Effect Of Stirring Research Articles

Effect of stirring on characteristics of electrochemically exfoliated graphene

Electrochemical exfoliation of graphite is a promising technique for the synthesis of graphene at a commercial scale. Electrochemical synthesis of graphene at high voltage (∼10 V) is widely reported. However, at high voltage, multilayer graphene platelets with high defect concentration are produced. In this study, high quality graphene nanoplatelets consisting of 1–5 layers were produced at low voltage (3–4 V) using KOH solution as electrolyte. The effect of electrolyte stirring on the characteristics of graphene was studied. The stirring of electrolyte during electrolysis showed profound effect on the characteristics of graphene. The scanning electron microscopic (SEM) analysis showed that the stirring of electrolyte increased the average size of graphene nanoplatelets to 360 nm from 253 nm (without stirring). Raman spectroscopy indicated the presence of 1–5 layers of carbon atoms and the same was confirmed by transmission electron microscopy (TEM). A decrease in the defect concentration was noted with the increase in number of layers of carbon atoms in graphene produced with stirring.

Effect of Microwave Irradiation on the Dielectric Characteristics of Semi-Conductive Nanoparticle-Based Nanofluids: Progress towards the Microwave Synthesis.

Studies on dispersing nanoparticles in base fluid to elevate its essential and critical properties have evolved significantly in the recent decade. Alongside the conventional dispersion techniques used for nanofluid synthesis, microwave energy at 2.4 GHz frequency is irradiated onto the nanofluids is experimented with in this study. The effect of microwave irradiation on the electrical and thermal properties of semi-conductive nanofluids (SNF) is investigated and presented in this article. Titanium dioxide and zinc oxide are the semi-conductive nanoparticles used for this study to synthesize the SNF, viz., titania nanofluid (TNF) and zinc nanofluid (ZNF). Flash and fire points are the thermal properties verified, and dielectric breakdown strength, dielectric constant (εr), and dielectric dissipation factor (tan δ) are the electrical properties verified in this study. AC breakdown voltage (BDV) of TNF and ZNF is improved by 16.78% and 11.25%, respectively, more than SNFs prepared without microwave irradiation. Results justify that the synergetic effect of stirring, sonication, and microwave irradiation in a rational sequence (microwave synthesis) exhibited better electrical and unaltered thermal properties. This microwave-applied nanofluid synthesis could be a simple and effective route to prepare the SNF with improved electrical properties.

Effect of Stir Casting Process Parameters and Stirrer Blade Geometry on Mechanical Properties of Al MMCs – A Review

Effect of Stir Casting Process Parameters and Stirrer Blade Geometry on Mechanical Properties of Al MMCs – A Review

The impact of flow induced by rotating magnetic fields on processes in a molten conductive medium

This paper studies a method of stirring liquid metal by the action of rotating magnetic fields using two ring inductors placed next to each other. These inductors generate magnetic fields rotating in opposite directions. The aim of this study is numerical investigation of the generated fluid flow and its impact on the homogenization of a two-phase medium, as well as on the crystallization process. The impact of these electromagnetic forces proves to cause the generation of intense poloidal flow component. The arising flow is accompanied by oscillatory motion of vortex structures and their interaction resulting in effective mixing of the liquid metal. The moderate values of the force parameter have been found to lead to the most homogeneous medium under stirring. Under non-stationary action, the force parameter modulations in a certain frequency range have practically no effect on the homogeneity occurrence time and the homogeneity value. The positive effect of stirring by magnetic fields of complex topology on the rate and homogeneity of metal solidification is stated. The obtained results are relevant for improving the quality of foundry ingots.

