Solid-state Diffusion Research Articles

Nickel ion (Ni2+) doping induced formation of W18O49/W3O8 bulk homojunction for enhancing photo-assisted energy storage

The photo-assisted charging supercapacitors that integrate solar energy conversion and energy storage in one device have inspired great interests. In this work, a bulk homojunction W18O49/W3O8 was prepared through doping Ni2+ in W18O49, and was used as the active material of photoelectrodes. The Ni-doped W18O49/W3O8 photoelectrodes exhibited superior photoelectric property and excellent capacity for energy storage. The optimal WN2 photoelectrode showed a specific capacitance of 667.7 F.g−1 at current density of 4 A.g−1 under light illumination, which was 19.4% higher than that in dark. The photogenerated charge carriers and the efficient separation of charge carriers induced by homojunction could be responsible for the photo-enhanced charge storage. After cycling test, WN2 photoelectrode retained about 92% of its initial specific capacitance without irradiation, and surprising 102% of its initial specific capacitance with irradiation. The electrochemical energy storage process of WN2 photoelectrode was found to be dominated by bulk solid-state diffusion, and the mechanism analysis provided theoretical evidence for photo-assist enhanced electrochemical performance of the prepared electrodes.

Extraction of lignin-containing nanocellulose fibrils from date palm waste using a green solvent

Lignin-containing nanocellulose (LNC) is a compelling alternative to traditional nanocellulose (NC), it offers enhanced yields and a reduction in the demand for toxic chemicals. This research involves the isolation of LNC from date palm waste using a green hydrolysis process and its subsequent characterization. The potential of using ionic liquids (ILs) as green solvents to isolate LNC has not yet been explored. Our findings suggest that 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) can hydrolyze partially delignified and unbleached lignocellulose, achieving LNC synthesis. The obtained LNC showed a higher yield than its NC counterpart and exhibited rod-shaped fibers with nanoscale diameters and micrometer lengths, indicating a high aspect ratio. Dynamic Light Scattering (DLS) results indicate average particle sizes of 143.20 nm for NC and 282.30 nm for LNC, with a narrow particle size distribution conforming their monodisperse behavior. Thermogravimetric analysis and differential scanning calorimetry revealed high thermal stability (initial degradation temperature = 222.50 °C and glass transition temperature = 84.45°C) of LNC. Moreover, the obtained LNC fibers were crystalline (crystallinity index = 52.76 %). Their activation energy (124.95 kJ/mol) was determined using the Coats–Redfern method by employing eight solid-state diffusion models. Overall, this study motivates the use of ILs as green solvents to produce lignocellulose derivatives that are suitable for various applications.

Improved plating/stripping in anode-free lithium metal batteries through electrodeposition of lithiophilic zinc thin films

The new concept of anode-free Li batteries (AFLBs) with no excess lithium, while retaining numerous strengths, does come with certain challenges, such as high capacity loss and low coulombic efficiency. These challenges can be addressed through the utilization of modified lithiophilic current collectors to enhance the electrochemical performances. Herein, we investigated the surface modification of the Cu current collector by zinc electrodeposition to provide a lithiophilic thin layer. This process aims to facilitate a smoother plating/stripping process, leading to a uniform and dendrite-free lithium deposition on the LixZny phase formed at the first stages of plating. The zinc-modified current collectors improved cell's performances, including smooth and dense lithium deposition, reduced overpotential at various applied current densities (44.5 mV to 16.8 mV @0.25 mA cm−2), prolonged cycling stability for about 300 cycles and provided high coulombic efficiency of 95 % when compared to bare Cu electrodes. These improvements are attributed to a favorable lithium alloying reaction on the Zn-coated surface. Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) revealed high diffusion coefficients for lithium (ranging from 10−9 to 10−6 cm² s-1), despite of the solid-state Li diffusion in the Zn film coating. We anticipate that implementing this modified current collector in a half-cell configuration could lead to the realization of a high-performance, anode-free lithium battery. This holistic approach proposes a scalable and cost-effective technique for boosting the performance of AFLBs.

