Sluggish Nucleation Research Articles

Eutectic Solidification Morphologies in Rapidly Solidified Hypereutectic Sn–Ag Solder Alloy

The effect of rapid solidification upon hypereutectic Sn–Ag solder alloy has been investigated using a 6.5 m drop tube. Powder sizes ranging from > 850 to < 38 μm were produced, with equivalent cooling rates of 250 to 14,800 K s−1 for 850 and 38 μm droplets, respectively. At all cooling rates investigated, dendritic β-Sn was observed as the primary solidification phase, not proeutectic Ag3Sn as predicted by the phase diagram. The volume fraction of interdendritic eutectic was observed to decrease with increasing cooling rate, with the Ag concentration in the residual interdendritic liquid estimated at 12.5–15 wt pct Ag, far in excess of the eutectic concentration of 3.8 wt pct. Much of the Ag3Sn observed within the eutectic had a blocky, divorced eutectic appearance. A model is proposed which can explain these observations in terms of sluggish nucleation of the Ag3Sn intermetallic, coupled with a metastable phase diagram that permits significant supersaturation of Ag at modest undercooling.

Platinum Electrocatalyst Promoting Redox Kinetics of Li2S and Regulating Li2S Nucleation for Lithium-Sulfur Batteries.

The development of lithium-sulfur batteries (LSBs) is impeded by the shuttle effect of polysulfides (LiPSs) and the sluggish nucleation of Li2S. To address these challenges, incorporating electrocatalysts into sulfur host materials represents an effective strategy for promoting polysulfide conversion, in tandem with the rational design of multifunctional sulfur host materials. In this study, Pt nanoparticles are integrated into biomass-derived carbon materials by solution deposition method. Pt, as an electrocatalyst, not only enhances the electrical conductivity of sulfur cathodes and effectively immobilizes LiPSs but also catalyzes the redox reactions of sulfur species bidirectionally. Additionally, Pt helps regulate the 3D deposition and growth of Li2S while reducing the reaction energy barrier. Consequently, this accelerates the conversion of LiPSs in LSBs. Furthermore, the catalytic ability of Pt for the redox reactions of sulfur species, along with its influence on the 3D deposition and growth of Li2S, is elucidated using electrochemical kinetic analyses and classical models of electrochemical deposition. The cathodes exhibit a high initial specific capacity of 1019.1mAhg-1 at 1C and a low decay rate of 0.045% over 1500 cycles. This study presents an effective strategy to regulate Li2S nucleation and enhance the kinetics of polysulfide conversion in LSBs.

Niobium Diboride Nanoparticles Accelerating Polysulfide Conversion and Directing Li2S Nucleation Enabled High Areal Capacity Lithium-Sulfur Batteries.

The shuttle effect of polysulfides and Li2S sluggish nucleation are the major problems hampering the further development of lithium-sulfur batteries. The reasonable design for sulfur host materials with catalytic function has been an effective strategy for promoting polysulfide conversion. Compared with other types of transition metal compounds, transition metal borides with high conductivity and catalytic capability are more suitable as sulfur host materials. Herein, a niobium diboride (NbB2) nanoparticle with abundant and high-efficiency catalytic sites has been synthesized by facile solid-phase reaction. The NbB2 with both high conductivity and catalytic nature could regulate 3D-nucleation and growth of Li2S, decrease the reaction energy barrier, and accelerate the transformation of polysulfides. Thus, the NbB2 cathode could retain a high capacity of 1014 mAh g-1 after 100 cycles. In addition, the high initial specific capacities of 703/609 mAh g-1 are also achieved at 5 C/10 C and could run for 1000/1300 cycles within a low decay rate of 0.057%/0.051%. Even with a high sulfur loading up to 16.5 mg cm-2, an initial areal capacity of 17 mAh cm-2 could be achieved at 0.1 C. This work demonstrates a successful method for enhancing the kinetics of polysulfide conversion and directing Li2S nucleation.