Effects of axial magnetic field on Fe-Ni interface macrosegregation of 9%Ni steel welds filled with Ni-based alloy

For the 9%Ni steel joint filled with nickel-based alloy, macrosegregation and wide partial mixing zone (PMZ) at Fe-Ni interface are critical factors to determine the cryogenic toughness. The pulsed gas metal arc welding (GMAW) assisted by the alternating axial magnetic field (AMF) is proposed to improve interface morphology and composition gradient. The welding without AMF assistance and with different AMF intensity are compared. The Lorentz force on arc and droplet caused by the alternating AMF is conductive to the stable transfer of viscous nickel-based alloy. The results show that AMF is effective to suppress the macrosegregation of Fe-Ni interface resulted from the temperature difference of melting point between base metal and filler metal. The temperature and flow speed of molten pool edge is enhanced by the stirring effect of AMF. The amount of filler metal in the PMZ of base metal increases. The melting point of mixing metal in PMZ decreases. Under the action of AMF, more PMZ is stripped from base metal. The PMZ continues to mix with liquid metal after entering the molten pool, instead of solidifying inside molten pool. After the alternating 12 mT AMF was applied, the cryogenic impact absorbed energy of fusion line increased from 0.85 J/mm2 to 1.29 J/mm2.

Effects of electromagnetic stirring and subsequent homogenization treatment on the microstructure and mechanical properties of Al70Zn10Mg10Cu5Si5 multi-component alloy

Coarse structure and composition segregation inevitably occurred in light-weight multi-component alloys that manufactured by traditional methods due to the high concentration of solute elements. This work proposes a novel idea to address this challenge by using a combination of electromagnetic stirring and homogenization treatment. The optimum ultimate compressive strength and compressive yield strength were 497 MPa and 432 MPa, which were 12.7% and 14.3% higher than those without electromagnetic stirring, respectively. The electromagnetic force increases the number of nuclei and the equiaxed crystal rate by breaking the primary Mg2Si dendrites and shedding the fine grains on the surface of the mold, so as to achieve the purpose of grain refinement. Furthermore, electromagnetic stirring with appropriate frequency can greatly increase the solid solubility, aggravate the lattice distortion, and consequently lead to a noticeable diffusion sluggish effect, resulting in fine and uniform dispersion of the precipitated MgZn2 phase during homogenization. Finally, a strengthening model was established, and the estimated values were highly consistent with the experimental data, with an error ranging within 5%. This study elaborated the microstructure evolution mechanism, offering guidance to fabricate light-weight multi-component alloys with large-size and excellent mechanical properties.

Effect of Different Melt Treatment Methods on Microstructure and Thermal Stability of Al-Si Alloy

The effects of modification, electromagnetic stirring and compound treatment (modification and electromagnetic stirring) on the microstructure and thermal stability of Al-13% Si alloy are experimentally investigated. The results show that the three melt treatments can change the microstructure of the alloy. The modification has obvious refining effect on primary silicon and eutectic silicon grains, electromagnetic stirring has refining effect on primary silicon grains, and eutectic silicon grains appear coarsening phenomenon. The latent heat is obviously decreased by electromagnetic stirring, while the latent heat is increased by modification. Refining eutectic silicon grains will increase the latent heat of phase transformation of the alloy. When 560 °C remains unchanged, the melting temperature of the alloy generally decreases with the increase of holding time, but fluctuates, with a decrease of 7 °C. The latent heat decreases with the increase of constant temperature time, and the decrease amplitude reaches 8.4%.

The synergistic hydrogen production of bicellular fermentation systems and fluid dynamics simulation in reactor under stirring

The effect of stirring (200–800 rpm) on the synergistic fermentation hydrogen production by bicellular system consisted of Bacillus cereus (A) and Brevundimonas naejangsanensis (B) was investigated. Results indicated that hydrogen yield is the highest (1.36 mol H2/mol glucose) at 800 rpm for bicellular system and its efficiency is 1.3 and 1.4 times higher than the highest value obtained from the single fermentation of Strain A at 800 rpm and Strain B at 400 rpm, respectively. Butyric acid-type fermentation is dominated during the co-cultured fermentation at preferred stirring speed. Results via computational fluid dynamics (CFD) simulations showed that the area-weighted average value of velocity (m/s) on the cross section (y = 4.365 mm) is 0.104, 0.198 and 0.358 for the co-cultured fermentation under different stirring speeds, respectively. Major hydrodynamic parameters increased with the increasing stirring speed. This preliminarily revealed that hydrogen yield is seriously limited by the main accumulated metabolites.

