Search

The numerical simulation length of the cassette model is determined by studying the effects of the cassette frame rotated alone and the rotated together with the agitator on mixing under different cassette lengths. The effects of different rotating speed, filling ratio of silicon particles, shape and number of agitators on the mixing characteristics of silicon particles in the cassette are studied when the outer frame of the cassette rotated alone and the cassette rotated together with the agitator. The mixing degree is quantitatively analyzed by particle trajectory, mixing index and rate, and the optimum working conditions of each influencing parameter are obtained. The results show that considering the computation time and the influence of the two motion modes on the mixing index and rate, the numerical simulation length of the cassette model is 115 mm. In order to obtain the best mixing effect and mixing speed, it is recommended that the rotating speed of the cassette is 8.91 rad/s, the filling rate is 23.60 %, and the shape of the agitator is rectangular and the number is 6. When the cassette and agitator rotate together, the filling rate has little effect on particle mixing. Considering the production efficiency, mixing effect and rate, as well as the stability of mixing, the recommended speed is 4.08 rad/s, the filling rate is 41.40 %, and the rectangular shape and number of six agitators are ideal choices. [ABSTRACT FROM AUTHOR]

The microstructures and fracture toughness properties of the aged Al–12.5Si–0.7Mg alloy plate were studied by transmission electron microscopy (TEM), optical microscopy (OM), tensile, and fracture toughness (the fracture toughness value, KIC) testing. The mechanism of fracture toughness properties of the alloys was discussed for different sizes of silicon particle and aging precipitates. The results show that the refined and rounded silicon particles will improve the fracture toughness property of the alloys. However, the silicon particles size is no longer the main factor to affect the fracture toughness property when the silicon particles are small and they have no sharp corners. The morphology and distribution of the precipitates play an important role in the fracture toughness property of the aged alloys. Their fracture toughness decreases gradually as the aging time increases. [ABSTRACT FROM AUTHOR]

In this work, in-situ TiB2/AlSi7Mg composites were successfully fabricated using TiB2 decorated AlSi7Mg alloy powder synthesized via salt-metal reaction and gas atomization, followed by powder metallurgy and hot extrusion. Microstructure and mechanical properties were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and tensile tests. The results show that the formation of fine grains and homogeneous subspherical silicon particles in as-extruded composites with high ductility (elongation of 21.7%) is achieved by perfect metallurgical bonding during severe plastic deformation. The covering effect of TiB2 aggregates around silicon particles as particle shells has hindered the dissolution of silicon in the composite. After T6 treatment, the ultimate strength, yield strength and elongation at fracture of the 2 wt% TiB2/AlSi7Mg composite reach up to 344 MPa, 298 MPa and 8.6%, respectively. The excellent mechanical properties are mainly attributed to grain refinement, silicon optimization and precipitation strengthening. This study provides a good solution for improving the strength and toughness of Al–Si alloy.

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Graphic abstract Highlights • Flexible Si-based nanocomposite films were facilely prepared by layer-by-layer self-assembly. • This material design way can avoid the particle agglomeration in the composite films. • The composite films combined the mechanical and electrical properties of the components. • The flexible films showed excellent cycling performance as anodes in Li-ion batteries. Abstract Silicon is a promising anode material for high-performance Li-ion batteries, but the high capacity of silicon is mainly restrained by its large volume change upon electrochemical cycling. Herein, flexible nanocomposite films of polyurethane/copper/silicon were facilely fabricated by an improved layer-by-layer self-assembly method. This method can not only avoid the particle agglomeration in the nanocomposites, but also effectively combine the typical property advantages of the three building blocks–Li storage capability of silicon, electro-conductivity of copper, and stretchability of polyurethane. The self-organization of the copper nanoparticles into necklace-like chains and three-dimensionally conductive networks during the preparation process furtherly facilitated the electron transfer in the composite films. The multifunctional films had improved mechanical flexibility (8.2 MPa tensile strength with 125.1% strain) and electro-conductivity (8 S cm−1), and can be directly used as anodes for accommodating the silicon volumetric change and preserving the electrical contact upon electrochemical cycle. Thus, the nanocomposite film electrodes showed high capacity of 574 mAh g−1 after 300 cycles at 1 C and average Coulombic efficiencies of 99.2–99.8%. This work offers an simple and effective material design way to fabricating multifunctional composite films with single-function building units for energy storage applications. [ABSTRACT FROM AUTHOR]

