Search Results (11)

The ZnO/hydroxyapatite nanocomposite was prepared by attrition in a planetary mill from hydroxyapatite (HA) and ZnO nanopowders. The photocatalytic degradation of synthetic dye, methyl orange (MO), was evaluated under stirring and UV irradiations by measuring the spectroscopically UV-VIS absorbance of the solution in order to determine the remanent dye concentration. The samples CZH3 (75% ZnO) and CZH4 (25% ZnO) highlighted the best MO retention from aqueous solution by adsorption and photodegradation effects. The high absorbance of the proposed nanocomposites showed their potential to be used as photocatalysts for wastewater treatment to enable the retention of organic pollutants. Full article

Aluminum 7075 alloys are widely utilized in aerospace, transportation, and marine industries due to their high strength and low density. However, further research is needed to understand their mechanical, thermomechanical, and vibrational behaviors when reinforced. This study focuses on the development of Al 7075 composites reinforced with zirconium silicate (ZrSiO₄), processed via sand stir casting. The mechanical properties, including tensile, compression, and impact strength, as well as thermomechanical and vibrational behaviors, were thoroughly investigated. A planetary ball mill was used to mix ZrSiO₄ with a wettability agent, and the results indicated that the addition of ZrSiO₄ with the wettability agent significantly enhanced the mechanical properties. Fourier Transform Infrared Spectroscopy (FTIR) was employed to identify the compounds formed after adding the reinforcement and wettability agent. Scanning Electron Microscope (SEM) images and Energy-dispersive X-ray (EDX) analysis revealed a uniform distribution of the particles within the matrix. The tensile, compression, and impact strengths increased by 20%, 21%, and 19%, respectively, with the addition of 8 wt% ZrSiO₄; however, strain decreased. Additionally, heat treatment further enhanced the mechanical properties of the composites. The thermomechanical properties showed improvement even at elevated temperatures, and the damping factor was enhanced with the addition of ZrSiO₄. The elemental composition of the reinforced composites was analyzed using EDX, confirming the presence of the reinforcement. This research highlights the potential of Al 7075-ZrSiO₄ composites for improved performance in various applications. Full article

Aluminum alloy–graphene metal matrix composite is largely used for structural applications in the aerospace and space exploration sector. In this work, the preprocessed powder particles (AA 2014 and graphene) were used as a reinforcement material in a squeeze casting process. The powder mixture contained aluminum alloy powder 2014 with an average particle size of 25 μm and 0.5 wt% graphene nano powder (Grnp) with 10 nm (average) particle size. The powder mixture was mixed using the high-energy planetary ball milling (HEPBM) technique. The experimental results indicated that the novel mixture (AA 2014 and graphene powder) acted as a transporting agent of graphene particles, allowing them to disperse homogeneously in the stir pool in the final cast, resulting in the production of an isotropic composite material that could be considered for launch vehicle structural applications. Homogeneous dispersion of the graphene nanoparticles enhanced the interfacial bonding of 2014 matrix material, which resulted in particulate strengthening and the formation of a fine-grained microstructure in the casted composite plate. The mechanical properties of 0.5 wt% graphene-reinforced, hot-rolled composite plate was strengthened by the T6 condition. When compared to the values of unreinforced parent alloy, the ultimate tensile strength and the hardness value of the composite plate were found to be 420 MPa and 123 HRB, respectively. Full article

The debromination of waste circuit boards (WCBs) used in computer motherboards and components has been studied with two different pieces of equipment. Firstly, the reaction of small particles (around one millimeter in diameter) and larger pieces obtained from WCBs was carried out with several solutions of K₂CO₃ in small non-stirred batch reactors at 200–225 °C. The kinetics of this heterogeneous reaction has been studied considering both the mass transfer and chemical reaction steps, concluding that the chemical step is much slower than diffusion. Additionally, similar WCBs were debrominated using a planetary ball mill and solid reactants, namely calcined CaO, marble sludge, and calcined marble sludge. A kinetic model has been applied to this reaction, finding that an exponential model is able to explain the results quite satisfactorily. The activity of the marble sludge is about 13% of that of pure CaO and is increased to 29% when slightly calcinating its calcite at only 800 °C for 2 h. Full article

