni-Cr-Ge system. The results of tests for three-point bending showed that the using of Pd-Ni-Cr-Ge brazing filler metals provides stable strength at the level of 34-37 MPa, destruction occurs along graphite.

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF6]) system

AbstractThis article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF6], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time‐dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume‐of‐fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.

Use of MD Simulation for Investigating Diffusion Behaviors between Virgin Asphalt and Recycled Asphalt Mastic

The study aims at investigating diffusion behaviors between virgin asphalt and recycled asphalt mastic (RAM) at an atomistic scale. Firstly, a mutual diffusion model of virgin asphalt–RAM considering the actual mass ratio of filler to asphalt binder (F/A) condition was developed by molecular dynamic (MD)simulation. Secondly, the indexes of relative concentration (RC), radial distribution function (RDF) and mean square displacement (MSD) were used to analyze the molecular arrangement characteristics of polar components in the diffusion processes at different temperatures. Then, the blending efficiency of virgin asphalt–RAM was evaluated by Fick’s second law and the binding energy. The results indicate that the reliability of the RAM model was validated by thermodynamics properties. The results of RC and RDF show that the diffusion direction of virgin asphalt–RAM is not changed by the presence of mineral fillers. However, it will inhibit the occurrence of diffusion behaviors, and the aggregation of molecules in the blending zone increases due to the adsorption of mineral fillers, which would become a barrier to molecular diffusion. The development of MSD indicates that the diffusion coefficients of molecules in both virgin–aged asphalt and virgin asphalt–RAM are on the rise with the increase in temperature. Compared with the virgin–aged asphalt, the molecular migration speed in virgin asphalt–RAM is relatively slow. According to Fick’s second law and the binding energy, diffusion behaviors are dominated by the nonpolar components. The existence of mineral fillers has the greatest effect on the nonpolar components in diffusion. It is suggested that rejuvenator containing more aromatic components should be added or the temperature controlled within 433.15–443.15 K to promote blending efficiency. The research results contribute to a deeper understanding about diffusion behaviors of virgin asphalt–RAM, serving as a benchmark for further study of rejuvenation using computational experiments.

Mutual friction and diffusion of two-dimensional quantum vortices

We present a microscopic open quantum systems theory of thermally-damped vortex motion in oblate atomic superfluids that includes previously neglected energy-damping interactions between superfluid and thermal atoms. This mechanism couples strongly to vortex core motion and causes dissipation of vortex energy due to mutual friction, as well as Brownian motion of vortices due to thermal fluctuations. We derive an analytic expression for the dimensionless mutual friction coefficient that gives excellent quantitative agreement with experimentally measured values, without any fitted parameters. Our work closes an existing two orders of magnitude gap between dissipation theory and experiments, previously bridged by fitted parameters, and provides a microscopic origin for the mutual friction and diffusion of quantized vortices in two-dimensional atomic superfluids.

Insights into the mechanochemical interfacial interaction between calcite and serpentine: Implications for ambient CO2 capture

Mineral carbonation of readily-available serpentine is a promising solution for massive atmospheric carbon dioxide (CO2) sequestration, in which process the most significant challenge is to overcome slow carbonation kinetics under atmospheric conditions. To enhance the mineral dissolution rate and overall carbonation efficiency, activation of serpentine is required. In this study, for the first time, a facile way to obtain activated serpentine by simply co-milling with calcite was discovered, and the as-prepared materials were applied to direct CO2 capture under atmospheric conditions. A series of analytical techniques were carried out to understand the interaction mechanism between serpentine and calcite during ball-milling process, demonstrating the occurrence of interfacial reaction with the mutual diffusion and replacement of sectional ion constituents. This robust interaction between two mineral phases endowed the minerals with superior reactivity compared to single serpentine phase, and meanwhile generated a certain amount of magnesium carbonate directly. From the confirmed cadmium precipitation as carbonate (otavite phase) from solution, methodologically, with Cd removal as quantitative index, the carbonation efficiency of co-milled materials at the molar ratio of 1:1 was about 4 times as high as that of singly-milled minerals within 2 h, indicating the tremendously enhanced CO2 capture capacity of co-milled materials. These findings about the mechanochemical interfacial reaction between calcite and serpentine may provide a novel concept and an alternative way for the activation of magnesium silicates, which can be potentially applicable to solve some tough environmental issues including CO2 sequestration.

Microstructure and strength of diffusion bonding W alloy/304 stainless steel joint using a Cu interlayer

To realize the high-performance diffusion bonding of W alloy (90 W-7Ni-3Cu) with 304 stainless steel (304SS), the microstructure and mechanical properties of the solid diffusion bonding joints of W alloy and 304SS with a pure Cu interlayer were conducted at 900 °C, 20 MPa and 2 h. The results showed that the solid diffusion bonding with a Cu interlayer, can achieve a reliable bonding between the W alloy and 304SS. Furthermore, all the interfaces have excellent bonding through mutual diffusion of atoms at the W/Cu and Cu/304SS interfaces. No intermetallic compounds, or other brittle phases were formed in the bonding area. At the W/Cu interface, the interplanar spacing increased due to the diffusion of Cu atoms into the W lattice. Moreover, a nano-indentation test across the joint interfaces demonstrated the effect of solid-solution strengthening and strain hardening in the 304SS/Cu diffusion zone. The tensile strength of the joint was as high as 265 MPa, which was about 58% higher than for the joint without a Cu interlayer. The fracture analysis showed that the mixed fracture mode of plastic fracture and intergranular fracture occurred in the Cu interlayer and at the Cu/304SS interface. Mechanical tension tests revealed the enhanced strength of the joint with a Cu interlayer.