Formation Of Dendritic Structures Research Articles

Dissimilar Cladding of Ni–Cr–Mo Superalloy over 316L Austenitic Stainless Steel: Morphologies and Mechanical Properties

The solid solution strengthened Inconel 625, a Ni-based alloy is known for its excellent strength and good corrosion resistance at extreme environments used in thermal plants, boiler tubes, petrochemical industry and power plant. The presence of Cr content (~ 20 wt%) along with Mo-rich, Nb and Fe makes Ni–Cr–Mo–Nb austenitic alloy called as Inconel 625 to achieve excellent corrosion resistance property. Using cold metal arc transfer (CMT) cladding, the metallurgical, mechanical and corrosion properties of Inconel 625 on 316L is evaluated. The process parameters selected includes welding current, torch angle and travel speed with a constant voltage. From the results of microstructural and EDS inferences, the formation of cellular dendritic structure with secondary phases like Laves phase, complex nitrides along with the interdendritic segregation of Mo and Nb as well as microsegregation of Cr, Ni and Fe. In case of Ni–Cr–Mo alloy, Ni and Cr contribute to resistance to corrosion in NaCl environments. The formation of Cr2O3 and the passivation action of the clad zone is due to the presence of Cr. The solid solution effect in Ni–Cr matrix is contributed by the presence of Nb and Mo. Apart from that the strengthening action happens due to the precipitation of Ni3 (Al, Ti, Nb) commonly known as γ′, γ″ and MC carbides confirmed through XRD. Uni-axial tensile tests and Vickers-micro hardness indentation tests were performed on Inconel 625 cladded over 316L. Based on the fractographic results fatigue striations, tear rigdes with river markings, dimples with fibrous structure and cleavages are observed. Unlike other studies, unique type of cuboidal precipitates are seen, which is due to the presence of Ti, which form carbonitrides containing Ti, which are further characterised as NbC. The potentiodynamic polarisation tests is performed on 3.5% NaCl solution. The results suggest that Ni–Cr–Mo alloy protects the substrate from corrosion.

Filtration Permeability of Dendritic Structure in Condition of Diffusion-Capillary Coalescence of Secondary Side Branches

The problem state of computer analysis of shrinkage defects in castings is analysed based on a review of theoretical and experimental studies the filtration permeability of solidifying alloys. It is shown that the use of the dimensionless permeability coefficient and its modification by introducing various corrections to the Karman-Kozeni equation, obtained for the stationary morphology of non-intersecting filtration channels, is inapplicable for the conditions of continuous change of their geometry during formation of dendrite structure. A computer model of the permeability for the mesoscale ensemble of secondary dendritic branches under the conditions of their diffusion-capillary coalescence is developed. Based on the thermodynamic apparatus and solidification modeling the influence of composition of Al-Cu-Mg alloys and heat removal velocity on the permeability coefficient under the evolution of the dendritic structure is analysed.

Controlling Electrochemical Lithium Deposition and Sulfur Reduction Mechanism through Liquid Electrolytes

Lithium metal anode has been regarded as the "Holy Grail" of next-generation battery technologies. In order to stabilize the electrodeposited Li metal for safe and high energy batteries, highly concentrated electrolytes (solvate electrolytes) have been proposed to suppress the formation of Li dendritic structure and polysulfide dissolution in lithium-sulfur (Li-S) batteries. (1-5) In this talk, we use in situ transmission X-ray microscopy (TXM) to study the effect of solvate electrolyte on Li plating/stripping process. In situ TXM images show that electrodeposited Li particles with uniform density are formed in solvate electrolyte during initial plating process. The effect of solvate electrolyte on the mechanism of Li growth is studied in detail. Additionally, in situ spectroscopy including Raman and X-ray spectroscopy (X-ray diffraction and X-ray absorption spectroscopy) are used to investigate sulfur reaction mechanism and the interaction between polysulfide and solvate electrolyte. We found that the sulfur species formed in the solvate electrolyte are different from the sulfur species formed in conventional DOL/DME electrolyte. These results suggest that solvate electrolyte changes both polysulfide solubility and sulfur reaction mechanism. We next propose different solvate electrolytes with low polysulfide solubility and high stability toward Li metal to enhance the capacity retention of Li-S batteries.

Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 2 – corrosion

AbstractIn pure magnesium and aluminum-containing magnesium alloys, the microstructure also plays a role in the corrosion properties. In Part 1, the grain sizes, secondary dendrite arm spacings (SDAS) and precipitates of β phase were determined by casting samples with 0, 3, 6, 9 and 12 % aluminum (all compositions in mass percentage) at different cooling rates. These samples were tested for corrosion properties by immersion and salt spray tests. The modeling of the corrosion process enables establishing a mathematical link between the microstructure and corrosion properties of an alloy. The results show an increase in the corrosion rate with increasing aluminum contents and the cooling rate. The precipitations at the grain boundaries have a relevant impact on corrosion properties of the magnesium–aluminum alloys. A random comparison using the salt spray test tends to confirm the results.

Phase-Field Microstructure Solidification of Al–2 wt% Si Alloys

In this work, we develop one- and two-dimensional phase-field simulations to approximate dendritic growth of a binary Al–2 wt% Si alloy. Simulations are performed for both isothermal as well as directional solidification. Anisotropic interface energies are included with fourfold symmetries, and the dilute alloy assumption is imposed. The isothermal results confirm the decrease in the maximum concentration for larger interface velocities as well as reveal the presence of parabolic, dendrite tips evolving along directions of maximum interface energy. The directional solidification results further confirm the formation of distinctive secondary dendritic arm structures that evolve at regular intervals along the unstable solid/liquid interface.

Preparation and characterization of porous iron oxide dendrites for photocatalytic application

In the present work, the role of the nonionic polymeric surfactant, pluronic P123 on the formation of porous iron oxide dendrite structures are explored. The iron oxide samples were prepared at different hydrothermal treatment time of 6, 12, 24 and 48 h using potassium ferricyanide as the raw material in presence and in absence of surfactant. The samples were characterized by XRD, FTIR, SEM, HRTEM, DRS, PL, BET-BJH and XPS analyses. The iron oxide dendrites prepared using surfactant by the hydrothermal treatment time of 12 h at 180 °C (PK12), show high photocatalytic degradation ability of 87 % towards methylene blue under visible light for a less amount of catalyst loading of 10 mg. Whereas the iron oxide prepared in absence of surfactant under similar conditions (K12) shows the incomplete phase formation with mixed dendrite and bulk cubic structures, exhibiting only 47 % of degradation towards methylene blue for the similar amount of catalyst loading. The sample PK12 exhibits a degradation rate constant value of 4.25 × 10−4 s−1 which was 2.3 times higher than the sample K12 with a rate constant value of 1.88 × 10−4 s−1. The enhanced catalytic performance of the sample PK12 prepared using surfactant are attributed to its bimodal porous nature, stronger visible light absorbance, and lower recombination of photo-generated electron-hole pairs. XPS results substantiates that significant oxygen vacancies in as prepared photocatalyst, facilitates the superior photocatalytic performance. The relative peak area ratio between Olattice/Ovac was found to be lower in PK12 (0.98) than in K12 (1.82). This indicates the sample PK12 have more oxygen vacancies than the sample K12. After the photocatalytic degradation, iron oxide was retrieved by simple sedimentation process and reused for four times without any considerable decrease in efficiency, proving its economic viability for large scale applications. Magnetic studies shows a coercivity of 1582 Oe and 1162 Oe for the samples PK12 and K12, respectively.

Superior coulombic efficiency of lithium anodes for rechargeable batteries utilizing high-concentration ether electrolytes

This study adopts high-concentration ether electrolytes to improve high-rate capability, cycling stability, and Coulombic efficiency (CE) for lithium ion batteries with lithium anode. A series of ether-based electrolytes including lithium bis(fluorosulfonyl)imide (LiFSI)-glyme/ethylene carbonate (EC), LiFSI-glyme/EC, LiFSI-diglyme/EC, LiFSI-triglyme/EC, LiFSI-tetraglyme (G4)/EC, and LiFSI-1,3-dioxolane (DOL)/EC, along with commonly used LiPF6-DEC/EC were prepared to delineate the influences of concentration, chain length, molecular structure (linear or ring ether), and EC additive on the electrochemical performance of Li anodes. An optimum composition for ether-based electrolyte was determined resulting in significant improvement in anti-flammability as well as CE at both low and high rates. At ultra-high current density operation (e.g. 6 mA cm−2), the CE was 95.5 and 97.1% with 3 M LiFSI-G4/EC and 3 M LiFSI-DOL/EC, respectively. Using 1 M LiPF6 carbonate-based electrolyte tend to grow a needle-like dendritic structure when depositing lithium metal on Cu foils, whereas high-concentration ether electrolyte promotes a knot-like and rounded Li metal microstructure. High concentration EC-based electrolytes, are capable of facilitating Li+ almost in tandem with solvent molecules, thereby reducing the number of free molecules, reducing the chance of side reaction with Li metal, and subsequently inhibiting the formation of dendritic Li structures.

