Ostwald Ripening Research Articles

Stabilization of Metal Alloy Nanocatalysts by Encapsulation with a Metal Oxide

The threat of climate change motivates us to reduce our reliance on fossil fuels and transition to renewable energy infrastructure. Many clean energy technologies including hydrogen fuel cells, direct methanol fuel cells, and water electrolyzers utilize electrocatalysts to generate electricity from chemical energy or vice versa. One direction for increasing the catalytic performance and tolerance to contaminants of the catalyst layers is the development of metal alloy-based catalysts. For instance, ruthenium (Ru) can be alloyed with platinum (Pt) to increase the tolerance of Pt to carbon monoxide, a contaminant that can be found in hydrogen fuel. However, metal alloy catalysts have an additional route for degradation beyond the well-established Ostwald ripening, coalescence, and dissolution mechanisms that are an issue for nanoparticle electrocatalysts. Harsh fuel cell conditions can lead to a separation of the two metals that were originally alloyed in the nanocatalyst and, as a result, this leads to a loss in catalytic performance and tolerance to contaminants.1 This project focuses on the durability of alloyed PtRu electrocatalysts, which facilitate the methanol oxidation reaction in a direct methanol fuel cell and the hydrogen oxidation reaction in a hydrogen fuel cell.This project explored an encapsulation of electrodeposited PtRu nanoparticle catalysts with a porous niobium oxide as a method to stabilize the PtRu alloy. Niobium oxide was chosen due to its high corrosion resistance and previous studies showing its stabilization of Ru.2 PtRu alloyed nanoparticles were synthesized via electrodeposition on a glassy carbon electrode substrate and subsequently encapsulated by an electrophoretic deposition method adapted from Jha et al.3 The morphology and composition of the catalyst and encapsulating layer were characterized by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and optical microscopy. The activity and durability of pristine and encapsulated PtRu catalysts were evaluated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Carbon monoxide stripping and the double layer capacitance methods were used to study changes in the electrochemically active surface area before and after deposition of the niobium oxide. Access to the electrocatalyst surfaces through the encapsulating layer was maximized by the addition of surfactants and through tuning the potentials applied during the deposition of the niobium oxide as a means to improve its porosity. The niobium oxide was shown to improve the stability of the PtRu alloy and maintain the CO tolerance of the alloy well beyond that of the un-encapsulated catalyst. The stabilization of PtRu imparted by the encapsulation of niobium oxide herein is promising for the stabilization of alloyed nanoparticle catalysts towards a wide range of electrocatalytic applications. Yang, Z.; Yu, X.; Zhang, Q. RSC Adv., 2016, 6, 114014-114018.Jha, G.; Tran, T.; Qiao, S.; Ziegler, J. M.; Ogata, A. F.; Dai, S.; Xu, M.; Thai, M. L.; Chandran, G. T.; Pan, X.; Penner, R. M. Mater. 2018, 30, 6549-6558.

Formation and coarsening of epitaxially-supported metal nanoclusters

This mini-review describes developments over the last ∼30 years in characterizing the nucleation & growth of epitaxially-supported metal nanoclusters (NCs) or islands during vapor deposition, as well as their post-deposition coarsening. A beyond-mean-field treatment for homogeneous nucleation & growth corrects the deficiencies of traditional treatments in describing, e.g., the island size distribution, but also necessitates consideration of the spatial distribution of islands and their capture zones. We discuss advances in modeling capabilities, including those based upon on an ab-initio level treatment of periphery diffusion kinetics, for description of the non-equilibrium growth shapes of these NCs, focusing on 2D NCs. For post-deposition coarsening of arrays of NCs, there is generally a competition between Ostwald Ripening (OR) and Smoluchowski Ripening (SR). SR is also known as Particle Migration & Coalescence. For 2D NCs in homoepitaxial systems, conventional OR is observed on pristine fcc(111) surfaces, dramatically enhanced OR in the presence of even trace amounts of chalcogens for Cu(111) and Ag(111), and anomalous OR on anisotropic fcc(110) surfaces. The unexpected discovery of SR for fcc(100) homoepitaxial systems prompted extensive analysis of the underlying diffusivities of 2D NCs as a function of size, as well as of NC coalescence dynamics. A comprehensive understanding of these processes is now available. Self-assembly of 3D NCs during deposition, issues related to heterogeneous nucleation, directed assembly, NC growth structure selection, and coarsening are addressed. For SR of 3D epitaxial NCs, recent insights into the size-dependence of diffusivity are described.