Ultrathin Defective Nanosheet Subunit ZnIn2S4 Hollow Nanoflowers for Efficient Photocatalytic Hydrogen Evolution

Constructing hierarchical and ultrathin‐structured metal sulfides is beneficial for achieving high‐efficiency hydrogen evolution catalysts. Herein, ZnIn2S4 (ZIS) hollow nanoflowers (HNFs) composed of ultrathin nanosheets are creatively synthesized via a facile trisodium citrate‐mediated and stirring‐assisted solvothermal method. Experimental results reveal that the synergy effect of ethanol, trisodium citrate, and continuous stirring during solvothermal synthesis process play a significant role in optimizing microstructure as well as physicochemical properties of as‐prepared ZIS samples. Importantly, the fabricated ZIS HNFs with the thinnest nanosheets (2.28 nm) manifest the highest average photocatalytic hydrogen generation rate of 301.5 μmol h−1, which is 2.3 times higher than that of the pristine ZIS microspheres composed of nanoparticles with Pt as the cocatalyst and triethanolamine (TEOA) as the sacrificial agent and outperforms most reported ZnIn2S4‐based materials under similar testing conditions. Moreover, the optimized sample also shows a hydrogen generation rate of 0.53 μmol h−1.in pure water without any cocatalyst. This controllable agitation of the reaction mixture during the hydro/solvothermal synthesis process offers an eco‐friendly and scalable approach for tuning the microstructure of nanomaterials with enhanced performance for various applications.

Numerical method to depict the time-varying Lorentz force field under harmonic magnetic field

The time-varying Lorentz force field(tvLFf), induced by harmonic magnetic field, is widely used in materials pocessing, one of its typical applications is electromagnetic stirring in continuous casting. However, knowledge about the tvLFf is quite limited, only its time-averaged component is studied, and the profile of its time-varying component is unknown up to now. In this paper, the author develops a method to depict the tvLFf using 11 features, which are classified into 3 categories: Strength features, Morphology features and Tide features. All 11 features are created or extracted based on an analysis of the time-varying force ellipse, ruled by the amplitudes and initial phase angles of the induced eletromagnetic field. The elliptical characteristics of the time-varying Lorentz force are derived mathematically and via necessary numerical calculations, by which the effect of stirring or driving is clarified. The author finds that, the amplitudes of the induced eletromagnetic field are proportional to the magnitude of the exciting current, and that Strength features are proportional to the square of the magnitude of the exciting current, while the initial phase angles, Morphology features, and Tide features do not change with the magnitude of the exciting current, when frequency is fixed and the physical properties are constant. Finally, the author presents a model to illustrate the analyzing process, and a detailed visualization of the tvLFf is presented, with revealed features in conformity to the published results.

TiC ceramic coating reinforced 304 stainless steel components fabricated by WAAM-LC integrated hybrid manufacturing

The development of integrated material-structure-function components raises increasing requirement on hybrid manufacturing technology. In this study we developed Wire Arc Additive Manufacturing (WAAM)-Laser Cladding (LC) hybrid manufacturing technology for the integrated preparation of 304 components reinforced with TiC ceramic coating. The microstructure and mechanical properties of 304 WAAM entity and TiC coating were systematically investigated. The results show that a well-bonded and no defects coating is obtained. 304 WAAM region shows two phases of γ-Fe and δ-Fe, and two phases of TiC and γ-Fe are detected inside the coating. Four kinds of TiC hard phases appear in the coating region. The intense convection of the molten pool promotes the uniform distribution of TiC, and the stirring effect also promotes the growth of TiC in non-directional dendrites. The microhardness of the coating reaches 654.7 ± 41.0 HV0.2, which is 3.15 times higher compared to WAAM-304. The coating obtains better wear resistance compared to WAAM-304, with 99.29 %–99.48 % less wear loss. The study shows that WAAM-LC integrated hybrid manufacturing can produce ceramic-metal matrix composites with complex structures. This hybrid process can provide a new solution for the manufacture of integrated components with surface performance requirements and individual structural features.

