Diffusion Path Length Research Articles

Design of new anode materials based on hierarchical, three dimensional ordered macro-mesoporous TiO2 for high performance lithium ion batteries

As anode materials for lithium ion batteries, two three dimensionally ordered macroporous TiO2, one with disordered inter-particle mesopores formed by the aggregation of nanoparticles (3DOM) and another with inner-particle mesopores generated by a surfactant templating strategy (3DOMM), have been synthesized using poly(styrene-methyl methacrylate-3-sulfopropyl methacrylate potassium) (P(St-MMA-SPMAP)) spheres as a hard template and their electrochemical properties are compared. SEM and TEM observations reveal that both 3DOM TiO2 and 3DOMM TiO2 have well-ordered macropores and interconnected macropore walls with a regular periodicity. 3DOMM TiO2 demonstrates a specific surface area of 139 m2 g−1, which is higher than that of 3DOM TiO2 (99 m2 g−1) due to the smaller crystallite size and inner-particle mesopores. The electrolyte adsorption results show that both 3DOM TiO2 and 3DOMM TiO2 have similar adsorption capacities despite a difference in the surface area. Electrochemical impendence spectroscopy analysis shows that 3DOMM TiO2 has a lower charge transfer resistance and faster Li+ diffusion coefficient than 3DOM TiO2. Moreover, both 3DOM TiO2 and 3DOMM TiO2 possess excellent initial capacity of 248 mA h g−1 and 235 mA h g−1 at 0.2 C and 208 mA h g−1 and 202 mA h g−1 at 1 C, respectively. The reversibility study demonstrates that the 3DOMM TiO2 displays higher cycling capacity, superior rate behavior and higher Coulombic efficiency because the higher surface area provides more active sites and the presence of the inner-particle mesopores in the walls of macropores serve as a bicontinuous transport path and affords a shorter path length for diffusion of Li ions compared with the 3DOM TiO2 and its crystallite aggregated mesopores. The reversible capacity of 106 mA h g−1 observed for the 3DOMM TiO2 can be retained after 200 charge–discharge cycles at a relatively high current rate of 4 C. This cycle stability performance can be equally attributed to the crystallite size and inner-particle mesopores in the 3DOMM TiO2. Moreover, the existence of a bicontinuous porous structure in the 3DOMM TiO2 can further enhance the lithium insertion/extraction capacity at high rates. We believe that this study can shed light on the 3DOMM structure as a promising material for highly enhanced performance in lithium ion batteries.

One-pot synthesis of SnS nanorods and their lithium storage properties

Tin sulfide (SnS) nanorods have been synthesized through a facile template-free solvothermal route and characterized using XRD, SEM, and TEM. Results indicate that the as-prepared SnS nanorods are 30–100 nm in diameter and ~1,000 nm in length. When used as an anode material, the nanorods exhibit enhanced lithium ion storage properties with high reversible capacity and good cyclic performance. The superior electrochemical performance can be ascribed to the unique one-diamensional nanostructure, which restrains volume expansion of the nanorods and reduces lithium ion diffusion path length efficiently.

Tracing Water and Cation Diffusion in Hydrated Zeolites of Type Li-LSX by Pulsed Field Gradient NMR

The pulsed field gradient (PFG) technique of NMR is exploited for recording the time-dependent mean diffusion path lengths of both the water molecules (via 1H NMR) and the cations (via 7Li NMR) in hydrated zeolite Li-LSX. The observed propagation patterns reveal, for both the water molecules and the cations, two types of transport resistances, acting in addition to the diffusion resistance of the genuine pore network. They are attributed to the interfaces at the boundary between the purely crystalline regions (crystallites) within the Li-LSX particles (intergrowths) under study and to the external surface of either the particles themselves or crystallite aggregates within these particles. The cation diffusivity is retarded by about 1 order of magnitude in comparison with the water diffusivity. This notably exceeds the retardation of cation diffusion in comparison with water in free solution, reflecting the particular influence of the zeolite lattice on the guest mobility.

S120 Hyperpolarised 3HE diffusion MRI and multiple breath inert gas washout in patients with asthma

BackgroundMultiple breath inert gas washout (MBW) is a technique for detecting abnormal ventilation distribution in patients with asthma and other airway diseases. Scond and Sacin are measures of convective-dependent inhomogeneity...

