Effects Of Acoustic Cavitation Research Articles

Hydrodynamic and acoustic cavitation effects on properties of cellulose fibers

The cellulose pulp refining process is crucial for achieving high-quality paper characteristics. This research aims to enhance energy efficiency while maintaining good fiber quality using hydrodynamic and acoustic cavitation (HAC). Experiments were conducted with an in-house developed flow-through sonicator combined with a novel Venturi nozzle for hydrodynamic cavitation. The Venturi design was determined by analytical modeling and verified by CFD simulation with multi-phase turbulence models to balance cavitation intensity and turbulence against the acoustic cavitation effect. Experimental evaluation of two batches of CTMP fibers, pre-processed in different ways, showed significant improvements in paper strength and fiber properties. The best results for Batch 1 (HC and LC) were obtained with 386 kWh/bdt for AC and 350 kWh/bdt for HC (60 °C, 2 % concentration). The tensile strength index increased by 26 %, and the TEA-index, related to freeness, increased by 55 %. HAC treatment (750 kWh/bdt, 70 °C, 1.5 % concentration) of the less refined Batch2 (HC) yielded results better than the Batch 1 reference. These findings confirm the energy-efficient potential of the sonicator concept compared to traditional industrial processes. The conclusion is that HAC-refining of softwood pulp requires a proper balance between hydrodynamic and acoustic cavitation intensities. Both fiber concentration by weight and temperature are critical for an energy-efficient process.

Starch nanoparticles with predictable size prepared by alternate treatments of ball milling and ultrasonication

In this study, starch nanoparticles (SNPs) were prepared by alternate treatments of liquid nitrogen ball milling and ultrasonication. The impact, shear and friction forces produced by ball milling, and acoustic cavitation and shear effects generated by ultrasonication disrupted starch granules to prepare SNPs. The SNPs possessed narrow particle size distribution (46.91–210.52 nm) and low polydispersity index (0.28–0.45). Additionally, the SNPs exhibited the irregular fragments with good uniformity. The relative crystallinity decreased from 34.91 % (waxy corn starch, WCS) to 0–25.91 % (SNPs), and the absorbance ratios of R1047/1022 decreased from 0.81 (WCS) to 0.60–0.76 (SNPs). The SNPs had lower thermal stability than that of WCS, characterized by a decrease in Td (temperature at maximum weight loss) from 309.39 °C (WCS) to 300.39–305.75 °C (SNPs). Furthermore, the SNPs exhibited excellent swelling power (3.48–28.02 %) and solubility (0.34–0.97 g/g). Notably, oil absorption capacity of the SNPs (9.77–15.67 g/g) was rather greater than that of WCS (1.33 g/g). Furthermore, the SNPs possessed the lower storage modulus (G′), loss modulus (G″) and viscosity than that of WCS. The SNPs with predictable size and high dispersion capability prepared in this study lay a foundation for expanding the application of SNPs.

Understanding the mechanisms behind ultrasonic vibration in resistance spot welding of aluminum and steel

An ultrasonic-assisted resistance spot welding process, which can improve the quality of aluminum/steel spot-welded joints, has been developed. However, the mechanism of the thermal-electrical-mechanical behavior caused by the ultrasonic longitudinal vibration to welding process has not been clarified. In this study, the role and impact mechanisms of ultrasonic longitudinal vibration during the welding process to form joints were confirmed by combining the microstructural characterization of the formed joints with the signal analysis of the process, as well as the analysis of the independent finite element numerical calculation results. Additionally, the interface metallurgical reaction behavior, welding defects, fracture behavior, and joint strength characteristics of ultrasonic-assisted aluminum/steel resistance spot welding joints were comprehensively analyzed, and the results indicated that the sizes of the aluminum/steel nuggets decreased. It could be attributed to the competition among multiple ultrasonic effects. Specifically, ultrasonic vibration decreased the contact resistance between the aluminum/steel sheets, whereas the acoustic cavitation and acoustic streaming effects increased the electrical conductivity of molten steel and thermal conductivity of molten aluminum, respectively. Moreover, ultrasonic vibration promoted the radial creep of molten and near-molten aluminum, which expanded in the effective bonding area between the two workpieces. Furthermore, ultrasonic vibration effectively reduced the thickness of the intermetallic compound layer (<3.0 µm), concurrently inhibited the formation of interfacial welding defects. Finally, the peak tensile-shear load of aluminum/steel joints is significantly increased under multiple ultrasonic optimization mechanisms.

