Solid-phase Diffusion Research Articles

Diffusion properties of n-type dopants diffused from spin on glass into Ge

Solid phase diffusion properties of three typical n-type dopants (P, As, and Sb) in Ge have been studied through experimental depth profiles of dopants diffused from spin on glass (SOG) films. Numerical calculations of dopant profiles in Ge are performed to extract the diffusion constant through comparison with the experimental profiles. It is pointed out that experimental results of diffusion at low temperature are important to correctly examine the influence of negative charge states of a vacancy on dopant diffusion. It is found that vacancies with the charge states of −2 mediate the diffusion of P and As without implantation-induced defects. The diffusion constants of P and As, obtained in this study, are larger than those for intrinsic diffusion, while that of Sb is almost the same as that for intrinsic diffusion. The present larger diffusion constants of P and As can be explained by the supply of vacancies from Ge surfaces via E-centers during diffusion from SOG.

Estimation of the Maximum Transverse Size of Multilayer Bimetallic Films for Self-Propagating High-Temperature Synthesis for the Ni/Al Structure as an Example

Self-propagating high-temperature synthesis (solid-flame combustion) is simulated based on a layered model in which the product is formed between the layers of initial reactants due to solid-phase diffusion in nonisothermal conditions; in this case, the combustion wave propagates along these layers. It is found that cords of thickness up to 50 μm made of aluminium and nickel layers are fully converted into high-temperature melt. The results of calculation make it possible to optimize processes of welding and soldering of thermosensitive materials and parts of electronic components of various devices.

Simulating the distribution of electrochemical characteristics: A case study of 4.35 V LiCoO2/graphite pouch cell

Understanding the relationships between electrochemical characteristics and the corresponding parameters of the battery is crucial for optimizing cell design, which creates new ideas for safe management and optimized service life of lithium-ion batteries. Herein, a pseudo two-dimensional (P2D) electrochemical model of 4.35 V prismatically wound LiCoO2 pouch cell is established and optimized to predict its electrochemical behaviors. Based on the significant factors of cell design parameters by analysis of variance, the distribution characteristics of solid and electrolyte-phase Li+ concentration, potential of solid and electrolyte-phase, over-potential and local current density are investigated and verified, which is conducive to provide quantitative guidance for battery design and optimization. Simulation results show that the change of electrolyte-phase Li+ concentration gradient is 14.3% at 1C rate, and the concentration gradient decreases with the increase of the electrolyte phase diffusion coefficient and Li+ transference number. In addition, the particle size shows a positive correlation with the surface lithium ion concentration, while the electrode thickness, solid phase volume fraction and solid phase diffusion coefficient are negatively correlated with the surface lithium ion concentration. The model indicates that the polarization of anode is more than twice as larger as than that of the cathode at 1C discharge. Moreover, simulation results demonstrate that the peak of local current density moved from the separator interface to the current collector interface as discharge proceeded, which further reveal the non-uniform distribution of the electrochemical reaction rate in the cell.

A Fractal-Based Correlation for Time-Dependent Surface Diffusivity in Porous Adsorbents

Fluid–solid adsorption processes are mostly governed by the adsorbate transport in the solid phase and surface diffusion is often the limiting step of the overall process in microporous materials such as zeolites. This work starts from a concise review of concepts and models for surface transport and variable surface diffusivity. It emerges that the phenomenon of hindered surface diffusion for monolayer adsorption, which is common in zeolites, and models able to fit a non-monotonic trend of surface diffusivity against adsorbate solid phase concentration, have received limited attention. This work contributes to the literature of hindered diffusion by formulating a time-dependent equation for surface diffusivity based on fractal dynamics concepts. The proposed equation takes into account the contributions of both fractal-like diffusion (a time-decreasing term) and hopping diffusion (a time-increasing term). The equation is discussed and numerically analyzed to testify its ability to reproduce the possible different patterns of surface diffusivity vs. time.