Growth Mechanisms of Amorphous Nanoparticles in Solution and During Heat Drying

The purpose of this study was twofold: to identify the growth mechanisms of amorphous nanoparticles in solution and during the drying process at high temperatures, and to guide the process condition and stabilizer selection for amorphous nanoparticle formulations. In contrast to nanocrystals that are mostly mechanically robust, amorphous nanoparticles tend to undergo deformation under stress. As a result, development of a stable formulation and evaluation of the drying process for re-dispersible amorphous nanoparticles presents considerable challenges. Although amorphous nanoparticles have stability issues, they have several pros in terms of production, high monodispersity, and diverse applications in drug delivery. In this study, amorphous nanoparticles were prepared via liquid-liquid phase separation, and their growth mechanisms were investigated both in solution and during the drying process. In solution, particles were found to be susceptible to flocculation, crystallization, coalescence, and Ostwald ripening, with coalescence being a preliminary step providing the driving force for Ostwald ripening. However, during the heat drying process, coalescence and crystallization were found to be the primary mechanisms for particle growth, with Ostwald ripening being negligible due to reduced molecular mobility. The glass transition temperature (Tg) of these amorphous nanoparticles was found to be a crucial factor both in solution and during the drying process. At temperatures < Tg, particles remained in a rigid, glassy state thereby inhibiting coalescence, whereas at or above Tg, particles transition from glassy to rubbery state, making them more susceptible to deformation and coalescence. The mechanistic understanding of particle growth from this study can also be extended to the stabilization of other types of soft nanoparticles.

Late-stage microstructures in Chang’E-5 basalt and implications for the evolution of lunar ferrobasalt

Abstract This study investigates silicate liquid immiscibility (SLI) microstructures in the Chang’E-5 (CE-5) lunar ferrobasalt sample, the youngest recovered mare basalt (ca. ~2.0 Ga). Employing advanced high-resolution imaging techniques and chemical analysis, we examined a subophitic fragment, revealing two distinct types of microstructures indicative of multi-stage SLI events. The first type is observed in the mesostasis pockets and exhibits both “sieve” and “maze” textures, where the Si-K rich glassy phases are interconnected with Fe-rich minerals, e.g., fayalite. This type of microstructure, similar to previous observations in Apollo and Luna samples, is the product of a stable SLI event. The second type is characterized by K-free but high-Si melt inclusions occurring as emulsions in the rims of plagioclase. The entrapment of these emulsions followed a metastable SLI event, with the Fe-rich liquids serving as precursors to subsequent stable SLI processes. Additionally, the Fe-rich droplets within the emulsions underwent coarsening via Ostwald ripening, a phenomenon in which smaller particles in solution dissolve and deposit on larger particles. Our simulation of this coarsening process suggests a duration of at least 15-32 days for the SLI processes, alongside a slow cooling rate (&amp;lt; 0.3 °C/hour) of the late-stage CE-5 lava. We propose that metastable SLI may have influenced the effusive signature of the CE-5 lava flow during its late-stage evolution. The metastable SLI process can potentially lead to the formation of various phases during the late-stage evolution of lunar ferrobasaltic magmas, thereby contributing to the diversity of lunar rock types.

An interesting phase transition in polyamide 6/nitrile rubber blend induced by temperature and pressure and its effect on tribological performance

AbstractThe preparation of high‐performance rubber‐plastic blending elastomers has always been a research hotspot in the field of petroleum equipment. The two‐phase separation structure of the blend determines the macroscopic properties of the materials. It is of great significance to deeply explore the influence of processing technology on the two‐phase separation structure. In this paper, polyamide 6 (PA6)/nitrile rubber blends were prepared via the melt–compounding method. To meet the requirements of oil production and oil transport equipment, we investigated systematically the mechanical properties of the specimens exposed to different environments. The oil resistance and high‐temperature resistance of the blends were enhanced considerably with the addition of PA6. The temperature and pressure fields induced a novel transition from particle into fibrous phase based on Ostwald's ripening. However, this brand new transformation showed no benefits to the improvement of the frictional performance. Meanwhile, the relationship between aggregate structure and mechanical performance was demonstrated from the aspects of crystallization behavior and phase morphology.