Solid State Diffusion Bonding of Alumina with Aluminum Alloy

The objective of this work is to study the effect of time during the bonding process of alumina with an industrial aluminum 6060 alloy by the technique of solid-state welding at 600°C. Optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, corrosion tests, and microhardness measurements were used as characterization techniques. The extended time during the bonding process had an effect on the microstructure of the interface and its mechanical properties. Oxygen diffusion was detected across the aluminum alloy/alumina interface. A recrystallization reaction developed on the aluminum side during the bonding process, which affected the aluminum alloy hardness values. By bonding metal to ceramic, it allows the use of ceramics in automotive engines to reduce weight, increase thrust-to-weight ratio and operating temperature, and improve working efficiency.

Mathematical modeling and optimization of vacuum diffusion bonding parameters for predicting and enhancing the strength of dissimilar IN-718/MSS-410 joints using RSM for power generation applications

The dissimilar welding of Inconel 718 (IN-718) alloy and AISI 410 martensitic stainless steel (MSS-410) is crucial in advanced gas turbines, and ultra-supercritical power plants to meet the demands of different operating conditions and lower the cost. However, the dissimilar fusion welding of IN-718/MSS-410 is challenging due to the differences in thermal expansion coefficient, physical and mechanical properties of base metals. In this study, the solid-state vacuum diffusion bonding (VDB) technology is employed to develop the dissimilar IN-718/MSS-410 joints. The aim of this study is to find the optimal combination of VDB parameters such as diffusion bonding pressure-DBP (MPa), diffusion bonding temperature-DBT (°C) and diffusion bonding time-DBt (min) for enhancing the strength of IN-718/MSS-410 joints. The response surface methodology (RSM) was integrated for designing the experimental matrix. The strength performance of VDB joints was evaluated by conducting the lap shear strength (LSS) and bonding strength (BS) tests. The mathematical LSS and BS predicting models were established using regression analysis and verified employing the variance analysis. The microstructural features were analyzed using optical and scanning electron microscopy (SEM). The X-ray diffractometer (XRD) was employed to identify the phases evolution in the joint interface. The experimental results revealed that the IN-718/MSS-410 joints diffusion bonded using the DBP of 14 MPa, DBT of 960 °C and DBt of 90 min exhibited the greater LSS of 280 MPa and BS of 373 MPa. The prediction models accurately predicted the LSS and BS of IN-718/MSS-410 joints within 2 % error at 95 % confidence. It is primarily concerned with developing the optimal bonding width with the fewest possible embrittlement implications and better joining interface coalescence. According to variance analysis, the DBt was the most significant parameter influencing the LSS and BS of joints followed by the DBP and DBT.

Wettability and microstructural evolution of copper filler in W and EUROFER brazed joints

In terms of wettability, active systems are characterized by a reduction in interfacial energy as the time at specific conditions is increased. This article aims to investigate the evolution of wettability and microstructure, which undergoes a critical transformation at temperatures and dwell times near brazing conditions due to their significant impact on resultant mechanical properties. The objective is to enhance wettability and prevent the formation of different phases that can occur rapidly within the brazing window conditions. Up to 1105 °C, complete fusion of the filler does not occur. However, once it happens, the expansion of the copper filler in EUROFER increases up to 400%, and the contact angle reduces from 100° to 10°, indicating an active wetting behavior. On the other hand, when copper is used with tungsten, an inert behavior is observed, maintaining the contact angle around 70°. Brazed joints carried out under the most promising wetting conditions demonstrated that at 1110 °C-1 min, various phenomena began to occur. This includes solid-state diffusion of copper in the EUROFER, following the austenitic grain boundaries, and partial dissolution of Fe in the copper braze. Increasing the brazing time from 2 to 5 min achieved high interfacial adhesion properties and controlled the diffusion layer and Fe-rich band formed at the W-braze interface, resulting in the best mechanical results (295 MPa).

