Sn Particles Research Articles

Analysis of microstructure formation in gas-atomised Al–12 wt.% Sn–1 wt.% Cu alloy powder

The microstructure of gas-atomised Al–12 wt.% Sn–1 wt.% Cu alloy powder has been investigated using scanning and transmission electron microscopy. Powder particles above approximately 8 μm in diameter exhibited a cellular–dendritic solidification morphology comprising α-Al dendrites and interdendritic Sn. In smaller powder particles, with diameters less than approximately 8 μm, the microstructure comprised an α-Al matrix with a dispersion of sub-micron Sn particles. The size of the dispersed Sn phase decreased with decreasing powder size (i.e. increased cooling rate). The formation of this dispersed phase microstructure is explained by the existence of a metastable liquid-phase miscibility gap in the system such that the reaction L → L 1 + L 2 occurred prior to the onset of solidification in particles below 8 μm in size. A heat transfer analysis was used to estimate the undercooling for the nucleation of α-Al in droplets cooled at different rates. The nucleation undercooling predicted for an 8 μm diameter droplet was 260 K and this represents a critical value which must be exceeded to enter the immiscibility region. The above value is in reasonable agreement with the temperature of the metastable immiscibility boundary, calculated from thermodynamic data, which occurs at an undercooling of approximately 280 K for Al–12 wt.% Sn.

Ru-Sn catalysts for selective hydrogenation of crotonaldehyde: Effect of the Sn/(Ru+Sn) ratio

Abstract The effects of the Sn/(Ru + Sn) ratio and Ru loading on the properties of silica-supported RuSn catalysts were investigated. Ru-Sn/SiO2 bimetallic catalysts were prepared by the impregnation method and characterized in situ by XPS and Mossbauer spectroscopy. The XPS results indicated the presence of two Sn species on the surface of the catalysts, in different oxidation states—Sn0 and Snn+, and 119Sn Mossbauer spectra revealed Sn(II), Sn(IV), and intermetallic particles with structures such Ru3Sn7 I, Ru3Sn7 II, and oxide species (RuOSn). The contents of the various species depended on Sn loading. The reaction data showed that the Ru/SiO2 catalyst was active only for hydrogenation of the C C bond, while the addition of a small amount of Sn (1 wt.% of Sn) made the catalyst active for hydrogenation of both the C C and C O bonds. Upon increasing the Sn loading from 1 to around 3.6 wt.%, the specific rate for C C hydrogenation is greatly reduced whereas the specific rate for C O hydrogenation decreases more gradually. The activity for C C hydrogenation remains unvarying for Sn loading higher than around 3.6 wt.%. This results in an optimum selectivity to crotyl alcohol at Sn/(Ru + Sn) molar ratio around 0.2–0.3. The abrupt change of activity toward C O hydrogenation is observed as a lower binding energy than expected is observed for the Ru0. This enhancement of the surface electron density of the Ru particle is crucial to improving the adsorption and reactivity of the C O bond, but has the opposite effect on hydrogenation of the C C bond. The geometric effect of formation of Sn-Ru intermetallic and SnOx compounds on the Ru particle surface may play a part in the suppression of C C bond hydrogenation.

High capacity disordered carbons obtained from coconut shells as anode materials for lithium batteries

Carbonaceous materials have been obtained by the pyrolysis of coconut shells at 800 and 900 °C with pore forming substances such as KOH and ZnCl 2. The prepared carbons were subjected to XRD, SEM, BET-surface area and charge–discharge studies. The structure and morphology were greatly changed by porogens, which in turn influence the electrochemical properties of the carbonaceous materials. Nanocrystalline tin (Sn) particles were prepared by chemical reduction method. The cycling tests showed that the addition of nanotin with the active material offers a stable cycling behavior. The electrochemical impedance spectra for the Li/C cells have been made and the results are discussed.

Synthesis and electrochemistry properties of Sn–Sb ultrafine particles as anode of lithium-ion batteries

Ultrafine particles of Sn–Sb alloys with different chemical composition have been prepared by hydrogen plasma-metal reaction. Structure, morphology, size and chemical composition of the Sn–Sb ultrafine particles were investigated by transmission electron microscopy, X-ray diffraction, BET gas adsorption, and induction-coupled plasma spectroscopy. It was found that all the particles have spherical shapes, with average particle size in the range of 100–300 nm. The electrochemistry properties as an alternative anode material for lithium-ion batteries have been characterized by constant current cycling and cyclic voltammetry. Electrochemical measurements showed that the alloys with Sn–46.5 at.% Sb have best reversible capacity and capacity retention. It exhibited a high reversible lithium-ion storage capacity of 701 mAh g −1 in the initial cycle, which has remained at 81% (i.e., 566 mAh g −1) of its original capacity after 20 cycles.