Nanofiber array growth mechanism based on dealloying of Ti-Cu/Cu multilayer precursor film

Metal oxide nanofiber array materials are a type of material with outstanding performance and application potential. Recently, an efficient dealloying method using Ti–Cu/Cu multilayer film as a precursor was proposed to prepare titanium oxide nanofiber array structure. However, the growth mechanism and formation process of such an oxide nanofiber array grown on multilayer-film is not clear. In this work, we use Ti-Cu/Cu multilayer film as the precursor, NaOH solution as the dealloying corrosion solution, and free dealloying at room temperature. On the basis of successfully obtaining TiO2 nanofiber array films, the morphology formation and evolution process of the nanoarray were carefully monitored, and the atomic percentage changes of Ti, Cu and O elements in the dealloying precursor films were tested, as well as the formation and crystalline phase evolution trends of TiO2. Based on the experimental data, we tried to draw a schematic diagram of the formation process of this TiO2 nanofiber array, and proposed that the growth mechanism of the TiO2 nanofiber array is the precipitation growth process both with Ostwald Ripening and Oriented Attachment mechanisms. Then, the photocurrent response characteristics of the obtained nanofiber array structure samples were analyzed, and it was found that the nanofiber array structure had a certain effect on the photocurrent response performance. The completion of the present work is expected to provide a theoretical reference for the preparation and application of other metal oxide nanofiber array by dealloying method.

Enhanced assembly stability for amine-based cationic glycolipid

Glycolipids incorporating positive charges, mediated by an imidazolium cation, have shown potential for effective formulation of vesicular drug carriers, reflecting repulsive electrostatic forces, promoting the formation of nanosized assemblies and preventing unwanted Oswald ripening (Goh et al. (2019), ACS Omega 4, 17,039). Our continuous development of an assembly-based drug delivery system prompted us to investigate a pH-sensitive analogue, leading to the synthesis of a 6-amino-Guerbet glycoside. However, in contrast to the imidazolium counterpart, the amine-mediated charge increased the intermolecular cohesions, furnishing bigger assemblies instead, which further increased upon introduction of acid. Moreover, assemblies exhibited a significantly reduced positive charge density. It is concluded that strong proton-initiated hydrogen bonding between amino groups provide cohesive head group interactions overcompensating possible repulsive charge interactions. While this behavior invalidates the application of the amino-glucoside as dispersing agent for the formulation of small vesicles, it potentially paves a route towards enhanced vesicle stability.

Evolution of microstructure and mechanical properties of Ti65 high-temperature titanium alloy after additive manufacturing and annealing

Ti65 was prepared by Laser Direct Energy Deposition (LDED) and subjected to Annealing Heat Treatment (AHT). The microstructure and mechanical properties of different specimens were evaluated. The results indicated that the prior β columnar crystals had a strong [0001] texture along the grain growth direction. The coarsening or spheroidization of α lath was attributed to the splitting of lamellar α, subsequent non-directional growth, element migration, and Ostwald ripening. The isotropy of the specimen annealed at 950 °C was caused by trimodal microstructure, discontinuous grain boundary α (αGB), precipitates dissolution, and low-angle grain boundary. A mathematical model was established to predict yield strength (YS) and microhardness based on the α lath thickness. The microhardness-strength correlation of LDED Ti65 followed an empirically derived model (Tabor's relationship). Improvements to the original models of the microhardness-strength relationship for Ti65, in conjunction with the strain-hardening effect and α orientation, made it possible to use these models to predict the strength of LDED Ti65 parts and improve the accuracy of the predicted values. Simultaneously, the model can provide data support for the industrial application of Ti65 or, where appropriate, provide a reference for other technical production (material applications).