(Invited) In-Situ Microscopy and Spectroscopy Probing of Li Dendrite Nucleation and Growth

Lithium (Li) metal has very low standard electrochemical redox potential and very high theoretical specific capacity, making it an ultimate anode material for rechargeable batteries. However, its application has been impeded by the formation of Li whiskers, which not only considerably consumes electrolyte and active Li, but also may lead to short-circuit of the battery. Tackling of these obstacles is limited by the elusive understanding on the intrinsic formation mechanisms of the Li whiskers and their growth behavior under the constraints from the separator. Here, by coupling an atomic force microscopy cantilever into a solid open-cell setup in environmental transmission electron microscopy, we directly captured the nucleation and growth behavior of Li whiskers under elastic constraint that mimics the effect of a separator. We show that Li deposition is initiated by a sluggish nucleation of a single crystalline Li particle with no preferential growth directions. Dramatically, we discovered that carbonate species in the initial solid electrolyte interphase that is very adjacent to the developing Li metal plays a decisive role in the subsequent formation of Li with a whisker morphology. Characteristically, the growing Li whisker, depending on both intrinsic and extrinsic conditions, can yield, buckle, kink, or stop (axial) growth under elastic constraint from the separator. These findings reveal the intrinsic cause and give a clear process on the formation and behavior of dendritic Li under stress, providing the much-needed insights for solving the Li whisker formation from the root cause rather than as currently containing it, and therefore potentially leading to the safe operation of Li metal anode in batteries.

Molecular dynamics simulations of radiation damage generation and dislocation loop evolution in Ni and binary Ni-based alloys

As a great potential structural-material candidate for nuclear power applications, single-phase concentrated solid-solution alloys containing different elements have outstanding mechanical properties. In order to explore the effects of their elemental compositions on their radiation tolerance properties, in this work, radiation-induced defect production, as well as defect cluster and dislocation loop evolution, are investigated for equiatomic NiCo and NiFe alloys, and pure Ni, using molecular dynamics simulations. We find that the binary alloys are more radiation-resistant than pure Ni, while the NiFe binary alloy has the best radiation tolerance due to a higher recombination of defects and a lower number of surviving Frenkel pairs after cascade, compared to NiCo and pure Ni. Small defect clusters appearing in the three materials exhibit different migration behaviors, which migrate in a simple one-dimensional mode in pure Ni, but randomly change directions in the binary alloys; this behavior in the latter is thought to enhance the recombination of defects. Vacancy-type stacking fault tetrahedra and mixed interstitial dislocation loops with different types of dislocation segments are also observed. Interstitial dislocation loops generated in the NiCo and NiFe alloys show delayed and sluggish nucleation and evolution processes, which may lead to a higher probability of defect recombination during their evolution. Moreover, the formation of mixed dislocation loops is also discussed.

Origin of lithium whisker formation and growth under stress.

Lithium metal has the lowest standard electrochemical redox potential and very high theoretical specific capacity, making it the ultimate anode material for rechargeable batteries. However, its application in batteries has been impeded by the formation of Li whiskers, which consume the electrolyte, deplete active Li and may lead to short-circuit of the battery. Tackling these issues successfully is dependent on acquiring sufficient understanding of the formation mechanisms and growth of Li whiskers under the mechanical constraints of a separator. Here, by coupling an atomic force microscopy cantilever into a solid open-cell set-up in environmental transmission electron microscopy, we directly capture the nucleation and growth behaviour of Li whiskers under elastic constraint. We show that Li deposition is initiated by a sluggish nucleation of a single crystalline Li particle, with no preferential growth directions. Remarkably, we find that retarded surface transport of Li plays a decisive role in the subsequent deposition morphology. We then explore the validity of these findings in practical cells using a series of carbonate-poisoned ether-based electrolytes. Finally, we show that Li whiskers can yield, buckle, kink or stop growing under certain elastic constraints.

Alkali feldspar dissolution in response to injection of carbon dioxide

The dissolution of alkali feldspar in CO2-saturated aqueous solutions has been investigated in a series of laboratory experiments in the temperature range 22–200 °C and at CO2-pressures from 0.3 to 20 MPa. To mimic the situation when CO2 is injected into feldspar-containing reservoirs, the unsaturated aqueous solutions were allowed to react with the solid phases before CO2 was injected. In the higher end of the temperature range, CO2-injection lead to precipitation of aluminium hydroxide and kaolinite. Thus, while alkalis were released at rates comparable to other studies at similar temperature and pH ranges, Al was lost from the fluid rather than gained. Based on fluid chemistry, precipitation of Al-Si phases occurred down to at least 100 °C, but was delayed after the injection. This may be because the fluids were not fully saturated with feldspar at injection or may reflect sluggish nucleation. In either case, the experiments show that aluminous precipitates are likely to form in natural feldspathic reservoirs as a consequence of CO2 injection. Kaolinite precipitation proceeds slower than feldspar dissolution, leading to kaolinite-supersaturated solutions. This implies that precipitation kinetics may control the extent of feldspar dissolution in a sandstone reservoir. Plotting the measured dissolution rates against inverse temperature has revealed changes in slope at around 100 °C, indicating that different mechanisms dominate the dissolution above and below this temperature.