Effect of Trace Addition of Sn in Al-Cu Alloy

The trace addition of Sn (0.01 at.%) to an Al-1.7Cu (at.%) alloy has been investigated using atom probe tomography (APT), transmission electron microscopy (TEM) and high resolution transmission electron microscope (HRTEM). We have studied samples in the as-quenched (AQ) condition and following ageing at both 160 and 200 °C for very short ageing times so as to better understand the early stages of the decomposition processes. Our data reveal independent Cu-Cu and Sn-Sn clusters in the AQ condition, though we did not observe Cu-Sn clustering. We observed for the first time that some of these initial Cu-clusters develop into GP zones during subsequent ageing at temperatures as high as 200 °C. The Sn atom clustering results in precipitation of independent 􀀂- Sn particles after aging for 30 sec. The GP zones consequently undergo reversion and this liberates Cu atoms which seem to participate in a cluster-assisted heterogeneous nucleation of the 􀀃􀀂 phase at the interface of the 􀀂-Sn. For ageing at 200 °C, this process is complete within 180 sec.

Microstructural Factors Affecting Fatigue Initiation in Various Al Based Bearing Alloys

Microscale fatigue damage mechanisms in various Al-Sn-Si based bearing alloys used as linings of plain automotive bearings are reported. Extensive work on previously developed alloys has concluded that secondary phase particles such as Sn and Si are potential fatigue initiation sites with a complex combination of various particle geometry parameters. A newly developed alloy contains a number of complex widely scattered intermetallics with much finer and fewer Sn and Si particles. This alloy system appears to be more resistant to initiate microscale fatigue damage compared to the previous systems.

Electrodeposition of Nano Sn particles in Room Temperature Molten Salts and Their Electrochemical Performance in Lithium Battery Application

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Effect of Capping Agents in Sn Particles on Electrochemical Properties

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Synthesis, transformation and superconductivity of dual phase In–Sn alloy nanoparticles embedded in an Al matrix

We report the synthesis of nanoembedded biphasic alloy particles of In–Sn near eutectic alloy compositions embedded in an aluminium matrix by rapid solidification processing. Detailed transmission electron microscopy indicates that the two phases present at room temperature in as-synthesized samples are β and γ phases with tetragonal and hexagonal crystal structures, respectively. These co-exist with a small amount of single phase In or Sn particles with sizes less than 10 nm. Low temperature magnetization measurements indicate a superconducting transition temperature of 5 K, suggesting complete decomposition of the β-phase at small sizes and at low temperature. The small particles show type II behavior with a critical field Hc1≈44 G and two values for Hc2 of 250 and 1000 G, respectively. These values are considerably lower than those observed in bulk In–Sn alloys.

Thermodynamics on the Nanoscale

Classical thermodynamics is applied to the melting of nanometer-sized Sn particles with radii in the range 5-50 nm. Such particles display a depression of both the melting point and the latent heat of fusion depending on the particle size. The size dependence can be explained with the formation of a structurally perturbed layer at the particle surface. The experimental measurement of both melting temperatures and latent heats of fusion allowed for estimation of the thickness of the perturbed layer. This permitted in turn the evaluation of the excess Gibbs free energy associated with the perturbed layer at melting and the determination of its variation with particle size and temperature.

Surface and bulk melting of small metal clusters

We present an analytical solution to the two-parabola Landau model, applied to melting of metal particles with sizes in the nanoscale range. The results provide an analytical understanding of the recently observed pseudo-crystalline phase of nanoscale Sn particles. Liquid skin formation as a precursor of melting is found to occur only for particles with radii greater than an explicitly given critical radius. The size dependences of the melting temperature, and of the latent heat, have been calculated, and a quantitative agreement is found with the experiment on tin particles.

Correlation between structural evolution and photoluminescence of Sn nanoclusters in SiO2 layers

Sn nanoclusters are synthesized in 180nm SiO2 layer after ion implantation and heat treatments in the 400–1100°C temperature range. The distribution and coarsening of nanoclusters is characterized by Rutherford backscattering spectrometry and transmission electron microscopy and the results are correlated with photoluminescence (PL) measurements. After annealing in N2 in the 400–600°C range, a monomodal array of Sn nanoclusters with diameters varying from 2 to 3.5nm is observed in the region around the maximum of the implanted profile. With increasing temperature, this array evolves to different regions of the SiO2 layer. For T⩾700°C, a cluster band with small particles is observed near to the SiO2 layer surface, whereas the deeper region undergoes a coarsening resulting in large Sn particles of different sizes in metallic and in oxidized phases. The blue–violet (≈3.2eV) PL of the SiO2 layers shows to be dependent of the structural evolution above mentioned. For the N2 annealed samples, the blue–violet PL intensity increases up to 600°C and then decreases for higher temperatures. On the other hand, for heat treatments in vacuum, the PL intensity is increased by a factor of ≈5 and the TEM data show a homogeneous size distribution of Sn nanoclusters. The low intensity of PL for the N2 annealed samples is associated with Sn oxidation.

Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes Obtained from Molecular Precursors

AbstractTin and lead nanoparticles and metal sponges were prepared by reducing Me2Si(NtBu)2Sn (7) and Me2Si(NtBu)2Pb (9) with [H2AlOtBu] (3), [HAl(OtBu)2] (13), [H2AlOSiMe2tBu] (8), and [(Me2tBuSiO)2AlH] (15). Together with dihydrogen and the metals in their elemental state the monomeric compounds [Me2Si(NtBu)2Al(OSiMe2tBu)(THF)] (10) and [Me2Si(NtBu)2Al(OtBu)(THF)] (11) can be obtained, to mention only two examples. Each monomer is stabilized by a THF molecule coordinated to aluminum, which on sublimation loses its donor molecule and dimerizes through Lewis acid–base interactions to the spiro compounds [Me2Si(NtBu)2AlOSiMe2tBu]2 (12) and [Me2Si(NtBu)2AlOtBu]2 (4), respectively. The molecular structures of 10, 11, and 12 were determined by single‐crystal X‐ray diffraction techniques. The reduction of 7 at –115 °C is gradually indicated by a color change of the reaction mixtures from red to dark brown with increasing temperature and depending on the reducing agent used. The tin powders that were obtained were identified as β‐tin using X‐ray powder diffraction techniques and their average crystallite size depends on the polarity of the solvent and hydride used. Under certain conditions metal sponges are formed. Pycnometric measurements were carried out on the tin and lead sponges. These showed almost the known densities for the metals when helium was used whereas significantly smaller ones were measured in water. Porous alumina membranes of different pore diameters were filled with tin and lead particles. Metal nanoparticles were prepared within the tubes of the membranes by reduction of the metal amides in the pores. The infiltration process can be repeated up to ten times increasing the amount of particles within the tubes monitored by SEM. The obtained brown or black membranes were characterized by SEM, EDX, and UV/Vis analysis. The filled membranes show sharp impervious ranges in the UV/Vis spectrum between 270 and 525 nm and could therefore be used as wavelength filters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The microstructures of a thermally sprayed and heat treated Al–20 wt.%Sn–3 wt.%Si alloy

High velocity oxy-fuel thermal spraying has been used to produce deposits of an Al–20 wt.%Sn–3 wt.%Si alloy approximately 300 μm thick on a steel substrate. The microstructures of the as-sprayed and annealed deposits were investigated by X-ray diffraction, scanning and transmission electron microscopy. The as-sprayed material comprised, mainly, elongated splats which were fully molten at the point of impact along with a small proportion of particles which had not been fully melted in the spray. The microstructure was composed of an α-Al matrix, a bimodal distribution of β-Sn and a small fraction of nanoscale Si precipitates. In partially molten splats, Sn formed as micron-sized particles. However, in fully molten splats the high cooling rate from the melt produced a dispersion of Sn particles, 20–100 nm in size, in the Al matrix. This is explained by the existence of a metastable liquid-phase miscibility gap in the Al–Sn phase diagram. Much of the Si, in the as-sprayed material, was retained in solid solution in the α-Al and the small amount of precipitate which formed appeared nano-sized. Following annealing at 300 °C for 1 h, the dispersed Sn particles coarsened and Si precipitated from the supersaturated α-Al as particles 50–200 nm in size.

Orientation of nanocrystals in rapidly solidified Al-based alloys and its correlation to the compound-forming tendency of alloys

The orientation of nanocrystals in rapidly solidified Al-based alloys has been investigated using transmission electron microscopy (TEM). It was found that the selected-area electron diffraction (SAED) patterns of nanocrystals in the melt-spun Al–Sr, Al–Ce, Al–Sb and Al–Ce–Sr alloys exhibit Bragg reflections with a monocrystalline characteristic, indicating that the nanocrystals in a local area form in the same growth orientation. In addition, there exist epitaxial orientation relationships between nanocrystals and the α-Al matrix in some areas. The nanoscale Sn and Si particles are randomly oriented in the melt-spun Al–Sn and Al–Si alloys, however, and the SAED patterns show spotty rings. The intensity of the interaction between relevant elements and Al increases in the following sequence: Si, Sn, Sb, Ce and Sr, as well as the compound-forming tendency of alloys. Furthermore, the orientation of nanocrystals in the melt-spun Al-based alloys is correlated to the compound-forming tendency of the alloys.