This study reports the use of engineering nanocarbon film with confined silicon nanoparticles as an anode material for lithium-ion batteries. The unique “concave” graphitic nanostructure, prepared in porous templates with morphology of interconnected arrays, makes nanocarbon electrodes a good lithium-ion intercalation medium and, more importantly, robust nanocontainers to effectively confine high-capacity silicon nanoparticles for lithium-ion storage. Open structures of the concave nanocarbon increase the accessibility of Li ions, and allow Li ions to diffuse active materials. In addition, the highly textured concave pores allow the volume expansion of the silicon nanoparticles to be confined to the nanospace during lithium-ion insertion/extraction. The specific capacity of the nanoconfined silicon/nanocarbon anode reaches up to 2500 mAh/g at 0.5 A/g. After long cycling, the anode materials becomes even more stable, showing the invariant lithium-ion storage capacity as the charge-discharge rate is increased by 10 times from 2–20 A/g. The capacity is retained constantly after 200 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Silicon powder was chosen to be deposited by cold spraying for the consideration of possible applications in lithium ion batteries. The influence of the silicon particle shapes other than spherical on the impact velocity and temperature for different working parameters of the gas streams have been numerically investigated by using computational fluid dynamics modeling. The results show that, for same equivalent diameter, the particle impact velocities increase to a maximum velocity when the shape factor increases to a certain value and then decreases to the impact velocity of spherical particles. In the cold-spraying process, the particle velocity profile for smaller shape factors is much closer to that of the gas stream due to the larger particle surface area. Furthermore, the particle impact velocity increment for smaller shape factors is much more remarkable with a higher main propulsion gas temperature and higher carrier gas pressure. The effect of raising the main propulsion gas pressure on the impact velocity of the particles with very smaller shape factors is negligible. The particle impact velocity and temperature can be altered by not only the change of the working parameters of the gas steams but also the change of the sizes and shapes of the sprayed particles. [ABSTRACT FROM AUTHOR]

A flame retardants containing phosphorus-silicon, DOPO-VTS, was synthesized and incorporated into polymethyl methacrylate (PMMA) matrix through sol-gel process at different loadings. The results from Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM) and Differential Scanning Calorimetry (DSC) showed that silicon particle were formed and dispersed well in the PMMA matrix. The addition of DOPO-VTS can not only enhance the flame retardancy of PMMA but also improve the thermal stability of PMMA. When compared to PMMA, the addition of only 15wt% DOPO-VTS results in 28.5% decrease in pHRR. Moreover, 15.0 wt% DOPO-VTS results in 32.0 °C increase in half degradation temperatures (T). The results of Hot Stage Microscopy (HSM) and FTIR showed that phosphorus-containing compound and the silicon crystal were formed in the char layers during the pyrolysis process, and the char layers can effectively prevent the degradation of PMMA/silicon particle composites. It's believed that this research will stimulate further efforts in silicon particle as the based flame retardants in different polymers for the property reinforcements. [ABSTRACT FROM AUTHOR]

The effects of silicon particle content and testing temperature on friction and wear properties of casting in-situ silicon particle reinforced ZA27 composites were investigated. The wear mechanisms were mainly discussed by observations of both worn surfaces and their side views. The results indicated that the variations of wear resistance with increasing of silicon particle content, at all of the testing temperatures applied, showed a similar tendency with a manner of non-monotonous change. It was surprised that the wear resistance decreased with the increase of silicon particle content from 2 vol.% to 5 vol.%, while it increased when the content was less than 2 vol.% or more than 5 vol.%. Similarly, the friction coeffi cient also did not change monotonously. The dominative wear mechanism changed from a relatively severe regime of plastic deformation accompanied by adhesion wear to a mild regime of smear, then to a very severe regime of severe plastic deformation induced wear, and fi nally again to a relatively mild regime of smear accompanied by abrasive wear as the silicon content increased. The wear resistance always decreased with elevating testing temperature, but the decrease ranges were different for the composites with different silicon contents. The friction coefficients changed irregularly for the different composites with the increase of testing temperature. Correspondingly, the wear mechanism alternated from a mild regime of smear accompanied by abrasive wear to a severe regime of plastic deformation accompanied by adhesion wear.