Fate of Nanobubbles Generated from CO2–Hydrate Dissociation: Coexistence with Nanodroplets—A Combined Investigation from Experiment and Molecular Dynamics Simulations

The evolution of CO2 nanobubbles generated by gas–hydrate dissociation is comprehensively studied in this research, employing a synergistic approach that combines laboratory experiments and molecular dynamics simulations. The results show that a higher concentration of nanobubbles can be observed in the early stages of hydrate dissociation, while smaller, thus‐generated, nanobubbles are less stable and prefer to amalgamate into larger bubbles through coalescence or Ostwald ripening. From the high Laplace pressure inside some nanobubbles as well as their higher local densities, they may transform into nanodroplets by densification fluctuations. Thus, the dynamic coexistence of nanobubbles and ‐droplets is confirmed from both experimental and simulation measurements. The number and size of the nanobubbles in the system affects the interaction between water molecules and their movements so that the water molecules diffuse faster upon this condition. The water–water interactions become more pronounced in the presence of nanobubbles and the hydrogen bond network is better preserved in the bulk. This study provides new insights into the microscale mechanisms of gas–hydrate dissociation and highlights the complex interactions between nanobubbles/ ‐droplets, and the aqueous environment after CO2–hydrate dissociation.

Bacterial cellulose nanocrystals or nanofibrils as Pickering stabilizers in low-oil emulsions: A comparative study

This investigation assessed the potential of bacterial cellulose (BC) in two distinct forms, nanocrystals (BC-NC) and oxidized nanofibrils (BC-NF), as stabilizers for low oil-in-water emulsions (1 % v/v). The research explored the impact of ionic strength and BC concentration on the physico-chemical characteristics, stability, and rheological properties of those emulsions. Nanofibrils had diameters ranging from 25 to 146 nm and lengths in the micrometer range, while nanocrystals varied in length from 133 to 870 nm and in diameter from 20 to 60 nm. Both BC-NF and BC-NC exhibited high zeta potential values (>−45 mV) and contact angles of 30-31°, indicating stability. Both nanocelluloses were effectively used as stabilizers in Pickering emulsions, namely in low-oil systems, producing small emulsion droplets with sizes between 1.42 and 4.13 μm. Further results revealed that ionic strength influenced emulsion stability, with both BC-NF and BC-NC preferentially located on the surfaces of emulsion droplets in the presence of salt, as demonstrated by microscopy images. The presence of BC at the interface contributed to creating a more robust barrier against coalescence and Ostwald ripening, influencing droplet size and rheological properties. Higher BC concentrations (1 %) increased emulsion stability in the absence of salt, while at lower BC concentrations (0.5 %), salt concentration was determinant for the long-term stability of the emulsions. These findings provide valuable insights into the production of Pickering emulsions using nanocelluloses, highlighting the advantages of bio-based nanomaterials for applications in the food industry.

Sub-micron colloidosomes with tuneable cargo release prepared using epoxy-functional diblock copolymer nanoparticles

HypothesisPickering emulsions stabilized using epoxy-functional block copolymer nanoparticles should enable the formation of sub-micron colloidosomes that are stable with respect to Ostwald ripening and allow tuneable small-molecule cargo release. ExperimentsEpoxy-functional diblock copolymer nanoparticles of 24 ± 4 nm were prepared via reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization of methyl methacrylate (MMA) in n-dodecane. Sub-micron water-in-n-dodecane Pickering emulsions were prepared by high-pressure microfluidization. The epoxy groups were then ring-opened using 3-aminopropyltriethoxysilane (APTES) to prepare cross-linked colloidosomes. The colloidosomes survived removal of the aqueous phase using excess solvent. The silica shell thickness could be adjusted from 11 to 23 nm by varying the APTES/GlyMA molar ratio. The long-term stability of the colloidosomes was compared to precursor Pickering emulsions. Finally, the permeability of the colloidosomes was examined by encapsulation and release of a small molecule. FindingsThe Pickering emulsion droplet diameter was reduced from 700 to 200 nm by increasing the salt concentration within the aqueous phase. In the absence of salt, emulsion droplets were unstable due to Ostwald ripening. However, emulsions prepared with 0.5 M NaCl are stable for at least one month. The cross-linked colloidosomes demonstrated much more stable than the precursor sub-micron emulsions prepared without salt. The precursor nanoemulsions exhibited complete release (>99 %) of an encapsulated dye, while higher APTES/GlyMA ratios resulted in much lower dye release, yielding nearly impermeable silica capsules that retained around 95 % of the dye.