Intensification of metal extraction with high-shear mixing

A laboratory flow reactor (Vr=9.5mL) with a high shear mixer was used to study the intensification of extraction and stripping. The stirring rate was 15,000rpm and the reactor space-time was varied from 1.3 to 13s in extraction experiments. The phases were separated with an in-line centrifuge. Results were compared to those made in batch reactor (Vr=7.7L) equipped with conventional pitched-blade turbine impeller. The residence time and drop size distributions of flow reactor were measured. Copper extraction was made from sulfate solution using a hydroxyoxime reagent (LIX 984). Both extraction and stripping reached equilibrium in a few seconds in the flow reactor, while the same required about 250s in the batch reactor. Residence time distribution was utilized in the model of extraction kinetics. Calculated pseudohomogeneous extraction kinetic constants of the flow reactor and the batch reactor were 5.9 and 0.034Lmol−1s−1, respectively. Difference was over 150-fold. Measured drop size distributions indicate that differences in generated interfacial area can explain only a part of rate increase. Such dramatic intensification of extraction in flow reactor is interpreted here to be due to both increased interfacial area and decreased diffusion path length.

Use of Sodium Lauryl Sulphate as a Surfactant in a Photogalvanic Cell for Solar Energy Conversion and Storage: A Sodium Lauryl Sulphate-Methylene Blue-Mannose System

Sodium lauryl sulphate is used as a surfactant with methylene blue as a photosensitizer and Mannose as a reductant for enhancement of the performance of the photogalvanic cell for its commercial viability. The generated photopotential and photocurrent were 809.0 mV and 80.0 μA, respectively. The effect of various parameters, such as concentrations of photosensitizer, reductant, and surfactant; variation of pH; diffusion path length; electrode area; and light intensity, were observed. The storage capacity of the photogalvanic cell was found to be 48.0 min in the dark. Current-voltage characteristics, fill factor, and conversion efficiency of the cell have been studied and a tentative mechanism has also been proposed for the generation of photocurrent in the photogalvanic cell. All observed performances of the system were found to be higher in the presence of surfactant.

Effects of hydrophobicity and mat thickness on release from hydrogel-electrospun fiber mat composites

Poly(ethylene glycol) (PEG)-based hydrogel-electrospun fiber mat (EFM) composites are a promising new controlled release system for hydrophilic drugs, providing longer and more linear release characteristics accompanied by a smaller initial burst than traditional hydrogel systems. However, the effect of EFM properties on release characteristics has not yet been examined. Here, we investigated the influence of EFM thickness and hydrophobicity on swelling and release behavior using bovine serum albumin as a model hydrophilic protein. EFMs investigated were comprised of poly(ϵ-caprolactone) (PCL) at thicknesses of 300, 800, or 1100 μm. Hydrophobicity was adjusted through surface modification: fluorinated PCL, core/shell PCL/PEGPCL, and acrylic acid (AAc)-treated PCL EFMs were examined. EFMs comprised of the external composite surface, forming a sandwich around PEG-poly(lactic acid) (PEGPLA) hydrogels, and significantly restrained hydrogel swelling in the radial direction while increasing swelling in the axial direction. Incorporation of EFMs also reduced initial hydrophilic protein release rates and extended the duration of release. Increased EFM thickness and hydrophobicity were equally correlated with longer and more linear release profiles. Increased thickness most likely increases the diffusional path length, whereas increased hydrophobicity hinders hydrophilic drug diffusion. These composites form a promising new class of tunable release materials having properties superior to those of unmodified hydrogels.

Evolution of microstructures and mechanical properties during dissimilar electron beam welding of titanium alloy to stainless steel via copper interlayer

The influence of operational parameters on the local phase composition and mechanical stability of the electron beam welds between titanium alloy and AISI 316L austenitic stainless steel with a copper foil as an intermediate layer has been studied.It was shown that two types of weld morphologies could be obtained depending on beam offset from the center line. Beam shift toward the titanium alloy side results in formation of a large amount of the brittle TiFe2 phase, which is located at the steel/melted zone interface and leads to reducing the mechanical resistance of the weld. Beam shift toward the steel side inhibits the melting of titanium alloy and, so, the formation of brittle intermetallics at the titanium alloy/melted zone interface. Mechanical stability of the obtained junctions was shown to depend on the thickness of this intermetallic layer. The fracture zone of the weld was found to be a mixture of TiCu (3–42wt%), TiCu1−xFex (x=0.72–0.84) (22–68wt%) and TiCu1−xFex (x=0.09–0.034) (0–22wt%). In order to achieve the maximal ultimate tensile strength (350MPa), the diffusion path length of Ti in the melted zone should be equal to 40–80µm.

