Wetting and oxidation during ultrasonic soldering of an alumina reinforced aluminum-copper-magnesium (2024 Al) matrix composite

The effect of ultrasonic vibration on the solderability of a 30 vol% Al₂O₃ reinforced Al-Cu alloy matrix composite in an air atmosphere was investigated. The results showed ultrasonic vibration gave the liquid filler an excellent ability to spread on the non-wetting base metal in both drop formation and soldering tests. Wetting was improved by removing the oxide film from the base metal, during which previous diffusion of the filler elements in the composite material producing partial melting played an important role. The joint strength increased significantly with soldering time, reaching a value equal to that of the filler metal after 3 s of ultrasonic vibration. The use of ultrasonic soldering is a possible solution to the problems in joining aluminum alloys highly reinforced with ceramic particles.     

铝合金超声波钎焊过程中液态钎料的填缝及界面润湿行为

研究了超声波振动作用下6061Al和2024Al合金焊缝中液态钎料的填缝过程,并分析了加热温度、焊缝预留间隙值对该过程的影响。结果表明,超声波振动作用下液态钎料的填缝行为与传统毛细填缝行为有很大差别,该条件下液态钎料在不润湿母材的基础上就迅速发生填缝过程,钎料初始液-气界面为凸状;随着填缝进行,填缝速度有所下降,填缝前沿钎料/母材界面润湿程度提高,钎料液-气界面形状转变为凹状。加热温度对超声波作用下液态钎料的填缝过程无明显影响,焊缝预留间隙值增加,钎料填缝长度减小,液-气界面形态发生变化。     

Ultrasonic assisted fabrication of particle reinforced bonds joining aluminum metal matrix composites

This paper presents a method of producing uniform particle strengthened bonds between pieces of aluminum metal matrix composite (Al-MMCs), of strength equal to that of the substrate material. SiC particle reinforced Zn-based filler metals were fabricated by mechanical stir casting and ultrasonic treatment, and then used to join pieces of SiC_p/A356 composite with the aid of ultrasonic vibration. The filler metals made by mechanical stirring were porous and contained many particle clusters. Ultrasonic vibration was used to disperse the agglomerates and prevent further coagulation of SiC particles during joining, but the method failed to eliminate the porosity, resulting in a highly porous bond. The filler metal treated by ultrasonic vibration was free of defects and produced a non-porous bond strengthened with uniform particles between pieces of SiC_p/A356 composite. The presence of surface oxide films at the bonding interface significantly degraded the performance of SiC particle reinforced bond. Removal of this oxide film by at least 4 s of ultrasonic vibration significantly increased the bond strength, reaching a value equal to that of the substrate metal.     

液态金属基油墨的印刷适性调控与可拉伸电子应用

目的 调整液态金属基油墨的印刷适性，用于可拉伸电极的印刷法构建。方法 通过超声破碎法减小液态金属微粒直径，降低其表面张力;探究聚氨酯种类和含量对液态金属微粒的分散性、油墨流变性、电极的印刷适性和可拉伸性的影响。结果 引入PU1185制备的液态金属油墨，丝印电极分辨率达58 µm;印制电极展现了良好的导电性和可拉伸性，预拉伸稳定后的电极在100%的应变下拉伸1 000次，电阻变化不超2倍。结论 液态金属基油墨能够用于高分辨电路的加工，在可拉伸电子领域具有可预见的应用前景。     

Improvement of impact toughness of AWS E6010 weld metal by adding TiO2 nanoparticles to the electrode coating

The effect of TiO₂ nanoparticles in the electrode coating on the impact toughness of three weld metals prepared by the shielded metal arc welding process was investigated and the main factors affecting the impact toughness were discussed. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. When the content of TiO₂ nanoparticles in the composition of electrode coating is increased, the morphology of ferrite in the microstructure of columnar zone will change from Widmanstätten ferrite to acicular ferrite. This finally changes to allotriomorphic ferrite when the amount of TiO₂ nanoparticles in the electrode coating goes relatively high. Furthermore, the addition of TiO₂ nanoparticles is effective in refining the ferrite grain size of the reheated microstructures of weld metals. This effect is attributed to the increased number of nucleation sites on the oxide nanoparticles. The impact toughness of the weld metal was improved by adding TiO₂ nanoparticles, especially when a medium TiO₂ nanoparticle content was used in the electrode coating. A significant increase in the impact toughness of weld metal was shown to be due to the increased percentage of acicular ferrite and refinement of microstructure.     