Influence of carbon nanotubes on the morphology of Cu6Sn5 in Cu/(Sn–Ag–Cu) solder joints

This study delves into the intricate interaction between multi-walled carbon nanotubes (MWCNTs) and the Sn–Ag–Cu solder system, highlighting its relevance in lead-free soldering applications. Reflow and isothermal aging induce the formation of intermetallic layers at the joint interface, including Cu6Sn5, Cu3Sn, and irregularly shaped Ag3Sn particles. The addition of MWCNTs leads to the flattening of Cu6Sn5 grains, restraining their growth and potentially improving mechanical strength. Notably, MWCNTs exhibit a relatively high affinity with Ag3Sn. Grain size distribution analysis indicates that MWCNTs reduce particle size, effectively suppressing intermetallic compound growth. Over time, grain size increases due to simultaneous coarsening and growth during isothermal aging. In the growth kinetics analysis of intermetallic compounds in SAC305-MWCNTs solder joints, stable behavior is observed for Cu3Sn growth, driven by solid-state diffusion between Cu6Sn5 and Cu. In contrast, Cu6Sn5 exhibits significant variations in growth behavior with temperature changes. Furthermore, the evaluation of activation enthalpy for Cu3Sn growth in the Cu/(SAC305-MWCNTs) and Cu/SAC305 diffusion couples reveals similar n and k values of the power function for the layer growth, indicating a comparable rate-controlling process for Cu3Sn growth. The presence of MWCNTs in the solder does not significantly influence the rate-controlling process or activation enthalpy for Cu3Sn growth, contrasting with the observed effects on Cu6Sn5 growth. This study provides valuable insights into the interactions within the SAC305-MWCNTs solder system, offering significant implications for lead-free soldering applications.

Microstructure evolution and mechanical properties of wire-arc-additively manufactured Al–Cu–Mg–Ag alloy

In this article, Al–Cu–Mg–Ag specimens were successfully wire-arc-additive-manufactured based on by gas metal arc process to investigate the evolution of microstructure and mechanical properties. The results showed that the grain morphology and pore size in the printed specimens varied in height direction. Under the influence of repeated thermal cycling, which affected the solid-state diffusion of the deviated elements at the grain boundaries, the distribution of the nanoscale second phase appeared significantly different in the height direction. The precipitation phase changes caused the microhardness of the printed specimens to decrease gradually from a peak of 125 HV and stabilise at around 100 HV. The changes in the printed specimens’ horizontal mechanical properties were insignificant mainly due to interlayer porosity.

Mechanism of solid-state diffusion reaction in vacuum between metal (Fe, Ni, and Co) and 4H–SiC

Experiments were conducted to investigate the vacuum diffusion reactions between 4H–SiC and various metals (iron (Fe), nickel (Ni), and cobalt (Co)). The effects of temperature, time, and metallic materials on the diffusion reactions were systematically analyzed. Notably, a solid-state diffusion reaction between the metal and 4H–SiC was observed at low temperatures, and the mechanism governing the solid-state interface diffusion reaction between the single-crystal 4H–SiC and metals was elucidated. The results indicate that a chemical reaction occurs between the metal and 4H–SiC during solid-state diffusion, leading to the formation of metal silicides under vacuum conditions. The temperature threshold for the solid-state diffusion reaction between 4H–SiC and metals falls within the range of 550–650 °C. Interestingly, the diffusion reaction proceeds without soaking. Furthermore, the metal type significantly influenced the diffusion rate.

On the role of microstructural defects on precipitation, damage, and healing behavior in a novel Al-0.5Mg2Si alloy

A recently developed healable Al-Mg2Si designed by the programmed damage and repair (PDR) strategy is studied considering the role microstructural defects play on precipitation, damage, and healing. The alloy incorporates sacrificial Mg2Si particles that precipitate after friction stir processing (FSP). They act as damage localization sites and are healable based on the solid-state diffusion of Al-matrix. A combination of different transmission electron microscopy (TEM) imaging techniques enabled the visualization and quantification of various crystallographic defects and the spatial distribution of Mg2Si precipitates. Intragrain nucleation is found to be the dominant mechanism for precipitation during FSP whereas grain boundaries and subgrain boundaries mainly lead to coarsening of the precipitates. The statistical and spatial analyses of the damaged particles have shown particle fracture as the dominant damage mechanism which is strongly dependent on the size and aspect ratio of the particles whereas the damage was not found to depend on the location of the precipitates within the matrix. The damaged particles are associated with dislocations accumulated around them. The interplay of these dislocations is directly visualized during healing based on in situ TEM heating which revealed recovery in the matrix as an operative mechanism during the diffusion healing of the PDR alloy.