Ultrasonic enhanced liquid-liquid interfacial reaction for improving the synthesis of Iron-doped carbon dots (Fe-CDs) for achieving superior photocatalytic performance

The precise and controllable preparation of carbon nanomaterials under mild conditions poses a great challenge, especially for metal-catalysed multiphase preparation. This work proposes an efficient method that utilizing high-density ultrasound to enhance the liquid-liquid interfacial reaction system. Iron-doped carbon dots (Fe-CDs) are successfully synthesized in such a normal temperature and atmospheric-pressure reaction condition. It is shown that transient cavitation provides a high-temperature and high-pressure microenvironment for the preparation of Fe-CDs. Moreover, the size of the reactant droplets is reduced from 200.0 ± 17.3 μm to 8.1 ± 2.9 μm owing to the acoustic flow and cavitation effects, which increases the specific surface area of the two reacting phases and improves the mass transfer coefficient by more than 252.0 %. As a result, the yield increases by more than an order of magnitude (from 0.7 ± 0.1 % to 11.9 ± 0.2 %) and the Fe doping rate reaches 20.9 %. The photocatalytic oxidation conversion of 1,4-Dihydropyridine (1,4-DHP) using the obtained Fe-CDs is as high as 98.2 %. This research gives a new approach for the efficient and safe production of Fe-CDs, which is promising for industrial applications.

One-step ultrasound-assisted recovery of yellow-orange-red natural coloring from defatted annatto seeds: A cleaner processing alternative

The interest in natural colorants derived from sustainable processes has prompted research into obtaining bixin from defatted annatto (Bixa orellana L.) seeds. Bixin is a compound that imparts yellow-orange-red coloration, known for its high biodegradability, low toxicity, and wide industrial applicability. Meanwhile, high-intensity ultrasound (HIUS) technology has emerged as a promising method for extracting natural colorants, offering higher yields through shorter processes and minimizing thermal degradation. Although some studies have demonstrated the efficiency of HIUS technology in bixin extraction, research on the effects of acoustic cavitation on the properties of the colorant remains limited. Therefore, this study aimed to investigate the influence of HIUS-specific energy levels (0.02, 0.04, 0.12, and 0.20 kJ/g) on the chemical, physical, and morphological characteristics of annatto extracts containing bixin and geranylgeraniol. Single-step extractions of bixin using ethanol as a solvent were evaluated at various acoustic powers (4.6, 8.5, 14.5, and 20 W) and extraction times (0.5, 1, 3, and 5 min) to determine their impact on the yield of natural colorant extraction. Increasing the acoustic power from 4.6 to 20 W and extending the extraction time from 0.5 to 5 min resulted in higher yields of natural colorant, likely due to the effects of acoustic cavitation and increased heat under more intense conditions. However, elevated levels of mechanical and thermal energy did not affect the chemical properties of the colorant, as indicated by UV–Vis and FTIR spectra. Conversely, higher specific energies yielded colorants with a more intense red hue, consistent with increased bixin content, and altered the microstructure and physical state, as observed in X-ray diffractograms. Nevertheless, these alterations did not impact the solubility of the colorant. Therefore, employing a cleaner extraction procedure aided by one-step ultrasound facilitated the recovery of natural colorants and contributed to the biorefining of annatto seeds, enabling the production of a rich geranylgeraniol colorant through a sustainable approach.

Acoustic Delivery of Plasma Low-Density Lipoprotein into Liver via ApoB100-Targeted Microbubbles Inhibits Atherosclerotic Plaque Growth.