The combined effect of melt stirring and ultrasonic agitation on the degassing efficiency of AlSi9Cu3 alloy

The combined effect of high intensity ultrasound and melt stirring on the degassing of AlSi₉Cu₃ using simultaneously the novel MMM (Multi-frequency Multimode Modulated) ultrasonic technology to promote cavitation, and low frequency mechanical vibration to induce melt stirring, was studied. On a first stage single low frequency mechanical vibration experiments were carried out in water in order to visualize and characterize its individual effect on the liquid dynamics. On a second stage ultrasonic vibration combined with different mechanical vibration frequencies, melt temperatures and processing times were tested in liquid AlSi₉Cu₃ alloy and their influence on the degassing efficiency was evaluated and compared with the results of the single MMM ultrasonic degassing technique. Fixed ultrasonic parameters (frequency and electric power) were used, according to the best results obtained in former experimental works developed by the authors. For the experimental conditions used in this research, it was found that melt stirring significantly improves degassing efficiency, and such improvement depends on the metal temperature and the mechanical vibration frequency. The experimental results suggest that combining melt agitation and ultrasonic vibration it is possible to achieve almost the aluminum alloy theoretical density without increasing the processing time.     

Ultrasonic collection of small particles by a tapered metal strip

A pi-shaped ultrasonic actuator can collect small particles by its two sharp edges. However, the collection of particles is weak in air and not very stable in water. In this paper, a refinement to the pi-shaped ultrasonic actuator is made for a more efficient collection of small particles in air and water. In the refined structure, an ultrasonic actuator with a metal strip is used to collect small particles. The metal strip is mechanically driven by one corner of a rectangular, sandwich-shaped ultrasonic transducer operating in the thickness mode vibration. The metal strip is tapered along its length and has a strong vibration at its tip. Small particles in air and water can be attracted to the radiation surface near the end of the metal strip. The dependence of the number of collected particles on driving frequency and voltage is investigated for shrimp eggs, mint seeds, and grass seeds. For a given driving voltage and particle type, the number of collected particles reaches a maximum value at some driving frequency. Increasing driving voltage increases this maximum number to some extent; but too large a driving voltage decreases it. The maximum number also depends on the weight per particle. It increases as the weight per particle decreases for the particles with close densities. Furthermore, the relationship between the number of collected particles and vibration amplitude at the end of the metal strip is investigated for shrimp eggs, mint seeds, and grass seeds. The number is approximately linearly proportional to the vibration amplitude when the vibration amplitude is not too large. In addition to the application in which the length of the metal strip is parallel to gravitation, the actuator also can be used with its length perpendicular to gravitation. However, the latter has a weaker capability of collecting small particles. It is also found that the actuator has a stronger capability to collect particles in water than in air.     

Additional Lithium Storage on Dynamic Electrode Surface by Charge Redistribution in Inactive Ru Metal

Beyond a traditional view that metal nanoparticles formed upon electrochemical reaction are inactive against lithium, recently their electrochemical participations are manifested and elucidated as catalytic and interfacial effects. Here, ruthenium metal composed of ≈5 nm nanoparticles is prepared and the pure ruthenium as a lithium‐ion battery anode for complete understanding on anomalous lithium storage reaction mechanism is designed. In particular, the pure metal electrode is intended for eliminating the electrochemical reaction‐derived Li₂O phase accompanied by catalytic Li₂O decomposition and the interfacial lithium storage at Ru/Li₂O phase boundary, and thereby focusing on the ruthenium itself in exploring its electrochemical reactivity. Intriguingly, unusual lithium storage not involving redox reactions with electron transfer but leading to lattice expansion is identified in the ruthenium electrode. Size‐dependent charge redistribution at surface enables additional lithium adsorption to occur on the inactive but more environmentally sensitive nanoparticles, providing innovative insight into dynamic electrode environments in rechargeable lithium chemistry.     