Optimal generation number in magnetic-cored dendrimers as Pb(II) and Cd(II) adsorbents

ABSTRACT As the generation number of dendrimers increases, more organic branches and terminal groups are synthesized on the surface. However, this may not be actual situations in all generations of dendrimers. Different generations of magnetic cored dendrimer (MCD) terminalized with amine functional groups were compared as adsorbents for heavy metal ions in water. To determine the optimal generation number as adsorbent, the maximal adsorption of lead and cadmium on generation 1, 2, and 3 (G1, G2, and G3) MCDs. Higher generation MCD had more organic contents and possibly terminal groups on its structure. However, G2 MCD was the highest in adsorbing both lead and cadmium. An acid–base titration was performed to quantify the amine functional groups. The active amine sites on G2 are 4.35 times as much as that of G1 and 0.12 times as much as that of G3, which coincided with the adsorption experimental result. Incomplete dendritic structure formation due to steric hindrance caused G2 MCD to be the most efficient among the three generations of MCDs in this research.

Impact of gravity-related phenomena on the grain structure formation: comparative study between horizontal and vertical solidification of a refined Al-20wt.%Cu alloy

On earth, gravity-related phenomena are unavoidable, such as thermo-solutal convection caused by density gradients in the melt and buoyancy when the liquid phase is denser than the solid phase. Such phenomena can drastically affect both the grain density and their morphology during equiaxed solidification processes. For these reasons, fundamental studies comparing the influence of solidification parameters with and without gravity effects are important to obtain benchmark data, which are useful to understand and then control the final structure of materials in industrial processes. In the present work, the impact of the solidification parameters on the dendritic grain structure formation and on the final grain size and shape was investigated in situ by using X-radiography for different growth orientations with respect to gravity. In a first step, experiments were carried out with various solidification parameters and with the furnace in horizontal position, with the main surface of the sample being perpendicular to gravity to limit gravity-related phenomena. In a second step, experiments were carried out with identical solidification parameters but with the furnace in a vertical position, and for two solidification directions (upward and downward). A comparative study between horizontal and vertical experiments was carried out. Phenomena related to gravity have been highlighted and their respective impact on the solidification front propagation was analysed.

The in situ observation of faceted dendrite growth during the directional solidification of GaSb

In this work, crystal–melt interfaces were directly observed during the directional solidification of molten GaSb having a stoichiometric composition, and the formation of dendrite structures was studied. With increases in growth velocity, the planar crystal–melt interface became unstable and dendrite growth was initiated. Dendrites having {111} facets were found to grow in either the 〈110〉 or 〈112〉 directions, and a pair of twin boundaries was identified at the center of a dendrite. The results show that the growth of dendrites in GaSb is associated with nucleation at twin-related reentrant corners.

Lithium Dendrites Inhibition via Diffusion Enhancement

AbstractThe dendritic structure is a disastrous problem of lithium metal batteries as well as other metal rechargeable batteries. The dendritic structures are usually caused by diffusion limitation. Here, a novel strategy is reported to inhibit lithium dendrites based on the understanding of their formation mechanism. An alternating current field perpendicular to the anode is set up, which promotes Li+movement along the anode surface and prevents ions' deposition on the tips from forming dendrites. Furthermore, an external direct current field parallel to the current is employed, which accelerates the transport of Li+in electrolytes to mitigate the concentration gradient nearby the anode and thus inhibits the formation of dendritic structures. A simultaneous employment of these two fields gains five times increase of the lifespan of batteries at the high charging current density of 2 mA cm−2, confirming the effectiveness of this strategy in protecting the metal anode and inhibiting lithium dendrites. This strategy may have a wide feasibility since it does not change the materials and structures of batteries.

Investigation of the thermo stability of aluminum thin-film filters with protective MoSi2 cap layers.