A new method called filtration squeeze casting (FSC) was presented to fabricate high volume fraction Si particle-reinforced aluminium matrix composites (Sip/Al) for electronic packaging applications. The Sip/Al composites exhibited a CTE of ~ 8.70 ppm/K, a TC above 119.80 W/(m·K) and a density of ~ 2.47 g/cm³ as well as a flexural strength above 163 MPa. Fracture of large Si particles occurred during FSC, resulting in a decreased size of Si particles and hence an increased mechanical property and a decreased TC. The average size of Si particles of ~ 29 μm is much smaller than that of the conventional hypereutectic Al-Si alloy but slightly larger than that of Sip/Al composites fabricated by spray deposition, resulting in balanced mechanical and physical properties. Dilution treatment decreased the amount of eutectic silicon in the matrix, leading to a considerable increase in TC and a negligible decrease in flexural strength and hardness. The flexural fracture mode is as follows. First, when the load borne by a silicon particle is beyond its fracture strength, it breaks. Then, the cracks caused by the fracture of Si particles propagate along interfaces between silicon particles and matrix Al. Finally, the link of these cracks result in the failure. [ABSTRACT FROM AUTHOR]

The hot deformation behaviors of three aluminum alloys containing different silicon contents (S1: Al–0.6 wt.% Si–0.5 wt.% Mg; S2: Al–7.0 wt.% Si–0.5 wt.% Mg; S3: Al–12.3 wt.% Si–0.5 wt.% Mg) were studied by hot compressive tests using a Gleebe-3500 thermal simulator. The compression tests were carried out in a temperature range of 573–773 K with strain rates of 0.01, 0.1, 1 and 5 s −1 , and the true strain up to 0.6. The new developed constitutive equation incorporating the effect of strain on material constants has been constructed, and a five-order polynomial has been ascertained. High correlation coefficient suggests that it can be used to accurately predict the flow stress during hot deformation of Al–Si–Mg alloys with different Si contents. Due to impeding dislocation motion by a great amount of silicon particles, both S2 and S3 alloys have much higher state steady flow stress σ and deformation activation energy Q than S1 alloy. The differences in σ and Q between S2 and S3 alloys are thought to be due to the difference of recrystallization maturity during hot deformation. Based on the constructed processing maps, the instability domain area of S2 alloy with 7 wt.% Si is the largest among the studied alloys at the same strain. Due to much larger mushy zone of S2 alloy during solidification, the pore defects are prone to form in it that induces instability during hot deformation. It is also found that the strain has no considerable influence on the peak power dissipation efficiency during hot compression, but the effect of silicon content on it is not ignorable. In S2 and S3 alloys with high Si content, the peak power dissipation efficiency is less than that in S1 alloy, meaning that S2 and S3 alloys are more difficult to hot deformation than S1 alloy. [ABSTRACT FROM AUTHOR]

Effective treatment of cancer metastasis to the bone relies on bone marrow drug accumulation. The surface proteins in the bone marrow vascular endothelium provide docking sites for targeted drug delivery. We have developed a thioaptamer that specifically binds to E-selectin that is overexpressed in the vasculature of tumor and inflammatory tissues. In this study, we tested targeted delivery of therapeutic siRNA loaded in the E-selectin thioaptamer-conjugated multistage vector (ESTA-MSV) drug carrier to bone marrow for the treatment of breast cancer bone metastasis. We evaluated tumor type- and tumor growth stage-dependent targeting in mice bearing metastatic breast cancer in the bone, and carried out studies to identify factors that determine targeting efficiency. In a subsequent study, we delivered siRNA to knock down expression of the human STAT3 gene in murine xenograft models of human MDA-MB-231 breast tumor, and assessed therapeutic efficacy. Our studies revealed that the CD31 + E-selectin + population accounted for 20.8%, 26.4% and 29.9% of total endothelial cells respectively inside the femur of mice bearing early, middle and late stage metastatic MDA-MB-231 tumors. In comparison, the double positive cells remained at a basal level in mice with early stage MCF-7 tumors, and jumped to 23.9% and 28.2% when tumor growth progressed to middle and late stages. Accumulation of ESTA-MSV inside the bone marrow correlated with the E-selectin expression pattern. There was up to 5-fold enrichment of the targeted MSV in the bone marrow of mice bearing early or late stage MDA-MB-231 tumors and of mice with late stage, but not early stage, MCF-7 tumors. Targeted delivery of STAT3 siRNA in ESTA-MSV resulted in knockdown of STAT3 expression in 48.7% of cancer cells inside the bone marrow. Weekly systemic administration of ESTA-MSV/STAT3 siRNA significantly extended survival of mice with MDA-MB-231 bone metastasis. In conclusion, targeting the overexpressed E-selectin provides an effective approach for tissue-specific drug delivery to the bone marrow. Tumor growth in the bone can be effectively inhibited by blockage of the STAT3 signaling. [ABSTRACT FROM AUTHOR]