Atherosclerosis is the main risk factor for cardiovascular disease, which accounts for the majority of mortality worldwide. A significantly increased plasma level of low-density lipoprotein cholesterol (LDL-C), surrounded by a monolayer of phospholipids, free cholesterol, and one apolipoprotein B-100 (ApoB-100) in the blood, plays the most significant role in driving the development of atherosclerosis. Commercially available cholesterol-lowering drugs are not sufficient for preventing recurrent cardiovascular events. Developing alternative strategies to decrease the plasma cholesterol levels is desirable. Herein, we develop an approach for reducing LDL-C levels using gas-filled microbubbles (MBs) that were coated with anti-ApoB100 antibodies. These targeted MBApoB100 could selectively capture LDL particles in the bloodstream through forming LDL-MBApoB100 complexes and transport them to the liver for degradation. Further immunofluorescence staining and lipidomic analyses showed that these LDL-MBApoB100 complexes may be taken up by Kupffer cells and delivered to liver cells and bile acids, greatly inhibiting atherosclerotic plaque growth. More importantly, ultrasound irradiation of these LDL-MBApoB100 complexes that accumulated in the liver may induce acoustic cavitation effects, significantly enhancing the delivery of LDL into liver cells and accelerating their degradation. Our study provides a strategy for decreasing LDL-C levels and inhibiting the progression of atherosclerosis.

Ultrasound-Controlled Prodrug Activation: Emerging Strategies in Polymer Mechanochemistry and Sonodynamic Therapy.

Ultrasound has gained prominence in biomedical applications due to its noninvasive nature and ability to penetrate deep tissue with spatial and temporal resolution. The burgeoning field of ultrasound-responsive prodrug systems exploits the mechanical and chemical effects of ultrasonication for the controlled activation of prodrugs. In polymer mechanochemistry, materials scientists exploit the sonomechanical effect of acoustic cavitation to mechanochemically activate force-sensitive prodrugs. On the other hand, researchers in the field of sonodynamic therapy adopt fundamentally distinct methodologies, utilizing the sonochemical effect (e.g., generation of reactive oxygen species) of ultrasound in the presence of sonosensitizers to induce chemical transformations that activate prodrugs. This cross-disciplinary review comprehensively examines these two divergent yet interrelated approaches, both of which originated from acoustic cavitation. It highlights molecular and materials design strategies and potential applications in diverse therapeutic contexts, from chemotherapy to immunotherapy and gene therapy methods, and discusses future directions in this rapidly advancing domain.

Influence of compound field-assisted on the mechanical properties of 316L stainless steel fabricated by laser powder bed fusion

The advantages of field-assisted laser additive manufacturing in optimizing microstructure and performance are increasingly recognized. Recently, we investigated the effects of acoustic field (AF) assisted laser powder bed fusion (LPBF) on the mechanical properties of 316L stainless steel (SS) and 316L SS/WC composite materials. Due to the effects of acoustic streaming and cavitation, acoustic field-assisted LPBF achieved optimized mechanical properties. Building on our previous research on AF-assisted LPBF, we introduced magnetic field (MF) and compound field (MF+AF) to study their effects on the microstructure and mechanical properties of 316L SS, 1 wt% and 3 wt% WC/316L SS. Application of the MF induces induced currents in the melt pool due to the Thomson-Seebek effect. The interaction between the MF and induced currents generates thermoelectric magnetic force (TEMF) and thermoelectric magnetic convection (TEMC), which inhibit the growth of columnar grains and enhance mass and heat transfer in the melt pool. Compound field-assisted LPBF reduced the dislocation density of 316L SS, refined grain size, alleviated the concentration distribution of grain orientation, and the ultimate tensile strength of the samples reached 777 MPa and the elongation at break reached 57.5%. Interestingly, for WC/316L SS, both MF and compound field resulted in a decrease in tensile performance, with ultimate tensile strengths as low as 677 MPa and elongations at break as low as 25.1%. This is because the MF affects the uniform distribution of WC particles, causing significant agglomeration and severe unmelted defects in the composite material, leading to a decrease in tensile performance.