Aluminum thin-film spectral filters are widely used in telescopes for space observations of the Sun in the extreme ultraviolet range of wavelengths. The main purpose of film filters is to block radiation in the UV, visible, and near-IR spectral ranges. In connection with the development of new projects for the observation of the Sun from close distances, the thermal stability of the entrance film filter is an important characteristic. In this paper, the thermal stability of Al films with 2.5nm thick MoSi2 protective cap layers has been studied. MoSi2 was chosen as a coating material because MoSi2 caps effectively protect the Al film from oxidation and simultaneously increase the mechanical strength of the Al film. Vacuum annealing of MoSi2/Al/MoSi2 films was carried out at temperatures up to 300°C. It has been demonstrated that at an annealing temperature of more than 200°C for 24h, a noticeable decrease in the blocking properties of the MoSi2/Al/MoSi2 film is observed in the visible wavelength range, which is caused by the appearance of semi-transparent crystalline silicon dendritic structures that are tens of micrometers in size in the film. In the annealed area of the film specimen, the intermetallic Al12Mo phase was detected by electron diffraction structure analysis, indicating a possible reason for the appearance of silicon atoms needed for dendrite growth as a result of the chemical interaction of Al and MoSi2. Due to the requirements for a high degree of visible radiation blocking (106 to 107 times), the appearance of even one dendritic structure significantly reduces the blocking properties of the film filter and is, therefore, not permissible. Based on the measurement of the transmission of MoSi2-2.5 nm/Al-72 nm/MoSi2-2.5 nm films at 633nm for isothermal annealing at 200°C-250°C, the activation energy for the formation of dendritic structures (E=1.55±0.1 eV) was measured and the maximum permissible film temperature (130°C) at which dendritic structures did not appear during a 5-year mission was predicted.

Dendritic structure formation of magnesium alloys for the manipulation of corrosion properties: Part 1 – microstructure

Abstract Besides impurities in magnesium alloys containing aluminum, the microstructure also plays a role in the corrosion properties of the alloy. By targeted manipulation of grain size, secondary dendrite arm spacings and segregation in terms of amount and position, the corrosion properties are expected to be improved. For this, experiments were carried out by casting alloys with 0, 3, 6, 9, and 12 % aluminum into a mold with different applied cooling rates. The samples were analyzed regarding microstructure and composition, and the grain size and secondary dendrite arm spacings, as a function of aluminum content and cooling rate, were modeled. The results show a decrease in grain size and secondary dendrite arm spacings with an increased cooling rate. The segregated β phase was predominantly situated at the grain boundaries as divorced eutectic and in lamellar form. The assumed influences on the corrosion properties will be examined in Part 2.