Stable and efficient CsPbI3 quantum-dot light-emitting diodes with strong quantum confinement

Even though lead halide perovskite has been demonstrated as a promising optoelectronic material for next-generation display applications, achieving high-efficiency and stable pure-red (620~635 nm) emission to cover the full visible wavelength is still challenging. Here, we report perovskite light-emitting diodes emitting pure-red light at 628 nm achieving high external quantum efficiencies of 26.04%. The performance is attributed to successful synthesizing strongly confined CsPbI3 quantum dots with good stability. The strong binding 2-naphthalene sulfonic acid ligands are introduced after nucleation to suppress Ostwald ripening, meanwhile, ammonium hexafluorophosphate exchanges long chain ligands and avoids regrowth by strong binding during the purification process. Both ligands enhance the charge transport ability of CsPbI3 quantum dots. The state-of-the-art synthesis of pure red CsPbI3 quantum dots achieves 94% high quantum efficiency, which can maintain over 80% after 50 days, providing a method for synthesizing stable strong confined perovskite quantum dots.

Capacitive attribute of vanadium-oxide embedded activated charcoal composite

This paper reports the study of hydrothermally synthesized coconut charcoal (EDL material) and vanadium-oxide (pseudocapacitive material) based composite material. SEM and TEM studies reveal the formation of embedded V2O5 nanorods (NRs) in the presence of activated charcoal (AC). Whereas, the formation of nanosheet (NSs) morphology of V2O5 was explained based on Ostwald ripening. Embedded V2O5 nanorods (NRs) in AC could be revealed in the form of the blurred dotted electron diffraction pattern of CS-AC/V2O5 NRs, indicating the presence of crystalline and amorphous phases at a point simultaneously in the composite. The VO, O–V‒O signatures observed in RAMAN and FTIR studies indicate the presence of the α phase of V2O5 NSs and NRs. An enhanced diffusion coefficient for CS-AC/V2O5 NRs compared to V2O5 NSs was observed; a decreased total resistance for CS-AC/V2O5 NRs compared to CS-AC was also noted. A characteristic of stable specific capacitance was observed at various current levels of this composite compared to the specific capacitances of coconut shell-based charcoal and vanadium oxide.

Stable SnAgCu solder joints reinforced by nickel-coated carbon fiber for electronic packaging

Today’s 3D electronic packaging is characterized by smaller size and higher functional density, which generally require multiple reflow cycles. However, due to the Ostwald ripening process of the interfacial intermetallic compound (IMC), the solder joint’s strength would decrease as the number of reflow cycles increases. To address this, we developed a novel composite solder by incorporating nickel-coated carbon fiber (Ni@CF) into the Sn–3.0Ag–0.5Cu (SAC305) solder connection. The study showed that Ni@CF effectively enhanced the stability and reliability of solder joints during multiple reflow processes. Compared with Ni@CF-free equivalents, Ni@CFs promoted the nucleation of interfacial IMC during the solid–liquid reaction and inhibited Ostwald ripening, leading to a refinement of the interfacial IMC grains. As a result, the interface was strengthened, and the shift of shear fracture to the brittle interface seen in the SAC305 solder joint with multiple reflows did not occur in the composite solder joint. Furthermore, carbon fiber strengthened the solder matrix through the load transfer and shear-off mechanisms, depending on its inclination angle with the shear plane. Consequently, the Ni@CFs-reinforced solder joints maintained a shear strength of over 42 MPa throughout ten reflow cycles, while the pristine SAC305 solder joint exhibited decreased shear strength to 33 MPa. This study provides new insights into composite solder joints’ stability and reinforcement characteristics when subjected to multiple reflows.