Development of prominent bonding strength in Al/Mg bimetal composites prepared by ultrasonic vibration-assisted compound casting: Effects of ultrasonic powers

In this work, the A356/AZ91D bimetal composites were prepared by ultrasonic vibration-assisted lost foam compound casting, and the effects of ultrasonic powers on interfacial microstructures and mechanical properties of the Al/Mg interfaces were investigated. Results revealed that the Al/Mg bimetal composites without ultrasonic vibration treatment (UVT) were heterogeneous, and the Al/Mg interface was composed of Al-Mg intermetallic compounds (IMCs, i.e., Al3Mg2 and Al12Mg17) area and Al-Mg eutectic structures (δ-Mg+Al12Mg17) area. The Mg2Si particles were gathered at the IMCs area and an oxide film that mainly composed of Al2O3 was existed between the IMCs area and eutectic structures area. With UVT, the oxide film was eliminated and the gathered Mg2Si particles were refined and dispersed by the acoustic cavitation effect, and part of the Al3Mg2 and Al-Mg eutectic structures were transformed into the Al12Mg17 due to the promoted solute interdiffusion, which improved the homogeneity of the Al/Mg interfaces. Besides, the grains of the Al/Mg interface with UVT under ultrasonic power of 75 W were significantly refined. The thickness of Al/Mg interface was increased with the increase of the ultrasonic power. Due to the excessive heat induced by UVT under the further increased ultrasonic power, the cooling rates and the degree of supercooling were reduced, resulting in the coarsening of interfacial grains. The microhardness of the Al/Mg interfaces was increased and got more uniform by UVT. The shear strengths of the Al/Mg bimetal composites with UVT were enhanced to 61.4 MPa from 32.4 MPa, with an increase of 89.5 % compared with that of the Al/Mg bimetal without UVT. This could be ascribed to the removal of the oxide film, the refinement of the interfacial grains and the dispersed and refined Mg2Si particles achieved by UVT, which hindered the crack propagation during deformation.

Effect of ultrasonic vibration on microstructural evolution, clad defects, and surface properties in laser direct energy deposition of Inconel 625

Laser direct energy deposition (DED) has some accompanying issues, such as existence of micropores, elemental segregation at grain boundaries, intergranular corrosion, etc. Therefore, the current work aims for a reduction in clad defects and enhancement in surface properties for laser direct deposition of Inconel 625 by implementing ultrasonic vibration. The acoustic streaming and cavitation effect induced by ultrasonic vibration results in the breaking of columnar grains, along with grain refinement and better elemental distribution in the matrix during the solidification process. The investigation is carried out for deposition using a 240 W Yb-fiber laser under the application of ultrasonic vibration with a variable amplitude of 6–13 μm (frequency: 33–28 kHz). A relatively higher vibration amplitude was found more efficient in converting long columnar grains into finer and uniformly distributed equiaxed grains, with a significant reduction in micropores. Further, it resulted in a shorter molten pool lifetime because of the generation of more nucleation centers, leading to better cooling. The above effects resulted in higher microhardness of the deposited layer. Further, the wear and corrosion resistance showed an improvement with the application of vibration, which may be due to the finer equiaxed grains, less porosity, and better elemental distribution at a higher vibration amplitude.

Monitoring acoustic cavitation effects in tissues under the action of HIFU based on ultrasound images

The cavitation effect plays a key role in the field of High-intensity focused ultrasound treatment. By monitoring cavitation to adjust the irradiation dose, effective control of cavitation effects can be achieved, which is crucial for ensuring the safety and efficacy of HIFU therapy. In this paper, a method for monitoring cavitation effects in tissues based on ultrasound images is proposed. First, support vector machine is used to rapidly and accurately determine whether cavitation has occurred. Then, the improved watershed algorithm is employed to extract the regions where cavitation occurs, and the extracted cavitation region images are reconstructed using the total focusing method based on sparse array elements. Finally, to validate the feasibility and stability of the proposed method and investigate the development patterns of cavitation effects. An experimental system was established to conduct cavitation effect monitoring experiments on fresh bovine liver and a simulated human tissue model. The experimental results showed that, except for the recall rate in the fresh bovine liver test set, all classification metrics are greater than 0.9, demonstrating the practicality of the model established in this paper. The improved watershed algorithm achieved average values of Dice Similarity Coefficient, accuracy and precision at 93.69%, 96.74% and 92.23% respectively, representing a significant improvement compared to the traditional watershed method. The proposed total focusing method based on sparse array elements can effectively improve imaging efficiency while ensuring reconstruction accuracy.