In this study, a numerical investigation based on the CFD method is carried out to study the unsteady laminar flow of Newtonian fluid with a high viscosity in a three-dimensional simulation of a twisted double planetary mixer, which is composed of two agitating rods inside a moving tank. The considered stirring protocol is a “Continuous sine squared motion” by using the dynamic mesh model and user-defined functions (UDFs)to define the velocity profiles. The chaotic advection is obtained in our active mixers by the temporal modulation of rotational velocities of the moving walls in order to enhance the mixing of the fluid for a low Reynolds number and a high Peclet number. For this goal, we applied the Poincaré section and Lyapunov exponent as reliable mathematic tools for checking mixing quality by tracking a number of massless particles inside the fluid domain. Additionally, we investigated the development of fluid kinematics proprieties, such as vorticity, helicity, strain rate and elongation rate, at various time periods in order to view the impact of temporal modulation on the flow properties. The results of the mentioned simulation showed that it is possible to obtain a chaotic advection after a relatively short time, which can deeply enhance mixing fluid efficiency. Full article

In order to solve the problem of insufficient convective heat transfer of uniaxial stirred melt, the temperature field and shear rate of melt under planetary stirring were studied based on CFD simulation. The microstructure and properties of this technology were also experimentally studied. The results show that compared with the uniaxial stirring semi-solid technology, the convective heat transfer ability of aluminum alloy, semi-solid slurry in planetary stirring mode is stronger. In addition, its temperature field can be reduced to the semi-solid range faster and more evenly, which is conducive to a large number of nucleation and improves the nucleation rate. The temperature difference of the whole melt is small, so the preferred direction growth and uniform growth of dendrites are avoided, and the morphology is improved. Properly increasing the revolution and rotation speed of the stirring shaft can refine the grains of semi-solid aluminum alloy parts, improve the grain morphology, and improve the tensile strength. The planetary stirring semi-solid process is very suitable for rheological high-pressure casting. Full article

This paper considers the general ocean circulation (GOC) within the thermodynamical closure of our climate theory, which aims to deduce the generic climate state from first principles. The preceding papers of this theory have reduced planetary fluids to warm/cold masses and determined their bulk properties, which provide prior constraints for the derivation of the upper-bound circulation when the potential vorticity (PV) is homogenized in moving masses. In a companion paper on the general atmosphere circulation (GAC), this upper bound is seen to reproduce the observed prevailing wind, therefore forsaking discordant explanations of the easterly trade winds and the polar jet stream. In this paper on the ocean, we again show that this upper bound may replicate broad features of the observed circulation, including a western-intensified subtropical gyre and a counter-rotating tropical gyre feeding the equatorial undercurrent. Since PV homogenization has short-circuited the wind curl, the Sverdrup dynamics does not need to be the sole progenitor of the western intensification, as commonly perceived. Together with GAC, we posit that PV homogenization provides a unifying dynamical principle of the large-scale planetary circulation, which may be interpreted as the maximum macroscopic motion extractable by microscopic stirring, within the confines of thermal differentiation. Full article

The transport by materially coherent surface-layer eddies was studied in a two-layer quasigeostrophic model driven by eastward mean shear. The coherent eddies were identified by closed contours of the Lagrangian-averaged vorticity deviation obtained from Lagrangian particles advected by the flow. Attention was restricted to eastward mean flows, but a wide range of flow regimes with different bottom friction strengths, layer thickness ratios, and background potential vorticity (PV) gradients were otherwise considered. It was found that coherent eddies become more prevalent and longer-lasting as the strength of bottom drag increases and the stratification becomes more surface-intensified. The number of coherent eddies is minimal when the shear-induced PV gradient is 10–20 times the planetary PV gradient and increases for both larger and smaller values of the planetary PV gradient. These coherent eddies, with an average core radius close to the deformation radius, propagate meridionally with a preference for cyclones to propagate poleward and anticyclones to propagate equatorward. The meridional propagation preference of the coherent eddies gives rise to a systematic upgradient PV transport, which is in the opposite direction as the background PV transport and not captured by standard Lagrangian diffusivity estimates. The upgradient PV transport by coherent eddy cores is less than 15% of the total PV transport, but the PV transport by the periphery flow induced by the PV inside coherent eddies is significant and downgradient. These results clarify the distinct roles of the trapping and stirring effect of coherent eddies in PV transport in geophysical turbulence. Full article