From microstructure evolution to thermoelectric and mechanical properties enhancement of SnSe

Defect existing form and its evolution play an important role in the thermoelectric transport process. Here different forms of Pb into the SnSe system were introduced in order to improve the thermoelectric and mechanical properties of SnSe. Pb/SnSe samples were fabricated by vacuum melting, solid phase diffusion, spark plasma sintering and annealing treatment. The element valence mapping diagram and the X-ray photoelectron spectra (XPS) characteristic peaks of Pb show that a certain amount of elemental Pb exists in the initial state, and evolves into Pb2+ ion after annealing treatment. The micro-structure evolution leads to significant enhancement of the power factor and the ZT value. The power factor (PF) and the ZT value for Pb/SnSe increases to 623 μW/m/K2 and 1.12 at 773 K after annealing treatment, respectively. Compared with SnSe matrix, the hardness and fracture toughness of Pb/SnSe samples increased by about 40% and 10%, respectively. Reasonable control of microstructure evolution is expected to be a design idea to improve thermoelectric and mechanical properties of SnSe.

Physics-based fractional-order model with simplified solid phase diffusion of lithium-ion battery

Abstract Solid phase diffusion plays an important role in the long-term performances of lithium-ion batteries. Current mechanistic model for describing the solid phase diffusion has low computational efficiency and obscure physical meanings. A simple but effective physics-based solid phase diffusion model is of great significance for the impedance characterization and aging diagnosis of lithium-ion batteries. In this paper, a physics-based fractional-order model is established by simplifying the solid phase diffusion process through Pade approximation. A full-cell fractional-order model is constructed by combining the medium-high frequency dynamic model. The proposed model has a clear physical meaning and can be used to characterize full-cell performances. Furthermore, this paper provides solutions to identifying the parameters of the full-cell fractional-order model by decoupling the dynamics in frequency and spatial domain. The established full-cell fractional-order model is validated under various working loads. The results show that the proposed physics-based fractional-order model with simplified solid phase diffusion improves the computational efficiency with little loss of accuracy, indicating that the proposed model is an appropriate candidate for online applications.

On the processes of migration and diffusion in the systems with solid-state reagents

This paper deals with peculiarities of diffusion and migration in electrochemical systems with solid-state reagents (ESSSR). Contradictions of the diffusion model are analyzed. It is the difference of applied potentials and the corresponding electric field strength in the bulk solid phase and at the interfaces which is the primary driving force of charge transfer in ESSSR. The time characteristic of diffusion processes is not comparable to the duration of electrode processes at charging/discharging of batteries and especially electrochemical capacitors. In many real systems involving ESSSR, the process of diffusion in solid phase is absent. Examples of charge transfer processes in ESSSR (nickel hydroxide electrode, sparingly soluble quinoid compounds, Li+ intercalation in graphite, etc.) are considered, and the processes are explained using the Grothuss, tunnel and other migration mechanisms. It is shown in this paper that the linear relationship between peak currents in voltammetric curves and the square root of potential scan rate cannot be presented as an ultimate support of the diffusion model, but as а more universal property of ESSSR. In this aspect, the efficient diffusion coefficient, Deff, could be at best discussed, not to distort the ideas of charge-transfer migration mechanisms in the ESSSR.

Phase formation and evolution during transient liquid phase sintering of MIM418 superalloy with master alloy addition

Phase formation and evolution during transient liquid phase sintering of MIM418 superalloy fabricated via master alloy approach have been investigated through a combination of thermo-dynamic calculation and diffusion couple method. Diffusion couple experimental results reveal that solid phase diffusion of Al from master alloy to Ni particles leads the formation of NiAl phase at Ni/master alloy interface initially before the formation of liquid phase, which transforms to γʹ(Ni3Al) phase subsequently. Thermo-dynamic calculation results reveal that Cr-rich liquid phase forms in the master alloy powder much lower than sintering temperature. The melting point of the Cr-rich phase increases gradually with the dissolution of Ni particles, resulting in the vanishing of the liquid in the sinter system. The Cr-rich transient liquid phase spreads and wets Ni particles, then transforms to M23C6 carbide mainly on grain boundaries after solidification, while the MCʹ carbide in master alloy powder tightly limits the migration of MC carbide forming elements (Ti, Nb), and the resultant MC carbide is confined in the original master alloy region. The tensile and yield strength of MIM418 superalloy are 53% and 99% higher than that of the cast K418 alloy, and the reduced ductility is associated with the uneven distribution of carbides.