Three-dimensional dust stirring by a giant planet embedded in a protoplanetary disc

ABSTRACT The motion of solid particles embedded in gaseous protoplanetary discs is influenced by turbulent fluctuations. Consequently, the dynamics of moderately to weakly coupled solids can be distinctly different from the dynamics of the gas. Additionally, gravitational perturbations from an embedded planet can further impact the dynamics of solids. In this work, we investigate the combined effects of turbulent fluctuations and planetary dust stirring in a protoplanetary disc on three-dimensional dust morphology and on synthetic ALMA continuum observations. We carry out 3D radiative two-fluid (gas + 1-mm-dust) hydrodynamic simulations in which we explicitly model the gravitational perturbation of a Jupiter-mass planet. We derived a new momentum-conserving turbulent diffusion model that introduces a turbulent pressure to the pressureless dust fluid to capture the turbulent transport of dust. The model implicitly captures the effects of orbital oscillations and reproduces the theoretically predicted vertical settling-diffusion equilibrium. We find a Jupiter-mass planet to produce distinct and large-scale three-dimensional flow structures in the mm-sized dust, which vary strongly in space. We quantify these effects by locally measuring an effective vertical diffusivity (equivalent alpha) and find azimuthally averaged values in a range δeff ∼ 5 × 10−3–2 × 10−2 and local peaks at values of up to δeff ∼ 3 × 10−1. In synthetic ALMA continuum observations of inclined discs, we find effects of turbulent diffusion to be observable, especially at disc edges, and effects of planetary dust stirring in edge-on observations.

Elucidating the Effect of Friction Stir Welding Variables on HDPE Sheets Using Grey Integrated with Fuzzy: Experimental Investigation and Parametric Optimization

Elucidating the Effect of Friction Stir Welding Variables on HDPE Sheets Using Grey Integrated with Fuzzy: Experimental Investigation and Parametric Optimization

Refining microstructures and enhancing mechanical properties of Inconel 718 weldment via fast-frequency double pulsed waveforms adopting in FFP-TIG

Raising the frequency of pulsed welding current in conventional tungsten inert gas (TIG) welding would stimulate the arc to stir the molten metal and thus refine microstructures and enhance mechanical properties of Inconel 718 (IN-718) weldment. In the high-frequency pulsed welding waveform, scholars are usually focused on the high-frequency pulses distributing above the low-frequency pulses while seldom considering the large space inside the low-frequency pulses to accommodate the high-frequency pulses. A fast-frequency double pulsed (FFDP) waveform is proposed to apply in fast-frequency pulsed TIG (FFP-TIG) welding. The effect of FFDP waveform modulation on the stirring of the molten pool and grain refinement was studied. The electromagnetic effect of FFDP waveform concentrated the welding energy and caused the increasing depth and decreasing width of IN-718 weldments, which enhanced the cooling rate during the solidification and formation of the weldments. Besides, the melt IN-718 within molten pool would be stirred due to the Marangoni effect induced by FFDP waveform. The increasing cooling rate and inducing stirring effect synergistically acted and thus refined the microstructures of IN-718 weldments, with the minimum size being 35.15 and 0.59 µm for irregular polygonal equiaxed grain and strip Laves phase, respectively. The tensile strength and the corresponding elongation of IN-718 weldments at high temperature (700 ℃) achieved 91% and 209% of the base metal. Current work provides an important direction towards the fabrication and development of high-reliability IN-718 weldment with good mechanical performance in high-temperature.