Micro-scale experimental investigations of CO2-WAG injection and Ostwald ripening analysis in carbonate rocks with different pore structures

Carbonate reservoirs are rich in hydrocarbon resources. However, carbonate reservoirs usually have strong pore structure heterogeneity, and thus it is necessary to understand the effect of heterogeneity on pore-scale fluid distributions during CO2 enhanced oil recover (CO2-EOR) process. We thus conducted water-alternating-gas (CO2-WAG) injection in the three carbonate samples with strong to weak heterogeneity. The 15 sets of images showed that the fractured-vuggy carbonate with the strongest heterogeneity had the highest additional oil recovery. CO2-WAG injection significantly changed the residual oil distribution, and further oil production can be achieved by increasing the number of CO2-WAG cycles. For CO2 geological storage, with the increase of carbonate heterogeneity, CO2 capillary-trapping capacity decreased, CO2 dissolution trapping potentiality decreased, but the stability of CO2 capillary trapping enhanced. These key parameters related to CO2 storage were described through the saturation of trapped gas, the types of trapped gas, and the surface area-volume relationship of CO2 clusters. For example, the higher amount of network gas is detrimental to the stability of CO2 capillary trapping because the network gas is easily displaced when the hydrodynamic force is enhanced. The specific surface area of CO2 cluster determines dissolution dynamics, and a higher specific surface area is beneficial for CO2 dissolution. Another interesting phenomenon - Ostwald ripening, is related to long-term CO2 transport. The CO2 concentration gradient in aquifer generates a vertically upward diffusive flux, causing CO2 remobilization. By calculating the height of the transition zone and the time to reach gravity-capillary pressure equilibrium, we found that as carbonate heterogeneity increased, the height of transition zone (the area where CO2 is trapped by capillary pressure) increased, while equilibrium time shortened. By comparing the results of previous gas-water two-phase flow experiments, we believe that the relationship between CO2 storage characteristics and carbonate heterogeneity summarized in this paper are universally applicable.

The Nanoparticle-induced Zener Pinning Effect on Strain-softening in a Cold-Worked Cu-Al2O3 Composite with 0.1 wt.% Al Content

The thermo-stability of microstructure during isothermal annealing at 900 °C and 1000 °C in a cold-worked Cu-Al2O3 composite with 0.1 wt.% Al content and its effect on resistance to softening were investigated in this paper. The results reveal that the microstructure following cold deformation consists of a Cu matrix with a refined grain size and high-density dislocations, accompanied by dispersed Al2O3 nanoparticles exhibiting an extremely low volume fraction. During isothermal annealing at 900 °C, the Al2O3 nanoparticles can strongly restrict the migration of the dislocations and suppress the recrystallization of the fine-grained Cu matrix by the Zener pinning effect. Furthermore, the presence of pinned dislocations facilitates the formation of sub-grain boundaries comprising high-density dislocations. Consequently, the Cu-Al2O3 composite with 0.1 wt.% Al content exhibits remarkable thermo-stability in its microstructure due to the incorporation of Al2O3 nanoparticles, resulting in a significantly elevated softening temperature of up to 1000 °C and thereby demonstrating excellent resistance against softening. However, the observed phenomenon of softening after isothermal annealing at 1000 °C for 5 hours can be attributed to extensive recrystallization growth that promotes twin boundary formation, primarily caused by the weakening Zener pinning effect resulting from Oswald ripening of Al2O3 and rod-like Al2O3 formation.

Improved understanding of carbon nanotube growth via autonomous jump regression targeting of catalyst activity

Catalyst control is critical to carbon nanotube (CNT) growth and scaling their production. In supported catalyst CNT growth, the reduction of an oxidized metal catalyst enables growth, but its reduction also initiates catalyst deactivation via Ostwald ripening. Here, we conducted autonomous experiments guided by a hypothesis-driven machine learning planner based on a novel jump regression algorithm. This planning algorithm iteratively models the experimental response surface to identify discontinuities, such as those created by a material phase change, and targets further experiments to improve the fit and reduce uncertainty in its model. This approach led us to identify conditions that resulted in the greatest CNT yields as a function of the driving forces of catalyst reduction in a fraction of the time and cost of conventional experimental approaches. By varying temperature and the reducing potential of the growth atmosphere, we identified discontinuous jumps in CNT growth for two thicknesses of an iron catalyst, resulting in largest observed yields in narrow and distinct regions of thermodynamic space where we believe the reduced catalyst is in equilibrium with its oxide. At these jumps, we also observed the longest growth lifetimes and a greater degree of diameter control. We believe that conducting CNT growth at these conditions optimizes catalyst activity by inhibiting Ostwald ripening-induced deactivation, thereby keeping catalyst nanoparticles smaller and more numerous. This work establishes a thermodynamic framework for a generalized understanding of metal catalysts in CNT growth, and demonstrates the capability of iterative, hypothesis-driven autonomous experimentation to greatly accelerate materials science.