Influence of chemical composition and structural heterogeneity of 06ХН28МДТ alloy on mechanisms of its pits formation in return waters

Purpose of the work. Determine the influence of chemical composition and structure of 06ХН28МДТ alloy on mechanisms of its pits formation in model return waters with pH = 4... 8 and chloride concentration 180 mg/l.Research methods. X-ray spectral analysis on СРМ-25 spectrometer, metallographic analysis on optical micro­scope МРР-2Р. Corrosion losses of metals in pittings were determined by photometric analysis of model chloride-containing recycled waters after holding samples therein. Straight-line regression relationships between corrosion losses of metals in pittings ΔCr, ΔNi, ΔFe and alloy parameters were determined by regression analysis by least squares method. In order to determine the influence of alloy parameters on the mechanisms of its pitting formation, previously established characteristic features of selective dissolution of metals in pittings were used.Results obtained. It has been found that in model return waters with pH = 4–6.8 06ХН28МДТ alloy pits to form stable, and with pH = 7 and chloride concentration 180 mg/l – metastable pittings. In stable pittings Cr contributes to the increase of ΔFe from them, and in metastable – vice versa. This is due to the direction of solid-phase diffusion of Fe atoms from the alloy volume to the surface of stable pittings and from the surface of metastable in its volume. Therefore, the increase in Cr content in the alloy contributes to the growth of stable pittings and the repassification of metastable ones due to the decrease in their growth intensity. However, it has been found that the smaller the sizes of titanium nitrides near which pittings are formed, the lower the ΔFe in metastable and stable pittings. This is due to the lower degree of defect of the structure of the alloy austenite solid solution about small titanium nitrides.Scientific novelty. Cr promotes the growth of solid phase diffusion of Fe atoms to the surface of stable and from the surface of metastable pittings into the volume of the 06ХН28МДТ alloy. This promotes the repassification of metasta-ble and, accordingly, the growth of stable pittings. Increasing the size of titanium nitrides in the alloy contributes to increasing the number of austenite structure defects near them and to the growth of stable and metastable pittings.Practical value. Manufacturers of heat exchangers are advised to use 06ХН28МДТ alloy smelts with minimum Cr content, as well as those having titanium nitrides size of not more than 5 mcm.

Thermodynamics, kinetics and crystal structure of γ/β-MnO2 in Li/MnO2 primary batteries

γ/β-MnO2 as a cathode material is a key factor for the performance of Li/MnO2 primary batteries. To clarify the thermodynamic and kinetic characteristics of γ/β-MnO2, its approximate entropy (ΔS) at various depths of discharge (DOD) in a quasi-equilibrium state is studied. The ΔS analysis reveals that the reduction process of γ/β-MnO2 with Li+ intercalation is divided into three stages (single-phase, two-phase and single-phase reaction) but these three stages are hard to distinguish by X-ray diffraction (XRD). This result is different from an earlier conclusion of only a single-phase reaction. The two-phase reaction of γ/β-MnO2 has a low charge transfer impedance (Rct) and solid phase diffusion impedance (Zw). This is advantageous for providing a high electrochemical reduction reaction rate of MnO2 and a high power output of the battery. The functional relationship between x in LixMnO2 and its corresponding open circuit voltage (OCV, the stable potential of MnO2 vs Li/Li+) is a mathematical formula similar to the Nernst equation. According to the formula parameters (m and n), the state of charge (SOC) of γ/β-MnO2 can be determined. Furthermore, the thermodynamics of γ/β-MnO2 during discharge demonstrates that the rate controlling steps (RCSs) are ion solid diffusion and electron transport, rather than the sole solid phase diffusion as previously reported.

Analytical Modeling of Solid Phase Diffusion in Single-Layer and Composite Electrodes Under Time-Dependent Flux Boundary Condition

Mathematical modeling of species diffusion in Li-ion cell electrodes is critical for improving performance and efficiency of electrochemical energy storage. There is a relative lack of literature in this direction for time-dependent flux boundary conditions. In this work, the method of Green’s functions is used to solve the solid-phase diffusion problem in electrodes with a time-dependent flux boundary condition. While Green’s functions have been used extensively for thermal transport problems, there is limited past work on application of Green’s functions for solving species transport problems in electrochemical systems. The concentration distribution is first determined for a thin film electrode and spherical electrode particle. The method is then extended to determine the concentration profile in two-layer composite electrodes. The mathematical models presented in this work are validated by comparison with past studies and numerical simulations. Concentration profiles for a variety of time-dependent boundary conditions are presented. It is expected that improved understanding of diffusion under time-dependent flux boundary conditions may help improve the performance and efficiency of Li-ion based electrochemical energy storage devices and systems.