Printed electronics are considered for wireless electronic tags and sensors within the future Internet-of-things (loT) concept. As a consequence of the low charge carrier mobility of present printable organic and inorganic semiconductors, the operational frequency of printed rectifiers is not high enough to enable direct communication and powering between mobile phones and printed e-tags. Here, we report an all-printed diode operating up to 1.6 GHz. The device, based on two stacked layers of Si and NbSi2 particles, is manufactured on a flexible substrate at low temperature and in ambient atmosphere. The high charge carrier mobility of the Si microparticles allows device operation to occur in the charge injection-limited regime. The asymmetry of the oxide layers in the resulting device stack leads to rectification of tunneling current. Printed diodes were combined with antennas and electrochromic displays to form an all-printed e-tag. The harvested signal from a Global System for Mobile Communications mobile phone was used to update the display. Our findings demonstrate a new communication pathway for printed electronics within loT applications. [ABSTRACT FROM AUTHOR]

Abstract: The low cycle fatigue behavior of A319-T6 aluminum alloy under the influence of microstructural heterogeneities has been studied. SEM and EDX have been used to examine the fracture surface and to measure element concentrations, respectively. The dominant fatigue crack nucleates from porosity near the specimen outside surface in all examined specimens. Quantitative measurements of the fatigue-crack-initiation site were conducted, and it shows that the decrease in fatigue life is directly correlated to the increase of defect size. A fracture mechanics approach has been used to fit the experimental data. After nucleation, the hard and brittle silicon particles show great influence on fatigue-crack propagation. Whether they act as obstacles or weak paths mainly depend on the value of crack-tip driving force. Large and elongated particles with their major axes parallel to the tensile axis are easier to crack than small ones. As fatigue crack grows, the favorite crack path change from α-Al dendrite cells into silicon accumulated areas, results in different silicon concentrations and surface roughness in various crack-propagation regions on the fracture surface. [Copyright &y& Elsevier]

The high-temperature behavior of Au clusters on a Si nanoparticle surface has been studied using the atomic-resolution high-temperature stage of a transmission electron microscope. Au atoms diffuse into the Si nanoparticle at 680°C and return to the surface at room temperature. The movement of diffused Au atoms on the Si surface steps and the movement of Guinier–Preston-zone-like contrast observed for the segregation of Au atoms on the (1 1 1) Si plane, have been directly observed. These phenomena, which can be detected only at high temperatures, are presented in this paper. [Copyright &y& Elsevier]

Directional, micron-scale honeycomb pores in Li-ion battery electrodes were fabricated using a layer-by-layer, self-assembly approach based on spray-printing of carbon nanofibers. By controlling the drying behavior of each printed electrode layer through optimization of (i) the volume ratio of fugitive bisolvent carriers in the suspension and (ii) the substrate temperature during printing, self-assembled, honeycomb pore channels through the electrode were created spontaneously and reliably on current collector areas larger than 20 cm × 15 cm. The honeycomb pore structure promoted efficient Li-ion dynamics at high charge/discharge current densities. Incorporating an optimum fraction (2.5 wt %) of high-energy-density Si particulate into the honeycomb electrodes provided a 4-fold increase in deliverable discharge capacity at 8000 mA/g. The spray-printed, honeycomb pore electrodes were then investigated as negative electrodes coupled with similar spray-printed LiFePO 4 positive electrodes in a full Li-ion cell configuration, providing an approximately 50% improvement in rate capacity retention over half-cell configurations of identical electrodes at 4000 mA/g.