Intercalation in Li-ion batteries: thermodynamics and its relation to non-ideal solid-state diffusion

Intercalation is the key phenomenon taking place in lithium-ion batteries: while its thermodynamics sets the equilibrium voltage of active materials, solid-state diffusion of intercalated lithium determines the rate at which the battery can operate. This study revisits the thermodynamics of intercalation by treating the active material as a binary mixture of filled and empty sites, thus relating the equilibrium potential to the chemical potential difference of intercalated lithium. By setting a reference to unitary activity at half state-of-lithiation, the non-ideal behaviour of the active material is quantified via a revisited form of the thermodynamic enhancement factor, revealing that common solid-solution cathode materials as LiNi x Mn y Co1-x-y O2, LiNi0.8Co0.15Al0.05O2, and LiCoO2 show strong super-ideal behaviour. The latter is related to the thermodynamic enhancement of the diffusion coefficient of intercalated lithium. A comprehensive overview of the functional forms of Li diffusion flux according to linear irreversible thermodynamics is provided and related to the chemical diffusion coefficient obtained by conventional characterisation techniques. A literature analysis made on solid-solution cathode active materials reveals that while the chemical diffusion coefficient varies significantly with state-of-lithiation, there exists a convenient functional form of diffusion flux according to linear irreversible thermodynamics that enables a fairly stable diffusion coefficient with state-of-lithiation. This has clear benefits from both modelling and experimental viewpoints and potentially sheds light on the mechanistic fundamentals of solid-state diffusion.

In situ tip-guided growth of nickel nanostructures through the application of electric current

Directional growth of individual nickel nanostructures guided by a nanoindentation tip was accomplished by in situ scanning electron microscopy. Agglomerates of nickel nanoparticles supported by nickel micropillars were electrically contacted with a conductive nanoindenter. Application of an electric bias led to dielectric breakdown of native surface oxide layers covering the nanoparticles and caused the formation of conductive pathways through particle agglomerates. Joule heating and mechanical retraction of the nanoindenter enabled growth of elongated nickel nanostructures through solid-state diffusion. Finite element modeling was used to estimate the amount of Joule heating and confirmed the activation of several mass transport mechanisms. The results of this study propose the ability of tip-guided growth of individual nanostructures with complex geometries and unprecedented feature sizes.Graphical abstract

Method—AMIDR: A Complete Pulse Method for Measuring Cathode Solid-State Diffusivity

The Atlung Method for Intercalant Diffusion and Resistance (AMIDR) is a novel, high accuracy method for measuring solid state diffusivity and interface resistance related to the Atlung Method for Intercalant Diffusion (AMID) with several key differences. Most notably, AMIDR is designed to analyze the voltage response over time of “complete” pulses, pulses that last until an impedance steady state is reached. These differences allow for AMIDR to return diffusivity results with a higher degree of confidence than Galvanostatic Intermittent Titration Technique (GITT) and at a faster rate with higher state of charge (SOC) resolution than Electrochemical Impedance Spectroscopy (EIS). In this study, three different lithium transition metal oxides were studied. These active materials showed very similar kinetic behaviour that varied with dependence on the fraction of Ni atoms filling sites in the Li layer. AMIDR comes with a user-friendly python program complete with a user interface that is intended to assist other researchers in measuring active material diffusivity in a controlled, repeatable manner. This program, along with instruction on its use, the results of this study from raw data to the final key kinetic metrics, and a video summary of AMIDR design are available for download at https://github.com/MitchBall/AMIDR.