Ion Vacancies and Transport in 1-Methylimidazolium Triflate Organic Ionic Plastic Crystal.

Organic ionic plastic crystals (OIPCs) are an important family of materials that have shown exciting possibilities as solid electrolytes for lithium ion batteries and other electrochemical devices. In this study we demonstrate for the first time that, although the X-ray shows sharp diffraction peaks, both cation and anion clearly exhibit significant ion diffusion in solid phase I. Two phases with ion diffusivities differing by 2 orders of magnitude can be identified. The populations of the cation and anion in both phases are found to be unequal, hinting at the existence of (negatively charged) cation vacancies in the plastic crystal phase and a positively charged grain boundary phase. These interesting properties of ion vacancies and unequal populations of cation and anion are likely to be ubiquitous in other OIPCs, and it is of paramount importance to be aware of these features to correctly understand the structure-property relationships of this important material family.

Влияние катодной поляризации стальной мембраны и кислотности среды на соотношение скоростей реакции выделения водорода и его твердофазной диффузии в спиртовых растворах HCl

Влияние катодной поляризации стальной мембраны и кислотности среды на соотношение скоростей реакции выделения водорода и его твердофазной диффузии в спиртовых растворах HCl

Особенности восстановления оксидного железа техногенного происхождения

The overview of existing models for iron oxides reducing and an analysis of their applicability to technogenic formations is presented. The thermodynamic analysis data of iron oxides reducing reactions through solid and gas phases and experiment results presenting features of technogenic iron oxide reducing under conditions of solid-phase diffusion (limited diffusion) and partially liquid-phase diffusion (easier diffusion) of iron oxide ions. It is shown that under conditions of iron oxide ions solid-phase diffusion the reduction processes rate is significantly affected by the briquettingpressure, which increases the contact area of reacting substances. The briquetting pressure does not affect the reduction processesrate under conditions of partially liquid-phase diffusionof iron oxide ions. An ion-diffusion catalytic mechanism is proposed to describe the observed effects of technogenic iron oxide reducing

Механизм формирования карбидокремниевого покрытия диффузионным методом в кремниевой засыпке на углерод-углеродных композиционных материалах

The pack cementation process, used for obtaining coatings, is described, as a rule, in terms of solid-phase diffusion, which leads to saturation of the near-surface layer of the workpiece with a certain element. This method allows the deposition of a silicon carbide coating on carbon-carbon composite materials, that increases its resistance to the action of high-temperature oxidizing environments. An analysis of the kinetic features of the formation of silicon carbide on a carbon material indicated the difference between this method and the classical diffusion saturation. It turned out that it is necessary to consider additional processes of gas formation that occurs in the powder filling. A mechanism has been proposed, according to which it is possible to transfer silicon through the gaseous reagent SiO, generated in the backfill with the help of oxide additives, like aluminum oxide, which were previously considered inert.

Оценка максимального поперечного размера многослойных биметаллических пленок для протекания в них самораспространяющегося высокотемпературного синтеза на примере структуры Ni/Al

To simulate self-propagating high-temperature synthesis (solid flame combustion), a layered model is taken as the basis in which the product is formed between the layers of the starting reagents due to solid-phase diffusion in non-isothermal conditions, while the combustion wave propagates along these layers.It turned out that the cords from layers of aluminum and nickel with a thickness of up to 50µmv will completely turn into a high-temperature melt The calculation results will optimize the processes welding-soldering of heat-sensitive materials and parts of electronic components of various devices.

Microstructural evolution and mechanical properties of h-BN composite ceramics with Y2O3–AlN addition by liquid-phase sintering

Hexagonal boron nitride (h-BN) composite ceramics were prepared by hot pressing with the addition of Y2O3 and AlN. The effects of different Y2O3–AlN contents on microstructural evolution, mechanical properties and thermal diffusion coefficients of h-BN composite ceramics were investigated. The results indicate that Y2O3–AlN forms a liquid phase during the sintering process, achieving a good wettability with h-BN grains. In pure h-BN ceramic and h-BN composite ceramic with 40 wt% Y2O3–AlN, the h-BN grains grow well when controlled through solid-phase and liquid-phase diffusion, respectively. With the increase in Y2O3–AlN content, mechanical properties and thermal diffusion coefficients of h-BN composite ceramics first decrease and then increase, and the properties of h-BN composite ceramic with 10 wt% Y2O3–AlN are the inflection points. Such properties are highly related to the phase compositions, porosity and microstructure.