Tensile properties and strengthening mechanisms of SiCp-reinforced aluminum matrix composites as a function of relative particle size ratio

Abstract

Tailoring zeolite morphology by Charge Density Mismatch for aromatics processing

Nano-crystalline zeolites UZM-5 and UZM-14 were synthesized via the Charge Density Mismatch (CDM) approach and were shown to have distinct morphologies that significantly impact aromatic alkylation and transalkylation reactions. UZM-5 has surface structure features and thin plate morphologies favorable for catalyzing the alkylation of benzene with ethene. The alkylation activity depends on the crystallinity and morphology, which affect acidity and access to surface cups and internal pores. Nano-crystalline mordenite, UZM-14, was characterized in terms of crystallite length in the direction of the 12-MR channels, mesoporosity, and accessibility of acid sites. Aromatics transalkylation performance was shown to correlate with mesoporosity and crystallite length along the pore direction. This was rationalized in terms of decreased diffusion path length in the micropores and improved accessibility of feed molecules to acid sites in the interior of the zeolite crystals.

Long Acting Betaxolol Ocular Inserts based on Polymer Composite

Poor bioavailability and therapeutic response of conventional therapy due to many pre-corneal constraints necessitate the development of novel controlled and sustained ocular drug delivery to become a standard one in modern pharmaceutical era. This investigation aimed to study the drug release kinetics of betaxolol hydrochloride from a hydrophobic matrix system of PMMA cast with incorporating different proportions of polyethylene oxide (PEO) and evaluate its ability to improve ocular bioavailability and duration of action for the drug. Matrix type ocular inserts were prepared by the film casting technique and characterized in vitro by drug release studies using a flow through apparatus that simulated the eye conditions. All the formulations were subjected to physicochemical evaluation. Rabbit model with steroid induced glaucoma was used to establish in vivo efficacy of inserts. Polymer composition and concentration significantly affected the drug release based on change in diffusional path length and formation of gelaneous pores by polymer erosion. Formulations released the drug by non-fickian diffusion including anomalous transport (0.5<n<1) and super case II transport (n>1). It was also observed that increasing the proportion of PEO in to PMMA does not affect the blend miscibility. IVIVC suggested no significant difference (P< 0.001) between in vitro and in vivo release of drug from inserts. In vivo IOP lowering activity was better for optimized insert F8 (for 24 h) as compared to eye drops (10 h). This ocular insert could be a promising once-a-day sustained release formulation for treating glaucoma.

Hierarchical Li4Ti5O12-TiO2 composite microsphere consisting of nanocrystals for high power Li-ion batteries

Highly mesoporous lithium titanate hierarchical microspheres (LTO-HS) consisting of nanosized octahedron-like crystals were innovatively designed as high performance and safe anode materials for lithium ion battery applications. This unique structural control allows us to capitalize on the exemplary surface areas (electrolyte contact) and short Li-ion diffusion path lengths of nanosized particles, while overcoming the challenge of low power tapping density by integrating them into microsized spheres. A thin carbon coating was applied on the surface of LTO-HS (C-LTO-HS) in order to overcome the inherently limited electronic conductivity of these oxide materials. Moreover, this coating technique was found to induce the formation of some anatase TiO2, resulting in uniquely structured anode materials with active multi-component duality. Notably, the C-LTO-HS composite electrode delivers a remarkable capacity of over 230mAhg−1 when discharged at 0.2C, which is much higher than the theoretical capacity of pure Li4Ti5O12 (175mAhg−1) and ascribed to the existence of anatase TiO2 (330mAhg−1) in the C-LTO-HS structure. Furthermore, this electrode yielded excellent cycling and rate capabilities of about 120mAhg−1 (compared to 90mAhg−1 for LTO-HS) at a current density of 10C for up to 100 cycles. These unique mesoporous spheres with deliberately controlled nanostructure arrangements show significant promise as anode materials for lithium ion batteries, fabricated by a simplistic two step hydrothermal procedures, and capable of providing high volumetric energy density and long cycle life.