Microstructure and Mechanical Properties of Cu-CoatedCarbon-Nanotubes-Reinforced Aluminum Matrix Composites Fabricated by Ultrasonic-Assisted Casting

Carbon nanotubes (CNTs) are considered ideal nanoscale reinforcement for the development of high-performance metal matrix composites due to their unique structure and excellent mechanical properties. However, CNTs are easy to agglomerate and have poor wettability with the aluminum matrix, resulting in unsatisfactory effects when added to the aluminum melt. In this study, Cu-coated carbon nanotubes (Cu@CNTs)-reinforced aluminum matrix composites were fabricated by high-energy ultrasonic-assisted casting. Moreover, the effects of different Cu@CNTs content on the microstructure and mechanical properties of aluminum matrix composites were explored. Meanwhile, Fluent 19.0 software was used to further explore the function of ultrasonic vibration in the melt. The results demonstrated that the mechanical properties of composite with 1.2 wt% Cu@CNTs are optimal. Compared with the matrix, the composite with 1.2 wt% Cu@CNTs displayed a 39.3% increase in yield strength, 53.5% increase in ultimate tensile strength, and 5.7% increase in elongation. The simulation results showed that the uniform dispersion of Cu@CNTs and grain refinement can be attributed to the acoustic streaming effect and cavitation effect of high-energy ultrasound. The improvement of the properties of the composites can be attributed to the grain refinement and the load-bearing effect of CNTs.

Influence of interactions between bubbles on physico-chemical effects of acoustic cavitation

Ultrasound technology has been extensively used as one of the efficient and economic methodology to achieve the desired outcomes in many applications by harnessing the physico-chemical effects of acoustic cavitation. However, the cavitation-associated effects, primarily determined by the oscillatory dynamics of cavitation bubbles, are considerably complex and still remain poorly understood. The main objective of this study was to perform a numerical analysis of the acoustic cavitation (i.e., the cavitation dynamics, the resultant temperature, pressure and chemical yields within collapsing bubbles), particularly focusing on the influence of the interactions between bubbles. A comprehensive model was developed to simulate the acoustic cavitation dynamics via combining the influences of mass transfer, heat conduction and chemical reactions as well as the interaction effects between bubbles. The results demonstrated that only the large bubble exerts a greater impact on the small one in a two-bubble system. Specifically, within parameter ranges covered this study, there are noticeable decreases in the expansion ratio of the small bubble, the resultant temperature, pressure and molar yields of free radicals, hence weakening the cavitation intensity and cavitation- associated physico-chemical effects. Moreover, the influences of the interactions between bubbles were further assessed quantitatively under various parameters, such as the ultrasound amplitude PA and frequency f, the distance between bubbles d0, the initial radius of the large bubble R20, as well as the liquid properties (e.g., surface tension σ and viscosity μ). It was found that the suppression effect can be amplified when subjected to ultrasound with an increased PA and/or a decreased f, probably due to a stronger cavitation intensity under this condition. Additionally, the suppression effect is also enhanced with a decrease in d0, σ and μ, but with R20 increasing. This study can contribute to deepening knowledge about acoustic cavitation and the resultant physical and/or chemical effects, potentially further facilitating the ultrasound-assisted various applications involving acoustic cavitation.

Ultrasound Activated Nanobowls with Deep Penetration for Enhancing Sonodynamic Therapy of Orthotopic Liver Cancer.