Study on the phase evolution, microstructure and densification behavior of (Ti,M)(C,N)-based cermets

(Ti,M)(C,N)-Based Cermets were synthesized from (Ti,M)(C,N)-Ni-Co composite powders by vacuum sintering. The material phase evolution, microstructure and densification behavior were investigated under different sintering temperature from 800 °C to 1400 °C. Results showed that deoxidation occurred and solid phase diffusion observed below 1200 °C. The solid phase liquidization appeared from 1200 °C to 1350 °C, resulting in decrease of pores in the material. Above 1350 °C, the liquid phase fully melted to fill the pores of material, and the cermets approach densification lead to the maximum value of its transverse rupture strength and hardness. (Ti,M)(C,N)-based cermets prepared by vacuum sintering have a hard phase of “weak core/rim structure".

Ultrasonic Application of Nanostructured Coatings on Metals

A method is developed for applying metallic, intermetallic, or ceramic coatings to a metal surface by means of ultrasound (high-frequency acoustic vibrations). The method may also be used to reinforce metallic surfaces by means of particles of another metal or ceramic. Under the action of ultrasound, chemical reactions and solid-phase diffusion are accelerated. That is accompanied by strong adhesion of the metal matrix to the particles; solid-phase transformations; and the formation of intermetallides, oxides, carbides, nitrides, and other compounds, depending on the surrounding gas and the powder composition. As a result, a composite coating or layer with nanostructure or microstructure is formed on the surface.

Thermodynamic Perspective on Co-Intercalation Behavior of Li/Mg Dual Cations in Intercalation Cathode Materials

Post Li-ion batteries using multivalent ions, such as Mg2+, Ca2+, Zn2+, have attracted much attention in recent years, but developing appropriate intercalation cathode materials for these multivalent cations remains a difficult task due to the sluggish solid-phase diffusion behavior, which is usually caused by the strong coulomb interaction between multivalent cations with the ionic cathode hosts. As an attempt to solve this problem, we proposed a new battery technology, which is referred to as Li-Mg dual-cation batteries.[1-2] The Li-Mg dual-cation batteries possess a so-called “rocking-chair”-type structure, where Li ion and Mg ion are involved in each half-cell reaction simultaneously. When exploring the characteristics of these batteries, we found an interesting phenomenon that Mg intercalation usually shows higher discharge potential in Li-Mg dual-cation electrolyte than in Mg single-cation electrolyte. The increase of discharge potential (i.e. decrease of the overpotential for Mg intercalation) strongly suggests that the co-existing Li ion is helpful to promote the Mg intercalation with cathode hosts. To elucidate what causes this phenomenon, we performed the first-principles calculations[3-4] with the Nudged Elastic Band (NEB) method[5] to estimate the activation energy of Mg cation migration in cathode hosts that are discharged in Li or Mg single-cation and Li-Mg dual-cation electrolytes and finally revealed a facilitating mechanism for the solid-phase diffusion of Mg cation.[6] In this presentation, we give a comprehensive explanation on the co-intercalation behavior of Li ion and Mg ion in Li-Mg dual-cation batteries, especially from a thermodynamic perspective. This work advances the fundamental understanding of ionic conduction phenomena of multivalent cations, which is indispensable for developing future energy storage devices. [1] T. Ichitsubo, S. Okamoto, T. Kawaguchi, Y, Kumagai, F. Oba, S. Yagi, N. Goto, T, Doi, E. Matsubara, J. Mater. Chem. A 3, 10188(2015). [2] H. Li, T. Ichitsubo, S. Yagi, E. Matsubara, J. Mater. Chem. A 5, 3534(2017). [3] P. E. Blöchl, Phys. Rev. B 50, 17953(1994). [4] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77, 3865(1996). [5] G. Henkelman, B. P. Uberuaga, H. Jónsson, J. Chem. Phys. 113, 9901(2000). [6] H. Li, N. L. Okamoto, T. Hatakeyama, Y, Kumagai, F. Oba, T. Ichitsubo, Adv. Energy Mater. 8, 1801475(2018).