Nb-Doped TiO2 Nanofibers for Lithium Ion Batteries

Niobium-doped nanofibers elaborated by facile, single-step electrospinning present a higher rate capability in electrochemical cycling experiments than nondoped materials. This is attributed to the reduction of Li+ diffusion path lengths and enhanced intimate interparticle contact, in combination with improved intraparticle conductivity. Niobium doping has a significant effect on the electronic structure and provokes a substantial decrease in particle size.

COMPUTATIONAL INVESTIGATION OF THE EFFECTS OF SPHERICAL FILLER MORPHOLOGY AND LOADING ON DIFFUSION TORTUOSITY AND RUBBER PERMEABILITY

ABSTRACT Inflation pressure loss in tires degrades performance, raises rolling resistance, and reduces fuel economy. The incorporation of solid fillers, such as carbon black, at relatively high loadings in tire innerliners helps minimize these pressure losses by reducing innerliner permeability due to increases in average gas molecule diffusion path lengths (tortuosity), as well as reductions in diffusion pathway density (capacity). The effects of filler morphology and loading on diffusion path tortuosity can be explored by modeling biased random-walk diffusion through impermeable sphere-filled matrices. Modeled diffusion rate was found to decrease with increased filler loading, reduced filler sphere sizes, increased random-walk step sizes, and the aggregation of filler spheres. Initial correlations with limited empirical permeability measurements are used to validate the model approach.

Evaluation of MD process performance: Effect of backing structures and membrane properties under different operating conditions

The paper presents investigations on the process performance of different membranes with and without backing structure in direct contact membrane distillation. Influences of backing structures and their orientation are identified. An integrated membrane and backing model was developed. Laminates with different backing designs were examined over a wide range of operating conditions and compared to results for the same membranes without backing. Experimental results and model predictions for flux and thermal efficiency are compared. The model predictions agree well with the experimental results. An influence on the effective area for diffusion, an increase in effective diffusion path length in the membrane and the formation of a complex network of thermal resistances are considered to be the main effects, leading to a significant reduction in process performance due to backing structures. The backing was identified to be one of the key components for further improvement in MD applications. An integrated assessment of membrane properties in combination with backing structures was carried out by analysing membranes with different thicknesses and different pore sizes. The experimental observations show good agreement with theoretical considerations. A combined analysis of specific flux and thermal efficiency leads to comprehensive understanding of the process and its potential for optimisation.

Comparative analysis of the effect of mechanical activation in an attritor on the structure and behavior of β-RuAl and β-NiAl alloy powder mixtures during reactive sintering

The structure of Ni + Al (two ductile fcc metals) and Al + Ru (ductile aluminum and hard-to-deform hcp ruthenium) powder mixtures subjected to short-term (≤16 h) mechanical activation (MA) is studied. During MA of a 50Ni + 50Al mixture, the powder particles undergo multiple compressive and shear deformation, and large layered granules form due to contact welding and flattening of the layers of both metals. The related increase in the internal stresses, the increase in the dislocation density in particles of both metals, and the decrease in the coherent domain size (CDS) lead to the fracture and fragmentation of the powder particles. In a 49Ru + 48Al + 3Re mixture, aluminum particles are deformed and “spread” over “rigid” ruthenium particles. The formed granules consist of disperse undeformable ruthenium particles connected by an Al binder. The work hardening of ruthenium occurs due to a decrease in CDS. An increase in the contact area between metal particles and a decrease in the diffusion path lengths (aluminum in nickel and ruthenium) cause a decrease in the temperature of the onset of interaction with the participation of liquid aluminum, the activation of solid-phase interaction, and the formation of aluminum-rich nickel (ruthenium) aluminide NiAl (RuAl). Nevertheless, unreacted nickel (ruthenium) particles are retained. A microhomogeneous distribution of the basic and alloying elements and phases in a compacted material is achieved Annealing at temperatures ≥0.8T m is required to complete reactive alloy formation.