A facile method to prepare noble metal nanoparticles modified Self-Assembly (SAM) electrode

Noble metal nanoparticles (NPs) modified electrodes have shown promising applications in the areas of catalysis, (electro)chemical analysis and biosensing due to their unique characters. In this paper, we introduced a so-called ligand exchange method to prepare self-assembly (SAM) electrode modified with noble metal nanoparticles. The noble metal nanoparticles protected by weakly adsorbed tetraoctylammonium bromide (TOAB) were synthesized firstly, then self-assembly (SAM) dithiol-modified Au electrode (Au-SH_SAM) was immersed into the solutions containing TOAB-protected nanoparticles. Due to the strong interaction between the dithiol groups on the electrode and noble metal nanoparticles, the weakly adsorbed TOAB on the surface of noble metal NPs were replaced by dithiol groups. As a result, the TOAB protected NPs were anchored on the Au-SH_SAM template electrode surface by ligand exchange, obtaining noble metal NPs modified electrode with high quality and stability. By adjusting the soaking time, the coverage of nanoparticles on the Au-SH_SAM electrode surface could be controlled. The morphology and distribution of noble metal NPs on Au-SH_SAM surface was analysis by scanning tunneling microscope (STM), and their electrochemical property was studied by cyclic voltammetry (CV) in H₂SO₄ solution. The approach is proved as a universal way to prepare noble metal NPs modified SAM electrode.     

Ionic liquid-assisted hydrothermal synthesis of TiO2 nanoparticles and its applications towards the photocatalytic activity and electrochemical sensor

This work reports the synthesis of TiO₂ nanoparticles via ionic liquid-assisted hydrothermal method at 130?°C for two days. The obtained product was characterised by various techniques. The X-ray diffraction data reveal the anatase phase TiO₂ nanoparticles with crystallite size 37 nm. The Fourier transform infrared spectrum shows a band at 400 cm^?1 due to Ti–O–Ti stretching vibration, in addition to the presence of ionic liquid. The UV–Vis spectrum of TiO₂ nanoparticles shows an absorption band at 314 nm which indicates a blueshift compared with that of bulk TiO_2. The transmission electron microscopy images show almost spherical-shaped nanoparticles with an average diameter of 40–80 nm. TiO₂ nanoparticles exhibit excellent photocatalytic activity for the degradation of trypan blue, and also help in the reduction of Cr⁺⁶ to Cr⁺³. TiO₂ nanoparticles modified glassy carbon electrode exhibits better electrocatalytic oxidation towards dopamine compared with bare glassy carbon electrode.     

Generation of metal and metal oxide nanoparticles by liquid flame spray process

A liquid flame spray (LFS) process has been investigated for the generation of single component nanoparticles. In the LFS process, a solution consisting of metal nitrate dissolved in water is sprayed into a turbulent, high temperature H₂-O₂-flame. The primary spray droplets evaporate and subsequent reactions in the flame produce metal or metal oxide vapours which nucleate to final particulate form. In the study, the process characteristics were examined to produce 10–60 nm particles from silver, palladium and iron containing precursors. A systematic study using variable process parameters proved that the size of the generated nanoparticles is set by the mass flow rate of the metal precursor, only. The geometric standard deviation of the size distributions was seen to vary in a limited range of 1.35–1.4. The particle size was verified by aerosol instrumentation, the composition and morphology by X-ray diffraction (XRD) and transmission electron microscopy (TEM), correspondingly. The Ag and Pd particles were seen to consist of pure metals. For iron, the presence of all three of the following compounds were detected: Fe, Fe₂O₃ and Fe₃O₄.     

New Insights into the Electrochemistry Superiority of Liquid Na–K Alloy in Metal Batteries