Controlling the Growth of Inorganic Solid Electrolyte Interphases on Lithium

The ability to utilize Li metal as the anode in Li-ion or Li batteries has been a long-sought target since the development of modern battery technology because of its high capacity compared to graphite-based anodes (3860 mAh/gLi vs. 372 mAh/ggraphite), thus offering the prospect of significantly higher cell energy densities. However, Li faces several drastic challenges that have impeded its successful use as an anode so far. These include:1 (1) Large volume expansion upon Li stripping and plating, leading to rapid mechanical degradation; (2) Poor Coulombic (round-trip) efficiencies during cycling, which leads to loss of active Li (formation of so-called “dead Li”); and (3) Formation of dendritic structures upon Li deposition, which grow catastrophically and ultimately short-circuit the cell. Researchers have attempted to address these issues by developing solid electrolyte materials of sufficient mechanical strength to physically block dendrites, but such composites generally have high ionic resistances2 and poor performance at high powers3 due to the minimum thicknesses required for fabricating and processing without breakage. Recently, attention has shifted towards the introduction of “designer” material layers on Li through pre-formed SEI structures.4-6 Such a motif can be accomplished, for example, by introducing clean Li surfaces to donor molecules or additives that contain desirable constituents, such as fluoride ligands, that will presumably be incorporated upon decomposition at the Li surface. However, one major challenge is a lack of fundamental understanding of how such molecules decompose when in contact with a Li surface, either under dry conditions or in the presence of electrolyte. Consequently, there remains little understanding regarding how to intentionally build SEI layers with targeted compositions, morphological and electronic properties, and how these properties translate into electrochemical metrics such as Coulombic efficiency and cycle life. In this work, we present our recent studies of the decomposition reactions of oxide- and fluoride-containing gases on Li surfaces for artificial SEI formation. We first demonstrate controllable growth (10 – 100’s of nm thickness) of targeted ionic materials such as Li2O and LiF which is achieved through judicious selection of the reactant gas and reaction conditions. In gases with multiple potential SEI-forming constituents, we find that reaction kinetics and the decomposition pathway determine which elements are ultimately imparted to an SEI, thereby introducing an ability to rationally tune the SEI by tuning the gas structure and chemistry. We report X-ray photoelectron (XPS) with depth-profiling and X-ray diffraction (XRD) analysis of films to describe their chemical composition and crystallinity. We also employ several methodologies to characterize the electronic and electrochemical behavior of such by-design films, including electrochemical impedance, Li-Li cycling, Li-Cu plating/stripping measurements, and constant-current discharge to failure to measure dendrite propagation times, and compare their behavior to bare Li. Special emphasis will be placed on the mechanistic origin of electrochemical properties, which are derived from Li+ transport through film grain boundaries, and on the failure modes of such films during cycling. Tikekar, M. D.; Choudhury, S.; Tu, Z. Y.; Archer, L. A., Design principles for electrolytes and interfaces for stable lithium-metal batteries. Nat Energy 2016, 1, 1-7.Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; Mitsui, A., A lithium superionic conductor. Nat Mater 2011, 10 (9), 682-686.Bachman, J. C.; Muy, S.; Grimaud, A.; Chang, H. H.; Pour, N.; Lux, S. F.; Paschos, O.; Maglia, F.; Lupart, S.; Lamp, P.; Giordano, L.; Shao-Horn, Y., Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction. Chem Rev 2016, 116 (1), 140-162.Li, Y.; Sun, Y.; Pei, A.; Chen, K.; Vailionis, A.; Li, Y.; Zheng, G.; Sun, J.; Cui, Y., Robust Pinhole-free Li3N Solid Electrolyte Grown from Molten Lithium. 2018, 4 (1), 97-104.Lin, D. C.; Liu, Y. Y.; Chen, W.; Zhou, G. M.; Liu, K.; Dunn, B.; Cui, Y., Conformal Lithium Fluoride Protection Layer on Three-Dimensional Lithium by Nonhazardous Gaseous Reagent Freon. Nano Lett 2017, 17 (6), 3731-3737.Lu, Y. Y.; Tu, Z. Y.; Archer, L. A., Stable lithium electrodeposition in liquid and nanoporous solid electrolytes. Nat Mater 2014, 13 (10), 961-969.

Microstructure characterization of cemented carbide fabricated by selective laser melting process

This article presents detailed microstructure characterization of cemented carbide fabricated by selective laser melting process. Nickel-coated tungsten carbide powders were used for this study; the selective laser melting process induced complex microstructure consisting of partially-melted carbide, carbide precipitates and dendritic microstructure. Four phases were identified, i.e. MC, M2C, FCC and η in the as-built specimen. CALPHAD phase diagram was utilized to describe possible phase formation sequence during selective laser melting process, which involved melting, solidification and repeated heating. Although the composition of initial powder was very simple (spherical W2C-WC and Ni-coating), selective laser melting allowed the decomposition of initial carbides, subsequent formation of dendritic structure and precipitation of additional carbides. To the best of authors' knowledge, for the first time, detailed microstructure characterization of cemented carbide fabricated by selective laser melting is presented.

Label-free electrochemical detection of HepG2 tumor cells with a self-assembled DNA nanostructure-based aptasensor

The development of rapid, sensitive and convenient methods for the monitoring of rare circulating tumor cells (CTCs) is of great significance in cancer diagnostics and therapy. Herein a label-free and competitive electrochemical aptasensor was proposed for the efficient capture, ultrasensitive detection and controlled release of CTCs. Firstly, the DNA nanotetrahedron (NTH)-based TLS11a aptamer probe was immobilized on a disposable screen-printed gold electrode (SPGE) surface via the Au−S bonds for the highly enhanced capture of liver cancer HepG2 cells. Then, hybrid nanoprobes of Pd-Pt nanocages labeled with complementary DNA (cDNA), hemin/G-quadruplex DNAzyme and horseradish peroxidase (HRP) were attached on the SPGE substrate by the DNA hybridization, resulting in the formation of dendritic structure (DS) nanoprobes with self-assembly methods for the greatly enhanced sensitivity. When the target HepG2 cells existed, they can compete with DS nanoprobes to bind with NTH-based aptamer probe, resulting in the release of the DS nanoprobes from the SPGE. This method exhibits ultrahigh selectivity and sensitivity toward HepG2 with detection limits of 5 cells per ml. Furthermore, our strategy allows for easy detachment of the captured cells from the SPGE without compromising cell viability by an electrochemical cleavage of the Au–S bonds. The present study provides a label-free technique for highly selective and efficient quantification of tumor cells, which is essential in the early cancer diagnosis and treatment of cancer.