A Facile Strategy To Design Zeolite L Crystals with Tunable Morphology and Surface Architecture

Tailoring the anisotropic growth rates of materials to achieve desired structural outcomes is a pervasive challenge in synthetic crystallization. Here we discuss a method to selectively control the growth of zeolite crystals, which are used extensively in a wide range of industrial applications. This facile method cooperatively tunes crystal properties, such as morphology and surface architecture, through the use of inexpensive, commercially available chemicals with specificity for binding to crystallographic surfaces and mediating anisotropic growth. We examined over 30 molecules as potential zeolite growth modifiers (ZGMs) of zeolite L (LTL type) crystallization. ZGM efficacy was quantified through a combination of macroscopic (bulk) and microscopic (surface) investigations that identified modifiers capable of dramatically altering the cylindrical morphology of LTL crystals. We demonstrate an ability to tailor properties critical to zeolite performance, such as external porous surface area, crystal shape, and pore length, which can enhance sorbate accessibility to LTL pores, tune the supramolecular organization of guest-host composites, and minimize the diffusion path length, respectively. We report that a synergistic combination of ZGMs and the judicious adjustment of synthesis parameters produce LTL crystals with unique surface features, and a range of length-to-diameter aspect ratios spanning 3 orders of magnitude. A systematic examination of different ZGM structures and molecular compositions (i.e., hydrophobicity and binding moieties) reveal interesting physicochemical properties governing their efficacy and specificity. Results of this study suggest this versatile strategy may prove applicable for a host of framework types to produce unrivaled materials that have eluded more conventional techniques.

Self-Assembled Fe2O3/Graphene Aerogel with High Lithium Storage Performance

In this study, graphene aerogel (GA)-supported Fe2O3 particles with three-dimensional (3D) architecture was prepared by a one-pot hydrothermal process. Fe2O3 particles were dispersed uniformly on the graphene sheets, and the resulting composites self-assembled into a 3D network via hydrothermal treatment. This strategy provides a facile and environmentally friendly method for the large-scale synthesis of Fe2O3/GAs without any additional reductant. As the anode material for lithium ion batteries, the Fe2O3/GAs in this study manifested an excellent reversible capacity of 995 mA h g(-1) after 50 cycles at a charge-discharge rate of 100 mA g(-1) and even delivered reversible capacity as high as 372 mA h g(-1) at a high rate of 5000 mA g(-1). The outstanding electrochemical performance of Fe2O3/GAs can be attributed to the synergistic interaction between uniformly dispersed Fe2O3 particles and graphene aerogel, in which a robust 3D framework of graphene provided highly conductive networks with a large surface area and short diffusion path length for the transport of lithium ions.

N-Heptane hydroisomerization over Pt/MFI zeolite nanosheets: Effects of zeolite crystal thickness and platinum location

Platinum was supported on MFI-type (ZSM-5) zeolites with various crystal thicknesses ranging from 300 to 2nm (i.e., from bulk crystal to nanosheet). Two series of Pt/MFI were prepared by the ion exchange of Pt(NH3)42+ and the impregnation of colloidal Pt nanoparticles. The ion exchange yielded Pt nanoparticles that were supported inside zeolite pores, whereas the impregnation yielded Pt nanoparticles supported exclusively on the external crystal surfaces. The two series of Pt/MFI were used as catalysts for the hydroisomerization of n-heptane to investigate the effects of zeolite crystal thickness and Pt location. This research showed that the product selectivity to branched isomers could be significantly improved by decreasing zeolite crystal thickness to nanosheets. The selectivity improvement was attributed to short diffusion path lengths for branched products to escape before cracking.

Reduced Graphite Oxide/Nano Sn: A Superior Composite Anode Material for Rechargeable Lithium‐Ion Batteries

The electrochemical performance of reduced graphite oxide (RGO) anchored with nano Sn particles, which are synthesized by a reduction method, is presented. The Sn nanoparticles are uniformly distributed on the surface of the RGO matrix and the size of the particles is approximately 5-10 nm. The uniform distribution effectively accommodates the volume expansion experienced by Sn particles during cycling. The observed electrochemical performance (97 % capacity retention) can be ascribed to the flexible RGO matrix with uniform distribution of Sn particles, which reduces the lithium-ion diffusion path lengths; therefore, the RGO matrix provides more stability to the Sn particles during cycling. Such studies on Sn nanoparticles anchored on RGO matrices have not been reported to date.