Owing to the high penetration ability and the safety of ultrasound (US) of sonodynamic therapy (SDT), it has gained significant attention in tumor treatment. However, its therapeutic efficiency depends on the performance of the sonosensitizers. The hypoxic microenvironment and abnormal stromal matrix restrict the full potential of sonosensitizers. In this study, a US-activated bowl-shaped nanobomb (APBN) is designed as a novel sonosensitizer to enhance the SDT effect through various means. This enhancement strategy combines three major characteristics: relieving tumor hypoxia, amplifying bubble cavitation damage, and US-movement-enhanced permeation. The unique bowl-shaped structure of APBN provides more favorable attachment sites for the generated oxygen gas bubbles. Thus, when catalase-like APBN catalyzes endogenous hydrogen peroxide to produce oxygen, bubbles accumulate at the groove, preventing the dissipation of oxygen and increasing the number of cavitation nuclei to improve the acoustic cavitation effect. This approach differs from traditional SDT strategies because it couples the sonodynamic effect with reactive oxygen species generation and bubble cavitation damage rather than a single action. Additionally, the asymmetric bowl-shaped structure generates a driving force under the US field, improving the distribution of sonosensitizers in the tumors. Using US and photoacoustic imaging for dual localization, these sonosensitizers can improve the accuracy of orthotopic liver tumor treatment, which presents a promising avenue for the treatment of deep tumors.

Dynamics and frequency response analysis of encapsulated microbubble under nonlinear ultrasound

Bubble dynamic behavior and frequency response of encapsulated microbubbles in nonlinear acoustic field is significant in applications such as tumor therapy, thrombolysis, tissue destruction, and ultrasonic lithotripsy. The acoustic cavitation effect includes stable cavitation and transient cavitation. The transformation from stable cavitation to transient cavitation requires a certain threshold, which is also called the transient cavitation threshold. Phospholipid-coated microbubbles are commonly used to enhance acoustic cavitation. However, the acoustic effects of different coating materials are not very clear, especially when considering the nonlinear effects caused by diffraction, scattering, and reflection during ultrasonic propagation. In this paper, the bubble dynamic behaviors and frequency responses of microbubbles under different frequencies, acoustic pressures, and viscoelastic properties of different shell materials are analyzed by coupling the Gilmore-Akulichev-Zener model with the nonlinear model of a lipid envelope and using the KZK equation to simulate the nonlinear acoustic field. At the same time, the influence of the coated material and nonlinear acoustic effects are considered. The bubble dynamic behavior and frequency response under the actually measured sound field are compared with those simulated by the KZK equation. The results show that the nonlinearity will lead the velocity of the microbubble wall to decrease, and when the pressure of ultrasound increases, the main frequency component of the microbubble oscillation increases, making the radial motion of the microbubble more violent. When the frequency changes, the closer the oscillation frequency of the microbubble is to the resonant frequency, the stronger the radial motion of the microbubble is. The coating material can change the harmonic component in the oscillation frequency. When the harmonic is close to the resonance frequency, the radial motion of the microbubble is enhanced. The elasticity of the coated material has almost no effect on the microbubble's frequency response, and the initial viscosity and surface tension of encapsulated microbubble will change the oscillation frequency distribution of encapsulated microbubble. When the initial viscosity of the coated microbubble is smaller, the subharmonic component of the microbubble oscillation increases. When the frequency of the subharmonic is closer to the resonance frequency than the main frequency, the acoustic cavitation effect is significantly enhanced. On the other hand, when the initial surface tension of the encapsulated microbubble increases, the main frequency and subharmonic component of the microbubble oscillation are enhanced, so that the acoustic cavitation effect is also enhanced. Therefore, this study can further elucidate the bubble dynamics of encapsulated microbubbles, stimulated by nonlinear ultrasound, benefiting the frequency response analysis of coated microbubbles under nonlinear acoustic fields.