Ceramic nanoparticle-reinforced aluminium metal matrix composites (AMMCs) have superior mechanical properties compared with matrix alloys, exhibiting great potential in structural applications in industries such as the aerospace and automotive sectors. This research proposes a new method for distributing SiC nanoparticles in an aluminium matrix alloy by powder metallurgy. The mixing of aluminium powder and SiC nanoparticles was processed by a two-step procedure, which included ultrasound-assisted stirring and planetary agitation. After that, the mixing powder was subjected to compaction, sintering and extrusion. A blank sample and three composite sheets containing 1, 2 and 3 wt % SiC nanoparticles were prepared and the mechanical properties were investigated by micro-hardness and tensile tests. A scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) were used for microstructural analysis of the composite. Experimental results revealed that by adding 1, 2, 3 wt % SiC nanoparticles, hardness was increased by 26%, 34.5%, 40.0% and tensile strength was increased by 22.3%, 28.6% and 29.3%, respectively. The grain size of the aluminium matrix decreased with the addition of SiC nanoparticles. Moreover, a decrease of elongation was observed with the increasing weight fraction of SiC. Full article

In this work, novel WO_3-x/polyurethane (PU) nanocomposites were prepared by ball milling followed by stirring using a planetary mixer/de-aerator. The effects of phase transformation (WO₃ → WO_2.8 → WO_2.72) and different weight fractions of tungsten oxide on the optical performance, photothermal conversion, and thermal properties of the prepared nanocomposites were examined. It was found that the nanocomposites exhibited strong photoabsorption in the entire near-infrared (NIR) region of 780–2500 nm and excellent photothermal conversion properties. This is because the particle size of WO_3-x was greatly reduced by ball milling and they were well-dispersed in the polyurethane matrix. The higher concentration of oxygen vacancies in WO_3-x contribute to the efficient absorption of NIR light and its conversion into thermal energy. In particular, WO_2.72/PU nanocomposites showed strong NIR light absorption of ca. 92%, high photothermal conversion, and better thermal conductivity and absorptivity than other WO₃/PU nanocomposites. Furthermore, when the nanocomposite with 7 wt % concentration of WO_2.72 nanoparticles was irradiated with infrared light, the temperature of the nanocomposite increased rapidly and stabilized at 120 °C after 5 min. This temperature is 52 °C higher than that achieved by pure PU. These nanocomposites are suitable functional materials for solar collectors, smart coatings, and energy-saving applications. Full article

Planets and stars are often capable of generating their own magnetic fields. This occurs through dynamo processes occurring via turbulent convective stirring of their respective molten metal-rich cores and plasma-based convection zones. Present-day numerical models of planetary and stellar dynamo action are not carried out using fluids properties that mimic the essential properties of liquid metals and plasmas (e.g., using fluids with thermal Prandtl numbers Pr < 1 and magnetic Prandtl numbers Pm ≪ 1). Metal dynamo simulations should become possible, though, within the next decade. In order then to understand the turbulent convection phenomena occurring in geophysical or astrophysical fluids and next-generation numerical models thereof, we present here canonical, end-member examples of thermally-driven convection in liquid gallium, first with no magnetic field or rotation present, then with the inclusion of a background magnetic field and then in a rotating system (without an imposed magnetic field). In doing so, we demonstrate the essential behaviors of convecting liquid metals that are necessary for building, as well as benchmarking, accurate, robust models of magnetohydrodynamic processes in Pm ≪ Pr < 1 geophysical and astrophysical systems. Our study results also show strong agreement between laboratory and numerical experiments, demonstrating that high resolution numerical simulations can be made capable of modeling the liquid metal convective turbulence needed in accurate next-generation dynamo models. Full article