Mechanical and Microstructural Characterization of Diffusion-Bonded Copper-Nickel Joint Interface

Solid-state diffusion bonding effectively joins dissimilar materials, even with varying metallurgical properties and melting points. In this study, a Cu/Ni joint was produced at a bonding temperature of 950°C for 60 minutes under a vacuum. The microstructural and mechanical properties of the bonding interface were evaluated using scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), microhardness tests, and X-ray diffraction (XRD). It was found that the EDS point scan analysis revealed the formation of a solid solution of Cu-Ni at the bonding interface. Since Cu-Ni exhibit complete solubility with each other, no intermetallic compounds (IMCs) were formed. The microhardness indicated that the bonding interface had a microhardness of 20% and 54% higher than the base metals (BM) of Ni and Cu, respectively.

Supramolecular Engineering of Ti3C2Tx MXene -Perylene Diimide Hybrid Electrodes for the Pseudocapacitive Electrochemical Storage of Calcium Ions.

The rare combination of metallic conductivity and surface redox activity enables 2D MXenes as versatile charge storage hosts for the design of high-rate electrochemical energy storage devices. However, high charge density metal ions including but not limited to Ca+2 and Mg+2 pose challenges such as sluggish solid-state diffusion and also inhibiting the charge transfer across electrode-electrolyte interfaces. In this work, free-standing hybrid electrode architectures based on 2D titanium carbide-cationic perylene diimide (Ti3C2Tx@cPDI) via supramolecular self-assembly are developed. Secondary bonding interactions such as dipole-dipole and hydrogen bonding between Ti3C2Tx and cPDI are investigated by zeta potential and Fourier-transformed infrared (FTIR) spectroscopy . Ti3C2Tx@cPDI free-standing electrodes show typical volumetric capacitance up to 260 F cm-3 in Mg2+ and Ca2+ aqueous electrolytes at charging times scales from 3minutes to a few seconds. Three-dimensional (3D) Bode maps are constructed to understand the charge storage dynamics of Ti3C2Tx@cPDI hybrid electrode in an aqueous Ca-ion electrolyte. ,Pseudocapacitance is solely contributed by the nanoscale distribution of redox-active cPDI supramolecular polymers across 2D Ti3C2Tx. This study opens avenues for the design of a wide variety of MXene@redox active organic charge hosts for high-rate pseudocapacitive energy storage devices.

Microstructure evolution and formation mechanism of interfaces in parallel gap resistance welding of stranded Ag-plated Cu conductor to Ag interconnector

In space flexible solar arrays, stranded Ag-plated Cu conductors and Ag interconnectors are preferred materials for energy transmission. Parallel gap resistance welding is a solderless micro-joining process that favors the reliability of joints between stranded Ag-plated Cu conductors and Ag interconnectors. It was found the interfacial microstructure presented diversity and complexity while mechanical and electrical properties showed unusual nonlinear variations with welding voltage. This study aims to clarify the interfacial microstructure evolution and its effects on the joint properties while elucidating the microstructure formation mechanisms. A shift in the bonding mechanism at interfaces from solid-state diffusion to brazing was found as welding voltage reached a critical value (1.5 V). It eliminated micro gaps and built nano-scale interlocking structures, resulting in substantial improvement in mechanical properties. Increasing the welding voltage from 1.2 V to 1.4 V improved electrical conductivity due to the enlarged bonding area at interfaces. However, high welding voltage (1.6 V) led to degradation in the electrical conductivity of joints due to excessive Ag-Cu solid solution formed at interfaces. The key to fabricating high-strength and high-conductivity joints lies in achieving appropriate interfacial melting while reducing alloying by controlling peak temperature and shortening the duration above the Ag-Cu eutectic point.