The significant issues with alkali metal batteries arise from their poor electrochemical properties and safety problems, limiting their applications. Herein, TiO₂ nanoparticles embedded into N‐doped porous carbon truncated ocatahedra (TiO₂?NPCTO) are engineered as a cathode material with different metal anodes, including solid Na or K and liquid Na–K alloy. Electrochemical performance and kinetics are systematically analyzed, with the aim to determine detailed electrochemistry. By using a galvanostatic intermittent titration technique, TiO₂?NPCTO/NaK shows faster diffusion of metal ions in insertion and extraction processes than that of Na‐ions and K‐ions in solid Na and K. The lower reaction resistance of liquid Na–K alloy electrode is also examined. The higher b‐value of TiO₂?NPCTO/NaK confirms that the reaction kinetics are promoted by the surface‐induced capacitive behavior, favorable for high rate performance. This superiority highly pertains to the distinct liquid?liquid junction between the electrolyte and electrode, and the prohibition of metal dendrite growth, substantiated by symmetric cell testing, which provides a robust and homogeneous interface more stable than the traditional solid?liquid one. Hence, the liquid Na–K alloy‐based battery exhibits to better cyclablity with higher capacity, rate capability, and initial coulombic efficiency than solid Na and K batteries.     

New type of piezo-damping aluminum matrix composites with ZnO:Al-coated LiNbO3 particles

A new type of piezo-damping aluminum matrix composite containing ZnO:Al-coated LiNbO₃ particles was prepared. The dependence of the damping properties of composites on the resistivity of ZnO:Al coatings, altered by Al doping concentration, was investigated. Dynamic mechanical thermal analysis revealed that decreasing the resistivity of ZnO:Al coatings causes the loss factors of the composites to initially increase until the maximum value, before rapidly decreasing. Based on this piezo-damping material, the LiNbO₃ particles contribute to the transformation of mechanical vibration energy into electric energy, which is then converted into Joule's heat in the networks within the ZnO:Al coatings and metal matrix. An optimum formulation for piezo-damping metal matrix composites can be designed based on the results of this study.     

Modelling behaviour of oxide film during vibration diffusion bonding of SiCp/A356 composite in air

Abstract

The vibration liquid phase diffusion bonding of SiC_p/A356 composite in air has been investigated. The surface of specimens to be bonded was treated with and without vibration under the bonding condition. It was found by atomic force microscopy analysis that some of the oxide film could be broken down when ridges on the surface of the matrix were ground down. Dissolution of the base metal by the filler metal occurred with removal of the oxide film during vibration liquid phase bonding, and SiC particles in the base metal entered the bond region. A removal process model for vibration bonding has been established with and without filler metal. Results show that shearing and impacting actions are the two main breaking mechanisms during vibration; the oxide film bulk is generally broken down by shear, and dissolution of the base metal by the filler metal promotes particle segregation from the matrix and their entry into the bond region.     

Photodecomposition of volatile organic compounds using TiO2 nanoparticles

This study examined the photodecomposition of volatile organic compounds (VOCs) using TiO2 catalyst fabricated by the Submerged Arc Nanoparticle Synthesis System (SANSS). TiO2 catalyst was employed to decompose volatile organic compounds and compare with Degussa-P25 TiO2 in terms of decomposition efficiency. In the electric discharge manufacturing process, a Ti bar, applied as the electrode, was melted and vaporized under high temperature. The vaporized Ti powders were then rapidly quenched under low-temperature and low-pressure conditions in deionized water, thus nucleating and forming nanocrystalline powders uniformly dispersed in the base solvent. The average diameter of the TiO2 nanoparticles was 20 nm. X-ray diffraction analysis confirmed that the nanoparticles in the deionized water were Anatase type TiO2. It was found that gaseous toluene exposed to UV irradiation produced intermediates that were even harder to decompose. After 60-min photocomposition, Degussa-P25 TiO2 reduced the concentration of gaseous toluene to 8.18% while the concentration after decomposition by SANSS TiO2 catalyst dropped to 0.35%. Under UV irradiation at 253.7 +/- 184.9 nm, TiO2 prepared by SANSS can produce strong chemical debonding energy, thus showing great efficiency, superior to that of Degussa-P25 TiO2, in decomposing gaseous toluene and its intermediates.     

Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T 1 and T 2 relaxivity of chitosan-coated particles

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe₂O₄ and Fe₃O₄) and by applying ultrasonic vibration (CoFe₂O₄ and Co_0.8Zn_0.2Fe₂O₄). Although magnetic anisotropy of CoFe₂O₄ nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe₃O₄ synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe₂O₄ increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T ₂ relaxivities than by chemical coprecipitation. We report that the T ₂ relaxivities of these particles are of two orders of magnitude higher than corresponding T ₁ relaxivities. Thus, these particles are evidently suitable as contrast agent for T ₂ weighted MR images.     