Wetting Effect Induced Depletion and Adsorption Layers: Diffuse Interface Perspective.

When a multi-component fluid contacts arigid solid substrate, the van der Waals interaction between fluids and substrate induces a depletion/adsorption layer depending on the intrinsic wettability of the system. In this study, we investigate the depletion/adsorption behaviors of A-B fluid system. We derive analytical expressions for the equilibrium layer thickness and the equilibrium composition distribution near the solid wall, based on the theories of de Gennes and Cahn. Our derivation is verified through phase-field simulations, wherein the substrate wettability, A-B interfacial tension, and temperature are systematically varied. Our findings underscore two pivotal mechanisms governing the equilibrium layer thickness. With an increase in the wall free energy, the substrate wettability dominates the layer formation, aligning with de Gennes' theory. When the interfacial tension increases, or temperature rises, the layer formation is determined by the A-B interactions, obeying Cahn's theory. Additionally, we extend our study to non-equilibrium systems where the initial composition deviates from the binodal line. Notably, macroscopic depletion/adsorption layers form on the substrate, which are significantly thicker than the equilibrium microscopic layers. This macroscopic layer formation is attributed to the interplay of phase separation and Ostwald ripening. We anticipate that the present finding could deepen our knowledge on the depletion/adsorption behaviors of immiscible fluids.

Suppression of helium migration in arc-melted and 3D-printed CoCrFeMnNi high entropy alloy

We compare the evolution and migration of helium cavities in 3D-printed and arc-melted CoCrFeMnNi high entropy alloys (HEAs), and 304 stainless steel (SS), using transmission electron microscopy (TEM). The materials are subjected to Ni and He sequential implantation as well as subsequent thermal annealing. After irradiation at room temperature, all samples initially display similar He cavity sizes. Annealing up to 673 K has a minimal impact on cavity size. However, annealing at 873 K leads to significant cavity growth. Both HEA materials exhibit larger average cavity sizes compared to 304 SS, while a higher proportion of small cavities is found in the 304 SS. This indicates that Ostwald Ripening is more prevalent in 304 SS, confirmed by in-situ thermal annealing in TEM. Depth distribution analysis reveals distinct cavity belts after annealing: from the narrowest in 3D printed HEA to the broadest belts in 304 SS. These results indicate that the He concentration at the peak of irradiation damage decreases in the same order. We suggest that the long-range migration of He atoms is limited in both the Cantor and 3D-printed Cantor HEAs, potentially due to the complex diffusion paths of the He atoms.

Thermal Stability of High-Entropy Alloy Nanoparticles Evaluated by In Situ TEM Observations.

High-entropy alloy (HEA) nanoparticles (NPs) have attracted attention in several fields because of their fascinating properties. The high mechanical strength, good thermal stability, and superior corrosion resistance of HEAs, which are derived from their high configurational entropy, are attractive features. Herein, we investigated the thermal stability of FeCoNiCuPd HEA NPs on reduced graphene oxide via in situ transmission electron microscopy observations at elevated temperatures. The HEA NPs maintained their structure, size, and composition at 700 °C, and their size gradually decreased accompanied by the preferential sublimation of Cu. On the contrary, the deterioration of the monometallic Pd NPs begins at temperatures greater than 700 °C according to Ostwald ripening, which involves the migration of adatoms or mobile molecular species. Theoretical calculations revealed that the detachment of adatoms from clusters (i.e., the first step of Ostwald ripening) was suppressed in the case of HEA NPs because of the high-configuration-entropy effect.