Electrodeposited honeycomb-like dendritic porous gold surface: An efficient platform for enzyme-free hydrogen peroxide sensor at low overpotential

In this work, a one-step electrodeposition so-called “dynamic hydrogen bubble template” (DHBT) method was proposed to fabricate a porous Au film electrode. Field emission scanning electron microscopy and cyclic voltammetry techniques were used to characterize the as-prepared film, and results confirmed the formation of honeycomb-like dendritic (HCLD) porous structures with enhanced surface area and roughness factor. The resulting HCLD-porous Au film electrode was explored for enzyme-free H2O2 reduction and a remarkable electrocatalytic activity was observed in terms of reducing the overpotential ~0.5V towards more positive potential with ~3-fold enhancement in current signal in comparison to the bare Au electrode. The fabricated sensor displayed excellent analytical response in amperometric mode at an applied potential of −0.1V in a linear range from 0.02–0.36mmol L−1 with a detection limit of 0.003mmol L−1 and a sensitivity of 1176μA mmol L−1cm−2. Besides, the sensor exhibited good selectivity and reproducibility. Lastly, the proposed sensor was evaluated for real application using mouthwash liquid samples via standard addition method and the recovery value was found to be ~97%.

Drying of colloidal solutions of fluoroalkyl oligomers

The change in the supramolecular structure upon drying (solvent removal) of colloidal solutions of fluoroalkyl oligomers at atmospheric pressure has been studied using atomic force microscopy. In an initial colloidal solution, micrometer-sized particles of the dense phase consist of randomly oriented oligomers in the form of rigid rods of a 3–5 nm length forming a porous framework filled with solvent molecules, which solvate the oligomer chains. The drying-induced capillary pressure, which in nanosized pores is of the same order of magnitude as the solvation energy, leads to framework deformation, collapse of the pores, and the formation of lamellar and dendritic structures on a 50–100 nm scale. The ordering of these structures (formation of blocks of parallel oriented fibers typical of a fluoroplastic) increases as the heat-treatment temperature and the drying rate are increased, increasing the roughness of the surface (ratio of real to smooth surface area) and its hydrophobicity.

Characterization of Lithium Inventory in Lithium Metal Anodes during Cycling

A rising interest in batteries has resulted from a need for improved energy storage systems for transportation and portable electronics applications. Lithium is of particular interest as an anode due to its low redox potential and high specific capacity. However, these systems have not been practically realized due to the nonuniform plating of lithium. Many studies have modeled this formation of dendritic or mossy structures as a function of parameters such as temperature, electrolyte composition, current density and overpotentials [1]. However, the majority of these efforts have focused on the influence of these parameters on the nucleation and growth of lithium at early stages; the processes for deplating of lithium during discharge and the continued growth of dendritic structures, once formed, are poorly understood. In this work, we use commercially available primary cells as a basis for understanding the movement of lithium during cycling. Specifically, we discharge both coin and pouch cells at a range of C rates to specified states of charge (SOC). During discharge, acoustic time of flight studies are used to provide insight on how mass is transferred between layers [2]. Once the cell has been discharged to the specified SOC, electrochemical impedance spectroscopy is conducted before dismantling the cell and observing the lithium electrode using scanning electron microscopy. The same characterization methods are subsequently used for cells that have been discharged and charged for a range of cycles. Through these techniques, we track how lithium is transferred between electrodes, as well as how lithium is spatially utilized across the anode.

Investigations of fluid flow effects on dendritic solidification: Consequences on fragmentation, macrosegregation and the influence of electromagnetic stirring

Solidification experiments and numerical simulations have been performed to improve the understanding of the complex interrelation between melt flow and the formation of dendritic structures during solidification of Al-Cu and Ga-In alloys. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Within this project special interest was focused on fragmentation and segregation phenomena. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. X-ray radioscopy was applied as a powerful tool for the visualization of dendritic growth and coarsening.