\u221260\u2009\xb0C solution synthesis of atomically dispersed cobalt electrocatalyst with superior performance

Temperature can govern morphologies, structures and properties of products from synthesis in solution. A reaction in solution at low temperature may result in different materials than at higher temperature due to thermodynamics and kinetics of nuclei formation. Here, we report a low-temperature solution synthesis of atomically dispersed cobalt in a catalyst with superior performance. By using a water/alcohol mixed solvent with low freezing point, liquid-phase reduction of a cobalt precursor with hydrazine hydrate is realized at −60 °C. A higher energy barrier and a sluggish nucleation rate are achieved to suppress nuclei formation; thus atomically dispersed cobalt is successfully obtained in a catalyst for oxygen reduction with electrochemical performance superior to that of a Pt/C catalyst. Furthermore, the atomically dispersed cobalt catalyst is applied in a microbial fuel cell to obtain a high maximum power density (2550 ± 60 mW m−2) and no current drop upon operation for 820 h.

Enhancement of hardening and thermal resistance of Mg–Sn-based alloys by addition of Cu and Al

Mg–Sn-based alloys are considered as a promising precipitation-hardening system for applications at elevated temperatures, but the hardening effect is not satisfactory owing to sluggish nucleation and rapid coarsening of the major Mg2Sn lath precipitates. In this study, Cu and Al are added to a Mg–6Sn–1Mn base alloy. The age-hardening response and the microstructures of these modified alloys have been investigated and are compared to that of the base alloy. The additional elements are found to bring several beneficial effects to the alloys for applications at elevated temperatures. Firstly, a eutectic structure consisting of strong intermetallic phases, i.e. Mg2Cu in the Mg–6Sn–1Mn–2Cu alloy and Al0.93Cu1.07Mg in the Mg–6Sn–1Mn–2Cu–2Al alloy, remains stable along the grain boundaries after solution and ageing heat treatments. Secondly, the precipitate density has been increased significantly and the precipitate size has been refined remarkably during ageing at 200 °C. Moreover, the growth of the precipitates is inhibited remarkably during the over-ageing period. Therefore, the age-hardening response and over-ageing resistance are notably improved.

Ultrafine Grained Duplex Structure Developed by ART-annealing in Cold Rolled Medium-Mn Steels

The microstructural evolutions of the cold rolled Fe-0.1C-5Mn steel during intercritical annealing were examined using combined advanced techniques. It was demonstrated that intercritical annealing results in an ultrafine granular ferrite and austenite duplex structure in cold rolled 0.1C-5Mn steel. The strong partitioning of manganese and carbon elements from ferrite to austenite was found during intercritical annealing by scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD). Strong effects of boundary characters on the austenite formation were indicated by austenite fast nucleation and growth in the high angle boundaries but sluggish nucleation and growth in the low angle boundaries. The ultrafine grained duplex structure in 0.1C-5Mn was resulted from the the sluggish Mn-diffusion and the extra high Gibbs free energy of ferrite phase. Based on the analysis of the microstructure evolution, it was pointed out that the intercritical annealing of the medium-Mn steels could be applied to fabricate an ultrafine duplex grained microstructure, which would be a promising approach to develop the 3rd generation austomobile steels with excellent combination of strength and ductility.