SU‐FF‐T‐02: Comparison of a 3D Multi‐Group Sn Particle Transport Code with Monte Carlo for Intracavitary Brachytherapy of the Cervix Uteri

Purpose: To calculate and compare 3‐D CT‐based patient dose distributions between Monte Carlo and a 3D multi‐group Sn particle transport code for intracavitary brachytherapy of the cervix uteri. Method and Materials: MCNPX version 2.5.c, a general purpose Monte Carlo code, was used to simulate the tandem and ovoids. An input file was created that simulated the tandem and ovoids together. A reference geometry was created in the input file whereby each applicator could be positioned in each patient CT derived geometry by applying a transformation obtained from the patient CT scan. A 3D multi‐group Sn particle transport code, Attila™ (Transpire, Inc., Gig Harbor, WA) was used to simulate the same applicator set. Each applicator was built in Solidworks™(Solidworks Corp., Concord, MA), a mechanical design package and then assembled with a coordinate transformation and rotation for each patient case. Solidworks™ exported applicator geometries as a parasolid geometry, which were imported into Attila™ for calculation. Water photon kerma rates were converted to dose delivered over the length of one insertion. Dose matrices were overlaid on each patient geometry. Dose volume histograms and point doses were compared for two patient cases. Applicator to applicator comparisons were performed between the two codes. Results: The Attila™ code calculated doses to within ±4% of MCNPX for 95% of the points in a comparison of the ovoid and to within ±4% of MCNPX for 94% of the points in a comparison of the tandem. On average, Attila™ calculated dose fourteen times as fast as MCNPX. Conclusion: The Attila™ code can calculate doses for the tandem and ovoids accurately and with less computational time than MCNPX. Further refinements may decrease calculation times for the Attila™ code. Conflict of Interest: This research was supported in part by a sponsored research agreement with Transpire, Inc., Gig Harbor, WA.

A new organometallic synthesis of size-controlled tin(0) nanoparticles

Tin(0) nanoparticles have been prepared by a new low temperature chemical reduction ofSnCl4 with t-BuONa activated NaH in THF. The size and the crystallinity of theparticles can be controlled by adjusting the reaction time. Subnanometricaland amorphous Sn(0) particles were produced after 1 h reaction at65 °C. Tetragonal Sn(0) particles with diameters of 3.2 and 40.0 nm were respectively preparedby further heating for 1 and 3.5 h. The colloidal solutions thus produced are stable at roomtemperature for long periods of time. Sn nanoparticles were characterized bytransmission electron microscopy, XPS and EDS analyses and x-ray powder diffraction.

Tin Nanoparticle Loaded Graphite Anodes for Li‐Ion Battery Applications.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structure and atoms mixing in electrodeposited Sn(Au) nanoaggregates

The tin (Sn) electrochemical deposition on insulating substrates has been performed to elaborate a distribution of supported nanoaggregates for gas sensors applications. Depending on current density, the deposit has either the shape of dendrites or of a homogeneous, continuous layer, thinner than 20 nm. In this study, fine current densities variation has been investigated to determine growth evolution, especially in the case of an additional transient layer of Au (vapor deposited). The deposits’ morphology and structure have been examined by grazing incidence X-ray diffraction (GIXD), in correlation with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with selected-area electron diffraction (SAED). Analysis of the electrochemical deposits shows systematically the formation of a SnAu alloy with clusters diameter in the range 8–20 nm, whereas Sn particles are observed only under certain conditions. The SnAu alloy nanometer-sized particles are single crystals, generated by quick and spontaneous mixing of Sn and Au at room temperature (such a behavior is very slow in bulk materials). The annealing of these deposits at 300 °C leads to the formation of SnO and SnO 2 active material.

Electrochemical lithiation and de-lithiation of MWNT–Sn/SnNi nanocomposites

Nanocrystalline multi-walled carbon nanotube (MWNT)–Sn and MWNT–SnNi composite anode materials were prepared by chemical reduction of SnCl 2 and NiCl 2 precursors in the presence of MWNTs. SEM and TEM observations showed that the Sn and SnNi particles are homogeneously dispersed on the MWNT surface and in the MWNT matrix. The electrochemical performance of MWNT–Sn and MWNT–SnNi nanocomposites has been investigated by charge/discharge tests, cyclic voltammetric experiments and the ac impedance technique. The MWNT–Sn and MWNT–SnNi anodes have demonstrated a high first discharge capacity (570 and 512 mA h/g for MWNT–Sn and MWNT–SnNi anodes, respectively), high charge/discharge efficiency in the first cycle (77.5% and 84.1% for MWNT–Sn and MWNT–SnNi anodes, respectively), and good cyclability (0.99 loss%/cycle for MWNT/SnNi anode). A reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the MWNT–Sn and MWNT–SnNi electrodes.