Interface characteristics and tensile fracture behavior of CoCrFeNi/6061Al matrix composites fabricated via spark plasma sintering and heat treatment

In this study, 3vol%CoCrFeNi high-entropy alloy (HEA) reinforced 6061Al matrix composites were prepared using spark plasma sintering (SPS), and a new strategy to regulate the interfacial structure of the diffusion layer by solid solution heat treatment was proposed. Based on the thermodynamics and kinetics of solid-state diffusion, the mechanism of the formation and growth of the diffusion layer and its influence on the mechanical properties of the composites were analyzed. At a solid solution temperature of 535 °C, a uniform diffusion layer forms between HEA and Al matrix, and the thickness of the diffusion layer increases with the extension of solid solution time. The diffusion layer is determined as a two-layer structure, with a columnar solid solution grain near HEA and an equiaxed crystal along with Al9Co2 solid solution layer near Al matrix. Optimal tensile strength and elongation of 211.5 MPa and 21.4% respectively are obtained at solid solution time of 60 min, with 12.8 μm in thickness. Superior interface bonding resulting from diffusion layer prevents the crack from expanding into the matrix, contributing to an enhanced ductility with the extension of solid solution time. This study provides valuable insights and theoretical guidance for developing HEA/Al composites with superior strength-ductility synergy.

Microstructure and weakening mechanism of additive-manufactured Al–Cu alloy under different heat input

The heterogeneous microstructure and mechanical properties of wire-arc additive manufactured 2219 Al–Cu alloy at several heat inputs (HIs) by adjusting the wire feeding speed were investigated. The partially melted zone (PMZ) was regarded as the weak region, and the weakening mechanism was analysed. Results indicated that the size and volume fraction of equiaxial grain increased with higher HI. The mass fraction of the segregated eutectics increased and the concentration of solid solution Cu in the α-Al matrix decreased. In addition, the morphology and distribution characteristics of eutectics were distinctly different at the inter-layer zone and inner-layer zone. The eutectics at the inter-layer PMZ were coarsened and continuous owing to the Cu solid-state diffusion and liquation.

Influence of Finite Diffusion on Cation Insertion-Coupled Electron Transfer Kinetics in Thin Film Electrodes

Materials that undergo ion-insertion coupled electron transfer are important for energy storage, energy conversion, and optoelectronics applications. Cyclic voltammetry is a powerful technique to understand electrochemical kinetics. However, the interpretation of the kinetic behavior of ion insertion electrodes with analytical solutions developed for ion blocking electrodes has led to confusion about their rate-limiting behavior. The purpose of this manuscript is to demonstrate that the cyclic voltammetry response of thin film electrode materials undergoing solid-solution ion insertion without significant Ohmic polarization can be explained by well-established models for finite diffusion. To do this, we utilize an experimental and simulation approach to understand the kinetics of Li+ insertion-coupled electron transfer into a thin film material (Nb2O5). We demonstrate general trends for the peak current vs scan rate behavior, with the latter parameter elevated to an exponent between limiting values of 1 and 0.5, depending on the solid-state diffusion characteristics of the film (diffusion coefficient, film thickness) and the experiment timescale (scan rate). We also show that values < 0.5 are possible depending on the cathodic potential limit. Our results will be useful to fundamentally understand and guide the selection and design of intercalation materials for multiple applications.

Luminescence investigation of red emitting CaAlSiO4F: Eu3+ doped phosphor for white LEDs based on oxyfluoride matrix

A series of Eu3+-doped of CaAlSiO4F red-emitting phosphors for different concentrations were successfully synthesized by using high temperature solid state diffusion method. The phase identification of the prepared phosphor was recorded using x-ray diffraction (XRD). In PL study, the emission peak of prepared phosphor was located at 595 nm and 618 nm due to 5D0 → 7F1 and 5D0 → 7F2 transitions at excitation of 257 nm, 395 nm and 465 nm. Morphological behaviour of prepared sample was analyzed by using scanning electron microscope (SEM). Commission de l'Eclairage chromaticity (CIE) coordinates were analyzed based on the PL emission spectra of the series CaAlSiO4F: Eu3+ activated phosphor. Therefore, these possible outcomes indicate that the CaAlSiO4F: Eu3+ products have great potential applications in solid state lighting industry.