Garnet zonation in metapelitic schists from the Eclogite Zone, Tauern Window, Austria: comparison of observed and calculated profiles

Three quartzitic metapelites with garnet-chloritoid-kyanite assemblage from the Eclogite Zone, Tauern Window, Austria have been studied based on pseudosections in the KNCFMMnASTH and partly KNCFMMnASTHO system compared with measured and calculated garnet zonations along three P-T paths. Deduced garnet core growth is in the range 502–521 °C, 20.2–21.4 kbar, corresponding to overstepping the garnet-in reaction by ~25–100 °C for P-T paths 1, 2 and ~72–133 °C for P-T path 3. The peak assemblage garnet-chloritoid-kyanite-phengite-paragonite-rutile-quartz in sample A is stable in a narrow maximum ~10 °C band from ~598 °C/14 kbar to ~570 °C/24.9 kbar. In sample B and C this stability is much more restricted with ~ 2 °C width from ~581 °C/22.3 kbar to ~572 °C/24.5 kbar and ~4 °C/0.7 kbar width at ~570 °C/24.8 kbar. Temperature differences between measured and calculated pyrope and grossular isopleths are generally in the range from 0 to 20 °C, however larger values are sometimes obtained. The proposed P-T paths reach peak values around 570–575 °C/24.6 kbar. Comparison of measured and calculated garnet zonation suggests a better accordance for unfractionated than for fractionated models. Several factors could be responsible for this and the partly large overstepping values, e.g . insufficient thermodynamic data, or non-equilibrium reactions due to sluggish nucleation or breakdown reactions and later garnet re-equilibration.

Jadeite formation in shocked ordinary chondrites

Albitic feldspar in shocked ordinary chondrites (Yamato 791384 L6 and Yamato 75100 H6) and albite recovered from static high-pressure and high-temperature synthetic experiments (Kubo et al., 2010) were investigated with a transmission electron microscope (TEM) subsequent to a conventional micro-Raman spectroscopy analysis to clarify albite dissociation reaction under high-pressure and high-temperature condition. When jadeite forms from albite, SiO2 phase as a residual phase of albite dissociation reaction should accompany jadeite from the stoichiometry. However, albitic feldspar in and adjacent to shock-melt veins of the shocked chondrites dissociates into jadeite+residual amorphous (or poorly-crystallized) material having varied chemical compositions between jadeite and SiO2 phase. TEM observations of albitic feldspar in the shocked chondrites and albite recovered from the static high-pressure and high-temperature synthetic experiments show that jadeite crystallization is initiated by grain refinement of albite (or albitic feldspar). Nucleation occurs along grain-boundaries or at triple-junctions of the fine-grained albite crystal assemblage. Jadeite crystal starts to grow from the nucleus through grain-boundary diffusion. Considering pressure condition recorded in the shock-melt veins of the shocked chondrites, stishovite is the most likely as a residual SiO2 phase accompanying jadeite. High-pressure and high-temperature condition induced by a dynamic event is very short. Stishovite would be hardy formed through a dynamic event due to sluggish nucleation rate of stishovite compared with that of jadeite, thus leading to induce heterogeneous and incomplete albite dissociation reaction; albite dissociates into jadeite+residual amorphous material.

Influence of amorphous degree on crystallization kinetics of Zr 60Al 15Ni 25 bulk metallic glass

The microstructure of as-cast Zr 60Al 15Ni 25 bulk metallic glass was investigated by high-resolution transmission electron microscopy. It is found that there exist numerous short-range order regions (SRORs) in the metallic glass though it is identified to be amorphous by X-ray diffraction method. Furthermore, the amorphous degree shows a close correlation with the microstructure of corresponding mother ingot. The crystallization kinetics was investigated by differential scanning calorimetry under isochronal and isothermal conditions. The results show that the crystallization is triggered by the growth of the pre-existing SRORs and the growth is three-dimension diffusion-controlled. The amorphous degree of Zr 60Al 15Ni 25 bulk metallic glass considerably influences its crystallization kinetics, namely, the more homogeneous distribution of atoms results in a more sluggish nucleation behavior.

Constraints on anthophyllite formation in thermally metamorphosed peridotites from southwestern Japan