Flexible electrochromic devices based on crystalline WO3 nanostructures produced with hot-wire chemical vapor deposition

Crystalline WO₃ nanoparticles are employed in the development of flexible electrochromic (EC) devices. The nanoparticles are synthesized at high-density with a hot-wire chemical vapor deposition process where the hot filament provides the source of the tungsten metal. Polyethylene terephthalate coated with indium tin oxide is employed as a transparent flexible substrate. A simple electrophoresis technique is employed to deposit the WO₃ nanoparticles on the polymer, resulting in a uniform thin film. The EC performance is optimized for WO₃ particles that were baked at ~ 300 °C for 2 h prior to electrode fabrication. The transmittance is modulated between ~ 94% and ~ 28% without degradation for 100 cycles.     

Synthesis of La-Doped CaTiO3 Perovskite Powders from the Mixture of Metal Salt Solutions by Ultrasonic Mist Combustion/Pyrolysis Processes

The CaTiO₃ and La-doped CaTiO₃ [Ca_1–x (La) _x TiO₃, x = 0.05–0.3] powders were prepared from aqueous solutions by the ultrasonic mist pyrolysis and ultrasonic mist combustion processes. Glycine provides carboxylic acid and amine groups as a fuel in the ultrasonic mist combustion process. In ultrasonic mist pyrolysis, the particles with hollow sphere morphology were obtained; whereas, particles prepared by the ultrasonic mist combustion process had a dense solid morphology with low porosity. The ultrasonic mist combustion process using metal nitrates and glycine as the fuel for a starting material has proved to be a simple and unique approach to preparing dense CaTiO₃ powder and a solid solution of CaTiO₃ with lanthanum.     

Behaviors of oxide film at the ultrasonic aided interaction interface of Zn–Al alloy and Al2O3p/6061Al composites in air

Ultrasonic aided interactions between Zn–Al alloy and Al₂O_3p/6061Al composites were investigated. Ultrasonic vibration imposed on the composite plate can cause high cavitation intensity in the liquid Zn–Al alloy which disrupts and flakes off surface oxides, thereby allowing the Zn–Al alloy to wet the bare composite surfaces and form a metallurgical bond. Whether the undermining phenomena occurred or not, the spreading of Zn–Al liquid over the composite did not occur until the ultrasonic vibration amplitude reached 10 μm. The Zn–Al liquid spread quickly over the composite despite that the surface oxide had not been fully disrupted when the ultrasonic vibration higher than 10 μm was applied. When undermining phenomena occurred during interaction, the oxide layer at the interaction interface was firstly lifted up by the undermining alloy, suspending in the Zn–Al liquid, and subsequently broke up by the ultrasonic excitation. Gas escaping from the base metal was observed to be helpful in decohesion of the oxide layer from the composite. When undermining phenomena did not occur during interaction, the removal of the oxide layer was based upon the melting of the nether base metal. The disruption of oxide initiated from the composite surface where the drop center located and the surface oxide layer near the drop edge was lastly removed.     

Preparation and characterization of carbon-encapsulated iron nanoparticles and their catalytic activity in the hydrogenation of levulinic acid

This study describes the synthesis of carbon-encapsulated iron nanoparticles using an ultrasonic method and also investigates their catalytic activity. These nanoparticles have been prepared using ultrasonic irradiation followed by annealing at various temperatures. As the annealing temperature of as-prepared α-Fe₂O₃ nanoparticles increased, the sample transformed into γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles via the reduction process without requiring any additional reducing agents such as H₂ gas, thus, creating a carbon shell surrounding the nanoparticles. By controlling the experimental conditions, Fe nanoparticles of various sizes can be formed with diameters in the range 100–800 nm; these nanoparticles are tightly encapsulated by 20-nm-thick carbon shells. Because of their high saturation magnetization 212 emu g^?1, the carbon-encapsulated Fe nanoparticles can be used for magnetic resonance imaging with a dramatically enhanced efficiency compared to commercially available T ₂ contrast agents. Moreover, the carbon-encapsulated Fe nanoparticles showed its superior catalytic activity and reusability for the hydrogenation of biomass-derived levulinic acid to GVL (99.6 %) in liquid phase.