Weld morphology and grain growth characteristics of driven moving arc hollow stud welding

During the welding process of hollow studs, several issues can arise, including arc deflection, local non-fusion, welding pores, and cracks. In response to these challenges, a rotating magnetic field device has been developed to enhance the welding arc movement, which in turn improves the joint formation and weld grain growth behavior. According to the results, the arc moves in a periodic manner along the end face of the stud when exposed to a rotating magnetic field, due to the application of the Lorentz force. This leads to an enhanced uniformity of the melting process, a reduction in the occurrence of localized un-fusion and porosity defects, and an overall improvement in the quality of the weld morphology. Under the electromagnetic stirring effect, the undercooling of the molten pool changes and the microalloying elements in high-strength steel diffuse into the welded joint. The microstructure of the welded joint area is transformed into martensite, lower bainite, and needle-like ferrite. Under the action of a rotating magnetic field, the coarse grain in the welded joint is broken and the size is refined from 2.91 μm to 1.48 μm. The number of high-angle grain boundaries increases while the number of low-angle grain boundaries decreases. The shear strength of the joint is improved from 227 MPa to 315 MPa.

Effect of mechanical stirring on the tubular heating process of crude oil

Research on thermal behaviors under the synergy of mechanical stirring and tubular heating can reveal the effect mechanism of mechanical stirring, and determine the optimal stirring parameters. In this paper, the physical and mathematical models of heat transfer in crude oil storage tank under the synergy of tubular heating and mechanical stirring are established, the sliding grid technique is used to model the stirring impeller, which are further numerical calculated by the FVM. Our outcomes demonstrate that through the enhancement of convection, mechanical stirring significantly changes the thermal behaviors and enhances the heat exchange. Precisely, for a 1,000 m3 crude oil storage tank, the stirring of 350 rpm can increase the average velocity by 329%, the heating rate by 89%, and rise the average crude oil temperature from 42.311 °C to 42.586 °C during 2 h of heating. However, the higher crude oil temperature will cause a 1,613 W increase in heat loss power. The heating efficiency has also increased by 10%. Furthermore, mechanical stirring can promote a more uniform temperature distribution. Thus, the volume ratio in the low-temperature region decreases by 10% and that in the high-temperature region increases by 26%. The temperature variance decreases from 4.517 °C2 to 0.275 °C2. However, the velocity and temperature fields are almost the same under different stirring rates. With increasing stirring rate from 100 rpm to 700 rpm, the average heating rate can only increase by 0.026 °C/h, and temperature variance decreases from 0.596 °C2 to 0.086 °C2. With increasing stirring rate, the efficiency of the heating tube does not change significantly. The optimal stirring rate is determined as 350 rpm based on the fitting curve of temperature variance stabilization time and the comprehensive effect.

The effect of permanent magnet stirring on the corrosion resistance of Sn-2.0Ag-0.5Cu-2Zn solder alloys in NaCl solution

Permanent magnet stirring (PMS) is adjusted to increase the alloy corrosion resistance by modifying the crystallographic texture. According to the findings, the lamellar structure had been converted into equiaxed grains by the PMS processing. Following exposure to a 3.5 wt percent NaCl solution, the corrosion behavior of the Sn-2.0Ag-0.5Cu-2Zn alloy was examined using electrochemical methods (polarization and electrochemical impedance spectroscopy (EIS)) and surface analysis using SEM, EDX and XRD. According to the PDP curves, the PMS treatment procedure significantly reduces the values of corrosion current density (icorr) and shifts the corrosion potential (Ecorr) to more positive noble values. The Ecorr values of SAC (205)-2Zn and SAC (205)-2Zn with PMS are increased from −936.66 to −756.18 mV (vs. SCE). Also, the pitting resistance is higher in case of PMS treated alloy as indicated from cyclic polarization (CP). PMS treated alloy possess higher Erep values than Ecorr values, confirming the ability of passive film to restore itself. EIS data showed that the diameter of capacitive loop for PMS-treated SAC (205)-2Zn alloy is approximately four times as the untreated alloy indicating less corrosion rate and higher protection.