Temperature impacts on the growth of hydrogen bubbles during ultrasonic vibration-enhanced hydrogen generation

To improve the hydrogen precipitation performance on the surface of the catalytic layer of the proton exchange membrane (PEM) hydrogen cathode, ultrasonic vibration was employed to accelerate the detachment of hydrogen bubbles on the surface of the catalytic layer. Based on the energy and mechanical analyses of nano and microbubbles, the hydrogen bubble generation mechanism and the effect of temperature on bubble parameters during the evolution process when the ultrasonic field is coupled with the electric field are investigated. The nucleation frequency of the hydrogen bubbles, the relationship between the pressure and temperature and the operating temperature during the generation and detachment of bubbles as well as the detachment radius of bubbles under the action of the ultrasonic field are obtained. The effects of ultrasound and temperature on hydrogen production were verified by visual experiments. The results show that the operating temperature affects the nucleation, growth, and detachment processes of hydrogen bubbles. The effect of temperature on the nucleation frequency of bubbles mainly comes from the Gibbs free energy required for the electrolysis reaction. The bubble radius and growth rate are both related to the temperature to the power of one-third. Ultrasonic waves enhance the separation of hydrogen bubbles from the catalyst surface by acoustic cavitation and impact effects. An increase in the working temperature reduces the activation energy barriers to be overcome for the electrolysis reaction of water, which together with a decrease in the Gibbs free energy and the surface tension coefficient, leads to an increase in the nucleation frequency of the catalytic layer and a decrease in the radius of bubble detachment, and thus improves the hydrogen precipitation performance. Visualization experiments show that in actual PEM hydrogen production, ultrasonic intensification can promote the formation of nucleation sites. The ultrasonic induced fine bubble flow not only has a drag effect on the bubble, but also intensifies the polymerization growth of the bubble due to the impact of the fine bubble flow, thus speeding up the detachment of the bubble, shortening the covering time of the hydrogen bubble on the surface of the catalytic electrode, reducing the activation voltage loss and improve the hydrogen production efficiency of PEM. The experimental results show that when the electrolyte is 60°C, the maximum hydrogen production efficiency of ultrasound is increased by 7.34%, and the average hydrogen production efficiency is increased by 5.83%.

Acoustic streaming and cavitation effect on microstructure evolution of Nb-Si-Ti alloy treated by ultrasound

Heat and mass transfer play a critical role in grain refinement by ultrasound treatment. In order to reveal the mechanism of ultrasonic in Nb-Si molten metal, a 3-D model was simulated on the acoustic, temperature and flow fields with different acoustic frequencies and displacement amplitudes by Comsol Multiphysics. Simulation results show that a new harmonic wave appears with frequency increasing, and the acoustic streaming effect is significant at 20 kHz. As the displacement amplitude increases from 10 μm to 20 μm, the maximum velocity varies from 0.01 m/s to 0.03 m/s. The distributions of three fields are dependent on frequency, and the displacement amplitude determines acoustic pressure value and fluid velocity. The displacement amplitude has a positive effect on the acoustic streaming effect improvement in the melt. In the UST ingots with different displacement amplitudes, the size of the broken dendrites decreases from 57.5 μm to 10 μm with the displacement amplitude lower than 16 μm, by 82.6%. γ-Nb5Si3 phase increases and the primary Nbss phases are elongated, coarsened and spheroidized with the increase of the displacement amplitudes. The simulation results of the flow directions can be verified by the elongated Nbss phase. The acoustic streaming effect promotes heat and mass transfer and the sluggish eutectoid reaction in Nb-Si-Ti alloy during the ultrasound treatment.