Anthophyllite or another species of Mg-amphibole commonly occurs in an intervening zone between the higher grade orthopyroxene zone and lower grade talc zone in progressively metamorphosed peridotites. However, the anthophyllite zone is absent in some of the thermally metamorphosed peridotite complexes in SW Japan despite the existence of the other zones. A comparative study presented here reveals similarities in rock composition and metamorphic pressure–temperature conditions at high-grade zones between the metaperidotite complexes, and differences in the following respects. The metaperidotite complex that contains an anthophyllite zone has less abundant magnetite and olivine that is more homogeneous than the complex where the anthophyllite zone is absent. It is likely that the degree of cation diffusion in olivine crystals depends on duration of heat retention in metaperidotites during thermal metamorphism, which is supported by the variation in mineralogy of intrusive rocks and pelitic hornfelses surrounding the metaperidotites, and by calculations based on a simplified model of thermal conduction. The long duration of heat retention looks to be a necessary condition for the formation of anthophyllite crystals, which have a sluggish nucleation rate. In addition, the circulation of reducing fluids during prolonged metamorphism likely promoted the decomposition of magnetite and the growth of anthophyllite, into which iron is preferentially distributed. This study cautions about kinetic controls and redox conditions for anthophyllite formation in metaperidotites.

Area-selectively sputtering the RuO 2 nanorods array

The RuO 2 nanorods array is grown selectively on the SiO 2-patterned sapphire (SA) wafers using reactive sputtering. The area-selectivity is attributed to an early nucleation of RuO 2 and its fast surface coverage on SA (1 0 0) and (0 1 2), in contrast to the sluggish nucleation on glassy SiO 2 in the initial sputtering period. The growth domain is explored by investigating the temperature windows at sputtering power 40, 50, and 60 W. The low-temperature bound is limited by the mobility of precursors on SiO 2 surface, which enables the precursors to depart before aggregating into a large size to smear the non-growth region. The high-temperature bound is set by the horizontal growth which enlarges the rod width and deteriorates its one-dimensional feature. The temperature window shrinks with increasing sputtering power. The X-ray photoelectron spectra indicate the as-sputtered rod surface is ruthenium rich. The X-ray diffraction analysis shows that RuO 2 growth on SA (1 0 0) and (0 1 2) follows the epitaxial relations between RuO 2 and SA crystals.

Experimental solidification of anhydrous latitic and trachytic melts at different cooling rates: The role of nucleation kinetics

Two sets of cooling experiments were run at atmospheric conditions for two anhydrous starting latitic and trachytic melts: 1) five cooling rates (25, 12.5, 3, 0.5, and 0.125 °C/min) between 1300° and 800 °C, and 2) a 0.5 °C/min cooling rate from 1300 °C with quench temperatures at 1200°, 1100°, 1000° and 900 °C. Trachytic run-products are invariably glassy. Nucleation is also suppressed in the latitic run-products at the three highest cooling rates. Conversely, in the 0.5 and 0.125 °C/min runs, latites have a crystal content of ∼ 90 vol.%. The phases are: plagioclase, clinopyroxene, glass and iron-bearing oxide (in order of abundance). The variable quench temperatures, investigated by coupling experiments with Pt wire and Pt capsule sample containers in set 2, again did not produce crystallization of trachyte, whereas latitic samples are characterized by ∼ 10 vol.% of oxides, pyroxenes and plagioclase (in order of appearance), at temperature < 1000 °C. Effects of (preferential) heterogeneous nucleation on sample holders, of superheating degree, and chemical species loss during cooling are absent for both melt compositions. The difference of solidification paths between these two silicate melts can be ascribed only to their small chemical differences. In comparison with calculated equilibrium conditions all the experimental latitic and trachytic run-products revealed strong kinetic effects, interpretable in the light of the nucleation theory. The glass-forming ability (GFA) of trachyte is higher, whereas their critical cooling rate ( Rc) is lower (< 0.125 °C/min), in comparison to latitic melts ( Rc > 0.5 °C/min). The experimental results carried out in this study can be applied to lava flows and domes; trachytic lavas are able to flow for longer period with respect to latitic ones in a metastable condition. Glass-rich terrestrial lavas, i.e. obsidians, can be the result of sluggish nucleation kinetics due to the relative high polymerisation of evolved silicate melts.