Effects of Mechanical Stirring and Ultrasound Treatment on the Separation of Graphite Electrode Materials from Copper Foils of Spent LIBs: A Comparative Study

In this paper, mechanical stirring and ultrasonic treatment are used to separate graphite electrode materials from copper foils in recycling spent lithium-ion batteries (LIBs). Firstly, the effects of ultrasonic power (60–180 W), ultrasonic time (1–8 min), stirring speed (420–2000 rpm), and stirring time (1–8 min) on the abscission rate of active material on copper foil were studied. It was found that the peeling-off ratio of electrode material under ultrasonic treatment was 91.34% compared with stirring treatment (84.22%). The removal of electrode material from copper foil during stirring was mainly through mechanical scrubbing. As a comparison, the generation of the microjets induced by ultrasound, the local high-temperature and high-pressure environment, and the free radicals during ultrasonic treatment are the key factors to further improve electrode material removal efficiency. An integrated ultrasound-mechanical stirrer technique can achieve a high-efficient separation performance (approximately 100% peeling-off ratio) of anode electrode materials from copper foils. The effects of mechanical stirring speed, temperature, and treatment time on the peeling-off ratios of the ultrasound-mechanical stirrer-assisted system were investigated. Finally, the results of XRF (X-ray fluorescence spectrometer), XRD (X-ray diffraction), and SEM-EDS (scanning electron microscopy coupled with energy dispersive X-ray spectroscopy) showed that the as-separated graphite electrode material had high purity and contained almost no copper foil impurities. Numerical simulation analyses briefly showed that the difference between pressure and ultrasonic temperature changes in the boundary between different anode layers (graphite on copper foil in aqueous solution) was the main effective factor in the considerable separation of graphite from copper anode foil under ultrasonic-assisted delamination.

Defect elimination and microstructure improvement of laser powder bed fusion β-solidifying γ-TiAl alloys via circular beam oscillation technology

To eliminate metallurgical defects and improve microstructures in laser powder bed fusion (LPBF) β-solidifying γ-TiAl alloys, circular beam oscillation technology was used to fabricate a Ti–43Al–9V-0.5Y alloy in this work. The metallurgical defects and microstructures under conventional linear (non-oscillating) scanning and circular oscillating scanning are first studied in comparison. Then, the microstructural evolution and defect suppression mechanisms under circular oscillating scanning are revealed based on the melt flow behavior. In contrast to the non-oscillating scanning, circular oscillating scanning can better eliminate the pores and cracks of LPBFed Ti–43Al–9V-0.5Y alloy. As the oscillating velocity is decreased, the crack density decreases and the microstructure changes from columnar to equiaxed grains. The crack-free samples with a relative density of 99.98% and fine equiaxed grains are obtained as the oscillating velocity is less than or equal to 100 mm/s. The microhardness (473–581 Hv) of the non-oscillating samples is higher than that (440–487 Hv) of the oscillating samples. The room-temperature compressive strengths (∼1222 MPa and ∼1931 MPa) and tensile strength (∼253 MPa) of the crack-free oscillating LPBFed samples are superior to those of the as-cast counterparts. The suppression of pores is ascribed to the improved keyhole stability, enhanced melt convection as well as escape of bubbles under circular beam oscillation. When the oscillating velocity is less than or equal to 100 mm/s, the sufficient stirring effect of the laser beam promotes the formation of fine equiaxed grains and the reduction of brittle B2 phase content, which effectively inhibits cracking.

Synthesis of Al–Sn alloys by direct chill casting under the effect of mechanical stirring: an experimental and simulation optimization study

Abstract Aluminium–tin (Al–Sn) immiscible alloys for bearing materials are difficult to cast by the conventional direct chill casting method. At higher concentrations, Sn accumulates at the bottom of the as-cast solid due to a significant density difference in Al and Sn. In the present investigation, Al–Sn alloys were fabricated by the direct chill (DC) casting method under the influence of mechanical forced convection (MFC). A computer-based simulation approach has been implemented to study the effect of MFC device position and impeller speed on melt flow and solidification. Optimized parameters were experimentally validated and the quality of as-cast ingots was evaluated. Hence, this optimization approach can be used to produce better quality Al–Sn bearing materials with uniformly distributed Sn phase in Al-matrix by the direct chill casting route.