Ultrasonic-assisted soldering of SiC ceramic and aluminum alloy with a commercial inactive Sn3.0Ag0.5Cu solder

Achieving the joining of SiC ceramic and Al alloy will be potential for the broad application of high-power IGBT packages. This work proposes a novel strategy of using the commercial Sn3.0Ag0.5Cu inactive solder to achieve an active bonding between SiC ceramics and 6063Al alloy. The ultrasound promotes the intensive dissolution of Al into the solder, resulting in the solder being activated and the interfacial reaction between the SiC ceramic and solder triggered by the acoustic cavitation effect. At a shorter ultrasonic action, The dissolution of Al-based metal by the Sn3.0Ag0.5Cu solder was low, and the Al/solder interface became uneven and precipitated fine Ag3Al2 and Al2Cu compounds in the solder. While the amount of Al dissolved by the Sn3.0Ag0.5Cu solder increased sharply, obvious notches were found at the Al/solder interface, and a large amount of α-Al precipitates in the solder under a longer ultrasonic duration (>10 s). The SiC/solder interface evolved from partial bonding to full metallurgical bonding with the prolongation of ultrasonic actions. The shear strength of the obtained SiC and 6063Al joints reached 35 MPa at the ultrasonic time of 40 s. The amorphous Al2O3 mixed with γ-Al2O3 grains was formed in the SiC/solder interface and 6063Al/solder interface. Based on the effect of acoustics cavitation and thermodynamics, the formation mechanism of the interfacial reaction layer was discussed in detail.

Sono-enhanced heterogeneous Fenton catalysis: magnetic halloysite nanotube synthesis and accelerated free radical generation.

Although heterogeneous Fenton catalysis has captured increasing attention compared to its homogeneous counterpart, it still confronts some inherent drawbacks in use, such as the dilemma in solid-liquid separation and greater mass transfer resistance. Driven by the acoustic cavitation effect, herein, a sono-enhanced heterogeneous Fenton catalysis process was built to overcome the above two shortcomings, by rapidly synthesizing magnetic Fenton-like catalysts and accelerating electron transfer during the catalytic reaction. The results show that, compared to the traditional chemical coprecipitation method, Fe3O4 with smaller particle size and better crystallinity grew on the surface of halloysite nanotubes (HNTs) by using the sonochemical strategy, leading to displaying the higher catalytic activity toward the degradation of methylene blue (MB, improved by ~2.5 times). In parallel, more •OH and •O2- were produced after the ultrasound was further introduced to the routine Fenton-like catalysis system, thus highly accelerating the removal of MB (improved by ~50%). Besides, benefiting from the robust chemical integration of Fe3O4 and HNTs, Fe3O4@HNTs-S had a lower iron ion leaching in use, showing superior catalytic stability. The speed, simplicity, and generality, together with the enhanced mass transfer rate, make the use of ultrasound an enabling methodology to improve the heterogeneous Fenton catalysis.

Development of Al/Mg Bimetal Processed by Ultrasonic Vibration-Assisted Compound Casting: Effects of Ultrasonic Vibration Treatment Duration Time.

In this work, ultrasonic vibration treatment (UVT) was introduced to improve the interfacial microstructure and bonding strength of A356/AZ91D bimetal processed via lost foam compound casting (LFCC). The interfacial microstructure and mechanical properties of the Al/Mg bimetal processed via LFCC with different UVT durations were investigated. Results revealed the UVT did not change the composition of phases at the interface. The Al/Mg bimetallic interface consisted of an intermetallic compound area (β-Al3Mg2 + γ-Al12Mg17 + Mg2Si) and eutectic area (δ-Mg + γ-Al12Mg17 + Mg2Si). When the duration of the UVT was increased, the gathered Mg2Si particles at the intermetallic compound area were refined to sizes of no more than 5 μm and became more homogeneously dispersed in the intermetallic compound area and diffused in the eutectic area, which could be attributed to the removal of oxide film and the acoustic cavitation and streaming flow effects induced by the UVT. The microhardness of the Al/Mg bimetallic interface was not obviously changed by the increase in UVT duration. The shear strength of the Al/Mg bimetal was increased with UVT and reached maximum with a UVT duration of 5 s, with a value of 56.7 MPa, which was increased by 70.3%, compared with Al/Mg bimetal without UVT. This could be attributed to the removal of the oxide film at the Al/Mg bimetallic interface, which improved the metallurgical bonding of the Al/Mg interface. Additionally, the refined and homogeneously dispersed Mg2Si particles played an important role in suppressing the propagation of cracks and enhancing the shear strength of the Al/Mg bimetal.