Metastability of sillimanite relative to corundum and quartz in the kyanite stability field: Competition between stable and metastable reactions

The formation of sillimanite, under metastable conditions, relative to corundum and quartz has been defined experimentally, approximately 700 to 800 MPa inside the kyanite stability field thereby allowing for the approximate location of the metastable Sil = Cnd + Qtz equilibrium to be outlined in P-T space from 600 to 800 °C. Experiments involved using a NaCl assembly with a graphite furnace in a two-piston-cylinder apparatus. The thermocouple tip was in direct contact with the flat-lying, folded Pt capsule thereby minimizing thermal gradients to <5 °C. Charges consisted of equimolar amounts of gem-quality sillimanite, corundum, and quartz, plus H2O as a flux, placed in a 1.3 cm long Pt capsule that was arc-welded shut and folded. During the course of the experiment, the metastability of the assemblage Sil-Cnd-Qtz implies that Sil ↔ Cnd + Qtz is, at some point, in direct competition with Cnd + Qtz → Ky and Sil → Ky. Early during the experiment it may be assumed that a steady state between dissolution and growth rates is established. However, due to the sluggish nucleation of kyanite, there is a P-T dependent induction period during which Cnd + Qtz → Sil is the controlling reaction. Once kyanite does appear, the reaction proceeds very fast to kyanite via reactions Cnd + Qtz → Ky and Sil → Ky. The kyanite surface area is probably a major factor in controlling the overall reaction rates. Under constant P and T, the system evolves from metastable sillimanite formation to sillimanite consumption, which is only dependent on the kyanite surface area. Similar competition between stable and metastable reactions could occur during contact metamorphism where metastable mineral growth is observed. The relative sluggishness of all three reactions under relatively dry conditions could help to explain the persistence of metastable corundum + quartz ± Al2SiO5 assemblages in nature.

Deformation-enhanced reaction in experimentally deformed plagioclase-olivine aggregates

The effects of deformation on the kinetics of the net-transfer reaction anorthite + forsterite → cpx + opx + spinel ± gt were studied using static and shear deformation experiments. Experiments were performed on dry anorthite-olivine (An92–Fo93) samples at 900°C and pressures between 1,000 and 1,600 MPa in a Griggs apparatus. Deformed (‘non-hydrostatic’) and undeformed (‘static’) samples are compared in terms of phase petrology, reaction rate and reaction mechanisms. Anorthite + olivine reactions are diffusion-controlled as seen from reaction rim structures. In undeformed samples, delayed reaction onset and low reaction rates demonstrate sluggish nucleation of reaction products and slow rates of diffusion at dry conditions, even at 700–900 MPa confining pressure overstepping. The reaction rate is enhanced in deformed An–Fo samples. The higher rate is mainly attributed to a combination of high stresses and viscous deformation processes of the reactants and products, which cause an increase in the nucleation rate of products. The results imply that viscous deformation processes alone can be responsible for the initiation and localisation of metamorphic reactions in dry rocks in the absence of fluid infiltration.

Glass formation and sluggish nucleation: Growth in ternary eutectic Co–Hf–B system

Four rapidly quenched (RQ) ribbons of Co–Hf–B alloys with the ternary eutectic compositions were obtained by melt-spinning. The thermal stability and glass forming ability (GFA) were studied using high-temperature differential scanning calorimetry (DSC) measurements. Very high GFA was found for all the alloys studied, which are characterized by high values (above 0.64) of the reduced crystallization temperature ( T rx = T x/ T m). The supercooled liquid region (Δ T x = T x − T g = 45 K) was found for Co 66Hf 6.5B 27.5 amorphous alloy with equilibrium microstructure composed of three intermetallic compounds (Co 2B, Co 21Hf 2B 6 and Co 3HfB 2). The high GFA was explained by the sluggish nucleation and slow growth of the complex structure intermetallic compounds in the ternary Co–Hf–B system. The Hf presence in the alloys studied plays an important role due to the slow diffusivity of relatively large atoms of this element.

Effect of Si and P on the Formation and Crystallization of Ti25Hf50Ni25 Metallic Glasses

ABSTRACTTi255Hf50Ni25 metallic glasses, prepared by rapid quenching, are strongly metastable with a 65°C separation between the glass transition temperature, Tg = 335°C, and the onset temperature for primary crystallization. The deep metastability of the glass is likely due to sluggish nucleation and growth kinetics, limited by the Hf diffusion. The glass crystallizes to a nano-scale microstructure consisting of an icosahedrally symmetric ordered phase. This phase is metastable and transforms to a stable Ti2Ni-type phase with annealing at higher temperatures. The primary crystallization to a metastable icosahedrally-ordered phase suggests that the local structure of the glass contains a high degree of icosahedral short-range order. Here, glass formation and crystallization were studied in alloys containing 2 at.% of Si and P.